Effect of Adding Stem Extension to a Short-Keeled Knee Implant on the Risk of Tibial Loosening: a Historical Cohort Study.

Abstract

Background: Short-keeled tibial implants may be at higher risk of aseptic loosening. Stem augmentation has been suggested to improve its fixation. We aimed to assess whether this technique could decrease the loosening rate of such tibial implants.

Methods: We retrospectively studied the knees receiving stemmed versus nonstemmed versions of a short-keeled prosthesis. A total of 932 patients undergoing total knee arthroplasty using a Persona prosthesis with >24-month follow-up (mean 53.7) were included, of whom 212 were at high risk of loosening due to osteoporosis or high body mass index (BMI). The rate of tibial aseptic loosening in high-risk patients and in the whole cohort was compared between those with and without stem extension. Multivariable analysis was conducted to identify the risk factors of loosening.

Results: In the whole cohort, in 203 knees (21.8%), a cemented short stem was used, versus 729 knees (78.2%) without. The tibial implant revision rates for loosening were 2.06% and 0.99% for nonstemmed and stemmed cases, respectively (P = 0.551). When the cohort was categorized based on the loosening risk factors, the loosening risk was significantly higher in the high-risk than in the low-risk group, regardless of stem status (log-rank test = 8.1, hazard ratio = 2.17, 95% CI = 1.78, 2.57, P = 0.005). 212 patients were at high risk of loosening, due to high BMI or osteoporosis, among whom the risk of aseptic loosening was higher when a stem was not used (log-rank = 32.1, hazard ratio = 4.95, 95% CI = 4.05, 5.86, P < 0.001). In multivariate analysis, osteoporosis, BMI ≥35, and smoking were correlated with loosening.

Conclusion: The failure rate was markedly lower in the stemmed group of the patients at elevated risk of aseptic loosening due to osteoporosis and/or high BMI. In the entire cohort, the risk of loosening in stemmed tibial implants was similar to the nonstemmed group. The findings support a protective role for the stem in patients at high risk of failure of the cemented tibial implant.

Level of evidence: III therapeutic.