Primary Repair of Posterior Cruciate Ligament Avulsion Fracture: The Effect of Occult Injury in the Midsubstance on Postoperative Instability

Background In the posterior cruciate ligament avulsion fracture, posterior instability cannot be completely restored by the anatomical reduction and fixation of an avulsed fragment. Hypothesis The occult midsubstance injury inside the posterior cruciate ligament may affect the residual posterior instability after anatomical reduction and internal fixation of the avulsed fragment. Study Design Prospective comparative clinical study. Methods Thirty-one patients were followed for a period of 2 to 8 years. Based on magnetic resonance images taken immediately after the injury, these patients were divided into 2 groups, the occult injury group (group O, 15 knees) and the uninjured group (group N, 16 knees). Results The side-to-side difference of the posterior knee instability was 3.2 mm in group O and 3.0 mm in group N. Approximately 60% of the knees examined showed mild posterior instability in both groups. There were no significant differences found between the 2 groups. Conclusion The occult posterior cruciate ligament midsubstance injury does not significantly affect postoperative posterior instability of the knee. This fact did not support the hypothesis that has been commonly considered thus far. Clinical Relevance It is not necessary for orthopaedic surgeons to be overly apprehensive about occult midsubstance injury in the treatment of posterior cruciate ligament avulsion fracture.