Biomechanical but Not Strength or Performance Measures Differentiate Male Athletes Who Experience ACL Reinjury on Return to Level 1 Sports

Validation of OpenCap: A low-cost markerless motion capture system for lower-extremity kinematics during return-to-sport tasks

Low-cost markerless motion capture systems offer the potential for 3D measurement of joint angles during human movement. This study aimed to validate a smartphone-based markerless motion capture system's (OpenCap) derived lower extremity kinematics during common return-to-sport tasks, comparing it to an established optoelectronic motion capture system. Athletes with prior anterior cruciate ligament reconstruction (12-18 months post-surgery) performed three movements: a jump-landing-rebound, single-leg hop, and lateral-vertical hop. Kinematics were recorded concurrently with two smartphones running OpenCap's software and with a 10-camera, marker-based motion capture system. Validity of lower extremity joint kinematics was assessed across 437 recorded trials using measures of agreement (coefficient of multiple correlation: CMC) and error (mean absolute error: MAE, root mean squared error: RMSE) across the time series of movement. Agreement was best in the sagittal plane for the knee and hip in all movements (CMC > 0.94), followed by the ankle (CMC = 0.84-0.93). Lower agreement was observed for frontal (CMC = 0.47-0.78) and transverse (CMC = 0.51-0.6) plane motion. OpenCap presented a grand mean error of 3.85° (MAE) and 4.34° (RMSE) across all joint angles and movements. These results were comparable to other available markerless systems. Most notably, OpenCap's user-friendly interface, free software, and small physical footprint have the potential to extend motion analysis applications beyond conventional biomechanics labs, thus enhancing the accessibility for a diverse range of users.

Unraveling sex-specific risks of knee osteoarthritis before menopause: Do sex differences start early in life?

OBJECTIVE

Sufficient evidence within the past two decades have shown that osteoarthritis (OA) has a sex-specific component. However, efforts to reveal the biological causes of this disparity have emerged more gradually. In this narrative review, we discuss anatomical differences within the knee, incidence of injuries in youth sports, and metabolic factors that present early in life (childhood and early adulthood) that can contribute to a higher risk of OA in females.

DESIGN

We compiled clinical data from multiple tissues within the knee joint-since OA is a whole joint disorder-aiming to reveal relevant factors behind the sex differences from different perspectives.

RESULTS

The data gathered in this review indicate that sex differences in articular cartilage, meniscus, and anterior cruciate ligament are detected as early as childhood and are not only explained by sex hormones. Aiming to unveil the biological causes of the uneven sex-specific risks for knee OA, we review the current knowledge of sex differences mostly in young, but also including old populations, from the perspective of (i) human anatomy in both healthy and pathological conditions, (ii) physical activity and response to injury, and (iii) metabolic signatures.

CONCLUSIONS

We propose that to close the gap in health disparities, and specifically regarding OA, we should address sex-specific anatomic, biologic, and metabolic factors at early stages in life, as a way to prevent the higher severity and incidence of OA in women later in life.

Return to sports after an ACL reconstruction in 2024 - A glass half full? A narrative review

A successful return to sports (RTS) after an anterior cruciate ligament reconstruction (ACLR) is multifactorial, and therefore difficult and challenging. Unfortunately, low percentages of patients RTS, and for those who succeed, one-fifth of patients will sustain a second ACL injury. Over the past years, test batteries were developed to assess whether patients can RTS with a low risk for a second ACL injury risk. Low rates of patients who meet RTS criteria were found, coupled with the insufficiency of current RTS test batteries in predicting second ACL injuries suggesting poor sensitivity. The result of an RTS test is likely to reflect the content of a rehabilitation program, raising critical questions regarding what we are offering patients within the rehabilitation programme. Are we preparing our patients well enough for the high demands of complex situations within pivoting team sports? This narrative review offers insights from key lessons of the last 15 years on 1) RTS testing, 2) the content of rehabilitation, and 3) the RTS continuum, all from a "helicopter perspective".

Anterior-Posterior Center of Pressure Is Associated With Knee Extensor Moment During Landing After Anterior Cruciate Ligament Reconstruction

CONTEXT

A reduced knee extensor moment (KEM) in the involved limb and asymmetry in the KEM during landing tasks are observed after anterior cruciate ligament reconstruction (ACLR). There is limited information about the association of kinetic and kinematic parameters with the KEM during landing after ACLR. This study investigated the association of the anterior-posterior center of pressure (AP-COP) position, vertical ground reaction force (VGRF), and lower limb joint angles with the KEM during landing in female athletes following ACLR.

DESIGN

Cross-sectional study.

METHODS

Twenty-two female athletes who underwent ACLR performed a drop vertical jump at 7.9 (1.7) months after surgery. We evaluated the KEM, AP-COP position, VGRF, and sagittal plane hip, knee, and ankle angles using a 3-dimensional motion analysis system with force plates.

RESULTS

The peak KEM in the involved limb was significantly smaller than that in the uninvolved limb during landing (1.43 [0.33] N·m/kg/m vs 1.84 [0.41] Nm/kg/m, P = .001). The VGRF in the involved limb was significantly smaller than that in the uninvolved limb (11.9 [2.3] N/kg vs 14.6 [3.5] N/kg, P = .005). The limb symmetry index of the KEM was predicted by that of the VGRF (P < .001, R2 = .621, β = 0.800). The KEM was predicted by the AP-COP position in the involved limb (P = .015, R2 = .227, β = 0.513) and by the VGRF in the uninvolved limb (P = .018, R2 = .213, β = 0.500). No significant correlation was noted between the KEM and the lower limb joint angles.

CONCLUSIONS

The AP-COP position and VGRF were associated with the KEM during landing. Evaluating the VGRF and AP-COP position, not the lower limb joint angles, may contribute to understanding the KEM during double-leg landing after ACLR in the clinical setting.

Knee Biomechanics During Cutting Maneuvers and Secondary ACL Injury Risk: A Prospective Cohort Study of Knee Biomechanics in 756 Female Elite Handball and Soccer Players

BACKGROUND

An athlete who returns to sport after an anterior cruciate ligament (ACL) injury has a substantially high risk of sustaining a new secondary ACL injury. Because ACL injuries most frequently occur during cutting maneuvers, such movements should be at the center of research attention.

PURPOSE

To investigate whether knee biomechanical parameters during side-step cutting maneuvers differ between female elite athletes with and without a history of ACL injury and to evaluate whether such parameters are associated with future secondary ACL injury.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

A total of 756 female elite handball and soccer players, of whom 76 had a history of ACL injury, performed a sport-specific cutting task while 3-dimensional kinematics and kinetics were measured. ACL injuries were registered prospectively over an 8-year follow-up period. Seven knee-specific biomechanical variables were the basis for all analyses. Two-way analyses of variance were applied to assess group differences, whereas logistic regression models served to evaluate associations between the knee-specific variables and future secondary ACL injury.

RESULTS

When players with a previous ACL injury performed the cutting maneuver with their ipsilateral leg, they exhibited lower knee abduction angles (mean difference [MD], 1.4°-1.5°; 95% CI, 0.2°-2.9°), lower peak knee flexion moments (MD, 0.33 N·m/kg-1; 95% CI, 0.18-0.48 N·m/kg-1), lower peak knee abduction moments (MD, 0.27 N·m/kg-1; 95% CI, 0.12-0.41 N·m/kg-1), and lower peak knee internal rotation moments (MD, 0.06 N·m/kg-1; 95% CI, 0.01-0.12 N·m/kg-1) compared with injury-free players. When players performed the cut with their contralateral leg, no differences were evident (P < .05). None of the 7 knee-specific biomechanical variables was associated with future secondary ACL injury in players with an ACL injury history (P < .05).

CONCLUSION

Approximately 4 years after ACL injury, female elite team-ball athletes still unloaded their ipsilateral knee during cutting maneuvers, yet contralateral knee loading was similar to that of injury-free players. Knee biomechanical characteristics were not associated with future secondary ACL injury.

Quadriceps and Hamstrings Activation Peaks Earlier as Athletes Repeatedly Hop, but There are Differences Depending on ACL Reconstruction Technique

Background

After Anterior Cruciate Ligament Reconstruction (ACLR) athletes face the challenge of regaining their previous competitive level while avoiding re-injury and early knee joint cartilage degeneration. Quadriceps and hamstrings strength reductions and neuromuscular alterations potentially related to risk of re-injury are present after ACLR and relate to deficits in muscle activation.

Design

Cross-sectional laboratory study.

Purpose

To examine quadriceps and hamstrings muscle activation during repeated hops in healthy pivoting-sport athletes and those who had undergone ACLR (bone-tendon-bone and semitendinosus graft) who had met functional criteria allowing return to training.

