Background: Migration after shoulder arthroplasty can induce muscular dysbalance and instability of the shoulder joint. The aim of this study was to analyse the frequency, causes and consequences of secondary migration after shoulder arthroplasty.
Methods: 107 shoulder arthroplasties in patients with primary osteoarthritis (OA, n = 83) or avascular necrosis of the humeral head (AVN, n = 24), were followed clinically and radiographically over a period of 1 to 10 years.
Results: 17 Patients (16 %) developed secondary migration of the prosthesis. These were determined after a mean period of 33 months after shoulder arthroplasty. Patients with secondary migration of the prosthesis showed a worse function with a mean Constant score (CS) of 52.3 points in comparison to the patient group without migrated shoulder arthroplasties (62 points) (p = 0.038). In patients with total shoulder arthroplasty (TSA, n = 75), migration was observed in 13 % of cases during follow-up. Lucent lines at the glenoid were found in radiographs in 55 % of migrated shoulders and in 52 % of non-migrated shoulders (p = 0.633). The Constant score showed no significant difference between the groups (non-migrated shoulders 63 points, migrated shoulders 61 points, p > 0.5). Migration was seen in 22 % (7/32 patients) after hemiarthroplasty, however, no significant difference could be found between the respective Constant scores for migrated (47.7 points) or non-migrated (55.1 points) shoulders (p = 0.447). In patients with OA there was no significant difference in Constant score between migrated and non-migrated shoulders (p = 0.331), whereas patients with AVN showed significantly worse function after migrated shoulder arthroplasty (p = 0.007).
Conclusion: Migration after total shoulder arthroplasty leads in the medium term neither to an increased frequency of lucent lines at the glenoid nor to a worsening of the functional score in comparison to non-migrated prosthesis. In patients with AVN, migration is accompanied by a worsening of the functional score and can consequently be regarded as a negative prognostic factor.