Risks and advantages in standardization of bores and cones for heads in modular hip prostheses

Abstract

Standardization of bores and cones for modular hip prosthesis heads has been addressed by both the International Standard Organisation (ISO) and the American Society for Testing and Materials (ASTM) in response to the need to control the conditions of head-trunnion fit that thereby improves implant safety. Standardization of these conditions could help the surgeon avoid fit mismatch, especially during revision surgery. Instituting a system of standardization without taking all critical parameters into consideration, however, could be more dangerous than no system at all. The current article discusses the main taper parameters that directly influence the performance of ceramic head-metallic trunnion assemblies and argue for standardization that integrates all these parameters. Several examples, based on experimental mechanical tests and finite element analysis, are given to support the argument.

The effects of manufacturing tolerances and assembly force on the volumetric wear at the taper junction in modular total hip arthroplasty

“…More brittle materials, such as ceramics, are more susceptible to fracture than metal components. The fracture risk of ceramics is greatly increased by the taper contact region, caused by the type of mismatch or taper offset, the taper roughness, and the taper straightness (Heimke 1994;Cales and Stefani 1998). A 'base fit' taper mismatch increases the risk of ceramic head fracture, therefore a 'tip fit' is advised in order to reduce the risk of ceramic fracture (Piconi and Maccauro 1999).…”

Prediction of taper performance using quasi static FE models: The influence of loading, taper clearance and trunnion length

“…Although it is assumed that the taper will engage at this location, it is not known where the taper will engage after surgical impaction, due to manufacturing tolerances which lead to variability. The original design of tapers using ceramic heads was implemented for proximal contact to prevent large tensile stresses thereby reducing the risk of head fracture . However, metal taper junctions can be designed to engage distally .…”

A case of bilateral hip mechanically assisted crevice corrosion after staged total hip arthroplasty

“…Our patient had 32-mm CrCo femoral heads on a titanium stem with a 12/14 taper on bilateral hips, both with Trilogy acetabular components and an M/L taper standard stem (right) and extended offset (left) (Zimmer Biomet, Warsaw, IN). The design of the trunnion itself may contribute to the development of MACC [22], [23]. The base of shorter trunnions lies within the taper of the femoral head, which may increase edge loading and base corrosion [24] and may increase material wear [25].…”