BACKGROUND: Failed anterior cruciate ligament reconstruction (ACLR) leads to reduced quality of life and sometimes the need for repeat surgery. The reason for failure can be multifactorial and difficult to determine. Reports on failure leading to revision are few with limited generalizability. Also, no studies have investigated the reasons for early (<
2 years) versus late (≥2 years) revision. PURPOSE: To describe patients undergoing revision surgery, the surgeon's reported cause of failure, and the risk of undergoing early versus late revision surgery. STUDY DESIGN: Cohort study
Level of evidence, 3. METHODS: Primary ACLR cases without concomitant ligament injuries or surgery, registered in the Norwegian Knee Ligament Register from 2004 throughout 2023, were eligible. Descriptive analyses were conducted on intraoperative findings and procedures, time from injury to surgery, activity at the time of injury, revision surgery, surgeon-reported cause of revision, and reporting method. The Kaplan-Meier method was used to calculate revision rates. A multivariable Cox regression model, adjusted for confounders, was used to calculate the hazard ratio of early and late revision surgery. RESULTS: A total of 30,035 primary ACLR cases were analyzed, of which 1599 resulted in revision surgery. The overall revision rate was 7.1% at 15 years. Female patients were younger at the time of both primary and revision surgery (23.8 and 22.5 years, respectively) compared with male patients (28.2 and 22.2 years, respectively). Age at the time of primary surgery was significantly lower for patients who underwent revision (20.4 years) compared with those who did not undergo revision (26.5 years). Male sex, lower age, hamstring tendon graft, and no cartilage injury at the time of primary reconstruction were all associated with a higher risk of early revision. Lower age, hamstring tendon graft, and no meniscal injury were associated with a higher risk of late revision. New trauma (38.1%) was found to be the most common cause of failure leading to revision. CONCLUSION: In the current study, representing one of the largest cohorts to date investigating failed primary ACLR leading to revision, the overall 15-year revision rate was estimated as 7.1%. Patients receiving hamstring tendon grafts were at a particular risk for early revision during the first 2 years after primary reconstruction. New trauma was the most common reported cause of failure leading to revision ACLR.