Complication rates of baseplate loosening in reverse total shoulder arthroplasty (RSA) have been reported to range from 1.8% to 10%. Initial fixation of non-cemented implants is critical to achieve a stable bone-to-implant interface to ensure bone ingrowth and reduce the risk of aseptic loosening.
Multiple options have been explored to improve the stability of the glenoid baseplate, one of which is the use of a single central compression screw. However, the amount of compression that can be achieved with this modification and its relationship with insertion torque has yet to be describe.
In a biomechanical study conducted at the Foundation for Orthopaedic Research and Education in Tampa, Florida, Diaz et al  evaluated the insertion torque and compressive force relationship of a commercially available RSA baseplate with central screw design across 3 foam block densities. The foam blocks were a stand-in for varying degrees of bone quality.
Figure 1. Detailed illustration of the biomechanical setup.
The researchers found that baseplate compression and insertion torque had a positive correlation: Mean baseplate compression increased significantly with a corresponding increase in insertion torque. This finding, the researchers said, “suggest[s] that larger compressive forces can be achieved with an increase in insertion torque in denser bone surrogates, but caution must be used when trying to achieve fixation in poor-quality bone.”
Describing this relationship is the first step in understanding the compression needed to adequately reduced micromotion and may be vital in the development of improved baseplate designs with a single central screw.
- Diaz MA, Garrigues GE, Ricchetti ET, Gutierrez S, Frankle MA. Relationship between insertion torque and compression strength in the reverse total shoulder arthroplasty baseplate. J Orthop Res. 2019 Nov 6. doi: 10.1002/jor.24506. [Epub ahead of print]