Association of knee ligament injury with pelvic and acetabular fractures: a retrospective cohort study.

BACKGROUND: Knee ligament injuries associated with pelvic and acetabular fractures are frequently overlooked during high-energy trauma, contributing to delayed diagnosis and long-term disability. Evidence describing their incidence and associated fracture patterns remains limited. OBJECTIVE: To determine the incidence of knee ligament injury and identify the fracture patterns associated with it in patients with pelvic or acetabular fractures. MATERIALS AND METHODS: We retrospectively reviewed 328 patients with pelvic or acetabular fractures (after excluding 44 of 372 eligible patients lost to follow-up) treated at a tertiary trauma centre between July 2014 and July 2024. Demographics, fracture characteristics, knee examination findings, imaging, and International Knee Documentation Committee (IKDC) scores were analyzed. Associations between fracture pattern and knee ligament injury were assessed using Fisher's exact test, with odds ratios estimated by the unconditional (Woolf) method. RESULTS: Knee injury of any type occurred in 25 of 328 patients (7.62%). Knee ligament injury was identified in 11 patients (3.35%; 95% CI 1.41-5.30%); posterior cruciate ligament (PCL) tears were most common (6 cases, 54.5% of ligament injuries), followed by knee dislocation (4 cases: 3 Schenck KD III-L, 1 KD II) and an isolated lateral collateral ligament (LCL) avulsion (1 case). Knee ligament injury was significantly associated with posterior wall fracture (OR 4.19, 95% CI 1.17-15.00; P = 0.039), combined posterior wall-column fracture (OR 11.52, 95% CI 2.04-65.11; P = 0.026), and posterior hip dislocation (OR 4.76, 95% CI 1.32-17.09; P = 0.028). Posterior column fracture showed a large point estimate that did not reach statistical significance (OR 15.75, 95% CI 1.32-188.39; P = 0.098). Among patients with knee ligament injury, associated injuries included other-extremity trauma (45%), head injury (27%), and chest injury (18%); one case (9%) of PCL injury was diagnosed three months after injury. CONCLUSION: Knee ligament injury occurs in 3.35% of patients with pelvic or acetabular fractures and is significantly associated with posterior wall and combined posterior wall-column acetabular fracture patterns and with posterior hip dislocation. Routine knee assessment is recommended in this population to reduce missed or delayed diagnosis.