Unicompartmental arthroplasty of the knee. Postoperative alignment and its influence on overall results.

One hundred consecutive medial compartment knee arthroplasties for osteoarthritis were reviewed for overall clinical result and postoperative alignment. Follow-up evaluation ranged from 24 to 123 months with 51 months being the median. The Marmor knee rating system was used. The alignment of the knee relative to the mechanical axis of the leg (center of the femoral head to the midpoint of the ankle mortise) was determined by a standing three-foot roentgenogram. Of the arthroplasties, 90% were excellent or good results. Superior results were obtained when the mechanical axis fell in the center of the knee (Zone C) or slightly medial to the center (Zone 2). Causes of failure included fractures, femoral component loosening, and excessive lateral compartment or patellofemoral wear. Cartier and Villers' preoperative templating system was modified for intraoperative alignment with the mechanical axis falling into Zone C or Zone 2.