April L. McPherson

Background: Understanding the risk of secondary contralateral (CL) anterior cruciate ligament (ACL) injury in young patients after ACL reconstruction (ACLR) may help identify targetable risk factors to optimize rehabilitation and return to sport. It is not clear if the autograft type used in the index procedure affects the risk of having a CL injury. Additionally, the aggregated CL injury rates across studies in young patients have not been well described. Purpose: To compare CL ACL injury rates by graft type in patients ≤25 years of age at a minimum follow-up of 24 months after ACLR, and to stratify CL injury rates by potential modifiers, including sex. Study Design: Systematic review and meta-analysis; Level of evidence, 4. Methods: A systematic review of the literature for studies reporting ACL autograft reinjury rates after ACLR using hamstring tendon (HT), bone–patellar tendon–bone (BPTB), or quadriceps tendon (QT) autograft in patients ≤25 years of age with a minimum follow-up of 24 months was conducted. From this data set, CL ACL injury rates from studies in which they were reported were evaluated. Results: The meta-analysis included 22 studies pooling 4435 total patients who received BPTB (n = 2349), HT (n = 1561), or QT (n = 525) autografts for their ALCR. The pooled CL ACL injury rate was 10.8% (95% CI, 8.2%-14.0%) for HT, 10.5% (95% CI, 7.4%-14.8%) for BPTB, 12.2% (95% CI, 9.7%-15.3%) for QT, and 10.6% (95% CI, 8.8%-12.8%) for all grafts together. There were no differences among primary ACLR graft types in CL ACL injury rates (χ ² = 0.7; P = .7). There were differences in CL injury rates by sex among graft types (risk ratio [RR], 0.8; 95% CI, 0.5-1.4; χ ² = 9.2; P < .01). Males had a significantly lower risk of CL ACL injury relative to females after primary BPTB ACLR (RR, 0.439), but not HT (RR, 1.050) or QT (RR, 1.219) ACLR. Conclusion: In patients ≤25 years of age, the rates of CL ACL injury are similar after primary HT, BPTB, and QT autograft ACLR. The risk of CL injury was lower in males relative to females after ACLR with BPTB, but not with HT or QT.

Background: Anterior cruciate ligament reconstruction (ACLR) is being increasingly performed in part because of higher injury rates among young athletes (≤25 years). High allograft failure rates support the use of autograft for ACLR in young patients. However, data examining the failure rates of the different autografts used in this population are lacking. Purpose: The purpose of this study was to compare graft failure rates among bone–patellar tendon–bone (BPTB), hamstring tendon (HT), and quadriceps tendon (QT) autografts in patients ≤25 years old. The secondary aim was to stratify graft failure by potential modifiers, including sex, mean follow-up, time to graft rupture, and concomitant meniscal surgery. Study Design: Systematic review and meta-analysis; Level of evidence, 4. Methods: Studies were included that reported anterior cruciate ligament graft (BPTB, HT, QT) reinjury rates in patients ≤25 years old with a minimum 24 months of follow-up. Studies were excluded if they examined revision ACLR, allograft ACLR, allograft augmentation ACLR, or concomitant lateral extra-articular tenodesis or if they failed to report reinjury rates by graft type and young age (≤25 years). Results: This review included 46 studies comprising 10,624 patients (HT: n = 6090, 47.0% female, 54.5-month mean follow-up; BPTB: n = 3990, 63.0% female, 63.6-month mean follow-up; QT: n = 544, 40.3% female, 41.6-month mean follow-up). HT exhibited the highest failure rate at 11.1% (95% CI, 8.8%-13.9%). Failure rates for BPTB and QT were 5.1% (95% CI, 3.5%-7.2%) and 2.5% (95% CI, 0.5%-11.2%), respectively. HT had a significantly higher failure rate than BPTB ( Q = 13.1; P < .001). There were no significant differences in failure rates between HT and QT ( Q = 3.7; P = .06) or between BPTB and QT ( Q = 0.8; P = .4). Males and females had a similar risk of graft failure regardless of graft type. Conclusion: The results of this meta-analysis suggest that HT grafts are not the optimal choice for young patients undergoing ACLR. Instead, these patients should consider BPTB to reduce the risk of graft failure. Further research including randomized controlled trials with larger sample sizes are required to determine how QT grafts compare with BPTB grafts in this population.

