Humeral fixation by press-fitting of a tapered metaphyseal stem: a prospective radiographic study.

Background: The technique of shoulder arthroplasty requires a method for securely and durably fixing the humeral component in the medullary canal of the proximal part of the humerus. As an alternative to fixation by cementing or tissue ingrowth, we explored the effectiveness of using a prosthesis with a metaphyseal taper from the anatomic neck to the diaphysis. This component is designed to obtain press-fit fixation in the cancellous bone of the metaphysis rather than in the cortical bone of the diaphysis. We tested the hypothesis that this press-fit humeral stem, designed to respect the taper of the proximal part of the humeral canal, would be associated with a low rate of loosening in patients managed with primary shoulder arthroplasty for osteoarthritis.
Methods: A prospective study was conducted to evaluate the prevalence of radiolucent lines around press-fit humeral prostheses. One hundred and thirty-one patients with glenohumeral osteoarthritis were followed for a minimum of two years. A zonal method of evaluating radiolucent lines was established. Shift in position and subsidence were judged qualitatively.
Results: No component showed subsidence or a shift in position. Fifty shoulders (39%) had no radiolucency. Two shoulders had radiolucency around the proximal part of the prosthesis, and seventy-five had radiolucency at the distal tip. Eleven radiolucencies were > or =1 mm in width. A neutral stem orientation was significantly less likely to be associated with radiolucency (p = 0.026). The prevalence of radiolucent lines did not differ between patients managed with hemiarthroplasty and those managed with total shoulder arthroplasty, and it did not increase with longer periods of follow-up.
Conclusions: In patients managed with shoulder arthroplasty, the fixation of a press-fit humeral component that has a tapered metaphyseal segment is comparable with that reported for cemented components and superior to that reported for press-fit cylindrical components.
Clinical Relevance: This type of fixation may provide an alternative to cementing of the humeral stem in individuals with glenohumeral osteoarthritis.