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Anterior cruciate ligament (ACL) reinjury rates among athletes remain very high despite screening protocols designed to assess readiness for return to sport. To better identify biomechanical risk factors for ACL injury, combining neurocognitive challenges and high-impact tasks would more closely resemble sporting demands. We investigated the influence of secondary cognitive tasks on landing mechanics during bilateral drop vertical jumps (DVJs) among athletes following ACL reconstruction and whether sex affected these results. We also assessed whether adding secondary cognitive tasks to DVJs influenced loading asymmetries. Forty individuals (20 males) performed three DVJ conditions: (1) without secondary cognitive tasks (DVJ), (2) with secondary cognitive tasks targeting fast decision-making and inhibitory control of the motor action (DVJmot), and (3) with secondary cognitive tasks targeting fast decision-making, inhibitory control, attention, and short-term memory (DVJcogmot). We collected movement mechanics time-series data during the first 100 ms of landing using a motion capture system and force plates and compared outcomes between the three DVJs using functional t-tests. Secondary cognitive tasks altered trunk, hip, knee, and ankle landing mechanics (adjusted p-values < 0.05), representing more upright and stiffer landings. Loading asymmetries were increased by unloading the injured limb (adjusted p-values < 0.05). We found no differences between DVJmot and DVJcogmot or between males and females. Adding secondary cognitive tasks to DVJs better identifies landing mechanics associated with an increased ACL injury risk and inadequate rehabilitation. Future research should focus on optimizing the challenge point of the cognitive and motor tasks and how to best integrate them in RTS testing.

Background: Chaotic sporting environments require the performance of concurrent cognitive and motor tasks. A reduced capacity for either or both of the tasks when performed concurrently is known as cognitive-motor interference (CMi) and is believed to increase the injury risk. A greater susceptibility to CMi after a rupture of the anterior cruciate ligament (ACL) has been suggested to be caused by central nervous system adaptations, thus possibly contributing to high secondary ACL injury rates.

Purpose: To investigate whether patients after ACL reconstruction (ACLR) demonstrate greater CMi than noninjured controls when adding secondary cognitive tasks to the drop vertical jump (DVJ) and explore the potential influence of sex on CMi.

Study Design: Controlled laboratory study.

Methods: A total of 40 (50% male) sports-active patients who had undergone ACLR (mean, 24.9 ± 16.1 months after surgery) and 40 (50% male) sports-active noninjured controls performed DVJs with and without secondary cognitive tasks targeting short-term memory, attention, fast decision-making, and inhibitory control. Outcomes included a letter position recall task and 3 motor variables: (1) correct action (landing or landing with a subsequent vertical jump), (2) relative jump height (relative between DVJs), and (3) relative peak vertical ground-reaction force (relative between DVJs). Participants also completed isolated cognitive tests (CANTAB) included as covariates in multivariate analysis.

Results: Multivariate analysis of variance revealed that the ACLR group had greater CMi than the control group (P < .001), as manifested by more incorrect answers for the cognitive letter recall task (mean difference [MD], –13.3% [95% CI, –20.8% to –5.9%]; P < .001), more incorrect motor actions (MD, –7.5% [95% CI, −12.4% to –2.6%]; P = .003), and a reduced relative jump height (MD, –4.5% [95% CI, –7.9% to –1.2%]; P = .010). No difference in relative peak vertical ground-reaction force was found (MD, 2.8% [95% CI, –7.7% to 13.3%]; P = .59). Isolated cognitive outcomes did not affect these results, and there were no significant differences between male and female participants.

Conclusion: Patients after ACLR showed greater CMi than noninjured controls, which was unrelated to isolated cognitive outcomes, thus indicating aberrant neurocognitive function.

Clinical Relevance: Clinicians should consider cognitive and dual-task training and screening during ACL rehabilitation to better prepare patients for chaotic and uncontrolled sporting environments in which dual tasking is prevalent. Such interventions may help to reduce the risk of secondary ACL injuries.

Investigations of kinetic asymmetries during bilateral squats following anterior cruciate ligament reconstruction (ACLR) are limited to mainly cross-sectional studies and discrete value data extracted at specific knee angles. We assessed loading asymmetries during squats longitudinally throughout rehabilitation using curve analysis and compared patient-reported outcome measures (PROMs) between those with and without asymmetry. Bodyweight squats were performed by 24 individuals (13 females) post-ACLR on three occasions: (1) Early 2.9 (1.1) months; (2) Mid 8.8 (3.1) months; (3) at Return to Sport (RTS) 13.1 (3.6) months; and 29 asymptomatic controls (22 females) once. Time-normalized between-leg asymmetry curves of sagittal plane hip, knee, and ankle moments and vertical ground reaction forces were compared using functional data analysis methods. Individual asymmetrical loading for ACLR was classified when exceeding the 95% confidence interval of controls during ≥50% of the squat. At Early, ACLR had greater asymmetry than controls for knee (15%–100% eccentric phase; 0%–100% concentric) and ankle flexion moments (56%–65% concentric). At Mid, ACLR had greater asymmetry for knee (41%–72% eccentric) and ankle flexion moments (56%–69% concentric). No between-group differences were found at RTS. From Early to RTS, ACLR reduced asymmetry for hip (21%–46% eccentric), knee (27%–58% concentric), and ankle flexion moments (21%–57% eccentric). At Early, 11/24 underloaded their ACLR knee and 1 overloaded compared with controls. At RTS, 4 underloaded and 6 overloaded. No differences in PROMs were found based on loading asymmetry. Beyond the early phase of rehabilitation from ACLR, individual-level analyses are required to reveal differing loading strategies during bilateral squats.

