Preoperative medial knee instability is an underestimated risk factor for failure of revision ACL reconstruction

PURPOSE: The purpose of this study was to carefully analyse the reasons for revision ACLR failure to optimize the surgical revision technique and minimize the risk of recurrent re-rupture. Large studies with a minimum of 2 years of follow-up that clinically examine patients with revision ACLR are rare. METHODS: Between 2013 and 2016, 111 patients who underwent revision ACLR were included in the retrospective study. All patients were examined for a minimum of 2 years after revision surgery (35 ± 3.4 months, mean ± STD) and identified as “failed revision ACLR” (side-to-side difference ≥ 5 mm and pivot-shift grade 2/3) or “stable revision ACLR”. RESULTS: Failure after revision ACLR occurred in 14.5% (n = 16) of the cases. Preoperative medial knee instability (n = 36) was associated with failure; thus, patients had a 17 times greater risk of failure when medial knee instability was diagnosed (p = 0.015). The risk of failure was reduced when patients had medial stabilization (n = 24, p = 0.034) and extra-articular lateral tenodesis during revision surgery (n = 51, p = 0.028). Increased posterior tibial slope (n = 11 ≥ 12°, p = 0.046) and high-grade anterior knee laxity (side-to-side difference > 6 mm and pivot-shift grade 3, n = 41, p = 0.034) were associated with increased failure of revision ACLR. Obese patients had a 9 times greater risk of failure (p = 0.008, n = 30). CONCLUSION: This study demonstrates the largest revision ACLR patient group with pre- and postoperative clinical examination data and a follow-up of 2 years published to date. Preoperative medial knee instability is an underestimated risk factor for revision ACLR failure. Additionally, high-grade anterior knee laxity, increased PTS and high BMI are risk factors for failure of revision ACLR, while additional medial stabilization and lateral extra-articular tenodesis reduce the risk of failure. LEVEL OF EVIDENCE: III.