Postoperative Joint Stability with Unicompartmental Knee Arthroplasty

GOTO Toshihiko, 中川 寛顕

doi:10.11551/jsjd.34.585

Objective: We performed unicompartmental knee arthroplasty (UKA) in patients with osteoarthritis and osteonecrosis of the knee. Appropriate joint stability is essential prior to UKA. We performed medial retinacular release from the medial tibia joint surface nearly 15mm, taking care intraoperatively to avoid over-correction of the femorotibial angle (FTA). This study was designed to evaluate the short-term and mid-term results of UKA in patients with osteoarthritis and osteonecrosis, and to determine whether joint stability was maintained postoperatively.<br>Methods: Seventy-four patients (74 affected knees; 15 males, 59 females) who had undergone UKA at least 6 months previously, were included in this study. The mean patient age was 77.5±5.1 years (range, 60-94 years). The Japanese Orthopaedic Association (JOA) score was used for the clinical evaluation of osteoarthritis of the knees. Radiological evaluation employed component angle, FTA on radiograph, the angle of inclination on stress radiograph and the femoral-component rotation angle (FCRA) on computed tomography scan. The component angle includes the femoral-component angle (FCA), the tibial-component angle (TCA), the lateral femoral-component angle (LFCA), and the lateral tibial-component angle (LTCA).<br>Results: The average JOA score improved significantly from 55.9±9.4 preoperatively to 86.0±5.5 postoperatively (P < 0.05). The average component angles were as follows: FCA 95.9±3.6°, TCA 88.8±2.0°, LFCA −1.0±6.1° and LTCA 87.7±2.3°, respectively. The average FTA also improved significantly from 181.4±5.3° preoperatively to 174.7±4.1° postoperatively (P < 0.05). The average FCRA was 0.22±4.7°, which was almost parallel to the epicondylar axis. In flexion, medial instability was found in seven patients (7 affected knees), and in extension, lateral instability was found in 17 patients (17 affected knees).<br>Conclusion: Short- and mid-term outcome and short-term joint stability after UKA were gener-ally favorable. The cases of joint instability after UKA included three patients (3 affected knees) who had required extensive medial retinacular release. These results suggest that joint stability after UKA may be influenced by prior lateral laxity, prior instability, and surgical technique.

Postoperative Joint Stability with Unicompartmental Knee Arthroplasty

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