Poor lumbar spine coordination in acute low back pain predicts persistent long-term pain and disability.

PURPOSE: Sitting balance on an unstable surface requires coordinated out-of-phase lumbar spine and provides sufficient challenge to expose quality of spine control. We investigated whether the quality of spine coordination to maintain balance in acute low back pain (LBP) predicts recovery at 6 months. METHODS: Participants in an acute LBP episode (n = 94) underwent assessment of sitting balance on an unstable surface. Seat, hip and spine (lower lumbar, lumbar, upper lumbar, thoracic) angular motion and force plate data were recorded. Coordination between the seat and hip/spine segments to maintain balance was quantified in the frequency domain to evaluate coordination (coherence) and relative timing (phase angle: in-phase [segments move together]; out-of-phase [segments move opposite]). Center of pressure (CoP) and upper thorax motion assessed overall balance performance. Hip and spine coordination with the seat were compared between those who did not recover (increased/unchanged pain/disability), partially recovered (reduced pain/disability) or recovered (no pain and disability) at 6 months. RESULTS: In both planes, coherence between the seat and lower lumbar spine was lower (and in-phase-unhelpful for balance) at baseline in those who did not recover than those who recovered. Coherence between the seat and hip was higher in partially recovered in both planes, suggesting compensation by the hip. LBP groups had equal overall balance performance (CoP, upper thorax motion), but non-recovery groups used a less optimal strategy that might have consequences for long-term spine health. CONCLUSION: These longitudinal data revealed that individuals with compromised contribution of the lumbar spine to the balance during unstable sitting during acute LBP are less likely to recover.

Trunk postural control during unstable sitting among individuals with and without low back pain: A systematic review with an individual participant data meta-analysis.

INTRODUCTION: Sitting on an unstable surface is a common paradigm to investigate trunk postural control among individuals with low back pain (LBP), by minimizing the influence lower extremities on balance control. Outcomes of many small studies are inconsistent (e.g., some find differences between groups while others do not), potentially due to confounding factors such as age, sex, body mass index [BMI], or clinical presentations. We conducted a systematic review with an individual participant data (IPD) meta-analysis to investigate whether trunk postural control differs between those with and without LBP, and whether the difference between groups is impacted by vision and potential confounding factors. METHODS: We completed this review according to PRISMA-IPD guidelines. The literature was screened (up to 7th September 2023) from five electronic databases: MEDLINE, CINAHL, Embase, Scopus, and Web of Science Core Collection. Outcome measures were extracted that describe unstable seat movements, specifically centre of pressure or seat angle. Our main analyses included: 1) a two-stage IPD meta-analysis to assess the difference between groups and their interaction with age, sex, BMI, and vision on trunk postural control; 2) and a two-stage IPD meta-regression to determine the effects of LBP clinical features (pain intensity, disability, pain catastrophizing, and fear-avoidance beliefs) on trunk postural control. RESULTS: Forty studies (1,821 participants) were included for the descriptive analysis and 24 studies (1,050 participants) were included for the IPD analysis. IPD meta-analyses revealed three main findings: (a) trunk postural control was worse (higher root mean square displacement [RMSdispl], range, and long-term diffusion; lower mean power frequency) among individuals with than without LBP; (b) trunk postural control deteriorated more (higher RMSdispl, short- and long-term diffusion) among individuals with than without LBP when vision was removed; and (c) older age and higher BMI had greater adverse impacts on trunk postural control (higher short-term diffusion; longer time and distance coordinates of the critical point) among individuals with than without LBP. IPD meta-regressions indicated no associations between the limited LBP clinical features that could be considered and trunk postural control. CONCLUSION: Trunk postural control appears to be inferior among individuals with LBP, which was indicated by increased seat movements and some evidence of trunk stiffening. These findings are likely explained by delayed or less accurate corrective responses. SYSTEMATIC REVIEW REGISTRATION: This review has been registered in PROSPERO (registration number: CRD42021124658).

The effects of osteopathic manipulative treatment on pain and disability in patients with chronic low back pain: a single-blinded randomized controlled trial.

