This author used osteopenic sawbones scapulae to model the force required to cause initial loosening of the glenoid baseplate and the force required to cause ultimate failure of the baseplate, and secondly, to distinguish trends in the design parameters resulting in increased fixation in order to optimize baseplate design.
An Instron was used to apply a load to cause displacement of the baseplate and record the applied loading; a Linear Variable Differential Transformer (LVDT) was used to measure and record the micro motion of the implant experiences. Each specimen was loaded in the inferior to superior direction until 150 μm of motion occurred for 30 cycles at 1 Hz. The assumption was made that if more than 150 μm of motion occurs between the implant and bone, ingrowth will not occur to permanently stabilize the baseplate.
As shown below, there were differences among the implants, they were not statistically significant.
The high variability and lack of significant differences in this sawbones model suggests that even greater variation may be expected in clinical practice. It is unclear how important bone ingrowth is to the fixation of the different reverse implants - some of which use large compression and locking screws without an ingrowth central post. The quality of the patient's bone and the surgical technique may be at least as important to preventing baseplate failure as the implant design.
Our approach to reverse total shoulder arthroplasty is shown in this link.
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