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Background: The function of the paraspinal muscles and especially the psoas muscle in maintaining an upright posture is not fully understood. While usually considered solely as a hip flexor, the psoas muscle and its complex anatomy suggest that the muscle has other functions involved in stabilizing the lumbar spine. The aim of this study is to determine how the psoas muscle and the posterior paraspinal muscles (PPM; erector spinae and multifidus) interact with each other., Methods: A retrospective review including patients undergoing posterior lumbar fusion surgery between 2014 and 2021 at a tertiary care center was conducted. Patients with a preoperative lumbar magnetic resonance imaging (MRI) scan performed within 12 months prior to surgery were considered eligible. Exclusion criteria included previous spinal surgery at any level, lumbar scoliosis with a Cobb Angle > 20° and patients with incompatible MRIs. MRI-based quantitative assessments of the cross-sectional area (CSA), the functional cross-sectional area (fCSA) and the fat area (FAT) at L4 was conducted. The degree of fat infiltration (FI) was further calculated. FI thresholds for FI PPM were defined according to literature and patients were divided into two groups (< or ≥ 50% FI PPM )., Results: One hundred ninetypatients (57.9% female) with a median age of 64.7 years and median BMI of 28.3 kg/m 2 met the inclusion criteria and were analyzed. Patients with a FI PPM  ≥ 50% had a significantly lower FI in the psoas muscle in both sexes. Furthermore, a significant inverse correlation was evident between FI PPM and FI Psoas for both sexes. A significant positive correlation between FAT PPM and fCSA Psoas was also found for both sexes. No significant differences were found for both sexes in both FI PPM groups., Conclusion: As the FI PPM increases, the FI Psoas decreases. Increased FI is a surrogate marker for a decrease in muscular strength. Since the psoas and the PPM both segmentally stabilize the lumbar spine, these results may be indicative of a potential compensatory mechanism. Due to the weakened PPM, the psoas may compensate for a loss in strength in order to stabilize the spine segmentally., (© 2023. The Author(s).)

Background Context: The lateral transpsoas approach to interbody fusion of the lumbar spine (lateral lumbar interbody fusion [LLIF]) with recombinant human bone morphogenetic protein-2 (BMP-2) augmentation has been increasingly performed in recent years. Potential side effects and adverse sequelae of BMP-2 in the acute setting remain to be fully elucidated., Purpose: To review the literature for reports of complications related to BMP-2 implantation in lumbar spinal surgery and present a case of a contralateral psoas muscle seroma after LLIF with BMP-2 implantation., Study Design: Case report and literature review., Methods: The PubMed database was searched for articles related to adverse events to BMP-2 in lumbar spinal surgery. We report the case of a 57-year-old woman who underwent routine right-sided transpsoas approach for LLIF with the use of BMP-2 at our institution and developed a left-sided psoas muscle fluid accumulation 2 weeks postoperatively., Results: No reports of complications contralateral to an LLIF approach attributable to an inflammatory response to BMP-2 were identified in the English literature. In the presented patient, a large (4.2×6.5×2.7 cm) left-sided sterile intramuscular psoas fluid collection was seen on a magnetic resonance imaging study obtained on postoperative day 14. At a 6-month follow-up, left-sided L5 radiculopathy resulting in 4/5 foot drop was confirmed by electromyography. The patient reported here represents the only case of a contralateral psoas seroma with suspected association to BMP-2 utilization in LLIF encountered at our institution., Conclusions: A serous psoas muscle fluid accumulation after BMP-2 implantation may rarely occur contralateral to the surgical approach for LLIF. Further characterization of complications related to BMP-2 implantation after lumbar spinal surgery will help guide preoperative informed decision making and the management of this unusual postoperative adverse event., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Purpose: This study aimed to investigate the impact of sarcopenia and lumbar paraspinal muscle composition (PMC) on patient-reported outcomes (PROs) after lumbar fusion surgery with 12-month follow-up (12 M-FU). Methods: A prospective investigation of patients undergoing elective lumbar fusion was conducted. Preoperative MRI-based evaluation of the cross-sectional area (CSA), the functional CSA (fCSA), and the fat infiltration(FI) of the posterior paraspinal muscles (PPM) and the psoas muscle at level L3 was performed. Sarcopenia was defined by the psoas muscle index (PMI) at L3 (CSAPsoas [cm2]/(patients' height [m])2). PROs included Oswestry Disability Index (ODI), 12-item Short Form Healthy Survey with Physical (PCS-12) and Mental Component Scores (MCS-12) and Numerical Rating Scale back and leg (NRS-L) pain before surgery and 12 months postoperatively. Univariate and multivariable regression determined associations among sarcopenia, PMC and PROs. Results: 135 patients (52.6% female, 62.1 years, BMI 29.1 kg/m2) were analyzed. The univariate analysis demonstrated that a higher FI (PPM) was associated with worse ODI outcomes at 12 M-FU in males. Sarcopenia (PMI) and higher FI (PPM) were associated with worse ODI and MCS-12 at 12 M-FU in females. Sarcopenia and higher FI of the PPM are associated with worse PCS-12 and more leg pain in females. In the multivariable analysis, a higher preoperative FI of the PPM (β = 0.442; p = 0.012) and lower FI of the psoas (β = −0.439; p = 0.029) were associated with a worse ODI at 12 M-FU after adjusting for covariates. Conclusions: Preoperative FI of the psoas and the PPM are associated with worse ODI outcomes one year after lumbar fusion. Sarcopenia is associated with worse ODI, PCS-12 and NRS-L in females, but not males. Considering sex differences, PMI and FI of the PPM might be used to counsel patients on their expectations for health-related quality of life after lumbar fusion. [ABSTRACT FROM AUTHOR]