CONTEXT: The evidence for the efficacy of osteopathic manipulative treatment (OMT) in the management of low back pain (LBP) is considered weak by systematic reviews, because it is generally based on low-quality studies. Consequently, there is a need for more randomized controlled trials (RCTs) with a low risk of bias. OBJECTIVES: The objective of this study is to evaluate the efficacy of an OMT intervention for reducing pain and disability in patients with chronic LBP. METHODS: A single-blinded, crossover, RCT was conducted at a university-based health system. Participants were adults, 21-65 years old, with nonspecific LBP. Eligible participants (n=80) were randomized to two trial arms: an immediate OMT intervention group and a delayed OMT (waiting period) group. The intervention consisted of three to four OMT sessions over 4-6 weeks, after which the participants switched (crossed-over) groups. The primary clinical outcomes were average pain, current pain, Patient-Reported Outcomes Measurement Information System (PROMIS) 29 v1.0 pain interference and physical function, and modified Oswestry Disability Index (ODI). Secondary outcomes included the remaining PROMIS health domains and the Fear Avoidance Beliefs Questionnaire (FABQ). These measures were taken at baseline (T0), after one OMT session (T1), at the crossover point (T2), and at the end of the trial (T3). Due to the carryover effects of OMT intervention, only the outcomes obtained prior to T2 were evaluated utilizing mixed-effects models and after adjusting for baseline values. RESULTS: Totals of 35 and 36 participants with chronic LBP were available for the analysis at T1 in the immediate OMT and waiting period groups, respectively, whereas 31 and 33 participants were available for the analysis at T2 in the immediate OMT and waiting period groups, respectively. After one session of OMT (T1), the analysis showed a significant reduction in the secondary outcomes of sleep disturbance and anxiety compared to the waiting period group. Following the entire intervention period (T2), the immediate OMT group demonstrated a significantly better average pain outcome. The effect size was a 0.8 standard deviation (SD), rendering the reduction in pain clinically significant. Further, the improvement in anxiety remained statistically significant. No study-related serious adverse events (AEs) were reported. CONCLUSIONS: OMT intervention is safe and effective in reducing pain along with improving sleep and anxiety profiles in patients with chronic LBP.

How Individuals With Low Back Pain Conceptualize Their Condition: A Collaborative Modeling Approach.

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.

The effects of osteopathic manipulative treatment on pain and disability in patients with chronic neck pain: A single-blinded randomized controlled trial.

BACKGROUND: Neck pain (NP) affects up to 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: Ninety-seven participants, 21 to 65 years of age, with chronic, nonspecific NP. INTERVENTIONS: Participants were randomized to two trial arms: immediate OMT intervention or waiting period first. The intervention consisted of three to four OMT sessions over 4 to 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 Patient-Reported Outcomes Measurement Information System-29 (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: A total of 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% confidence interval [CI] -1.72, -0.32; p = .005), current pain (-1.02, 95% CI -1.75, -0.30; p = .006), disability (-5.30%, 95% CI -9.2%, -1.3%; p = .010) and improved secondary outcomes (PROMIS) related to sleep (-3.25, 95% CI -6.95, -1.54; p = .003), fatigue (-3.26, 95% CI -6.04, -0.48; p = .022), and depression (-2.59, 95% CI -4.73, -0.45; p = .018). The effect sizes were in the clinically meaningful range between 0.5 and 1 standard deviation. 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 to 6 weeks.

Stability threshold during seated balancing is sensitive to low back pain and safe to assess.

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 < 0.001, 7-day pain p = 0.023), reflecting that people experiencing more pain have poorer trunk neuromuscular control. There was no evidence that disability was associated with KCrit, although the limited range in disability scores in subjects may have impacted the analysis. AEs were reported in 13 out of 79 total sessions (AE Severity: 12 mild, 1 moderate; AE Relatedness: 1 possibly, 11 probably, 1 definitely-related to the study). Stability threshold is sensitive to pain and appears safe to assess in people with LBP, suggesting it could be useful for identifying trunk neuromuscular impairments and guiding rehabilitation.

Cohort profile: why do people keep hurting their back?

