Very late spinal accessory nerve to infraspinatus nerve transfer to restore glenohumeral external rotation in brachial plexus birth injury

Background: Poor recovery of active glenohumeral external rotation (aGHER) after brachial plexus birth injury (BPBI) is common. Late spinal accessory nerve to infraspinatus motor branch (SAN-IS) transfer has been reported as effective. We investigated its efficacy in children over 4 years with BPBI. Methods: This case series involved children with no aGHER undergoing SAN-IS transfer. Indications included absent aGHER in shoulder abduction and a positive external rotation drop test. Subscapularis release was done for passive GHER (pGHER) <30º in patients without glenohumeral dysplasia, while external derotational humeral osteotomy (DHOT) was performed for those with dysplasia and pGHER <0º. Data collected included demographics, Narakas group classification, preoperative and postoperative hand-to-neck Mallet scores, postoperative aGHER, aGHER strength (British Medical Research Council scale), and parental satisfaction. Results: Twenty-six patients, with a mean age of 9.9 years (range 4-26) and mean follow-up of 27.9 months (range 12-74), were included. Five patients (19%) had a concurrent upper subscapularis release, and eight (31%) underwent DHOT. Infraspinatus was macroscopically normal and contractile in all but one case. Twenty-one patients (80%) achieved a mean aGHER of 71º (range 60-80). Of these, 90% scored M4 on the BMRC scale, and 85% had a hand-to-neck Mallet score of 4. Shoulder forward flexion improved a mean of 35º (range 20-60º) in 40% of patients. Six parents were satisfied, and 20 were extremely satisfied. Conclusions: Late SAN-IS transfer is both effective and safe for restoring aGHER in patients over 4 years old with BPBI.