Using Coordinate Measuring Machine Validated with White Light Interferometry to Identify Contributors to Material Loss Due to Corrosion of Total Hip Replacement Modular Junctions

Abstract

Clinical sequelae have been associated with corrosion of modular junctions in total hip arthroplasty. These sequelae, including local adverse reactions to corrosion by-products, have been observed with metal-on-metal and conventional metal-on-polyethylene systems. Retrieval analysis can quantify material loss at modular interfaces, permitting correlation with prosthetic and patient factors. The purpose of this study was to quantify and characterize material loss at the head-stem junction of retrieved metal-on-polyethylene systems exhibiting imprint corrosion to identify parameters associated with corrosion in vivo and to establish a model of error for ex vivo material loss measurements. A coordinate measuring machine (CMM) was used to measure volume loss, maximum linear depth (MLD), and taper angle of 18 head bores and four stem tapers of the same manufacturer. The CMM used a 3-mm diameter ruby stylus to trace 72 axial lines across the taper surfaces. Five heads were bivalved for white light profilometry to validate MLD measured by the CMM. An error budget model, comparing interferometry with CMM measurements, was mathematically calculated and experimentally measured, providing error bounds for interpreting CMM-based material loss data. Median volume loss and MLD on the head bores were 1.63 (−2.56,12.49) mm3 and 27.94 (1.85,74.93) µm, respectively. Median head taper angle was statistically smaller than stem tapers angles, indicating distal engagement (p = 0.009). Maximum material loss was found to be on the portion of the head bore closest to the lesser trochanter, in an area of high stress and greatest contact with stem taper. This suggests continuous disturbance of the protective oxide in this region, promoting corrosive action. Stress may play a role in promoting corrosion, but further experimentation is necessary to fully characterize imprinting processes. A model of error was created for the interpretation of CMM measurements. The magnitude of material loss closely matched the interferometry results.

Role of corrosion in taper failure and head disassociation in total hip arthroplasty of a single design

“…Direct comparisons between CMM and white light interferometry taper profiles showed good agreement in maximum linear depth measurements. Median absolute error between the two techniques was measured to be 0.90 (0.43, 5.06) μm, consistent with prior validations establishing technique reliability of 3–5 μm, depending on the total loss …”

The effect of altering head length on corrosion using a material loss method

“…[13][14][15] The technique is accurate and repeatable to better than 7 µm for any retrieved bore, and better than 3 µm for the specific surface topographies examined in this study. 15 Results 56 heads were examined and all had been in situ for a minimum of 2 years, and the patient demographics and reason for revision were collected (Table 1). Heads were either −3, 0, +4 or +8 mm design and 3 different stems from the same manufacturer (Synergy [Titanium alloy], Spectron and Echelon [Cobalt chrome]).…”

“…Maximum linear wear depth, which is both reliable and validated, was used, as this method represents a quantitative measurement of trunnion wear as opposed to previously described qualitative methods. 13–15 The technique is accurate and repeatable to better than 7 µm for any retrieved bore, and better than 3 µm for the specific surface topographies examined in this study. 15…”

“…Material loss calculations were performed in a laboratory specialising in this area using a validated technique. 10,14,15 The heads were prepared by soaking in 70% alcohol and 10% neutral solution and carefully cleaned by a fellowship trained arthroplasty surgeon. Bores were measured using a Zeiss Contura G2 Coordinate Measurement Machine (CMM) running Calypso software (Oberkochen, Germany).…”

Standardizing terms for tribocorrosion-associated adverse local tissue reaction in total hip arthroplasty

“…The discoloration and debris are likely a combination of tribocorrosion mechanisms and may or may not lead to discoloration of the surrounding tissues or joint fluid. Ideally, retrieval analysis with a coordinate measuring machine to assess material loss due to corrosion could confirm with certainty the diagnosis of MACC [26].…”