gms | German Medical Science

Objectives: This study evaluates the performance of convertible metal-back glenoid systems in total shoulder arthroplasty (aTSA), focusing on complications and the necessity for revision surgeries in stemless versus stemmed designs for primary glenohumeral osteoarthritis.

Methods: A retrospective analysis involved 69 shoulders from 65 patients with primary aTSA. They were categorized into Group 1 (n=31), receiving convertible cementless stemmed aTSA (Lima SMR) and Group 2 (n=38), receiving humeral head replacement aTSA (Arthrex, Eclipse) both with metal-back glenoid components. Clinical and radiological assessments were conducted 2, 5, and 10 years postoperatively or if the patient has presented himself due to complaints, including: Constant Score, DASH, SPADI, SSV, Glenohumeral Distance, Critical Shoulder Angle and Lateral Acromion Index. Additional we compared complications, revision rates and survival rates between groups using Kaplan-Maier curves and Log-Rank-test.

Results and conclusion: Baseline demographics and preoperative outcome scores showed no significant differences between groups (p>0.05). The overall revision rate did not significantly differ between the groups (G1: 32% vs. G2: 24%, p=0.60), nor did the mean time to revision (p=0.27). The mean follow-up was 71±41 months (G1: 94±48 months, G2: 53±23 months, p<0.001). Kaplan-Meier analysis showed similar mid-term survival probabilities (p=0.94). Revision reasons included rotator cuff insufficiency (n=4 in Group 1, n=2 in Group 2) and glenoid wear/loosening (n=5 in Group 1, n=7 in Group 2). Notably, Group 1 showed no instances of glenoid metal baseplate or humeral loosening, while complex revisions were more common in the Group 2, especially in 2 cases of baseplate breakout. One occurred 4 years postoperatively with need for removal and bone stock reconstruction using allograft, and one 5 years postoperative treated with removal and cerament glenoid augmentation. At 2 and 5 years, non-revised patients in both groups had similar outcome scores.

Both stemless and stemmed metal-backed glenoid implants in aTSA exhibit comparable revision rates and survival probabilities. Rotator cuff insufficiency and polyethylene wear are the two most common complications leading to revision. The study underscores the unsolved disadvantages in metal-back components and the importance of a mid- to long-term longitudinal assessment of those patients.