Introduction

Distal femoral replacement (DFR) prostheses are increasingly used in revision knee arthroplasty, especially in cases of significant bone loss or periprosthetic fractures. However, early loosening of the femoral component remains a significant concern, particularly in cemented stems. This study aims to evaluate the rate of early femoral stem loosening in cemented DFR prostheses and to explore the factors associated with this complication.

Methods

A retrospective multicenter study was conducted across four knee arthroplasty revision centers. We included 70 patients who underwent DFR with cemented femoral stems between 2015 and 2019 and had a minimum of two years of follow-up. Patients with tumor-related indications were excluded. Data collected included demographic information, surgical history, indications for DFR, intraoperative and postoperative complications, and radiographic evidence of loosening. Radiographic loosening was defined as component mobilization, demarcation lines exceeding 2 mm, or progression of demarcation lines on consecutive radiographs. The primary outcome was the rate of femoral component loosening within the first two years. Secondary outcomes included prosthetic survival and the impact of patient characteristics, including age, sex, and prior femoral canal cementation.

Results

The median age of the cohort was 73.5 years, with 71.4% being female. The primary indications for DFR were aseptic loosening (35.7%), periprosthetic fracture (22.9%), and prosthetic infection (27.1%). The overall rate of femoral component loosening within two years was 15.7% (11 patients). Women had a significantly lower risk of loosening compared to men (OR 0.258, 95% CI 0.068 – 0.098, p = 0.038). No significant differences in loosening rates were observed between age groups (<75 years vs. ≥75 years) or based on prior femoral canal cementation. A total of 17 patients (24.3%) required reoperation during the follow-up period, with aseptic loosening being the most common cause (52.9%).

Discussion

The findings of this study highlight a notable rate of early loosening in cemented DFR prostheses, which is consistent with previous reports. The higher risk of loosening in men compared to women warrants further investigation into sex-specific biomechanical factors that may influence prosthetic stability. Although prior femoral canal cementation did not show a statistically significant impact on loosening rates, the trend towards earlier loosening in these cases suggests that alternative fixation strategies may be warranted in patients with multiple prior cementations. The study's retrospective design and limited sample size are recognized limitations, but the multicenter approach enhances the generalizability of the findings.

Conclusion

Early loosening of cemented femoral stems in DFR prostheses is a significant concern, particularly in male patients. The results suggest a need for optimizing fixation strategies, especially in cases with prior femoral canal cementation. Future research should focus on improving prosthetic design and exploring the potential benefits of cementless stems in reducing early loosening rates. These findings are crucial for improving the long-term outcomes of patients undergoing revision knee arthroplasty with DFR.