OBJECTIVE: Low back pain (LBP) is one of the most disabling and costly conditions worldwide. It remains unclear why many individuals experience persistent and recurrent symptoms after an acute episode whereas others do not. A longitudinal cohort study was established to address this problem. We aimed to; (1) evaluate whether promising and potentially modifiable biological, psychological, social and behavioural factors, along with their possible interactions, predict LBP outcome after an acute episode; (2) compare these factors between individuals with and without acute LBP; and (3) evaluate the time-course of changes in these factors from LBP onset. This paper outlines the methodology and compares baseline characteristics between acute LBP and control, and LBP participants with and without follow-up. RESULTS: 133 individuals with acute LBP and 74 pain-free individuals participated. Bio-psycho-social and behavioural measures were collected at baseline and 3-monthly for 12 months (LBP) or 3 months (control). Pain and disability were recorded fortnightly. Baseline characteristics were mostly similar between those who did and did not return for follow-up. Initial analyses of this cohort have revealed important insights into the pathways involved in acute-to-chronic LBP. These and future findings will provide new targets for treatment and prevention of persistent and recurrent LBP.

Trunk stiffness decreases and trunk damping increases with experimental low back pain.

Movement adaptations to low back pain (LBP) are believed to protect the painful area. Increased trunk stiffness and decreased trunk damping have been shown in people with recurrent LBP. However, no study has examined these properties using external force perturbations to the trunk during acute LBP when protective adaptations might be expected to have most relevance. Adaptations to an acute painful stimulus via unilateral injection of hypertonic saline into the right longissimus muscle were assessed using a trunk force perturbation paradigm and a mass-spring-damper model to describe effective trunk dynamical properties. Equal weights (15% body weight) were connected to the front and back of the trunk via a cable. Either one was dropped at random to perturb the trunk. Effective trunk dynamical properties were estimated in fourteen males (mean (standard deviation) age 25 (6) years) assuming that trunk movement can be modelled as a second order linear system. Effective trunk dynamical properties were compared before, during and after the experimentally induced painful period. Estimates of effective trunk stiffness (K) decreased and damping (B) increased during pain compared to both before ([mean contrast, 95% CI] K: -403 [-651 to -155] Nm-1, B: 28 [9-50] Nms-1) and after (K: -324 [-58 to -591] Nm-1, B: 20 [4-33] Nms-1) the experimentally induced painful period. We interpret our results to show that, when challenged by a step force perturbation, a healthy system adapts to noxious input by controlling trunk velocity rather than trunk displacement, in contrast to observations during remission from recurrent clinical LBP.

Quantifying trunk neuromuscular control using seated balancing and stability threshold.

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 (kCrit), was used to quantify the subjects' trunk neuromuscular control. A higher kCrit 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 kCrit and its reliability were assessed. Height and age did not affect kCrit; whereas, being heavier (p < 0.001) and female (p = 0.042) significantly increased kCrit. Reliability was also affected by anthropometric and demographic factors, highlighting the potential problem of inflated reliability estimates from non-control related attributes. kCrit measurements appear reliable even after removing anthropometric and demographic influences, with adjusted correlations of 0.612 (95%CI: 0.433-0.766) versus unadjusted correlations of 0.880 (95%CI: 0.797-0.932). Besides assessment, trainers and therapists prescribing exercise could use the seated balance task and kCrit to precisely set difficulty level to a percentage of the subject's stability threshold to optimize improvements in trunk neuromuscular control and spine health.

Building a Collaborative Model of Sacroiliac Joint Dysfunction and Pelvic Girdle Pain to Understand the Diverse Perspectives of Experts.

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.

Time to Reflect on the Role of Motor Control in Low Back Pain.

The articles in this special issue on low back pain are the outcome of work undertaken by a series of working parties established during the meeting, "State-of-the-Art in Motor Control and Low Back Pain: International Clinical and Research Expert Forum," held in Chicago in October 2015. This multidisciplinary meeting provided an opportunity for discussion of key issues that interconnect motor control, pain, and the spine. What started as a relatively straightforward objective to summarize the field subsequently developed into an extensive process of literature review and discussion that culminated in the commentaries and articles presented in this special issue. We hope that the up-to-date information and in-depth insights into pain, motor control, and rehabilitation provide novel insights and a clear trajectory for future work and form the foundation for ongoing lively discussion. J Orthop Sports Phys Ther 2019;49(6):367-369. doi:10.2519/jospt.2019.0104.

Model Simulations Challenge Reductionist Research Approaches to Studying Chronic Low Back Pain.

