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Introduction: Mobile health (mHealth) lifestyle interventions can help mitigate cardiometabolic disease. However, Hispanic adults are underrepresented in these interventions, report lower physical activity (PA) levels and are disproportionately affected by cardiometabolic disease compared to non-Hispanic White (NHW) adults. We conducted a secondary analysis of the effects of an 8-week mHealth exercise intervention on exercise behavior in Hispanic and NHW adults. Hypothesis: A remotely delivered mHealth exercise program involving a wearable sensor, mobile application and wellness education would promote similar exercise behavior in both Hispanic and NHW adults. Methods: Thirty-eight Hispanic and 21 NHW sedentary (< 60 min/week of exercise) adults were randomized (1:1:1) to 8 weeks of increasing behavioral resources: Level 1 (wellness education, n=16), Level 2 (wellness education + pre-recorded exercise videos, n=24), or Level 3 (wellness education + livestream group exercise, n=19). Participants were given a chest strap sensor (Myzone MZ-3) to use during exercise and a mobile app to interact with other participants. A weekly email delivered wellness education, feedback and PA encouragement. Level 2 (videos) and Level 3 (classes) performed 35-min 3x/wk of instructor-led, high-intensity functional training designed to improve cardiometabolic risk factors. Sensor use (3x/wk encouraged) and time spent in moderate-to-vigorous exercise effort (MVET) were captured by the MZ-3. MVET was calculated as the time spent in effort >64% maximum heart rate. Baseline and post-intervention PA were captured using the International Physical Activity Questionnaire. Differences between groups were tested using univariate ANOVA with Bonferroni-adjusted t tests in post hoc analyses. Results: Hispanic participants were younger (30.6 ± 10.1 yr, mean ± SD) and performed less PA (22.6 ± 70.2 min/wk) at baseline compared to NHW (39.7 ± 16.8 yr, 90.1± 90.2 min/wk; p0.05), or in weekly sensor use during the intervention (Hispanic 1.7 ± 1.8 sessions/wk, NHW 2.4 ± 1.6 sessions/wk, p>0.05). Self-reported PA increased from baseline to post-intervention in both groups (p Conclusion: An 8-week mHealth lifestyle program increased PA behavior in sedentary participants. However, Hispanic participants exercised at lower intensities than non-Hispanic White participants. Future work is needed to identify barriers in meeting MVPA recommendations in minority populations so that culturally tailored interventions can be developed.

Background Diminished gluteus maximus muscle strength has been proposed to be contributory to various lower-limb injuries. As such, it is of clinical importance to perform hip extensor strength testing in a position that biases torque contribution of the gluteus maximus relative to the other hip extensors (i.e. hamstrings). Objectives To determine the relative torque contributions of the gluteus maximus and hamstring muscles in various hip extensor strength testing positions. Methods 13 Young, healthy participants performed maximum isometric hip extension on a dynamometer in 4 different positions that varied in terms of hip and knee flexion. Surface electromyography (EMG) was used to assess activation of gluteus maximus and hamstrings during the maximum isometric contractions. Normalized EMG data were used as an input to determine individual muscle contribution to hip extension torque production using SIMM modeling software. The gluteus maximus/hamstring torque contribution ratio was compared across the 4 positions using a one-way repeated-measures ANOVA. Results The highest gluteus maximus torque contribution value occurred in positions where the hip was flexed to 45°, while the highest hamstring torque contribution occurred in positions in which the knee was fully extended. The gluteus maximus/hamstring torque contribution ratio was highest at 0° of hip extension and 90° of knee flexion. Conclusion Testing isometric hip extensor strength at 0° of hip extension and 90° of knee flexion should be considered in order to bias torque production of the gluteus maximus relative to the hamstrings.

To evaluate short-term effects of a four-week gait retraining program using visual feedback on trunk flexion angle, patellofemoral joint (PFJ) stress, lower extremity biomechanics and motor skill automaticity.Longitudinal interventional study.University research laboratory.Twelve asymptomatic recreational runners (seven male and five female).Trunk kinematics as well as lower extremity kinematics and kinetics were assessed prior to training at week 1 (baseline) and week 2, 3, 4 and 8 (retention). PFJ stress was computed using a sagittal plane model. A dual-task procedure was performed to examine automaticity.At week 8, runners demonstrated 10.1° increase in trunk flexion angle (p .001) and 17.8% reduction in peak PFJ stress (p .001) compared to baseline. This is associated with a 16.8% decrease in knee extensor moment and less than 2.5° change in knee flexion angle. Participants also showed 33.3% increase in peak hip extensor moment and small reduction in peak ankle plantar flexor moment. Lastly, runners demonstrated automaticity of the modified skill with a dual-task cost of less than 3%.The gait retraining program is effective to elicit short term changes in trunk position, PFJ stress, and automaticity of the new motor skill.

