The influence of assembly on stem taper texture and measurement uncertainty

Characterisation of revised orthopaedic surfaces is recognised as an essential requirement for understanding long-term implant performance. Pre-wear data (from which to define material loss) is not often available, so this must be reconstructed by mathematically modelling a small amount of as-manufactured surface. This paper examines the influence of the surgical assembly process and taper design on the contact deformation of CoCrMo head tapers and threaded Ti-6Al-4V stem tapers, and hence how reliable these surfaces are when used for the reconstruction of a pre-implantation surface. Three implant cohorts (n=5) of differing design were measured in an as-manufactured condition, then assembled, dis-assembled, and re-measured. Measurements were aligned using a validated procedure and deformation quantified in terms of amplitude and volume. No damage or imprinting was evident on the head taper bore, but surface texture compression could be more prevalent in stem taper designs with larger surface texture height. Based on the reviewed cohort of implants, the maximum error contribution to volume of material loss was <0.4mm3.