Comparative Study of Mobile- and Fixed-Bearing Unicompartmental Knee Arthroplasty in Medial Osteoarthritis: A Prospective Randomized Study of Bone Preservation and Early Clinical Outcomes
Chumroonkiet Leelasestaporn MD1, Udom Tantipanpipat MD2
Affiliation : 1 Department of Orthopaedic Surgery, Bhumibol Adulyadej Hospital, Bangkok, Thailand 2 Department of Orthopaedic Surgery, Panyanantapikkuchonprathan Medical Center, Srinakarinwirot University, Bangkok, Thailand
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. Intraoperative 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 II. 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
