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.
