Abstract
Background:
The number of young patients undergoing total knee arthroplasty is rapidly increasing. Long-term follow-up of modern type implants is needed to provide a benchmark of implant longevity for these patients.
Methods:
Between January 1995 and October 1997, 245 consecutive total knee arthroplasties were performed in 217 patients by a single surgeon. In 156 knees, the Genesis I implant was used, and in 89 knees the Genesis II implant was used. Mean age at surgery was 69.3 years for the Genesis I cohort and 66 years for the Genesis II (p = 0.016). At 15 to 17 years, cumulative survivorship was calculated using Kaplan-Meier statistics whilst outcomes were rated with the ‘Knee society score’ and with the ‘Knee Injury and Osteoarthritis Outcome Score’. Radiological assessment included coronal alignment measured on full leg standing X-rays, and analysis of radiolucent lines and polyethylene thickness on AP, Lateral and Axial X-rays, positioned under fluoroscopic control.
Results:
At 15 to 17 years, 79 patients had died (56 with Genesis I) and 27 were lost to follow-up. Eleven TKA had been revised including 10 Genesis I for infection (1), recurrent dislocation (1), loosening (1), patellar maltracking (2) or polyethylene (PE) wear (5) and 1 Genesis II for PE wear. 139 knees in 129 patients were in situ. Overall, the cumulative survivorship with endpoint revision for any reason was 92.4% at 15.7 years (95%CI: 91.0–93.8). In the Genesis I cohort, cumulative survivorship was 90.1% at 15.1 years (95%CI: 88.0–92.2). In the Genesis II cohort, cumulative survivorship was 98.1% at 14.9 years (95%CI: 97.9–98.3). The difference in survivorship was not statistically significant (log rank 3.136; p = 0.077), but the odds ratio for failure was 7.6 for the Genesis I compared to Genesis II. Logistic regression further identified gamma-air sterilization of PE as a significant predictor of failure, with an odds ratio of 13.4 compared to ETO sterilization. There was no difference in survivorship between patients younger or older than 55 years at surgery or between genders. Patients who underwent a revision had a significantly higher BMI (p = 0.027). There was no statistically significant difference in clinical outcome, radiographic radiolucencies or PE thickness changes between the surviving Genesis I and II cohorts.
Conclusions:
At 15 years, the overall 92.4% survivorship of the Genesis I TKA is good with excellent 98.1% survivorship for the Genesis II with the adapted femoral trochlear design. The results confirm the risk of PE wear when gamma-air sterilisation is used. Excellent longer-term outcome is obtained with a contemporary TKA implant using non cross-linked polyethylene.
