BACKGROUND:Anterior cruciate ligament reconstruction (ACLR) is often recommended for treatment of an ACL injury; however, the literature reports similar outcomes for those undergoing rehabilitation alone. We assessed the clinical, functional, sports participation, and osteoarthritis outcomes following our treatment algorithm, and compared 10-year outcomes among participants who chose progressive rehabilitation alone, early ACLR, or delayed ACLR. METHODS:We included 276 participants who had a unilateral ACL injury without substantial concomitant knee injuries in a prospective cohort study. Treatment choice was based on shared decision-making after a 5-week progressive rehabilitation program. At the 10-year follow-up, we assessed patient-reported outcomes (International Knee Documentation Committee Subjective Knee Form [IKDC-SKF], Knee injury and Osteoarthritis Outcome Score [KOOS], and patient acceptable symptom state [PASS] achievement), quadriceps strength, hop performance, sports participation, and weight-bearing radiographs. RESULTS:Sixty-nine percent of the participants (191 participants; 99 male and 92 female; 6 African American, 7 Asian, 59 Caucasian, 119 unknown) attended the 10-year follow-up, including 98% (53) of 54 participants who had rehabilitation alone, 68% (114) of 167 with early ACLR, and 69% (24) of 35 with delayed ACLR. Among the entire cohort, 78% (126 of 162) reported having a PASS, 72% (109 of 151) had symmetrical quadriceps strength, ≥85% (≥116 of ≤137) had a symmetrical hop performance, 93% (162 of 174) were still engaged in some kind of sports, only 1% (1 of 139) had symptomatic osteoarthritis, and 12% (17 of 139) had radiographic evidence of osteoarthritis. We found similar outcomes after rehabilitation alone and early ACLR. The participants who underwent delayed ACLR had similar outcomes to the other 2 groups except for significantly lower KOOS Sports scores, KOOS Quality of Life scores, and hop performance (p ≤ 0.03). Participants who had rehabilitation alone were older, less active, and more likely to have concomitant lateral meniscal injuries than those who underwent ACLR. CONCLUSIONS:Participants who followed our treatment algorithm after ACL injury had high percentages of satisfaction and of symmetrical quadriceps strength and hop performance, high sports participation rates, and low prevalences of osteoarthritis. Participants who chose progressive rehabilitation alone, despite being older and less active, had similar clinical, functional, sports participation, and osteoarthritis outcomes compared with those who chose early ACLR. Participants who underwent delayed ACLR scored lower on KOOS Sports, KOOS Quality of Life, and hop performance compared with both other groups. LEVEL OF EVIDENCE:Therapeutic Level II . See Instructions for Authors for a complete description of levels of evidence.

Background: Anterior cruciate ligament reconstruction (ACLR) often involves harvesting a bone–patellar tendon–bone (BPTB) autograft. How graft harvest affects tendon strain across the 3 distinct regions (medial, lateral, and central) is not known. Purpose: To (1) quantify strain in the 3 regions of the patellar tendon during 60% of maximum voluntary isometric contraction (MVIC) in 90° of knee flexion and (2) assess how effort level in 2 different knee joint angles (60° and 90°) impacts strain in the medial and lateral regions of the patellar tendon, in 2 cohorts of patients after ACLR using a BPTB autograft (one group <24 months after surgery and another group ≥24 months after surgery). Study Design: Descriptive laboratory study. Methods: Effort levels ranging from 20% to 100% of MVIC were performed at 90° and 60° of knee flexion on an isokinetic dynamometer, with simultaneous ultrasound imaging of tendon length to calculate regional strain. Linear mixed-effects models were used to evaluate regional strain at 60% of MVIC in 90° of knee flexion. The fixed effects of percentage of MVIC, joint angles, and time from surgery groups on patellar tendon strain were evaluated using separate models for the medial and lateral regions. Results: Fourteen participants in the short-term group (7.5 ± 1.9 months from surgery) and 15 participants in the long-term group (71.5 ± 16.5 months from surgery) were included. At 60% of MVIC in 90° of knee flexion, the short-term group demonstrated lower patellar tendon strain than the long-term group regardless of region ( P < .01). The central region also had lower strain than the medial and lateral regions regardless of group (both P < .01). Finally, the rate at which strain increased with increasing effect levels differed between time from surgery groups in both medial and lateral regions. Conclusion: The short-term group had lower strain in all regions of the patellar tendon after ACLR using BPTB autograft. The medial and lateral regions showed varying strain based on time from surgery and effort level. Varying knee joint angles and effort levels for graft site rehabilitation may have to be considered to target specific regions of the patellar tendon. Clinical Relevance: Clinicians should consider the time elapsed since surgery and the manipulation of knee angle as factors that can exert varying levels of strain on different regions of the patellar tendon after ACLR. Accelerating quadriceps strengthening to enhance strain distribution across the patellar tendon to promote tendon healing may be of benefit for optimizing postsurgery rehabilitation.

