ASSESSING THE INFLUENCE OF BONE REMODELLING ON REVISION RISK OF CEMENTED HIP PROSTHESES: A PATIENT-SPECIFIC RETROSPECTIVE STUDY

Abstract

Aseptic loosening can be considered as a combination of both mechanical and biological failure scenarios. This study investigated the influence of including bone remodelling in the simulation of aseptic loosening of cemented hip prostheses.

A combined strain and damage stimulated bone adaptation algorithm (Mulvihill et al., Proc. ESB Summer Workshop, p.114–115, 2007) was modified for use on an apparent tissue level. Constant rate resorption or deposition occurs if local strain falls outside a quiescent reference strain range. Furthermore, damage accumulates as a function of tensile stress. Resorption and simultaneous repair is activated above a critical damage level. Model parameters are related to specific surface area expressed as a function of apparent tissue density. Elastic modulus was also a function of accumulated damage. This algorithm was applied in conjunction with a bone cement and cement-metal interfacial damage accumulation algorithm to simulate aseptic loosening for a retrospective dataset of early revision and long-term-unrevised patients (Lennon et al. JOR, 779-88, 2007). One year of walking activity was simulated and resultant migrations of the prostheses were used to indicate revision risk.

The current implementation demonstrated increased migration for simulations with bone remodelling (p= 0.01). Variability was increased but mean predicted migration for early revisions was significantly higher than for the unrevised group (p= 0.03). Bulk bone remodelling was predicted primarily in the proximal regions. Interfacial bone remodelling demonstrated oscillation in damage at the interface due to alternate resorption-repair and deposition cycles. Interfacial bone density changes were more prominent in proximal regions but some models did show small amounts of resorption in more distal Gruen zones.

We conclude that bone remodelling has potential to predict more realistic migration patterns but further development and assessment is needed to identify the correct parameters for the bone adaptation algorithm.