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Background: Together with an increased interest in minimally invasive lateral transpsoas approach to the lumbar spine goes a demand for detailed anatomical descriptions of the lumbar plexus. Although definitions of safe zones and essential descriptions of topographical anatomy have been presented in several studies, the existing literature expects standard appearance of the neural structures. Therefore, the aim of this study was to investigate the variability of the extrapsoas portion of the lumbar plexus in regard to the lateral transpsoas approach., Methods: A total of 260 lumbar regions from embalmed cadavers were utilized in this study. The specimens were dissected as per protocol and all nerves from the lumbar plexus were morphologically evaluated., Results: The most common variation of the iliohypogastric and ilioinguinal nerves was fusion of these two nerves (9.6%). Nearly in the half of the cases (48.1%) the genitofemoral nerve left the psoas major muscle already divided into the femoral and genital branches. The lateral femoral cutaneous nerve was the least variable one as it resembled its normal morphology in 95.0% of cases. Regarding the variant origins of the femoral nerve, there was a low formation outside the psoas major muscle in 3.8% of cases. The obturator nerve was not variable at its emergence point but frequently branched (40.4%) before entering the obturator canal. In addition to the proper femoral and obturator nerves, accessory nerves were present in 12.3% and 9.2% of cases, respectively., Conclusion: Nerves of the lumbar plexus frequently show atypical anatomy outside the psoas major muscle. The presented study provides a compendious information source of the possibly encountered neural variations during retroperitoneal access to different segments of the lumbar spine., (© 2024. The Author(s).)

Objectives: To evaluate whether computed tomography (CT)-derived psoas major muscle measurements could predict preoperative cardiopulmonary exercise testing (CPET) performance and long-term mortality in patients undergoing major colorectal surgery and to compare predictive performance of psoas muscle measurements using 2D approach and 3D approach., Methods: A retrospective cohort study compliant with STROCSS standards was conducted. Consecutive patients undergoing major colorectal surgery between January 2011 and January 2017 following CPET as part of their preoperative assessment were included. Regression analyses were modelled to investigate association between the CT-derived psoas major muscle mass variables [total psoas muscle area (TPMA), total psoas muscle volume (TPMV) and psoas muscle index (PMI)] and CPET performance and mortality (1-year and 5-year). Discriminative performances of the variables were evaluated using Receiver Operating Characteristic (ROC) curve analysis., Results: A total of 457 eligible patients were included. The median TPMA and TPMV were 21 ​cm 2 (IQR: 15-27) and 274 ​cm 3 (IQR: 201-362), respectively. The median PMI measured via 2D and 3D approaches were 7 ​cm 2 /m 2 (IQR: 6-9) and 99 ​cm 3 /m 2 (IQR: 76-120), respectively. The risks of 1-year and 5-year mortality were 7.4% and 27.1%, respectively. Regression analyses showed TPMA, TPMV, and PMI can predict preoperative CPET performance and long-term mortality. However, ROC curve analyses showed no significant difference in predictive performance amongst TPMA, TPMV, and PMI., Conclusion: Radiologically-measured psoas muscle mass variables may predict preoperative CPET performance and may be helpful with informing more objective selection of patients for preoperative CPET and prehabilitation., Competing Interests: Declaration of competing interest Damian M. Bailey is Editor-in-Chief of Experimental Physiology, Chair of the Life Sciences Working Group, a member of the Human Spaceflight and Exploration Science Advisory Committee to the European Space Agency, a member of the Space Exploration Advisory Committee to the UK Space Agency, and a member of the National Cardiovascular Network for Wales and South East Wales Vascular Network. Damian M. Bailey is also affiliated to the companies FloTBI Inc. and Bexorg Inc., focused on the technological development of novel biomarkers of brain injury in humans. All other authors declare no conflict of interest., (Copyright © 2024 Royal College of Surgeons of Edinburgh (Scottish charity number SC005317) and Royal College of Surgeons in Ireland. Published by Elsevier Ltd. All rights reserved.)

Objectives: We aimed to develop an automated method for measuring the volume of the psoas muscle using CT to aid sarcopenia research efficiently., Methods: We used a data set comprising the CT scans of 520 participants who underwent health check-ups at a health promotion centre. We developed a psoas muscle segmentation model using deep learning in a three-step process based on the nnU-Net method. The automated segmentation method was evaluated for accuracy, reliability, and time required for the measurement., Results: The Dice similarity coefficient was used to compare the manual segmentation with automated segmentation; an average Dice score of 0.927 ± 0.019 was obtained, with no critical outliers. Our automated segmentation system had an average measurement time of 2 min 20 s ± 20 s, which was 48 times shorter than that of the manual measurement method (111 min 6 s ± 25 min 25 s)., Conclusion: We have successfully developed an automated segmentation method to measure the psoas muscle volume that ensures consistent and unbiased estimates across a wide range of CT images., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Hip flexor musculature was instrumental in the evolution of hominin bipedal gait and in endurance running for hunting in the genus Homo. The iliacus and psoas major muscles were historically considered to have separate tendons with different insertions on the lesser trochanter. However, in the early 20th century, it became "common knowledge" that the two muscles insert together on the lesser trochanter as the "iliopsoas" tendon. We revisited the findings of early anatomists and tested the more recent paradigm of a common "iliopsoas" tendon based on dissections of hips and their associated musculature (n = 17). We rediscovered that the tendon of the psoas muscle inserts only into a crest running from the superior to anterior aspect of the lesser trochanter, separate from the iliacus. The iliacus inserts fleshly into the anterior portion of the lesser trochanter and into an inferior crest extending from it. We developed 3D multibody dynamics biomechanical models for: (a) the conjoint "iliopsoas" tendon hypothesis and (b) the separate insertion hypothesis. We show that the conjoint model underestimates the iliacus' capacity to generate hip flexion relative to the separate insertion model. Further work reevaluating the primate lower limb (including human) through dissection, needs to be performed to develop those datasets for reconstructing anatomy in fossil hominins using the extant phylogenetic bracket approach, which is frequently used for tetrapods clades outside of paleoanthropology., (© 2021 American Association for Anatomy.)

Background: Lumbar nerve root injury is a serious complication of transpsoas lumbar interbody fusion. Researchers have reported lumbar nerve roots and psoas muscle anatomy in the supine position, but no previous studies have used prone position magnetic resonance imaging to evaluate these structures., Objective: The purpose of this study was to show the changes in the lumbar nerve roots and psoas muscle related to the lumbar intervertebral disc using supine and prone magnetic resonance imaging., Methods: Thirty volunteers without spinal or hip abnormalities were included in this observational study. Each volunteer underwent supine and prone lumbosacral magnetic resonance imaging without abdominal compression. The lumbar nerve roots, psoas muscle, aorta, superior vena cava, common iliac artery, and vein were identified at each lumbar disc level. The lumbar plexus position relative to the transpsoas working channel, psoas muscle morphology, and great vessels relative to the anterior and posterior aspects of the annulus fibrosus in the axial plane were measured by 1 observer, and intraobserver reliability was calculated., Results: Fifteen men and 15 women were included in this study. There were no significant differences in the axial image distance of the lumbar nerve roots, psoas/disc ratio, and location of other related anatomy between the supine and prone positions. More lordosis (both upper and lower arc lordosis) was noted in the prone position (51.98° ± 10.54°) than in the supine position (42.12° ± 10.13°)., Conclusions: Lumbar nerve roots, psoas morphology, and great vessel position were not affected by the prone position compared with the supine position., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Introduction: There is currently no standard definition of sarcopenia, which has often been associated with frailty. A commonly cited surrogate measure of sarcopenia is psoas muscle size. The purpose of this prospective study is to assess medical providers' capabilities to identify frail elderly trauma patients and consequent impact on outcomes after intensive care unit admission., Methods: Trauma intensive care unit patients over the age of 50 were enrolled. A preadmission functional status questionnaire was completed on admission. Attendings, residents, and nurses, blinded to their patient's sarcopenic status, completed surveys regarding 6-month prognosis. Chart review included cross-sectional psoas area measurements on computerized tomography scan. Finally, patients received phone calls 3 and 6 months after admission to determine overall health and functional status., Results: Seventy-six participants had an average age of 70 years and a corrected psoas area of 383 ± 101 mm 2 /m 2 . Injury Severity Score distribution (17.2 ± 8.9) was similar for both groups. Patients also had similar preinjury activities of daily living. Both groups had similar hospital courses. While sarcopenic patients were less likely to be predicted to survive to 6 months (60% vs. 76%, P = 0.017), their actual 6-month mortality was similar (22% vs. 21%, P = 0.915)., Conclusion: Despite similar objective measures of preadmission health and trauma injury severity, medical providers were able to recognize frail patients and predicted they would have worse outcomes. Interestingly, sarcopenic patients had similar outcomes to the control group. Additional studies are needed to further delineate factors influencing provider insight into functional reserves of elderly trauma patients.

