Effect of arm lengthening on functional outcomes and nerve injury after reverse shoulder arthroplasty: A prospective electrodiagnostic study.

BACKGROUND

The original Grammont Reverse Total Shoulder Arthroplasty (RTSA) increases the deltoid moment arm by medializing the centre of rotation, which is biomechanically advantageous. However, excessive tension can also produce complications, being one of the main risk factors for nerve injury. The purpose of the present study was to correlate arm lengthening after a medialized RTSA implant with functional outcomes and neurological injuries in the setting of rotator cuff tear arthropathy (CTA).

METHODS

Prospective cohort study enrolled 40 consecutive patients who underwent RSA for CTA. Electrodiagnostic evaluation was performed preoperatively and at 3 months post-surgery. Deltoid lengthening through acromion-tuberosity distance (AT) was measured with XR/CT and correlated with functional scores and nerve injuries.

RESULTS

At final follow-up (average, 28.4 ± 4.4 months), 31 of 40 patients were available for final study. The mean post-surgery AT on the CT for patients without and with acute postoperative injuries was 27 ± 8 vs 32 ± 3 mm (p .045). Twenty-two patients had ≥25 mm arm lengthening with 11 cases (50 %) of acute neurological injury and 9 patients had <25 mm with no cases of acute neurological injury (p .012). The increased risk of nerve injury was more evident for the axillary nerve (p .068). The patients with arm lengthening ≥25 mm had superior functional outcomes in abduction (p .046) and the patients with forward elevation ≥120° had superior AT distance (p .065).

CONCLUSIONS

A post-surgical acromion-tuberosity distance greater than 25 mm increases functional results after RSA and the possibility of acute nerve injuries. As these injuries have little clinical impact, we recommend with the employment of a globally medialized design arm lengthening of at least 25 mm to obtain better functional results.

LEVEL OF EVIDENCE: Level II, Prospective Cohort Design, Prognosis Study.