ABSTRACT Patellar tendinopathy is more prevalent in males versus female athletes and commonly presents in the medial region of the tendon. Separate measures of patellar tendon strain in the medial, central, and lateral regions of the tendon, however, have not been quantified. The purpose was to investigate the differences in tendon strain between the medial, lateral, and central regions of the patellar tendon in healthy men and women. Strain in the medial and lateral regions of the patellar tendon in healthy participants (10 males, 10 females) was evaluated using ultrasound during isometric quadriceps contractions at 20%, 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVIC) in 60° and 90° of knee flexion. Central strain was also measured at 60% MVIC in 90° of knee flexion. Mixed models were used to determine strain between tendon regions and sex at 60% MVIC in 90° of knee flexion. Sequential modeling was used to fit region, sex, %MVIC, and angle to predict strain. The central region had less strain compared with both medial and lateral regions. The lateral region had higher strain compared with the medial region regardless of sex. Females had higher strain compared with males, regardless of region. Knee position did not influence tendon strain. Patellar tendon strain differs by region and sex. The varying prevalence between sex and in location of patellar tendinopathy may in part be explained by the unbalanced strains. Differential assessment of regional patellar tendon strain may be of importance for understanding injury risk and recovery with exercise.

BACKGROUND: Restoring quadriceps strength is essential for successful rehabilitation of knee injuries, but many athletes return to their previous activity with persisting muscle weakness. Strong evidence supports using neuromuscular electrical stimulation (NMES) to improve quadriceps strength, however, there is a lack of widespread clinical implementation. We believe there is a critical need to provide clinical approaches that promote using NMES to improve patients' quadriceps strength and ensuring clinicians provide high-value rehabilitation care. CLINICAL QUESTION: What is best practice when using NMES to facilitate strength after injury, what are barriers to its use, and how can they be addressed? KEY RESULTS: We discuss the low clinical implementation of NMES, perceived barriers to using NMES, and provide recommendations for set-up and dosage parameters for effective use of NMES. CLINICAL APPLICATION: We aim for this commentary, with accompanying videos, to serve as a resource for clinicians who are using commercially-available NMES units in clinical practice.

Graft site morbidities after bone-patellar tendon-bone (BPTB) autograft harvest for anterior cruciate ligament reconstruction (ACLR) negatively impacts rehabilitation. The purpose of this study was to establish tendon structural properties 1-month after BPTB autograft harvest compared to the uninvolved patellar tendon, and subsequently to quantify the healing trajectory of the patellar tendon over the course of rehabilitation. Patellar tendon morphology (ultrasound) and mechanical properties (continuous shear wave elastography) from 3 regions of the tendon (medial, lateral, central) were measured in 34 participants at 1 month, 3-4 months, and 6-9 months after ACLR. Mixed models were used to compare tendon structure between limbs at 1 month, and quantify healing over 3 timepoints. The involved patellar tendon had increased cross-sectional area and thickness in all regions 1-month after ACLR. Thickness reduced uniformly over time. Possible tendon elongation was observed and remained stable over time. Tendon viscosity was uniform across the three regions in the involved limb while the medial region had higher viscosity in the uninvolved limb, and shear modulus was elevated in all three regions at 1 month. Viscosity and shear modulus in only the central region reduced over time. Statement of Clinical Significance: The entire patellar tendon, and not just the central third, is altered after graft harvest. Tendon structure starts to normalize over time, but alterations remain especially in the central third at the time athletes are returning to sport. Early rehabilitation consisting of tendon loading protocols may be necessary to optimize biologic healing at the graft site tendon.

