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.