Is There A Long Term Deterioration in Deltoid Muscle Function after Reverse Shoulder Replacement?

Ehud Atoun 1,2,3 George Mazis 1 Caroline Witney-Lagen 1 Ernest Fawzy 1 George Arealis 1 Giuseppe Sforza 1 Juan Bruguera 1 Ofer Levy 1
1Reading Shoulder Unit, Royal Berkshire Hospital & Berkshire Independent Hospital, UK
2Orthopaedic Department, Barzilai Medical Centre, Israel

Reverse shoulder arthroplasty changes the anatomy of the shoulder and lengthens the humero-acromial distance. The long-term effects to the deltoid function and, thereby, to the clinical outcome remain

Objectives: To examine the long term results to the deltoid function and clinical outcome.

Methods: The study comprised 48 reverse shoulder replacements in 46 patients with a follow up of 6 or more years. The patients underwent clinical and radiological assessment preoperatively and postoperatively, at regularly set appointments after the reverse shoulder arthroplasty. The ROM and Constant score (CS) were evaluated. Deltoid strength was measured using the digital gauge myometer.

Results: Mean age at latest follow up was 79. Complete preoperative and postoperative scores were available for all 48 cases. Mean preoperative deltoid pull strength was 2.6N (0.266 kgr x 9.8 m/s2), mean active forward flexion 53 degrees, abduction 48 degrees and mean CS was 15.5. At 1 year post op, mean deltoid pull strength was 23.7N (2.42 kgr), mean active forward flexion 140 degrees, abduction 133 degrees and mean CS was 60.3. At the latest follow up (mean 83 months, range from 72 to 122 months), mean deltoid pull strength was 21.5N (2.19 kgr), mean active forward flexion 130 degrees, abduction 124 degrees and mean CS was 60.2. The mean strength of the contralateral shoulder at the latest follow up was 25.9N (2.64 kgr).

There was significant improvement in all parameters between the preoperative and the postoperative follow ups. No significant difference was seen in the deltoid pull strength (p=0.4071), forward flexion (p=0.2367), abduction (p=0.3253) and CS (p=0.9916) at 1 year versus the latest follow up. No significant difference was seen in the deltoid pull strength between the evaluated and the contralateral side (p=0.187).

Conclusions: This study showed no evidence of long term deterioration of the deltoid function after reverse shoulder replacement.