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Background Accurate sizing is critical for the overall success of a total knee arthroplasty (TKA). This study's primary purpose was to investigate the ability to predict the tibial and femoral component size in a single implant system from patient demographics and anthropometric data. A secondary goal was to compare the predicted tibial and femoral component sizes from our statistical model with a previously validated electronic application used to predict the implant size. Methods A consecutive series of 484 patients undergoing a primary TKA at a single institution was reviewed. Data on height, weight, body mass index, sex, age, and component size were collected. A proportional odds model was developed to predict tibial and femoral component sizes. The relationship between the proportional odds model predictions was also compared with the component sizes determined by the Arthroplasty Size Predictor electronic application. Results Weight, height, and sex predicted the implanted component size with an accuracy of 54.0% (n = 247/484) for the tibia and 51.1% (n = 231/484) for the femur. The accuracy improved to 94.4% (n = 457/484) for the tibia and 93.4% (n = 452/484) for the femur within ±1 component size. Our data are highly correlated to the Arthroplasty Size Predictor for the predicted tibial component size (ρ = 0.91, P < .001) and femoral component size (ρ = 0.89, P < .001). Conclusions Our novel templating model may improve operative efficiency for a single TKA system. Our findings have a high concordance with a widely available electronic application used to predict implant sizes for a variety of TKA systems.

BACKGROUND Neck pain (NP) affects as much as 70% of individuals at some point in their lives. Systematic reviews indicate that manual treatments can be moderately effective in the management of chronic, nonspecific NP. However, there is a paucity of studies specifically evaluating the efficacy of osteopathic manipulative treatment (OMT). OBJECTIVE To evaluate the efficacy of OMT in reducing pain and disability in patients with chronic NP. DESIGN Single-blinded, cross-over, randomized controlled trial. SETTING University-based, osteopathic manipulative medicine outpatient clinic. PARTICIPANTS 97 participants, 21-65 years old, with chronic, nonspecific NP. INTERVENTIONS Participants were randomized to two trial arms: immediate OMT intervention or waiting period first. The intervention consisted of 3-4 OMT sessions over 4-6 weeks, after which the participants switched groups. MAIN OUTCOME MEASURES Primary outcome measures were pain intensity (average and current) on the numerical rating scale and Neck Disability Index. Secondary outcomes included PROMIS-29 health domains and Fear Avoidance Beliefs Questionnaire. Outcomes obtained prior to the cross-over allocation were evaluated using general linear models and after adjusting for baseline values. RESULTS 38 and 37 participants were available for the analysis in the OMT and waiting period groups, respectively. The results showed significantly better primary outcomes in the immediate OMT group for reductions in average pain (-1.02, 95%CI:[-1.72, -0.32], P = 0.005), current pain (-1.02, 95%CI:[-1.75, -0.30], P = 0.006), disability (-5.30%, 95%CI:[-9.2%, -1.3%], P = 0.010) and improved secondary outcomes (PROMIS) related to sleep (-3.25, 95%CI: [-6.95, -1.54], P = 0.003), fatigue (-3.26, 95%CI:[-6.04, -0.48], P = 0.022), and depression (-2.59, 95%CI:[-4.73, -0.45], P = 0.018). The effect sizes were in the clinically meaningful range between 0.5 and 1 SD. No study-related serious adverse events were reported. CONCLUSIONS OMT is relatively safe and effective in reducing pain and disability along with improving sleep, fatigue, and depression in patients with chronic NP immediately following treatment delivered over approximately 4-6 weeks. TRIAL REGISTRATION ClinicalTrials.gov NCT# 02261259. This article is protected by copyright. All rights reserved.

Low back pain (LBP) is complex. This study aimed to use collaborative modeling to evaluate conceptual models that individuals with LBP have of their condition, and to compare these models with those of researchers/clinicians. Twenty-eight individuals with LBP were facilitated to generate mental models, using "fuzzy cognitive maps," that represented conceptualization of their own LBP and LBP "in general." "Components" (ie, causes, outcomes and treatments) related to pain, disability and quality of life were proposed, along with the weighted "Connections" between Components. Components were classified into thematic categories. Weighting of Connections were summed for each Component to judge relative importance. Individual models were aggregated into a metamodel. When considering their own condition, participants' models included 19(SD = 6) Components and 43(18) Connections with greatest weight on "Biomechanical" components. When considering LBP in general, models changed slightly. Patient models contrasted the more complex models of researchers/clinicians (25(7) Components; 77(42) Connections), with most weight on "Psychological" components. This study provides unique insight into how individuals with LBP consider their condition, which is largely biomedical and narrower than clinician/researcher perspectives. Findings highlight challenges for changing public perception of LBP, and provide a method with potential utility to understand how individuals conceptualize their condition. PERSPECTIVE: Collaborative modeling was used to understand how individuals with low back pain conceptualize their own condition, the condition in general, and compare this with models of expert researchers/clinicians. Data revealed issues in how individuals with back pain conceptualize their condition, and the method's potential utility for clinical evaluation of patients.

Although quadriceps weakness after ACL reconstruction (ACLR) is well documented, the magnitude of reported weakness varies considerably. Such variation raises the possibility that certain patients may be more susceptible to quadriceps weakness after ACLR. This meta-analysis identified factors explaining between-study variability in quadriceps weakness post-ACLR.Studies between 2010 and 2020 were screened for the following criteria: human subjects, unilateral ACLR, and strength reported both for the ACLR leg and the uninjured or healthy-control leg. 122 studies met the criteria, resulting in 303 and 152 Cohen's d effect sizes (ESs) comparing ACLR legs to uninjured legs (a total of 4135 ACLR subjects) and to healthy controls (a total of 1,507 ACLR subjects vs. 1-193 healthy controls), respectively. Factors (time, graft, sex, activity, mass/height, geographic area, concomitant injury, and type of strength testing) that may affect study ES were examined.Meta-regressions indicated an association between time post-ACLR and study ESs (P 0.001) and predicted full recovery (ES = 0) to occur at 54-59 months post-ACLR. When compared to uninjured legs, patients with patellar tendon autografts had greater deficits than studies using hamstring tendon autografts (P = 0.023). When compared to uninjured legs, studies including only males reported greater deficits than studies combining males and females (P = 0.045); whereas when compared to healthy controls, studies combining males and females reported greater deficits than studies with males (P = 0.013). When compared to controls, studies from USA reported greater deficits than studies from Europe (P = 0.003). Increased isokinetic-testing speed was associated with smaller deficits (P ≤ 0.025). Less than 25% of patients achieved a between-limb symmetry in quadriceps strength 90% between 6 and 12 months post-ACLR.Time post-surgery, graft, sex, geographic location, and isokinetic speed influenced the magnitude of post-ACLR quadriceps weakness. Patients with patellar tendon autografts demonstrated greater between-limb asymmetry in quadriceps strength, while female strength deficits were underestimated to a greater extent. A slower isokinetic speed provided a more sensitive assessment of quadriceps strength post-ACLR. The overwhelming majority of patients were returning to sport with significantly impaired quadriceps strength.III.

