A prospective cohort study that will be conducted at Sultan Qaboos University Hospital. It aims to determine the outcomes, in terms of, activity level, functional level, subjective knee function, range of motion, stability, and failure, among patients with acute ACL injuries, who undergo arthroscopic primary ACL repair; and to compare these results with patients who undergo arthroscopic ACL reconstruction. To the investigators' knowledge, there is a dearth of studies looking into the outcomes of arthroscopic primary ACL repair and this going to be the first study in the Middle East. The investigators believe that arthroscopic primary ACL repair is superior to arthroscopic ACL reconstruction; and conducting this research project will elucidate the previously abandoned facts about acute ACL repair; and will eventually have a huge impact in the field of orthopedic surgery.

Hypothesis Null hypothesis: no difference in outcomes between arthroscopic primary ACL repair and arthroscopic ACL reconstruction in patients with acute ACL tear.

Alternative hypothesis: the arthroscopic primary ACL repair is superior to arthroscopic ACL reconstruction.

Background Anterior cruciate ligament (ACL) is an important mechanical stabilizer during knee-joint movement; it is the primary restraint against anterior tibial translation relative to the femur; and it acts as secondary restraint to tibial rotation and varus/valgus rotation. ACL injuries are commonly seen among athletics; and the number is increasing, with a reported incidence of 38/100,000 per year. Although there is still some debate about the optimal treatment for acute ACL tears, surgical management in the young and active patient is recommended. The surgical management options to an isolated ACL tear vary from acute repair to ligament reconstruction. Acute ACL repair can be classified into: acute primary repair, acute repair with the use of a ligament augmentation device, and acute repair with augmentation with an autologous hamstring tendon graft. The outcome of acute repair of ACL rupture from its femoral attachment or a proximal tear close to it, is the aim to be accomplished at the end of this project.

Several studies demonstrated that the results of acute repair of ACL ruptures deteriorate with time and the procedure was shown to be ineffective. However, most of the published studies are retrospective and nonrandomized, and they compare different surgical techniques, rehabilitation, and follow-up protocols. The surgeries were open and lengthy, the repairs were done on all injury types, on wide variety of ages, with varied concomitant injuries, and the rehab was primeval. Furthermore, there is no study that has described the long-term results of acute ACL repair.

Although the concept of ACL potential healing has been deserted in the past, there is renewed interest in the primary healing capacity of this ligament. One would argue why there is a need for the repair of a torn ACL. First, the operation is simple and takes less time and less risk in comparison to ACL reconstruction. Second, ACL treatment aims to provide immediate knee stability; resolve the pain and avoiding long-term complications, primarily osteoarthritis. ACL reconstruction using an autologous or allogenic tendon graft, is universally accepted as the gold standard treatment for complete ACL tears, as it yields excellent results for instability and pain in most the patients. However, there is a higher failure rate in adolescents than in other age groups with up to 20% to 25% of patients experiencing problems postoperatively. This mandates to find a better solution for this group of patients. In addition, patients post ACL reconstructions were found to have higher rates of osteoarthritis, despite the treatment; these findings are based on long-term follow up studies. This emphasizes on the need to find an alternative surgical management option to improve the ultimate outcomes. Third, the incidence of ACL injuries in skeletally immature patients are increasing; and so far, there are no standardized treatment options. For this group of patients, the transphyseal ACL reconstruction with grafts carries a risk for limb length and angular deformities, although several studies have proven no increase in the rate of such complications. Hence, the pre-pubescent population has the potential to benefit greatly from this regenerative treatment, which does not violate the physes; and they respond remarkably to certain biological stimuli implemented in the current enhanced repair techniques. Fourth, regeneration of the ACL over reconstruction preserves the remaining proprioceptive fibers within the ligament substance, and maintains the complex insertion sites of the ligament. This could potentially lead to more normal biomechanics of the knee if adequate regeneration is achieved.

Material and methods This is a prospective cohort study that will be conducted at Sultan Qaboos University Hospital (SQUH) and it involves patients with acute ACL injury attending the orthopedic clinic. The ACL rupture will be assessed clinically by anterior drawer test (ADT), Lachman's test, and pivot shift test. The ACL tear will be confirmed by knee MRI.

The ethical approval and permission from the concerned institution is required to start the study. All eligible patients who consent to participate will be included in the study.