Purpose: Intervertebral vacuum phenomenon (IVP) and paraspinal muscular atrophy are age-related changes in the lumbar spine. The relationship between both parameters has not been investigated. We aimed to analyze the correlation between IVP and paraspinal muscular atrophy in addition to describing the lumbar vacuum severity (LVS) scale, a new parameter to estimate lumbar degeneration. Methods: We analyzed patients undergoing spine surgery between 2014 and 2016. IVP severity was assessed utilizing CT scans. The combination of vacuum severity on each lumbar level was used to define the LVS scale, which was classified into mild, moderate and severe. MRIs were used to evaluate paraspinal muscular fatty infiltration of the multifidus and erector spinae. The association of fatty infiltration with the severity of IVP at each lumbar level was assessed with a univariable and multivariable ordinal regression model. Results: Two hundred and sixty-seven patients were included in our study (128 females and 139 males) with a mean age of 62.6 years (55.1—71.2). Multivariate analysis adjusted for age, BMI and sex showed positive correlations between LVS-scale severity and fatty infiltration in the multifidus and erector spinae, whereas no correlation was observed in the psoas muscle. Conclusion: IVP severity is positively correlated with paraspinal muscular fatty infiltration. This correlation was stronger for the multifidus than the erector spinae. No correlations were observed in the psoas muscle. The lumbar vacuum severity scale was significantly correlated with advanced disc degeneration with vacuum phenomenon. [ABSTRACT FROM AUTHOR]

Background: Aortic abdominal calcification (AAC) is associated with spine-related conditions, such as lower back pain and reduced bone mineral density. Similar to peripheral vascular disease, AAC possibly reduces blood flow to the lumbar posterior paraspinal muscles (PPM) which may lead to atrophy and increased fatty infiltration. Methods: Imaging of patients with lower back pain was analyzed. AAC was assessed on lateral lumbar radiographs according to the Kauppila classification. The cross-sectional area of the PPM was measured on a T2-weighted axial MRI sequence and the functional cross-sectional area (fCSA) and fatty infiltration (FI) were calculated with custom software. The association of AAC and FI as well as AAC and fCSA was assessed by multivariable linear regression, adjusted for age, sex, body mass index (BMI), diabetes, and smoking. Results: Two hundred and thirty patients (47.8% female) with a median age of 60 years (IQR 48–68) were analyzed. In patients, without AAC the median FI of the PPM was 33.3% (IQR 29.1–37.6%), compared to 44.6% (IQR 38.5–54.3%) in patients with AAC (p < 0.001). In the multivariable linear regression, both fCSA and FI of the PPM were significantly and independently associated with the degree of AAC (p = 0.037 and p = 0.015, respectively). Conclusions: This is the first study to demonstrate a significant and independent association between AAC and PPM morphology. The results of this study improve our understanding of the interaction between AAC and spinal musculature, with AAC being a reason for atrophy of the PPM. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to investigate the changes of the posterior paraspinal muscles (PPM) and psoas muscle in patients with low back pain (LBP) over time. Methods: Patients with LBP who had a repeat lumbar MRI with a minimum of 3-years apart at a tertiary referral center were analyzed. MRI-based quantitative assessments of the PPM and the psoas muscle were conducted for the baseline and follow-up MRI. The cross sectional area (CSA), the functional cross sectional area (fCSA) and the fat area (FAT) were calculated using a dedicated software program. The fatty infiltration (FI,%) of the regions of interest was calculated. Differences between the 1st and 2nd MRI were calculated for all assessed muscular parameters. Results: A total of 353 patients (54.4%female) with a median age of 60.1 years and BMI of 25.8 kg/m2 at baseline were analyzed. The mean time between the 1st and 2nd MRI was 3.6 years. The fCSAPPM declined in both sexes significantly from the 1st to the 2nd MRI, whereas the FATPPM increased. In line with this result, the FIPPM increased in both males (29.9%) and females (19.4%). Females had a higher FIPPM and FIPsoas than males in both MRIs. In females, no significant changes were found for the psoas muscle. The CSAPsoas and fCSAPsoas in males were significantly smaller in the 2nd MRI. With increasing age, a significant trend in a decrease in ∆FIPPM was observed for both sexes. Conclusion: The study revealed significant quantitatively muscular changes in males and females, especially in the posterior paraspinal muscles in only three years' time. [ABSTRACT FROM AUTHOR]

