Fixed posterior subluxation in posterior cruciate ligament-deficient knees: diagnosis and treatment of a new clinical sign.

Among 248 patients seen for posterior cruciate ligament insufficiency, 109 (44%) had fixed posterior subluxation of the tibia, defined as a condition in which posterior sag could not be reduced to a neutral position, as evidenced by posterior tibial displacement of 3 mm or more on anterior stress radiographs at 200 N. The mean fixed posterior displacement was 6.23 mm (range, 3 to 20). The fixed posterior subluxation was divided into three grades: I, 3 to 5 mm (57.8%); II, 6 to 10 mm (33.9%); and III, more than 10 mm (8.3%). Comparison of the 109 study patients with the 139 control patients revealed a history of a failed posterior cruciate ligament operation or of a patellar tendon harvest, male sex, and a long history of posterior cruciate ligament insufficiency as significant risk factors for the development of a fixed posterior subluxation. After patients were treated with a posterior tibial support brace, the fixed posterior subluxation could be reduced to a mean of 2.58 +/- 5.22 mm within an average treatment period of 180 days. Fixed posterior subluxation can be detected in patients with posterior cruciate ligament deficiency by anterior and posterior stress radiographs and should be addressed before posterior cruciate ligament reconstruction to prevent early overloading of the graft.