Long-term outcomes of primary constrained condylar knee arthroplasty

Background: Although constrained condylar knee (CCK) inserts are widely used for total knee arthroplasty (TKA), their long-term outcomes remain unclear. We sought to evaluate patients with at least 10 years' follow-up after CCK TKA to identify potential adverse events (osteolysis, loosening, constraintmechanism failure), assess functional outcomes with special emphasis on range of motion, and determine prosthesis survival. Hypothesis: Increasing constraint by implantation of a CCK insert does not increase the long-term frequencies of osteolysis or mechanical loosening. Material and methods: We studied 43 knees after Legacy CCK TKA. The indication was severe deformity (n= 20), pre-operative laxity (n= 6), or failure to achieve intra-operative balancing (n= 17). There were 41 patients with a mean age of 66 years (21-88). A history of one or more surgical procedures was noted for 27 (63%) knees. Outcome measures were the Hospital for Special Surgery (HSS) knee score, Knee Society Score (KSS), and change in the hip-knee-ankle (HKA) angle. Prosthesis survival was assessed using revision surgery for any reason or for reasons other than infection as the censoring criterion. Results: Complications other than venous thrombosis occurred in 16% of patients, including 3 who required revision surgery (septic loosening, n= 2; and major instability in a patient with ipsilateral hip arthrodesis). No cases of osteolysis or aseptic loosening were recorded. Mean follow-up was 12.7 years (range, 10-14). At last follow-up, the HSS score had improved from 53 (26-83) pre-operatively to 80 (55-93), the KSS knee component from 42 (16-77) to 90 (77-99), and the KSS function component from 31(0-80) to 61(10-90) (13< 0.001). Mean range of flexion increased from 109 (50 -140) to 112 (90 -130) (13= 0.12). The HKA angle changed from 182 I 15.5 (150 -210) to 179.5 I 2.5 (174 -184) (13= 0.5). The 11-year prosthesis survival rate was 88.5% (95% confidence interval, 0.69-0.94) overall and 97.7% (0.76-0.99) after excluding the cases of infection. Discussion: Long-term functional gains after CCK TKA were similar to those reported after standard posterior-stabilised TKA, with no cases of constraint-mechanism failure or osteolysis. The complication rate was higher, with decreased survival compared to standard TKA, but the knee deformities and/or instability were particularly severe and two-thirds of knees had a history of one or more surgical procedures. Level of evidence: Level IV, retrospective case-series study. (C) 2015 Elsevier Masson SAS. All rights reserved.