Modular femoral head hip replacement components connect to the femoral stem via matching tapers. Metals commonly used to manufacture femoral heads and stems rely on a passive oxide layer to resist corrosion. Under cyclic loading (i.e. gait) relative micromotion between the head and stem causes wear, removal of the oxide layer and subsequent corrosion by a process called tribocorrosion. Metallic debris released by tribocorrosion may result in adverse local tissue reactions called trunnionosis and may require revision surgery.

The objective of this research was to investigate factors affecting head-neck taper tribocorrosion, including head size, material and taper geometry. A systematic review of prosthetic design, manufacturing and surgical technique factors related to taper connection tribocorrosion was performed. The review included 91 studies investigating 35 unique factors, of which only 7 had adequate evidence to support a recommendation. In particular, a gap in evidence related to taper connection design was identified. It was found that poor study design resulted in inconclusive or contradictory evidence for the majority of factors.

A second review was performed of taper tribocorrosion in-vitro test methods to improve study design and increase clinical translation of results. A deficiency in current in-vitro test methods was identified where samples are only cyclically axially compressed. Frictional torques due to joint movement that may be larger with larger femoral heads are excluded. Therefore, a novel instrumented hip simulator was developed to measure corrosion related electrical activity during simulated gait.

The test apparatus was employed to investigate susceptibility to corrosion of different head sizes (28 vs 36mm cobalt-chrome femoral heads), materials (cobalt-chrome, ceramic and oxidized zirconium) and taper geometry (angle, diameter, length and surface finish). The study of taper geometry followed design of experiments methodology. Twenty-five uniquely designed test samples with a range of taper angles, diameters, lengths and surface finishes were custom manufactured and tested. It was found that large diameter cobalt-chrome femoral heads are most susceptible to corrosion, oxidized zirconium exhibits similar corrosion resistance to ceramic, and that thicker, shorter tapers with either low roughness and high angle, or high roughness and low angle, are least susceptible to short term corrosion.