Natural history of glenoid bone loss in primary glenohumeral osteoarthritis: how does bone loss progress over a decade?

Introduction: Progressive glenoid bone loss and humeral head subluxation occur in primary glenohumeral osteoarthritis (GHOA), but less is known about the rate and pattern by which this occurs. The purpose of this study was to determine how glenohumeral subluxation and glenoid bone loss changed over time in shoulders that underwent arthroplasty and had been evaluated with radiographs at 1 or more time points over the 5-15 years before arthroplasty.
Methods: We retrospectively identified 48 shoulders that had been evaluated with high-quality radiographs both before arthroplasty and at least once 5-15 years earlier. Axillary radiographs were used to classify glenoid morphology using the modified Walch classification on the oldest, most recent, and all intervening radiographs. The mean interval time between the oldest and most recent radiographs was 8.9 years (range 5-15 years). Nineteen patients had a single intervening radiograph (mean, 6.7 years from most recent radiograph; range 4.4-8.9 years), 6 patients had 2 (mean, 5.6 years; range 0.2-13.9 years), 3 had 3 (mean, 5 years; range 2.4-8.3 years), 2 had 5 (mean, 3.4 years; range 1.1-5.7 years), and 1 had 6 (0.5 years).
Results: Glenoid morphology on the earliest radiograph was classified as A1 in 22, A2 in 13, B1 in 1, B2 in 9, B3 in 1, and D in 2 shoulders. Walch A patterns identified on early radiographs most commonly maintained an A pattern over time, but 20% developed eccentric wear with 5 of 35 becoming B type and 2 of 35 becoming a D type before arthroplasty. All B-type glenoids remained B type. Classic progression of bone loss along the same concentric or eccentric "track" occurred 41% of the time, with 9 of 22 A1 glenoids becoming A2 glenoids, the only B1 glenoid becoming a B2 glenoid, and 56% (5/9) of B2 glenoids becoming B3 glenoids before arthroplasty. Only 15% (2/13) of A2 glenoids developed eccentric wear compared with 32% (7/22) of A1 glenoids.
Conclusion: In primary GHOA, humeral head subluxation and glenoid bone loss do progress over time, but not universally and not always through the same pathway. Shoulders presenting with posterior subluxation (B types) remained posteriorly subluxed. Shoulders presenting with concentric arthritis developed an eccentric pattern 20% of the time. For concentric arthritis, progression of bone loss from A1 to A2 occurred 41% of the time. For eccentric arthritis, progression of bone loss from B2 to B3 occurred 56% of the time.
(Copyright © 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)