Challenging trunk neuromuscular control maximally using a seated balancing task is useful for unmasking impairments that may go unnoticed with traditional postural sway measures and appears to be safe to assess in healthy individuals. This study investigates whether the stability threshold, reflecting the upper limits in trunk neuromuscular control, is sensitive to pain and disability and is safe to assess in low back pain (LBP) patients. Seventy-nine subjects with non-specific LBP balanced on a robotic seat while rotational stiffness was gradually reduced. The critical rotational stiffness, KCrit, that marked the transition between stable and unstable balance was used to quantify the individual’s stability threshold. The effects of current pain, 7-day average pain, and disability on KCrit were assessed, while controlling for age, sex, height, and weight. Adverse events (AEs) recorded at the end of the testing session were used to assess safety. Current pain and 7-day average pain were strongly associated with KCrit (current pain p

Patients with Low Back Pain (LBP) are suggested to follow a protective coping strategy. Therefore, rehabilitation of these patients requires estimating their motor control strategies (the control intent). In this letter, we present an approach that infers the control intent by solving an inverse Model Predictive Control (iMPC) problem. The standard Model Predictive Control (MPC) structure includes constraints, therefore, it allows us to model the physiological constraints of motor control. We devised an iMPC algorithm to solve iMPC problems with experimentally collected output trajectories. We used experimental data of one healthy subject during a seated balance test that used a physical Human-Robot Interaction (pHRI). Results show that the estimated MPC weights reflected the task instructions given to the subject and yielded an acceptable goodness of fit. The iMPC solution suggests that the subject’s control intent was dominated by minimizing the squared sum of a combination of the upper-body and lower-body angles and velocities.

A current trend in equine research is technology development to minimize the subjective nature of gait analysis. One such technology is the Tekscan Hoof System, which records force and area loaded by the hooves during motion. The objective of this study was to determine the test-retest reliability of the Tekscan Hoof System between two sessions, and the recordings within those sessions. Four mature Standardbred geldings wore Tekscan Hoof System sensors on both front hooves, secured by glue-on shoes (SoundHorse Technologies). Horses were exercised in AM and PM sessions. In each session, horses walked and trotted for three recordings of at least 10 steps. Statistical analysis was performed in SAS 9.4 with fixed effects of gait, horse, leg, and recording nested within session (significance at P ≤ .05). Intraclass Correlation Coefficients (ICC; 3,k) and confidence intervals between AM and PM sessions and recordings were calculated with SPSS. Average force and area were higher in AM sessions than PM sessions (P.0001). Between AM and PM sessions, ICC for the walk had good reliability (0.96, 95% CI = 0.80 - 0.99) and excellent reliability at the trot (0.98, 95% CI = 0.91-0.99). Within the AM and PM sessions, reliability was excellent at both the walk, and trot (ICCs0.96). The Tekscan Hoof System has been found to have excellent reliability within sessions. Caution should be taken when comparing between sessions, as the system is found to have lower force and area output during later sessions due to potential sensor damage.

A case-control study.To determine whether parity and abdominal surgeries are associated with degenerative spondylolisthesis (DS).DS is considered to be a major cause of low back pain (LBP) in the older population, with greater prevalence of DS among women. Because LBP and impaired abdominal muscle function are common during pregnancy and post-partum, parity-related abdominal muscle deficiency, resulting in poor spinal mechanics, could be a factor in the development of DS in women. Indeed a relationship between the number of pregnancies and DS was reported in one study.A total of 322 women between the ages of 40 and 80 (149 with DS and 173 controls) filled out a questionnaire providing information about their demographics, the number of full-term pregnancies, the number and types of abdominal surgeries (including cesarean section and hysterectomies), and age at menopause among other items. A binary logistic regression was used as a multivariate model to identify the variables associated with DS.Along with age and body mass index as covariates, the number of full-term pregnancies and the hysterectomy were significant predictors of DS. Other abdominal surgeries, cesarean section, or the number of years postmenopause were not significant predictors of DS in this regression model after adjusting for all other significant variables.Each full-term pregnancy seems to be associated with the 22% increase in odds of developing DS. Hysterectomy nearly doubles the odds of DS as compared to women who did not have hysterectomy.4.

Background: Multiple techniques for patellar fixation with classic solid suture anchors (SAs) in medial patellofemoral ligament (MPFL) reconstruction have been described. Fixation of the graft to the patella with all-soft suture anchors (ASAs) has not been studied. Purpose/Hypothesis: To evaluate the biomechanical performance of 2 different MPFL patellar fixation techniques: ASA fixation and SA fixation. We hypothesized that the ASA group would show no statistical difference in the ultimate failure load and stiffness compared with the SA group. Study Design: Controlled laboratory study. Methods: Reconstruction of the MPFL with gracilis autografts was performed in 16 fresh-frozen cadaveric knees (mean age, 52.6 ± 9.0 years). The specimens were randomly assigned to 2 groups of 8 specimens each based on the method used to fix the graft to the medial patella: ASA or SA fixation. Patellar fixation with ASAs was completed with 2 parallel 1.8-mm anchors (Q-Fix, Smith & Nephew). Fixation with SAs was completed with 2 parallel 2.9-mm anchors (Osteoraptor, Smith & Nephew). The reconstructions were cyclically loaded for 10 cycles to 25 N and then loaded in tension at 6 mm/s until failure. Ultimate failure load (N), displacement (mm), stiffness (N/mm), and mode of failure were recorded for each specimen. Results: Load to failure testing showed an ultimate failure load of 228.5 ± 53.1 N in the ASA group. In the SA group, the ultimate failure load was 156.2 ± 84.9 N. The difference between the 2 groups was not statistically significant ( P = .064). Stiffness values between the ASA and SA groups were not significantly different (21.3 ± 4.1 N/mm vs 20.9 ± 9.3 N/mm, respectively, P = .905). The most common mode of failure in both groups was anchor pullout (8 of 8 in the ASA group; 6 of 8 in the SA group). Conclusion: This experimental study showed no statistically significant differences in biomechanical performance between 1.8-mm ASAs and 2.9-mm SAs. Clinical Relevance: Patellar fixation with 2 parallel ASAs may provide adequate patellar fixation for MPFL reconstruction, while their smaller diameter could potentially decrease the risks for patella fracture and violation of the articular surface in the cadaver model.