BACKGROUND:The purpose was to explore quadriceps electromechanical function (quadriceps latency) during gait after anterior cruciate ligament injury as a predictor for radiographic knee osteoarthritis 6-years after anterior cruciate ligament reconstruction. Change in latency after preoperative physical therapy was also examined. METHODS:Quadriceps latency (time between peak knee moment and quadriceps electromyography) was calculated before preoperative physical therapy (2.4 [0.5-7.5] months after anterior cruciate ligament injury) and after preoperative physical therapy in 24 athletes. Participants were dichotomized into osteoarthritis (Kellgren and Lawrence grade ≥ 2) and non-osteoarthritis groups at 6-years. Forward selection logistic regression was performed using z-score normalized quadriceps latency and demographics. A 2 × 2 repeated measure ANOVA was performed for quadriceps latency between groups before and after preoperative physical therapy. FINDINGS:Quadriceps latency before preoperative physical therapy was the only predictor of 6-year radiographic osteoarthritis (p = 0.014, odds ratio [95% confidence interval] = 5.859 [1.435-23.924]). Time by group interaction was observed for quadriceps latency (p = 0.039, η2p = 0.179). In the osteoarthritis group, latency may reduce after training (before preoperative physical therapy = 115.7 ± 20.6 ms, after preoperative physical therapy = 99.5 ± 24.0 ms, p = 0.082). INTERPRETATION:Prolonged latency after anterior cruciate ligament injury may predict post-traumatic knee osteoarthritis 6-years after anterior cruciate ligament reconstruction. Latency may shorten with preoperative physical therapy, yet athletes still moved on to develop osteoarthritis. Quadriceps function may need intervention immediately following anterior cruciate ligament injury for prevention of post-traumatic knee osteoarthritis.

# Background Landing with poor knee sagittal plane biomechanics has been identified as a risk factor for Anterior Cruciate Ligament (ACL) injury. However, it is unclear if the horizontal hop test battery reflects knee function and biomechanics. # Hypothesis/Purpose To investigate the correlation between clinical limb symmetry index (LSI) and landing and propulsion knee biomechanics during the hop test battery using markerless motion capture. # Study Design Cross-sectional biomechanics laboratory study # Methods Forty-two participants with and without knee surgery (age 28.0 ± 8.0 years) performed the hop test battery which consisted of a single hop for distance, crossover hop, triple hop, and 6-m timed hop in the order listed. Eight high speed cameras were used to collect simultaneous 3D motion data and Theia 3D (Theia Markerless Inc.) was used to generate 3D body model files. Lower limb joint kinematics were calculated in Visual3D. Correlation (Spearman’s ρ) was computed between clinical LSI and symmetry in peak and initial contact (IC) knee flexion angle during propulsion and landing phases of each movement. # Results In the single hop, clinical LSI showed positive correlation with kinematic LSI at peak landing (ρ= 0.39, p=0.011), but no correlation at peak propulsion (ρ= -0.03, p=0.851). In the crossover hop, non-significant correlations were found in both propulsion and landing. In the triple hop, positive correlation was found at peak propulsion (ρ= 0.38, p=0.027), peak landing (ρ= 0.48 – 0.66, p<0.001), and last landing IC (ρ= 0.45, p=0.009). In the timed hop, peak propulsion showed positive correlation (ρ= 0.51, p=0.003). # Conclusions Single hop and triple hop distance symmetry reflected landing biomechanical symmetry better than propulsion symmetry. Poor scores on the hop test battery reflect asymmetrical knee landing biomechanics, emphasizing the importance of continuing to use the hop test battery as part of clinical decision making. # Level of Evidence 3b

