Influence of glenoid implant depth on the bone–polymethylmethacrylate interface

Purpose: Preservation of glenoid bone stock in shoulder arthroplasty is a general surgical guideline. The objective of this study was to investigate the influence of implant depth on the mechanical behaviour of the bone–cement interface, in order to confirm the general assumption of maximum bone stock preservation. Materials and methods: A three-dimensional (3D) model of a scapula was derived from CT scans. Various implant depths (from 0 to 2.0 mm) were modelled using a 3D reaming procedure. Through integration of bone density into the simulation model, a finite element analysis with best-possible patient specificity was conducted. Results: The results show that mostly subchondral bone was removed during the reaming procedure for implant depths between 0.0 and 0.5 mm, whereas mostly cortical bone at the glenoid rim was removed between 0.5 and 2.0 mm. In all simulated load cases, the mean and maximum von Mises stresses as well as tensile and compressive stress within bone cement increased steadily with increasing implant depth. Conclusion: Implant depth has a substantial influence on stress distributions within bone cement. The fatigue stress of bone cement is more likely to be exceeded at higher implant depths, and higher micromotions could contribute to bone resorption and early implant failure in the long term.