Femur Strength is Similar Before and After Iatrogenic Fracture During Total Hip Arthroplasty: A Biomechanical Analysis

Abstract

Background: The purpose of this study was to compare the biomechanical strength of femurs before an iatrogenic periprosthetic fracture vs after an initial fracture with supporting cerclage fixation during cementless total hip arthroplasty. Material and methods: Nineteen composite femurs and 5 matched pairs of cadaveric femurs were implanted with a single-wedge or dual-wedge tapered femoral stem and tested for ultimate load to failure producing a periprosthetic fracture. Following initial fracture, each femur was cerclaged with Vitallium cables and retested for ultimate load to failure. The mean force eliciting iatrogenic fracture before cabling and that after cabling were compared with a two-sided paired Student’s t-test. Results: All composite femurs developed periprosthetic fractures with an average length extension from the calcar of 75.17 mm. For the 19 composite femurs, the mean ultimate load to failure before cabling and that after cabling were not significantly different (2422.95 N vs 2505.14 N, P = .678). For the 10 cadaveric femurs, the mean ultimate load to failure for the initial fracture vs that after cabling was statistically comparable (5828.62 N vs 7002.63 N, P = .126). Subanalysis of the 5 cadaveric femurs with a double-wedge stem revealed a significantly higher mean load to failure following cabling (5007.38 N vs 7811.17 N, P = .011). Conclusion: Biomechanical strength was similar for femurs that sustained an initial iatrogenic periprosthetic fracture and the same femurs cabled with cerclage wires after being fractured. These data may assist in operative decision-making for treating iatrogenic fractures during total hip arthroplasty.

Keywords

• Biomechanical
• Hip
• Stem
• Periprosthetic fracture
• Total hip arthroplasty
• Femur