The effect of radial mismatch on radiographic glenoid loosening.

Background: The ideal glenohumeral radial mismatch following anatomic total shoulder arthroplasty (TSA) remains ill defined, with biomechanical and clinical studies recommending a range between 4 and 10 mm. This study evaluates the effect of radial mismatch on the formation of radiolucent lines after TSA.

Methods: We evaluated 451 TSAs at a mean follow-up of 5.4 years. All TSAs were performed using a single implant system that allows radial mismatch between 3.4 and 7.7 mm. Shoulders were retrospectively evaluated for radiographic glenoid loosening according to the Lazarus score. Shoulders were evaluated according to radial mismatch: 3.4 mm in 23, 4.3 mm in 154, 5.1 mm in 72, 5.9 mm in 81, 6.7 mm in 103, and 7.7 mm in 18. Clinical outcome measures included range of motion and American Shoulder and Elbow Surgeons, University of California, Los Angeles, and Shoulder Pain and Disability Index scores.

Results: At similar follow-up times, all groups demonstrated a similar incidence of glenoid radiolucencies and similar mean Lazarus scores. Shoulders in female patients were more commonly treated with implant combinations resulting in 4.3, 5.9, and 7.7 mm of radial mismatch ( < .001). Improvements in range of motion and American Shoulder and Elbow Surgeons, University of California, Los Angeles, and Shoulder Pain and Disability Index scores were similar among all groups. Rates of reoperation secondary to glenoid loosening were similar among groups ( = .57). Moreover, the incidence of radiographic loosening (Lazarus grade 4 or 5) was similar among the groups ( = .22).

Discussion: Variation in mismatch between 3.4 and 7.7 mm did not affect the incidence of glenoid lucent lines or Lazarus score. This finding suggests that optimal radial mismatch may extend below 5.5 mm, as previously recommended by Walch et al, without affecting the incidence and grade of glenoid lucencies.