Rotational Subluxation Patterns on Stress Radiography and Clinical Relevance in PCL-Deficient Knees: A 2D-3D Registration Study.

Background: There is distinct tibial subluxation in posterior cruciate ligament (PCL)-deficient knees on stress radiographs, including posteromedial and posterolateral subluxation. PCL injuries have been emphasized in previous literature to be frequently associated with posterolateral rotatory instability. However, diagnosis of posterolateral corner (PLC) injuries often relies on the dial test, given the limited detection of these lesions on magnetic resonance imaging, and the incidence of concomitant PLC injury is uncertain. Purpose/Hypothesis: The purpose of this study was to evaluate rotational subluxation patterns and to identify factors associated with a positive dial test. It was hypothesized that the posterolateral subluxation pattern would be more prevalent and severe due to concomitant PLC injury and that a positive dial test would be associated with posterolateral subluxation pattern. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Patients who underwent primary PCL reconstruction were reviewed retrospectively. Three-dimensional models reconstructed from postoperative computed tomography were registered to preoperative stress radiographs. Posterior translation was assessed by measuring posterior tibial translation (PTT) of each compartment and side-to-side difference (STSD) on both radiographs and models. Rotational subluxation patterns were classified using the medial-lateral difference in side-to-side PTT changes. Clinical outcomes, distribution of suspected PLC involvement, and factors associated with dial test were assessed according to rotational subluxation patterns. Student Results: A total of 127 patients who underwent consecutive primary PCL reconstruction were included. Posteromedial subluxation (93 cases; 73.2%) was more prevalent than posterolateral laxity (34 cases; 26.8%) when compared with the contralateral side. Rotational laxity was greater in posteromedial subluxation than posterolateral subluxation (median, 5.07 vs 1.66 mm; Conclusion: Posteromedial subluxation pattern was markedly more prevalent than the posterolateral pattern in PCL deficiency. The dial test was associated with posterior laxity but was not specific for posterolateral subluxation. Patients with dominant posteromedial subluxation may be at risk of overtreatment if surgical decisions rely solely on rotational assessments.