Methods

Surface electromyography (SEMG) was recorded from vastus medialis and lateralis and medial and lateral hamstrings bilaterally during 30 seconds' repeated hopping in male athletes on average eight months after ACLR surgery (5-12 months). All patients underwent hamstring (HS) (n=24) or bone-tendon-bone (BTB) reconstruction (n=20) and were compared to healthy controls (n=31). The SEMG signals were normalized to those obtained during maximal voluntary isometric contraction.

Results

A significant time shift in peak muscle activation (earlier) was seen for: vastus medialis and vastus lateralis activation in the control group, in the BTB group's healthy (but not injured) leg and both legs of the HS group. A significant time shift in peak muscle activation was seen for lateral hamstrings (earlier) in all but the BTB group's injured leg and the medial hamstrings in the control group only. Lower peak activation levels of the vastus lateralis (p\<0.001) and vastus medialis (p\<0.001) were observed in the injured compared to healthy legs and lower peak lateral hamstrings activity (p\<0.009) in the injured leg compared to control leg. Decline in medial hamstring peak activation (p\<0.022) was observed between 1st and 3rd phase of the hop cycle in all groups.

Conclusion

Repeated hop testing revealed quadriceps and hamstring activation differences within ACLR athletes, and compared to healthy controls, that would be missed with single hop tests.

Level of evidence

3.

Exploring the Role of Sprint Biomechanics in Hamstring Strain Injuries: A Current Opinion on Existing Concepts and Evidence

Hamstring strain injuries are one of the most common injuries in sprint-based sports with the mechanism of injury considered the result of an interaction between applied mechanical strain and the capacity of the muscle to tolerate strain. To date, injury prevention and rehabilitation strategies have frequently focused on enhancing the capacity of the hamstrings to tolerate strain, with little consideration of factors directly influencing mechanical strain. Sprint running biomechanics are one factor proposed to influence the mechanical strain applied to the hamstrings that may be modified (towards reduced strain) within rehabilitation and injury prevention programs. This article aims to explore the theoretical mechanistic link between sprint running mechanics and hamstring strain injury, along with the available supporting evidence. In doing so, it hopes to provide practitioners with an understanding of mechanical parameters that may influence hamstring strain injury whilst also identifying areas for further research exploration.

Return to the Pre-Injury Level of Sport after Anterior Cruciate Ligament Reconstruction: A Practical Review with Medical Recommendations

Returning to sport after anterior cruciate ligament reconstruction (ACLR) can be a challenging and complex process for the athlete, with the rate of return to the pre-injury level of sport observed to be less than athlete expectations. Of the athletes that do return to sport (RTS), knee re-injury rates remain high, and multiple studies have observed impaired athletic performance upon RTS after ACLR as well as reduced playing time, productivity, and career lengths. To mitigate re-injury and improve RTS outcomes, multiple RTS after ACLR consensus statements/clinical practice guidelines have recommended objective RTS testing criteria to be met prior to medical clearance for unrestricted sports participation. While the achievement of RTS testing criteria can improve RTS rates after ACLR, current criteria do not appear valid for predicting safe RTS. Therefore, there is a need to review the various factors related to the successful return to the pre-injury level of sport after ACLR, clarify the utility of objective performance testing and RTS criteria, further discuss safe RTS decision-making as well as present strategies to reduce the risk of ACL injury/re-injury upon RTS. This article provides a practical review of the current RTS after ACLR literature, as well as makes medical recommendations for rehabilitation and RTS decision-making after ACLR.

Knee extension deficit during gait and knee extensor weakness persisting after saucerization and repair of discoid lateral meniscus tears

BACKGROUND

Physical function and knee kinematics recovery after discoid lateral meniscus (DLM) tear surgery are essential for a better prognosis. However, these alterations remain unclear. Therefore, this study aimed to investigate changes in physical function and knee kinematics following saucerization and DLM tear repair.

METHODS

We enrolled 16 patients who underwent saucerization and DLM tear repair. Postoperative changes in knee kinematics during gait, and physical function, were evaluated at 3, 6, and 12 months.

RESULTS

The peak flexion angle of the operated limb during weight acceptance was significantly higher than that of the contralateral limb at 3 (operated limb: 34.6 ± 8.9°, contralateral limb: 23.7 ± 8.3°; P < 0.01) and 6 months (operated limb: 32.1 ± 9.7°, contralateral limb: 24.6 ± 8.2°; P = 0.03) postoperatively, but not at 12 months (operated limb: 27.1 ± 7.1°, contralateral limb: 23.1 ± 9.5°; P = 0.22) postoperatively. The knee extensor strength of the operated limb was significantly lower than that of the contralateral limb at 3 (operated limb: 1.00 ± 0.59 Nm/kg, contralateral limb: 1.37 ± 0.59 Nm/kg; P = 0.01), 6 (operated limb: 1.22 ± 0.55 Nm/kg, contralateral limb: 1.48 ± 0.60 Nm/kg; P < 0.01), and 12 months (operated limb: 1.39 ± 0.57 Nm/kg, contralateral limb: 1.55 ± 0.64 Nm/kg; P = 0.04) postoperatively.

CONCLUSION

Knee extension deficits and extensor weakness persisted at 6 months after saucerization and repair of DLM tears. Postoperative rehabilitation should be focused on knee extension function.

Influence of Graft Type and Meniscal Involvement on Short-Term Outcomes Following Anterior Cruciate Ligament Reconstruction

CONTEXT

The purpose of this study was to compare short-term clinical outcomes between meniscus procedures performed with anterior cruciate ligament reconstruction (ACLR), ACLR (ACLR-only), ACLR with meniscectomy/resection (ACLR-resect), and ACLR with meniscal repair (ACLR-repair) for bone patellar tendon bone grafts (BPTB) and hamstring tendon grafts, separately.

DESIGN

This was a cross-sectional study conducted in a controlled laboratory setting as part of a large point-of-care collaborative research program.

METHODS

This study included 314 participants (168 females; mean [SD]: age, 19.7 [4.8]) with primary unilateral ACLR with a BPTB or hamstring tendon. Patients were divided into 3 groups depending on meniscal procedure (ACLR-only, ACLR-resect, and ACLR-repair). Postsurgical testing included: isokinetic assessment of knee extension and flexion, single-leg hop tests, and patient-reported outcomes. Multivariate analysis of covariance compared differences between meniscal procedures on the battery of tests, and for each statistically significant variable an analysis of covariance assessed the effect of meniscal procedure within each graft type. Chi-square analysis assessed the influence of meniscal procedure on tests' pass rates defined as 90% of limb symmetry index.

RESULTS

BPTB: ACLR-only had greater hamstring strength than ACLR-resect (P = .05) and ACLR-repair (P = .005). ACLR-only had the highest proportion of participants to pass the hamstring strength test (P = .02). Hamstring tendon: ACLR-only (P = .03) and ACLR-resect (P = .003) had higher International Knee Documentation Committee scale scores than ACLR-repair. There was a significant difference in the proportion of participants who scored >90% limb symmetry index on the timed hop test (P = .05).

CONCLUSIONS

The influence of meniscal repair on clinical outcomes is dependent on the graft choice. Following an ACLR with BPTB and a meniscal procedure, hamstring function should be more closely monitored for optimal short-term recovery.

Functional Return-to-Sport Testing Demonstrates Inconsistency in Predicting Short-Term Outcomes Following Anterior Cruciate Ligament Reconstruction: A Systematic Review

PURPOSE

To systematically review the relationship between functional testing at the time of return to sport (RTS) and short-term outcomes, such as second anterior cruciate ligament (ACL) tear and return to a preinjury level of sport, among athletes who underwent anterior cruciate ligament reconstruction (ACLR).

METHODS

A systematic literature search was performed in MEDLINE, EMBASE, Scopus, and Web of Science to identify studies examining athletes who underwent functional RTS testing and were followed for at least 12 months following ACLR. Studies were screened by 2 reviewers. A standardized template was used to extract information regarding study characteristics, ACLR information, functional test results, and risk factors associated with retear or reduced RTS.

RESULTS

Of the 937 studies identified, 22 met the inclusion criteria. The average time between ACLR and RTS testing was 8.5 months. Single leg hop for distance performance had no association with retear risk in any study and no association with RTS rates in most studies. Quadriceps strength had conflicting results in relation to retear risk, whereas it had no relationship with RTS rates. Rates of reinjury and RTS were similar between patients who passed and did not pass combined hop and strength batteries. Asymmetric knee extension and hip moments, along with increased knee valgus and knee flexion angles, demonstrated increased risk of retear.

CONCLUSIONS

Individual hop and strength tests that are often used in RTS protocols following ACLR may have limited and inconsistent value in predicting ACL reinjury and reduced RTS when used in isolation. Combined hop and strength test batteries also demonstrate low sensitivity and negative predictive value, highlighting conflicting evidence to suggest RTS testing algorithm superiority. Biomechanical assessment is promising for stratifying ACL reinjury risk, but further research is necessary.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I-IV studies.

