Lower Limb Joint Mechanics during Maximal Accelerative and Decelerative Running.

INTRODUCTION: Maximal acceleration and deceleration tasks are frequently required in team sports, often occurring rapidly in response to external stimuli. Accelerating and decelerating can be associated with lower limb injuries, thus knowledge of joint mechanics during these tasks can improve the understanding of both human high performance and injury mechanisms. The current study investigated the fundamental differences in lower limb joint mechanics when accelerating and decelerating by directly comparing the hip, knee and ankle joint moments and work done between the two tasks. METHODS: Twenty participants performed maximal effort acceleration and deceleration trials, with three-dimensional marker trajectories and ground reaction forces collected simultaneously. Experimental data was combined with inverse dynamics analysis to compute joint moments and work. RESULTS: Net joint work for all lower limb joints was positive during acceleration, and negative during deceleration. This occurred due to significantly greater positive work production from the ankle and hip during acceleration, and significantly greater negative work production from all joints during deceleration. The largest contributions to positive work during acceleration came from the ankle, followed by the hip and knee joints; whilst the largest contributions to negative work during deceleration came from the knee and hip joints, followed by the ankle. Peak joint moments were significantly greater when decelerating compared to accelerating, except for the peak ankle plantarflexion and hip flexion moments which were significantly greater when accelerating. CONCLUSIONS: Our findings may help to guide training interventions which aim to enhance the performance of acceleration and deceleration tasks, whilst also mitigating the associated injury risk.

Epidemiology of quadriceps muscle strain injuries in elite male Australian football players.

OBJECTIVE: To describe the epidemiology of quadriceps muscle strain injury (QMSI) in elite Australian Football League (AFL) players, explore recovery milestones and determine whether recovery is impacted by factors such as injury type (index vs. re-injury), the primary muscle injured and the mechanism of injury. MEASURES: All QMSI data reported to the Soft Tissue Injury Registry of the AFL from the 2014 to 2020 seasons were evaluated. Player demographic data, circumstances of injury, MRI reports and recovery outcomes following injury were extracted. Descriptive statistics and frequency distributions are presented. Recovery outcomes for injury type, primary muscle injured and the mechanism of injury were compared using univariate analyses. RESULTS: There were 164 QMSIs from 122 players reported (134 index; 30 re-injuries). Almost all (91.3%) QMSIs involved the rectus femoris. Half (48.4%) of the QMSIs occurred during kicking and most commonly affected the dominant kicking leg (72%). The majority occurred at training (64.6%). All re-injuries involved the rectus femoris, most occurred from kicking (63.0%) and within 6 months of the preceding injury (70%). The mean return to play (RTP) time was 25.4 days (95%CI = 22.6-28.2) and rectus femoris injuries took around 14 days longer to RTP than vastii injuries (p = 0.001). QMSIs with a kicking mechanism took the longest to RTP of all injury mechanisms. CONCLUSION: In AFL players, QMSIs occur mostly in the dominant leg from a kicking mechanism. Rectus femoris injuries are more prevalent and result in longer RTP time frames. Re-injuries exclusively involved the rectus femoris, primarily from kicking.

Is quadriceps strength associated with patellofemoral joint loading after anterior cruciate ligament reconstruction?

OBJECTIVE: To test whether quadriceps strength is associated with measures of patellofemoral (PF) joint loading during running and hopping in people after an anterior cruciate ligament reconstruction (ACLR). DESIGN: Cross-sectional study. SETTING: Biomechanics laboratory. PARTICIPANTS: Sixty-five participants (24 women; 41 men) 1-2 years post-ACLR. MAIN OUTCOME MEASURES: Peak isometric quadriceps strength for the surgical limb was measured using a dynamometer. Motion analysis and ground reaction force data were combined with musculoskeletal modelling to measure PF joint loading variables for the reconstructed knee (peak knee flexion angle; peak/impulse of the PF joint contact force; time to peak PF joint contact force) during the stance phase of running and during the landing phase of a standardised forward hop. Linear regression analysis (adjusting for age and sex) assessed the association between quadriceps strength and PF joint loading variables. RESULTS: Two significant, albeit modest, associations were revealed. Quadriceps strength was associated with the time to peak PF joint contact force during running (ß = -0.001; 95%CI -0.002 to -0.000; R2 = 0.179) and the impulse of the PF joint contact force during hopping (ß = 0.014; 95%CI 0.003 to 0.024; R2 = 0.159). CONCLUSIONS: A strong link between quadriceps strength and PF joint loading was not evident in people 1-2 years post-ACLR.

