Open-wedge osteotomy of the lateral femoral condyle for extensor mechanism instability.

Objective: To achieve extensor mechanism stability in postpatellectomy patients by elevating the lateral femoral condyle, thus creating a deeper trochlear groove.

Indications: Instability of the quadriceps tendon after patellectomy and other realignment interventions, including but not limited to the release of the lateral patellofemoral ligaments, advancement of the vastus medialis obliquus muscle and, in some cases, transfer of the tibial tubercle. Stabilization of a normal dislocating patella in presence of a hypoplastic lateral femoral condyle.

Contraindications: Medical conditions precluding surgery.

Surgical Technique: An open-wedge osteotomy of the lateral femoral condyle is performed. Predrilling at the osteotomy level is followed by a multiple-step curved-type osteotomy starting laterally, directed upward to the trochlea. Bone wedges are inserted under the levered bony fragment and the intrinsically stable osteotomy is secured with one or more countersunk screws.

Postoperative Management: A removable splint is applied in 30 degrees of knee flexion. With patellectomy, the splint is applied in 90 degrees of knee flexion for the first 3 days. Continuous passive motion and partial weight bearing are started 4 days after surgery in all patients. Use of the splint is advocated for 6 weeks in total.

Results: Eight knees (six patients) with extensor mechanism instability underwent this procedure. In five knees patellectomy had been performed earlier, one patient underwent an osteotomy combined with patellectomy bilaterally, in one patient a normal patella was left in situ. No instability was reported after surgery (average follow-up 8 years, range 2-17 years). Modified Lysholm Knee Scores showed two excellent, two good, and four fair results. Follow-up radiographs showed a healed osteotomy and an increase in trochlear depth.