The arthroscopic ACL repair will be carried out by one expert orthopedic surgeon. Because arthroscopy is a reference standard for the diagnosis of internal derangements of the knee, and because it is unethical to sacrifice a torn ACL that can be repaired; the patients will be assessed intra-operatively, and will be divided into two groups (group 1= ACL repair); group 2= ACL reconstruction) based on ACL amenability for repair or reconstruction. If the ACL was found to have a good tissue quality and fulfilling the inclusion criteria, it will be repaired using fiberwires and anchored to the femoral condyle using SwiveLock screw. If the ACL found irreparable, then it will be reconstructed using hamsting tendons graft. A minimum of 20 patients will be included in each group.

Post-operatively, the patients will undergo a specific rehabilitation program and will be followed up for, at least, one year to determine their activity level, functional level, subjective knee function, range of motion, stability, and failure of the repair.

The activity level will be evaluated using Tegner activity score, which is a scale that aims to provide a standardized method of grading work and sporting activities. It describes the current level of activity and that before injury. The score varies from 0-10; a score of 0 represents sick leave or disability pension because of knee problems, whereas a score of 10 corresponds to participation in national and international elite competitive sports.

The functional state will be graded using Lysholm scale, which is designed to assess how the knee problems have affected the patient's ability to manage in everyday life. It consists of 8 items that assess: pain (25 points), instability (25 points), locking (15 points), swelling (10 points), limp (5 points), stair climbing (10 points), squatting (5 points), and need for support (5 points). Every question response has been assigned an arbitrary score on an increasing scale. The total score is the sum of each response to the eight questions, and may range from 0-100. The scores are categorized as: Poor (<65); Fair (65-83); Good (84-90); and Excellent (>90).

Both scales will be translated into Arabic; then back-translation will be done into English, all by experts, to ensure absolute quality and accuracy.

The subjective knee function will be graded as poor, fair, good, and excellent.

The knee stability/anterior laxity will be assessed using ADT, Lachman's test, and pivot shift test. The ADT is graded as:

• Negative (0)
• +1: <5 mm translation,
• +2: 5 to 10 mm,
• +3: >10 mm translation.

The Lachman's test is graded as:

• Negative (0),
• Slight (1+): <5 mm of displacement,
• Moderate (2+): 5 to 10 mm,
• Severe (3+): >10 mm compared with that of the normal knee.

The pivot shift is graded as:

• Negative (0)
• Trace positive (1+),
• Moderate shift (2+),
• Subluxation (3+).

The patients will be evaluated by an independent observer.

The participants' data, including the personal information, will be kept safe and secure. The date will be anonymised with ID numbers. The hard copies will be in a locked filing cabinet and the soft copies will be securely password protected. The data will only be accessed by the agreed members of the research team. These records are not to be transferred to or shared with any other institute.

The Statistical Package for the Social Sciences (SPSS) will be used for the statistical analyses. Data collection and entry will be done by trained personnel. To assess relationship between variables: as univariate analysis, we will use Chi-square, t-test, ANOVA or non-parametric tests according to the nature of data. The nonparametric analysis of variance (Kruskal-Wallis test) will be used to determine the significance of the overall difference in the outcome measures among the two groups at a particular follow-up time-point. Paired comparisons among the two groups at each time-point will be made with use of the Mann-Whitney test. The Wilcoxon test for paired data will also be used to test for the significance of the changes in the outcome measures for a particular group between any two time points. Also, odd ratio will be calculated, where applicable. As adjusted multivariate analysis, we will use logistic regression. Relations between variables will be assessed by correlation coefficient.

Feasibility of the project This study is going to be a pilot study. Its primary mission is to provide immediate knee stability, resolve the pain and avoid long-term complications via simple and straightforward arthroscopic ACL repair. It is an evolving procedure and its results are promising. ACL injuries are common and the procedures are being done by one experienced orthopedic surgeon. The assessment scales that will be used are validated and have been used internationally in previous studies yielding valid information. To the investigator's knowledge, there is a dearth of studies looking into the outcomes of arthroscopic primary ACL repair and this is going to be the first study in the Middle East. Therefore, conducting this research project will yield reliable and helpful results; will elucidate the previously abandoned facts about acute ACL repair; and will eventually have a huge impact in the field of orthopedic surgery.

Inclusion Criteria:

• Acute ACL injuries. i.e., within 3 month.
• ACL rupture from its femoral attachment or a proximal tear close to it
• Concomitant meniscal injuries

Exclusion Criteria:

• Chronic ACL injuries
• Mid-substance ACL tears
• Previous surgery on the injured knee
• Associated knee pathology (e.g. infection; fractures, osteoarthritis, etc).

A full manuscript write-up will be shared at the end of the study.