Are hip biomechanics during running associated with symptom severity or cam morphology size in male football players with FAI syndrome?

BACKGROUND: Femoroacetabular impingement (FAI) syndrome is considered a motion-related condition. Little is known about the influence of symptom severity and cam morphology on hip biomechanics for individuals with FAI syndrome. RESEARCH QUESTION: Are hip biomechanics during running associated with symptom severity or cam morphology size in male football players with FAI syndrome? METHODS: Forty-nine male, sub-elite football (soccer or Australian football) players (mean age= 26 years) with FAI syndrome completed the International Hip Outcome Tool-33 (iHOT-33) and Copenhagen Hip and Groin Outcome Score (HAGOS) and underwent radiographic evaluation. Biomechanical data were collected during overground running (3-3.5 m∙s-1) using three-dimensional motion capture technology and an embedded force plate. Various discrete hip angles and impulses of joint moments were analysed during the stance phase. Linear regression models investigated associations between running biomechanics data (dependent variables) and iHOT-33 and HAGOS scores and cam morphology size (independent variables). RESULTS: Hip joint angles during running were not associated with symptom severity in football players with FAI syndrome. A positive association was found between the impulse of the hip external rotation moment and HAGOS-Sport scores, such that a smaller impulse magnitude occurred with a lower HAGOS-Sport score (0.026 *10-2 [95%CI <0.001 *10-2 to 0.051 *10-2], P = 0.048). Larger cam morphology was associated with a greater peak hip adduction angle at midstance (0.073 [95%CI 0.002-0.145], P = 0.045). SIGNIFICANCE: Hip biomechanics during running did not display strong associations with symptom severity or cam morphology size in male football players with FAI syndrome who were still participating in training and match play. Future studies might consider investigating associations during tasks that utilise end range hip joint motion or require greater muscle forces.

Patellofemoral joint loading and early osteoarthritis after ACL reconstruction.

Patellofemoral joint (PFJ) osteoarthritis is common following anterior cruciate ligament reconstruction (ACLR) and may be linked with altered joint loading. However, little is known about the cross-sectional and longitudinal relationship between PFJ loading and osteoarthritis post-ACLR. This study tested if altered PFJ loading is associated with prevalent and worsening early PFJ osteoarthritis post-ACLR. Forty-six participants (mean ± 1 SD age 26 ± 5 years) approximately 1-year post-ACLR underwent magnetic resonance imaging (MRI) and biomechanical assessment of their reconstructed knee. Trunk and lower-limb kinematics plus ground reaction forces were recorded during the landing phase of a standardized forward hop. These data were input into a musculoskeletal model to calculate the PFJ contact force. Follow-up MRI was completed on 32 participants at 5-years post-ACLR. Generalized linear models (Poisson regression) assessed the relationship between PFJ loading and prevalent early PFJ osteoarthritis (i.e., presence of a PFJ cartilage lesion at 1-year post-ACLR) and worsening PFJ osteoarthritis (i.e., incident/progressive PFJ cartilage lesion between 1- and 5-years post-ACLR). A lower peak PFJ contact force was associated with prevalent early PFJ osteoarthritis at 1-year post-ACLR (n = 14 [30.4%]; prevalence ratio: 1.37; 95% confidence interval [CI]: 1.02-1.85) and a higher risk of worsening PFJ osteoarthritis between 1- and 5-years post-ACLR (n = 9 [28.1%]; risk ratio: 1.55, 95% CI: 1.13-2.11). Young adults post-ACLR who exhibited lower PFJ loading during hopping were more likely to have early PFJ osteoarthritis at 1-year and worsening PFJ osteoarthritis between 1- and 5-years. Clinical interventions aimed at mitigating osteoarthritis progression may be beneficial for those with signs of lower PFJ loading post-ACLR.

Trajectory of knee health in runners with and without heightened osteoarthritis risk: the TRAIL prospective cohort study protocol.

