An observational study in Anterior Cruciate Ligament (ACL) Tear, Anterior Cruciate Ligament Reconstruction and Isokinetic Test, sponsored by Gazi University. Recruiting at 1 site in Turkey (Türkiye). Open to participants aged 18 Years to 40 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-08-25.
Sponsored by Gazi University · Observational
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.
The anterior cruciate ligament (ACL), one of the key stabilizers of the knee joint, plays a crucial role in maintaining both anteroposterior and rotational stability. The increasing popularity of recreational and competitive sports has contributed to a rising incidence of ACL injuries in recent years. Until the late 1980s, primary repair was widely accepted as the standard treatment for ACL injuries. Although short-term outcomes were generally satisfactory, this technique was largely abandoned due to high failure rates observed in medium- and long-term follow-ups. The probable causes of these unfavorable outcomes include suboptimal patient selection, invasive open repair techniques performed with absorbable sutures, and nonfunctional rehabilitation approaches characterized by prolonged cast immobilization. Considering the limited healing potential of the ligament, reconstruction surgery-performed using allografts or autologous tendon grafts-emerged as the new standard for the treatment of ACL injuries.
However, several disadvantages associated with reconstruction have raised the notion that a single surgical method may not be appropriate for all patients. These drawbacks include graft rerupture or contralateral ACL injury, loss of proprioception, physeal disturbances in pediatric populations, donor site morbidity in autografts or higher failure rates in allografts, the potential need for complex revision surgery, and the risk of early-onset osteoarthritis. In recent years, advances in patient selection criteria, minimally invasive surgical techniques, and modern rehabilitation protocols have renewed interest in arthroscopic primary ACL repair. This method preserves the native ligament and its proprioceptive properties while avoiding donor site morbidity, thereby offering the potential for a smoother and more accelerated postoperative rehabilitation process. Additionally, if primary repair fails, ACL reconstruction remains a viable subsequent treatment option. Primary repair has been described as a less morbid surgical alternative for patients presenting with acute proximal ACL tears, although high-quality evidence for its use is still limited.
Recent studies have shown improved success rates following primary repair of proximal ACL tears. In one investigation, researchers reported a 0% failure rate among 75 patients treated with primary ACL repair. Furthermore, 88% of patients demonstrated a negative pivot-shift test, 87% exhibited 0 or +1 Lachman test findings, and 89% successfully returned to sport. Similarly, numerous studies have evaluated the clinical effectiveness of ACL repair, and several recent systematic reviews have suggested that primary repair may be an effective treatment strategy with reasonable clinical outcomes compared to ACL reconstruction. Nonetheless, concerns remain that some evidence includes older cohorts that may not reflect contemporary surgical practices. A systematic review of only five comparative studies found no significant differences between treatments regarding clinical outcome scores, knee laxity, or graft rerupture rates. More recent randomized controlled trials have yielded conflicting results; some authors report that ACL repair provides non-inferior clinical outcomes compared to reconstruction, while others emphasize higher rates of adverse events and failure associated with repair. These issues underscore the need for further research comparing the medium- to long-term outcomes of ACL repair and ACL reconstruction.
Given the recent increase in clinical studies evaluating ACL repair versus reconstruction, synthesizing and expanding evidence from such research is critical for achieving a comprehensive and transparent understanding of the advantages, disadvantages, and clinical implications of both procedures.
The purpose of the present study is to compare postoperative clinical outcomes and patient-reported measures in individuals undergoing ACL reconstruction or primary ACL repair. Long-term outcomes of both procedures will be examined in terms of knee flexor and extensor muscle strength and endurance, torque-generating capacity and fatigue resistance, muscle oxygenation, knee joint proprioception, lower-extremity balance, and knee laxity. In this context, the findings of this study aim to provide valuable insights that may inform postoperative rehabilitation strategies and contribute to evidence-based clinical decision-making.
174 studies on the registry are indexed under Lacerations; 43 are open to participants now.
This study's planned enrollment of 45 is below the median of 100 across 37 observational studies indexed under Lacerations.
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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.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Inclusion Criteria for the ACL Reconstruction Group
Exclusion Criteria for the ACL Reconstruction Group
Inclusion Criteria for the Primary ACL Repair Group
Exclusion Criteria for the Primary ACL Repair Group
Inclusion Criteria for the Healthy Control Group
Exclusion Criteria for the Healthy Control Group
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Demographic data, injury history, and surgical details will be recorded for all participants. The International Physical Activity Questionnaire, IKDC, and ACL-RSI scales will be administered. Assessments will be completed over two days. Isokinetic knee flexor/extensor strength, fatigue protocol, and H/Q ratios will be measured using the Cybex Norm dynamometer. Quadriceps and hamstring muscle oxygenation will be assessed with Train.Red NIRS. Knee proprioception will be evaluated via active joint repositioning, and postural control and dynamic stability will be measured using the KFORCE force platform. Knee laxity will be assessed with the GNRB arthrometer.
Demographic data, injury history, and surgical details will be recorded for all participants. The International Physical Activity Questionnaire, IKDC, and ACL-RSI scales will be administered. Assessments will be completed over two days. Isokinetic knee flexor/extensor strength, fatigue protocol, and H/Q ratios will be measured using the Cybex Norm dynamometer. Quadriceps and hamstring muscle oxygenation will be assessed with Train.Red NIRS. Knee proprioception will be evaluated via active joint repositioning, and postural control and dynamic stability will be measured using the KFORCE force platform. Knee laxity will be assessed with the GNRB arthrometer.
Demographic data and physical activity levels will be recorded for healthy participants. All individuals will complete the International Physical Activity Questionnaire, IKDC, and ACL-RSI scales. Assessments will be conducted over two days. Knee flexor/extensor strength and H/Q ratios will be measured using the Cybex Norm isokinetic dynamometer. Quadriceps and hamstring muscle oxygenation will be assessed with the Train.Red NIRS device. Knee proprioception will be measured using an active joint repositioning test, while postural control and dynamic stability will be evaluated with the KFORCE force platform. Knee laxity will be assessed using the GNRB arthrometer.
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)
Time frame: First Day
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 (%)
Time frame: First day
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
Time frame: First day
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
Time frame: First day
Functional Range
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 (%)
Time frame: First Day
Fatigue-Induced Peak Torque Decline
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 (%)
Time frame: First Day
Muscle Oxygenation
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.
Time frame: First Day
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.
Time frame: First Day
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.
Time frame: Second Day
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.
Time frame: Second Day
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.
Time frame: First Day
IKDC Subjective Knee Evaluation
The International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form will be used to assess patient-reported knee symptoms, function, and sports activity levels. Scores range from 0 to 100, with higher scores indicating better knee function and fewer symptoms. This measure provides a validated assessment of functional recovery following ACL surgery.
Time frame: First Day
ACL-RSI (Return to Sport Index)
The Anterior Cruciate Ligament-Return to Sport after Injury (ACL-RSI) scale will be administered to evaluate psychological readiness to return to sport. The 12-item scale assesses emotions, confidence, and risk appraisal related to returning to physical activity. Scores range from 0 to 100, with higher scores indicating greater psychological readiness. This measure allows comparison of psychological recovery after ACL reconstruction and primary repair.
Time frame: First Day
Plan to share: No
Started Aug 2026 (actual). Primary completion is estimated for Jul 2027, 10 months after the start.
Of 20 observational studies under Lacerations, half reached primary completion within 25 months of starting (the median), counting those still running; a quarter within 12 and three quarters within 35. This study's planned 10 months is below that.
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