To examine the clinical outcomes and return to sport rates after treatment of combined, complete (grade III) injuries of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL).A literature search of the following databases was completed using key words related to combined ACL and (MCL) tears: MEDLINE, Embase, Cochrane Controlled Trials Register, Cochrane Database of Systematic Reviews, Cumulative Index to Nursing and Allied Health Literature, and SPORTDiscus. Level I-IV studies that examined patients with complete tears of the ACL and grade III tears of the MCL, diagnosed by either magnetic resonance imaging or clinical examination of valgus instability, were included. Study inclusion was determined by 2 independent reviewers. Patient demographics, treatment choices, and patient outcomes, including clinical examination (i.e., range of motion, hamstring strength) and subjective assessments (i.e., International Knee Documentation Committee, Lysholm scores, Tegner activity scores) were collected.Six possible treatment combinations were assessed. Good or excellent outcomes related to range of motion, knee stability, subjective assessments, and return to play were reported after ACL reconstruction regardless of MCL treatment. Those with combined ACL and MCL reconstruction returned to their previous level of activity at a high rate (range, 87.5%-90.6%) with low rates of recurrent valgus instability. Triangular MCL reconstruction with a posterior limb that serves to reconstruct the posterior-oblique ligament best-restored anteromedial rotatory stability of the knee when compared with anatomic MCL reconstruction (90.6% and 65.6%, respectively). Nonsurgical management of the ACL injury, regardless of MCL treatment, demonstrated low return to activity (29%) and frequent secondary knee injuries.High rates of return to sport with low risk of recurrent valgus instability have been demonstrated after MCL reconstruction, and triangular MCL reconstruction can more effectively restore anteromedial rotatory instability compared with MCL repair. Restoration of valgus stability can be common after reconstruction of the ACL with or without surgical management of the MCL, although patients with grade III tibial-sided or mid-substance injuries were less likely to regain valgus stability with nonoperative treatment than femoral-sided injuries.Level IV; systematic review of Level I-IV studies.

Patellar tendons are assumed to be uniform in morphology and mechanical properties despite a higher prevalence of tendinopathies observed in the medial region. The purpose of this study was to compare the thickness, length, viscosity, and shear modulus of the medial, central, and lateral regions of healthy patellar tendons of young males and females in vivo. B-mode ultrasound and continuous shear wave elastography were performed on 35 patellar tendons (17 females, 18 males) over three regions of interest. A linear mixed-effects model (α = 0.05) was used to determine differences between the three regions and sexes followed by pairwise comparisons for significant findings. The lateral region (mean [95% confidence interval] = 0.34 [0.31-0.37] cm) was thinner compared with the medial (0.41 [0.39-0.44] cm, p < 0.001), and central (0.41 [0.39-0.44] cm, p < 0.001) regions regardless of sex. Viscosity was lower in the lateral (19.8 [16.9-22.7] Pa-s) versus medial region (27.4 [24.7-30.2] Pa-s, p = 0.001). Length had a region-by-sex interaction (p = 0.003) characterized by a longer lateral (4.83 [4.54-5.13] cm) versus medial (4.42 [4.12-4.72] cm) region in males (p < 0.001), but not females (p = 0.992). Shear modulus was uniform between regions and sexes. The thinner, and less viscous lateral patellar tendon may reflect the lower load the tendon experiences explaining the differences in regional prevalence of developing tendon pathology. Statement of Clinical Significance: Healthy patellar tendons are not uniform in morphology or mechanical properties. Considering regional tendon properties may help guide targeted interventions for patellar tendon pathologies.

Purpose: Many young adults develop knee osteoarthritis (OA) and have poor knee function long-term after an anterior cruciate ligament (ACL) injury, regardless of treatment with ACL reconstruction (ACLR) or rehabilitation alone. There is a need to investigate how to provide better outcomes. We aimed to describe 10-year radiographic and symptomatic knee OA, patient-reported symptoms, and function in participants who followed the Delaware-Oslo ACL cohort treatment algorithm. We further aimed to compare outcomes between participants who chose early (<6 months) ACLR with pre- and postoperative rehabilitation, delayed (>6 months) ACLR with pre- and postoperative rehabilitation, and progressive rehabilitation alone.

# Background The Basas Spanish Squat with electrical stimulation (E-stim) has shown promising results as a potential key exercise in treatment of athletes with patellar tendinopathy. Gold standard exercise therapy for tendon injuries consists of tendon loading exercises, or exercises that appropriately applies high levels of mechanical strain to the tendon. The theoretical pathway in which the Basas Spanish Squat with E-stim improves tendinopathy has been speculated to be the additional strain applied through the patellar tendon during superimposition of E-stim. This theory, however, has yet to be confirmed. # Purpose The purpose of this case series was to compare patellar tendon strain, during the Basas Spanish Squat with, and without E-stim, and open kinetic chain knee extension. # Methods Four healthy participants performed the three exercises while a physical therapist collected simultaneous unilateral ultrasound images from the patellar tendon. Strain was calculated as the change in patellar tendon length during contraction divided by the resting length. # Results Amongst all participants, patellar tendon strain was smallest during the Basas Spanish Squat without E-stim, followed by the open kinetic chain knee extension at 60% maximum voluntary isometric contraction. The Basas Spanish Squat with E-stim yielded approximately double or more strain compared to the without E-stim condition and demonstrated higher level of strain compared to open kinetic chain knee extension in all participants. # Conclusion The findings reflect a clear trend of increased strain through the patellar tendon when E-stim was superimposed. The results support the theory that the Basas Spanish Squat with E-stim increases patellar tendon strain and could explain the reported clinical benefits in individuals with patellar tendinopathy. # Level of Evidence 4, Case series