INTRODUCTION: Running is one of the most popular recreational activities worldwide, due to its low cost and accessibility. However, little is known about the impact of running on knee joint health in runners with and without a history of knee surgery. The primary aim of this longitudinal cohort study is to compare knee joint structural features on MRI and knee symptoms at baseline and 4-year follow-up in runners with and without a history of knee surgery. Secondary aims are to explore the relationships between training load exposures (volume and/or intensity) and changes in knee joint structure and symptoms over 4 years; explore the relationship between baseline running biomechanics, and changes in knee joint structure and symptoms over 4 years. In addition, we will explore whether additional variables confound, modify or mediate these associations, including sex, baseline lower-limb functional performance, knee muscle strength, psychological and sociodemographic factors. METHODS AND ANALYSIS: A convenience sample of at least 200 runners (sex/gender balanced) with (n=100) and without (n=100) a history of knee surgery will be recruited. Primary outcomes will be knee joint health (MRI) and knee symptoms (baseline; 4 years). Exposure variables for secondary outcomes include training load exposure, obtained daily throughout the study from wearable devices and three-dimensional running biomechanics (baseline). Additional variables include lower limb functional performance, knee extensor and flexor muscle strength, biomarkers, psychological and sociodemographic factors (baseline). Knowledge and beliefs about osteoarthritis will be obtained through predefined questions and semi-structured interviews with a subset of participants. Multivariable logistic and linear regression models, adjusting for potential confounding factors, will explore changes in knee joint structural features and symptoms, and the influence of potential modifiers and mediators. ETHICS AND DISSEMINATION: Approved by the La Trobe University Ethics Committee (HEC-19524). Findings will be disseminated to stakeholders, peer-review journals and conferences.

Muscle function during single leg landing.

Landing manoeuvres are an integral task for humans, especially in the context of sporting activities. Such tasks often involve landing on one leg which requires the coordination of multiple muscles in order to effectively dissipate kinetic energy. However, no prior studies have provided a detailed description of the strategy used by the major lower limb muscles to perform single-leg landing. The purpose of the present study was to understand how humans coordinate their lower limb muscles during a single-leg landing task. Marker trajectories, ground reaction forces (GRFs), and surface electromyography (EMG) data were collected from healthy male participants performing a single-leg landing from a height of 0.31 m. An EMG-informed neuromusculoskeletal modelling approach was used to generate neuromechanical simulations of the single-leg landing task. The muscular strategy was determined by computing the magnitude and temporal characteristics of musculotendon forces and energetics. Muscle function was determined by computing muscle contributions to lower limb net joint moments, GRFs and lower limb joint contact forces. It was found that the vasti, soleus, gluteus maximus and gluteus medius produced the greatest muscle forces and negative (eccentric) mechanical work. Downward momentum of the centre-of-mass was resisted primarily by the soleus, vasti, gastrocnemius, rectus femoris, and gluteus maximus, whilst forward momentum was primarily resisted by the quadriceps (vasti and rectus femoris). Flexion of the lower limb joints was primarily resisted by the uni-articular gluteus maximus (hip), vasti (knee) and soleus (ankle). Overall, our findings provide a unique insight into the muscular strategy used by humans during a landing manoeuvre and have implications for the design of athletic training programs.

The Assessment, Management and Prevention of Calf Muscle Strain Injuries: A Qualitative Study of the Practices and Perspectives of 20 Expert Sports Clinicians.