Background: Pelvic girdle pain (PGP) and sacroiliac joint (SIJ) dysfunction/pain are considered frequent contributors to low back pain (LBP). Like other persistent pain conditions, PGP is increasingly recognized as a multifactorial problem involving biological, psychological, and social factors. Perspectives differ between experts and a diversity of treatments (with variable degrees of evidence) have been utilized. Objective: To develop a collaborative model of PGP that represents the collective view of a group of experts. Specific goals were to analyze structure and composition of conceptual models contributed by participants, to aggregate them into a metamodel, to analyze the metamodel's composition, and to consider predicted efficacy of treatments. Design: To develop a collaborative model of PGP, models were generated by invited individuals to represent their understanding of PGP using fuzzy cognitive mapping (FCM). FCMs involved proposal of components related to causes, outcomes, and treatments for pain, disability, and quality of life, and their connections. Components were classified into thematic categories. Weighting of connections was summed for components to judge their relative importance. FCMs were aggregated into a metamodel for analysis of the collective opinion it represented and to evaluate expected efficacy of treatments. Results: From 21 potential contributors, 14 (67%) agreed to participate (representing six disciplines and seven countries). Participants' models included a mean (SD) of 22 (5) components each. FCMs were refined to combine similar terms, leaving 89 components in 10 categories. Biomechanical factors were the most important in individual FCMs. The collective opinion from the metamodel predicted greatest efficacy for injection, exercise therapy, and surgery for pain relief. Conclusions: The collaborative model of PGP showed a bias toward biomechanical factors. Most efficacious treatments predicted by the model have modest to no evidence from clinical trials, suggesting a mismatch between opinion and evidence. The model enables integration and communication of the collection of opinions on PGP.

Although biomechanics plays a role in the development and perhaps the persistent or recurrent nature of low back pain (LBP), whether biomechanics alone can provide the basis for intervention is debated. Biomechanics, which refers to the mechanics of the body, including its neuromuscular control, has been studied extensively in LBP. But, can gains be made in understanding LBP by research focused on this component of biology in the multifactorial biopsychosocial problem of LBP? This commentary considers whether biomechanics research has the potential to advance treatment of LBP, and how likely it is that this research will lead to better treatment strategies. A point-counterpoint format is taken to present both sides of the argument. First, the challenges faced by an approach that considers biomechanics in isolation are presented. Next, we describe 3 models that place substantial emphasis on biomechanical factors. Finally, reactions to each point are presented as a foundation for further research and clinical practice to progress understanding of the place for biomechanics in guiding treatment of LBP.

STUDY DESIGN. Analytical and numerical simulations. BACKGROUND. Traditionally, low back pain (LBP) is studied using a reductionist approach, in which the factors contributing to the clinical presentation of LBP are studied in isolation to identify the primary pathology or condition linked to LBP. We argue that reductionism may not be suitable for studying LBP considering the complex, multi-factorial nature of this condition. OBJECTIVES. To quantify the likelihood of successfully subclassifying LBP patients and effectively targeting treatment based on a single, dominant factor contributing to LBP. METHODS. Both the analytical and numerical simulations (Monte Carlo) of one million patients with LBP were performed. A number of factors contributing to LBP were randomly assigned to each individual. The following outcome measures were computed based on a number of factors: (1) The percentage of individuals that could be subclassified by identifying a single factor exceeding a certain threshold and (2) The average reduction in LBP when a treatment eliminates the largest contributing factor versus a multimodal treatment that eliminates a number of the randomly selected factors. RESULTS. With an increasing number of factors, the probability of subclassifying an individual to a subgroup based on a single factor tends to zero. A multimodal treatment arbitrarily addressing any two or more factors was more effective than diagnosing and treating a single factor that maximally contributed to LBP. CONCLUSION. Results suggest that reductionism is not appropriate for subclassifying LBP or targeting treatment. The use of reductionist approaches may explain some of the challenges with creating LBP classification system and designing more effective treatment interventions.

Human motor control has constraints in terms of its responsiveness, which limit its ability to successfully perform tasks. In a previous study, it was shown that the ability to balance an upright stick became progressively more challenging as the natural frequency (angular velocity without control) of the stick increased. Furthermore, forearm and trunk agonist and antagonist muscle activation increased as the natural frequency of the stick increased, providing evidence that the central nervous system produces agonist-antagonist muscle activation to match task dynamics. In the present study, visual feedback of the stick position was influenced by changing where subject focused on the stick during stick balancing. It was hypothesized that a lower focal height would degrade motor control (more uncertainty in tracking stick position), thus making balancing more challenging. The probability of successfully balancing the stick at four different focal heights was determined along with the average angular velocity of the stick. Electromyographic signals from forearm and trunk muscles were also recorded. As expected, the probability of successfully balancing the stick decreased and the average angular velocity of the stick increased as subjects focused lower on the stick. In addition, changes in the level of agonist and antagonist muscle activation in the forearm and trunk was linearly related to changes in the angular velocity of the stick during balancing. One possible explanation for this is that the central nervous system increases muscle activation to account for less precise motor control, possibly to improve the responsiveness of human motor control.

While the impact of load magnitude on spine dynamic parameters (stiffness and damping) has been reported, it is unclear how load history (exposure to prolonged loading) affects spine dynamic parameters in sagittal rotation. Furthermore, it is unknown if both spine stiffness and damping are equally affected to prolonged loading. Using a pendulum testing apparatus, the effect of load magnitude and load history on spine sagittal rotational stiffness and damping was assessed. Nine porcine lumbar functional spine units (FSUs) were tested in an increasing compressive load phase (ICP: 44.85, 68.55, 91.75, 114.6 kg) and then a decreasing compressive load phase (DCP: 91.75, 68.55, and 44.85 kg). Each trial consisted of flexing the FSU 5° and allowing it to oscillate unconstrained. During the ICP, both stiffness and damping linearly increased with load. However, in the DCP, stiffness and damping values were significantly higher than the identical load collected during the ICP, suggesting load history affects sagittal rotational dynamic parameters. In addition, spine damping was more affected by load history than spine stiffness. These results highlight the importance of controlling load magnitude and history when assessing spine dynamic parameters.