Purpose: Standalone lateral lumbar interbody fusion (SA-LLIF) without posterior instrumentation can be an alternative to 360° fusion in selected cases. This study aimed to investigate quantitative changes in psoas and paraspinal muscle morphology that occur on index levels after SA-LLIF. Methods: Patients undergoing single- or multi-level SA-LLIF at L2/3 to L4/5 who had preoperative and postoperative lumbar MRI scans, the latter performed between 3 and 18 months after surgery for any reason, were retrospectively included. Muscle measurements were performed of the psoas and posterior paraspinal muscles (PPM; erector spinae and multifidus) on index levels using manual segmentation and an automated pixel intensity threshold method to differentiate muscle from fat signal. Changes in the total cross-sectional area (TCSA), the functional cross-sectional area (FCSA), and the percentage of fat infiltration (FI) of these muscles were assessed. Results: A total of 67 patients (55.2% female, age 64.3 ± 10.6 years, BMI 26.9 ± 5.0 kg/m2) with 125 operated levels were included. Follow-up MRI scans were performed after an average of 8.7 ± 4.6 months, primarily for low back pain. Psoas muscle parameters did not change significantly, irrespective of the approach side. Among PPM parameters, the mean TCSA at L4/5 (+ 4.8 ± 12.4%; p = 0.013), and mean FI at L3/4 (+ 3.1 ± 6.5%; p = 0.002) and L4/5 (+ 3.0 ± 7.0%; p = 0.002) significantly increased. Conclusion: Our study demonstrated that SA-LLIF did not alter psoas muscle morphology, underlining its minimally invasive nature. However, FI of PPM significantly increased over time despite the lack of direct tissue damage to posterior structures, suggesting a pain-mediated response and/or the result of segmental immobilization. [ABSTRACT FROM AUTHOR]

Purpose: Lumbar fusion surgery has become a standard procedure in spine surgery and commonly includes the posterior placement of pedicle screws. Bone quality is a crucial factor that affects pedicle screw purchase. However, the relationship between paraspinal muscles and the bone quality of the pedicle is unknown. The aim of the study was to determine the relationship between paraspinal muscles and the ex vivo bony microstructure of the lumbar pedicle. Methods: Prospectively, collected data of patients undergoing posterior lumbar fusion for degenerative spinal conditions was analyzed. Pre-operative lumbar magnetic resonance imaging (MRI) scans were evaluated for a quantitative assessment of the cross-sectional area (CSA), functional cross-sectional area (fCSA), and the proportion of intramuscular fat (FI) for the psoas muscle and the posterior paraspinal muscles (PPM) at L4. Intra-operative bone biopsies of the lumbar pedicle were obtained and analyzed with microcomputed tomography (µCT) scans. The following cortical (Cort) and trabecular (Trab) bone parameters were assessed: bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), connectivity density (CD), bone-specific surface (BS/BV), apparent density (AD), and tissue mineral density (TMD). Results: A total of 26 patients with a mean age of 59.1 years and a mean BMI of 29.8 kg/m2 were analyzed. fCSAPPM showed significant positive correlations with BV/TVTrab (ρ = 0.610; p < 0.001), CDTrab (ρ = 0.679; p < 0.001), Tb.NTrab (ρ = 0.522; p = 0.006), Tb.ThTrab (ρ = 0.415; p = 0.035), and ADTrab (ρ = 0.514; p = 0.007). Cortical bone parameters also demonstrated a significant positive correlation with fCSAPPM (BV/TVCort: ρ = 0.584; p = 0.002; ADCort: ρ = 0.519; p = 0.007). FIPsoas was negatively correlated with TMDCort (ρ = − 0.622; p < 0.001). Conclusion: This study highlights the close interactions between the bone microstructure of the lumbar pedicle and the paraspinal muscle morphology. These findings give us further insights into the interaction between the lumbar pedicle microstructure and paraspinal muscles. [ABSTRACT FROM AUTHOR]

