The risk of bearing dislocation in lateral unicompartmental knee arthroplasty using a mobile biconcave design

A safety study was conducted on a cohort of 25 patients who underwent lateral unicompartmental arthroplasty with a biconcave mobile-bearing insert. The first 25 lateral mobile-bearing unicompartmental knee replacements, performed in a general hospital by one surgeon, were prospectively reviewed, with a minimum follow-up of 1 year. One bearing dislocation occurred 4 months postsurgery. The Oxford knee score improved in all patients from a preoperative mean of 23.3 (range 8-40, SD 8.4) to a postoperative mean of 42.1 (range 23-48, SD 6.7). General patient satisfaction at a mean follow-up of 20 months was excellent in 84 %, good in 12 % and fair in 4 %. The mechanical axis as a measure on full-leg standing radiographs improved from 5.7A degrees valgus (range 1A degrees-16A degrees, SD 4.1A degrees) to 1.7A degrees valgus (7A degrees to -3A degrees, SD 2.1A degrees). Mechanical alignment correction averaged 4.0A degrees (range -1A degrees to 15A degrees, SD 3.9A degrees). The mobile biconcave insert design in the lateral unicompartmental knee replacement seems appropriate as a innovative, anatomy imitating solution, resulting in a good clinical outcome. Still, bearing dislocation remains a concern, especially in extended indication