Background: Medial osteoarthritis performed with fixed-bearing UKA and with mobile-bearing UKA have both had excellent survivorship reports. However, there have been no clinical studies of outcomes of the two systems or studies of bone preservation.

Objective: The objectives of this study were to compare intraoperative bone preservation and early clinical and radiological outcomes between fixed-bearing and mobile-bearing unicompartmental knee arthroplasty in medial osteoarthritis.

Materials and Methods: Between July 2012 and June 2013, 40 consecutive, unicompartmental knee arthroplasties were performed on 40 patients. The authors prospectively randomized those patients
into two groups: twenty fixed-bearing unicompartmental knee arthroplasties [UKA] were conducted in group 1 and 20 mobile-bearing unicompartmental knee arthroplasties were conducted in group 2. Tntraoperative data recorded included the amount of bone resection, operative time, blood loss, wound length, length of stay, and post-operative knee alignment, the latter assessed using the
Kennedy and White classification system. Knee Society scores and Functional scores were recorded postoperatively at one month, three months, six months, one year and two years for clinical evaluation.

Results: Group 1 (fixed-bearing) had significantly more bone weight resection than group 2 (mobile-bearing) at 22.0 mg versus 15.90 mg (p = 0.002). Differences in early clinical outcomes between the two groups were not statistically significant. Postoperative mechanical axis alignment, based on radiographic assessment with the Kennedy and White classification, showed 75% of the mobile-bearing UKA patients in Zone C and 70% of the fixed-bearing UKA patients in zone TT. Three patients (7.5%) had postoperative complications: one in the fixed-bearing group had a medial tibial
plateau fracture and one in the mobile-bearing group had a superficial wound infection, both of which were successfully treated conservatively. The remaining patient, had a bearing dislocation
treated with a revision with thicker polyethylene.

Conclusion: This study demonstrated that mobile-bearing UKA achieves significantly better bone preservation due to lower bone loss when compared with fixed-bearing UKA. However, fixed-bearing
UKA requires less surgical time and involves fewer safety procedures. Both fixed-bearing UKA and mobile-bearing UKA patients had excellent early clinical outcomes.

Keywords: Medial compartment knee disease, Unicompartmental knee arthroplasty, Fixed-bearing, Mobile-bearing, UKA