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, multifactorial nature of this condition. OBJECTIVES: To quantify the likelihood of successfully subclassifying patients with LBP and effectively targeting treatment based on a single dominant factor contributing to LBP. METHODS: Both analytical and numerical simulations (Monte Carlo) of 1 million patients with LBP were performed. Several factors contributing to LBP were randomly assigned to each individual. The following outcome measures were computed, as a function of the number of factors: the percentage of individuals who could be subclassified by identifying a single factor exceeding a certain threshold, and the average reduction in LBP when 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 toward zero. A multimodal treatment arbitrarily addressing any 2 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 patients with LBP or for targeting treatment. The use of reductionist approaches may explain some of the challenges when creating LBP classification systems and designing effective treatment interventions. J Orthop Sports Phys Ther 2019;49(6):477-481. Epub 15 May 2019. doi:10.2519/jospt.2019.8791.

Can Biomechanics Research Lead to More Effective Treatment of Low Back Pain? A Point-Counterpoint Debate.

SYNOPSIS: 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. J Orthop Sports Phys Ther 2019;49(6):425-436. Epub 15 May 2019. doi:10.2519/jospt.2019.8825.

Are Stability and Instability Relevant Concepts for Back Pain?

SYNOPSIS: Individuals with back pain are often diagnosed with spine instability, even though it is unclear whether the spine is susceptible to unstable behavior. The spine is a complex system with many elements that cannot be directly observed, which makes the study of spine function and direct assessment of spine instability difficult. What is known is that trunk muscle activation is adjusted to meet stability demands, which highlights that the central nervous system closely monitors threats to spine stability. The spine appears to be protected by neural coupling and mechanical coupling that prevent erroneous motor control from producing segmental instability; however, this neural and mechanical coupling could be problematic in an injured spine. Finally, instability traditionally contemplated from a mechanical and control perspective could potentially be applied to study processes involved in pain sensitization, and possibly back pain that is iatrogenic in nature. This commentary argues for a more contemporary and broadened view of stability that integrates interdisciplinary knowledge in order to capture the complexity of back pain. J Orthop Sports Phys Ther 2019;49(6):415-424. Epub 25 Apr 2019. doi:10.2519/jospt.2019.8144.

Feasibility of Incorporating Test-Retest Reliability and Model Diversity in Identification of Key Neuromuscular Pathways During Head Position Tracking.

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.

Development of a collaborative model of low back pain: report from the 2017 NASS consensus meeting.

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.

Selecting Sensitive Parameter Subsets in Dynamical Models With Application to Biomechanical System Identification.

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.

Reliability of assessing postural control during seated balancing using a physical human-robot interaction.

This study evaluated the within- and between-visit reliability of a seated balance test for quantifying trunk motor control using input-output data. Thirty healthy subjects performed a seated balance test under three conditions: eyes open (EO), eyes closed (EC), and eyes closed with vibration to the lumbar muscles (VIB). Each subject performed three trials of each condition on three different visits. The seated balance test utilized a torque-controlled robotic seat, which together with a sitting subject resulted in a physical human-robot interaction (pHRI) (two degrees-of-freedom with upper and lower body rotations). Subjects balanced the pHRI by controlling trunk rotation in response to pseudorandom torque perturbations applied to the seat in the coronal plane. Performance error was expressed as the root mean square (RMSE) of deviations from the upright position in the time domain and as the mean bandpass signal energy (Emb) in the frequency domain. Intra-class correlation coefficients (ICC) quantified the between-visit reliability of both RMSE and Emb. The empirical transfer function estimates (ETFE) from the perturbation input to each of the two rotational outputs were calculated. Coefficients of multiple correlation (CMC) quantified the within- and between-visit reliability of the averaged ETFE. ICCs of RMSE and Emb for all conditions were ≥0.84. The mean within- and between-visit CMCs were all ≥0.96 for the lower body rotation and ≥0.89 for the upper body rotation. Therefore, our seated balance test consisting of pHRI to assess coronal plane trunk motor control is reliable.

Degenerative Spondylolisthesis Is Related to Multiparity and Hysterectomies in Older Women.

STUDY DESIGN: A case-control study. OBJECTIVE: To determine whether parity and abdominal surgeries are associated with degenerative spondylolisthesis (DS). SUMMARY OF BACKGROUND DATA: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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. LEVEL OF EVIDENCE: 4.