Purpose: Implantation of a single-compartment lateral prosthesis can be proposed to patients with primary or secondary osteoarthritis uniquely involving the lateral femorotibial compartment. Many surgeons hesitate to use this procedure which does not have a particularly good reputation. We report a series analysed retrospectively to determine the impact of aetiology, operative findings, and pre- and post-operative radiographic findings on final outcome. We searched for the ‘ideal’ indication and specific technical difficulties encountered.

Material and methods: The review included 81 single-compartment medial implants (complete pre- and postoperative radiological and clinical data were available for 87% of the files, all were reviewed). Minimum follow-up was two years (mean 6.5 years). Clinical assessment was based on the IKS score and radiological analysis included a complete series (AP, lateral, axial, full knee, preoperative stress views).

Results: Mean IKS score was clearly improved from 49/100 preoperatively to 90.2/100 postoperatively. Severe pain was noted in 12% of the patients preoperatively versus 1.2% postoperatively. Sixty-three percent of the patients had completely forgotten their knee. Mean amplitude was 0.5–123°. Clinical lateral laxity was less than 5° in 93% of the patients and the knee was stable in the sagittal plane in 96.5%. Mean function score improved from 59/100 preoperatively to 73.3/100 postoperatively, limited basically by going up and down stairs (normal values in 36% of the patients). Walking distance was greater than 1 km in 68% of the patients (29% preoperatively). In the frontal plane, the mean mechanical femorotibial angle was 183.31 ± 3.01° (189.9 ± 5° preoperatively) with a mean mechanical femoral angle of 91.06 ± 3.01 (and a mean mechanical tibial angle of 90.6 ± 1°. Implant survival at five years was 97.15% and 93.33% at ten years (three loosenings and one metallosis).

Discussion: At last follow-up, the final result was significantly affected by diverse factors: osteoarthritis status at surgery (p < 0.02), patient age (p < 0.01), raising the anterior tibial tuberosity (p < 0.01), initial aetiology. The results were compared with data in the literature and discussed by type of indication and therapeutic options for lateral femoral osteoarthritis. The problem of indications in case of tibial plateau fractures and lateral meniscectomy is discussed.

Conclusion: These clinical and radiological results show that the lateral single-compartment prosthesis is a safe and reliable procedure for the treatment of primary or secondary osteoarthritis of the lateral femorotibial compartment.