Introduction: Lifestyle interventions incorporating exercise and nutrition can help prevent and manage cardiometabolic disease. However, not all interventions readily reach individuals who are most in need. A mobile health (mHealth) exercise program could be a cost-effective approach to broadening accessibility and providing support for physical activity behavior change. We tested the feasibility and acceptability of a mHealth exercise intervention in this 8-week pilot study. Hypothesis: A remotely delivered mHealth lifestyle program involving a wearable sensor, mobile application and social support is feasible and acceptable in sedentary adults. Methods: A total of 84 sedentary (< 30 min/week of exercise) adults (females 31.5 ± 11.3 yr, males 34.1 ± 28.9 yr, mean ± SD) were randomized (1:1:1) to 8 weeks of increasing physical activity behavioral support: Level 1 (wellness education, n=26), Level 2 (wellness education + pre-recorded exercise videos, n=30), or Level 3 (wellness education + livestream group exercise, n=28). Participants used a chest strap sensor (Myzone MZ-3) during exercise and a mobile application for interaction. A weekly email was used to deliver wellness education and encourage physical activity. Level 2 exercise videos and Level 3 livestream (Zoom) group classes were 35 min long, instructor-led, delivered 3x/wk and designed to meet national guidelines for weekly physical activity. Participants were surveyed at baseline and 8 weeks. Feasibility was defined through accrual and attrition; acceptability through sensor use (3x/wk encouraged) and survey data. Results: Between August 2020 and August 2021, 204 adults were screened for eligibility. Out of 135 eligible participants, 84 (62%) enrolled in the study. Preliminary analysis indicated 65% retention at 8-week follow-up. Participants were primarily Hispanic/Latinx (47%), 71% had 2-year college or more education, 45% reported income below federal poverty thresholds, and 36% reported qualifying for public assistance. Program acceptability varied by group with weekly median sensor use of 1 day/wk (Level 1), 2 days/wk (Level 2) and 3 days/wk (Level 3). Good-to-high program enjoyment was reported by 90% of Level 3 and 83% of Level 2 participants. Conclusions: This pilot study demonstrates that a livestream group-based or video-based exercise program is feasible and acceptable in sedentary adults. A randomized controlled trial investigating health-related outcomes using this mHealth program is warranted.

The biomechanics of the trunk and lower limbs during walking and running gait are frequently assessed in individuals with low back pain (LBP). Despite substantial research, it is still unclear whether consistent and generalizable changes in walking or running gait occur in association with LBP. The purpose of this systematic review was to identify whether there are differences in biomechanics during walking and running gait in individuals with acute and persistent LBP compared with back-healthy controls.A search was conducted in PubMed, CINAHL, SPORTDiscus, and PsycINFO in June 2019 and was repeated in December 2020. Studies were included if they reported biomechanical characteristics of individuals with and without LBP during steady-state or perturbed walking and running. Biomechanical data included spatiotemporal, kinematic, kinetic, and electromyography variables. The reporting quality and potential for bias of each study was assessed. Data were pooled where possible to compare the standardized mean differences (SMD) between back pain and back-healthy control groups.Ninety-seven studies were included and reviewed. Two studies investigated acute pain and the rest investigated persistent pain. Nine studies investigated running gait. Of the studies, 20% had high reporting quality/low risk of bias. In comparison with back-healthy controls, individuals with persistent LBP walked slower (SMD = -0.59, 95% confidence interval (95%CI): -0.77 to -0.42)) and with shorter stride length (SMD = -0.38, 95%CI: -0.60 to -0.16). There were no differences in the amplitude of motion in the thoracic or lumbar spine, pelvis, or hips in individuals with LBP. During walking, coordination of motion between the thorax and the lumbar spine/pelvis was significantly more in-phase in the persistent LBP groups (SMD = -0.60, 95%CI: -0.90 to -0.30), and individuals with persistent LBP exhibited greater amplitude of activation in the paraspinal muscles (SMD = 0.52, 95%CI: 0.23-0.80). There were no consistent differences in running biomechanics between groups.There is moderate-to-strong evidence that individuals with persistent LBP demonstrate differences in walking gait compared to back-healthy controls.