BACKGROUND: Despite calf muscle strain injuries (CMSI) being problematic in many sports, there is a dearth of research to guide clinicians dealing with these injuries. The aim of this study was to evaluate the current practices and perspectives of a select group of international experts regarding the assessment, management and prevention of CMSI using in-depth semi-structured interviews. RESULTS: Twenty expert clinicians working in elite sport and/or clinician-researchers specialising in the field completed interviews. A number of key points emerged from the interviews. Characteristics of CMSI were considered unique compared to other muscle strains. Rigor in the clinical approach clarifies the diagnosis, whereas ongoing monitoring of calf capacity and responses to loading exposure provides the most accurate estimate of prognosis. Athlete intrinsic characteristics, injury factors and sport demands shaped rehabilitation across six management phases, which were guided by key principles to optimise performance at return to play (RTP) while avoiding subsequent injury or recurrence. To prevent CMSI, periodic monitoring is common, but practices vary and data are collected to inform load-management and exercise selection rather than predict future CMSI. A universal injury prevention program for CMSI may not exist. Instead, individualised strategies should reflect athlete intrinsic characteristics and sport demands. CONCLUSIONS: Information provided by experts enabled a recommended approach to clinically evaluate CMSI to be outlined, highlighting the injury characteristics considered most important for diagnosis and prognosis. Principles for optimal management after CMSI were also identified, which involved a systematic approach to rehabilitation and the RTP decision. Although CMSI were reportedly difficult to prevent, on- and off-field strategies were implemented by experts to mitigate risk, particularly in susceptible athletes.

Patellofemoral and tibiofemoral joint loading during a single-leg forward hop following ACL reconstruction.

Altered biomechanics are frequently observed following anterior cruciate ligament reconstruction (ACLR). Yet, little is known about knee-joint loading, particularly in the patellofemoral-joint, despite patellofemoral-joint osteoarthritis commonly occurring post-ACLR. This study compared knee-joint reaction forces and impulses during the landing phase of a single-leg forward hop in the reconstructed knee of people 12-24 months post-ACLR and uninjured controls. Experimental marker data and ground forces for 66 participants with ACLR (28 ± 6 years, 78 ± 15 kg) and 33 uninjured controls (26 ± 5 years, 70 ± 12 kg) were input into scaled-generic musculoskeletal models to calculate joint angles, joint moments, muscle forces, and the knee-joint reaction forces and impulses. The ACLR group exhibited a lower peak knee flexion angle (mean difference: -6°; 95% confidence interval: [-10°, -2°]), internal knee extension moment (-3.63 [-5.29, -1.97] percentage of body weight × participant height (body weight [BW] × HT), external knee adduction moment (-1.36 [-2.16, -0.56]% BW × HT) and quadriceps force (-2.02 [-2.95, -1.09] BW). The ACLR group also exhibited a lower peak patellofemoral-joint compressive force (-2.24 [-3.31, -1.18] BW), net tibiofemoral-joint compressive force (-0.74 [-1.20, 0.28] BW), and medial compartment force (-0.76 [-1.08, -0.44] BW). Finally, only the impulse of the patellofemoral-joint compressive force was lower in the ACLR group (-0.13 [-0.23, -0.03] body weight-seconds). Lower compressive forces are evident in the patellofemoral- and tibiofemoral-joints of ACLR knees compared to uninjured controls during a single-leg forward hop-landing task. Our findings may have implications for understanding the contributing factors for incidence and progression of knee osteoarthritis after ACLR surgery.

A Delphi survey and international e-survey evaluating the Doha agreement meeting classification system in groin pain: Where are we 5 years later?

OBJECTIVES: To evaluate the adoption of and opinions on the Doha agreement meeting classification in groin pain in athletes. DESIGN: Delphi survey and e-survey. METHODS: A 2-round Delphi survey among the Doha agreement meeting expert group, and a separate international e-survey among clinicians who regularly assess athletes with groin pain. Clinical cases were presented, and participants provided their preferred terms for the diagnoses. All participants reported if they had adopted the Doha agreement meeting classification system in their practice. The Doha agreement meeting experts also shared opinions on amendments to the classification system, and reported their level of agreement with suggested statements. RESULTS: In the Delphi survey, the Doha agreement meeting experts (n = 21) reported 8-11 different terms for their primary diagnosis of each presented case. The Doha agreement meeting terminology was used by 50-67% of these experts. In the international e-survey (n = 51), 12-15 different diagnostic terms were reported in each clinical case, and 43-55% of clinicians used the Doha agreement meeting terminology. Adoption of the Doha agreement classification system in practice was reported by 73-82% of the Doha agreement meeting experts and 57-69% of the clinicians in the international e-survey. The experts suggested 49 statements regarding amendments to the classification system. Seven of these reached >75% agreement or disagreement. CONCLUSIONS: Five years after publication, the majority of the Doha agreement expert group and independent international clinicians report adopting the Doha agreement meeting classification system. There is still considerable heterogeneity in diagnostic terminology when clinical cases are presented, and disagreement on statements related to amendments of the current classification system.