Introduction: Lumbo-sacral transitional vertebrae (LSTV) are accompanied by changes in soft tissue anatomy. The aim of our retrospective study was to evaluate the effects of LSTV as well as the number of free lumbar vertebrae on surgical approaches of ALIF, OLIF and LLIF at level L4/5. Material and methods: We assessed the CTs of 819 patients. Of these, 53 had LSTV from which 11 had six (6LV) and 9 four free lumbar vertebrae (4LV). We matched them for sex and age to a control group. Results: Patients with LSTV had a higher iliac crest and vena cava bifurcation, a greater distance between the common iliac veins and an anterior translation of the psoas muscle at level L4/5. In contrast, patients with 6LV had a lower iliac crest and aortic bifurcation, no differences in vena cava bifurcation and distance between the iliac veins compared to the control group. Conclusions: For patients with LSTV and five or four free lumbar vertebrae, the LLIF approach at L4/5 may be hindered due to a high riding iliac crest as well as anterior shift of the psoas muscle. Whereas less mobilization and retraction of the iliac veins may reduce the risk of vascular injury at this segment by ALIF and OLIF. For patients with 6LV, a lower relative height of the iliac crest facilitates lateral approach during LLIF. For ALIF and OLIF, a stronger vessel retraction due to the deeper-seated vascular bifurcation is necessary during ALIF and is therefore potentially at higher risk for vascular injury. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to determine the effect of age on the psoas and posterior paraspinal muscles (PPM; multifidus muscle and erector spinae) and to evaluate potential sex-related differences.Methods: MRI-based quantitative assessments of the cross-sectional area (CSA), the functional cross-sectional area (fCSA), the fat area (FAT) and the proportion of intramuscular fat (FI) were conducted on patients undergoing lumbar fusion surgery between 2014 and 2021. The regions of interest were the psoas muscle and the PPM at the superior endplate of L4. The left and right sides of the muscle groups were summarized and normalized by the patient's height (cm2/m2). The relationships between age and muscular parameters were analyzed stratified by sex.Results: A total of 195 patients (57.9%female) with a median age of 64.2 years and a body mass index of 28.3 kg/m2 were analyzed. The CSAPsoas was 7.7 cm2/m2 and differed significantly between females and males (p < 0.001); likewise, the fCSAPsoas differed significantly between the sexes. The CSAPPM was 18.8 cm2/m2 with no sex-specific differences. Significant differences were found in the FIPPM (males: 41.1% vs. females: 47.9%; p < 0.001), but not in the FIPsoas (males: 3.7% vs. females: 4.5%; p = 0.276). Considering the effect of age on FI, a significant positive correlation was observed for the PPMs for both sexes. Only in women, there was a negative correlation between age and CSAPsoas (ρ =  - 0.248; p = 0.008), FATPsoas (ρ =  - 0.421; p < 0.001) and FIPsoas (ρ =  - 0.371; p < 0.001).Conclusion: This study demonstrated sex-specific differences in spinal muscle morphology in relation to patient age. With increasing age there was a decrease in FIPsoas in women only, unlike in the PPMs in which there was increased FI that was significantly higher in women compared to men. [ABSTRACT FROM AUTHOR]

Background: Lateral lumbar interbody fusion (LLIF) is a relatively new procedure. It was established as a minimally invasive alternative to traditional open interbody fusion. LLIF allows the surgeon to access the disc space via a retroperitoneal transpsoas muscle approach. Theoretical advantages of the LLIF technique include preservation of the longitudinal ligaments, augmentation of disc height with indirect decompression of neural elements, and insertion of large footprint cages spanning the dense apophyseal ring bilaterally1,2. The original 2-incision LLIF technique described by Ozgur et al., in 2006, had some inherent limitations3. First, it substantially limited direct visualization of the surgical field and may have endangered nerve and vascular structures. Additionally, it often required multiple separated incisions for multilevel pathologies. Finally, for surgeons with experience in traditional open retroperitoneal surgery, utilization of their previously acquired skills may have been difficult with this approach. To overcome these limitations, we adopted the mini-open lateral approach, which allows for visualization, palpation, and electrophysiologic neurologic confirmation during the procedure4. Description: As detailed below, the patient is positioned in the lateral decubitus position and a single incision is carried out centered between the target discs. For single-level LLIF, the incision spans approximately 3 cm and can be lengthened in small increments for multilevel procedures. After blunt dissection, the retroperitoneal space is entered. The psoas muscle is split under direct visualization, carefully avoiding the traversing nerves with neurosurveillance5. A self-retaining retractor is used, and after thorough discectomy, the disc space is sized with trial components. The implant is filled with bone graft materials and is introduced using intraoperative fluoroscopy. Alternatives: The 2-incision LLIF technique or traditional anterior or posterior lumbar spine interbody fusion techniques might be used instead. Rationale: LLIF offers the reported advantages of minimally invasive surgery, such as reduced tissue trauma during the approach, low blood loss, shorter length of stay, decreased recovery time, and less postoperative pain. LLIF allows for the placement of a relatively larger interbody cage spanning the dense apophyseal ring bilaterally. The lateral approach preserves the anterior longitudinal ligament and posterior longitudinal ligament. These structures allow for powerful ligamentotaxis and provide extra stability for the construct. Compared with other approaches, LLIF has a reduced risk of visceral and vascular injuries, incidental dural tears, and perioperative infections. Although associated with approachrelated complications such as motor and sensory deficits, LLIF can be a safe and versatile procedure1,2. [ABSTRACT FROM AUTHOR]