Objective: To describe the anatomical feature positioned beneath the psoas muscle at the lateral aspect of the lower lumbar, and to create a new location system to identify the risk factors of lateral lumbar interbody fusion., Methods: Six cadavers were dissected and analyzed. The anatomy and neurovascular distribution beneath the psoas major from L 3 to S 1 was observed and recorded, with particular focus on the L 4/5 disc and below. The psoas major surface was divided homogeneously into four parts, from the anterior border of psoas major to the transverse process. The cranial-to-caudal division was from the lower edge of the psoas muscle attachment on the L 4 vertebrae to the upper part of the S 1 vertebrae, and was divided into five segments. Then a grid system was used to create 20 grids on the psoas major surface, from the anterior border of the muscle to the transverse process and from L 4 to superior S 1 , which was used to determine the anatomical structures' distribution and relationship beneath the psoas major., Results: A cleft was identified beneath the psoas major, from the level of L 4/5 downwards. It was filled with loose connective tissue and neurovascular structures. We termed it the cleft of psoas major (CPM). The sympathetic trunk, ascending lumbar vein, iliolumbar vessels, obturator nerve, femoral nerve and occasionally the great vessels are contained within the CPM, although there is significant interpersonal variation. The grid system on the psoas major surface helped to identify the anatomical structures in CPM. There was a considerably lower frequency of occurrence of neurovascular structures in the grids of I/II at the L 4/5 level where can be considered the "safe zones" for the lateral lumbar interbody fusion. In contrast, the distribution of neurovascular structures at the L 5 S 1 level is dense, where the operation risk is high., Conclusion: The CPM exists lateral to the vertebral surface from L 4 and below. Although the occurrence and distribution of neurovascular structures within the CPM is complex and varies greatly, it can provide a potential cavity for visualization during lateral lumbar interbody fusion. Using psoas major as a reference, this novel grid system can be used to identify the risk factors in CPM and thus identify a safe entry point for surgery., (© 2021 The Authors. Orthopaedic Surgery published by Chinese Orthopaedic Association and John Wiley & Sons Australia, Ltd.)

Objectives: Low psoas muscle mass previously has been associated with mortality after transcatheter aortic valve replacement (TAVR). Evidence from other clinical disciplines suggests that psoas density (PD) may be a better predictor than psoas muscle cross-sectional area indexed to body surface area (PI). The authors hypothesized that PD would be more strongly correlated with patient discharge disposition and survival after TAVR than PI., Design: The authors performed a single-center, retrospective study of TAVR patients from 2013 to 2016. PI and PD were assessed at the third lumbar spine level using computed tomography imaging. Propensity-score matching was used to investigate the association of PI and PD with discharge disposition and mortality., Setting: Tertiary university hospital PARTICIPANTS: Cohort of 245 TAVR patients., Interventions: None MEASUREMENTS AND MAIN RESULTS: A total of 245 patients met inclusion criteria. Following propensity score matching, patients with PI <4 cm 2 /m 2 and PD <25 Hounsfield units (HU) were less likely to survive and to be discharged home compared with patients with PI ≥4 cm 2 /m 2 or PD >25 HU. After repeating the propensity score matching with PI as a covariable, PD remained associated with mortality (90 days: odds ratio [OR] 4.59; 95% confidence interval [CI] 2.96-10.31, p < 0.001, 1 year: OR 6.14; 95% CI 3.45-28.57, p = 0.01, 3 years: OR 4.55; 95% CI 2.41-40.00, p = 0.03)., Conclusions: PD may be more relevant than PI in risk stratification for TAVR patients., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objective: The aim of the present paper was to evaluate cases of lumbar degenerative diseases treated with oblique lateral interbody fusion (OLIF) using a modified lateral approach (i.e. anteroinferior psoas exposure under direct vision) and to analyze the effect and safety of this approach., Methods: From June 2016 to April 2019, a total of 226 patients with an average age of 65.5 ± 16.2 years (98 men and 128 women) with degenerative lumbar diseases who underwent the AIP approach of OLIF were followed up and analyzed retrospectively. Data concerning operative and clinical parameters were collected, including operative time, intraoperative estimated blood loss, duration of postoperative hospital stay, and time to ambulation after surgery. For the assessment of clinical outcomes, the visual analogue scale (VAS) score (for back pain) and the Oswestry disability index (ODI) were calculated. Complications were also recorded as surgical exposure approach-related complications. More than 6 months after surgery, 132 patients consented to having MRI examinations to evaluate the psoas muscle atrophy when they were followed up., Results: The mean operative time was 82.5 ± 31.6 min. The mean operative time for each segment of OLIF was 43.3 ± 15.5 min. The mean blood loss was 48.0 ± 11.6 mL. The mean blood loss for each segment of OLIF was 25.3 ± 10.1 mL. No patients needed blood transfusion intraoperatively or postoperatively. The mean hospital stay was 4.1 ± 2.1 days. All patients were followed up for 12-31 months (mean 18.2 months). Clinical assessment showed that the VAS and ODI scores at 6 months after surgery were markedly lower than the preoperative scores (P < 0.001) but did not differ from the scores at the final follow-up (P > 0.05). There was no significant difference in percentage changes of the cross-sectional area of the lean psoas muscle and the T2 signal intensity ratio of gross psoas to quadratus lumborum muscles between the left side (operative side) and the right side (nonoperative side) (P > 0.05). A total of 11 surgical exposure approach-related complications were reported, with an incidence of 4.9%: transient thigh pain/numbness, psoas weakness (2.2%), sympathetic chain injury (1.3%), cage subsidence (0.9%), and segmental artery injury (0.4%). There was no permanent motor neurological deficit, and no injury of vascular, ureter or peritoneal membranes., Conclusion: The anteroinferior psoas approach for OLIF is safe and can preserve the psoas and lumbar plexus., (© 2021 The Authors. Orthopaedic Surgery published by Chinese Orthopaedic Association and John Wiley & Sons Australia, Ltd.)

Background: The ventral elevation (VE) of the psoas from the vertebral column as seen on axial magnetic resonance imaging has been suggested as a preclusion of a safe working zone for lateral lumbar interbody fusion (LLIF) at L4-5. However, no quantitative study has been conducted to verify this., Methods: L4-5 LLIF was attempted using 22-mm wider cages whenever feasible over 18-mm standard cages in a consecutive series of 62 patients. The degree of VE of the psoas measured from the anterior border of the L5 endplate and the anteroposterior cage position measured from the posterior vertebral border to the center of the cage normalized to the anteroposterior width of the L5 endplate were recorded on axial images., Results: LLIF was successfully performed in all cases despite 18 patients (29%) harboring elevated psoas. Standard cage was applied in 25 (40%) patients due to nerve proximity. Wider cage was applied equally frequent in both elevated (56%) and nonelevated groups (60%, P = 0.78). The mean cage position was found to be 0.54 ± 0.10 (standard deviation) and no difference was detected between the elevated (0.54 ± 0.11) and nonelevated (0.53 ± 0.10, P = 0.78) groups. Multivariate analyses and receiver operating characteristic analysis demonstrated that VE displayed low performance in predicting the choice of cages., Conclusions: LLIF is feasible in patients with ventrally elevated psoas, and the choice of cages does not appear to be influenced by the location of the psoas. Relying on the rising psoas sign on magnetic resonance imaging as a case selection criterion may unjustly exclude patients from LLIF., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Sarcopenia might have impact on the outcome of patients with hepatoma carcinoma (HCC). This study was to determine whether pre-sarcopenia is associated with the outcome of HCC patients undergoing radiofrequency ablation (RFA).Patients with newly diagnosed HCC undergoing RFA were enrolled. We excluded patients without pre-RFA abdominal computed tomography or with incomplete ablation. Psoas muscle area index was calculated at the mid-lumbar 3 level of computed tomography images with the manual trace method. Pre-sarcopenia was defined as psoas muscle area index less than 4.24 and 2.50 cm/m for males and females respectively. The demographics and clinical characteristics were recorded before RFA.All patients were followed regularly until death or end of 2018. A total of 136 patients, including - BCLC stage 0 (n = 44, 32.4%) and - stage A (n = 92, 67.6%), were enrolled (males/females: 78/58, age: 65.4 years) with a mean follow-up period of 3.84 years. There were 75 patients (55.1%) with HCC recurrence and 47 patients (34.6%) with mortality during follow-up. Twenty-two (16.2%) patients were diagnosed with pre-sarcopenia. Multivariate analysis showed pre-sarcopenia (HR: 2.110 (1.092-4.078); P = .026) was the only factor significantly associated with overall survival (OS); however, there were no factors associated with HCC recurrence.For patients without and with pre-sarcopenia, the 1-, 3-, and 5-year OS rates were 92.0%, 77.6%, 68.9%, and 81.8%, 54.5%, 44.1% respectively (P = .007). For early-stage HCC patients undergoing RFA, pre-sarcopenia is the prognostic factor of OS, but not of recurrence, with a worse 5-year OS rate of 44.1%.

The iliopsoas is a deep muscle group which anatomically connects the spine to the lower limbs. It is composed of the iliacus, psoas major, and psoas minor muscles. The iliopsoas functions as the primary hip flexor. Because the iliopsoas is important for daily activities, including sports, impairments and pathology associated with this muscle group can cause significant limitations. Evaluating pathology associated with the iliopsoas muscle group can be challenging because the patient's complaints are often vague and difficult to discern from other hip problems. This article will review relevant anatomy, discuss common pathologies, present clinical based examination methods, and outline conservative treatment interventions focusing on manual therapy and active exercises.

