Lateral Retinacular Release Rates in Mobile- versus

Controversy exists as to whether bearing mobility facilitates centralization of the extensor mecha- nism after TKA. To assess the incidence of lateral retinacular release, we retrospectively reviewed 1318 consecutive primary TKAs (1032 patients) performed by one surgeon using either a rotating-platform bearing (940) or a fixed bearing (378) from the same implant system. The selection of a fixed- versus mobile-bearing TKA was pri- marily based on age with patients younger than 70 years receiving a mobile-bearing TKA. We performed a lateral release whenever continuous symmetric patellar facet contact with the trochlear groove from 0 to 90 of flexion was not obtained using the rule of no thumb after tourni- quet release. One hundred four of 1318 knees (7.9%) had a lateral release. We performed more lateral releases in the fixed-bearing group (14.3% (54 of 378)) than in the mobile-bearing group (5.3% (50 of 940)). Patellar tilt occurred more often in the mobile-bearing group (10% (94 of 940)) than in the fixed-bearing group (6.9% (26 of 378)), although the magnitude of mean patellar tilt was small in both groups (mobile-bearing 3.0; fixed bearing 2.55). No patient had patellar subluxation greater than 5 mm. We suspect the fewer lateral releases in the mobile-bearing group is the result of better extensor mechanism central- ization provided by bearing rotation. Level of Evidence: Level III, prognostic study. See the Guidelines for a complete description of levels of evidence.