Degenerative lumbar spondylolisthesis (DLS) is a prevalent spinal condition that can result in significant disability. DLS is thought to result from a combination of disc and facet joint degeneration, as well as various biological, biomechanical, and behavioral factors. One hypothesis is the progressive degeneration of segmental stabilizers, notably the paraspinal muscles, contributes to a vicious cycle of increasing slippage. To examine the correlation between paraspinal muscle status on MRI and severity of slippage in patients with symptomatic DLS. Retrospective cross-sectional study at an academic tertiary care center. Patients who underwent surgery for DLS at the L4/5 level between 2016–2018 were included. Those with multilevel DLS or insufficient imaging were excluded. The percentage of relative slippage (RS) at the L4/5 level evaluated on standing lateral radiographs. Muscle morphology measurements including functional cross-sectional area (fCSA), body height normalized functional cross-sectional area (HI) of Psoas, erector spinae (ES) and multifidus muscle (MF) and fatty infiltration (FI) of ES and MF were measured on axial MR. Disc degeneration and facet joint arthritis were classified according to Pfirrmann and Weishaupt, respectively. Descriptive and comparative statistics, univariable and multivariable linear regression models were utilized to examine the associations between RS and muscle parameters, adjusting for confounders sex, age, BMI, segmental degeneration, and back pain severity and symptom duration. The study analyzed 138 out of 183 patients screened for eligibility. The median age of all patients was 69.5 years (IQR 62 to 73), average BMI was 29.1 (SD±5.1) and average preoperative ODI was 46.4 (SD±16.3). Patients with Meyerding-Grade 2 (M2, N=25) exhibited higher Pfirrmann scores, lower MF fCSA and MF HI , and lower BMI, but significantly more fatty infiltration in the MF and ES muscles compared to those with Meyerding Grade 1 (M1). Univariable linear regression showed that each cm2 decrease in MF fCSA was associated with a 0.9%-point increase in RS (95% CI -1.4 to - 0.4, p<.001), and each cm2/m2 decrease in MF HI was associated with an increase in slippage by 2.2%-points (95% CI -3.7 to -0.7, p=.004). Each 1%-point rise in ES FI and MF FI corresponded to 0.17%- (95% CI 0.05–0.3, p=.01) and 0.20%-point (95% CI 0.1–0.3 p<.001) increases in relative slippage, respectively. Notably, after adjusting for confounders, each cm2 increase in Psoas fCSA and cm2/m2 in Psoas HI was associated with an increase in relative slippage by 0.3% (95% CI 0.1–0.6, p=.004) and 1.1%-points (95% CI 0.4–1.7, p=.001). While MF fCSA tended to be negatively associated with slippage, this did not reach statistical significance (p=.105). However, each 1%-point increase in MF FI and ES FI corresponded to increases of 0.15% points (95% CI 0.05–0.24, p=.002) and 0.14% points (95% CI 0.01–0.27, p=.03) in relative slippage, respectively. This study found a significant association between paraspinal muscle status and severity of slippage in DLS. Whereas higher degeneration of the ES and MF correlate with a higher degree of slippage, the opposite was found for the psoas. These findings suggest that progressive muscular imbalance between posterior and anterior paraspinal muscles could contribute to the progression of slippage in DLS. [ABSTRACT FROM AUTHOR]

Study Design. Retrospective analysis of prospectively enrolled patients. Objective. To evaluate the relationship between paraspinal muscle (PM) atrophy and Oswestry Disability Index (ODI) improvement after spinal fusion surgery for degenerative lumbar spondylolisthesis. Background. Atrophy of the PM is linked to multiple spinal conditions, sagittal malalignment, and increased postoperative complications. However, only limited evidence for the effect on patient-reported outcomes exists. Methods. Patients with degenerative lumbar spondylolisthesis undergoing decompression and fusion surgery were analyzed. Patients with missing follow-up, no imaging, or inadequate image quality were excluded. The ODI was assessed preoperatively and two years postoperatively. A cross-sectional area of the PM was measured on a T2-weighted magnetic resonance imaging sequence at the upper endplate of L4. On the basis of the literature, a 10-point improvement cutoff was defined as the minimum clinically important difference. Patients with a baseline ODI below the minimum clinically important difference were excluded. Logistic regression was used to calculate the association between fatty infiltration (FI) of the PM and improvement in ODI, adjusted for age, sex, and body mass index. Results. A total of 133 patients were included in the final analysis, with only two lost to follow-up. The median age was 68 years (IQR 62--73). The median preoperative ODI was 23 (IQR 17--28), and 76.7% of patients showed improvement in their ODI score by at least 10 points. In the multivariable regression, FI of the erector spinae and multifidus increased the risk of not achieving clinically relevant ODI improvement (P=0.01 and <0.001, respectively). No significant association was found for the psoas muscle (P= 0.158). Conclusions. This study demonstrates that FI of the erector spinae and multifidus is significantly associated with less likelihood of clinically relevant ODI improvement after decompression and fusion. Further research is needed to assess the effect of interventions. [ABSTRACT FROM AUTHOR]