To identify the biomechanical risk factors associated with symptomatic progression at 1-year follow-up in persons with patellofemoral joint (PFJ) osteoarthritis (OA). Patients' self-reported Knee Injury and Osteoarthritis Outcome Score questionnaires, magnetic resonance (MR) imaging, and three-dimensional gait analysis were obtained in 53 subjects with PFJ OA at baseline and after 1 year. Joint OA was diagnosed on knee MR images if cartilage lesions existed. Progression was defined by worsening of patients' self-reported symptoms from baseline to 1 year exceeding the minimal detectable change score. Analysis of covariance was used to compare peak knee flexion moment, knee flexion moment impulse, and vertical ground reaction force loading rate between progressors and non-progressors. Seven (13.2%) subjects exhibited progression in self-reported symptoms at 1-year follow-up. When comparing to non-progressors, significantly higher peak knee flexion moment during first half of stance (p = 0.017) and higher moment impulse during the both halves of stance were observed among progressors (p = 0.020-0.040). Persons with symptomatic PFJ OA progression with or without concurrent tibiofemoral OA exhibited abnormal joint loading mechanics when compared with individuals who did not progress. Further work is needed to determine if modification to these loading variables results in a change in the symptomatic progression in these individuals. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2593-2600, 2019.

PURPOSE High vertical ground reaction force (vGRF) loading rates are thought to contribute to lower extremity injuries in runners. Given that elevated lower extremity stiffness has been reported to be associated with increased GRFs, the purpose of the current study was to determine if overall lower extremity stiffness, individual joint angular excursions and/or torsional stiffness are predictive of the average vGRF loading rate during running. METHODS Forty heel strike runners (20 men and 20 women) ran overground at a speed of 3.4 m·s. Average vGRF loading rate, lower extremity stiffness, and hip, knee, and ankle joint excursions and torsional stiffness from initial contact to the first peak of the vGRF were quantified. Stepwise multiple linear regression was performed to determine the best predictor(s) of average vGRF loading rate. RESULTS Lower extremity stiffness was found to the best predictor of average vGRF loading rate (R = 0.68, P < 0.001). The second variable that entered the stepwise regression model of average vGRF loading rate was knee joint excursion (ΔR = 0.03, P = 0.023). CONCLUSIONS Increased lower extremity stiffness immediately after initial contact may expose heel strike runners to higher vGRF loading rates.

Objectives Previous studies showed that adopting forward trunk lean and forefoot strike patterns may reduce risk of running-related knee injuries. However, the process of learning such forms is unclear. The purpose of the study was to investigate the effects of a 4-week training using simple postural instructions to elicit these changes. Design Longitudinal intervention study. Setting A training included postural instructions: 1) lean your trunk forward, and 2) land on the front part of your feet. Participants Eighteen recreational runners. Main outcome measures Participants were assessed prior to training (PRE), immediately after the instructions (iPST), during training at 2 weeks (2WK) and 4 weeks (4WK), and 7–10 days after the conclusion of training (RET). Assessment consisted of running trials performed at self-selected and controlled speeds, during which the trunk and foot strike angles were assessed. Results Comparing to PRE, forward trunk angle significantly increased by approximately 3.5° and foot strike angle by approximately 7° at 2WK, 4WK and RET. Conclusions A 4-week training with simple postural instructions induced significant changes in trunk and foot strike patterns in recreational runners. Future study is needed to develop clinical therapeutic protocols for runners with and at risk of running-related knee injuries.

Background This study aimed to utilize voxel-based relaxometry (VBR) to examine local correlations between patellofemoral joint (PFJ) stress during gait and PFJ cartilage relaxation times. Methods Eighty-three subjects with and without PFJ osteoarthritis (OA) underwent knee magnetic resonance (MR) images using fast spin-echo, T1ρ and T2 relaxation time sequences. Patellar and trochlear cartilage relaxation times were computed for each voxel. Peak PFJ stress was computed during the stance phase from three-dimensional gait analysis. Statistical Parametric Mapping was used to perform VBR analyses. Pearson partial correlations were used to evaluate the associations between peak PFJ stress and cartilage relaxation times while controlling for age, sex, and body mass index. Results A higher percentage of the trochlear cartilage (15.9–29.1%) showed significant positive correlations between PFJ stress and T1ρ and T2 than the patellar cartilage (7.4–13.6%). Average correlation coefficient (R) of the voxels showing significant positive correlations ranged from 0.27 to 0.29. Subcompartment analysis revealed a higher percentage of lateral compartment cartilage (trochlea: 30.2–34.7%, patella: 8.1–14.8%) showed significant correlations between peak PFJ stress and T1ρ and T2 than the medial compartment cartilage (trochlea: 7.1–27.2%, patella: 5.5–5.9%). Subgroup analysis showed that larger percentages of PFJ cartilage demonstrated significant positive correlations with PFJ stress in subjects with PFJ OA than those without PFJ OA. Conclusions The findings of this study suggest that peak PFJ stress has a greater influence on the biochemical composition of the trochlear than the patellar cartilage, and the lateral than the medial PFJ compartment.

