DISLOCATION FOLLOWING PRIMARY POSTERIOR-STABILIZED TOTAL KNEE ARTHROPLASTY

From 1981 through 1991, 3,032 primary total knee arthroplasties were p erformed using the insall-Burstein Posterior Stabilized Condylar Prost hesis (IB-I, IB-II, and IB-II modified) (Zimmer, Warsaw, IN). Fifteen posterior dislocations occurred: 4 with the IB-I system occurring 2 or more years after surgery, 10 with the IB-II system (8 occurring 6 mon ths after surgery and 2 occurring 2-3 years after surgery), and 1 with the IB-II modified system occurring 9 months after surgery. Statistic ally significant differences for the rate of dislocation between both the IB-I and IB-II modified arthroplasties versus the IB-II arthroplas ties were found (P < .001). In an attempt to identify a cause for thes e dislocations, the authors retrospectively assessed the 15 dislocated cases with respect to sex, age, weight, height, preoperative and post operative Hospital for Special Surgery scores, preoperative and postop erative alignment, preoperative versus postoperative reconstruction di mensions, patellar thickness and height, and postoperative flexion and compared the results with those patients who did not experience dislo cation. Possible etiologies and mechanisms of dislocation were sought. There were no significant differences between the control and study g roups for any variable assessed, with the exception of postoperative f lexion, which averaged 118-degrees for the study group and 105-degrees for the control group (P < .001). Conservative management was success ful in 11 cases. In September 1988 the IB-II system was introduced; mo dification of the tibial insert was made in January 1990. The 10 IB-II dislocations occurred prior to the modification of the modular tibial polyethylene insert, and the 3 recurrent dislocations in this group w ere successfully treated with revision to this modified insert. Since this modification, 656 IB-II modified systems have been implanted with one dislocation (0.15%).