Study Design: Cross-sectional radioanatomical study., Objective: The aim of this study was to analyze the prevalence, size, and location of the oblique corridor (OC), and the morphology of the psoas muscle at the L4-L5 disc level., Summary of Background Data: Lateral lumbar interbody fusion via the OC has the advantage of avoiding injury to the psoas muscle and lumbar plexus. However, the varying anatomy of major vascular structures and the iliopsoas may preclude a safe oblique access to the L4-L5 level., Methods: Five hundred axial magnetic resonance images of the L4-L5 disc level were shortlisted. OCs were categorized into four grades: Grade 0 = no corridor, Grade 1 = small corridor (≤1 cm), Grade 2 = moderate corridor (1-2 cm) and Grade 3 = large corridor (>2 cm). OC location was labeled as antero-oblique, oblique, or oblique-lateral. Psoas morphology was categorized based on a modified Moro's classification, where the anterior section was further subdivided into types AI-AIV. Oblique approach was considered nonviable either when there was no corridor due to vascular obstruction (Grade 0) or when the psoas was high-rising (Types AII-AIV)., Results: 10.5% of the selected 449 patients had no measurable OC (grade 0) at the L4-L5 level. There were 35% and 37.2% patients with a grade 1and 2 OC, respectively. The location of the OC was anterior oblique, oblique, and oblique lateral in 3.7%, 89.6%, and 6.7%, respectively. According to the modified Moro's classification, 19.4% had a high-rising psoas. Predominantly, psoas was either in line with the disc (Type I; 30.7%) or low-rising (Type AI; 47.4%)., Conclusion: Twenty-five percent of the patients did not have an accessible OC either due to obstruction by vascular structures or due to a high-rising psoas. Hence, proper evaluation of the relevant anatomy preoperatively is recommended for early adopters of this technique, as varying anatomy precludes universal suitability of oblique lateral interbody fusion for the L4-L5 level., Level of Evidence: 3.

Background: The proximal course of the obturator nerve as related to the psoas major has been described differently among various authors. Because this relationship is important for better understanding of clinical presentations and during surgical approaches, this study aimed to elucidate this anatomy via cadaveric dissection., Methods: Twenty obturator nerves from 10 white cadaveric specimens underwent dissection. Observations were made of the relationship between the nerve and psoas major muscle., Results: On all sides, the obturator nerve descended posterior to the psoas major and never through it., Conclusions: These results might be important to clinicians who interpret radiology of this region, to clinicians who treat patients with presumed obturator compression syndromes, or to surgeons who operate near the intracavitary part of the obturator nerve., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Introduction: Emergency laparotomy in patients over the age of 80 is associated with high morbidity and mortality. Accurate risk prediction in this patient population is desirable. Sarcopenia has been shown to be associated with outcome in multiple clinical settings and the psoas major muscle as measured on computed tomography (CT) imaging has been demonstrated as a marker of sarcopenia. We aim to assess the use of psoas major measurement on pre-operative CT as a prognostic indicator in over-80s undergoing emergency laparotomy and compare this measurement to P-POSSUM., Methods: A retrospective interrogation of the prospectively collected National Emergency Laparotomy Database including all over-80s undergoing emergency laparotomy between January 2014 and September 2016 was conducted. Demographic, operative data and P-POSSUM data were collected and analysed. Computed tomography (CT) images were accessed and analysed, and cross-sectional areas of psoas major and the corresponding lumbar vertebral body at the level of the L3 inferior end plate were calculated. The ratio of psoas major-to-L3 cross-sectional area (PM:L3) was calculated for each patient. Mann-Whitney U test and receiver-operating characteristics (ROC) curves were used for statistical analysis., Results: One hundred and three over-80s underwent emergency laparotomy. Male:female ratio was 60:43. Median age was 84 years (range 80-98 years). 30-day mortality was 19.4%.90-day mortality was 25.2%. Median PM:L3 ratio in patients who died as an inpatient was 0.3 and PM:L3 ratio in patients who survived to discharge was 0.52 (p < 0.0001). Median PM:L3 ratio in patient who died within 30 days post-op was 0.28 and 0.48 in those patients who survived to 30 days (p < 0.0001). Median PM:L3 ratio in patient who died within 90 days post-op was 0.28 and 0.51 in those patients who survived to 90 days (p < 0.0001). ROC analysis gave an area under the curve (AUC) of 0.85 for in-patient mortality, 0.86 for 30-day mortality, and 0.88 for 90-day mortality. ROC analysis for P-POSSUM in this data set demonstrated an AUC of 0.51 for in-patient mortality and 0.75 for 30- and 90-day mortality., Conclusion: CT imaging of the abdomen and pelvis is routinely used in over-80s prior to emergency laparotomy making PM:L3 calculation feasible for the majority of patients in this group. PM:L3 ratio is a useful prognostic indicator for prediction of mortality in patients over the age of 80. PM:L3 is superior to the P-POSSUM score in this series.

Background: The accurate estimation of a muscle's line of action is a fundamental requirement in computational modelling. We present a novel anatomical muscle wrapping technique and demonstrate its clinical use on the evaluation of the Psoas muscle mechanics in hip arthroplasty., Methods: A volume preserving, spring model to parameterize muscle anatomy changes during motion is presented. Validation was performed by a CT scan of a cadaver model in multiple positions. The predicted psoas musculotendinous path was compared with the actual imaging findings. In a second stage, psoas kinetics were compared between a conventional versus a resurfacing hip arthroplasty during gait., Findings: Anatomy prediction error was found to be 2.12 mm on average (SD 1.34 mm). When applied to psoas mechanics during walking, the muscle was found to wrap predominantly around the femoral head providing a biomechanically efficient and nearly constant moment arm for flexion during the entire gait cycle. However, this advantage was found to be lost in small diameter hip arthroplasty designs resulting in an important mechanical disadvantage. The moment arm for flexion, was on average 36% (SD 0.03%) lower in the small diameter conventional hip arthroplasty as compared to the large diameter head of the hip resurfacing and this difference was highly significant. (p < 0.001)., Interpretation: Despite the shortcomings of an "in silico" and cadaveric study, our findings are in accordance with previous clinical and gait studies. Furthermore, the findings are strongly in favour of large diameter implant designs, warranting their further development and optimisation., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Purpose: Although muscle mass has been associated with survival in patients with various types of solid tumors, the relationship between muscle mass and survival in patients with prostate cancer remains unclear. We retrospectively investigated the association of muscle mass with survival after radical prostatectomy in patients with prostate cancer., Materials and Methods: We reviewed the records of 2,042 patients who underwent radical prostatectomy of prostate cancer between 1998 and 2013. Muscle mass was evaluated by measuring the psoas muscle index on preoperative computerized tomography images., Results: In the lowest, second, third and highest psoas muscle index quartiles the 10-year distant metastasis-free survival rate was 72.5%, 83.8%, 92.3% and 93.7% (p <0.001), the 10-year cancer specific survival rate was 85.7%, 92.1%, 96.8% and 97.6%, and the 10-year overall survival rate was 74.5%, 79.6%, 89.8% and 90.6%, respectively (each p <0.001). The psoas muscle index positively correlated with the body mass index, serum concentrations of IGFBP-3 and bioavailable testosterone, and inversely correlated with patient age, the serum SHBG concentration and the neutrophil-to-lymphocyte ratio. On multivariable analysis the psoas muscle index was independently associated with increased risks of biochemical recurrence, distant metastasis, and cancer specific and overall death., Conclusions: Low muscle mass may be associated with increased risks of recurrence and mortality in patients who undergo radical prostatectomy of prostate cancer regardless of the body mass index. Large-scale prospective studies are warranted.

Objective: To provide anatomic evidence of preoperative assessment of oblique lumbar interbody fusion (OLIF) for Chinese patients., Methods: From the hospital picture archiving and communication system, 400 lumbar magnetic resonance imaging studies of adults performed between November 2016 and January 2017 were selected. L2-3, L3-4, L4-5, and L5-S1 transverse and sagittal images were studied, and anatomic parameters associated with OLIF surgery, including bare window and psoas window, were measured and recorded. SPSS software was used for data summarization, sorting, and analysis to explore the significance of various anatomic parameters., Results: OLIF surgical corridors to the L2-S1 discs were found in most magnetic resonance imaging scans studied. The size of the psoas affects the difficulty of psoas muscle traction. It is relatively easy to perform OLIF surgery in older women. Most of the human iliac arteries were bifurcated and aggregated in front of the L4-5 intervertebral disc. The lower the aggregate level of the common iliac vein, the less likely it was to have the OLIF surgical corridor in the L5-S1 segment. The most frequently used lengths for a lumbar interbody cage for OLIF for Chinese patients are 50 mm and 55 mm., Conclusions: OLIF can be a good choice for lumbar intervertebral fusion, including L5-S1 segment, in most Chinese patients. Older women are likely to have more scope of OLIF surgery. As a routine preoperative examination, lumbar magnetic resonance imaging is of great importance to OLIF surgery preoperative assessment., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Objective: Safe surgical approaches to the anterolateral lumbar spine require a good working knowledge of the anatomy and anatomic variations of this region. As the iliolumbar vein is in the vicinity of both oblique and lateral transpsoas approaches to the lower lumbar spine, the following study was performed to better elucidate its anatomy, variations, and position during such surgical procedures., Methods: Fifteen (30 sides) fresh frozen adult cadavers underwent dissection of the iliolumbar vein (ILV). The origin, course, variants, relations, and morphometrics of each vein were documented. Fluoroscopy of the vessels was performed. Lastly, anterior oblique and lateral transpsoas approaches to the lumbar spine were carried out in order to evaluate for potential ILV injury., Results: An ILV was found on all but 2 sides (93.3%). It arose as a common trunk from the common iliac vein on 14 sides. Left ILVs tended to have a more distal origin than right ILVs. ILVs had a mean length of 3.7 cm and a mean width of 0.9 cm and were significantly larger on right versus left sides (P < 0.05). Left-sided ILVs tended to have more branches than right-sided veins. The majority of vertical branches of the ILV traveled anterior to the ventral rami of the lumbar spinal nerves, most commonly L4. The ILV and, in particular, its vertical branches coursed next to the L4 and L5 vertebrae., Conclusions: The ILV should be considered during both oblique and lateral transpsoas approaches to the lumbar spine., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: Early extubation after liver transplantation is safe and accelerates patient recovery. Patients with end-stage liver disease undergo sarcopenic changes, and sarcopenia is associated with postoperative morbidity and mortality. We investigated the impact of core muscle mass on the feasibility of immediate extubation in the operating room (OR) after living donor liver transplantation (LDLT)., Methods: A total of 295 male adult LDLT patients were retrospectively reviewed between January 2011 and December 2017. In total, 40 patients were excluded due to emergency surgery or severe encephalopathy. A total of 255 male LDLT patients were analyzed in this study. According to the OR extubation criteria, the study population was classified into immediate and conventional extubation groups (39.6 vs. 60.4%). Psoas muscle area was estimated using abdominal computed tomography and normalized by height squared (psoas muscle index [PMI])., Results: There were no significant differences in OR extubation rates among the five attending transplant anesthesiologists. The preoperative PMI correlated with respiratory performance. The preoperative PMI was higher in the immediate extubation group than in the conventional extubation group. Potentially significant perioperative factors in the univariate analysis were entered into a multivariate analysis, in which preoperative PMI and intraoperative factors (i.e., continuous renal replacement therapy, significant post-reperfusion syndrome, and fresh frozen plasma transfusion) were associated with OR extubation. The duration of ventilator support and length of intensive care unit stay were shorter in the immediate extubation group than in the conventional extubation group, and the incidence of pneumonia and early allograft dysfunction were also lower in the immediate extubation group., Conclusions: Our study could improve the accuracy of predictions concerning immediate post-transplant extubation in the OR by introducing preoperative PMI into predictive models for patients who underwent elective LDLT.