Background: Osteoarthritis of the medial tibiofemoral joint (MTFJ) is prevalent among patients undergoing anterior cruciate ligament reconstruction (ACLR). Magnetic resonance T1ρ and T2 relaxation times provide noninvasive methods to quantify early cartilage degeneration. Altered sagittal-plane gait biomechanics have been observed after ACLR, but their associations with longitudinal changes in MTFJ cartilage T1ρ and T2 remain unclear. Hypothesis/Purpose: To examine whether the peak knee flexion moment (KFM), knee flexion angle (KFA), and vertical ground-reaction force (vGRF) during gait are associated with prospective changes in medial tibiofemoral cartilage T1ρ and T2 in ACL-reconstructed knees and to compare these gait characteristics between patients undergoing ACLR and healthy control participants. We hypothesized that a higher KFM, KFA, and vGRF would be associated with greater increases in cartilage relaxation times and that patients undergoing ACLR would demonstrate altered gait characteristics compared with healthy controls. Study Design: Controlled laboratory study. Methods: Thirty-three patients undergoing ACLR underwent gait analysis before and 6 months and 1 year after ACLR and knee magnetic resonance imaging (MRI) before and 6 months, 1 year, and 2 years after ACLR. Twelve healthy controls underwent knee MRI and gait analysis at baseline and 1 year. Cartilage T1ρ and T2 were calculated for the medial tibia and medial femoral condyle. Linear regressions were used to evaluate associations between gait characteristics and changes in cartilage relaxation times from before ACLR to follow-up time points. Independent t tests were used to compare differences in gait between patients undergoing ACLR and control participants. Results: A higher KFM and KFA before ACLR were related to greater increases in medial femoral condyle T1ρ and T2 at 6 months after ACLR. Similarly, a higher KFM, KFA, and vGRF at 6 months were associated with greater increases in medial tibia and medial femoral condyle T1ρ and T2 at 1 and 2 years after ACLR. Gait characteristics at 1 year were not associated with changes in cartilage relaxation times at 2 years after ACLR. Compared with healthy controls, patients undergoing ACLR demonstrated a lower KFM at 6 months after ACLR. Conclusion/Clinical Relevance: The findings of this study revealed that a higher KFM, KFA, and vGRF during gait, especially at 6 months after ACLR, were associated with greater deterioration of MTFJ cartilage health at later time points.

Background Few studies have investigated the associations between patient-reported outcome and gait in patients with anterior cruciate ligament (ACL) injury and reconstruction over time. Because there is an association between ACL rupture and the presence of osteoarthritis later in life, a better understanding of these relationships will help to elucidate how patients' gait pattern may affect pain and symptoms, potentially leading to better treatment for or preventing the development of knee OA. Objective To evaluate the associations between gait characteristics and self-reported pain and symptoms before, 6 months after, and 1 year after anterior cruciate ligament reconstruction. Design Prospective cohort study. Setting The Human Performance Center at the Orthopedic Institute at the University of California, San Francisco. Patients Patients with full unilateral ACL tears were enrolled. A total of 43 patients were included at 12 months postsurgery. Methods The independent variable in this study comprised specific gait variables in patients who had undergone ACL reconstruction. At each time point, 3-dimensional motion analysis was performed. Participants also completed the Knee Osteoarthritis Outcome Score (KOOS) questionnaire. Main Outcomes Measurements The primary study outcome measurement was the KOOS and was planned before data collection began. Partial correlations were used to examine cross-sectional associations between gait characteristics and KOOS pain and symptom scores at all time points. In addition, partial correlations were performed to examine the associations between change in postoperative KOOS from 6 months to 1 year and gait characteristics at baseline and 6 months. Results Significant associations between KOOS and gait characteristics were found at all time points, including an association between peak medial ground reaction force and pain (r = −0.344, P = .02) and symptoms ( r = −0.407, P = .007) at baseline. Conclusions Specific gait variables may be predictive of greater pain and symptoms and less improvement over time postreconstruction. This could help to inform rehabilitation exercises post injury and pre reconstruction. Level of Evidence IV