Purpose: This study evaluated motor control recovery at different times following anterior cruciate ligament reconstruction (ACLR) by investigating lower-limb spatiotemporal symmetry during stair descent performances.

Methods: We used a cross-sectional design to compare asymptomatic athletes (Controls, n = 18) with a group of people with ACLR (n = 49) divided into three time-from-ACLR subgroups (Early: <6 months, n = 17; Mid: 6–18 months, n = 16; Late: ≥18 months, n = 16). We evaluated: “temporal symmetry” during the stance subphases (single-support, first and second double-support) and “spatial symmetry” for hip-knee-ankle intra-joint angular displacements during the stance phase using a dissimilarity index applied on superimposed 3D phase plots.

Results: We found significant between-group differences in temporal variables (p ≤ 0.001). Compared to Controls, both Early and Mid (p ≤ 0.05) showed asymmetry in the first double-support time (longer for their injured vs. non-injured leg), while Early generally also showed longer durations in all other phases, regardless of stepping leg. No statistically significant differences were found for spatial intra-joint symmetry between groups.

Conclusion: Temporal but not spatial asymmetry in stair descent is often present early after ACLR; it may remain for up to 18 months and may underlie subtle intra- and inter-joint compensations. Spatial asymmetry may need further exploration.

Background: Individuals with a recent anterior cruciate ligament reconstruction may demonstrate an altered movement strategy for protecting the knee and maintaining stability. Altered knee movement might lead to abnormal intra-articular load, potentially contributing to early knee osteoarthritis onset. A protective strategy may be particularly evident during active tasks that induce a pivot-shift manoeuvre, such as a step-down and cross-over task. In this study, we investigated whether knee joint mechanics and muscle activity differed between participants early (∼3 months) following reconstruction (n = 35) to uninjured controls (n = 35) during a step-down and cross-over task with a 45° change-of-direction.

Methods: We used motion capture, force plates and surface electromyography to compare time-normalised curves of sagittal and transverse-plane knee mechanics and muscle activity during the cross-over phase between groups using functional t-tests. We also compared knee mechanics between sides within the injured group and compared discrete outcomes describing the cross-over phase between groups.

Findings: Compared to controls, the injured participants had greater knee flexion angle and moment, lower internal rotation moment, more preparatory foot rotation of the pivoting leg, a smaller cross-over angle, and a longer cross-over phase for both the injured and uninjured sides. The injured leg also had greater biceps femoris and vastus medialis muscle activity compared to controls and different knee mechanics than the uninjured leg.

Interpretation: Individuals with anterior cruciate ligament reconstruction showed a knee-stabilising and pivot-shift avoidance strategy for both legs early in rehabilitation. These results may reflect an altered motor representation and motivate considerations early in rehabilitation.

Athletes with an anterior cruciate ligament (ACL) injury followed by ACL reconstruction (ACLR) often perform various testing to guide return to sport, but preinjury data are rarely available for comparison. This longitudinal case-control study reports absolute value and between-leg symmetry data on maximal performances for single-leg hop height and distance, muscle strength, and side hop landing mechanics of an 18-year-old female soccer athlete collected 5 months before sustaining an ACL injury and again at 10, 13, and 29 months post-ACLR. Her data were compared across test sessions and to cross-sectional data of 15 asymptomatic female athletes.

Background: Between-leg symmetry in 1-leg hop and knee strength performances is considered important after anterior cruciate ligament reconstruction (ACLR) to facilitate a safer return to sport. While few athletes with ACLR demonstrate symmetry in test batteries, reference data for noninjured athletes are lacking, thus questioning how ACLR-specific poor symmetry is.

Hypothesis: Athletes with ACLR (hamstring autograft) show lower symmetry and have a lower proportion of symmetric individuals than noninjured athletes for knee flexion strength but not for hop for distance, vertical hop, and knee extension strength.

Study design: Cross-sectional.

Level of Evidence: Level 3.

Methods: A total of 47 athletes with ACLR (median 13.0 months post-ACLR) who had returned to their sport, and 46 noninjured athletes participated. Symmetry was calculated between the worse and better legs for each test and combinations of them using the limb symmetry index (LSIWORSE-BETTER, ranging from 0% to 100%). The 2 groups were compared for these values and the proportions of individuals classified as symmetric (LSIWORSE-BETTER ≥90%) using independent t-tests and Fisher’s exact tests, respectively.

