Acceptable mid- to long-term survival rates and functional outcomes following a single design rotating hinge total knee arthroplasty.

PURPOSE

This study first analyzes implant survival of this single design modular rotating hinge knee and identifies potential risk factors for failure and evaluates joint function using the postoperative WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) score, active flexion and extension deficit.

METHODS

131 prostheses implanted for failure of prior total knee arthroplasty (n = 120) or complex primary procedures (n = 11) using a single modular implant (MUTARS-modular universal tumor and revision system GenuX, Implantcast, Buxtehude, Germany) between 2006 and 2014 including 73 patients treated for periprosthetic joint infection with a two-stage revision protocol were retrospectively identified. Implant survival was assessed using the Kaplan-Meier method; potential risk factors were identified using the log-rank test, as well as non-parametric analysis. Postoperative function was assessed using the WOMAC and measurement of range of motion.

RESULTS

After a median follow-up of 62 months, 37 implants required implant revision (28%). Five-year survival was 69.7% [95% CI (confidence interval) 60.9-78.5] with periprosthetic (re-) infection being the main cause for failure (15%), followed by aseptic loosening (9%). In cases of periprosthetic infection, infection-free survival was 83% at 5 years (95% CI 74-92) with twelve patients suffering reinfection (16%).While body mass index (p = 0.75), age (p = 0.16) or indication for rotating hinge knee arthroplasty (p = 0.25) had no influence on survival, Charlson comorbidity score (CCI) (p = 0.07) and number of previous revision surgeries (p = 0.05) correlated with implant failure. There was trend (p = 0.1) for improved survival in fully cemented implants. Mean postoperative WOMAC was 127(range 55-191), 11 patients (15%) had limited knee extension.

CONCLUSIONS

Rotating hinge total knee arthroplasty using a single modular implant shows acceptable survival rates and function compared to previous studies with (re-)infection being the most relevant mode of failure. Patients with a high CCI and multiple previous surgeries are at increased risk for failure.

LEVEL OF EVIDENCE

Retrospective cohort study, III.