[Unicompartmental-knee arthroplasty for treatment of lateral gonarthrosis: about 30 cases. Midterm results].

PURPOSE OF THE STUDY: The appropriate treatment when joint degeneration is limited to the lateral compartment remains controversial. Total-knee arthroplasty and alignment osteotomy are well studied for genu valgum. Little is known about the results with lateral-unicompartmental prostheses. The purpose of this work was to evaluate the midterm results in a series of lateral unicompartmental-knee prostheses.

MATERIAL AND METHODS: From 1985 through 2005, 35 lateral unicompartmental prostheses were implanted among a total of 703 unicompartmental arthroplasties. The indication for surgery was established on the findings of the plain X-rays and stress films to evaluate the medial compartment. Preoperatively, the overall misalignment was 6 valgus (range: 0 to 15). The mean preoperative IKS was 102 (range: 54 to 164). Implants used were: Miller-Galante (n=20), ZUK (n=4), Marmor (n=5) and Alpina (n=1). Mean polyethelene thickness was 9 mm (range: 6 to 17 mm). The IKS score was established preoperatively and at last follow-up. Outcome assessment searched for clinical, radiological and surgical criteria affecting survival. The Kaplan-Meier method was used to determine implant survival. Surgical revision for implant replacement or adjunction of a new implant was considered as the endpoint of implant survival.

RESULTS: Twenty-nine patients (30 knees) were reviewed at mean nine years (range: two to 22 years). Mean IKS at one year was 185. At last follow-up, mean IKS was 166 (range: 28 to 200). Overall misalignment without revision was 3 (range: -6 to +11). Five arthroplasties were revised, four for extension of the degenerative disease (two supplementary unicompartmental prostheses and two total-knee arthroplasties) and one for depression of the tibial plateau after manipulation for stiffness and revision by total-knee arthroplasty. Two associated procedures were performed: arthroscopy for pseudoblockage at two years and one patellar osteosynthesis for fracture at 10 years.

DISCUSSION: We have used unicompartmental lateral prostheses regularly since initiating our experience, but for rare indications (5% of all unicompartmental implantations). The lateral unicompartmental prosthesis is a surgical solution for isolated femorotibial degeneration. Results at mean nine years follow-up have been encouraging, that is, similar to those with a medial prosthesis.