Quadriceps dysfunction is ubiquitous after anterior cruciate ligament reconstruction, especially when using bone-patellar tendon-bone (BPTB) autografts. The role of patellar tendon hypertrophy after graft harvest on knee extensor strength is unknown. The purpose of this study was to determine the predictive ability of patellar tendon (PT) and quadriceps muscle (Quad) cross-sectional area (CSA) on knee extensor strength 1–2 months after ACLR using BPTB autografts. This is a cross-sectional analysis of a cohort 1–2 months after ACLR using BPTB autograft. Peak knee extensor torque, and PT and Quad CSA measured using ultrasound imaging, were collected in 13 males and 14 females. Simple linear regressions compared quadriceps strength index (QI) against limb symmetry index (LSI) in PT and Quad CSA. Multiple linear regressions with sequential model comparisons predicting peak knee extensor torque were performed for each limb. The base model included demographics. Quad CSA was added in the first model, then PT CSA was added in the second model. Both PT (p < 0.001, R2 = 0.693) and Quadriceps CSA (p = 0.013, R2 = 0.223) LSI had a positive linear relationship with QI. In the involved limb, addition of PT CSA significantly improved the model (R2 = 0.781, ΔR2 = 0.211, p for ΔR2 < 0.001). In the uninvolved limb, the addition of Quad CSA improved the model, but the addition of PT CSA did not. PT LSI was more predictive of QI than Quad CSA LSI. Involved limb PT CSA mattered more in predicting peak knee extensor torque than did Quad CSA, but in the uninvolved limb, Quad CSA was the most important predictor of peak knee extensor torque. Graft site patellar tendon hypertrophy is key for strong quadriceps early after ACLR. Early targeted loading via exercise to promote healing of the graft site patellar tendon may bring patients a step closer to winning their battle against quadriceps dysfunction. Level I.

ABSTRACT Purpose Bone–patellar tendon–bone (BPTB) graft harvest for anterior cruciate ligament reconstruction alters patellar tendon properties, which inflict poor quadriceps neuromuscular function. BPTB autografts are associated with higher rates of posttraumatic osteoarthritis, which in turn is associated with pathological gait. The purpose of this study was to investigate the latency between the time of peak quadriceps activity and the peak knee flexion moment during gait, between those with BPTB grafts (n = 23) and other graft types (hamstring autograft or allografts, n = 54), 5 ± 2 months and 2 yr (25 ± 3 months) after anterior cruciate ligament reconstruction. We hypothesized that longer latencies would be observed in the BPTB graft group in the involved limb. We expected latencies to shorten over time. Methods Knee moments and quadriceps EMG were collected during gait, and vastus medialis, vastus lateralis, rectus femoris (RF), and quadriceps latencies were calculated. Linear mixed-effects models were used to compare latencies between graft types and over the two time points. Results The main effects of graft type were observed for vastus medialis (P = 0.005) and quadriceps (P = 0.033) latencies with the BPTB graft group demonstrating longer latencies. No main effects of graft type were observed for vastus lateralis (P = 0.051) and RF (P = 0.080) latencies. Main effects of time were observed for RF latency (P = 0.022). Conclusions Our hypothesis that the BPTB graft group would demonstrate longer extensor latency was supported. Contrary to our second hypothesis, however, latency only improved in RF and regardless of graft type, indicating that neuromuscular deficits associated with BPTB grafts may persist 2 yr after surgery. Persistent deficits may be mediated by changes in the patellar tendon’s mechanical properties. Graft-specific rehabilitation may be warranted to address the long-term neuromechanical deficits that are present after BPTB graft harvest.