Performance during seated balancing is often used to assess trunk neuromuscular control, including evaluating impairments in back pain populations. Balancing in less challenging environments allows for flexibility in control, which may not depend on health status but instead may reflect personal preferences. To make assessment less ambiguous, trunk neuromuscular control should be maximally challenged. Thirty-four healthy subjects balanced on a robotic seat capable of adjusting rotational stiffness. Subjects balanced while rotational stiffness was gradually reduced. The rotational stiffness at which subjects could no longer maintain balance, defined as critical stiffness (k(Crit)), was used to quantify the subjects’ trunk neuromuscular control. A higher k(Crit) reflects poorer control, as subjects require a more stable base to balance. Subjects were tested on three days separated by 24 hours to assess test-retest reliability. Anthropometric (height and weight) and demographic (age and sex) influences on k(Crit) and its reliability were assessed. Height and age did not affect k(Crit); whereas, being heavier (p

BACKGROUND CONTEXT Low back pain (LBP) continues to be a costly problem in the United States. Unfortunately, current treatment options are limited when patients have predominantly LBP without instability or radicular symptoms. Neuromodulation has been shown to be effective, particularly in patients with chronic pain conditions such as failed back surgery and chronic regional pain syndrome. As such, the field of neuromodulation is evolving and spinal cord stimulator (SCS) implantation may provide a benefit to individuals who have chronic otherwise non-operable LBP. Considering SCS continues to advance with respect to stimulation parameters (eg, frequency, burst), combined with recent reports of improvements in both radicular lower extremity pain and axial LBP, further investigation into how SCS may benefit individuals experiencing chronic non-operative axial LBP is warranted. PURPOSE The purpose of this study was to determine the effects of SCS implantation on reducing pain and disability in chronic axial LBP patients who failed conservative treatment. STUDY DESIGN/SETTING Retrospective pre-test/post-test observational study design. PATIENT SAMPLE Twenty-four patients with chronic axial LBP who underwent SCS implantation. OUTCOME MEASURES Pain (Visual Analog Scale-VAS) and Disability (Oswestry Disability Index-ODI). METHODS A total of 24 patients with chronic axial LBP underwent SCS implantation and 1-year followup. All patients were diagnosed with chronic axial LBP with minimal or no radicular pain and had failed conservative treatment for a minimum of 12 months. All patients had >70% reduction of pain with trial stimulator before referral for placement of permanent implant. Patients were excluded if their primary complaint was radicular leg pain, had previous lumbar surgeries, no response to trial stimulator, RESULTS Baseline (pre-SCS implantation) measures for VAS and ODI were 7.9±1.5 and 24.2±10.2, respectively. At 1-year follow-up (post-SCS implantation), VAS and ODI were 3.4±2.6 and 12.0±10.9, respectively. These findings represent statistically significant effect sizes and clinically meaningful improvements in both pain (56.6% reduction in VAS, P CONCLUSIONS Patients with axial non-operable LBP demonstrated significant improvements in pain and disability at 1-year post-SCS implantation as VAS and ODI scores both surpassed minimal clinically important difference thresholds. This demonstrates that neuromodulation may play an important role in decreasing the burden that chronic LBP places on society. As SCS implantation technology improves, there is an increasing role for spine surgeons to understand the role of neuromodulation in the management of patients with spinal conditions. Further randomized controlled trials are needed to compare SCS implantation to other treatment interventions for chronic axial LBP. FDA DEVICE/DRUG STATUS Boston Scientific Coverage Lead with Precision Spectra Spinal Cord Stimulator System (Approved for this indication)

BACKGROUND CONTEXT The development of proximal junctional kyphosis (PJK) is an ongoing issue in adult spinal deformity (ASD) patients following spine surgery, with an incidence reported to be as high as 61.7%. Approximately 47.4% of patients who develop PJK will require revision surgery within 6 months. Currently, there are no reports in the literature on the effects of postoperative bracing on the incidence of PJK. We sought to determine whether postoperative bracing results in decreased rates of PJK in ASD treated with open posterior instrumented fusion (PSF) greater than six levels. PURPOSE To determine whether postoperative bracing results in decreased rates of PJK in ASD patients treated with PSF greater than six levels. We hypothesized that postoperative bracing would result in lower rates of PJK. STUDY DESIGN/SETTING We performed a retrospective analysis of prospectively collected data comparing patients treated with a thoracic lumbar sacral orthosis (TLSO) postoperatively for 3 months vs no brace following PSF. PATIENT SAMPLE Consecutive cohort of ASD patients (n=112) from a single surgical spine practice who underwent PSF were included. OUTCOME MEASURES Clinical and functional outcomes assessed: Oswestry Disability Index (ODI) and Visual Analog Scale pain (VAS). Radiographic measures: spinopelvic parameters, thoracic kyphosis (T5-T12), junctional kyphosis (T10-L2), lumbar lordosis (T12-S1), sagittal and coronal alignment, and PJK angle with corresponding level. METHODS Clinical and radiographic data of 112 (78 braced and 34 non-braced) consecutive adult patients who underwent PSF (> 6 levels) for deformity correction were analyzed. Radiographic measurements were performed preoperatively and postoperatively at 6 weeks and 6 months. PJK was defined as more than 10 degrees of abnormal kyphotic angulation measured at the superior end plate of one adjacent vertebra above the upper instrumented vertebra (UIV), to the inferior endplate of the UIV. Chi-square test and ANCOVA were used to analyze data. Statistical significance was set at p≤0.05. RESULTS The baseline clinical and radiographic demographics between the two cohorts were similar. The incidence of PJK was not statistically different (p=0.98) between patients who were braced (n=13/34; 38.2%) versus those not braced (n=30/78; 38.5%) postoperatively. Women had five times greater odds of developing PJK than men [OR=5.44;(95%CI =1.51-19.64)]. There were no significant differences at 6 months follow-up between the braced and not braced groups in ODI, VAS, or radiographic features, with the exception of T10-L2 thoracolumbar kyphosis, which was 3.08 versus 7.95 degrees in the braced and non-braced groups, respectively (p=0.03). CONCLUSIONS There was no statistical difference in the incidence of PJK in the braced versus non-braced groups. Interestingly, thoracolumbar kyphosis was significantly decreased in ASD patients who were braced postoperatively. Further investigation is needed to determine if postoperative bracing is protective against excessive postoperative kyphosis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

