Jordan et al. report a prospective, consecutive, multicenter study of the Mathys-Affinis stemless shoulder prosthesis with a minimum of four-year follow-up. This ceramic on polyethylene articulation was performed on 207 patients, of which 27% (56 patients) underwent hemiarthroplasty. They report 2.7% humeral radiolucencies, 14% glenoid radiolucencies and 6.3% revision rate at a minimum of 48-month follow-up and conclude that these results are comparable to other stemless arthroplasty systems as well as with standard stemmed implants.
Of course, the use of a ceramic humeral head is what makes this implant different than currently utilized implants. The rationale for a stemless system has been well described. The rationale for use of a ceramic head as stated by the authors is “the expectation that wear rates on polyethylene may improve performance by reduction of particulate debris and associated synovitis and loosening.” However, it is important to note that polyethylene wear with the associated particulate debris and synovitis has not been a significant problem following shoulder arthroplasty as it has been in total hip arthroplasty. The use of ceramic components in patients with metal allergies is an important indication and certainly justified.
There are some issues that require consideration. The indications for hemiarthroplasty vs. TSA, particularly in the large group of patients with primary osteoarthritis, are unclear. The authors point out that their clinical results are better than what has been reported previously when hemiarthroplasty was used for primary osteoarthritis. However, it is important to take this as the “exception rather than the rule.” This should not be considered an endorsement for the use of humeral head resurfacing alone in patients with primary osteoarthritis. In the patients who underwent hemiarthroplasty, there was no analysis of glenoid erosion. This is particularly meaningful as there is little, if any, documentation of the results of ceramic on bone. This would have been an area worthy of careful analysis and could have enhanced our understanding of the nature of these articulations. Although the authors assessed the incidence of radiolucent lines around the glenoid component, there was no evaluation of the degree of polyethylene wear. If the rationale for ceramic on poly was to reduce polyethylene wear, this specific issue should have been assessed. The use of ceramic also requires a discussion of the cost. It is my understanding that ceramic is more costly than cobalt-chrome humeral heads. If this was not the case, it would have been helpful for the authors to include this in their discussion.
This study certainly contributes to our understanding of the evolving role of stemless humeral components in TSA. The use of a ceramic on polyethylene articulation is a different approach. Perhaps if the authors obtain much longer follow-up, i.e. 10 years, they will be able to make comments about two important areas: the impact of a ceramic on polyethylene articulation on polyethylene wear and the outcomes of a ceramic on bone articulation.