In vitro and in silico investigation of factors affecting damage related to hip impingement

Femoroacetabular impingement (FAI) can cause hip pain; this can be debilitating, and surgery can be used to alleviate some symptoms. Prevalence of surgical interventions with the aim of alleviating pain and reducing tissue degeneration have increased in recent years. Data from the most recent Non-arthroplasty Hip Registry indicates that 95.6% of non-Arthroplasty hip femoral procedures performed were for the removal of cams (NAHR, 2024). Cam-type FAI is caused by an excess of bone on the femoral neck that in flexion abuts the acetabular rim. This can cause cartilage and labral damage due to increased contact pressure as the cam moves into the acetabulum. Damage mechanisms and the influence of individual mechanical factors are poorly understood. Understanding the biomechanics of FAI has the potential to modify existing and design new interventions to improve surgeries.

This thesis developed a method for parametrically assessing mechanical factors that may be associated with damage in hip impingement, using both experimental and computational methods. An adapted natural tissue in vitro simulation method was used to conduct parametric tests using porcine tissue. Three key parameters were investigated: sliding distance, load and direction. Damage to the natural tissue observations was recorded using photogrammetry and compared between parameter sets. A computational cam impingement hip shape model was used to quantify parameter ranges for a range of activities. Computationally and experimentally quantified real-world parameters were combined and assessed to determine their clinical relevance across findings.

To the author's knowledge, this thesis is the first to have assessed the impact of individual parameters on damage to the hip joint. The most severe types of damage observed experimentally were “blushing” and “bubbling” of the cartilage. The latter was thought to be a precursor to delamination, the type of damage often associated with in vivo cam FAI damage. Computational investigation resulted in identifying a set of quantified parameters that were likely to cause damage to the joint. However, it was not possible to highlight a single activity that would be considered the most likely to result in damage. Findings from both experimental and computational studies showed that an increased load (2500N), shorter sliding distance (±5°) and movements parallel to the cartilage labral junction resulted in the most severe/detrimental types of damage.