Study Design.: Prospective cross-sectional study. Objective.: To determine if an accumulation of advanced glycation endproducts (AGEs) is associated with impaired paraspinal muscle composition. Background.: Impaired bone integrity and muscle function are described as osteosarcopenia. Osteosarcopenia is associated with falls, fragility fractures, and reduced quality of life. Bone integrity is influenced by bone quantity (bone mineral density) and quality (microarchitecture and collagen). The accumulation of AGEs stiffens collagen fibers and increases bone fragility. The relationship between paraspinal muscle composition and bone collagen properties has not been evaluated. Methods.: Intraoperative bone biopsies from the posterior superior iliac spine were obtained and evaluated with multiphoton microscopy for fluorescent AGE cross-link density (fAGEs). Preoperative magnetic resonance imaging measurements at level L4 included the musculus (m.) psoas and combined m. multifidus and m. erector spinae (posterior paraspinal musculature, PPM). Muscle segmentation on axial images (cross-sectional area, CSA) and calculation of a pixel intensity threshold method to differentiate muscle (functional cross-sectional area, fCSA) and intramuscular fat (FAT). Quantitative computed tomography was performed at the lumbar spine. Univariate and multivariable regression models were used to investigate associations between fAGEs and paraspinal musculature. Results: One hundred seven prospectively enrolled patients (50.5% female, age 60.7 y, BMI 28.9 kg/m2) were analyzed. In all, 41.1% and 15.0% of the patients demonstrated osteopenia and osteoporosis, respectively. Univariate linear regression analysis demonstrated a significant association between cortical fAGEs and CSA in the psoas (ρ=0.220, P =0.039) but not in the PPM. Trabecular fAGEs revealed no significant associations to PPM or psoas musculature. In the multivariable analysis, higher cortical fAGEs were associated with increased FAT (β=1.556; P =0.002) and CSA (β=1.305; P =0.005) in the PPM after adjusting for covariates. Conclusion.: This is the first investigation demonstrating that an accumulation of nonenzymatic collagen cross-linking product fAGEs in cortical bone is associated with increased intramuscular fat in the lumbar paraspinal musculature. [ABSTRACT FROM AUTHOR]

The effect of psoas and paraspinal muscle parameters on cage subsidence after minimally invasive techniques, such as standalone lateral lumbar interbody fusion (SA-LLIF), is unknown. This study aimed to determine whether the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae), and psoas FCSA normalized to the vertebral body area (FCSA/VBA) differ among levels with severe cage subsidence after SA-LLIF when compared to levels without severe cage subsidence. Retrospective single center cohort study. Patients who underwent SA-LLIF between 2008 and 2020 for degenerative conditions using exclusively polyetheretherketone (PEEK) cages, had a lumbar magnetic resonance imaging (MRI) scan within 12 months, a lumbar computed tomography (CT) scan within 6 months prior to surgery, and a postoperative clinical and radiographic follow-up at a minimum of 6 months were included. Severe cage subsidence. MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA and FCSA/VBA at the L3-L5 pedicles. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8.0), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat and muscle. Mean volumetric bone mineral density (vBMD) at L1/2 was measured by quantitative CT. The primary endpoint was severe cage subsidence per level according to the classification by Marchi et al. Multivariable logistic regression analysis was performed using generalized linear mixed models. All analyses were stratified by biological sex. 95 patients (45.3% female) with a total of 188 operated levels were included in the analysis. The patient population was 92.6% Caucasian with a median age at surgery of 65 years. Overall subsidence (Grades 0-III) was 49.5% (53/107 levels) in men versus 58.0% (47/81 levels) in women (p=.302), and severe subsidence (Grades II-III) was 22.4% (24/107 levels) in men versus 25.9% (21/81 levels) in women (p=.608). In men, median psoas FCSA and psoas FCSA/VBA at L3 and L4 were significantly greater in the severe subsidence group when compared to the non-severe subsidence group. No such difference was observed in women. Paraspinal muscle parameters did not differ significantly between non-severe and severe subsidence groups for both sexes. In the multivariable logistic regression analysis with adjustments for vBMD and cage length, psoas FCSA at L3 (OR 1.002; p=.020) and psoas FCSA/VBA at L3 (OR 8.655; p=.029) and L4 (OR 4.273; p=.043) were found to be independent risk factors for severe cage subsidence in men. Our study demonstrated that greater psoas FCSA at L3 and psoas FCSA/VBA at L3 and L4 were independent risk factors for severe cage subsidence in men after SA-LLIF with PEEK cages. The higher compressive forces the psoas exerts on lumbar segments as a potential stabilizer might explain these findings. Additional pedicle screw fixation might be warranted in these patients to avoid severe cage subsidence. [ABSTRACT FROM AUTHOR]

