Trunnion-Head Stresses in THA: Are Big Heads Trouble?

The effects of large heads on stresses at the THA trunnion-head junction and their impact on tribocorrosion/metal ion release remain controversial. A 12/14 3D-model of a stem with different head sizes was investigated. Material properties of titanium were assigned to the trunnion and cobalt-chrome/alumina to the heads. A load simulating walking single-leg stand phase was applied to the head. A total contact head-trunnion interface was assumed. The area underneath the junction underwent significant elevations in stresses as head size increased from 28- to 40-mm. Maximum principal stress doubled between 28 and 40-mm heads, regardless of head material. Stress levels had a direct correlation to head diameter. Stress increases observed using increasingly larger heads will probably contribute to head-trunnion tribocorrosion and ion release.