Failure Analysis following Osteochondroplasty for Hip Impingement in Osteoporotic and Non-osteoporotic Bones

Abstract

Femoral osteochondroplasty is the most common treatment for femoroacetabular impingement (FAI). The risk of femoral neck fracture is increased following surgery and increases further when the bone is osteoporotic. The current requirement to undertake osteochondroplasty on patients with osteoporosis is forecast to increase; however, the effect of osteoporosis on the risk of post operative fracture is currently unknown. We developed three three-dimensional (3D) finite element models using computerised tomography (CT) scan data for a hip with cam-type impingement and used them to investigate the association between osteoporosis and the increased possibility of femoral neck fracture after femoral osteochondroplasty. Femoral osteochondroplasty was performed “virtually” on the intact hip model to two different resection depths, a ‘standard’ (6 mm) and a ‘critical’ resection (12 mm) depth, corresponding to 18% and 36% of the overall femoral neck diameter, respectively. Cortical and trabecular bone were included in the intact and resection hip models, and material properties representing both non-osteoporotic and osteoporotic cases employed, overall, 18 scenarios were analysed. Loading corresponding to “descending stairs” and “stumbling” activities were applied in the models enabling fracture propensity to be estimated. Our model predicted that fracture propagation can occur in the bone of osteoporotic patients following osteochondroplasty during typical daily activities, such as descending stairs. The level of damage increases significantly when patients are subjected to high load conditions and activities, even in non-osteoporotic patients, indicating an increased likelihood of fracture occurring. In the “stumbling activity” simulation, osteoporotic trabecular bone damage volume approached 50% for the 6 mm resection, rising to 70% at a resection depth of 12 mm. The corresponding rise in osteoporotic cortical bone volume damage was from 6% to 10%. Our findings support the recommendation for protected weight-bearing in patients in the postoperative phase and suggest an extended period of protected weight-bearing in osteoporotic patients could be considered.