Study Design: This is a cross-sectional study., Objective: To investigate the oblique corridor to the L1-S1 intervertebral disc space between the psoas muscle and the great vessels in cadaveric specimens bilaterally and the location of genitofemoral nerve and the diaphragmatic crura relative to the oblique corridor., Summary of Background Data: Although use of oblique lumbar interbody fusion is rapidly expanding, the morphometric data related to the procedure are limited., Methods: Twelve fresh-frozen full-torso cadaveric specimens were dissected to examine the oblique corridor to access the L1-S1 space in a static state and with mild retraction of the psoas. The level at which the genitofemoral nerve pierces from the psoas major and the diaphragmatic crura originate from the lumbar vertebral body was also investigated., Results: The mean width of oblique corridor in the static state and with mild psoas retraction, respectively, were as follows: on the right side: (L1-2) 13.33 and 16.75 mm; (L2-3) 15.42 and 21.42 mm; (L3-4) 16.58 and 22.67 mm; (L4-5) 12.75 and 21.17 mm; (L5-S1) 5.92 and 12.00 mm; on the left side: (L1-2) 16.75 and 19.67 mm; (L2-3) 18.50 and 25.33 mm; (L3-4) 20.58 and 28.00 mm; (L4-5) 18.17 and 26.08 mm; and (L5-S1) 5.83 and 12.00 mm. The level at which the genitofemoral nerve pierces from the psoas major was between L2 and L4. The diaphragmatic crura originates from L1 to L3., Conclusion: The oblique corridor allows access to the L1-L5 discs from both sides, but it is larger on the left side. The corridor between the iliac vessels and the psoas for L5-S1 is difficult to be applied clinically. Mild psoas retraction can moderately enlarge the oblique corridor. The genitofemoral nerve and diaphragmatic crura may be encountered in this approach and should be carefully observed., Level of Evidence: 5.

Background: In lung transplantation, preoperative sarcopenia was reported to be associated with short-term outcomes based on cross-sectional image. This study aimed to investigate the influence of psoas muscle mass (PMM) on the operative outcome and survival using three-dimensional reconstruction of PMM and to evaluate the effect of preoperative sarcopenic overweight on postoperative outcomes and survival., Methods: A total of 107 patients who underwent double lung transplantation in one institute from January 1, 2014, to June 30, 2017, were enrolled. The PMM was measured by Synapse 3D (Fujifilm, Seoul, Korea) visualization software based on computed tomography and three-dimensional reconstruction images. Patients were separated into two groups according to tercile of PMM (below the first tercile was defined as sarcopenia) and then subdivided according to PMM and overweight (body mass index ≥23 kg/m 2 )., Results: Sarcopenia had a significant relation with higher rate of postoperative tracheostomy (p = 0.040) and operative mortality (p = 0.023). For survival analysis, patients with sarcopenia showed a trend toward poorer outcome, but it was not significant (3-year survival rate 50.2% versus 73.2%, p = 0.054). Moreover, PMM was significantly associated with the length of mechanical ventilation (ß = -0.368, p = 0.047) and length of intensive care unit stay (ß = -0.372, p = 0.046). Sarcopenic overweight has no significant difference in terms of length of mechanical ventilation and length of intensive care unit. However, overall survival was significantly lower among patients with sarcopenic overweight than among those without sarcopenia (p = 0.026 and p = 0.024, respectively)., Conclusions: Sarcopenia was associated with poorer short-term outcome, and sarcopenic overweight with poorer overall survival of lung transplant patients., (Copyright © 2019 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Objective: To evaluate the quality of the iliopsoas muscle complex after pertrochanteric femoral fracture, using MRI; to propose an anatomy-based evaluation of the iliopsoas muscle complex; and to determine the inter-reader reliability of two classifications of fatty muscle degeneration., Materials and Methods: We included adult patients with a displaced lesser trochanter following pertrochanteric femoral fracture. Muscle quality was evaluated using the Goutallier and Slabaugh classifications at three levels (L4/L5, L5/S1, and the anterior inferior iliac spine). Two radiologists independently reviewed the MRIs, and force measurement was performed on both hips. Linear mixed-effects models were used to determine the effect of fracture on muscle quality and strength, and Cohen's kappa statistic was used to assess inter-reader agreement., Results: In the 18 patients included, the iliopsoas muscle complex showed higher grades of fatty muscle degeneration on the fractured side than on the non-fractured side. The mean difference between muscle strength on the fractured vs the non-fractured side was -12 N (p > 0.05). Inter-reader agreement for the Goutallier and Slabaugh classifications was good and very good respectively (weighted K = 0.78 and 0.85 respectively)., Conclusion: Fatty muscle degeneration of the iliopsoas muscle complex after pertrochanteric femoral fracture was evident using both classification systems; however, fatty muscle degeneration resulted in only a minimal reduction of muscle strength. To provide a thorough assessment of iliopsoas muscle complex quality, we suggest evaluating it at different anatomical levels. Regarding inter-reader agreement, the Slabaugh classification was superior to the Goutallier classification.

Objectives: Chemical shift encoding-based water-fat MRI derived proton density fat fraction (PDFF) of the paraspinal muscles has been emerging as a surrogate marker in subjects with sarcopenia, lower back pain, injuries and neuromuscular disorders. The present study investigates the performance of paraspinal muscle PDFF and cross-sectional area (CSA) in predicting isometric muscle strength., Methods: Twenty-six healthy subjects (57.7% women; age: 30 ± 6 years) underwent 3T axial MRI of the lumbar spine using a six-echo 3D spoiled gradient echo sequence for chemical shift encoding-based water-fat separation. Erector spinae and psoas muscles were segmented bilaterally from L2 level to L5 level to determine CSA and PDFF. Muscle flexion and extension maximum isometric torque values [Nm] at the back were measured with an isokinetic dynamometer., Results: Significant correlations between CSA and muscle strength measurements were observed for erector spinae muscle CSA (r = 0.40; p = 0.044) and psoas muscle CSA (r = 0.61; p = 0.001) with relative flexion strength. Erector spinae muscle PDFF correlated significantly with relative muscle strength (extension: r = -0.51; p = 0.008; flexion: r = -0.54; p = 0.005). Erector spinae muscle PDFF, but not CSA, remained a statistically significant (p < 0.05) predictor of relative extensor strength in multivariate regression models (R 2 adj = 0.34; p = 0.002)., Conclusions: PDFF measurements improved the prediction of paraspinal muscle strength beyond CSA. Therefore, chemical shift encoding-based water-fat MRI may be used to detect subtle changes in the paraspinal muscle composition., Key Points: • We investigated the association of paraspinal muscle fat fraction based on chemical shift encoding-based water-fat MRI with isometric strength measurements in healthy subjects. • Erector spinae muscle PDFF correlated significantly with relative muscle strength. • PDFF measurements improved prediction of paraspinal muscle strength beyond CSA.

Objectives: This study sought to assess the incremental prognostic value of the psoas muscle area in patients scheduled for transcatheter aortic valve implantation (TAVI)., Methods: A total of 1076 consecutive patients undergoing TAVI at 2 centres between 2010 and 2017 were prospectively included in this study. Computed tomography-derived cross-sectional area of the psoas muscle was measured at the superior border of the third (L3) and fourth (L4) lumbar vertebra and indexed to body surface area (PMAi) as well as stratified into tertiles. Multivariable logistic regression and Cox regression analyses were performed to investigate the value of PMAi as a predictor of 30-day and cumulative mortality. The incremental prognostic value of PMAi over the Society of Thoracic Surgeons (STS) score was assessed using a net reclassification analysis., Results: The rate of 30-day mortality was 5.8% (n = 62). PMAi at the level of L3 [odds ratio 0.082, 95% confidence interval (CI) 0.011-0.589; P = 0.013] and L4 (odds ratio 0.049, 95% CI 0.005-0.536; P = 0.013) was independently associated with 30-day mortality. During a median follow-up of 435 days (interquartile range 139-904), 292 patients (27.1%) died. PMAi of L3 (hazard ratio 0.200, 95% CI 0.083-0.482; P < 0.001) and L4 (hazard ratio 0.083, 95% CI 0.029-0.235; P < 0.001) was independently associated with mortality during follow-up. The addition of PMAi to the STS score led to a net reclassification improvement for 30-day and cumulative mortality., Conclusions: PMAi emerged as a valuable outcome predictor in patients undergoing TAVI. The addition of PMAi to the established STS score led to an increase in its prognostic ability.