Purpose To couple quantitative compositional MRI, gait analysis, and machine learning multidimensional data analysis to study osteoarthritis (OA). OA is a multifactorial disorder accompanied by biochemical and morphological changes in the articular cartilage, modulated by skeletal biomechanics and gait. While we can now acquire detailed information about the knee joint structure and function, we are not yet able to leverage the multifactorial factors for diagnosis and disease management of knee OA. Materials and Methods We mapped 178 subjects in a multidimensional space integrating: demographic, clinical information, gait kinematics and kinetics, cartilage compositional T1ρ and T2 and R2-R1ρ (1/T2–1/T1ρ) acquired at 3T and whole-organ magnetic resonance imaging score morphological grading. Topological data analysis (TDA) and Kolmogorov–Smirnov test were adopted for data integration, analysis, and hypothesis generation. Regression models were used for hypothesis testing. Results The results of the TDA showed a network composed of three main patient subpopulations, thus potentially identifying new phenotypes. T2 and T1ρ values (T2 lateral femur P = 1.45*10-8, T1ρ medial tibia P = 1.05*10-5), the presence of femoral cartilage defects (P = 0.0013), lesions in the meniscus body (P = 0.0035), and race (P = 2.44*10-4) were key markers in the subpopulation classification. Within one of the subpopulations we observed an association between the composite metric R2-R1ρ and the longitudinal progression of cartilage lesions. Conclusion The analysis presented demonstrates some of the complex multitissue biochemical and biomechanical interactions that define joint degeneration and OA using a multidimensional approach, and potentially indicates that R2-R1ρ may be an imaging biomarker for early OA. Level of Evidence: 3 J. Magn. Reson. Imaging 2017.

Summary Objective This study aimed to investigate the associations between patellofemoral cartilage T 1ρ and T 2 relaxation times and knee flexion moment (KFM) and KFM impulse during gait. Method Knee magnetic resonance (MR) images were obtained from 99 subjects with and without patellofemoral joint (PFJ) osteoarthritis (OA), using fast spin-echo, T 1ρ and T 2 relaxation time sequences. Patellar and trochlear cartilage relaxation times were computed for the whole cartilage, and superficial and deep layers (laminar analysis). Subjects also underwent three-dimensional (3D) gait analysis. Peak KFM and KFM impulse were calculated during the stance phase. Linear regressions were used to examine whether cartilage relaxation times were associated with knee kinetics during walking while adjusting age, sex, body mass index (BMI) and walking speed. Results Higher peak KFM and KFM impulse were significantly related to higher T 1ρ and T 2 relaxation times of the trochlear and patellar cartilage, with standardized regression coefficients ranging from 0.21 to 0.28. Laminar analysis showed that overall the superficial layer of patellofemoral cartilage showed stronger associations with knee kinetics. Subgroup analysis revealed that in subjects with PFJ OA, every standard deviation change in knee kinetics was related to greater increases in PFJ cartilage T 1ρ and T 2 (standardized coefficients: 0.29 to 0.41). Conversely, in subjects without OA, weaker relationships were observed between knee kinetics and PFJ cartilage T 1ρ and T 2 . Conclusions Our findings suggest that increased peak KFM and KFM impulse were related to worse cartilage health at the PFJ. This association is more prominent in superficial layer cartilage and cartilage with morphological lesions.

Background Patellofemoral joint osteoarthritis is a highly prevalent disease and an important source of pain and disability. Nonetheless, biomechanical risk factors associated with this disease remain unclear. The purpose of this study was to compare biomechanical factors that are associated with patellofemoral joint loading during walking between individuals with isolated patellofemoral joint osteoarthritis and no osteoarthritis. Methods MR images of the knee were obtained using a 3D fast-spin echo sequence to identify patellofemoral joint cartilage lesions. Thirty-five subjects with isolated patellofemoral joint osteoarthritis (29 females) and 35 control subjects (21 females) walked at a self-selected speed and as fast as possible. Peak knee flexion moment, flexion moment impulse and peak patellofemoral joint stress during the first and second halves of the stance phase were compared between groups. Findings When compared to the controls, individuals with patellofemoral joint osteoarthritis demonstrated significantly higher peak knee flexion moment (P = .03, Eta2 = .07), higher knee flexion moment impulse (P = .03, Eta2 = .07) and higher peak patellofemoral joint stress (P = .01, Eta2 = .10) during the second half of the stance phase. No significant group difference was observed during the first half of the stance phase. Interpretation Findings of this study suggest that increased mechanical loading (i.e. knee flexion moment, impulse and patellofemoral joint stress) during the second half of the stance phase is associated with patellofemoral joint osteoarthritis. Prevention and rehabilitation programs for patellofemoral joint osteoarthritis may focus on reducing the loading on the patellofemoral joint, specifically during late stance.