Female Athletes With Better Psychological Readiness Are at Higher Risk for Second ACL Injury After Primary ACL Reconstruction

BACKGROUND

Approximately 1 in 4 athletes returning to sports will sustain a second anterior cruciate ligament (ACL) injury. Psychological factors related to kinesiophobia, confidence, and psychological readiness are associated with second ACL injury; however, the evidence is conflicting.

HYPOTHESIS

Athletes who sustain a second ACL injury (ie, graft rupture or contralateral ACL rupture) within 2 years of ACL reconstruction (ACLR) would have greater kinesiophobia, less confidence, and lower psychological readiness prior to return to sport (RTS) compared with athletes who do not sustain a second ACL injury.

STUDY DESIGN

Secondary analysis of a prospective randomized trial.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 39 female Level I/II athletes completed the following measures after postoperative rehabilitation and a 10-session RTS and second ACL injury prevention program: ACL Return to Sport after Injury (ACL-RSI) scale, the 11-item Tampa Scale of Kinesiophobia (TSK-11), and question 3 on the Knee injury and Osteoarthritis Outcome Score (KOOS) quality of life (QoL) subscale. Athletes were dichotomized based on whether they sustained a second ACL injury within 2 years of ACLR or not. Independent t tests determined group differences in TSK-11, KOOS-QoL, ACL-RSI, and the 3 individual components of the ACL-RSI (ie, emotions, confidence, risk appraisal).

RESULTS

Nine athletes sustained a second ACL injury (4 graft ruptures and 5 contralateral ACL ruptures). The group that sustained a second ACL injury had higher scores on the ACL-RSI (P = 0.03), higher on the risk appraisal questions of the ACL-RSI (P < 0.01), and met RTS criteria sooner than athletes who did not (P = 0.04). All second ACL injuries occurred in athletes who underwent primary ACLR with hamstring tendon autografts.

CONCLUSION

Athletes who sustained a second ACL within 2 years of ACLR had a more positive psychological outlook, higher scores on the specific questions related to the risk appraisal construct of the ACL-RSI, and met RTS criteria sooner than athletes who did not sustain a second ACL injury.

CLINICAL RELEVANCE

Counseling athletes about delaying RTS to reduce the risk of second ACL injury may be especially important in athletes who display high psychological readiness and meet RTS criteria sooner.

AI-Assisted Fatigue and Stamina Control for Performance Sports on IMU-Generated Multivariate Times Series Datasets

BACKGROUND

Optimal sports performance requires a balance between intensive training and adequate rest. IMUs provide objective, quantifiable data to analyze performance dynamics, despite the challenges in quantifying athlete training loads. The ability of AI to analyze complex datasets brings innovation to the monitoring and optimization of athlete training cycles. Traditional techniques rely on subjective assessments to prevent overtraining, which can lead to injury and underperformance. IMUs provide objective, quantitative data on athletes' physical status during action. AI and machine learning can turn these data into useful insights, enabling data-driven athlete performance management. With IMU-generated multivariate time series data, this paper uses AI to construct a robust model for predicting fatigue and stamina.

MATERIALS AND METHODS

IMUs linked to 19 athletes recorded triaxial acceleration, angular velocity, and magnetic orientation throughout repeated sessions. Standardized training included steady-pace runs and fatigue-inducing techniques. The raw time series data were used to train a supervised ML model based on frequency and time-domain characteristics. The performances of Random Forest, Gradient Boosting Machines, and LSTM networks were compared. A feedback loop adjusted the model in real time based on prediction error and bias estimation.

RESULTS

The AI model demonstrated high predictive accuracy for fatigue, showing significant correlations between predicted fatigue levels and observed declines in performance. Stamina predictions enabled individualized training adjustments that were in sync with athletes' physiological thresholds. Bias correction mechanisms proved effective in minimizing systematic prediction errors. Moreover, real-time adaptations of the model led to enhanced training periodization strategies, reducing the risk of overtraining and improving overall athletic performance.

CONCLUSIONS

In sports performance analytics, the AI-assisted model using IMU multivariate time series data is effective. Training can be tailored and constantly altered because the model accurately predicts fatigue and stamina. AI models can effectively forecast the beginning of weariness before any physical symptoms appear. This allows for timely interventions to prevent overtraining and potential accidents. The model shows an exceptional ability to customize training programs according to the physiological reactions of each athlete and enhance the overall training effectiveness. In addition, the study demonstrated the model's efficacy in real-time monitoring performance, improving the decision-making abilities of both coaches and athletes. The approach enables ongoing and thorough data analysis, supporting strategic planning for training and competition, resulting in optimized performance outcomes. These findings highlight the revolutionary capability of AI in sports science, offering a future where data-driven methods greatly enhance athlete training and performance management.

Detecting side-to-side differences of lower limb biomechanics during single-legged forward landing after anterior cruciate ligament reconstruction

BACKGROUND

Motion analysis can be used to evaluate functional recovery after anterior cruciate ligament (ACL) reconstruction; however, the biomechanics parameters of the lower limb that are specifically altered in ACL-reconstructed knees compared to the contralateral side are not well understood. This retrospective study aimed to compare side-to-side differences in lower limb biomechanics during the first 100 milliseconds (ms) after initial contact in a single-leg forward landing task.

METHODS

Using three-dimensional motion analysis, lower joint kinematic and kinetic variables were measured 8-10 months postoperatively in 22 patients who had undergone ACL reconstruction. We determined side-to-side differences in lower limb biomechanics over the 100-ms timeframe after landing, and receiver operating characteristic (ROC) curve analyses were performed to calculate the area under the curve (AUC) for parameters showing significant side-to-side differences.

RESULTS

During the 100-ms timeframe after landing, 58 kinematic and kinetic items showed significant side-to-side differences. Side-to-side differences in lower limb biomechanics over the 40-ms timeframe after landing existed. The ROC curve analysis identified 11 items with AUC values ≥ 0.70, including hip flexion, abduction moment, and knee joint power, and their AUC values were not significantly different.

CONCLUSION

Hip flexion/abduction moment and knee power after GRF max could be used as outcomes for assessing functional recovery in patients who have undergone ACL reconstruction.

Comparison of Strength and Power Characteristics Before ACL Rupture and at the End of Rehabilitation Before Return to Sport in Professional Soccer Players

BACKGROUND

Strength and power is often reduced on the involved versus contralateral limb and healthy controls after anterior cruciate ligament (ACL) reconstruction, but no study has compared with preinjury values at the time of return to sport (RTS).

HYPOTHESIS

Divergent recovery patterns in strength and power characteristics will be present at RTS relative to preinjury baseline data and healthy matched controls.

STUDY DESIGN

Cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Isokinetic strength tests, bilateral and single-leg countermovement jumps (CMJ; SLCMJ) were measured before ACL rupture in 20 professional soccer players. These then had surgical reconstruction (ACL group) and completed follow-up testing before RTS. Healthy controls (uninjured group) were tested at the same time as the ACL group preinjury. Values recorded at RTS of the ACL group were compared with preinjury. We also compared the uninjured and ACL groups at baseline and RTS.

RESULTS

Compared with preinjury, ACL normalized quadriceps peak torque of the involved limb (difference = -7%), SLCMJ height (difference = -12.08%), and Reactive Strength Index modified (RSImod) (difference = -5.04%) were reduced after ACL reconstruction. No significant reductions in CMJ height, RSImod, and relative peak power were indicated at RTS in the ACL group when compared with preinjury values, but deficits were present relative to controls. The uninvolved limb improved quadriceps (difference = 9.34%) and hamstring strength (difference = 7.36%) from preinjury to RTS. No significant differences from baseline were shown in SLCMJ height, power, and reactive strength of the uninvolved limb after ACL reconstruction.

CONCLUSION

Strength and power in professional soccer players at RTS after ACL reconstruction were often reduced compared with preinjury values and matched healthy controls.

CLINICAL RELEVANCE

Deficits were more apparent in the SLCMJ, suggesting that dynamic and multijoint unilateral force production is an important component of rehabilitation. Use of the uninvolved limb and normative data to determine recovery may not always be appropriate.

The MyJump App is a Valid Method of Assessing and Classifying Limb Symmetry During Recovery from Anterior Cruciate Ligament Reconstruction

Background

Jump testing performance and limb symmetry measures are important metrics for clinicians to monitor during rehabilitation after Anterior Cruciate Ligament (ACL) reconstruction, however they require hardware and software which is not commonly available in clinical practice. Video-based solutions may present a feasible alternative, but their veracity in classifying patients using limb-symmetry of 90% has not been established, nor have the clinimetric values for the performance measures been reported in this population.

Purpose

To describe the diagnostic accuracy (pass/fail using 90% LSI) and clinimetrics of an iPad-based app ("MyJump") compared to reference force plate analyses for limb symmetry, jump/hop height, contact time, flight time, and reactive strength index.

Study design

Prospective cohort, diagnostic accuracy.

Methods

Fifty-one consecutive patients recovering from ACL reconstruction undertaking routine independent clinical evaluation of their hop and jump performance were concurrently and independently examined using force plates and the MyJump app. Diagnostic accuracy of MyJump was compared to reference force plate analyses using a criterion of 90% limb symmetry.

