Lateral retinacular release rates in mobile- versus fixed-bearing TKA

Abstract

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 degrees to 90 degrees 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 degrees ; fixed bearing 2.55 degrees ). 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.

Level of evidence: Level III, prognostic study. See the Guidelines for a complete description of levels of evidence.

Fig. 1A–B

Diagrams illustrate the radiographic measurements used to determine (A) patellar tilt angle (α) and (B) patellar subluxation from the center of the trochlear groove (X). (Reprinted with permission and copyright © 1993 of Lippincott Williams & Wilkins from Bindelglass DF, Cohen JL, Dorr LD. Patellar tilt and subluxation in total knee arthroplasty: relationship to pain, fixation, and design. Clin Orthop Relat Res. 1993;286:103–109.)

Fig. 2

A diagram demonstrates how placement of a fixed-bearing tibial component internally rotated on the proximal tibia results in lateralization of the tibial tubercle, an increase in Q angle, and a subsequent increased lateral force vector on the patella.