Osteoarthritis of the medial tibiofemoral joint (MTFJ) is prevalent among patients undergoing anterior cruciate ligament reconstruction (ACLR). Magnetic resonance TControlled laboratory study.Thirty-three patients undergoing ACLR underwent gait analysis before and 6 months and 1 year after ACLR and knee magnetic resonance imaging (MRI) before and 6 months, 1 year, and 2 years after ACLR. Twelve healthy controls underwent knee MRI and gait analysis at baseline and 1 year. Cartilage TA higher KFM and KFA before ACLR were related to greater increases in medial femoral condyle TThe findings of this study revealed that a higher KFM, KFA, and vGRF during gait, especially at 6 months after ACLR, were associated with greater deterioration of MTFJ cartilage health at later time points.

OBJECTIVE: This study aimed to utilize voxel-based relaxometry (VBR) to examine local correlations between patellofemoral joint (PFJ) stress during gait and PFJ cartilage relaxation times. METHODS: Eighty-three subjects with and without PFJ osteoarthritis (OA) underwent knee magnetic resonance (MR) images using fast spin-echo, T(1ρ) and T(2) relaxation time sequences. Patellar and trochlear cartilage relaxation times were computed for each voxel. Subjects also underwent three-dimensional gait analysis. Peak PFJ stress was computed during the stance phase. Statistical Parametric Mapping was used to perform VBR analyses. Pearson partial correlations were used to evaluate the associations between peak PFJ stress and cartilage relaxation times for the whole compartment, medial and lateral compartments, and in subjects with and without PFJ OA. RESULTS: A higher percentage of the trochlear cartilage (15.9–29.1%) showed significant positive correlations between PFJ stress and T(1ρ) and T(2) than the patellar cartilage (7.4–13.6%). Average correlation coefficient (R) of the voxels showing significant positive correlations ranged from 0.27 to 0.29. Subcompartment analysis revealed a higher percentage of lateral compartment PFJ cartilage (trochlea: 30.2–34.7%, patella: 8.1–14.8%) showed significant correlations between peak PFJ stress and T(1ρ) and T(2) than the medial compartment PFJ cartilage (trochlea: 7.1–27.2%, patella: 5.5–5.9%). Subgroup analysis showed that there were larger percentages of PFJ cartilage that demonstrated significant positive correlations with PFJ stress in subjects with PFJ OA than those without PFJ OA. CONCLUSIONS: The Findings of this study suggest that peak PFJ stress has a greater influence on the biochemical composition of the trochlear than patellar cartilage, and the lateral than medial PFJ compartment.

To couple quantitative compositional MRI, gait analysis, and machine learning multidimensional data analysis to study osteoarthritis (OA). OA is a multifactorial disorder accompanied by biochemical and morphological changes in the articular cartilage, modulated by skeletal biomechanics and gait. While we can now acquire detailed information about the knee joint structure and function, we are not yet able to leverage the multifactorial factors for diagnosis and disease management of knee OA.We mapped 178 subjects in a multidimensional space integrating: demographic, clinical information, gait kinematics and kinetics, cartilage compositional TThe results of the TDA showed a network composed of three main patient subpopulations, thus potentially identifying new phenotypes. TThe analysis presented demonstrates some of the complex multitissue biochemical and biomechanical interactions that define joint degeneration and OA using a multidimensional approach, and potentially indicates that R3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:78-90.

