Minimally invasive approaches for unicompartmental knee arthroplasty are well-accepted for treating knee arthritis because of the smaller implant size, shorter operative time, and tissue-sparing nature of the procedure. With the introduction of computer alignment systems, a well-aligned and balanced total knee arthroplasty (TKA) can be achieved even with smaller surgical exposures. We hypothesized a unicompartmental knee arthroplasty would provide better midterm outcomes than a computer-assisted minimally invasive TKA in patients with isolated medial compartment knee arthritis. We matched (preoperative arthritis severity, age, gender, and preoperative range of motion) 64 knees that had a medial unicompartmental knee arthroplasty or a mini-incision computer-assisted TKA. All patients had a varus deformity no greater than 8° and a body mass index lower than 30 kg/m2. Patients were followed a minimum of 48 months. In the mini-incision computer-assisted TKA group, all the implants were positioned within 4° of ideal alignment. The surgical time and hospital stay were longer in the computer-assisted TKA group. A unicompartmental knee arthroplasty was estimated to cost at least 3100 euros (approximately US $4100) less. The clinical assessment showed higher functional and Italian Orthopaedic UKA Users Group scores for the unicompartmental knee arthroplasty group.

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