Flexion instability without dislocation after posterior stabilized total knees.

UNLABELLED: Flexion instability after cruciate-retaining total knee arthroplasty has been well documented. We identified an analogous patient group with symptomatic flexion instability without dislocation after primary posterior stabilized total knee arthroplasty. We sought to determine the typical symptoms and exam findings that lead to the diagnosis, to assess the reliability of revision total knee arthroplasty as a treatment, and to assess the technical difficulties encountered during revision total knee arthroplasty. Between 1995 and 2001, 10 patients had revision of a well-fixed posterior stabilized total knee arthroplasty for isolated symptomatic flexion instability. The typical constellation of symptoms and physical findings included a sense of instability without giving way, recurrent knee effusions, multiple areas of soft tissue tenderness about the knee, and substantial anterior tibial translation at 90 degrees of flexion. The revision operation focused on balancing the flexion and extension gaps while taking care to fill the enlarged flexion gap. Revision total knee arthroplasty was reliable in alleviating pain (mean Knee Society Pain scores improved from 68 points preoperatively to 89 points postoperatively), improving stability (nine of 10 patients had < 5 mm anterior tibial translation postoperatively) and improving patient satisfaction (nine of 10 patients were satisfied). We had no particular technical difficulties with the revision total knee arthroplasty procedures and had reliably achieved well-balanced flexion and extension gaps. LEVEL OF EVIDENCE: Therapeutic study, Level IV-1 (case series). See the Guidelines for Authors for a complete description of levels of evidence.