Results: Athletes with ACLR were less symmetric than noninjured athletes for knee flexion strength with a lower LSIWORSE-BETTER (83% vs 91%, P < 0.01) and a lower proportion of symmetric individuals (39% vs 63%, P = 0.04). No differences between groups were revealed for the hop tests, knee extension strength, or combinations of tests (P > 0.05). Only 17% of the athletes with ACLR and 24% of the noninjured athletes demonstrated symmetric performances for all 4 tests.

Conclusion: Athletes with ACLR (hamstring autograft) showed poorer symmetry in knee flexion strength than noninjured athletes, although both groups had few individuals who passed the test battery’s symmetry criteria.

Clinical relevance: Symmetry is uncommon among athletes irrespective of ACLR and should be considered regarding expected rehabilitation outcomes and return-to-sport decisions post-ACLR.

We compared knee landing mechanics with presumed relation to risk of anterior cruciate ligament (ACL) injury among three single-leg hop tests and between legs in individuals with unilateral ACL reconstruction. Thirty-four participants (>10 months' post-surgery, 23 females) performed the standardised rebound side hop (SRSH), maximal hop for distance (OLHD) and maximal vertical hop (OLVH). We calculated the following knee outcomes from motion capture and force plate data: finite helical axis inclination angles (approximates knee robustness), frontal and transversal plane angles at initial contact, peak angles of abduction and internal rotation during landing, and peak external moments of flexion, abduction and internal rotation during landing. Repeated-measures MANOVA analysis ('sex' as covariate) confirmed that SRSH induced greater angles and moments, particularly in the frontal plane, compared to OLHD and OLVH. There was between-leg asymmetry for peak knee flexion moment for males during OLHD and OLVH, and for females during SRSH. Our results advocate the SRSH over OLHD and OLVH for assessment of knee landing control to screen for movement patterns potentially related to ACL injury risk. However, clear differences in both knee kinematics and kinetics between OLHD and SRSH motivate the use of both tests to evaluate different aspects of landing control.

INTRODUCTION: Kinetic loading asymmetries during bilateral squats have been reported following anterior cruciate ligament reconstruction (ACLR). Evidence is however limited to discrete value data extracted at specific knee angles from cross-sectional studies where side-toside strategies are presented only at group level. It is therefore unclear whether loading asymmetries occur throughout the entire squat, whether they change during rehabilitation and how they are distributed between sides.

METHODS: Bilateral bodyweight squats were performed by 24 individuals (13 females) post-ACLR on three occasions: 1) Early rehab - 2.9(1.1) months; 2) Mid-rehab - 8.8 (3.1) months; 3) Return to sport (RTS) - 13.1 (3.6) months; and 29 asymptomatic controls (22 females) on one occasion. Motion capture and two force plates were used to calculate time-normalized curves of vertical ground reaction forces andhip, knee, and ankle moments. Outcomes were compared between sides and groups, and over time, using functional t-tests with p-values adjusted by the interval-wise testing procedure. Individual knee loading strategies, i.e., under-/overloading of the ACLR side, were classified when asymmetry in favour of the respective side exceeded the 95% pointwise confidence interval of controls during at least 50% of the squat.

RESULTS: At Early rehab, ACLR had significantly greater (adjusted P < .05) asymmetry in knee flexion moment than controls during thetime-normalized interval of 15-100% of the eccentric phase and the entire concentric phase, as well as ankle flexion moment during 56-65% of the concentric phase. At Mid-rehab, ACLR had significantly greater asymmetry than controls for knee flexion moment during 41-72% of the eccentric phase and for ankle flexion moment during 56-69% of the concentric phase. No significant between-group differences were found at RTS. At RTS compared with Early rehab, ACLR significantly reduced asymmetry for hip (21-46%, eccentric phase), knee (27-58%, concentric phase), and ankle flexion moment (21-57%, eccentric phase). Individual asymmetry strategies for knee flexion moment atEarly rehab were mainly due to individuals underloading the ACLR side (46%) rather than overloading (4%). At RTS, however, more individuals overloaded (25%) than underloaded (17%) the ACLR side.

CONCLUSION: Curve analyses revealed significant kinetic loading asymmetries throughout bilateral bodyweight squats for our ACLR group compared with controls at Early rehab and Mid-rehab, but not at RTS. Significant reductions in hip, knee and ankle flexion moment asymmetry from Early rehab to RTS showed modifications during rehabilitation. An expected underloading strategy was evident for almost half of the ACLR participants at Early rehab, but an overloading strategy was the main reason for knee flexion moment asymmetry at RTS.Loading asymmetries during bilateral tasks should thus not be assumed due to underloading of the ACLR side, but may depend on anoverloading strategy, particularly late in rehabilitation.