Controversy exists as to whether bearing mobility facilitates centralization of the extensor mechanism 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 primarily 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 tourniquet 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 centralization provided by bearing rotation.