The radiographic evaluation of keeled and pegged glenoid component insertion

Background: Radiolucent lines about the glenoid component of a total shoulder replacement are a common finding, even on initial postoperative radiographs. The achievement of complete osseous support of the component has been shown to decrease micromotion. We evaluated the ability of a group of experienced shoulder surgeons to achieve complete cementing and support in a series of patients managed with keeled and pegged glenoid components. Methods: We reviewed the initial postoperative radiographs of 493 patients with primary osteoarthritis who had been managed with total shoulder arthroplasty by seventeen different surgeons. One hundred and sixty-five patients were excluded because of inadequate radiographs, leaving 328 patients available for review. Of these, thirty-nine patients had a keeled component and 289 had a pegged component. The method of Franklin was used to grade the degree of radiolucency around the keeled components, and a modification of that method was used to grade the degree of radiolucency around the pegged components. The efficacy of component seating on host subchondral bone was evaluated with a newly constructed five-grade scale based on the percentage of the component that was supported by subchondral bone. Each radiograph was graded four times, by two separate reviewers on two separate occasions. Results: Radiolucencies were extremely common, with only twenty of the 328 glenoids demonstrating no radiolucencies. On a numeric scale (with 0 indicating no radiolucency and 5 indicating gross loosening), the mean radiolucency score was 1.8 +/- 0.9 for keeled components and 1.3 +/- 0.9 for pegged components (p = 0.0004). After defining categories of "better" and "worse" cementing, we found that pegged components more commonly had "better cementing" than did keeled components (p = 0.0028). Incomplete seating was also common, particularly among patients with keeled components. Ninety-five of the 121 pegged components that had been inserted by the most experienced surgeon had "better cementing," compared with eighty-five of the 168 pegged components that had been inserted by the remaining surgeons (p < 0.00001). Conclusions: Perfectly cementing and seating a glenoid replacement is a difficult task. Radiolucencies and incomplete component seating occur more frequently in association with keeled components compared with pegged components. Surgeon experience may be an important variable in the achievement of a good technical outcome.