Numerous studies indicate that total knee arthroplasty (TKA) achieves excellent long-term success whether the posterior cruciate ligament (PCL) is saved or excised. In 13 patients, 16 PCL-retaining TKAs were identified with incapacitating instability secondary to early PCL deficiency. Patients with clinical PCL insufficiency present with a triad of subjective complaints: persistent swelling/effusions, anterior knee pain, and giving-way or instability episodes with activities of daily living. Of 13 patients, 12 had at least three postoperative visits with identical subjective complaints before PCL deficiency was diagnosed. On examination all patients exhibited effusion, posterior sag, positive quadriceps active test, and a visible anterior translation of the tibia on the femur while extending the leg from a seated, 90 degree flexed position. This sign has not been previously described to our knowledge but was present in all of our study patients. No patients had radiographic evidence of loosening or osteolysis. Joint aspiration was negative for infection in all patients. No patient had lateral patellofemoral maltracking. By radiographic measurement, the PCL-deficient knees had an average joint line elevation of 10.3 mm, compared with well-functioning TKAs which had an average joint line elevation of 5.0 mm. There was no correlation of PCL deficiency with excessive proximal tibial resection. Nonsurgical intervention provided no improvement in pain or instability. Six patients had improvement of pain, effusion, and stability after revision to a cruciate-substituting implant. We believe that this complication occurs more frequently than is currently being identified and should be considered in problem TKAs with normal radiographs.

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