Lateral unicondylar knee arthroplasty (UKA): contemporary indications, surgical technique, and results

Abstract

Unicompartmental femoro-tibial osteoarthritis usually affects the medial compartment of the knee, but in 10%, the lateral compartment is primarily involved. Femoral osteotomy is attractive to avoid TKA in younger patients with low-grade unicompartmental osteoarthritis and a valgus deformity. However, only limited functional results can be expected for patients with Ahlback grade 2 or greater osteoarthritis. Moreover, because of previous skin incisions and hardware removal, TKA after femoral osteotomy remains a complex procedure with poor functional results. Unicompartmental knee arthroplasty for both the medial and the lateral compartments has been performed since the 1970s. In a patient with involvement of only one compartment, a medial or a lateral UKA can provide a quicker recovery and enhanced function when compared to TKA. In addition, it preserves bone stock and can be "easily" revised by a TKA. Technical improvements, combined with strict patient selection, have resulted in ten year survivorships greater than 90%. However, lateral UKA is technically more challenging than medial UKA due to the lower number of indications, as well as the functional anatomy of the lateral compartment. The goals of this article are to present up-to-date information concerning indications, patients' selection, surgical technique and results of lateral compartment UKA.

Fig. 1

This intra-operative photograph depicts the skin incision. The upper limit is the superior pole of the patella, while the incision is extended distally toward the lateral side of the tibial tuberosity

Fig. 2

After the lateral arthrotomy, the joint is opened and the lateral part of the fat pad is excised to expose the lateral femoral condyle, tibial plateau and ACL

Fig. 3

Intra-operative photograph showing the thickness of the tibial resection, as the disease is more often on the femoral side, the tibial resection should be conservative and correlated to the implant thickness

Fig. 4

The sagittal tibial cut should be performed respecting the tibial spine eminence, and should follow the line joining the most medial point of the mid-portion of lateral plateau (posterior to the ACL insertion) and the most medial border of the lateral plateau (anterior to the ACL insertion)

Fig. 5

Search for the best compromise between an anatomically centered position on the femoral condyle and the long axis perpendicular to the resected tibial plateau

Fig. 6

The flexion-extension gaps are stressed with the trial components in place, including a trial polyethylene liner

Fig. 7

Effect of the “screw home mechanism” on femoral implant positioning (flexion-extension)

Fig. 8

Post-operative long axis X-rays of a 55-year-old man, operated for osteoarthritis limited to the lateral compartment of the knee