Anterior cruciate ligament (ACL) injury is a common sports-related injury, particularly in sports that require extensive jumping and cutting movements. Although anterior cruciate ligament reconstruction (ACLR) surgery can restore knee stability, many athletes still face the risk of re-injury after returning to competition.Current return-to-play assessment relies primarily on single-plane horizontal hop tests and symmetry indices (LSI ≥ 90%); however, an increasing body of research suggests that these tests may not comprehensively reflect functional deficits in the vertical plane, repeated hopping, or high-intensity sport-specific activities.This study hypothesizes that incorporating multiple vertical jump tests-including single-leg vertical jumps and 10-second repeated vertical jumps-combined with advanced force plate analytics (such as Reactive Strength Index \[RSI\] and Time to Stabilization \[TTS\])-can more sensitively reveal residual neuromuscular control deficits following surgery. This approach would provide evidence-based guidance for return-to-play decision-making, thereby improving athletes' long-term athletic performance and safety.
1.Age 18-35 years
Other lower extremity injuries or pathologies (including other knee ligament injuries)
Contralateral lower limb injury within the past 3 months
Quadriceps strength symmetry index <90%
Non-elite athlete status (no prior national-level competition participation)
The study population consists of two distinct groups: (1) ACLR athletes: elite athletes aged 18-35 years who have undergone unilateral anterior cruciate ligament reconstruction using hamstring or gracilis autograft with a minimum of 6 months post-operative. These participants will be recruited from orthopedic clinics, sports medicine centers, and rehabilitation facilities in the region. (2) Healthy controls: age, sex, and athletic-level matched individuals aged 18-35 years with no history of lower extremity injuries, recruited from local athletic facilities, university sports programs, and community sports organizations. Both groups must have elite athlete status, defined as prior participation in national-level sports competitions. The ACLR group represents athletes in the late rehabilitation phase preparing for return-to-play, while the healthy control group serves as a reference for normal biomechanical performance.
Case-control
Cross-sectional
Not listed
Limb asymmetry index,LSI
Limb Symmetry Index (LSI) calculated as (\|Uninvolved limb value - Involved limb value\| / (Uninvolved limb value + Involved limb value)) × 100% for each of the four jump tasks: Single-Legged Hop for Distance (SHD), Crossover Hop for Distance (CHD), Single-Legged Vertical Countermovement Jump (SLVJ), and 10-Second Repeated Single-Legged Vertical Jump (SLVJs). LSI values will be compared between ACLR athletes and healthy controls to determine whether vertical jump protocols reveal greater limb asymmetries than traditional horizontal hop tests. Primary analysis will examine whether LSI differences in vertical jump tasks are statistically significantly lower (indicating greater asymmetry) than horizontal hop tasks, revealing residual neuromuscular deficits not detected by conventional return-to-play assessment.
Modified Reactive Strength Index
Modified Reactive Strength Index (mRSI) calculated as Flight Time(s) divided by Time to Take-off(s) for the 10-Second Repeated Single-Legged Vertical Jump (SLVJs) task.
Time to Stabilization (seconds)
Time to Stabilization (TTS) measured during the Single-Legged Vertical Countermovement Jump (SLVJ) task, defined as the time required for vertical ground reaction force (vGRF) to return to and stabilize within ±5% of the participant's body weight following landing.
Single-Legged Hop for Distance (centimeter)
Single-Legged Hop for Distance (SHD) measured as the maximum horizontal distance(centimeter) achieved during a single maximal hop on the tested leg, performed bilaterally.
Crossover Hop for Distance (centimeter)
Crossover Hop for Distance (CHD) measured as the total horizontal distance covered during three consecutive hops crossing a centerline, performed bilaterally with emphasis on stability and continuity.
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