We evaluated the test–retest reliability of a comprehensive, multitask virtual reality (VR)–based sensorimotor assessment designed to capture and quantify aspects of body movement during standardized visuomotor, auditory, gait, oculomotor, and balance tasks. Twenty healthy adults completed 3 sessions of the Dynamic Assessment of Sensorimotor Health protocol on nonconsecutive days at a university research center. Dynamic Assessment of Sensorimotor Health includes 7 VR tasks (Trail Making, Sound Localization, Tandem Gait, Reaction Board, Smooth Pursuit, Single-Leg Balance, and Target Matching Balance). Session-level performance metrics were derived from head-, hand-, and eye-tracking data, and intraclass correlation coefficients (ICC[3,1]) and session means were calculated for each metric. Reliability ranged from poor to excellent (ICC = .07 to .81). Metrics from the Reaction Board (reaction time) and Target Matching Balance (head path length) tasks demonstrated the highest reliability (ICC up to .81), and several measures from the Trail Making, Smooth Pursuit, and Sound Localization tasks showed fair-to-good reliability. These findings identify specific VR-derived body movement metrics that show promise for tracking sensorimotor performance over time and highlight others that may require redesign or alternative processing before use in longitudinal or clinical applications.

Sport-related concussion (SRC) increases the risk of subsequent lower extremity musculoskeletal injury, particularly in youth athletes. This may be due to SRC-altered movement patterns, particularly under neurocognitive challenges. Specifically, dual-tasking—simultaneously completing motor and cognitive tasks—can distinguish patients with a higher risk of lower extremity musculoskeletal injury, offering a unique and unexplored intervention target for clinical, rehabilitation, strength and conditioning practitioners, and coaches. This narrative provides evidence outlining the addition of cognitive components to movement-based interventions to reduce injury risk after SRC. We propose a theoretical framework for a virtual reality-based neuromuscular training intervention that incorporates dual-tasking to target deficits underlying potential mechanisms of increased injury risk after SRC. Virtual reality technology offers a unique environment that may help reduce lower extremity musculoskeletal injury risk after SRC to improve long-term health, well-being, and athletic performance.

Context: There is a well-established increased risk of lower-extremity (LE) musculoskeletal (MSK) injury following a sport-related concussion (SRC). Neuromuscular training programs improve biomechanics associated with LE MSK injury and reduce LE MSK injury incidence, but their relative effectiveness in athletes with history of SRC is unknown. The purpose of this study was to evaluate LE MSK injury incidence in female adolescent athletes with history of SRC following a neuromuscular training intervention. Design: Prospective case-control. Methods: Seventy-seven adolescent female athletes aged 12–18 years who participated in soccer, volleyball, or basketball were recruited from a single institutional sports medicine research and performance center to complete a 6-week neuromuscular training program prior to competitive athletic season. Group (Control, History of SRC) comparisons of athlete exposure and relative LE MSK injury risk and rates during the competitive athletic season were assessed. Results: Ten injuries were recorded by 9 athletes. Female athletes who reported history of SRC had increased injury risk (Risk Ratio 3.9, 95% CI, 1.1–13.8, P = .01) and increased injury rate (rate ratio 4.1, 95% CI, 1.1–15.8, P = .03) compared with female athletes without history of SRC. Conclusions: Female adolescent athletes with history of SRC showed a greater risk of LE MSK injury compared with athletes with no history of SRC. Future work is still needed to understand the underlying mechanisms associated with future LE MSK injury following SRC and interventions that ameliorate elevated injury risk.