Running biomechanics in football players with and without hip and groin pain. A cross-sectional analysis of 116 sub-elite players.

OBJECTIVE: Examine whether football players with hip and/or groin (hip/groin) pain have impaired running biomechanics when compared to pain-free players, analysing men and women independently. DESIGN: Cross-sectional. SETTING: Biomechanics laboratory. PARTICIPANTS: Seventy-eight (62 men, 16 women) football players with >6months of hip/groin pain and a positive flexion-adduction-internal rotation test and 38 (25 men, 13 women) asymptomatic players. MAIN OUTCOME MEASURES: Pelvis angles and hip, knee, and ankle joint angles and moments were analysed during the stance phase of overground running at 3-3.5 m⋅s-1. Continuous joint angle and moment data were compared between symptomatic and asymptomatic football players of the same sex using statistical parametric mapping. Joint moment impulses (area under the curve) were compared between groups using linear regression models. RESULTS: Symptomatic football players did not display significant differences in pelvis angles or lower-limb joint angles, moments, or moment impulses during the stance phase of running, when compared to asymptomatic players of the same sex. CONCLUSION: Our large sample of football players with hip/groin pain who were still participating in competitive sport displayed similar running biomechanics to asymptomatic players. Impaired running biomechanics might exist in people with worse hip/groin pain, warranting future investigation.

Sprinting Biomechanics and Hamstring Injuries: Is There a Link? A Literature Review.

Hamstring strain injury (HSI) is a common and costly injury in many sports such as the various professional football codes. Most HSIs have been reported to occur during high intensity sprinting actions. This observation has led to the suggestion that a link between sprinting biomechanics and HSIs may exist. The aim of this literature review was to evaluate the available scientific evidence underpinning the potential link between sprinting biomechanics and HSIs. A structured search of the literature was completed followed by a risk of bias assessment. A total of eighteen studies were retrieved. Sixteen studies involved retrospective and/or prospective analyses, of which only three were judged to have a low risk of bias. Two other case studies captured data before and after an acute HSI. A range of biomechanical variables have been measured, including ground reaction forces, trunk and lower-limb joint angles, hip and knee joint moments and powers, hamstring muscle-tendon unit stretch, and surface electromyographic activity from various trunk and thigh muscles. Overall, current evidence was unable to provide a clear and nonconflicting perspective on the potential link between sprinting biomechanics and HSIs. Nevertheless, some interesting findings were revealed, which hopefully will stimulate future research on this topic.

How muscles maximize performance in accelerated sprinting.

We sought to provide a more comprehensive understanding of how the individual leg muscles act synergistically to generate a ground force impulse and maximize the change in forward momentum of the body during accelerated sprinting. We combined musculoskeletal modelling with gait data to simulate the majority of the acceleration phase (19 foot contacts) of a maximal sprint over ground. Individual muscle contributions to the ground force impulse were found by evaluating each muscle's contribution to the vertical and fore-aft components of the ground force (termed "supporter" and "accelerator/brake," respectively). The ankle plantarflexors played a major role in achieving maximal-effort accelerated sprinting. Soleus acted primarily as a supporter by generating a large fraction of the upward impulse at each step whereas gastrocnemius contributed appreciably to the propulsive and upward impulses and functioned as both accelerator and supporter. The primary role of the vasti was to deliver an upward impulse to the body (supporter), but these muscles also acted as a brake by retarding forward momentum. The hamstrings and gluteus medius functioned primarily as accelerators. Gluteus maximus was neither an accelerator nor supporter as it functioned mainly to decelerate the swinging leg in preparation for foot contact at the next step. Fundamental knowledge of lower-limb muscle function during maximum acceleration sprinting is of interest to coaches endeavoring to optimize sprint performance in elite athletes as well as sports medicine clinicians aiming to improve injury prevention and rehabilitation practices.

Physiotherapist-led treatment for femoroacetabular impingement syndrome (the PhysioFIRST study): a protocol for a participant and assessor-blinded randomised controlled trial.