To study the complex neuromuscular control pathways in human movement, biomechanical parametric models and system identification methods are employed. Although test-retest reliability is widely used to validate the outcomes of motor control tasks, it was not incorporated in system identification methods. This study investigates the feasibility of incorporating test-retest reliability in our previously published method of selecting sensitive parameters. We consider the selected parameters via this novel approach to be the key neuromuscular parameters, because they meet three criteria: reduced variability, improved goodness of fit, and excellent reliability. These criteria ensure that the parameter variability is below a user-defined value, the number of these parameters is maximized to enhance goodness of fit, and their test-retest reliability is above a user-defined value. We measured variability, the goodness of fit, and reliability using Fisher information matrix, variance accounted for, and intraclass correlation, respectively. We also incorporated model diversity as a fourth optional criterion to narrow down the solution space of key parameters. We applied this approach to the head position tracking tasks in axial rotation and flexion/extension. A total of forty healthy subjects performed the tasks during two visits. With variability and reliability measures ≤0.35 and ≥0.75, respectively, we selected three key parameters out of twelve with the goodness of fit >69%. The key parameters were associated with at least two neuromuscular pathways out of four modeled pathways (visual, proprioceptive, vestibular, and intrinsic), which is a measure of model diversity. Therefore, it is feasible to incorporate reliability and diversity in system identification of key neuromuscular pathways in our application.

Background Context Low back pain (LBP) is a multifactorial problem with complex interactions among many biological, psychological and social factors. It is difficult to fully appreciate this complexity because the knowledge necessary to do so is distributed over many areas of expertise that span the biopsychosocial domains. Purpose This study describes the collaborative modeling process, undertaken among a group of participants with diverse expertise in LBP, to build a model to enhance understanding and communicate the complexity of the LBP problem. Study Design The study involved generating individual models that represented participants’ understanding of the LBP problem using fuzzy cognitive mapping (FCM), and 4 subsequent phases of consultation and consensus with the participants to characterize and refine the interpretation of the FCMs. Methods The phases consisted of: proposal of Categories for clustering of model Components; preliminary evaluation of structure, composition and focal areas of participant's FCMs; refinement of Categories and Components with consensus meeting; generation of final structure and composition of individual participant's FCMs. Descriptive statistics were applied to the structural and composition metrics of individual FCMs to aid interpretation. Results From 38 invited contributors, 29 (76%) agreed to participate. They represented 9 disciplines and 8 countries. Participants’ models included 729 Components, with an average of 25 (SD = 7) per model. After the final FCM refinement process (Components from separate FCMs that used similar terms were combined, and Components from an FCM that included multiple terms were separated), there were 147 Components allocated to ten Categories. Although individual models varied in their structure and composition, a common opinion emerged that psychological factors are particularly important in the presentation of LBP. Collectively, Components allocated to the “Psychology” Category were the most central in almost half (14/29) of the individual models. Conclusions The collaborative modeling process outlined in this paper provides a foundation upon which to build a greater understanding and to communicate the complexity of the LBP problem. The next step is to aggregate individual FCMs into a metamodel and begin disentangling the interactions among its Components. This will lead to an improved understanding of the complexity of LBP, and hopefully to improved outcomes for those suffering from this condition.

Estimating many parameters of biomechanical systems with limited data may achieve good fit but may also increase 95% confidence intervals in parameter estimates. This results in poor identifiability in the estimation problem. Therefore, we propose a novel method to select sensitive biomechanical model parameters that should be estimated, while fixing the remaining parameters to values obtained from preliminary estimation. Our method relies on identifying the parameters to which the measurement output is most sensitive. The proposed method is based on the Fisher information matrix (FIM). It was compared against the nonlinear least absolute shrinkage and selection operator (LASSO) method to guide modelers on the pros and cons of our FIM method. We present an application identifying a biomechanical parametric model of a head position-tracking task for ten human subjects. Using measured data, our method (1) reduced model complexity by only requiring five out of twelve parameters to be estimated, (2) significantly reduced parameter 95% confidence intervals by up to 89% of the original confidence interval, (3) maintained goodness of fit measured by variance accounted for (VAF) at 82%, (4) reduced computation time, where our FIM method was 164 times faster than the LASSO method, and (5) selected similar sensitive parameters to the LASSO method, where three out of five selected sensitive parameters were shared by FIM and LASSO methods.

OBJECTIVES To compare the strength of augmented versus nonaugmented fixation techniques for stabilizing vertical shear femoral neck fractures. METHODS Two surgical screw constructs were tested with and without augmentation using 40 composite femurs: (1) 7.3-mm cannulated screws placed in an inverted triangular configuration and (2) 135-degree dynamic hip screw (DHS). The augmentation consisted of a 2.7-mm locking plate placed on the anterior-inferior femoral neck. Specimens in all 4 groups were tested with load to failure, while failure loads, energy absorbed to failure, and axial stiffness were determined. These data were then analyzed using a two-way (construct × augmentation) analysis of variance. RESULTS There was no statistically significant interaction between screw construct and augmentation for load to failure (P = 0.11). Augmentation with the 2.7-mm locking plate increased failure loads in both constructs on average by 83% (2409 vs. 4417 N, P < 0.01). Femurs instrumented with cannulated screws had 26% higher loads to failure than those instrumented with DHS (3879 vs. 3087 N, P < 0.01). On average, the augmentation increased energy absorbed to failure by 183% and constructs' stiffness by 35%. CONCLUSIONS The strength of surgical repairs of the vertical shear femoral neck fractures can be significantly augmented with the 2.7-mm locking plate. The construct with the cannulated screws was significantly stronger than the DHS construct.

In this brief, we present a set of techniques for finding a cost function to the time-invariant linear quadratic regulator (LQR) problem in both continuous- and discrete-time cases. Our methodology is based on the solution to the inverse LQR problem, which can be stated as: does a given controller $K$ describe the solution to a time-invariant LQR problem, and if so, what weights $Q$ and $R$ produce $K$ as the optimal solution? Our motivation for investigating this problem is the analysis of motion goals in biological systems. We first describe an efficient linear matrix inequality (LMI) method for determining a solution to the general case of this inverse LQR problem when both the weighting matrices $Q$ and $R$ are unknown. Our first LMI-based formulation provides a unique solution when it is feasible. In addition, we propose a gradient-based, least-squares minimization method that can be applied to approximate a solution in cases when the LMIs are infeasible. This new method is very useful in practice since the estimated gain matrix $K$ from the noisy experimental data could be perturbed by the estimation error, which may result in the infeasibility of the LMIs. We also provide an LMI minimization problem to find a good initial point for the minimization using the proposed gradient descent algorithm. We then provide a set of examples to illustrate how to apply our approaches to several different types of problems. An important result is the application of the technique to human subject posture control when seated on a moving robot. Results show that we can recover a cost function which may provide a useful insight on the human motor control goal.

