Evaluation of healing of the injured posterior cruciate ligament : Analysis of instability and magnetic resonance imaging

Purpose: Knees with an acute posterior cruciate ligament (PCL) injury and soft endpoint on posterior drawer test often develop less instability and a firm endpoint at later follow-up. This type of healing is rarely seen in the acutely injured anterior cruciate ligament (ACL) and seems to be a unique feature of healing for PCL injury. The purpose of this study was to explore the healing process of the injured PCL by means of instability measurement and magnetic resonance imaging (MRI). Type of study: Consecutive sample. Methods: Forty-eight acute PCL deficient knees were followed up and evaluated. We evaluated the detection of a so-called firm endpoint using a posterior drawer test. We also determined the degree of posterior sag and categorized them as 3 grades. Quantitative assessment of total anteroposterior (AP) translation of the tibia with a KT-1000 knee arthrometer (MedMetric, San Diego, California) was performed by manual maximum AP drawer test with the knee flexed 70°. The continuity of the PCL was evaluated with sagittal and coronal T1- and T2-weighted MRIs. Results: Thirty-three (69%) cases exhibited a so-called firm endpoint with a posterior drawer test. These cases showed statistically less total AP translation (mean, 7.0 mm) in KT-1000 evaluation, compared with 15 cases without an endpoint (mean, 11.9 mm). In addition, 36 cases (75%) with continuous low-intensity MRI showed statistically less AP translation (mean 7.6 mm), compared with 12 cases (mean 11.4 mm) with disrupted PCL image. Conclusions: These results suggest that a high percentage of acutely injured PCLs are likely to develop somewhat slack but continuous ligament-like tissue, and this continuous PCL-like tissue might function as a posterior restraint of the tibia to certain extent. The elongated but continuous PCL might partly explain the relatively favorable prognosis of this injury.