INTRODUCTION: This double-blind, randomised controlled trial (RCT) aims to estimate the effect of a physiotherapist-led intervention with targeted strengthening compared with a physiotherapist-led intervention with standardised stretching, on hip-related quality of life (QOL) or perceived improvement at 6 months in people with femoroacetabular impingement (FAI) syndrome. We hypothesise that at 6 months, targeted strengthening physiotherapist-led treatment will be associated with greater improvements in hip-related QOL or greater patient-perceived global improvement when compared with standardised stretching physiotherapist-led treatment. METHODS AND ANALYSIS: We will recruit 164 participants with FAI syndrome who will be randomised into one of the two intervention groups, both receiving one-on-one treatment with the physiotherapist over 6 months. The targeted strengthening physiotherapist-led treatment group will receive a personalised exercise therapy and education programme. The standardised stretching physiotherapist-led treatment group will receive standardised stretching and personalised education programme. Primary outcomes are change in hip-related QOL using International Hip Outcome Tool-33 and patient-perceived global improvement. Secondary outcomes include cost-effectiveness, muscle strength, range of motion, functional task performance, biomechanics, hip cartilage structure and physical activity levels. Statistical analyses will make comparisons between both treatment groups by intention to treat, with all randomised participants included in analyses, regardless of protocol adherence. Linear mixed models (with baseline value as a covariate and treatment condition as a fixed factor) will be used to evaluate the treatment effect and 95% CI at primary end-point (6 months). ETHICS AND DISSEMINATION: The study protocol was approved (La Trobe University Human Ethics Committee (HEC17-080)) and prospectively registered with the Australian New Zealand Clinical Trials Registry. The findings of this RCT will be disseminated through peer reviewed scientific journals and conferences. Patients were involved in study development and will receive a short summary following the completion of the RCT. TRIAL REGISTRATION NUMBER: ACTRN12617001350314.

Lower-limb work during high- and low-impact activities in hip-related pain: Associations with sex and symptom severity.

BACKGROUND: Hip-related pain (HRP) is described as a movement-related disorder. However, little attention is given to the way people with HRP move, especially in populations still participating in sport. Thus, limiting our understanding of movementbased impairments in HRP and their potential relationships with pain/symptoms. RESEARCH QUESTION: (1) What are the differences in absolute and relative amounts of positive and negative lower-limb joint work during walking and the single-leg drop jump (SLDJ) in football players with and without HRP? (2) What are the relationships between lower-limb joint work and HRP burden? METHODS: 88 football players with HRP and 30 control football players were recruited. Positive and negative work done by the hip, knee, and ankle (and each joint's relative contribution to total work done) were calculated. The effect of sex on the relationship between HRP and work done, as well as the association between work done and International Hip Outcome Tool (iHOT33) scores, were assessed using linear and beta regressions models. RESULTS: Walking: No joint work variables were significantly different between groups, nor were any relationships with iHOT33 scores evident. SLDJ: The knee's relative contribution to total lower-limb negative work done was 37.7 % and 42.4 % for women with and without HRP, respectively (P = 0.04). The iHOT33 was significantly associated with positive (P = 0.03 to <0.01) and negative (P = 0.02 to <0.01) work done by the hip as well as negative work done by the ankle (P = 0.03 to 0.01), independent of sex. SIGNIFICANCE: Only one significant between-group comparison was revealed, involving the knee in female football players. In addition, football players with a greater selfreported burden of HRP tended to display lower hip joint work during the SLDJ. Rehabilitation programs could be targeted to address these impairments and normalize work done during high impact tasks in the management of HRP.

Return to Play and Recurrence After Calf Muscle Strain Injuries in Elite Australian Football Players.