Determining the reliability of measurements used to quantify head–neck motor control is necessary before they can be used to study the effects of injury or treatment interventions. Thus, the purpose of this study was to determine the within- and between-day reliability of position tracking, position stabilization and force tracking tasks to quantify head–neck motor control. Ten asymptomatic subjects performed these tasks on two separate days. Position and force tracking tasks required subjects to track a pseudorandom square wave input signal by controlling their head–neck angular position (position tracking) or the magnitude of isometric force generated against a force sensor by the neck musculature (force tracking) in the sagittal plane. Position stabilization required subjects to maintain an upright head position while pseudorandom perturbations were applied to the upper body using a robotic platform. Within-day and between-day reliability of the frequency response curves were assessed using coefficients of multiple correlations (CMC). Root mean square error (RMSE) and mean bandpass signal energy, were computed for each task and between-day reliability was calculated using intra-class correlation coefficients (ICC). Within- and between-day CMCs for the position and force tracking tasks were all ≥0.96, while CMCs for position stabilization ranged from 0.72 to 0.82. ICCs for the position and force tracking tasks were all ≥0.93. For position stabilization, ICCs for RMSE and mean bandpass signal energy were 0.66 and 0.72, respectively. Measures of sagittal plane head–neck motor control using position tracking, position stabilization and force tracking tasks were demonstrated to be reliable.

The authors regret that “rheumatoid arthritis; cancer; or diabetes” were listed as examples of components in the “Tissue injury or pathology” category instead of the “Comorbidities” category in Table 2 on page 1035 of our article. Additionally, the last sentence in the “Outcomes” category was removed. The corrected Table 2 is shown below. The authors would like to apologize for any inconvenience this may have caused.

Purpose: Hip muscle weakness has been associated with altered lower extremity mechanics and the increased likelihood of receiving treatment for low back problems, although biomechanical injury mechanisms focused on the trunk have not been investigated. The purpose of this study was to compare lumbopelvic kinematic variables and muscle activation of the trunk and gluteal muscles in females with strong and weak hip muscle strength during a demanding single-leg task. Methods: Twenty-two asymptomatic females were categorized into a strong or weak group (11 per group) as determined by isometric hip extension and abduction dynamometry profiles. Participants performed a single-leg landing task during which three-dimensional lumbopelvic kinematics and trunk (lumbar erector spinae, external obliques, and rectus abdominis) and gluteal (gluteus maximus and gluteus medius) muscle activities were recorded. Peak lumbopelvic angular displacement, total angular excursion, and mean and peak angular velocity during the first 0.5 s of landing were reported. Mean normalized EMG and muscle cocontraction index (between the lumbar erector spinae and the external obliques) were also reported. Results: Significant between-group differences existed for each of the following: peak displacement, excursion, velocity, and muscle activity. Differences in peak angular displacement occurred in the frontal plane, whereas excursion differences were observed in all planes. Differences in peak velocity were noted in the sagittal and frontal planes. Weaker subjects showed increased muscle activation (across all muscles except the rectus abdominis) and cocontraction index. Conclusions: Individuals with diminished hip muscle strength exhibit greater lumbopelvic angular displacement, velocity, and muscle activity during the single-leg landing task. Future studies targeting hip strengthening may provide more insight to rehabilitation protocols as well as the relation between hip strength, low back motion, and muscle activity

In this study, we investigated trunk coordination during rate-controlled bipedal vertical dance jumps. The aims of the study were to investigate the pattern of coordination and the magnitude of coordination variability within jump phases and relative to phase-defining events during the jump. Lumbar and thoracic kinematics were collected from seven dancers during a series of jumps at 95 beats per minute. The vector coding technique was used to quantify the pattern and variability of trunk coordination. Coordination was predominantly anti-phase during propulsion and landing. Mean coordination variability peaked just before the landing phase and at the transition from landing to propulsion phases, and was lowest during the propulsion phase just before toe-off. The results indicate that peaks in variability could be explained by task and phase-specific biomechanical demands.

Controlled laboratory study using a cross-sectional design.To analyze lower extremity kinematics during takeoff of a "saut de chat" (leap) in dancers with and without a history of Achilles tendinopathy (AT). We hypothesized that dancers with AT would demonstrate different kinematic strategies compared to dancers without pathology, and that these differences would be prominent in the transverse and frontal planes.AT is a common injury experienced by dancers. Dance leaps such as the saut de chat place a large demand on the Achilles tendon.Sixteen female dancers with and without a history of AT (mean ± SD age, 18.8 ± 1.2 years) participated. Three-dimensional kinematics at the hip, knee, and ankle were quantified for the takeoff of the saut de chat, using a motion analysis system. A force platform was used to determine braking and push-off phases of takeoff. Peak sagittal, frontal, and transverse plane joint positions during the braking and push-off phases of the takeoff were examined statistically. Independent samples t tests were used to evaluate group differences (α = .05).The dancers in the tendinopathy group demonstrated significantly higher peak hip adduction during the braking phase of takeoff (mean ± SD, 13.5° ± 6.1° versus 7.7° ± 4.2°; P = .046). During the push-off phase, dancers with AT demonstrated significantly more internal rotation at the knee (13.2° ± 5.2° versus 6.9° ± 4.9°; P = .024).Dancers with AT demonstrate increased peak transverse and frontal plane kinematics when performing the takeoff of a saut de chat. These larger displacements may be either causative or compensatory factors in the development of AT.

Aesthetic constraints allow dancers fewer technique modifications than other athletes to negotiate the demands of leaping. We examined vertical ground reaction force and knee mechanics during a saut de chat performed by healthy dancers. It was hypothesized that vertical ground reaction force during landing would exceed that of take-off, resulting in greater knee extensor moments and greater knee angular stiffness. Twelve dancers (six males, six females; age 18.9 ± 1.2 years, mass 59.2 ± 9.5 kg, height 1.68 ± 0.08 m, dance training 8.9 ± 5.1 years) with no history of low back pain or lower extremity pathology participated in the study. Saut de chat data were captured using an eight-camera Vicon system and AMTI force platforms. Peak ground reaction force was 26% greater during the landing phase, but did not result in increased peak knee extensor moments. Taking into account the 67% greater knee angular displacement during landing, this resulted in less knee angular stiffness during landing. In conclusion, landing was accomplished with less knee angular stiffness despite the greater peak ground reaction force. A link between decreased joint angular stiffness and increased soft tissue injury risk has been proposed elsewhere; therefore, landing from a saut de chat may be more injurious to the knee soft tissue than take-off.