Results

Diagnostic accuracy of the MyJump app was very good: positive predictive value for jump height was 0.83 and 1.0 for reactive strength index, and negative predictive value was 0.95 and 1.0 for the same metrics, respectively. Of the 131 classifications made using the MyJump app, there were five false positives and three false negatives - all of these were in classification of jump height with no misclassifications of RSI. Irrespective of jump type, the MyJump app displayed excellent reliability (ICC>0.95) for both height and reactive strength index. Minimum detectable changes were approximately 1cm for height, 0.1 for reactive strength index, 0.02s for contact time, and 0.3s for flight time.

Conclusion

Where force plates are unavailable, the MyJump app is a valid and reliable substitute for criteria assessment of jump/hop height and reactive strength index in those recovering from ACL surgery using a 90% limb symmetry threshold. The minimum detectable changes vary by metric but are likely sufficiently accurate to detect clinical changes.

Level Of Evidence

Level 3.

The Influence of Quadriceps Strength and Rate of Torque Development on the Recovery of Knee Biomechanics During Running After Anterior Cruciate Ligament Reconstruction

BACKGROUND

After anterior cruciate ligament reconstruction (ACLR), altered surgical knee biomechanics during running is common. Although greater quadriceps strength is associated with more symmetrical running knee kinetics after ACLR, abnormal running mechanics persist even after resolution of quadriceps strength deficits. As running is a submaximal effort task characterized by limited time to develop knee extensor torque, quadriceps rate of torque development (RTD) may be more closely associated with recovery of running knee mechanics than peak torque (PT).

PURPOSE

To assess the influence of recovery in quadriceps PT and RTD symmetry on knee kinematic and kinetic symmetry during running over the initial 2 years after ACLR.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A total of 39 Division I collegiate athletes (106 testing sessions; 19 female) completed serial isometric performance testing and running analyses between 3 and 24 months after ACLR. Athletes performed maximal and rapid isometric knee extension efforts with each limb to assess PT and RTD between-limb symmetry indices (PTLSI and RTDLSI), respectively. Peak knee flexion difference (PKFDIFF) and peak knee extensor moment limb symmetry index (PKEMLSI) during running were computed. Multivariable linear mixed-effects models assessed the influence of PTLSI and RTDLSI on PKFDIFF and PKEMLSI over the initial 2 years after ACLR.

RESULTS

Significant main effects of RTDLSI (P < .001) and time (P≤ .02) but not PTLSI (P≥ .24) were observed for both PKFDIFF and PKEMLSI models. For a 10% increase in RTDLSI, while controlling for PTLSI and time, a 0.9° (95% CI, 0.5°-1.3°) reduction in PKFDIFF and a 3.5% (95% CI, 1.9%-5.1%) increase in PKEMLSI are expected. For every month after ACLR, a 0.2° (95% CI, 0.1°-0.4°) reduction in PKFDIFF and a 1.3% (95% CI, 0.6%-2.0%) increase in PKEMLSI are expected, controlling for PTLSI and RTDLSI.

CONCLUSION

Quadriceps RTDLSI was more strongly associated with symmetrical knee biomechanics during running compared with PTLSI or time throughout the first 2 years after ACLR.

Foot rotation and pelvic angle correlate with knee abduction moment during 180° lateral cut in football players

BACKGROUND

Lateral movements are challenging for 2D video-analysis and are therefore often omitted in functional tests for Anterior Cruciate Ligament (ACL) injury risk assessment. The purpose of the present study was to investigate the association between frontal and transverse plane angles obtained from 2D video-analysis and knee abduction moment (KAM) from gold standard 3D motion capture in a 180° lateral cut task. The hypothesis was that 2D angles other than the knee joint effectively explain variations in KAM.

METHODS

Thirty-four healthy football players (age 22.8 ± 4.1 years) performed a series of 180° lateral cut (lateral shuffles) tasks. The peak KAM was collected through a 3D motion capture system. A 2D video-analysis movement assessment identified frontal and transverse plane joint kinematics: foot projection angle (FPA), Frontal Plane Knee Projection Angle (FPKPA), Pelvis tilt angle (PA), and Trunk tilt angle (TA). A forward stepwise regression model was used to assess significant 2D predictors of KAM (p < 0.05).

RESULTS

FPA and PA were the only significant predictors (R2-ajdusted = 9.2%, p < 0.001), with external foot rotation and contralateral pelvic drop associated with higher KAM. Based on the regression model, the "High FPA & PA group" was defined and showed higher KAM than the rest of the cohort (p = 0.012, ES = 0.71).

CONCLUSIONS

The external foot rotation and the contralateral pelvic drop from 2D video-analysis were associated with higher peak KAM during the 180° lateral cut. A qualitative assessment of the 180° lateral cut could offer precious insights on ACL injury risk mitigation.

LEVEL OF EVIDENCE

Descriptive Laboratory Study.

Content validity, interpretability, and internal consistency of the "Quality First" assessment to evaluate movement quality in hop tests following ACL rehabilitation. A cross-sectional study

Introduction

Current approaches fail to adequately identify sport readiness after anterior cruciate ligament (ACL) rehabilitation. Altered landing biomechanics after ACL reconstruction are associated with increased risk of a noncontact ACL reinjury. There is a lack of objective factors to screen for deficient movement patterns. Therefore, the aim of this study was to investigate content validity, interpretability, and internal consistency for the newly developed "Quality First" assessment to evaluate movement quality during hop tests in patients after ACL rehabilitation.

Method

Participants in this cross-sectional study were recruited in collaboration with the Altius Swiss Sportmed Center in Rheinfelden, Switzerland. After a successful ACL reconstruction, the movement quality of 50 hop test batteries was evaluated between 6 and 24 months postoperatively with the "Quality First" assessment. Content validity was assessed from the perspective of professionals. To check the interpretability, classical test theory was employed. Cronbach's α was calculated to evaluate internal consistency.

Results

Content validity resulted in the inclusion of three different hop tests (single-leg hop for distance, vertical hop, and side hop). The "Quality First" assessment is enabled to evaluate movement quality in the sagittal, vertical, and the transversal plane. After the exclusion process, the "Quality First" assessment was free from floor and ceiling effects and obtained a sufficient Cronbach's α. The final version consists of 15 items, rated on a 4-point scale.

Discussion

By means of further validations, the "Quality First" assessment could offer a possibility to evaluate movement quality after ACL rehabilitation during hop tests.

Three-dimensional magnetic resonance imaging analysis shows sex-specific patterns in changes in anterior cruciate ligament cross-sectional area along its length

Smaller anterior cruciate ligament (ACL) size in females has been hypothesized to be a key contributor to a higher incidence of ACL tears in that population, as a lower cross-sectional area (CSA) directly corresponds to a larger stress on the ligament for a given load. Prior studies have used a mid-length CSA measurement to quantify ACL size. In this study, we used magnetic resonance imaging to quantify the CSA along the entire length of the intact ACL. We hypothesized that changes in the ACL CSA along its length would have different patterns in males and females. We also hypothesized that changes in ACL CSA along its length would be associated with body size or knee size with different associations in females and males. MR images of contralateral ACL-intact knees of 108 patients (62 females, 13-35 years) undergoing ACL surgery were used to measure the CSA along the ACL length, using a custom program. For both females and males, the largest CSA was located at 37%-39% of ACL length from the tibial insertion. Compared to females, males had a significantly larger CSA only within the distal 41% of the ACL (p < 0.001). ACL CSA was associated with patient height and weight in males (r > 0.3; p < 0.05), whereas it was associated with intercondylar notch width in females (r > 0.3; p < 0.05). These findings highlight the importance of standardizing the location of measurement of ACL CSA.

Recurrence quantification analysis of isokinetic strength tests: A comparison of the anterior cruciate ligament reconstructed and the uninjured limb

BACKGROUND

Despite widespread use of return to sport testing following anterior cruciate ligament reconstruction, studies suggest inadequacy in current testing criteria, such as limb symmetry index calculations, to determine athletes' readiness to return to play. Recurrence quantification analysis, an emerging non-linear data analysis tool, may reveal subtle neuromuscular differences between the injured and uninjured limb that are not captured by traditional testing. We hypothesized that isokinetic torque curve data of the injured limb would demonstrate lower determinism and entropy as compared to the uninjured limb.

METHODS

102 patients (44 M, 58F, 10 ± 1 months post-anterior cruciate ligament reconstruction) underwent isokinetic quadriceps strength testing using a HumacNorm dynamometer. Patients completed maximum effort knee extension and flexion at 60°/sec. Data were post-processed with a MATLAB CRQA Graphical User Interface and determinism and entropy values were extracted. Paired-sample t-tests (α = 0.05) were used to compare data from the injured and uninjured limb.