Background Patellar malalignment is thought to be an etiological factor with respect to the development of patellofemoral pain. Although previous studies have suggested that the geometry of the femoral trochlea and the height of the patella play an important role in determining patellar alignment, no investigation has systematically examined these relationships during weight bearing. The aim of this study was to determine whether patellar height and/or trochlear geometry predicts patellar alignment (lateral patellar displacement and lateral patellar tilt) during weight bearing. Methods MR images of the patellofemoral joint were acquired from 36 participants during weight bearing (25% of body weight) at 4 knee flexion angles (0°, 20°, 40° and 60°). Using the axial images, patellar alignment (lateral displacement and tilt) and femoral trochlear geometry (sulcus angle and inclination of the lateral femoral trochlea) were measured. Patellar height (Insall–Salvati ratio) was measured on reconstructed sagittal plane images. Results Stepwise regression analysis revealed that at 0° of knee flexion, the height of the patella was the best predictor of lateral patellar tilt while the lateral trochlea inclination angle was the best predictor of lateral patellar displacement. Lateral trochlear inclination was the best predictor of patellar lateral displacement and tilt at 20°, 40° and 60° of knee flexion. Conclusion Similar to a previous study performed under non-weight bearing condition, our findings suggest that lateral trochlear inclination is an important determinant of patellar alignment in weight bearing. Level of Evidence Level III

In this chapter we review magnetic resonance imaging (MRI) techniques for the assessment of cartilage morphology and cartilage biochemistry in vivo in human subjects. Methods for lesion identification, volume and thickness changes, and biochemical changes associated with cartilage degeneration and injury are discussed. The advances and challenges in MRI in this realm are vast, and a concise summary is presented.

Context: Diminished hip-muscle performance has been proposed to contribute to various knee injuries. Objective: To determine the association between hip-extensor muscle strength and sagittal-plane trunk posture and the relationships among hip-extensor muscle strength and hip- and knee-extensor work during running. Design: Descriptive laboratory study. Setting: Musculoskeletal biomechanical laboratory. Patients or Other Participants: A total of 40 asymptomatic recreational runners, 20 men (age = 27.1 ± 7.0 years, height = 1.74 ± 0.69 m, mass = 71.1 ± 8.2 kg) and 20 women (age = 26.2 ± 5.8 years, height = 1.65 ± 0.74 m, mass = 60.6 ± 6.6 kg), participated. Main Outcome Measure(s): Maximum isometric strength of the hip extensors was assessed using a dynamometer. Sagittal-plane trunk posture (calculated relative to the global vertical axis) and hip- and knee-extensor work (sum of energy absorption and generation) during the stance phase of running were quantified while participants ran over ground at a controlled speed of 3.4 m/s. We used Pearson product moment correlations to examine the relationships among hip-extensor strength, mean sagittal-plane trunk-flexion angle, hip-extensor work, and knee-extensor work. Results: Hip-extensor strength was correlated positively with trunk-flexion angle (r = 0.55, P < .001) and hip-extensor work (r = 0.46, P = .003). It was correlated inversely with knee-extensor work (r = −0.39, P = .01). All the correlations remained after adjusting for sex. Conclusions: Our findings suggest that runners with hip-extensor weakness used a more upright trunk posture. This strategy led to an overreliance on the knee extensors and may contribute to overuse running injuries at the knee.

Summary Objective To determine if cartilage T1ρ and T2 relaxation time measures after ACL injury and prior to reconstruction (baseline) are associated with patient-reported outcomes at baseline, 6-months, and 1-year after surgery. Design Fifty-four ACL-injured participants were scanned in both knees at baseline using 3T MR T1ρ and T2 mapping. Participants also completed Knee-injury and Osteoarthritis Outcome Score (KOOS) and Marx activity level questionnaires at baseline, 6-months, and 1-year after reconstruction. The difference between cartilage T1ρ or T2 of the injured and contralateral knee (side-to-side difference, SSD) was calculated to account for physiological variations among patients. Linear regression models were built to evaluate the association between the baseline SSD T1ρ or T2 and KOOS or Marx at all time points. Results Higher baseline SSD T1ρ posterolateral tibia (pLT) was associated with worse KOOS in all subscales except symptoms at baseline, worse KOOS pain at 6-months, and worse KOOS in all subscales except sports function at 1-year. Higher baseline SSD T2 femoral trochlea (TrF) was associated with worse KOOS activities of daily living (ADL) at 1-year. Higher baseline SSD T1ρ pLT was associated with lower Marx activity level at 1-year. More severe cartilage lesions, as assessed by Whole-Organ MRI Scoring (WORMS), was significantly associated with worse KOOS pain at 6-months and 1-year. Conclusion T1ρ and T2 of cartilage after ACL injury were associated with KOOS after injury and both KOOS and Marx after reconstruction. Such associations may help clinicians stratify outcomes post-injury, and thus, improve patient management.

