Clinical and Functional Outcomes After ACL Reconstruction Versus Primary Repair

Condition(s) studied

Study summary

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.

Eligibility

Primary outcome measure(s)

• Peak Torque (Isokinetic Strength) — First Day
  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) — First day
  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) — First day
  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 — First day
  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
• Functional Range — First Day
  Functional range will be defined as the angular range in which at least 85% of peak torque is maintained during isokinetic testing. Unit of Measure: Percentage (%)
• Fatigue-Induced Peak Torque Decline — First Day
  Fatigue-related performance decline will be calculated as the percentage decrease in peak torque following a 33-repetition isokinetic fatigue protocol at 300°/s. Unit of Measure: Percentage (%)
• Muscle Oxygenation — First Day
  Muscle oxygenation will be assessed using the Train.Red FYER wireless near-infrared spectroscopy (NIRS) system (Train.Red, Gelderland, Netherlands). The device provides continuous, non-invasive measurements of tissue oxygen saturation (StO₂) and the oxy-deoxyhemoglobin difference (HbDiff). Sensors will be placed over the quadriceps and hamstring muscles following SENIAM guidelines. Muscle oxygenation will be recorded before and immediately after the isokinetic fatigue protocol to evaluate changes in local oxygen utilization and metabolic stress.

Trial sites (1)

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