Patellar position and lateral approach for total knee arthroplasty in degenerative knees with lateral femoropatellar arthrosis

PURPOSE OF THE STUDY: Patellar malposition is a well-recognized patellar complication after total knee arthroplasty. Such residual malposition is particularly frequent when the knee presents lateral femoropatellar arthrosis. We compared the radiological position of the patella after total knee arthroplasty in degenerative knees with lateral femoropatellar arthrosis performed via a medial or lateral approach with elevation of the anterior tibial tuberosity. MATERIAL AND METHODS: Twenty-six total knee arthroplasties were reviewed retrospectively. Thirteen prostheses had been inserted via a medial approach and thirteen via a lateral approach. A posterior stabilized implant was used with an original technique for insertion of the patellar implant. The only difference between the groups was the approach. In the "lateral" group, the lateral approach was used to raise the tibial tuberosity and perform lateral marginal patellectomy. The tibial tuberosity was reinserted in all cases without transposition. Preoperative and 3-month postoperative radiographs (weight-bearing, AP, lateral, femoropatellar 30 degrees flexion) were reviewed. Preoperative patellar displacement was at least 5 mm. There was no difference between the two groups for age, gender, weight, height, joint motion, pre- and postoperative mechanical alignment (HKA), or preoperative patellar gliding (7.6 mm in the "medial" group and 9.7 mm in the "lateral" group). RESULTS: Recurrent patellar dislocation occurred in one patient in the "medial" group and one patient in the "lateral" group had an anterior impaction of the tibial plateau following a fall. Patellar gliding was corrected in both groups: 0.7 +/- 1.8 mm in the "medial group" and 0.0 +/- 0 in the lateral group (p > 0.05). Residual patellar tilt was +4.2 +/- 3 degrees in the medial group (lateral tilt) and -3.3 +/- 5.4 degrees in the lateral group (medial tilt) (p = 0.003). DISCUSSION: Pateller gliding was corrected irrespective of the approach. Conversely, the medial approach did not allow effective correction of patellar tilt. The lateral approach with elevation of the anterior tibial tuberosity did not increase morbidity compared with the medial approach. It enabled avoiding residual lateral patellar tilt which can be a source of patellar complications. We prefer this approach for arthroplasty on degenerated knees with lateral femoropatellar arthrosis.