BACKGROUND: Calf muscle strain injuries (CMSI) are prevalent in sport, but information about factors associated with time to return to play (RTP) and recurrence is limited. PURPOSE: To determine whether clinical and magnetic resonance imaging (MRI) data are associated with RTP and recurrence after CMSI. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Data of 149 CMSI reported to the Soft Tissue injury Registry of the Australian Football League were explored to evaluate the impact of clinical data and index injury MRI findings on RTP and recurrence. Clinical data included age, previous injury history, ethnicity, and the mechanism of injury. RESULTS: Irrespective of the anatomical location, players with CMSI with severe aponeurotic disruption (AD) took longer to RTP than players with CMSI with no AD: 31.3 ± 12.6 days vs 19.4 ± 10.8 days (mean ± SD; P = .003). A running-related mechanism of injury was associated with a longer RTP period for CMSI overall (adjusted hazard ratio [AHR], 0.59; P = .02). The presence of AD was associated with a longer RTP period for soleus injuries (AHR, 0.6; P = .025). Early recurrence (ie, ≤2 months of the index injury) was associated with older age (AHR, 1.3; P = .001) and a history of ankle injury (AHR, 3.9; P = .032). Older age (AHR, 1.1; P = .013) and a history of CMSI (AHR, 6.7; P = .002) increased the risk of recurrence within 2 seasons. The index injury MRI findings were not associated with risk of recurrence. CONCLUSION: A running-related mechanism of injury and the presence of AD on MRI were associated with a longer RTP period. Clinical rather than MRI data best indicate the risk of recurrent CMSI.

Between-Limb Differences in Patellofemoral Joint Forces During Running at 12 to 24 Months After Unilateral Anterior Cruciate Ligament Reconstruction.

BACKGROUND: Patellofemoral joint (PFJ) osteoarthritis may occur after anterior cruciate ligament reconstruction (ACLR). The mechanisms underpinning the development of PFJ osteoarthritis are not known but may relate to altered PFJ loading. Few studies have assessed PFJ loads during high-impact tasks, such as running, beyond the acute rehabilitation phase (ie, >12 months) after ACLR. PURPOSE/HYPOTHESIS: The purpose was to compare between-limb joint angles, joint moments, and PFJ contact force during running in individuals at 12 to 24 months after unilateral ACLR. We hypothesized that peak knee flexion angle, knee extension moment, and PFJ contact force during stance would be lower in the ACLR limb compared with the uninjured limb. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 55 participants (mean ± SD age, 28 ± 7 years), 12 to 24 months after ACLR, ran at a self-selected speed (2.9 ± 0.3 m/s). Measured kinematics and ground-reaction forces were input into musculoskeletal models to calculate joint moments and muscle forces. These values were subsequently input into a PFJ model to calculate contact force peak and impulse. Outcome measures were compared between the ACLR and uninjured limbs. RESULTS: In the ACLR limb, compared with the uninjured limb, the PFJ contact force displayed a lower peak (ACLR, 6.1 ± 1.3 body weight [BW]; uninjured, 6.7 ± 1.4 BW; P < .001) and impulse (ACLR, 0.72 ± 0.17 BW*seconds [BWs]; uninjured, 0.81 ± 0.17 BWs; P < .001). At the time of the peak PFJ contact force, the knee extension moment was lower in the ACLR limb (ACLR, 14.0 ± 2.4 %BW*height [%BW*HT]; uninjured, 15.5 ± 2.5 %BW*HT; P < .001). The opposite was true for the ankle plantarflexion moment (ACLR, 12.1 ± 2.6 %BW*HT; uninjured, 11.5 ± 2.7 %BW*HT; P = .019) and the hip extension moment (ACLR, 2.3 ± 2.5 %BW*HT; uninjured, 1.6 ± 2.3 %BW*HT; P = .013). The foot-ground center of pressure was located more anteriorly with respect to the ankle joint center (ACLR, 5.8 ± 0.9 %height [%HT]; uninjured, 5.4 ± 1.0 %HT; P = .001). No differences were found for the sagittal plane hip, knee, and ankle angles. CONCLUSION: The ACLR limb experienced lower peak PFJ loads during running, explained by a small anterior shift in the foot-ground center of pressure during stance that offloaded the torque demand away from the ACLR knee. CLINICAL RELEVANCE: Lower net PFJ loading during running in the ACLR limb more than 12 months after ACLR suggests that underloading might play a role in the onset of PFJ osteoarthritis after ACLR.

Muscle contributions to tibiofemoral shear forces and valgus and rotational joint moments during single leg drop landing.

