Effect of trunnion roughness and length on the modular taper junction strength under typical intraoperative assembly forces

- A stable fixation of modular tapers is critical to minimize interface micromotions.
- Trunnion-head pairs were assembled and their taper strengths assessed.
- Pull-off forces increased with rising peak assembly force.
- Smooth tapers showed higher strengths than grooved ones following moderate impactions.
- A higher taper strength may reduce the risk of fretting-induced complications.

Modular hip implants are at risk of fretting-induced postoperative complications most likely initiated by micromotion between adjacent implant components. A stable fixation between ball head and stem-neck taper is critical to avoid excessive interface motions. Therefore, the aim of this study was to identify the effect of trunnion roughness and length on the modular taper strength under typical intraoperative assembly forces.Custom-made Titanium trunnions (standard/mini taper, smooth/grooved surface finish) were assembled with modular Cobalt-chromium heads by impaction with peak forces ranging from 2 kN to 6 kN. After each assembly process these were disassembled with a materials testing machine to detect the pull-off force as a measure for the taper strength.As expected, the pull-off forces increased with rising peak assembly force (p < 0.001). For low and moderate assembly forces, smooth standard tapers offered higher pull-off forces compared to grooved tapers (p < 0.038). In the case of an assembly force of 2 kN, mini tapers showed a higher taper strength than standard ones (p = 0.037).The results of this study showed that smooth tapers provided a higher strength for taper junctions. This higher taper strength may reduce the risk of fretting-related complications especially in the most common range of intraoperative assembly forces.