FINDINGS

Determinism and entropy values in the torque curves were lower in the injured limb than the uninjured limb (p < 0.001). Our findings indicate there is less predictability and complexity present in the torque signals of injured limbs.

INTERPRETATION

Recurrence quantification analysis can be used to assess neuromuscular differences between limbs in patients who have undergone anterior cruciate ligament reconstruction. Our findings offer further evidence that there are changes to the neuromuscular system which persist following reconstruction. Further investigation is needed to establish thresholds of determinism and entropy values needed for safe return to sport and to evaluate the utility of recurrence quantification analysis as a return to sport criterion.

Effect of Quadriceps and Hamstring Strength Relative to Body Weight on Risk of a Second ACL Injury: A Cohort Study of 835 Patients Who Returned to Sport After ACL Reconstruction

Background

Anterior cruciate ligament (ACL) injuries are common sports-related injuries with a high risk of reinjury after return to sport (RTS). Rehabilitation aims to regain symmetrical knee strength and function to minimize the risk of a second ACL injury after RTS.

Purpose

To determine the effect of absolute quadriceps and hamstring strength, normalized by body weight, on the risk of a second ACL injury during the first 2 years after RTS in patients who have undergone ACL reconstruction (ACLR).

Study Design

Cohort study; Level of evidence, 3.

Methods

Data from patients after index ACLR at the time of RTS were extracted from a rehabilitation registry-Project ACL. Patients who had performed isokinetic tests for quadriceps and hamstring strength and hop tests before RTS were included. The endpoint was a second ACL injury or a follow-up of 2 years after RTS after ACLR.

Results

A total of 835 patients (46% women), with a mean age of 23.9 ± 7.7 years, were included. During the study period, 69 (8.3%) second ACL injuries (ipsilateral and contralateral) occurred. Greater relative quadriceps strength in the injured leg increased the risk of a second ACL injury (relative risk [RR], 1.69 [95% CI, 1.05-2.74]; P = .032). In patients who had recovered symmetrical quadriceps strength (limb symmetry index ≥90%), there was no effect of quadriceps strength on the risk of second ACL injury (RR, 1.33 [95% CI, 0.69-2.56]; P = .39). Quadriceps strength on the healthy side or hamstring strength, regardless of side, had no effect on the risk of a second ACL injury.

Conclusion

Greater relative quadriceps strength in the injured leg at the time of RTS after ACLR was associated with an increased risk of a second ACL injury. There was no effect of relative quadriceps strength on the risk of a second ACL injury in patients who had recovered symmetrical quadriceps strength.

Graft-Specific Surgical and Rehabilitation Considerations for Anterior Cruciate Ligament Reconstruction with the Quadriceps Tendon Autograft

Anterior cruciate ligament reconstruction (ACLR) with a bone-patellar tendon-bone (BPTB) or hamstring tendon (HT) autograft has traditionally been the preferred surgical treatment for patients returning to Level 1 sports. More recently, international utilization of the quadriceps tendon (QT) autograft for primary and revision ACLR has increased in popularity. Recent literature suggests that ACLR with the QT may yield less donor site morbidity than the BPTB and better patient-reported outcomes than the HT. Additionally, anatomic and biomechanical studies have highlighted the robust properties of the QT itself, with superior levels of collagen density, length, size, and load-to-failure strength compared to the BPTB. Although previous literature has described rehabilitation considerations for the BPTB and HT autografts, there is less published with respect to the QT. Given the known impact of the various ACLR surgical techniques on postoperative rehabilitation, the purpose of this clinical commentary is to present the procedure-specific surgical and rehabilitation considerations for ACLR with the QT, as well as further highlight the need for procedure-specific rehabilitation strategies after ACLR by comparing the QT to the BPTB and HT autografts.

Level of Evidence

Level 5.

Is muscular strength a predictor for primary or secondary ACL injury? A scoping review of prospective studies

OBJECTIVE

To identify strength-related risk factors of ACL injury by conducting a scoping review of the peer-reviewed literature.

METHODS

PubMed and EBSCO host (CINAHL Complete, MEDLINE Complete, SPORTDiscus) were searched from inception to August 2022. Prospective studies that examined strength strength-related risk factors for ACL injury (primary and secondary) were included. PRISMA Extension for Scoping Reviews guided data charting/extraction.

RESULTS

17 studies were included (eight primary ACL injury, nine secondary ACL injury). Knee flexor strength was the most studied predictor (10 studies), followed by hip abductor strength (9 studies). Across studies, measures of muscle performance were inconsistent. Significant strength-related risk factors were reported in seven of 17 studies. Potential strength-related risk factors of primary ACL injury included measures of hip strength (abductor or external rotator) and knee strength (knee flexor/extensor ratio and knee extensor strength symmetry) for secondary ACL injury. Limited/conflicting evidence was found for all strength-related risk factors.

CONCLUSION

Measures of muscle strength appear to be predictive of primary and secondary ACL injury in a subset of identified studies. The heterogeneity of study designs and lack of standardization related to strength testing make it difficult to determine the overall impact of strength in predicting ACL injury.

Is there any biomechanical justification to use hopping as a return to running test? A cross-sectional study

OBJECTIVE

To assess the agreement and the correlation between asymmetry indexes of leg stiffness (AI(K_leg)) in running and hopping and the correlation between leg stiffness (K_leg) in running and hopping.

DESIGN

Cross-sectional study.

SETTING

Clinical facility.

PARTICIPANTS

Twelve healthy runners (5 women and 7 men; mean (SD) age = 36.6 (10.1) years; activity level = 6.4 (0.9) on Tegner scale).

MAIN OUTCOME MEASURES

A treadmill instrumented by photoelectric cells was used to collect data (flight and contact times) during running assessment (preferential and imposed velocity (3.33 m s^-1) and during a hopping test. K_leg and AI(K_leg) were computed for each modality. Correlation tests were performed, and Bland Altman's plot was created.

RESULTS

A significant and large correlation was found between K_leg in hopping and running at imposed speed (r = 0.6, p = 0.001). An acceptable agreement was found between the AIs in hopping and running, with a bias of 0.04 (-0.15-0.06) at imposed speed and 0.03 (-0.13-0.07) at preferred speed.

CONCLUSION

Our results suggest that testing an athlete for asymmetry in hopping might help to understand what happens in running. For this purpose, further research is needed, especially in an injured population, to better understand the association between biomechanical asymmetry in hopping and running.

Evidence Review for Preventing Osteoarthritis After an Anterior Cruciate Ligament Injury: An Osteoarthritis Action Alliance Consensus Statement

CONTEXT

The Osteoarthritis Action Alliance formed a secondary prevention task group to develop a consensus on secondary prevention recommendations to reduce the risk of osteoarthritis after a knee injury.

OBJECTIVE

Our goal was to provide clinicians with secondary prevention recommendations that are intended to reduce the risk of osteoarthritis after a person has sustained an anterior cruciate ligament injury. Specifically, this manuscript describes our methods, literature reviews, and dissenting opinions to elaborate on the rationale for our recommendations and to identify critical gaps.

DESIGN

Consensus process.

SETTING

Virtual video conference calls and online voting.

PATIENTS OR OTHER PARTICIPANTS

The Secondary Prevention Task Group consisted of 29 members from various clinical backgrounds.

MAIN OUTCOME MEASURE(S)

The group initially convened online in August 2020 to discuss the target population, goals, and key topics. After a second call, the task group divided into 9 subgroups to draft the recommendations and supportive text for crucial content areas. Twenty-one members completed 2 rounds of voting and revising the recommendations and supportive text between February and April 2021. A virtual meeting was held to review the wording of the recommendations and obtain final votes. We defined consensus as >80% of voting members supporting a proposed recommendation.

RESULTS

The group achieved consensus on 15 of 16 recommendations. The recommendations address patient education, exercise and rehabilitation, psychological skills training, graded-exposure therapy, cognitive-behavioral counseling (lacked consensus), outcomes to monitor, secondary injury prevention, system-level social support, leveraging technology, and coordinated care models.

CONCLUSIONS

This consensus statement reflects information synthesized from an interdisciplinary group of experts based on the best available evidence from the literature or personal experience. We hope this document raises awareness among clinicians and researchers to take steps to mitigate the risk of osteoarthritis after an anterior cruciate ligament injury.

Unilateral tests of lower-limb function as prognostic indicators of future knee-related outcomes following anterior cruciate ligament injury: a systematic review and meta-analysis of 13 150 adolescents and adults

OBJECTIVE

To investigate the prognostic capacity of individual hop tests, hop test batteries and other unilateral functional performance tests following anterior cruciate ligament (ACL) injury.

DESIGN

Systematic review with meta-analysis.

DATA SOURCES

Six databases searched up to June 2021.

ELIGIBILITY CRITERIA

Studies reporting associations between unilateral lower-limb function (eg, hop tests) following ACL injury and future (≥3 months) knee-related outcomes.