Context: Epidemiological studies have shown an increased risk of musculoskeletal injury after concussion. The purpose of this study was to determine whether the reverse relationship exists, specifically whether there is an increased risk of concussion after an anterior cruciate ligament (ACL) injury in a population-based cohort. Design: Retrospective cohort. Methods: The Rochester Epidemiology Project was searched between 2000 and 2017 for International Classification of Diseases, 9th and 10th Revision codes relevant to the diagnosis and treatment of concussion and ACL tear. A total of 1294 unique patients with acute, isolated ACL tears and no previous history of concussion were identified. Medical records for cases were reviewed to confirm ACL tear diagnosis and to determine history of concussion after the ACL injury. Cases were matched by age, sex, and Rochester Epidemiology Project availability to patients without an ACL tear (1:3 match), resulting in 3882 controls. Medical records of matched control patients were reviewed to rule out history of ACL injury. The hazard ratio of concussion injury following an ACL injury was determined. Results: Nine patients with an ACL injury suffered concussion up to 3 years after the ACL injury. The rate of concussion was no different between ACL-injured cases (0.7%) compared with matched controls with no ACL injury (1.2%), which corresponded to a hazard ratio of 0.55 (95% confidence interval, 0.3–1.1; P = .10). Conclusions: Based on the current evidence, there does not appear to be a significant association between ACL injury and subsequent concussion, which suggests that a concussion uniquely affects the risk of future subsequent musculoskeletal injury.

Introduction: It is well documented that marked weakness of the quadriceps is present after knee joint injury. This joint trauma induces a presynaptic reflex inhibition of musculature surrounding the joint, termed arthrogenic muscle inhibition (AMI). The extent to which anterior cruciate ligament (ACL) injury affects thigh musculature motor unit activity, which may affect restoration of thigh muscle strength after injury, is undetermined.Methods: A randomized protocol of knee flexion and extension isometric contractions (10%–50% maximal voluntary isometric contraction) were performed for each leg on 54 subjects with electromyography array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus, and biceps femoris. Longitudinal assessments for motor unit recruitment and average firing rate were acquired at 6-month intervals for 1 year post ACL injury.Results: The ACL-injured population demonstrated smaller quadriceps and hamstrings motor unit size (assessed via motor unit action potential peak-to-peak amplitude) and altered firing rate activity in both injured and uninjured limbs compared to healthy controls. Motor unit activity remained altered compared to healthy controls at 12 months post ACL reconstruction (ACLR).Discussion: Motor unit activity was altered after ACLR up to 12 months post-surgery. Further research is warranted to optimize rehabilitation interventions that adequately address altered motor unit activity and improve safety and success with return to sport after ACLR. In the interim, evidence based clinical reasoning with a focus on development of muscular strength and power capacity should be the impetus behind rehabilitation programming to address motor control deficits.

Joint trauma induces a presynaptic reflex inhibition termed arthrogenic muscle inhibition (AMI) that prevents complete activation of muscles. Reduced motor unit (MU) output is a hypothesised mechanism for persistent strength deficits. The objective of this study was to determine MU characteristics of thigh musculature and determine how they change with anterior cruciate ligament (ACL) injury compared to healthy controls. A randomised protocol of knee flexion/extension isometric contractions (10–50% maximal voluntary isometric contraction) was performed for each leg with surface EMG 5‐pin array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus and biceps femoris. Longitudinal assessments for average rate coding, recruitment thresholds and MU action potentials were acquired at 6‐month intervals. With exception of the vastus medialis, all thigh musculature of ACL‐injured demonstrated smaller MU action potential peak‐to‐peak amplitude. For average rate coding, ACL‐injured demonstrated lower coding rates than Controls for the quadriceps (p < .05) and higher rates than Controls for the hamstrings (p < .05). These MU characteristics were different from Controls after ACL reconstruction up to 12 months post‐surgery, yet maximal strength increased during this time frame. As thigh MU characteristics are known across phases of ACL rehabilitation, future studies can assess these patterns of motor control and their potential to determine risk of re‐injury. Further, future rehabilitation can target specific intervention programmes to restore motor control.Highlights Motor unit strategies of arthrogenic muscle inhibition are characterised for the first time via decomposed EMG. Motor unit deficits of thigh musculature persist throughout all phases of ACL rehabilitation, even after return‐to‐sport. After ACL injury, motor unit sizes at similar recruitment thresholds were smaller than those of healthy controls.