Coracobrachialis muscle and the musculocutaneous nerve: a study using human embryonic sections

The results of decompression of the musculocutaneous nerve entrapment in children with obstetric brachial plexus palsy

PURPOSE

Elbow flexion is a key indicator of functional recovery in obstetric brachial plexus palsy (OBPP). However, lack of flexion could be a result of an entrapped musculocutaneous nerve during the healing period. The purpose of this study was to investigate the possible compression of the musculocutaneous nerve and outcomes of decompression.

METHODS

The study included 11 children aged with a mean age of 10.9 ± 2.7 months (range, 8-16 months) with Narakas 2 involvement OBPP, who had insufficient elbow flexion but had satisfactory shoulder abduction. Prior to surgery, magnetic resonance imaging (MRI) was performed to identify the entrapment. The children were evaluated pre-operatively and at 3 and 12 months postoperatively using the Active Movement Scale and Faradic Excitability Test. The musculocutaneous nerve was explored and decompressed in all the children. Regular physiotherapy and a home exercise programme were prescribed after surgery.

RESULTS

The MRI findings were consistent with the surgical exploration in all the infants. Statistical analyses showed that decompression of the musculoskeletal nerve improved active movement scale scores on elbow flexion and faradic excitability test values of biceps brachii within 3 months after surgery.

CONCLUSION

Children with delayed elbow flexion and satisfactory shoulder abduction may have an entrapped musculocutaneous nerve in the proximal arm and decompression of the nerve improves elbow function.

Teres major and latissimus dorsi muscles in human embryos: A reconsideration of the so-called brother muscles

The teres major and latissimus dorsi muscles (TM, LD) are considered to be the so-called brother muscles. Actually, being similar to the TM, an uppermost part of the LD usually arises from the scapular plate. In embryos of 11 mm CRL, anlagen of the TM and LD appeared to be fused to provide a single mass at an angle between the axillary and radial nerves. However, splitting had already finished in not only the TM and LD but also the other muscles at and around the shoulder in specimens of 14 mm CRL. Thus, muscle splitting at the region appeared to occur simultaneously at a short stage of 12-13 mm CRL.The TM and LD carried a common tendon still at 6 weeks (14-16 mm CRL), but their muscle bellies were separated clearly. A concept of brother muscles might be applied to the TM and LD according to a bias from the gross and comparative anatomy, not from the embryological view.