RESULTS

Of 42 included studies (13 150 participants), all assessed the single-forward hop test and 32 assessed a repeated-forward hop test (crossover hop, triple hop, 6m-timed hop), mostly within a year after ACL injury/reconstruction. Results of meta-analyses indicated that higher single-forward and repeated-forward hop limb symmetry were associated with higher odds of return-to-sport 1-3 years post-ACL reconstruction (OR 2.15; 95% CI 1.30 to 3.54; OR 2.11; 95% CI 1.23 to 3.60, respectively). Higher single-forward and repeated-forward hop limb symmetry was associated with better self-reported symptoms and function 1-37 years after ACL injury (OR 2.51; 95% CI 1.62 to 3.88; OR 4.28; 95% CI 1.65 to 11.08, respectively). Higher limb symmetry on a repeated-forward hop does not appear to be associated with higher odds of successful rehabilitation without ACL reconstruction (OR 1.51; 95% CI 0.94 to 2.44). Achieving ≥90% limb symmetry on the single-forward hop was associated with reduced odds of knee osteoarthritis 5-37 years after ACL injury (OR 0.46; 95% CI 0.23 to 0.94).

CONCLUSION

Very low certainty evidence suggests single-forward and repeated-forward hop tests are prognostic indicators for important knee-related outcomes in individuals after ACL injury and may help stratify individuals at risk of poor outcomes to target rehabilitation interventions.

PROSPERO REGISTRATION NUMBER

CRD42018092197.

Return to Sports: A Risky Business? A Systematic Review with Meta-Analysis of Risk Factors for Graft Rupture Following ACL Reconstruction

BACKGROUND

The risk of sustaining a graft rupture after anterior cruciate ligament reconstruction (ACLR) is high. Contributing risk factors are, however, still not clearly identified.

OBJECTIVE

The aim of this systematic review was to identify and quantify risk factors for graft rupture after ACLR.

METHODS

A systematic review with meta-analysis (PROSPERO CRD42020140129) based on PRISMA guidelines was performed. MEDLINE, CINAHL and EMBASE were searched from inception to September 2021. Prospective and retrospective studies addressing risk factors for graft rupture after ACLR in males/females of all ages were considered. Meta-analyses using a random effect model (effect measure: odds ratio [OR] with 95% confidence interval [CI]) were performed. The GRADE tool was used to assess evidence quality.

RESULTS

Following full-text screening of 310 relevant papers, 117 were eventually included, incorporating up to 133,000 individuals in each meta-analysis. Higher Tegner activity level (≥ 7 vs < 7) at primary injury (OR 3.91, 95% CI 1.69-9.04), increased tibial slope (degrees) (OR 2.21, 95% CI 1.26-3.86), lower psychological readiness to return to sport (RTS) (OR 2.18, 95% CI 1.32-3.61), early surgery (< 12 vs ≥ 12 months) (OR 1.87, 95% CI 1.58-2.22), RTS (pre-injury level) (OR 1.87, 95% CI 1.21-2.91) and family history of ACL injury (OR 1.76, 95% CI 1.34-2.31) were all associated with increased odds of graft rupture. Higher age (OR 0.47, 95% CI 0.39-0.59), female sex (OR 0.88, 95% CI 0.79-0.98), fewer self-reported knee symptoms pre-reconstruction (OR 0.81, 95% CI 0.69-0.95) and concomitant cartilage injuries (OR 0.70, 95% CI 0.62-0.79) instead decreased the odds. Meta-analysis revealed no association between body mass index, smoking, joint laxity, RTS time, knee kinematics, muscle strength or hop performance and graft rupture.

CONCLUSION

Conspicuous risk factors for graft rupture were mainly sports and hereditary related. Few studies investigated function-related modifiable factors or included sports exposure data.

Asymmetries in Two-Dimensional Trunk and Knee Kinematics During a Single-Leg Drop Landing Post Anterior Cruciate Ligament Reconstruction

The purpose of this study was to compare interlimb asymmetries in trunk and knee kinematics during a single-leg drop landing between athletes 9 months post anterior cruciate ligament reconstruction (post-ACLR) and healthy athletes using two-dimensional analysis. Thirty-three recreational athletes (12 post-ACLR and 21 healthy) participated in the study. Participants post-ACLR showed significantly higher limb symmetry indices in peak trunk flexion (144.0%, SE drop landing kinematics: 22.7%) when compared to healthy participants (100.6%, SE: 10.5%; z = 2.17, p = .03) and lower limb symmetry indices in peak knee flexion (85.3%, SE: 3.6%) when compared to healthy participants (98.0%, SE: 3.3%; z = −2.43, p = .01). Two-dimensional analyses of a single-leg drop landing is a clinically applicable tool that can identify interlimb asymmetries in peak trunk flexion and peak knee flexion kinematics in athletes greater than 9 months post-ACLR when compared to healthy athletes.

Inter-Rater and Intra-Rater Reliability of Return-to-Work Screening Tests for UK Firefighters Following Injury

The aim of this study was to assess the inter-rater and intra-rater reliability of a return-to-work (RTW) screening test to be used on UK firefighters following injury. The inter rater and intra-rater reliability of eight tasks involved in a screening test was used to assess readiness to RTW for UK firefighters following injury. These tasks included the following: (1) putting on and removing a breathing apparatus set (BA), (2) a ladder lift simulation, (3) a ladder carry simulation, (4) a light portable pump (LPP) lift and carry simulation, (5) a hose run, (6) a ladder climb with leg lock, (7) a casualty evacuation and (8) a confined space crawl simulation. The inter-rater reliability between each individual screening task was interpreted as Excellent (ICC = 0.94-1.00) for eleven (68.75%) of the screening task videos and as Good (ICC = 0.75-0.88) for five (31.25%) of the screening task videos. Intra-rater reliability was interpreted as Excellent (ICC = 1) for twenty-six participants (74.3%), Good (ICC = 0.76-0.88) for eight participants (22.9%) and Moderate for one participant (2.8%). Due to the reliability of this screening test, it allows conclusions to be made from the results which can inform a RTW decision for a firefighter.

Changes in the Cross-Sectional Profile of Treated Anterior Cruciate Ligament Within 2 Years After Surgery

Background:

The cross-sectional area (CSA) of the anterior cruciate ligament (ACL) and reconstructed graft has direct implications on its strength and knee function. Little is known regarding how the CSA changes along the ligament length and how those changes vary between treated and native ligaments over time.

Hypothesis:

It was hypothesized that (1) the CSA of reconstructed ACLs and restored ACLs via bridge-enhanced ACL restoration (BEAR) is heterogeneous along the length. (2) Differences in CSA between treated and native ACLs decrease over time. (3) CSA of the surgically treated ACLs is correlated significantly with body size (ie, height, weight, body mass index) and knee size (ie, bicondylar and notch width).

Study Design:

Cohort study; Level of evidence, 2.

Methods:

Magnetic resonance imaging scans of treated and contralateral knees of 98 patients (n = 33 ACL reconstruction, 65 BEAR) at 6, 12, and 24 months post-operation were used to measure the ligament CSA at 1% increments along the ACL length (tibial insertion, 0%; femoral insertion, 100%). Statistical parametric mapping was used to evaluate the differences in CSA between 6 and 24 months. Correlations between body and knee size and treated ligament CSA along its length were also assessed.

Results:

Hamstring autografts had larger CSAs than native ACLs at all time points (P < .001), with region of difference decreasing from proximal 95% of length (6 months) to proximal 77% of length (24 months). Restored ACLs had larger CSAs than native ACLs at 6 and 12 months, with larger than native CSA only along a small midsubstance region at 24 months (P < .001). Graft CSA was correlated significantly with weight (6 and 12 months), bicondylar width (all time points), and notch width (24 months). Restored ACL CSA was significantly correlated with bicondylar width (6 months) and notch width (6 and 12 months).

Conclusion:

Surgically treated ACLs remodel continuously within the first 2 years after surgery, leading to ligaments/grafts with heterogeneous CSAs along the length, similar to the native ACL. While reconstructed ACLs remained significantly larger, the restored ACL had a CSA profile comparable with that of the contralateral native ACL. In addition to size and morphology differences, there were fundamental differences in factors contributing to CSA profile between the ACL reconstruction and BEAR procedures.

Registration:

NCT 02664545 (ClinicalTrials.gov identifier).

Reactive strength index during single-limb vertical continuous jumps after anterior cruciate ligament reconstruction: cross-sectional study

BACKGROUND

The association of the reactive strength index (RSI) during single-limb vertical continuous jumps (SVCJs) with single-limb hop tests in athletes after anterior cruciate ligament reconstruction (ACLR) is unclear. Thus, this study aimed to confirm the measurement properties of the RSI during SVCJs in athletes with ACLR at the phase of determining the timing of their return to sport.

METHODS

RSI during SVCJs and single-limb hop (single, triple, and crossover) tests were measured for post-ACLR and healthy athletes. The limb symmetry index (LSI) was calculated using the measurements of each parameter. For each test, patients were divided into two subgroups according to their LSI score (≥ 90%, satisfactory; < 90%, unsatisfactory). Fisher's exact test was used to examine the association of single-limb hop tests with RSI during the SVCJs.