Study Design: A retrospective cross-sectional study.Objective: To assess the association between spinal muscle morphology and spinopelvic parameters in lumbar fusion patients, with a special emphasis on lumbar lordosis (LL).Summary Of Background Data: Maintenance of sagittal alignment relies on muscle forces, but the basic association between spinal muscles and spinopelvic parameters is poorly understood.Materials and Methods: Patients operated between 2014 and 2017 who had both lumbar magnetic resonance imaging scan and standing whole-spine radiographs within six months before surgery were included. Muscle measurements were conducted on axial T2-weighted magnetic resonance images at the superior endplate L3-L5 for the psoas and L3-S1 for combined multifidus and erector spinae (paraspinal) muscles. A pixel intensity threshold method was used to calculate the total cross-sectional area (TCSA) and the functional cross-sectional area (FCSA). Spinopelvic parameters were measured on lateral standing whole-spine radiographs and included LL, pelvic incidence (PI), PI-LL mismatch, pelvic tilt, sacral slope, thoracic kyphosis, and sagittal vertical axis. Analyses were stratified by biological sex. Multivariable linear regression analyses with adjustments for age and body mass index (BMI) were performed.Results: A total of 104 patients (62.5% female) were included in the analysis. The patient population was 90.4% White with a median age at surgery of 69 years and a median BMI of 27.8 kg/m 2 . All muscle measurements were significantly smaller in women. PI, pelvic tilt, and thoracic kyphosis were significantly greater in women. PI-LL mismatch was 6.1° (10.6°) in men and 10.2° (13.5°) in women ( P =0.106), and sagittal vertical axis was 45.3 (40.8) mm in men and 35.7 (40.8) mm in women ( P =0.251). After adjusting for age and BMI, paraspinal TCSA at L3-L5, and paraspinal FCSA at L4 showed significant positive associations with LL in women. In men, psoas TCSA at L5 and psoas FCSA at L5 showed significant negative associations with LL, but none of the paraspinal muscle measurements.Conclusion: Our findings indicate that psoas and lumbar spine extensor muscles interact differently on LL among men and women, creating a unique mechanical environment.Level Of Evidence: Level 4. [ABSTRACT FROM AUTHOR]

Lumbar fusion surgery has become a standard procedure in spine surgery and commonly includes posterior placement of pedicle screws. Bone quality is a critical factor that affects pedicle screw purchase, whereas the role of paraspinal musculature is less well understood. Pedicle screw loosening is a devastating complication often leading to revision surgery. However, the relationship of paraspinal muscles and the pedicle is unknown. Therefore, we aimed to determine the relationship between paraspinal muscle composition and bony microstructure of the lumbar. Lumbar fusion surgery has become a standard procedure in spine surgery and commonly includes posterior placement of pedicle screws. Bone quality is a critical factor that affects pedicle screw purchase, whereas the role of paraspinal musculature is less well understood. Pedicle screw loosening is a devastating complication often leading to revision surgery. However, the relationship of paraspinal muscles and the pedicle is unknown. The aim of the study was to determine the relationship between paraspinal muscle composition and bony microstructure of the lumbar pedicle. Prospective study. Twenty-four patients undergoing open posterior lumbar fusion at a single academic institution. Preoperative lumbar magnetic resonance imaging (MRI) scans were evaluated using a dedicated software for a quantitative assessment of the cross-sectional area (CSA), the functional cross-sectional area (fCSA), and the proportion of intramuscular fat. The regions of interest were the psoas muscle and the paraspinal muscles at the superior endplate of the L4 level. Left and right side of the muscle groups were averaged and normalized by the patient's height (cm2/m2). Intraoperative bone biopsies of the lumbar pedicle were obtained and analyzed with microscopic computed tomography (microCT) scans. Parameters of cortical (Cort) and trabecular (Trab) bone were collected and the following parameters assessed: bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), connectivity density (CD), specific bone surface (BS/BV), apparent density (AD) and total mineral density (TMD). The relationship between microCT parameters and paraspinal CSA, fCSA and fat infiltration were determined by the Spearman correlation. The relationship between microCT parameters and paraspinal CSA, fCSA and fat infiltration were determined by the Spearman correlation. Statistical significance was defined as p<0.05. Twenty-four patients (50% female) with a median age of 62.2 years (IQR: 54.7-68.2) and a mean (±SD) BMI of 29.8 (6) kg/m2 were analyzed. fCSA of the paraspinal muscles showed significant positive correlations with BV/TV Trab (r=0.582, p=0.003), CD Trab (r=0.639; p < 0.001), Tb.N Trab (r=0.469, p=0.021), Tb.Th (r=0.405, p=0.0049) and AD Trab (r=0.510, p=0.011). Cortical bone parameters also demonstrated a significant positive correlation with fCSA (BV/TVCort: r= 0.551, p=0.005; ADCort: r=0.551, p=0.005). fCSA of the psoas showed no correlation with cortical or trabecular microCT parameters, but fat infiltration of the psoas was negatively correlated with TMD Cort (r=-663, p < 0.001). This study provides evidence that the bone microstructure of the lumbar pedicle is significantly correlated with the fCSA of the paraspinal musculature. Whether this finding is related to mechanical coupling or to biochemical processes cannot be conclusively stated. However, this finding gives us further insight in the mutual interactions between lumbar vertebral bone and paraspinal muscles. This abstract does not discuss or include any applicable devices or drugs. [ABSTRACT FROM AUTHOR]

