The insidious risk of periprosthetic fracture in clinically functional total hip arthroplasties: A biomechanical study of willed joints

Femoral bone quality is a major risk factor of periprosthetic fracture after total hip arthroplasty (THA), which has mortality similar to native hip fractures but higher short-term morbidity. The goal of this study was to quantify cortical strains at the site of expected Vancouver Type-B periprosthetic fracture as a function of bone mineral density, femoral stem material, and fixation method using a series of 29 autopsy-retrieved, clinically asymptomatic hip joints with THA. Periprosthetic bone mineral content and density was assessed using dual-energy X-ray absorptiometry by Gruen Zone. Specimens then underwent combined cyclic axial and torsional loading, increasing incrementally from 100 N and +/- 1 Nm to peaks of 700 N and +/- 5 Nm. All specimens experienced significantly higher strains on the lateral surface than on the anterior surface, indicating that the bending loads in the frontal plane, rather than axial/torsional loads, had the predominant effect. Multiple significant relationships (p = 0.04, p = 0.02) were found between predicted periprosthetic strains calculated from radiographic measurements and observed principal strains. Though THA in the present study were in successful clinical service, the produced results indicated that some femurs with rigid cemented or noncemented implants were potentially at high risk for Vancouver Type-B fractures, which may be predicted radiographically.