RESULTS

A total of 21 post-ACLR and 17 healthy athletes completed all the tests. RSI during SVCJs was significantly lower on the involved limb than on the uninvolved limb in post-ACLR athletes (P < 0.001). The LSI of RSI during SVCJs of post-ACLR athletes was significantly lower than that of the healthy athletes (P < 0.01). Among the post-ACLR athletes, < 30% of those with LSIs > 90% in the single-limb hop tests had an LSI > 90% of the RSI during SVCJs.

CONCLUSIONS

RSI during SVCJs of post-ACLR athletes was significantly lower on the involved limb than on the uninvolved limb, and the asymmetry was more remarkable in the SVCJs than in the single-limb hop tests.

Do healthy athletes exhibit at-risk biomechanics for anterior cruciate ligament injury during pivoting movements?

A consistent injury mechanism involving multiple joints has been highlighted in athletes experiencing anterior cruciate ligament (ACL) rupture. However, if and to what extent healthy athletes incur an unsafe biomechanical profile during high-dynamics movements is unknown. The present study aimed to investigate the occurrence of the ACL risk profile in a competitive pivoting sports population.Thirty-four athletes (22.8 ± 4.1 y) performed a frontal deceleration and a change of direction at 90°. Full-body kinematics was collected through 15 wearable inertial sensors (Awinda, Xsens). Nine ACL risk factors were defined based on four categories: limited lower limb flexion, valgus collapse, foot rotation and trunk rotation. A movement trial was considered 'at-risk' in the presence of at least 5 simultaneous risk factors. The rate of athletes with at-risk movements was assessed and multivariate regression for associated outcomes was conducted.The overall rate of injury profile occurrence was 9-12%. The injury profile was identified at least in one trial in 24 athletes (71%) and three trials in 5 athletes (15%). Significant associations were found for higher approaching speed (OR = 4.3) and female sex (OR = 4.8). A large occurrence of the typical ACL injury biomechanical profile was noticed. Large screenings are advisable to identify at-risk athletes and promote preventative strategies.

The effects of curve registration on linear models of jump performance and classification based on vertical ground reaction forces

Functional principal components define modes of variation in time series, which represent characteristic movement patterns in biomechanical data. Their usefulness however depends on the prior choices made in data processing. Recent research showed that better curve alignment achieved with registration (dynamic time warping) reduces errors in linear models predicting jump height. However, the efficacy of registration in different preprocessing combinations, including time normalisation, padding and feature extraction, is largely unknown. A more comprehensive analysis is needed, given the potential value of registration to machine learning in biomechanics. We evaluated popular preprocessing methods combined with registration, creating 512 models based on ground reaction force data from 385 countermovement jumps. The models either predicted jump height or classified jumps into those performed with or without arm swing. Our results show that the classification models benefited from registration in various forms, particularly when landmarks were placed at critical points. The best classifier achieved a 5.5 percentage point improvement over the equivalent unregistered model. However, registration was detrimental to the jump height models, although this performance variable may be a special case given its direct relationship with impulse. Our meta-models revealed the relative contributions made by various preprocessing operations, highlighting that registration does not generalise so well to new data. Nonetheless, our analysis shows the potential for registration in further biomechanical applications, particularly in classification, when combined with the other appropriate preprocessing operations.

Impaired Stretch-Shortening Cycle Function Persists Despite Improvements in Reactive Strength After Anterior Cruciate Ligament Reconstruction

ABSTRACT

Read, PJ, Pedley, JS, Eirug, I, Sideris, V, and Oliver, JL. Impaired stretch-shortening cycle function persists despite improvements in reactive strength followingafter anterior cruciate ligament reconstruction. J Strength Cond Res 36(5): 1238-1244, 2022-Reactive strength index (RSI) during a single-leg drop jump (SLDJ) has been indicated to determine return-to-sport readiness after anterior cruciate ligament (ACL) reconstruction, but only cross-sectional studies are available. Ground reaction force data and characterization of stretch-shortening cycle (SSC) function also remain sparse. Single-leg drop jump performance, ground reaction force, and SSC function were examined in soccer players with ACL reconstruction (n = 26) and matched controls (n = 25). Injured players were tested at 2 time points (32 and 42 weeks postsurgery). Stretch-shortening cycle function was classified as good (no impact peak and spring like), moderate (impact peak but still spring like or no impact peak and not spring like), or poor (impact peak and not spring like). The involved limb displayed lower-jump height, poorer RSI, less spring-like behavior, earlier peak landing force, and a greater ratio of landing peak to take-off peak force compared with the uninvolved limb and controls at the initial assessment (p < 0.001). Proportionally, more involved limbs were categorized as poor or moderate at the initial assessment (69.2%) and follow-up (50%) in comparison with the control limbs (14%). The reactive strength index was the only variable to change significantly between the initial assessment and follow-up on the involved limb (p < 0.05). No changes in the proportion of ACL reconstructed individuals categorized as poor or moderate SSC function at the follow-up assessment were observed. Residual deficits are present in SLDJ performance, SSC function, and ground reaction force characteristics after ACL reconstruction. The reactive strength index should not be the sole metric, as observed increases did not correspond with changes in SSC function.

Application of the 4-Element Movement System Model to Sports Physical Therapy Practice and Education

The 4-Element Movement System Model describes primary elements (motion, force, motor control, and energy) essential to the performance of all movements. The model provides a framework or scaffolding which allows for consistent processes to be used in examination and intervention decisions. The process starts with task identification followed by a systematic observation of control, amount, speed, symmetry, and symptoms during movement. Testable hypotheses are generated from the observations which inform the examination and the interventions. This commentary describes the use of the 4-Element Movement System Model in entry level and post-graduate residency educational programs and in clinical care with three common sports-related diagnoses.

LEVEL OF EVIDENCE

5.

Rehabilitation and Return to Sport Testing After Anterior Cruciate Ligament Reconstruction: Where Are We in 2022?

Athletes who sustain an anterior cruciate ligament (ACL) injury often opt for an ACL reconstruction (ACLR) with the goal and expectation to return to sports at the preinjury level. The proportion of athletes who successfully return to preinjury-level sport is low and disappointing, whereas the rate of second ACL injury in athletes under the age of 20 has been reported to be as high as 40% after return to sport (RTS). Although in recent years, new insights pertaining to RTS have been published, the lack of validity of RTS criteria after ACLR remain. The purpose of this clinical commentary is to present a critical overview of the current literature on RTS testing after ACLR.

Think outside the box: Incorporating secondary cognitive tasks into return to sport testing after ACL reconstruction

The optimal set of return to sport (RTS) tests after anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) remains elusive. Many athletes fail to pass current RTS test batteries, fail to RTS, or sustain secondary ACL injuries if they do RTS. The purpose of this review is to summarize current literature regarding functional RTS testing after ACLR and to encourage clinicians to have patients "think" (add a secondary cognitive task) outside the "box" (in reference to the box used during the drop vertical jump task) when performing functional RTS tests. We review important criteria for functional tests in RTS testing, including task-specificity and measurability. Firstly, tests should replicate the sport-specific demands the athlete will encounter when they RTS. Many ACL injuries occur when the athlete is performing a dual cognitive-motor task (e.g., attending to an opponent while performing a cutting maneuver). However, most functional RTS tests do not incorporate a secondary cognitive load. Secondly, tests should be measurable, both through the athlete's ability to complete the task safely (through biomechanical analyses) and efficiently (through measures of performance). We highlight and critically examine three examples of functional tests that are commonly used for RTS testing: the drop vertical jump, single-leg hop tests, and cutting tasks. We discuss how biomechanics and performance can be measured during these tasks, including the relationship these variables may have with injury. We then discuss how cognitive demands can be added to these tasks, and how these demands influence both biomechanics and performance. Lastly, we provide clinicians with practical recommendations on how to implement secondary cognitive tasks into functional testing and how to assess athletes' biomechanics and performance.

A 2D video-analysis scoring system of 90° change of direction technique identifies football players with high knee abduction moment

PURPOSE

Abnormal joint biomechanics and poor neuromuscular control are modifiable risk factors for Anterior Cruciate Ligament (ACL) injury. Although 3D motion capture is the gold standard for the biomechanical evaluation of high-speed multidirectional movements, 2D video analysis is a growing-interest alternative because of its higher cost-effectiveness and interpretability. The aim of the present study was to explore the possible association between a 2D evaluation of a 90° change of direction (COD) and the KAM measured with gold standard 3D motion analysis.