Study design In vitro study of genipin crosslinking effect on disc water content changes under compressive loading and unloading. Objective To investigate the influence of collagen crosslinking on hydration and fluid flow in different regions of intact discs, and to evaluate the nutritional implications. Summary of background data Age-related reductions of nutrient supply and waste product removal are critically important factors in disc pathogenesis. Diffusion and fluid flow are blocked by subchondral bone thickening, cartilaginous endplate calcification, loss of hydrophilic proteoglycans, and clogging of anular pores by degraded matrix molecules. Previous studies demonstrated increased hydraulic permeability and macromolecular transport through crosslinked collagenous matrices. Genipin has also demonstrated the capability to increase retention of proteoglycans. Methods A total of 57 bovine lumbar motion segments were divided randomly into phosphate buffered saline and 0.33% genipin-soaked treatment groups. Water content changes were measured using a mass-loss technique in 3 intervertebral disc regions following successive stages of compressive loading and unloading (post-treatment, after 1 hour 750 N compression, and after a subsequent 24-hour period of nominal loading). Net flow of fluid into or out of a region was determined from the percentage change in mean water content from successive groups. Results Fluid flow to and from the nucleus doubled with genipin crosslinking. Relative to the buffer-only controls, overall net fluid flow increased 103% in the nucleus pulposus, 36% in the inner anulus, and was 31% less in the outer anulus of genipin treated discs. Conclusion The effects of genipin crosslinking on matrix permeability and proteoglycan retention can alter hydration levels and fluid flow in the intervertebral disc. Resulting increases in fluid flow, including a doubling of flow to and from the nucleus, could lead to enhanced nutritional inflow and waste product outflow for the disc, and may have implications for emerging cell-based therapies.

BACKGROUND CONTEXT Low back pain (LBP) is a bio-psycho-social condition and LBP patients are treated by various health professionals with different training and presumed beliefs. Considering that theoretical foundations and emphases vary among health disciplines, it is possible that these professionals (eg, researchers and clinicians from different disciplines) possess different “mental models” of what and how various factors relate to LBP. A novel way to investigate individual thinking about particular processes is through the development and analysis of fuzzy-logic cognitive maps (FCM). FCMs are particularly useful for modeling interactions between variables in complex systems, such as LBP. This study aimed to use this approach to describe similarities and differences by which different health professionals think about LBP. METHODS Participants from different disciplines (n=28), who have contributed significantly to the understanding of LBP (eg, publications, contributions to societies, etc.), were selectively recruited for this study and represented the following disciplines: (1) basic science (n=6), (2) chiropractic (n=4), (3) spine surgery (n=2), (4) physical medicine & rehabilitation (n=2), (5) physical or exercise therapy (n=12), and (6) psychology (n=2). Each participant underwent a structured one-on-one interview to construct an FCM that represented the individual's understanding (mental model) of how factors related to LBP using Mental Modeler software ( www.mentalmodeler.org ). This process involved nomination of factors contributing to patients’ outcomes (ie, pain, disability, and quality of life) and the weighting of the connections (strength of the effect) between these factors. Factors from each model were tabulated and categorized into eight domains: (1) nociceptive detection and processing, (2) behavioral or lifestyle (3) tissue injury or pathology, (4) contextual, (5) psychological(6) social or work, (7) biomechanical, and (8) individual factors. To determine the importance of each factor expressed in the FCM, centrality was computed as: Centrality = |a|*(# of connections in)+|b|*(# of connections out), where a and b are the weighting or strength of the connections. Based on this definition, centrality of a factor increases by the number of connections to and from the specific factor in the FCM, as well as by the weighting of these connections. Centrality of each domain (sum of centrality for each factor within the designated domain) was expressed as a percentage of the eight domains and grouped by discipline. RESULTS A total of 263 factors were generated from the 28 FCM. Psychological factors was the most prominent domain accounting for 33% of the centrality across all six participant groups, and was the most “central” domain for four groups (chiropractic, physical medicine and rehabilitation, physical or exercise therapy, and psychology). Tissue injury or pathology accounted for 14.7% of the centrality across all groups and was the most “central” for the remaining two groups (basic science and spinal surgery). CONCLUSIONS Psychological factors were considered to be the most central or important to understanding LBP across disciplines, yet many of these professions do not specialize in the psychology of LBP. Although the selection of individuals and the relatively small sample size representing each discipline may bias the results, such findings support the notion that multidisciplinary interventions (which includes consideration of psychological factors) to treating patients with LBP is sensible.

BACKGROUND CONTEXT Low back pain (LBP) is a very complex problem with numerous bio-psycho-social factors interacting to impact pain, disability, and quality of life. To understand the dynamics of such a complex problem, it needs to be studied in its entirety (systems approach). Although this concept is accepted by the scientific and clinical communities, much research to date is conducted by specialized teams focusing on isolated factors related to LBP. Such a reductionist approach may be useful in some circumstances, but it also creates barriers for integrating knowledge between disciplines and ultimately precludes the understanding of the dynamics of the entire LBP problem. To leverage the knowledge shared among various stakeholders, an innovative process called collaborative modeling was developed within the field of systems science specifically for enhancing the understanding of complex, multifactorial systems dynamics. This study assessed the feasibility of using this approach for integrating multidisciplinary knowledge of LBP. METHODS Participants (n=29), who have contributed significant knowledge to the area of LBP (eg publications, contributions to societies, etc.), were selectively recruited for this study and represented diverse disciplines: Basic Science (n=7), Chiropractic (n=4), Spine Surgery (n=2), Physical Medicine & Rehabilitation (n=2), Physical or Exercise Therapy (n=12), and Psychology (n=2). Each participant underwent a structured one-on-one interview to construct a fuzzy-logic cognitive map (FCM) (Mental Modeler software, www.mentalmodeler.org ) representing his or her understanding of how factors related to LBP interact and affect patient outcomes (pain, disability and quality of life). All individual FCMs were then converted to adjacency matrices and integrated into one meta-model (Gephi software, www.gephi.org ). To demonstrate the integrated meta-model's potential, various intervention strategies listed in all FCMs were simulated and their relative effects on pain, disability, and quality of life were investigated. RESULTS The meta-model, that integrated the understanding of LBP of all participants, consisted of 272 factors and 1,429 connections representing interactions among these factors. Simulations of individual treatment interventions predicted that combined aerobic exercise, counseling, and education are likely to be the most effective intervention to reduce pain. Meditation, followed by cognitive behavioral therapy, had the greatest impact on reducing disability and improving quality of life. CONCLUSIONS The integration of 29 FCMs, representing diverse participants’ views of LBP dynamics, resulted in a model that was extremely complex, but still feasible to produce meaningful interpretations. The simulations provided outcomes that broadly agreed with data in the literature, which suggests that aerobic exercise, counseling, education, meditation, and cognitive behavioral therapy are effective LBP interventions. Although the selection of participants and the relatively small sample size may influence the results, the findings suggest that it is possible to integrate multidisciplinary knowledge of LBP into one meta-model. This approach could provide the framework for a larger, community-wide platform for further development and refinement of this meta-model. Such a meta-model could then be used to simulate other “what if” scenarios, to identify gaps in knowledge, and to inform new essential research directions to ultimately improve patient care and outcomes for LBP.

