Patterns of motor branching of the musculocutaneous nerve in human fetuses and clinical significance

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The purpose of this morphologic study is to investigate the course and the branching pattern of motor branches of musculocutaneous nerve (MCN) in human fetuses. Twenty upper limbs (10 right, 10 left) of spontaneously aborted formalin-fixed fetuses were dissected under a stereomicroscope to determine motor branches for the biceps brachii and brachialis and the communicating branches between the MCN and median nerve (MN). The MCN entered the proximal and middle part of coracobrachialis in 13/20 and 5/20 of arms, respectively, and the remaining 2/20 did not pierce coracobrachialis. The communication between MCN and MN was observed in 5/20 of the arms and detected only in the distal part of the coracobrachialis. The most frequently observed innervation is the type wherein a single branch to biceps brachii, which bifurcated for supplying the short and long heads (12/20). For the innervation of brachialis, the most frequent type was a single branch from the main trunk of the MCN (15/20). During the dissections, the distance between the acromion and the emerging point of the motor branches was measured. The mean distance between the acromion and the emerging point of the all motor branches for biceps brachii in all types of specimens was 33.8 ± 6.1% of acromion-lateral epicondyle length and for brachialis was 50.6 ± 11.5% of acromion-lateral epicondyle length. The data of the MCN variations in the human fetus may be useful for the clinicians and pediatric surgery.