METHODS

Thirty-four competitive football (soccer) players (age 22.8 ± 4.1, 18 male and 16 females) were enrolled. Each athlete performed a series of pre-planned 90° COD at the maximum speed possible in a laboratory equipped with artificial turf. 3D motion analysis was recorded using 10 stereophotogrammetric cameras, a force platform, and three high-speed cameras. The 2D evaluation was performed through a scoring system based on the video analysis of frontal and sagittal plane joint kinematics. Five scoring criteria were adopted: limb stability (LS), pelvis stability (PS), trunk stability (TS), shock absorption (SA), and movement strategy (MS). For each criterion, a sub-score of 0/2 (non-adequate), 1/2 (partially adequate), or 2/2 (adequate) was attributed to the movement, based on objective measurements. The intra-rater and inter-rater reliability were calculated for each criterion and the total score. The Knee Abduction Moment (KAM) was extracted from the 3D motion analysis and grouped according to the results of the 2D evaluation.

RESULTS

Excellent intra-rater reliability (ICC > 0.88) and good-to-excellent inter-rater reliability (ICC 0.68-0.92) were found. Significantly higher KAM was found for athletes obtaining a 0/2 score compared to those obtaining a 2/2 score in all the sub-criteria and the total score (20-47% higher, p < 0.05). The total score and the LS score showed the best discriminative power between the three groups.

CONCLUSION

The 2D video-analysis scoring system here described was a simple and effective tool to discriminate athletes with high and low KAM in the assessment of a 90° COD and could be a potential method to identify athletes at high risk of non-contact ACL injury.

LEVEL OF EVIDENCE

IV.

Whole-Body Reactive Agility Metrics to Identify Football Players With a Core and Lower Extremity Injury Risk

Clinical prediction models are useful in addressing several orthopedic conditions with various cohorts. American football provides a good population for attempting to predict injuries due to their relatively high injury rate. Physical performance can be assessed a variety of ways using an assortment of different tests to assess a diverse set of metrics, which may include reaction time, speed, acceleration, and deceleration. Asymmetry, the difference between right and left performance has been identified as a possible risk factor for injury. The purpose of this study was to determine the whole-body reactive agility metrics that would identify Division I football players who were at elevated risk for core, and lower extremity injuries (CLEI). This cohort study utilized 177 Division I football players with a total of 57 CLEI suffered who were baseline tested prior to the season. Single-task and dual-task whole-body reactive agility movements in lateral and diagonal direction reacting to virtual reality targets were analyzed separately. Receiver operator characteristic (ROC) analyses narrowed the 34 original predictor variables to five variables. Logistic regression analysis determined the three strongest predictors of CLEI for this cohort to be: lateral agility acceleration asymmetry, lateral flanker deceleration asymmetry, and diagonal agility reaction time average. Univariable analysis found odds ratios to range from 1.98 to 2.75 for these predictors of CLEI. ROC analysis had an area under the curve of 0.702 for any combination of two or more risk factors produced an odds ratio of 5.5 for risk of CLEI. These results suggest an asymmetry of 8-15% on two of the identified metrics or a slowed reaction time of ≥0.787 s places someone at increased risk of injury. Sixty-three percent (36/57) of the players who sustained an injury had ≥2 positive predictors In spite of the recognized limitation, these finding support the belief that whole-body reactive agility performance can identify Division I football players who are at elevated risk for CLEI.

Current perspectives and clinical practice of physiotherapists on assessment, rehabilitation, and return to sport criteria after anterior cruciate ligament injury and reconstruction. An online survey of 538 physiotherapists

OBJECTIVES

To evaluate the perspectives and clinical practice of physiotherapists regarding rehabilitation after anterior cruciate ligament reconstruction (ACLR).

DESIGN

Online survey.

SETTING

Survey platform.

PARTICIPANTS

Greek physiotherapists.

OUTCOME MEASURES

The survey consisted of 7 sections: participant demographics, importance of ACLR rehabilitation, clinical measurements, practice, criteria to progress rehabilitation, return to running and return to sport.

RESULTS

Significant variability in measures and criteria used for clinical decision-making were found including: limb symmetry in strength and function, knee range of motion and effusion, progression, and return to sport criteria. The majority of the practitioners (28.3%) extrapolate knee strength from hop capacity. Return to running ranged from 3 to 5 months post-operatively reflecting that this was tied to physical capacities, not time from surgery. 70.0% of the Greek physiotherapists would allow return to sport ≤9 months after ACLR. Agreement was found in using: physical measures, function, and dynamic stability in ACLR rehabilitation, but the mode and interpretation varied substantially. Less than 29.0% of the physiotherapists reported using patient-reported outcome measures in their decision-making.

CONCLUSION

Current ACLR rehabilitation practices in Greece are largely not aligned with the contemporary scientific evidence and guidelines.

Combining Inertial Sensors and Machine Learning to Predict vGRF and Knee Biomechanics during a Double Limb Jump Landing Task

(1) Background: Biomechanics during landing tasks, such as the kinematics and kinetics of the knee, are altered following anterior cruciate ligament (ACL) injury and reconstruction. These variables are recommended to assess prior to clearance for return to sport, but clinicians lack access to the current gold-standard laboratory-based assessment. Inertial sensors serve as a potential solution to provide a clinically feasible means to assess biomechanics and augment the return to sport testing. The purposes of this study were to (a) develop multi-sensor machine learning algorithms for predicting biomechanics and (b) quantify the accuracy of each algorithm. (2) Methods: 26 healthy young adults completed 8 trials of a double limb jump landing task. Peak vertical ground reaction force, peak knee flexion angle, peak knee extension moment, and peak sagittal knee power absorption were assessed using 3D motion capture and force plates. Shank- and thigh- mounted inertial sensors were used to collect data concurrently. Inertial data were submitted as inputs to single- and multiple- feature linear regressions to predict biomechanical variables in each limb. (3) Results: Multiple-feature models, particularly when an accelerometer and gyroscope were used together, were valid predictors of biomechanics (R² = 0.68–0.94, normalized root mean square error = 4.6–10.2%). Single-feature models had decreased performance (R² = 0.16–0.60, normalized root mean square error = 10.0–16.2%). (4) Conclusions: The combination of inertial sensors and machine learning provides a valid prediction of biomechanics during a double limb landing task. This is a feasible solution to assess biomechanics for both clinical and real-world settings outside the traditional biomechanics laboratory.

Poor Motor Coordination Elicits Altered Lower Limb Biomechanics in Young Football (Soccer) Players: Implications for Injury Prevention through Wearable Sensors

Motor coordination and lower limb biomechanics are crucial aspects of anterior cruciate ligament (ACL) injury prevention strategies in football. These two aspects have never been assessed together in real scenarios in the young population. The present study aimed to investigate the influence of motor coordination on lower limb biomechanics in young footballers during an on-the-pitch training. Eighteen juvenile football players (10 y ± 2 m) were enrolled. Each player performed a training drill with sport-specific movements (vertical jump, agility ladders, change of direction) and the Harre circuit test (HCT) to evaluate players' motor coordination. Wearable inertial sensors (MTw Awinda, Xsens) were used to assess lower limb joint angles and accelerations. Based on the results of the HCT, players were divided into poorly coordinated (PC) and well-coordinated (WC) on the basis of the literature benchmark. The PC group showed a stiffer hip biomechanics strategy (up to 40% lower flexion angle, ES = 2.0) and higher internal-external hip rotation and knee valgus (p < 0.05). Significant biomechanical limb asymmetries were found only in the PC group for the knee joint (31-39% difference between dominant and non-dominant limb, ES 1.6-2.3). Poor motor coordination elicited altered hip and knee biomechanics during sport-specific dynamic movements. The monitoring of motor coordination and on-field biomechanics might enhance the targeted trainings for ACL injury prevention.

Rehabilitation and Return to Sport Assessment after Anterior Cruciate Ligament Injury: Quantifying Joint Kinematics during Complex High-Speed Tasks through Wearable Sensors

The aim of the present study was to quantify joint kinematics through a wearable sensor system in multidirectional high-speed complex movements used in a protocol for rehabilitation and return to sport assessment after Anterior Cruciate Ligament (ACL) injury, and to validate it against a gold standard optoelectronic marker-based system. Thirty-four healthy athletes were evaluated through a full-body wearable sensor (MTw Awinda, Xsens) and a marker-based optoelectronic (Vicon Nexus, Vicon) system during the execution of three tasks: drop jump, forward sprint, and 90° change of direction. Clinically relevant joint angles of lower limbs and trunk were compared through Pearson’s correlation coefficient (r), and the Coefficient of Multiple Correlation (CMC). An excellent agreement (r > 0.94, CMC > 0.96) was found for knee and hip sagittal plane kinematics in all the movements. A fair-to-excellent agreement was found for frontal (r 0.55–0.96, CMC 0.63–0.96) and transverse (r 0.45–0.84, CMC 0.59–0.90) plane kinematics. Movement complexity slightly affected the agreement between the systems. The system based on wearable sensors showed fair-to-excellent concurrent validity in the evaluation of the specific joint parameters commonly used in rehabilitation and return to sport assessment after ACL injury for complex movements. The ACL professionals could benefit from full-body wearable technology in the on-field rehabilitation of athletes.