Approximately 700 TKRs (Total Knee Arthroplasty) were performed in our department from 1992–2000. In 13 cases, patellar dislocation occurred post-operation - 12 with no trauma and one following a fall and trauma to the medial aspect of the knee. Dislocation occurred from 2 months following the operation until 1 year postoperative (average 4.5 months). None of the patients had malalignment of the components. The average femorotibial angle was 5° (range 8° valgus to 3° varus). No patient had preoperative valgus deformity. Postoperative range of motion was 105° (range 90–125°). All dislocations were treated by operative lateral relapse and medial capsular implication followed by 6 weeks of immobilization with a brace in full extension and then physiotherapy, range of motion, patellar taping and Vastus medialis strengthening.

The patella stabilized in 11 cases following the operation. In 2 cases, dislocation recurred following the operation and they were operated on again where medialization of the tibial tubercle was performed. Both cases stabilized following the second operation. One case developed a stress fracture of the tibia at the end of the tubercle osteotomy which healed conservatively. All dislocations occurred in the IBII prosthesis.

During the past 3 years since using the PFC Sigma and Legacy prosthesis, we have had no dislocations of the patella, probably for the following reasons:

Use of the mid vastus exposure.