Purpose: Cycling is widely practiced as a mode of transportation, a leisurely pursuit, and a competitive sport. Approximately half of cyclists experience low back pain. Yet, there has been limited study of spine tissue adaptations due to cycling., Methods: To investigate potential risk factors for spinal pain, we compared 18 high-volume cyclists (>150 km·wk for ≥5 yr) to 18 height-matched nonsporting referents. Participants had no history of spinal pathology. Magnetic resonance imaging was used to quantify intervertebral disc (IVD) morphology and hydration, and psoas, erector spinae, quadratus lumborum, and multifidus muscle size and fat content. Endurance of trunk muscles (flexors and extensors) was measured, and physical activity levels were assessed objectively using accelerometry., Results: Cyclists' IVD showed prolonged T2 time (+10.0% ± 17.3%; P = 0.021), implying better IVD hydration and glycosaminoglycan content, compared with referents. Lower thoracic and upper lumbar IVD T2 time were longer in cyclists (P ≤ 0.029) but not at the lower lumbar spine. T2 time differences were larger in the nucleus pulposus compared with the annulus fibrosus. Cyclists showed larger psoas muscles with less fat content compared with referents. Cyclists also exhibited longer isometric trunk endurance times (P ≤ 0.036) and higher physical activity levels (osteogenic index, P = 0.038)., Conclusion: Despite previous studies reporting higher than average prevalence of back pain in cyclists, the high-volume road cyclists in our cohort showed no anatomical or functional deficiency in spinal structures. By contrast, we found evidence for beneficial adaptations to the IVD and psoas muscles in high-volume cyclists compared with referents. These data support the notion that cycling is not detrimental to the spine, rather, by contrast, may be associated with beneficial changes at the spine.

Background: Appendicular skeletal muscle mass index and muscle attenuation (density) are negatively associated with mortality in European-derived populations., Objectives: The present analyses assessed association between axial skeletal muscle density and muscle index with mortality in European Americans with type 2 diabetes mellitus (T2D)., Design: Single-center observational study., Setting: Diabetes Heart Study., Participants: 839 European Americans with T2D., Methods: Computed tomography-measured psoas and paraspinous muscle mass index (cross sectional area/height2) and radiographic density (Hounsfield Units) were assessed in all participants. A Cox proportional hazards model was computed. The fully-adjusted model included covariates age, sex, body mass index, smoking, alcohol use, diabetes duration, insulin use, hormone replacement therapy (women), prevalent cardiovascular disease (CVD), hypertension, and coronary artery calcified atherosclerotic plaque mass score. Deaths were recorded in the National Death Index data through December 31, 2015., Results: Participants included 428 women and 411 men with median (25th, 75th quartile) age 62.8 (56.1, 69.1) years and diabetes duration 8.0 (5.0, 14.0) years. After 11.9 (9.4, 13.3) years of follow-up, 314 (37.4%) of participants were deceased. In the fully-adjusted model, psoas muscle density (hazard ratio [HR] 0.81, p<0.001), psoas muscle index (HR 0.82, p=0.008), and paraspinous muscle density (HR 0.85, p=0.003) were inversely associated with mortality. Paraspinous muscle index was not significantly associated with mortality (HR 0.90, p=0.08). Results did not differ significantly between men and women., Conclusions: In addition to established risk factors for mortality and CVD, higher psoas muscle index, psoas muscle density, and paraspinous muscle density were significantly associated with lower all-cause mortality in European Americans with T2D., Competing Interests: No conflicts exist

Purpose: This cadaver study was initiated to identify safe zones for psoas abscess debridement using a dorsal spinal approach., Methods: Twenty total specimens were dissected and lumbar transverse process (TP) and psoas muscles were identified. The distance from the lateral psoas muscle to the transverse process tip was measured. The lumbar plexus was dissected from the psoas and the distance from the TP to the lateral border of the lumbar plexus was measured. The area between the lateral edge of the psoas and lumbar plexus at each lumbar level was considered a safe zone of approach for entry into the psoas muscle for abscess debridement., Results: The most lateral portion of the lumbar plexus was 9.3 mm medial to the superior tip of the L1 TP and 9.2 mm medial to the inferior tip at L1, it was 11.8 and 11.7 mm medial at L2, 10.5 and 9.8 mm medial at L3, 6.6 and 6.2 mm medial at L4, and 1.0 and 0.9 mm medial at L5. The distances from the TP tip to the lateral edge of the psoas muscle were 5.7 and 5.5 mm medial to the superior and inferior tip of the TP at L1, 5.1 and 4.7 mm medial at L2, 2.5 and 1.8 mm medial at L3, 0.4 and 0 mm medial at L4 and 3.7 and 3.8 mm lateral at L5., Conclusions: This study provides landmarks to avoid the critical structures in the lumbar spine.

We performed a meta-analysis of currently available studies assessing prognostic value of psoas-muscle area (PMA) on mortality in patients who underwent transcatheter aortic valve implantation (TAVI). MEDLINE and EMBASE were searched through May 2018 to identify studies reporting ≥1-year all-cause mortality in PMA-stratified TAVI patients. A hazard ratio of follow-up (including early) mortality for "lowest-quantile" versus "higher-quantiles" PMA. Study-specific estimates were combined in the random-effects model. Our search identified 6 eligible studies enrolling a total of 1,237 TAVI patients with 1-year to 2-year (midterm) follow-up. A primary meta-analysis pooling all hazard ratios for "lowest-quantile versus higher-quantiles" PMA demonstrated significantly higher mortality in "lowest-quantile" than "higher-quantiles" patients (p <0.0001). A subgroup meta-analysis indicated no significant difference in mortality between "<50th- and ≥50th-percentile" patients (p = 0.95), but significantly higher mortality in "lowest-tertile" than "higher-tertiles" patients (p = 0.0009) and in "lowest-quartile" than "higher- quartiles" patients (p = 0.0003). A secondary meta-analysis revealed significantly higher mortality in "lowest-tertile" than "mid-tertile" patients (p = 0.01) and in "lowest-tertile" than "highest-tertile" patients (p = 0.01). A gender-stratified meta-analysis showed significantly higher mortality in "lowest-quantile" than "higher-quantiles" patients in both men (p = 0.0008) and women (p = 0.01). In conclusion, low PMA, especially "lowest-tertile/quartile" PMA, is a predictor of high all-cause mortality at midterm follow-up after TAVI for both men and women. However, PMA categorization into 50th percentiles may be invalid to predict mortality., (Copyright © 2018. Published by Elsevier Inc.)

Objective: To trace anatomic variations of the lateral femoral cutaneous nerve (LFCN) in its intrapelvic course., Methods: Forty cadavers (80 sides) fixed in 10% formalin solution were dissected. The following parameters were recorded: LFCN diameter and variations in its origin and number. The dissection comprised exposure and excision of the lumbar plexus, together with the roots of LFCN, followed by retrograde intraneural fascicular dissection using microsurgical instruments., Results: Several types of LFCN origin from the lumbar plexus were observed. Typically, the LFCN appears as a single trunk arising from dorsal divisions of the ventral rami of the lumbar plexus. The most prevalent origin of the nerve was from the L2 and L3 roots (47 cases; 58.75%). The LFCN took an origin from the L1-L2 level in 12 cases (15%) and from the L2 nerve in 9 cases (11.25%). The main observed variations were the presence of the accessory LFCN (2 cases; 2.5%) and branching of the LFCN from the femoral nerve (6 cases; 7.5%). Communications between the LFCN and the femoral or genitofemoral nerves also were observed occasionally. An atypical course of the LFCN with respect to the anterior psoas was observed in our material in 3 of the 80 sides (3.75% of the examined LFCN specimens)., Conclusions: Considerable variability in the origin and the course of the LFCN was observed, which should be taken into account during clinical assessment of nerve lesions and during surgery via transpsoas approaches to the lumbar spine., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: The relationship between sarcopenia and patient outcomes after pancreaticoduodenectomy (PD) for distal cholangiocarcinoma (DCC) remains unclear. We assessed the impact of sarcopenia on the outcomes after PD for DCC., Methods: We retrospectively analysed 65 patients who underwent PD for DCC. The quality of skeletal muscle indicated by the psoas muscle mass index (PMI) were measured on pre-operative computed tomography images. The impact of pre-operative sarcopenia on short- and long-term outcomes was evaluated., Results: Regarding short-term surgical outcomes, there were no marked differences between the high and low PMI groups. Regarding long-term oncological outcomes, the rates of recurrence (23.5% versus 58.3%, P = 0.011) was significantly lower in the high PMI group than in the low PMI group. Furthermore, the recurrence-free survival and disease-specific survival were longer in the high PMI group (P = 0.023 and P = 0.043, respectively). On multivariate analyses, low PMI was an independent predictor of recurrence (hazard ratio (HR) 11.06; P = 0.022) and disease-specific death (HR 11.88; P = 0.043)., Conclusions: Our findings suggested an association between pre-operative sarcopenia and poor long-term oncological outcomes after PD for DCC., (© 2018 Royal Australasian College of Surgeons.)

