Dimock and his co-authors have provided us with a comprehensive review of the results of the bony increased offset reverse shoulder arthroplasty (Bio-RSA). This approach to lateralization was utilized to address some of the problems that developed following RTSA using a Grammont design implant. Paul Grammont and his colleagues deserve tremendous recognition for their work in developing a successful reverse (fixed fulcrum) shoulder arthroplasty. They succeeded where many others had previously failed. The Grammont design with a center of rotation at the glenoid surface combined with an inset 155° humeral component expanded our ability to address complex problems in shoulder reconstruction. However, this design resulted in a number of issues including high scapular notching rates leading to bone loss and the potential for glenoid component loosening. The Bio-RSA was designed to address the unintended consequences of the Grammont design – i.e. scapular notching. Introducing a structural bone graft between the glenoid baseplate and the native glenoid is one way of achieving lateralization. However, it can also be achieved with a humeral component design with a reduced neck shaft angle, increasing the offset of the glenosphere and making certain that the baseplate is placed in an appropriate inferior position on the glenoid.
The meta-analysis identified 8 studies for inclusion representing a total of 235 Bio-RSA shoulders with 150 shoulders in the comparison group (STD-RSA). The authors concluded that the use of the Bio-RSA did reduce the incidence of scapular notching which had been a problem with the Grammont design. This is not surprising since the impact is to lateralize the construct. However, the available literature indicated that there was “little statistically” significant differences in outcomes scores and range of motion with the Bio-RSA compared with STD-RSA. It is evident that the Bio-RSA did address limitations of the Grammont design by inserting a structural bone graft between the glenoid baseplate and the native glenoid. This is one way of achieving lateralization, which in my opinion, is less attractive than achieving it through use of different glenoid and/or humeral designs.
The authors review indicated that 92% of the Bio-RSA grafts were reported as “fully healed.” This is an area I generally take issue with. I think it is more accurate to say that the grafts did not resorb rather than indicate they were fully healed. I say this based upon an understanding of the histology of bone healing. An avascular structural cancellous graft placed on the native glenoid requires revascularization. Revascularization, in turn, initiates a cascade of reabsorption and deposition of new bone (creeping substitution). I do not think it is possible to conclude with certainty that revascularization, i.e. healing, has occurred. Rather, it can be concluded that graft resorption has not occurred based upon the continued structural integrity of the graft. The problems that develop with structural bone grafts are generally a result of revascularization and reabsorption. I am quite pleased when any structural bone graft I utilize remains in place and intact. If it does then it is serving its intended purpose. I worry less about whether it is truly revascularized. This may be an issue of terminology, but I think it is important to integrate our understanding of histology into our description of the results of the bone graft used in the Bio-RSA.
For those surgeons using the Grammont design, the Bio-RSA approach will provide important advantages and offset the potential for complications resulting from scapular notching. For other surgeons, use of other methods to increase lateralization can achieve the same results without the need for bone grafting.