Markerless motion capture (mocap) could be the future of motion analysis. The purpose of this report was to describe our team of clinicians and scientists’ exploration of markerless mocap (Theia 3D) and share data for others to explore (link: https://osf.io/6vh7z/?view_only=c0e00984e94a48f28c8d987a2127339d). Simultaneous mocap was performed using markerless and marker-based systems for walking, squatting, and forward hopping. Segment lengths were more variable between trials using markerless mocap compared to marker-based mocap. Sagittal plane angles were most comparable between systems at the knee joint followed by the ankle and hip. Frontal and transverse plane angles were not comparable between systems. The data collection experience using markerless mocap was simpler, faster, and user friendly. The ease of collection was in part offset by the added data transfer and processing times, and the lack of troubleshooting flexibility. If used selectively with proper understanding of limitations, markerless mocap can be exciting technology to advance the field of motion analysis.

ABSTRACT Purpose Asymmetrical gait mechanics after anterior cruciate ligament reconstruction (ACLR) are associated with the development of posttraumatic knee osteoarthritis. Current measures of gait mechanics have focused heavily on peak magnitudes of knee kinematics, kinetics, and joint contact forces but have seldom considered the rate of knee loading, cumulative knee load, or the timing of motor input surrounding peaks. The purpose of this study was to introduce and describe novel metrics of gait using temporal characteristics of kinetics and EMG to identify neuromuscular deficits of the quadriceps in patients after ACLR. Methods Gait mechanics were assessed 6 months (n = 145) and 24 months (n = 116) after ACLR. External knee flexion rate of moment development (RMD) and knee flexion moment impulse (KFMI) leading up to the time of peak knee flexion moment (pKFM), peak RMD between initial contact to pKFM, and cumulative KFMI were calculated. Extensor latencies from the quadriceps, vastus medialis, vastus lateralis, and rectus femoris (time of pKFM – time of peak EMG activity) during the weight acceptance phase of gait were also calculated. Paired-sample t-tests (α = 0.05) were performed between limbs at both time points. Results Slower RMD, smaller KFMI, and longer extensor latencies in the involved compared with uninvolved limb were observed across all measures at 6 months (P < 0.005). At 24 months, RMDpeak was slower, and KFMI50ms, KFMI100ms, and KFMItotal were lower in the involved limb (P < 0.003), but no other asymmetries were found. Conclusions Slower RMD, smaller KFMI, and prolonged extensor latencies may characterize neuromuscular deficits underlying aberrant gait mechanics early after ACLR. RMD, KFMI, and extensor latencies during gait should be considered in the future to quantify asymmetrical movement patterns observed after ACLR and as markers of recovery.

OBJECTIVES:Patellar tendon injuries occur via various mechanisms such as overuse, or due to surgical graft harvest for anterior cruciate ligament reconstruction (ACLR). Quantified patellar tendon stiffness after injury may help guide clinical care. Continuous shear wave elastography (cSWE) allows for the assessment of viscosity and shear modulus in tendons. The reliability of the measure, however, has not been established in the patellar tendon. The purpose of this study was to investigate the interrater reliability, intrarater reliability, and between-day stability of cSWE in both healthy and pathological patellar tendons.METHODS:Participants with patellar tendinopathy (n = 13), history of ACLR using bone-patellar tendon-bone autograft (n = 9), and with no history of patellar tendon injury (n = 13) were recruited. cSWE was performed 4 times by multiple raters over 2 days. Intraclass correlations (ICC) and minimum detectable change (MDC95% ) were calculated.RESULTS:Good to excellent between-day stability were found for viscosity (ICC = 0.905, MDC95%  = 8.3 Pa seconds) and shear modulus (ICC = 0.805, MDC95%  = 27.4 kPa). The interrater reliability measures, however, were not as reliable (ICC = 0.591 and 0.532).CONCLUSIONS:cSWE is a reliable assessment tool for quantifying patellar tendon viscoelastic properties over time. It is recommended, however, that a single rater performs the measure as the interrater reliability was less than ideal.

