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The objective of this paper is to describe the incidence of different types of re-operations following total knee replacement (TKR) with mobile bearing designs and to understand the extent to which they are susceptible to spin-out, a specific complication that may arise with these designs. The design is a systematic review of the incidence of re-operations, classified by the type of re-operation and stratified by study date, reported by clinical publications following TKR with fixed and mobile bearings from a single manufacturer. A search for relevant papers was conducted in online databases including EMBASE and Medline and a manual search of bibliographies. Studies following 8739 mobile bearing knees implanted in 1985–1997 and studies following 3413 mobile bearing knees implanted in 1997–2006 were identified. In the pre- and post-1997 studies, the number of insert revisions was 190 (2.3%) and 16 (0.4%), respectively; the number of revisions of the tibial tray/ femoral components was 295 (3.6%) and 43 (1.2%), respectively; the number of revisions for spin-out,dislocation, and instability was 117 (1.4%) and 10 (0.26%), respectively. In the fixed bearing studies there were no spin-outs, but the number of revisions for instability were 6 (0.16%) and 6 (0.21%) in pre- and post-1997 studies. For knees implanted between 1985 and 1997 the incidence of all wear related insert or component revision was 2% in the fixed bearing knee studies and 2% in the mobile bearing knee studies. For knees implanted in 1997–2006, the incidence of all wear related insert or component revision was 0.1% in the fixed bearing knee studies and 0.3% in the mobile bearing knee studies. In conclusion, polyethylene spin-out remains a unique complication of mobile bearing knees symptomatic of instability. Recent trends (after 1997) suggest that improved awareness of surgical technique and/or changes in design (posterior stabilization) have significantly decreased the incidence of this complication, with no evidence of a higher overall risk of revision for instability with contemporary mobile bearing versus fixed bearing knees.
knee, arthroplasty, mobile bearing, low contact stress, press fit condylar, Sigma
DePuy International Ltd., Leeds,
Univ. of Pittsburgh, Pittsburgh, PA