Canal Fill Ratio in Hemiarthroplasty Compared to Total Hip Arthroplasty: A Case Control Study.

Background: Cementless stems are commonly used in hemiarthroplasty (HA) for femoral neck fractures. Recent studies have reported increased risk of periprosthetic fracture with cementless stems compared to cemented HA. In elective total hip arthroplasty (THA), lower proximal canal fill ratios (CFR) of cementless stems have been associated with worse outcomes. The purpose of this study was to compare CFRs and complications following HA for femoral neck fracture compared to THA for arthritis. We hypothesized that HA would have lower CFRs.

Methods: 130 patients undergoing cementless hemiarthroplasty for femoral neck fracture were identified and matched by age, sex, and BMI to 328 patients undergoing elective cementless THA. Postoperative radiographs were independently evaluated by two investigators to determine Dorr femur type and CFR at four points. Interrater agreement was calculated for CFR and Dorr type. Complication rates were compared between HA and THA groups.

Results: Dorr type and CFR measurements showed strong agreement between investigators. Dorr type was similar between groups. Hemiarthroplasties had significantly lower CFR at each level, with the greatest difference at the lesser trochanter. Dorr C femurs had worse CFR, specifically in the HA group. Complications rates were similar between HA and THA.

Conclusion: Worse CFR in HA compared to THA further suggests that cemented stems should be considered in HA. Suboptimal CFR represents a potential cause of complications including periprosthetic fracture following HA. Level of Evidence: III.