Accuracy of stress radiography techniques in grading isolated and combined posterior knee injuries

Background: Stress radiography techniques have been shown to be superior to the arthrometer and clinical examination in evaluating the posterior cruciate ligament-deficient knee, but no precise relationship has been established between the extent of the lesion and the laxity measured by stress radiography. Hypothesis: It is possible to establish a precise relation between posterior laxity and the anatomical lesions of the posterior cruciate ligament and posterior structures using stress radiography. Study Design: Controlled laboratory study. Methods: Measurements were performed on 15 fresh-frozen cadaveric knee specimens. A partial posterior cruciate ligament lesion was created by sectioning the anterolateral bundle, followed by a complete section. Then the lateral collateral ligament and the posterolateral corner were transected, and finally the medial collateral ligament and the posteromedial corner were sectioned. Stress radiography was performed first on the intact knee and again after each lesion was created using 4 techniques: Gravity Sag View, PCL-Press, Telos at 80 degrees, and Telos at 30 degrees of flexion. Results: Telos 30 and Telos 80 revealed the best overall performance as a diagnostic test in terms of accuracy in discriminating between the different types of lesions. Using the Telos device, we determined the following cut-off points: for a partial lesion, less than 3 mm at 30 degrees and less than 6 mm at 80 degrees; for a complete lesion, between 4 mm and 9 mm at 30 degrees and between 7 mm and 12 mm at 80 degrees; for associated peripheral lesions, more than 9 mm at 30 degrees and more than 12 mm at 80 degrees. Conclusion: The Telos 30 degrees and 80 degrees allow us to accurately distinguish between the different types of lesion and permit grading of posterior knee laxity. Clinical Relevance: Stress radiography allows characterization of posterior knee injuries and helps to determine treatment strategy.