The purpose of this study was 2-fold: (1) to analyze the degree and the location of lumbar multifidus asymmetry among patients scheduled for L4-L5 microdiscectomy, and (2) to determine the amount of asymmetry recognizable by a radiologist on magnetic resonance imaging.Bilateral multifidi cross-sectional areas were measured on magnetic resonance axial images of 20 patients scheduled to undergo L4-L5 microdiscectomy. The sides were compared and the location and amount of asymmetry (%)determined. The axial slices were assigned to two different categories based on their anatomical proximity to the L4-L5 disc (Disc(Ref)) and to the fascicles of the lumbar multifidus attaching to the spinous process of L5 (Muscle(Ref)). The maximal percent difference in cross-sectional area was compared between these categories. A radiologist rated the degree of asymmetry visually. These ratings were compared slice by slice to the computed percent difference in the cross-sectional area.Mean differences in multifidus cross-sectional area were 11.5 +/- 5.6% in the Disc(Ref) and 15.8 +/- 9.5% in the Muscle(Ref) categories and were statistically significant (P = 0.03). The radiologist recognized asymmetry when the quantitative difference was at least 12.6%. This level of asymmetry was identified in the Muscle(Ref) category in 45% of cases and in Disc(Ref) in 30% of cases.Nearly half of the cases scheduled for lumbar microdiscetomy exhibited asymmetry of at least 12.6% in the lumbar multifidus innervated by the L5 nerve root, which is located below the level of the injured disc. A trained radiologist can readily identify this multifidus asymmetry.

This study sought to evaluate opioid consumption, hospitalization costs, and length of stay when surgical site periarticular infiltration of liposomal bupivacaine is used after total knee arthroplasty (TKA). Sixty-six consecutive primary TKA cases performed with a single-injection femoral nerve block before this date were compared with 59 consecutive TKA cases performed with the liposomal bupivacaine cocktail after this date. The mean amount of postsurgical opioids consumed was 199 mg versus 121 mg (p = .075), the average hospitalization cost was $28,546 versus $26,472 (p.001), and the average length of stay was 2.05 days versus 1.58 days (p.001) in the femoral nerve block versus liposomal bupivacaine group, respectively. There were no significant demographic differences between the two groups. Liposomal bupivacaine infiltration before primary wound closure may be an effective means in lowering hospitalization costs, decreasing length of stay, and decreasing postsurgical opioid consumption after TKA.

We are developing a series of systems science-based clinical tools that will assist in modeling, diagnosing, and quantifying postural control deficits in human subjects. In line with this goal, we have designed and constructed a seated balance device and associated experimental task for identification of the human seated postural control system. In this work, we present a quadratic programming (QP) technique for optimizing a time-domain experimental input signal for this device. The goal of this optimization is to maximize the information present in the experiment, and therefore its ability to produce accurate estimates of several desired seated postural control parameters. To achieve this, we formulate the problem as a nonconvex QP and attempt to locally maximize a measure (T-optimality condition) of the experiment’s Fisher information matrix (FIM) under several constraints. These constraints include limits on the input amplitude, physiological output magnitude, subject control amplitude, and input signal autocorrelation. Because the autocorrelation constraint takes the form of a quadratic constraint (QC), we replace it with a conservative linear relaxation about a nominal point, which is iteratively updated during the course of optimization. We show that this iterative descent algorithm generates a convergent suboptimal solution that guarantees monotonic nonincreasing of the cost function value while satisfying all constraints during iterations. Finally, we present successful experimental results using an optimized input sequence.

Background and Purpose. Navicular drop (ND) measurement may be a valuable examination technique for patients with rheumatoid arthritis (RA). However, no data exist on reliability for this technique in patients with RA. The purposes of this study were: (1) to determine interrater and intrarater reliability of ND measurements in people with RA, (2) to compare ND values of people with RA with published normative data, and (3) to investigate ND measurement error associated with the use of skin markings. Subjects. Ten women (20 feet) with RA consented to participate. Methods. Patients completed demographic and function questionnaires. Navicular height (NH) measurements were taken by 2 physical therapists and 1 physical therapist student, following four 1-hour training sessions, using standardized methods and a digital height gauge. Four different NH measurements were taken 3 times on each foot by each of the 3 examiners during a morning session and then repeated during an afternoon session on the same day. Navicular drop values were calculated, including ND1 (as reported in the literature), ND2 (compensating for skin error), and ND3 (single-limb stance). Intraclass correlation coefficients (ICCs) and standard errors of measurement (SEMs) were used to establish reliability. Results. Means (±SD) for each ND measure for sessions 1 and 2, respectively, were as follows: ND1=8.36±5.29 mm and 8.29±5.24 mm, ND2=9.95±5.44 mm and 9.57±5.37 mm. The ICCs (2,1 and 2,k, respectively) for all interrater measurements ranged from .67 to .92 (SEM=2.0–3.3 mm) and from .85 to .97 (SEM=1.1–2.0 mm). The ICCs (2,1 and 2,k, respectively) for intrarater measurements ranged from .73 to .95 (SEM=1.3–2.8 mm) and from .90 to .98 (SEM=0.7–1.6 mm). Paired t tests showed the means of ND1 and ND2 for each examiner and for both sessions were significantly different. Discussion and Conclusion. The results suggest that ND measurements for people with RA can be taken reliably by clinicians with varied experience. The ND values for our subjects were slightly greater than reported normal values of 6 to 8 mm. Error associated with skin markings was statistically significant for all sessions and examiners.