Background: Frailty is an important predictor of outcomes after cardiac surgery, but utility is limited by difficult assessment and quantification. We hypothesize that sarcopenia defined as psoas muscle cross-sectional area is a useful predictor of surgical aortic valve replacement outcomes in moderate to high-risk patients., Methods: Moderate to high risk patients (predicted risk of mortality greater than 3%) who underwent surgical aortic valve replacement with or without coronary artery bypass were extracted from an institutional database (2009 to 2016). Psoas index was calculated as the cross-sectional area of the psoas muscle at the L4 vertebral level normalized to body surface area. Patients were stratified by sarcopenia status, defined as less than 25th sex-specific percentile. Multivariable regression analysis identified risk-adjusted associations with psoas index using The Society of Thoracic Surgeons predicted risk scores., Results: Of the 240 patients included, the median predicted risk of mortality was 6%, median age 80 years, and 40% were female. Patients with (33.3%) and without (66.7%) sarcopenia had equivalent baseline risk (median predicted risk of mortality 5.7% versus 6.0%, p = 0.29). Patients with sarcopenia had higher 1-year mortality (31.9% versus 16.9% p = 0.03). Psoas index significantly predicted risk-adjusted 1-year mortality (odds ratio 0.84, p = 0.02) and long-term mortality (hazard ratio 0.92, p = 0.04), as well as risk-adjusted major morbidity, prolonged ventilation, length of stay, discharge to a facility, and hospital cost. Finally, psoas index measurements were highly reproducible (Pearson correlation coefficient 0.944)., Conclusions: Psoas index is an easily obtained and reproducible measure of frailty that predicts risk-adjusted resource utilization, morbidity, and long-term mortality. Psoas index may improve procedural selection and risk adjustment in high-risk patients with aortic valve disease., (Copyright © 2018 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: Frailty is a recognized predictor of poor outcome in patients undergoing surgical intervention. Frailty is intricately linked with body morphology, which can be evaluated using morphometric assessment via computerized tomographic (CT) imaging. We aimed to assess the predictive power of such objective assessments in a broad cohort of vascular surgical patients., Methods: A consecutive series of patients aged over 65 years admitted to a vascular unit, who had undergone CT imaging of the abdomen, were analyzed. Demographic and patient-specific data were collated alongside admission relevant information. Outcomes included mortality, length of stay, health care-related costs, and discharge destination. Images were analyzed for 4 morphometric measurements: (1) psoas muscle area, (2) mean psoas density, (3) subcutaneous fat depth, and (4) intra-abdominal fat depth, all taken at the level of the fourth lumbar vertebra., Results: Two hundred and ten patients were initially analyzed. Forty-four patients had significant retroperitoneal and abdominal abnormalities that limited appropriate CT analysis. Decreased subcutaneous fat depth was significantly associated with mortality, readmission within 12 months, and increased cost of health care (P < 0.01, adjusted for confounders). Psoas muscle area was significantly associated with readmission-free survival., Conclusions: Morphometric analysis predicts poorer outcome in a broad cohort of vascular surgery patients. Such assessment is likely to enhance patient counseling regarding individual risk as well as enhancing the ability to undertake risk-modified surgical audit., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objectives: Loss of muscle mass has been associated with poor survival in several surgical patient populations, including those with an abdominal aortic aneurysm (AAA). We wanted to replicate these findings and assess the association between psoas muscle area (PMA) and survival in patients with an asymptomatic AAA., Methods: Patients with an asymptomatic infrarenal AAA who underwent computed tomography (CT) scanning between January 1, 2007, and December 31, 2013, were included in this single-centre retrospective cohort study. PMA was measured with thresholding on an axial image at the centre level of the third lumbar vertebra. The lowest tertile of PMA in all patients was used as a cutoff value for a low PMA. Then, in separate analyses for conservatively and surgically managed patients, survival was estimated with the Kaplan-Meier method. Differences in survival between patients with and without a low PMA were tested with the log-rank test., Results: Of 228 patients, 104 were managed conservatively and 124 underwent AAA repair. Seventy-seven patients (62%) had an endovascular repair. In these 228 patients, the median PMA was 16.83 cm 2 , while the cutoff value for low PMA was 14.56 cm 2 . Patients who were managed conservatively were more often classified as having low PMA (45/104, 43%, vs. 31/124, 25%; p = .004) and were significantly older (mean 73.44 ± 9.05 years vs. 69.03 ± 7.46 years; p < .001). Low PMA was not associated with survival, either in patients managed conservatively, or in those who underwent AAA repair (p = .512 and p = .311, respectively)., Conclusions: The association between low PMA and poor survival could not be replicated; in this study, low PMA was not associated with survival in patients with an asymptomatic AAA. Further research is recommended before PMA can be used for pre-operative risk stratification., (Copyright © 2017 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.)

Study Design: Retrospective imaging review., Objective: Utilize magnetic resonance imaging (MRI) to expand the anatomical description of psoas morphology and its association with neurovascular structures at L4-5., Summary of Background Data: Anatomical psoas muscle variants may present a greater risk of neurovascular injury at the L4-5 level during lateral transpsoas approaches., Methods: Axial L4-5 sections of consecutive patients who obtained lumbar MRIs were analyzed. Teardrop psoas morphology was assessed qualitatively. MRI described psoas morphology and proximity of neurovascular structures, whereas plain radiographs were evaluated for lumbosacral transitional vertebrae (LSTV). Teardrop morphology was tested for associations with radiographic measurements using t tests and χ analysis., Results: Fifty teardrop and 476 nonteardrop psoas muscles were identified. Teardrop morphology was associated with greater longitudinal length (53.1 vs. 49.3 mm, P = 0.012), and shorter transverse length (34.9 vs. 44.8 mm, P < 0.001) compared with nonteardrop. Teardrop morphology was associated with anterior and lateral migration of the psoas with greater distance between the anterior borders of the psoas and disc (13.5 vs. 6.3 mm, P < 0.001), and greater distance between the medial border of the psoas to the lateral disc border (1.6 vs. 0.5 mm, P < 0.001). Teardrop morphology was associated with a higher incidence of the lumbar plexus migrating anteriorly adjacent to the middle-third of the disc (43.4% vs. 17.6%, P < 0.001) and the iliac vasculature being more laterally and posteriorly located, adjacent to the anterior-third of the disc (43.4% vs. 30.0%, P = 0.047). Teardrop morphology was not associated with presence of LSTV (3.8% vs. 7.6%, P = 0.306)., Conclusion: The current study provides detailed metrics of teardrop psoas muscles and surrounding structures. The study confirms that the presence of teardrop anatomy on L4-5 axial imaging is associated with anterior migration of the lumbar plexus and posterolateral migration of the iliac vasculature which may increase the risk of neurovascular injury during direct and oblique-lateral lumbar spine procedures., Level of Evidence: 3.

Background: In total hip arthroplasty (THA) surgery, hip muscle preservation is important in strengthening the stability of the hip and improving the activities of the patient. However, whether the type of femoral stem affects the recovery of the hip muscles remains unknown. The aim of this study was to compare the postoperative hip muscle recovery among femoral stem varieties after THA., Methods: The computed tomography (CT) images of 44 patients (44 hips) who underwent THA using an anterolateral approach were reviewed. Twenty-two patients received a fit-and-fill (FF) stem and 22 received the tapered-wedge (TW) stem. The volumes of the gluteus maximus (GMA), gluteus medius (GME), and obturator internus (OI) were measured on three-dimensional models reconstructed using preoperative and 6-month postoperative CT images. Relationships between muscle volume changes and factors including the femoral stem length were evaluated., Results: The GMA and GME volumes increased postoperatively by 8.2% and 8.3%, respectively, in the FF stem group and 7% and 6%, respectively, in the TW stem group, with no group differences. In contrast, the OI volume decreased postoperatively by 17.8% in the FF group and was preserved in TW group (p < 0.001). Moreover, OI volume was decreased in 19 patients (86%) in the FF group and in 11 patients (50%) in the TW group (p = 0.01). The normalized stem length was significantly associated with the postoperative change in OI volume (r = -0.45, p = 0.002)., Conclusions: The TW stem showed a significant advantage over the FF stem in terms of OI preservation. Surgeons should pay close attention during surgery to avoid OI injury when using different femoral stem types. We suggest that a short and reduced lateral shoulder femoral stem is a better choice for the preservation of external rotation muscles., (Copyright © 2017 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Background: There is a high morbidity rate after digestive surgery in patients with nutritional disorders such as high body mass index and depletion of skeletal muscle., Materials and Methods: The ratio of psoas muscle area to trunk area was defined as the Psoas and All trunk Ratio (PandA Ratio) and used as an index of the balance between muscle and adipose tissue. This ratio was determined in 77 patients undergoing laparoscopy-assisted gastrectomy (LAG) for gastric cancer. Patients were classified into groups with and without postoperative complications. Clinicopathological factors were compared between the groups, and relationships of PandA Ratio with other nutritional indices were examined. PandA Ratios were also analyzed in males and females in each Clavien-Dindo grade., Results: Complications developed in 22 patients (28.6%) after LAG. The PandA Ratio was significantly lower in patients with complications in univariate (2.76 ± 0.22% versus 3.66 ± 0.14%, P = 0.0009) and multivariate (P = 0.0064) analyses. A low PandA Ratio was also associated with more severe complications in males., Conclusions: Measurement of the areas of the psoas muscle and trunk on CT is useful for evaluation of the balance between skeletal and adipose tissue. The PandA Ratio derived from these measurements is a predictor of the clinical course after LAG in males., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: Recently, sarcopenia has been reported as a new predictor for patient outcomes or likelihood of post-operative complications. The purpose of this study was to evaluate the association of the psoas muscle volume with the length of hospitalization among patients undergoing radical cystectomy., Methods: A total of 63 (80.8%) male patients and 15 (19.2%) female patients who underwent radical cystectomy for their bladder cancer in our institution from 2000 to 2015 were analyzed. The psoas muscle index (PMI) was calculated by normalizing the psoas muscle area calculated using axial computed tomography at the level of the umbilicus (cm 2 ) by the square of the body height (m 2 ). Longer hospitalization was defined as hospitalization exceeding 30 days after surgery., Results: The median PMIs (mean ± standard deviation) were 391 (394 ± 92.1) and 271 (278 ± 92.6) cm 2 /m 2 in men and women, respectively. Thus, the PMIs of male patients were significantly larger than those of females (p < 0.001). Based on the differences in gender, we analyzed 63 male patients for a further analysis. In male patients, those hospitalized longer showed a significantly smaller PMI than those normally discharged (377 ± 93.1 vs. 425 ± 83.4; p = 0.04). Similarly, male patients with a small PMI (<400) had a significantly worse overall survival (p = 0.02) than those with a large PMI (≥400)., Conclusions: The presence of sarcopenia was found to be associated with significantly longer hospitalization after radical cystectomy in male patients. Furthermore, in men, a PMI <400 may suggest a significantly worse prognosis.

