Vanhegan, IS; (2014) A study comparing the primary stability of two uncemented, modular titanium femoral stems. Doctoral thesis , UCL (University College London).

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Abstract

As the annual incidence of revision total hip replacement (THR) rises so too do the technical, biomechanical and socioeconomic challenges it presents. This thesis investigated many of the key clinical and pre-clinical aspects of this surgery. Improving implant stability was addressed through biomechanical analyses and the cost and complications of revision THR were explored. The biomechanical investigation compared two designs of tapered, fluted, modular, titanium-alloy stems. The Redapt® stem featured a novel flute configuration and chamfered tip. It was hypothesised that this would improve axial and rotational stability compared to the Modular Restoration® control stem. Each stem was implanted into one of 7 matched pairs of human cadaveric femora with simulated proximal bony defects. A photoelastic coating compared surface strains in the medial femoral cortex for the intact and operated femora. Under incremental static loads each operated bone showed marked stress-shielding with a statistically significant reduction in strain. This effect was diminished with the Redapt® stem because of reduced distal endosteal contact (‘fill’) as confirmed by radiographic analysis. Primary stability was measured using micromotion transducers and radiostereometric analysis. Under cyclical loading both stems were stable by agreed standards at x1 body weight. As load increased 85% of the Redapt stems remained stable compared to 100% of the Restoration (p=0.055). Overall transducer recorded axial subsidence was 0.1 mm for the Redapt and 0.17 mm for the Restoration. Both stems achieved results commensurate with their expected successful application in revision cases with extensive bony defects. Clinical and financial data was collected from 305 consecutive revision THRs between 1999-2008 performed at our institution. Analysis revealed a large variation in costs by indication from £10893 (SD £5476) for dislocation to £21937 (SD £10965) for septic revisions. A large shortfall in reimbursement was found questioning the ability of smaller units to continue providing this service.

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