Abstract
The glenoid is the ‘weak link’ in total shoulder arthroplasty. Concerns exist over loosening of all glenoid components. Metal back glenoid components have, in some reports, had early problems with liner dissociation, polyethylene wear, osteolysis and component fracture. In November 2003 the first metal back SMR total shoulder replacement was implanted in New Zealand (NZ). We reviewed the NZ joint registry information on anatomical total shoulder replacements over a 5-year period from the end of 2003.
There were 192 metal back SMR prostheses (Lima) implanted and 484 cemented prostheses (all brands). 70% of patients in each group completed an Oxford score at 6 months. The mean score in both groups was 40.39. There was no statistically significant difference in the revision rate in this period for revisions of any kind (p=0.07). 6/192 metal back cases had a revision procedure, but none were for the glenoid component. 7/484 cemented cases had a revision procedure with 3 being for glenoid loosening. None of the metal back glenoids were revised in this period. 5 of the cemented glenoids were revised in this period. There was a higher revision rate for instability in the metal back group with 5 in the metal back group and 2 in the cemented group being revised for instability (p=0.01). In the metal back group there were 3 revisions to a reverse shoulder arthroplasty without removal of the metal back glenoid base plate.
We have not identified an early cause for concern with the use of the metal back SMR prosthesis in anatomical total shoulder replacement in New Zealand. It is possible, but not proven, that the modularity of the implant may lower the revision threshold for some cases. Reassuringly, there were no revisions of the metal back glenoid in this early period
