Computational and experimental biomechanics of total hip wear increase due to femoral head damage

Aseptic loosening due to wear-induced osteolysis remains a leading cause of failure in total hip arthroplasty (THA), particularly in revision cases beyond the second decade of use. Historically, there have been large amounts of variability of wear within individual THA patient cohorts. Evidence indicates that femoral head damage can be a cause of this variability. While femoral head damage as a result of third body particles and subluxation and dislocation events has been well documented, direct quantifiable linkage between femoral head damage and wear acceleration remains to be established. Due to large ranges of observed retrieval damage, wear testing protocols for simulating third body and other damage effects have been subject to a wide range of variability, making it difficult to know where the clinical reality lies.

To study the effect of retrieval femoral head damage on total hip implant wear, a damage-feature-based finite element (FE) formulation which allowed for wear prediction due to individual damage features developed. A multi-scale imaging procedure was also developed to globally map and quantify micron-level damage features appearing on retrieval femoral heads. This allowed for wear simulations of damage patterns observed on specific retrieval femoral heads. Retrieval damage was shown to be highly variable among patients, and capable of producing up to order-of-magnitude wear increases when compared to undamaged head wear rates. Damage following dislocation and subsequent closed reduction maneuvers was particularly detrimental, with average wear rate increases equal to half an order of magnitude. These data were used to develop wear testing protocols for simulating clinically-occurring third body and other damage effects.