Study designControlled laboratory study, longitudinal design.ObjectiveTo examine whether baseline knee flexion moment or impulse during walking is associated with the progression of osteoarthritis (OA) with magnetic resonance imaging of the patellofemoral joint (PFJ) at 1 year.BackgroundPatellofemoral joint OA is highly prevalent and a major source of pain and dysfunction. The biomechanical factors associated with the progression of PFJ OA remain unclear.MethodsThree-dimensional gait analyses were performed at baseline. Magnetic resonance imaging of the knee (high-resolution, 3-D, fast spin-echo sequence) was used to identify PFJ cartilage and bone marrow edema-like lesions at baseline and a 1-year follow-up. The severity of PFJ OA progression was defined using the modified Whole-Organ Magnetic Resonance Imaging Score when new or increased cartilage or bone marrow edema-like lesions were observed at 1 year. Peak external knee flexion moment and flexion moment impulse during the first and second halves of the stance phase of gait were compared between progressors and nonprogressors, and used to predict progression after adjusting for age, sex, body mass index, and presence of baseline PFJ OA.ResultsSixty-one participants with no knee OA or isolated PFJ OA were included. Patellofemoral joint OA progressors (n = 10) demonstrated significantly higher peak knee flexion moment (P = .01) and flexion moment impulse (P = .04) during the second half of stance at baseline compared to nonprogressors. Logistic regression showed that higher peak knee flexion moment during the second half of the stance phase was significantly associated with progression at 1 year (adjusted odds ratio = 3.3, P = .01).ConclusionPeak knee flexion moment and flexion moment impulse during the second half of stance are related to the progression of PFJ OA and may need to be considered when treating individuals who are at risk of or who have PFJ OA.

Background Patients with acetabular cartilage defects reported increased pain and disability compared to those without acetabular cartilage defects. The specific effects of acetabular cartilage defects on lower extremity coordination patterns are unclear. The purpose of this study was to determine hip and knee joint coordination variability during gait in those with and without acetabular cartilage defects. Methods A combined approach, consisting of a semi-quantitative MRI-based quantification method and vector coding, was used to assess hip and knee joint coordination variability during gait in those with and without acetabular cartilage lesions. Findings The coordination variability of the hip flexion–extension/knee rotation, hip abduction–adduction/knee rotation, and hip rotation/knee rotation joint couplings were reduced in the acetabular lesion group compared to the control group during loading response of the gait cycle. The lesion group demonstrated increased variability in the hip flexion–extension/knee rotation and hip abduction–adduction/knee rotation joint couplings, compared to the control group, during the terminal stance/pre-swing phase of gait. Interpretation Reduced variability during loading response in the lesion group may suggest reduced movement strategies and a possible compensation mechanism for lower extremity instability during this phase of the gait cycle. During terminal stance/pre-swing, a larger variability in the lesion group may suggest increased movement strategies and represent a compensation or pain avoidance mechanism caused by the load applied to the hip joint.

TENG, H., and C. M. POWERS. Influence of Trunk Posture on Lower Extremity Energetics during Running. Med. Sci. Sports Exerc., Vol. 47, No. 3, pp. 625–630, 2015. Purpose: This study aimed to examine the influence of sagittal plane trunk posture on lower extremity energetics during running. Methods: Forty asymptomatic recreational runners (20 males and 20 females) ran overground at a speed of 3.4 mIs j1 . Sagittal plane trunk kinematics and lower extremity kinematics and energetics during the stance phase of running were computed. Subjects were dichotomized into high flexion (HF) and low flexion (LF) groups on the basis of the mean trunk flexion angle. Results: The mean (TSD) trunk flexion angles of the HF and LF groups were 10.8 -T 2.2- and 3.6 -T 2.8-, respectively. When compared with the LF group, the HF group demonstrated significantly higher hip extensor energy generation (0.12 T 0.06 vs 0.05 T 0.04 JIkg j1 , P G 0.001) and lower knee extensor energy absorption (0.60 T 0.14 vs 0.74 T 0.09 JIkg j1 , P = 0.001) and generation (0.30 T 0.05 vs 0.34 T 0.06 JIkg j1 , P = 0.02). There was no significant group difference for the ankle plantarflexor energy absorption or generation (P 9 0.05). Conclusions: Sagittal plane trunk flexion has a significant influence on hip and knee energetics during running. Increasing forward trunk lean during running may be used as a strategy to reduce knee loading without increasing the biomechanical