Primary modular total knee replacement in severe and unstable osteoarthritis. Predictive factors for failure.

PURPOSE: Severe cases of osteoarthritis with ligamentous instability require the use of a modular knee arthoplasty. To assess the survival, the complications, the clinical, radiological and functional outcomes, and the quality of life of those patients in whom a Optetrak Condylar Constrained Knee (CCK) had been implanted as a primary implant. To study how the pre-operative conditions (deformity, age, sex …) and the characteristics of the arthroplasty (stems, supplements, constrained component …) could change the survival or the clinical outcomes of the implants. METHODS: We performed an observational retrospective study of 105 CCKs implanted between 1999 and 2005. The mean follow-up was nine years (7, 13). Mean age was 70.5 years. The mortality was 6.9 %. There were 9.3 % of the patients lost during the follow-up. We studied all the medical files of the patients in order to assess the pre-operative, surgical and postoperative conditions. We used the Knee Society Score (KSS), both clinical and functional, to study the functional and clinical situation. We analysed the X-ray using the Knee Society roentgenographic evaluation. The quality of life was studied using the Oxford Knee Score (OKS). Then in order to find predictor conditions, we made statistical multivariable predictive studies attending to the preoperative factors and to the arthroplasty conditions to compare both outcomes and survival (Kaplan-Meier groups curves and Cox Multivariable Models [hazard ratio]). Processing and data analysis was performed using SPSS 15.0. RESULTS: The outcomes did not show differences between all the groups. While the mean result of the clinical KSS was 75.8, the mean functional KSS was 73.1. We did not find a condition associated with worst results of the knees (p > 0.05). The KSS obtained was excellent or good in 74.9 %. The global survival at 24 months was 93.8 % and at 96 months was 90.1 %. There were some conditions associated with poorest survival of the arthroplasties: patients younger than 70 years old, tibial tuberosity osteotomy, use of long stems and new surgery two months after arthoplasty (p < 0.05). The 11.1 % of the arthroplasties required more surgeries (3.3 % were soft tissue surgeries and 7.8 % were revisions). The mean OKS obtained was 34.78. Satisfaction was obtained by 86.2 % of the patients. CONCLUSIONS: All severe and unstable knees obtained similar and overall excellent-good outcomes and survival using the Optetrak CCK. Although we found that there are some factors that could change the survival of the total knee replacement, these did not change the outcomes.