Loss of paraspinal muscle mass over time can affect spinal degeneration and promote lumbar back pain. New methods to determine muscle quantity and quality have been established, including the evaluation of the functional cross-sectional area (fCSA) and fat infiltration. However, little is known about the aging processes that occur in spinal muscle groups and sex-specific differences. Aim of this study was to determine if the processes of aging are comparable in the psoas and posterior paraspinal muscles (PPM; musclus multifidus and erector spinae), and to evaluate potential sex-related differences. Retrospective cohort study. A total of 176 patients undergoing open posterior lumbar fusion surgery. MRI-based quantitative assessments of the cross-sectional area (CSA), the functional cross-sectional area (fCSA), and the proportion of intramuscular fat were conducted. The regions of interest were the psoas muscle and the PPM at the superior endplate of the L4 level. The left and right side of the muscle groups were averaged and normalized by the patient's height (cm2/m2). The relationship between age and 1) psoas CSA, fCSA and fat infiltration, and 2) PPM CSA, fCSA and fat infiltration was determined by Pearson´s correlation coefficients, stratifying all analyses by sex. Statistical significance was defined as p<0.05. A total of 176 patients (59% female) were included in the final analysis with a median age of 64.7 years (IQR: 56.6-71.5]) and a median BMI of 28.2 kg/m2 (IQR: 25.1.7-32.6). The mean normalized CSA of the psoas was 4.07±0.1cm2/m2 (mean±standard deviation) and differed significantly between females (3.5±1.2cm2/m2) and males (4.9±1.0cm2/m2) likewise, the fCSA of psoas differed significantly between the sexes. The mean CSA of the PMMs was 9.9 cm2/m2 (±0.2) with no sex specific differences and showed no correlation in both groups with age. Significant differences in the fatty infiltration between men and women in the paraspinal muscles (m:41.7%; f:47.3%; p < 0.001), and there were no differences found in the psoas regarding fatty infiltration (m:5.7%; f:6.1%; p=0.631). Considering the effect of age on the fat infiltration, a significant positive correlation was observed in the PMMs for both sexes (f: r=0.651, p < 0.001; m: r=0.429, p < 0.001). In women, there was a negative correlation between age and psoas CSA (r=-0.228; p=0.02), and fat infiltration of psoas (r=-0.297; p=0.002). This study demonstrated sex-specific differences in spinal muscle morphology in relation to patient´s age. There was a decrease in fat infiltration of the psoas in women with increasing age, unlike in the posterior paraspinal musclesin which there was increased fat infiltration. This phenomenon is controversial to the assumption that fatty infiltration increases with age. The work provides further evidence on sex differences within different paraspinal muscle groups in patients undergoing posterior lumbar fusion. This abstract does not discuss or include any applicable devices or drugs. [ABSTRACT FROM AUTHOR]

Pathophysiological conditions during aging can affect bone and muscle simultaneously, such as in osteosarcopenia. The vertebral bone quality (VBQ) score based on magnetic resonance imaging (MRI) was recently introduced as a novel measure of bone quality in the lumbar spine and shown to be a significant predictor of healthy versus osteopenic/osteoporotic bone. However, the association between quantitative lumbar spinal muscle parameters and the VBQ score, is unknown. This study aimed to assess possible associations between the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae) and the VBQ score. Retrospective cohort study. Patients who underwent open posterior lumbar fusion for degenerative conditions between 2014 and 2017 at a single academic institution and had both a lumbar MRI and a computed tomography (CT) scan within 6 months prior to surgery were included. FCSA and VBQ score. MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA at the L3-L5 superior endplate. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat (high intensity) and muscle (low intensity). VBQ measurements included the signal intensity of the medullary portion of the vertebrae L1-L4 and the cerebrospinal fluid (CSF) at L3 on mid-sagittal T1-weighted MR images. The VBQ score was calculated by dividing the median signal intensity L1-L4 through the signal intensity of the CSF. Lumbar volumetric bone mineral density (vBMD) was assessed by quantitative CT using the L1/2 average, categorizing patients with a vBMD of <120 mg/cm³ as osteopenic/osteoporotic. All analyses were stratified by biological sex. Sperman correlation and multivariate linear regression analysis with adjustments for age and body mass index (BMI) were performed. Eighty patients (58.8% female) were included in the analysis. The patient population was 93.8% Caucasian with a median age at surgery of 68.8 years. The prevalence of chronic low back pain >12 weeks was 83.8%, and the prevalence of osteopenia/osteoporosis was 65%, with no significant differences between men and women. All muscle measurements were significantly greater in men. The mean (SD) VBQ score was significantly smaller in men, at 2.26 (0.45) versus women at 2.59 (0.39) (p = 0.001). In men, a significant negative correlation was seen between psoas FCSA at L3-5 and the VBQ score, with correlation coefficients ranging from -0.487 to -0.405. After adjusting for age and BMI, a significant negative association was seen between psoas FCSA at L3 and the VBQ score in men (β = -0.373; 95% CI -0.687 - -0.058; p = 0.022). In women, there was a significant negative correlation between paraspinal FCSA at L3 and the VBQ score, with a correlation coefficient of -0.367 (p = 0.011), but no significant association was seen in the adjusted analysis. We found the VBQ score to be negatively associated with psoas FCSA at L3 among male individuals, irrespective of age and BMI. Our results highlight sex differences in the VBQ score that were not demonstrated by vBMD or categorial bone status, and suggest a potential role of this novel measure to assess not only bone quality, but also spinal muscle quantity. Further studies are needed to assess the clinical utility of the VBQ score as a non-invasive screening tool for osteosarcopenia. This abstract does not discuss or include any applicable devices or drugs. [ABSTRACT FROM AUTHOR]