Operative treatment of high-grade medial collateral ligament injury and chronic medial knee instability: a systematic review.

High-grade medial collateral ligament (MCL) injury and chronic medial knee instability can compromise both valgus and rotational control, especially in cruciate or multiligament injury. This systematic review evaluated operative treatment according to clinical phenotype rather than MCL grade alone. PubMed/MEDLINE and Web of Science Core Collection were searched from January 1, 2000, to August 10, 2026; a Cochrane CENTRAL update was completed on September 7, 2026. Eligible clinical reports included operative treatment of acute high-grade MCL/medial-complex injury or chronic symptomatic medial instability. Risk of bias was assessed with RoB 2, ROBINS-I, or the Joanna Briggs Institute case-series checklist. Thirty-five reports were included: 5 randomized or quasi-randomized trials, 9 nonrandomized comparative studies, and 21 case series. Routine acute medial surgery during ACL reconstruction was not consistently superior across heterogeneous grade III populations. In contrast, selected displaced distal or Stener-like lesions were plausible repair targets because interposition can prevent healing in apposition. Chronic symptomatic valgus and/or anteromedial rotatory insufficiency was most often treated with reconstruction, with directional improvement in objective stability and patient-reported outcomes in case series. Evidence for augmentation, the optimal reconstruction construct, and timing remains low certainty. Decisions should integrate repairability, residual valgus and rotational instability, associated ligament injury, alignment, and tissue quality. Prospective phenotype-stratified comparative studies using standardized stability, return-to-sport, complication, and long-term joint-preservation outcomes are required.Level of evidence: Level IV, systematic review of Level I-IV therapeutic studies.