A rare human variation: the relationship of the axillary and inferior subscapular nerves to an accessory subscapularis muscle.

A case of bilateral occurrence of a variant subscapularis muscle is reported. The superior lateral aspect of each subscapularis muscle presented a small accessory muscle with an accompanying tendon that inserted into the lesser tubercle of the humerus along with the primary tendon of the subscapularis muscle. Each accessory subscapularis muscle was separated from the primary subscapularis muscle by the axillary and inferior subscapular nerves. No branches of the axillary or inferior subscapular nerves supplied the primary subscapularis muscle or the accessory muscle while the nerves passed through the myotendinous tunnel. The relationship of the nerves with the variant subscapularis muscles has clinical significance with regard to entrapment neuropathy.