Background Gait asymmetries after anterior cruciate ligament reconstruction (ACLR) may lead to radiographic knee osteoarthritis. Slower walking speeds have been associated with biomarkers suggesting cartilage breakdown. The relationship between walking speed and gait symmetry after ACLR is unknown. Hypothesis/Purpose To determine the relationship between self-selected walking speeds and gait symmetry in athletes after primary, unilateral ACLR. Study Design Secondary analysis of a clinical trial. Methods Athletes 24±8 weeks after primary ACLR walked at self-selected speeds as kinematics, kinetics, and electromyography data were collected. An EMG-driven musculoskeletal model was used to calculate peak medial compartment contact force (pMCCF). Variables of interest were peak knee flexion moment (pKFM) and angle (pKFA), knee flexion and extension (KEE) excursions, peak knee adduction moment (pKAM), and pMCCF. Univariate correlations were run for walking speed and each variable in the ACLR knee, contralateral knee, and interlimb difference (ILD). Results Weak to moderate positive correlations were observed for walking speed and all variables of interest in the contralateral knee (Pearson’s r=.301-.505, p≤0.01). In the ACLR knee, weak positive correlations were observed for only pKFM (r=.280, p=0.02) and pKFA (r=.263, p=0.03). Weak negative correlations were found for ILDs in pKFM (r=-0.248, p=0.04), KEE (r=-.260, p=0.03), pKAM (r=-.323, p<0.01), and pMCCF (r=-.286, p=0.02). Conclusion Those who walk faster after ACLR have more asymmetries, which are associated with the development of early OA. This data suggests that interventions that solely increase walking speed may accentuate gait symmetry in athletes early after ACLR. Gait-specific, unilateral, neuromuscular interventions for the ACLR knee may be needed to target gait asymmetries after ACLR. Level of Evidence III

BackgroundAnterior cruciate ligament injuries are among the most common knee injuries. Mechanism of injury is classified as contact or non-contact. The majority of anterior cruciate ligament ruptures occur through a non-contact mechanism of injury. Non-contact anterior cruciate ligament ruptures are associated with biomechanical and neuromuscular risk factors that can predispose athletes to injuries and may impact future function. Non-contact mechanism of injury may be preceded by poor dynamic knee stability and therefore those with a non-contact mechanism of injury may be prone to poor dynamic knee stability post-operatively. Understanding how mechanism of injury affects post-operative functional recovery may have clinical implications on rehabilitation.PurposeThe purpose of this study was to determine if mechanism of injury influenced strength, functional performance, patient-reported outcome measures, and psychological outlook in athletes at four time points in the first two years following anterior cruciate ligament reconstruction.Study DesignSecondary analysis of a clinical trial.MethodsSeventy-nine athletes underwent functional testing at enrollment after impairment resolution. Quadriceps strength, hop testing, and patient-reported outcome measures were evaluated post-operatively at enrollment, following return-to-sport training and one year and two years after anterior cruciate ligament reconstruction. Participants were dichotomized by mechanism of injury (29 contact, 50 noncontact). Independent t-tests were used to compare differences between groups.ResultsThere were no meaningful differences between contact and non-contact mechanism of injury in any variables at enrollment, post-training, one year, or two years after anterior cruciate ligament reconstruction.ConclusionFunction did not differ according to mechanism of injury during late stage rehabilitation or one or two years after anterior cruciate ligament reconstruction.Level of EvidenceIII.

Early-onset knee osteoarthritis (OA) is associated with gait asymmetries after anterior cruciate ligament reconstruction (ACLR). Women have higher risks of sustaining non-contact injuries, and are more likely to present with aberrant movement patterns associated with the mechanism of injury (MOI). We hypothesized that sex and MOI would influence gait after ACLR. Seventy participants, grouped by sex and MOI, completed biomechanical testing during over-ground walking when they had full knee range of motion, trace or less knee effusion, greater than 80% quadriceps strength limb symmetry index, ability to hop on each leg without pain, and initiated running. Bilateral knee kinetics, kinematics, and joint contact forces were compared using mixed-model analysis of variance (α = .05). There was a three-way interaction effect of sex × MOI × limb for peak medial compartment contact force (P = .002), our primary outcome measure previously associated with OA development. Men with non-contact injuries walked with asymmetry characterized by underloading of the involved limb. Men with contact injuries walked with the most symmetrical loading. In women, no clear pattern emerged based on MOI. Targeting, and possibly prioritizing interventions for athletes who present with gait asymmetries after ACLR based on sex and MOI, may be necessary to optimize outcomes. Statement of Clinical Significance: Sex and MOI may influence walking mechanics, and could be considered in future interventions to target gait symmetry, as a response to interventions may vary based on differences in sex and MOI.