Objective: To evaluate intraoperative and postoperative efficacy of ultrasound (US)-guided femoral (FN) and obturator (ON) nerves block, in the iliopsoas muscle compartment (IPM), using an in-plane technique., Study Design: Anatomical research and randomized, prospective, 'blinded' clinical study., Animals: Six dog cadavers and 20 client-owned dogs undergoing tibial plateau levelling osteotomy (TPLO) surgery., Methods: In phase 1, anatomical dissections and US imaging of the IPM were performed to design an US-guided nerve block involving the FN and ON simultaneously. The technique was considered successful if new methylene blue solution injection (0.1 mL kg -1 ) stained FN-ON for ≥2 cm. In phase 2, the US-guided nerve block designed in phase 1, combined with US-guided sciatic nerve (ScN) block, was performed in 20 dogs undergoing TPLO surgery. Patients were assigned randomly to one of two treatment groups: ropivacaine 0.3% (R3, n=10) and ropivacaine 0.5% (R5, n=10) at a volume of 0.1 mL kg -1 for each nerve block. Intraoperative success rate (fentanyl requirement < 2.1 mcg kg -1  hour -1 ) and postoperative pain score [Short Form-Glasgow Composite Measure Pain Scale (SF-GCMPS) ≥ 5/20] were evaluated., Results: In phase 1, the US image of FN-ON was detected between L6 and L7. In-plane needling technique produced a staining of >4 cm in six of six cases. No abdominal or epidural dye spread was found. In phase 2, median fentanyl infusion rates were 0.5 (0.0-0.9) μg kg -1  hour -1 for R3 and 0.6 (0.0-2.2) μg kg -1  hour -1 for R5. At 9 and 11 hours after the peripheral nerve blocks, an SF-GCMPS ≥ 5 was observed for R3 and R5, respectively., Conclusions and Clinical Relevance: The US-guided FN-ON block in the IPM, using an in-plane technique, combined with US-guided ScN block, provided sufficient analgesia to minimize the use of fentanyl during TPLO surgery. A longer postoperative analgesia was observed in group R5 compared with R3., (Copyright © 2017 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Background Context: Injuries to the lumbar plexus during lateral approaches to the spine are not uncommon and may result in permanent deficits. However, the literature contains few studies that provide landmarks for avoiding the branches of the lumbar plexus., Purpose: The present anatomical study was performed to elucidate the course of these nerves in relation to lateral approaches to the lumbar spine., Study Design: This is a quantitative anatomical cadaveric study., Methods: The lumbar plexus and its branches were dissected on 12 cadaveric sides. Metal wires were laid on the nerves along their paths on the posterior abdominal wall. Fluoroscopy was performed in the anteroposterior and lateral positions. The relationships between regional bony landmarks and the branches of the lumbar plexus were observed., Results: When viewed laterally, the greatest concentration of nerves occurred from the posteroinferior aspect of L4, inferior along the posterior one-third of the body of L5, then at the level of the sacral promontory. On the basis of our study, approaches to the anterior two-thirds of the L4 vertebra and anterior third of L5 will result in the lowest chance of lumbar plexus nerve injury. In addition, lateral muscle dissection through the psoas major should be in a superior to inferior direction in order to minimize nerve injury. Laterally, the widest corridor between branches in the abdominal wall was between the subcostal and iliohypogastric nerves., Conclusions: The findings of our cadaveric study provide surgeons who approach the lateral lumbar spine with data that could decrease injuries to the branches of the lumbar plexus, thus lessening patient morbidity., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: This review seeks to synthesize emerging literature on the effects of back muscle size on outcomes in spine surgery. Risk factors that contribute to poor surgical outcomes continue to be an area of interest in spine surgery because proper risk stratification can result in reduction in morbidity and enhanced patient care. However, the impact of muscle size on spine surgical outcomes is an understudied avenue with paucity of data evaluating the relationship among back muscles and surgical outcomes, patient's quality of life, and functional improvement postoperatively., Methods: This review was centered around identifying studies that assessed the impact of back muscle size on spine surgery outcomes., Results: Five retrospective studies were selected for review. All studies set out to see if differences in muscle size existed in patients with disparate post-operative outcomes as a primary objective. The studies support the association between larger back muscles and improved outcomes. The size and relative cross sectional area of paraspinal muscles and the size of the psoas muscle were associated with functional outcomes, incidence of complications and also fusion rates., Conclusion: With reduction in surgical complications and improvement in postoperative functional outcomes, back muscle morphometry ought to be included in the preoperative surgical planning as a predictor of outcomes., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Objective: To demonstrate the superiority of total psoas volume (TPV) over total psoas area (TPA) in terms of predicting post-operative complications in living-donor liver transplantation (LDLT)., Methods: The TPA and TPV were assessed in 32 recipients who underwent CT before LDLT. The TPA was measured using an axial CT image at the level of the upper margin of the fourth lumbar vertebral body. The TPV was calculated using all the CT images from the muscle origin through the level of the pubic symphysis. Patients were divided into a sarcopenia group and no-sarcopenia group based on the medians of normalized TPA (nTPA) and normalized TPV (nTPV). We calculated the odds ratio (OR) of post-operative respiratory complications in relation to nTPA and nTPV, respectively., Results: Out of 32 recipients, 17 recipients experienced at least 1 post-operative respiratory complication. The OR for males according to nTPV [OR = 15.00, 95% confidence interval (CI) = 1.03-218.31; p = 0.031] was higher than that for nTPA (OR = 3.33, 95% CI = 0.36-30.70; p = 0.280). The OR for females according to nTPV (OR = 4.00, 95% CI = 0.56-28.40; p = 0.16) was the same as that for nTPA (OR = 4.00, 95% CI = 0.56-28.40; p = 0.16)., Conclusion: Pre-operative volume of the skeletal muscle might be a better predictor for post-operative risks in LDLT recipients than pre-operative area of the skeletal muscle. Advances in knowledge: Post-operative risks for respiratory complications in LDLT recipients might be evaluated more accurately by using TPV instead of TPA.

The iliopsoas of the rat is composed of two muscles - the psoas major muscle and the iliacus muscle. The psoas major muscle arises from all the lumbar vertebrae and the iliacus muscle from the fifth and sixth lumbar vertebrae and ilium. Their common insertion point is the lesser trochanter of the femur, and their common action is the lateral rotation of the femur and flexion of the hip joint. Unlike humans, the rat is a quadruped and only occasionally rises up on its hind legs. Therefore, it is expected that the fibre type composition of the rat iliopsoas muscle will be different than that of humans. The iliopsoas muscle of the rat is generally considered to be a fast muscle. However, previous studies of the fibre type composition of the rat psoas muscle showed different results. Moreover, very little is known about the composition of the rat iliacus muscle. The aim of our study was to examine the fibre type composition of the rat iliopsoas muscle in order to better understand the complex function of the listed muscle. The psoas major muscle was examined segmentally at four different levels of its origin. Type I, IIA, IIB and IIX muscle fibres were typed using monoclonal antibodies for myosin heavy chain identification. The percentage of muscle fibre types and muscle fibre cross-sectional areas were calculated. In our study we showed that in the rat iliopsoas muscle both the iliacus and the psoas major muscles had a predominance of fast muscle fibre types, with the highest percentage of the fastest IIB muscle fibres. Also, the IIB muscle fibres showed the largest cross-sectional area (CSA) in both muscles. As well, the psoas major muscle showed segmental differences of fibre type composition. Our results showed changes in percentages, as well as the CSAs of muscle fibre types in cranio-caudal direction. The most significant changes were visible in type IIB muscle fibres, where there was a decrease of percentages and the CSAs from the cranial towards the caudal part of the muscle. From our results it is evident that the rat iliopsoas muscle has a heterogeneous composition and is composed of all four muscle fibre types. Primarily, it is a fast, dynamic muscle with a predominance of fast type IIB muscle fibres with the largest CSAs. The composition of the rat psoas major muscles changes in a cranio-caudal direction, thus pointing to a more postural role of the caudal part of the muscle., (© 2017 Anatomical Society.)