Anterior cruciate ligament (ACL) injuries commonly occur during single-leg landing tasks and are a burdensome condition. Previous studies indicate that muscle forces play an important role in controlling ligamentous loading, yet these studies have typically used cadaveric models considering only the knee-spanning quadriceps, hamstrings, and gastrocnemius muscle groups. Any muscles (including non-knee-spanning muscles) capable of opposing the anterior shear joint reaction force and the valgus joint reaction moment are thought to have the greatest potential for protecting the ACL from injury. Thus, the purpose of this study was to investigate how lower-limb muscles modulate knee joint loading during a single-leg drop landing task. An electromyography-informed neuromusculoskeletal modeling approach was used to compute lower-limb muscle force contributions to the anterior shear joint reaction force and the valgus joint reaction moment at the knee during a single-leg drop landing task. The average shear joint reaction force ranged from 153 N of anterior shear force to 744 N of posterior shear force. The muscles that generated the greatest posterior shear force were the soleus, medial hamstrings, and biceps femoris, contributing up to 393 N, 359 N, and 162 N, respectively. The average frontal plane joint reaction moment ranged from a 19 Nm varus moment to a 6 Nm valgus moment. The valgus moment was primarily opposed by the gluteus medius, gluteus minimus, and soleus, with these muscles providing contributions of up to 38, 22, and 20 Nm toward a varus moment, respectively. The findings identify key muscles that mitigate loads on the ACL.

Muscle contributions to medial and lateral tibiofemoral compressive loads during sidestep cutting.

The tibiofemoral compressive forces experienced during functional activities are believed to be important for maintaining tibiofemoral stability. Previous studies have shown that both knee-spanning and non-knee-spanning muscles contribute to tibiofemoral joint compressive forces during walking. However, healthy individuals typically engage in more vigorous activities (e.g. jumping and cutting) that provide greater challenges to tibiofemoral stability. Despite this, no previous studies have investigated how both knee-spanning and non-knee-spanning muscles contribute to tibiofemoral compressive loading during such tasks. The present study investigated how muscles contributed to the medial and lateral compartment tibiofemoral compressive forces during sidestep cutting. Three-dimensional marker trajectories, ground reaction forces and muscle electromyographic signals were collected from eight healthy males whilst they completed unanticipated sidestep cutting. OpenSim was used to perform musculoskeletal simulations to compute the contribution of each lower-limb muscle to compressive loading of each compartment of the knee. The greatest contributors to medial compartment loading were the vasti, gluteus maximus and medius, and the medial gastrocnemius. The greatest contributors to lateral compartment loading were the vasti, adductors, medial and lateral gastrocnemius, and the soleus. The soleus displayed the greatest potential for unloading the medial compartment, whereas the gluteus maximus and medius displayed the greatest potential for unloading the lateral compartment. These findings may help to inform interventions aiming to modulate compressive loading at the knee.

Lower-Limb Biomechanics in Football Players with and without Hip-related Pain.

PURPOSE: This study aimed to evaluate the differences in lower-limb biomechanics between adult subelite competitive football players with and without hip-related pain during two contrasting tasks-walking and single-leg drop jump (SLDJ)-and to determine whether potential differences, if present, are sex dependent. METHODS: Eighty-eight football players with hip-related pain (23 women, 65 men) and 30 asymptomatic control football players (13 women, 17 men) who were currently participating in competitive sport were recruited. Biomechanical data were collected for the stance phase of walking and SLDJ. Pelvis, hip, knee, and ankle angles, as well as the impulse of the external joint moments, were calculated. Differences between groups and sex-specific effects were calculated using linear regression models. RESULTS: Compared with their asymptomatic counterparts, football players with hip-related pain displayed a lower average pelvic drop angle during walking (P = 0.03) and a greater average pelvic hike angle during SLDJ (P < 0.05). Men with hip-related pain displayed a smaller total range of motion (excursion) for the transverse plane pelvis angle (P = 0.03) and a smaller impulse of the hip external rotation moment (P < 0.01) during walking compared with asymptomatic men. Women with hip-related pain displayed a greater total range of motion (excursion) for the sagittal plane knee angle (P = 0.01) during walking compared with asymptomatic women. CONCLUSION: Overall, few differences were observed in lower-limb biomechanics between football players with and without hip-related pain, irrespective of the task. This outcome suggests that, despite the presence of symptoms, impairments in lower-limb biomechanics during function do not appear to be a prominent feature of people with hip-related pain who are still participating in sport.