Posteromedial corner injuries result in the same posterior translation as posterolateral corner injuries in PCL ruptures

Purpose: Ruptures of the posterior cruciate ligament (PCL) are often accompanied by posterolateral corner (PLC) and posteromedial corner (PMC) injuries. This study investigates the incidence and impact of PMC and PLC injuries on posterior tibial translation (PTT). It was hypothesized that PMC injuries are more common and impactful than previously reported. Methods: In this retrospective study, all patients with a PCL injury between January 2016 and December 2023 and received magnetic resonance imaging (MRI) within 30 days of trauma were included. Patients with atraumatic PCL instability, missing MRI or additional anterior cruciate ligament (ACL) rupture were excluded. Posttraumatic MRI was analyzed for peripheral injuries. Preoperative stress radiographs for PTT were measured, and the side-to-side difference was calculated. The statistical significance level was set at p < 0.05. Results: Ninety-two patients were included, predominantly male (71.7%) with a mean age of 35.8 ± 15.6 years at injury. The mean time from injury to MRI was 7.3 ± 7.9 days. There were 16 patients (27.4%) with isolated PCL injuries. The prevalence of medial injuries (37.0% superficial medial collateral ligament [sMCL], 66.3% deep medial collateral ligament and 51.1% posterior oblique ligament [POL]) was comparable to lateral injuries (22.8% LCL, 55.4% PLC and 13.0% popliteus tendon). Injuries of the PMC (sMCL ± POL) occurred in 53 patients (57.6%) and of the PLC (POP ± PLC ± LCL) in 59 (64.1%) patients. PTT was significantly increased in the presence of a peripheral-associated injury compared to isolated PCL injury (p < 0.01). With a combined injury of PMC + PLC the PTT was significantly larger than in the case of a unilateral injury (p < 0.05 compared to PLC; p < 0.05 compared to PMC). Conclusion: PCL injuries are commonly associated with PMC and/or PLC injuries. A PTT of >10 mm is equally caused by PLC and PMC-associated injuries. Knowledge about the severity and localization of peripheral-associated injuries is therefore essential for therapeutic decision-making. Level of Evidence: Level III retrospective cohort study.