Surgical Management of Symptomatic Instability After Failed Primary Total Knee Arthroplasty

The etiology of instability as a failure mode is multifactorial. In this study, we attempt to identify those parameters with regard to the clinical history, physical examination, and objective radiographic analyses that help identify the patient at risk. One hundred nine revision total knee arthroplasty procedures in 105 patients were performed for symptomatic instability as the primary diagnosis. The average time to follow-up was 4.2 years (range, 2.0-8.6 years). The average Knee Society score improved from 43 to 87 with an improvement in the function score from 56 to 82. The total range of motion increased from 103° to 115° (P < .01). The average intraoperative measured changes included an increase in the distal femoral condylar distance of −1 mm and a concomitant change in the posterior femoral condylar distance of +4 mm. Polyethylene thickness was increased by an average of 11 mm. There were 6 reoperations: two for aseptic loosening of the tibial baseplate, two for recurrent instability requiring polyethylene insert exchange, one for infection requiring two-stage revision, and one for patellar tendon rupture requiring allograft reconstruction. In conclusion, good results can be achieved in this difficult patient population. Modular augments on the femoral side help restore the anatomic condylar profile whereas increasing polyethylene thickness corrects ligamentous laxity in flexion and extension.