The anterior cruciate ligament (ACL) is the primary structure responsible for controlling anterior-posterior translation and rotational stability of the knee joint. Although ACL reconstruction has long been considered the gold standard among surgical interventions following ACL injury, arthroscopic primary repair techniques have recently regained interest. With advances in minimally invasive surgical procedures, refined patient selection criteria, and improved rehabilitation strategies, the clinical effectiveness of primary repair is once again being re-evaluated. However, there remains a limited body of literature directly comparing the medium- to long-term effects of these two surgical techniques on neuromuscular performance, fatigue tolerance, and functional outcomes.
The aim of this study is to comparatively investigate postoperative muscle strength and endurance, isokinetic fatigue response, muscle oxygenation, proprioception, knee stability, postural control, and patient-reported outcome measures in individuals who have undergone ACL reconstruction or primary repair. Assessments will include low- and high-velocity tests performed on the Cybex Norm isokinetic dynamometer, a 33-repetition fatigue protocol at 300°/s, muscle oxygenation analysis using Train.Red NIRS, knee laxity measurement via the GNRB arthrometer, single-leg balance and landing evaluations using the KFORCE force platform, and subjective outcome measures (IKDC, ACL-RSI).
The findings of this study are expected to provide a more comprehensive understanding of how surgical technique influences physiological, biomechanical, and functional outcomes. This knowledge may contribute to the development of individualized rehabilitation approaches and evidence-based return-to-sport criteria.
Age 18-40 years
History of complete ACL rupture treated with ACL reconstruction
Surgery performed at Gazi University Department of Orthopedics and Traumatology
At least 12 months postoperative at the time of evaluation
Previous surgery for partial or chronic ACL tear
Concomitant multi-ligament knee injuries
Prior surgery on the ipsilateral or contralateral knee
Lower extremity malalignment (e.g., significant varus/valgus)
The study will include a total of 45 participants. All participants will be adults aged 18-40 who meet the study's eligibility criteria, are able to comply with the assessment procedures, and provide informed consent.
Other
Prospective
Not listed
Peak Torque (Isokinetic Strength)
Peak torque of the knee flexor and extensor muscles will be measured using an isokinetic dynamometer (Cybex NORM® isokinetic dynamometer, Humac, CA, USA). Measurements will be performed in the following modes: concentric contraction at 60°/s, eccentric contraction at 60°/s, concentric contraction at 180°/s, and concentric contraction at 300°/s. Peak torque values will be recorded for each testing velocity and contraction mode and expressed in Newton-meters (Nm). Unit of Measure: Newton-meter (Nm)
Extremity Symmetry Index (ESI)
Extremity Symmetry Index will be calculated by comparing the involved and uninvolved limbs using peak torque values obtained from isokinetic testing. Unit of Measure: Percentage (%)
Conventional Hamstring-to-Quadriceps Ratio (H/Q Ratio)
The conventional H/Q ratio will be calculated as the ratio of concentric hamstring peak torque to concentric quadriceps peak torque. Unit of Measure: Ratio
Functional Hamstring-to-Quadriceps Ratio
The functional H/Q ratio will be calculated as the ratio of eccentric hamstring peak torque to concentric quadriceps peak torque. Unit of Measure: Ratio
Knee Joint Proprioception
Knee proprioception will be assessed using an active joint repositioning test performed on the Cybex NORM® isokinetic system (Humac, CA, USA). Participants will actively reproduce a target angle (30° knee flexion) starting from 90° flexion. Three trials will be recorded, and the absolute angular error will be calculated as the mean difference between the target angle and the reproduced angles. This measure reflects the accuracy of joint position sense and will be used to evaluate proprioceptive function.
Single Leg Balance
Postural control will be assessed using the KFORCE Plates force platform (Kinvent, Montpellier, France). Participants will perform a single-leg balance task, and Center of Pressure (CoP)-based variables such as mean CoP velocity, path length, sway area, and stabilization time will be recorded. Measurements will be obtained under standardized testing conditions for both limbs.
Single Leg Landing
Dynamic stability will be assessed using the KFORCE Plates force platform. Participants will perform a single-leg landing task, and Center of Pressure (CoP)-based variables including stabilization time, CoP displacement, sway area, and CoP velocity will be analyzed. This measure evaluates the participant's ability to achieve stable posture following landing.
Knee Laxity
Knee anterior laxity will be assessed using the GNRB® arthrometer at 20° of knee flexion. The primary outcome variable will be Anterior Tibial Translation (ATT) measured in millimeters under standardized forces (134 N and 200 N). The side-to-side difference in ATT and the slope value (stiffness index) will also be recorded to evaluate anterior cruciate ligament integrity. These parameters provide an objective and quantitative measure of ligamentous stability.
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