Patients who underwent knee joint arthroplasty between 2004 and 2007 with either a TKA (Stryker Scorpio NRG, Japan Stryker Company, Tokyo, Japan) or fixed-bearing UKA (Stryker EIUS UKA) were retrospectively identified from our database and reviewed. There were 48 patients with 50 primary TKAs and 25 patients with 28 UKAs performed at our institution. This study was performed in accordance with the ethical standards established in the 1964 Declaration of Helsinki and its amendments, and was approved by the local ethics committee. The exclusion criteria for UKA were more than 15° varus deformity, over 5° flexion contracture, less than 90° active ROM, dysfunction of the anterior cruciate ligament (ACL), non-isolated medial compartment involving the patellofemoral joint, or rheumatoid arthritis [
7‐
10]. Those who met any of the exclusion criteria for UKA underwent TKA. All patients with follow-up clinical data were enrolled in this trial, and the data were collected prospectively. The clinical analysis data included preoperative and postoperative femoro-tibial angle (FTA), ROM, Japanese Orthopedic Association (JOA) scores [
11], and Japanese Knee Osteoarthritis Measure (JKOM) [
12]. The mean follow-up period was 9 years (TKA: mean, 10.5 years; range, 7–12 years; UKA: mean, 9 years; range, 6–11 years). Survivorship was defined as freedom from revision surgery. All TKAs were performed by the medial parapatellar approach, which induced eversion of the patella [
13]. The UKA surgical procedure was a mini-invasive technique that involved a medial parapatellar approach with a 1-Qfb (Querfingerbreite, about 1.5 cm) incision from the upper pole of the patella to 1-Qfb distal to the medial tibial plateau by subluxation of the patella and exposure of the ACL [
14]. All surgeries were performed by a single surgeon (H.K.). After the operation, patients were encouraged to undergo physiotherapy with mobilization and weight-bearing under the assistance and control of a physiotherapist. Clinical outcomes, such as FTA, ROM, and JOA scores, were assessed at 2 weeks, 1 month, 3 months, 6 months, 1 year, and the latest follow-up. The clinical outcomes were then compared between the TKA and UKA groups. At every follow-up, a clinical and radiographic review was performed. Differences in sex distribution were assessed using the chi-square test. Differences in BMI, age, and follow-up time between TKA and UKA were evaluated using the chi-square test or non-matched pair analysis for two-group comparisons. All outcome measures (FTA, ROM, JOA score, JKOM) were evaluated preoperatively and postoperatively by the Mann-Whitney
U test.
Kaplan-Meier survival analysis was performed to assess implant durability. Statistical analysis was performed using Microsoft Office Excel and Statcel 3 (OMS, Inc., Tokyo, Japan).