(P 265) IS THERE AN IDEAL STEM TO CANAL RATIO IN LOWER EXTREMITY ONCOLOGIC ENDOPROSTHESIS RECONSTRUCTION?

Objective: Stem-related complications, such as aseptic loosening, periprosthetic fracture, and implant breakage, are among the most common failure mechanisms for endoprostheses. Our purpose was to identify if stem to canal ratio is associated with stem-related complication.

Methods: A prospectively maintained database of patients who received an endoprosthesis between 2000 and 2021 from a single academic hospital was queried. Patients with a cemented lower extremity endoprosthesis performed after malignant tumor resection and with minimum 2-year follow-up were identified. The stem to canal ratio was measured on the AP radiograph. To obtain stem width, the stem length was bisected, and the width of the stem (mm) was measured at the midpoint of the stem. The stem width was then divided by the width of the endosteal canal (mm) (Figure 1).

Results: In 127 patients, 13% (16/127) had a stem-related complication. Patients with a stem-related complication were younger (51.1 vs. 60.7 years, p=0.039). When stratified by low, moderate, and high stem to canal ratios (low ratio < 0.5; moderate ratio, 0.5-0.9; high ratio > 0.9), there was a greater proportion of stem-related complications in the low ratio (21.4%, 3/14) and high ratio (17.6%, 3/17) cohorts compared to the moderate ratio cohort (10.4%, 10/96, p=0.41), though not statistically significant.

Conclusion: There may be an ideal range of stem to canal ratios to minimize stem related complication in cemented endoprostheses. We saw a trend towards decreasing complications at a ratio of between 0.5 to 0.9. Multicenter analysis will be useful to increase sample size and power.