On the Failure of Total Ankle Replacement: A Retrieval Analysis

Total ankle replacement (TAR) has been under development for 40 years but is not considered as successful as other lower limb total joint replacements (TJR). The failure rate of TAR is more than double that of total hip replacement at 10 years, yet the failure mechanisms remain largely unknown. The research in this thesis aimed to identify the wear modes and possible origins of failure for a cohort of failed TARs using a retrieval analysis approach. Explants, medical imaging and periprosthetic tissue samples were retrieved for 44 participants following revision TAR surgery. Five TAR brands were retrieved, all of which were uncemented, three-component, mobile-bearing designs. Each resource was investigated using established and novel retrieval analysis methods including, but not limited to: photogrammetry, microscopy, non-contacting 3D surface profilometry, computed tomography and wear particle isolation. Ballooning osteolysis was highly prevalent. Component alignment was within alignment variations considered acceptable in the published literature, yet high rates of edge-loading (70.5%) and impingement (57%) were evident. Fixation and bearing surface wear affected 98% of tibial components. The volumetric wear rate for eight bearing inserts was 2.5 times higher than the greatest wear rate reported by in-vitro simulation studies. Hydroxyapatite wear particles were micron-sized with a high aspect ratio (AR = 3.7). Flake-like micron-sized cobalt chromium alloy and large titanium wear particles (>10 μm) were also isolated and characterised. The total wear particle population for TAR was generally larger and more elongated than the wear particle characteristics identified for other TJRs. Edge-loading, bearing insert subluxation and impingement contributed to wear modes 2, 3 and 4, which indicate device dysfunction and should be minimised by design. Mobile-bearing constraint, cortical window surgical approach and the rapid accrual of wear particles may be important contributors to the failure of TAR.