Bilateral Additional Slips of Triceps Brachii Forming Osseo‑Musculo‑Fibrous Tunnels for Ulnar Nerves

Abstract

Rare additional slips of triceps brachii muscle was found bilaterally in a sixty two year old South Indian male cadaver during routine dissection of upper limb for undergraduate students at Melaka‑Manipal Medical College, Manipal University, Manipal, India. On left side, the variant additional muscle slip took origin from the lower part of the medial intermuscular septum about 4 cm proximal to the medial humeral epicondyle. From its origin, the muscle fibres were passing over the ulnar nerve and were joining the triceps muscle to get inserted to the upper surface of olecranon process of ulna. On right side, the additional muscle slip was larger and bulkier and was arising from the lower part of the medial border of the humerus about 4 cm proximal to the medial epicondyle in addition to its attachment to the medial intermuscular septum. On both sides, the additional slips were supplied by twigs from the radial nerve. On both sides, the ulnar nerve was passing between variant additional slip and the lower part of the shaft of the humerus in an osseo‑musculo‑fibrous tunnel. Such variant additional muscle slips may affect the function of triceps muscle and can lead to snapping of medial head of triceps and ulnar nerve over medial epicondyle and also can dynamically compress the ulnar nerve during the contraction of triceps leading to ulnar neuropathy around the elbow.

Keywords: Cubital tunnel syndrome, Nerve entrapment, Snapping triceps syndrome, Triceps brachii, Ulnar nerve