Determining material loss from the femoral stem trunnion in hip arthroplasty using a coordinate measuring machine

Abstract

In contrast to the articulating and taper surfaces of failed total hip replacements, volumetric wear analysis of trunnions is not routinely performed. Metal wear particles from the trunnion may contribute not only to the failures of metal-on-metal total hip replacements but also to all hip replacements utilising metal trunnions. A validation study was performed with the material removed in stages from the trunnions of an Exeter V40 stem, a Corail stem and an Accolade stem to simulate different magnitudes of wear. The material loss from the trunnions was measured both volumetrically with a coordinate measuring machine and gravimetrically with a high-precision balance. A cohort of 28 ex vivo trunnions was also measured using the coordinate measuring machine. The maximum error between the two methods was found to be 0.13 mm(3). This result was comparable with the coordinate measuring machine method for the taper surface (0.2 mm(3)). The ex vivo trunnions had a median wear volume of 0.14mm(3) (range: 0.04-0.28 mm(3)). This is the first study to determine the accuracy of volumetric wear measurements of trunnions by comparing against gravimetric measurements. Volumetric wear analysis of trunnions may provide additional insights into failures of modular total hip prostheses and will be performed routinely at our centre.

A large taper mismatch is one of the key factors behind high wear rates and failure at the taper junction of total hip replacements: A finite element wear analysis

“…The wear fractions for a CoCr alloy head and Ti alloy stem combination have been specified as 0.9 and 0.1 respectively. This is due to preferential oxidation of the Ti alloy over the CoCr, which increases the hardness of the Ti and wears the un-oxidised CoCr, as has been published previously (Bishop et al, 2013;Bone et al, 2015;Langton et al, 2011a;Moharrami et al, 2013). …”

“…It is known that design variables such as head diameter, head offset, material combination and taper angles have a significant effect on taper debris generation in THRs (Bone et al, 2015;Jani et al, 1997;Langton et al, 2012;Schmidt et al, 1997). There is inevitable variability in the manufacturing tolerances for the taper and trunnion cone angles of these THRs.…”

“…The third stage measures the entire surface and compares the data points with the perfect cone to determine any deviations, which represent wear depths, which are summed to calculate volumetric wear. The technique and validation process has been published previously (Bone et al, 2015;Langton et al, 2011b;Langton et al, 2014;Lord et al, 2011).…”

A computational approach to fretting wear prediction at the head–stem taper junction of total hip replacements

“…The wear fractions associated with the cobalt chrome 'head' and titanium 'stem' in this work have been specified as 0.9 for the Co-28Cr-6Mo and 0.1 for the Ti-6Al-4V following work by Bone, et al [30] and Langton, et al [15]. The findings from their work indicate that the cobalt chrome head taper wears by around a factor of 10 more than the titanium alloy stem trunnion surface.…”

The Performance of Mixed Manufacturer Metal On Metal Total Hip Replacements

“…A positive clearance indicates that the taper would have contacted at the proximal / narrow diameter end of the taper, while a negative clearance is the opposite, with a distal contact at the larger diameter end of the interface. The angles for the ASR and Articuleze joints presented by Langton et al [2] were 5.670° (5.568° to 5.798°) and 5.639° (5.584° to 5.685°) (taper engagement level identified data) which, when paired with the 5° 43' Corail trunnion [3], provide clearances of -0.047° (-0.149° to 0.081°) and -0.078° (-0.133° to -0.032°) degrees. This range of clearance angles and differences in design specification is further reflected in the study of Kocagöz et al [1] whose cohort of 50 metal femoral head had a 35:15 split between positive and negative clearance angles.…”