Purpose: XLIF ® is a widely used minimally invasive technique to treat different spine pathologies. The aim of this study was to quantify nerve distortion of lumbar plexus during XLIF ® approach and to correlate it with morphometric data., Methods: Nine fresh frozen cadaveric specimens were used. All specimens were subjected to the same dissection procedure cored on a left XLIF® approach at L2/L3 and L4/L5 levels. Distortion of cutaneous superficial nerves, femoral nerve (FN) at L4/L5 and genitofemoral nerve (GN) at L2/L3 and L4/L5 while opening the retractor were assessed and analyzed with respect to psoas muscle features., Results: Superficial nerves were slightly displaced but never stretched. FN, as well as GN at L4/L5 level, could be displaced and stretched by the blades. Statistically significant correlation between FN distortion and the amount of psoas fibers interposed between the posterior blade of the retractor and the nerve itself (TCK) was found. GN distortion was found to be related to its clock position on an axial section of psoas muscle seen from cranially at L4/L5., Conclusion: FN was in close connection with the deep psoas muscle fibers and it is subjected to anterior translation that correlates with TCK. This mechanism may partly explain the rate of femoral nerve palsy that occurs despite neuromonitoring and safe entry zones respect. The GN location at L4/L5 should be considered not only for its projection in Zone I, but also for its clock position on the psoas muscle surface, since it affects its distortion.

Purpose: Although the course of the ureter is described as a straight descent in the retroperitoneum, kinking of the upper ureter is often seen at imaging. The aim of this study was to investigate kinking of the ureter and its underlying anatomico-clinical significance., Methods: We evaluated 176 computed tomography (CT) images and classified kinking into three grades: no/mild kinking as Grade 1, moderate as Grade 2, and severe as Grade 3. We defined the "crossing point" (CP) as where the ureter crosses over the gonadal vein and assessed its relation to the kinking. Fourteen halves from seven cadavers were used for examination. Approaching anteriorly, we macroscopically observed the ureter and surrounding structures., Results: On CT, the rate of the radiologically "significant" kinking classified into either Grade 2 or 3 was 18.4 % on the right and 21.8 % on the left. All kinking was either at or above the level of the CP. In cadavers, the ureter was relatively mobile in the perirenal fat and then beginning at approximately the level of the CP became firmly fixed to the anteromedial aspect of the psoas major muscle., Conclusions: Kinking of the upper ureter is not a clinically significant finding and arises from the ureter having a relatively mobile portion in the perirenal space compared to its caudal portion. The fixation boundary can be identified by observing the CP.

Objectives: Previous research has shown that motor control training improved size and function of trunk muscles in elite football players with and without low back pain (LBP). Imbalances in hip muscles have been found in athletes with LBP and it is not known if motor control training can change these muscles. This study investigated if a motor control intervention program affected hip muscle size in elite football players with and without LBP., Design: Panel-randomised intervention design., Methods: Forty-six players from one club in the Australian Football League (AFL) participated in a motor control training program delivered across the season as a stepped-wedge intervention design with 3 treatment arms: 15 weeks intervention, 8 weeks intervention and a wait-list control who received 7 weeks intervention toward the end of the playing season. Presence of LBP was assessed by interview and physical examination. Cross-sectional areas of iliacus, psoas, iliopsoas, sartorius, gluteus minimus, and gluteus medius muscles were measured from magnetic resonance images taken at 3 time points during the season., Results: Iliopsoas, sartorius and gluteus medius muscle size increased for players who received intervention (p<0.05). For players with current LBP, sartorius and gluteus medius muscle size increased for those who received motor control training (p<0.05)., Conclusions: Motor control training programs aimed at the lumbo-pelvic region also benefit the hip muscles. For players with current LBP, the intervention mitigated sartorius muscle atrophy and increased gluteus medius muscle size. These findings may help guide the management of LBP in elite football players., (Copyright © 2016. Published by Elsevier Ltd.)

Objectives: Low skeletal muscle, referred to as sarcopenia, has been shown to be an independent predictor of lower overall survival in various kinds of diseases. Several studies have evaluated the low skeletal muscle mass using computed tomography (CT) imaging. However, the cutoff values based on CT imaging remain undetermined in Asian populations., Methods: Preoperative plain CT imaging at the third lumbar vertebrae level was used to measure the psoas muscle mass index (PMI, cm(2)/m(2)) in 541 adult donors for living donor liver transplantation (LDLT). We analyzed PMI distribution according to sex or donor age, and determined the sex-specific cutoff values of PMI to define low skeletal muscle mass., Results: PMI in men was significantly higher than observed in women (8.85 ± 1.61 cm(2)/m(2) versus 5.77 ± 1.21 cm(2)/m(2); P < 0.001). PMI was significantly lower in individuals ≥50 y than in younger donors in both men and women (P < 0.001 and P < 0.001, respectively). On the basis of the younger donor data, we determined the sex-specific cutoff values for the low skeletal muscle mass were 6.36 cm(2)/m(2) for men and 3.92 cm(2)/m(2) for women (mean - 2 SD)., Conclusion: Data from healthy young Asian adults were used to establish new criteria for low skeletal muscle mass that would be applicable for defining sarcopenia in Asian populations., (Copyright © 2016 Elsevier Inc. All rights reserved.)

This study examined the influence of regular training in competitive cycling on individual muscle volume of the thigh and psoas major cross-sectionally and longitudinally. T1-weighted magnetic resonance (MR) images of the trunk and right thigh were obtained from eight experienced varsity male cyclists (experience: > 4 years) and 10 untrained men (experiment 1), and from 12 (10 males, two females) varsity cyclists before and after competitive cycling training for 6 months (experiment 2). From the MR images, the volumes of each of the quadriceps femoris and hamstrings, total adductors, gracilis, sartorius, and psoas major were determined. The volumes of the monoarticular thigh muscles, semitendinosus, and psoas major muscles were significantly greater in the experienced cyclists than in the untrained men (experiment 1), and increased significantly after the competitive training for 6 months (experiment 2). In contrast, the volumes of the other biarticular thigh muscles were similar among the experienced cyclists and untrained men (experiment 1), and did not change by competitive cycling training (experiment 2). The results indicate that competitive cycling training induces muscle-specific hypertrophy of the synergistic muscles, especially between the monoarticular and biarticular muscles, leading to quantitative profiles of the musculature in experienced cyclists., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Objective: We investigate whether psoas or paraspinous muscle area measured on a single L4-L5 image is a useful measure of whole lean body mass (LBM) compared to dedicated midthigh magnetic resonance imaging (MRI)., Design: Observational study., Setting: Outpatient dialysis units and a research clinic., Subjects: One hundred five adult participants on maintenance hemodialysis. No control group was used., Intervention: Psoas muscle area, paraspinous muscle area, and midthigh muscle area (MTMA) were measured by magnetic resonance imaging., Main Outcome Measure: LBM was measured by dual-energy absorptiometry scan., Results: In separate multivariable linear regression models, psoas, paraspinous, and MTMA were associated with increase in LBM. In separate multivariate logistic regression models, C statistics for diagnosis of sarcopenia (defined as <25th percentile of LBM) were 0.69 for paraspinous muscle area, 0.81 for psoas muscle area, and 0.89 for MTMA. With sarcopenia defined as <10th percentile of LBM, the corresponding C statistics were 0.71, 0.92, and 0.94., Conclusions: We conclude that psoas muscle area provides a good measure of whole-body muscle mass, better than paraspinous muscle area but slightly inferior to midthigh measurement. Hence, in body composition studies a single axial MR image at the L4-L5 level can be used to provide information on both fat and muscle and may eliminate the need for time-consuming measurement of muscle area in the thigh., (Copyright © 2016 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Study Design: In vivo analysis in swine model., Objective: The purpose of this study was to determine the accuracy of triggered EMG (t-EMG) and its reliability in lateral lumbar interbody fusions surgery. We also aim to document changes in psoas muscle produced during the approach., Summary of Background Data: Lateral lumbar interbody fusions is preferred over direct anterior approach because of lower complications, blood loss, and shorter recovery time. Threshold-EMGs are utilized for real-time feedback about nerve location; however, neurological deficits are widely reported, and are unique to this approach. Multiple factors have been hypothesized including neuropraxia from retractors and compression from psoas hematoma/edema. The variable reports of neurological complication even with t-EMGs indicate the need to study them further., Methods: Eight swines underwent left-sided retroperitoneal approach. The nerve on the surface of the psoas was identified and threshold-EMGs were obtained utilizing a ball-tip, and needle probe. First EMG and threshold responses required to elicit 20-μV responses were recorded for 2 mm incremental distances up to 10 mm. In the second part, a K-wire was inserted into the mid-lumbar disc space, and a tubular retractor docked and dilated adequately. Postmortem CT scans were carried out to evaluate changes in psoas muscle., Results: A t-EMG stimulus threshold of <5 mA indicates a higher probability that the probe is close to or on the nerve, but this was not proportional to the distance suggesting limitations for nerve mapping. Negative predictive value of t-EMGs is 76.5% with the ball-tipped probe and 80% with the needle probe for t-EMG ≥10 mA and indicates that even with higher thresholds, the nerve may be much closer than anticipated. Postoperative hematoma was not seen on CT scans., Conclusion: Threshold measurements are unreliable in estimating distance from the nerve in an individual subject and higher values do not always correspond to a 'safe zone.", Level of Evidence: 5.