An aberrant tendo-aponeurotic extension of biceps brachii muscle: a possible factor for neurovascular compression in the antebrachium

Introduction Biceps brachii is described as a superficial muscle in the anterior compartment of the arm. It is a flexor of the elbow joint and a powerful supinator of the forearm. Standard anatomical textbooks describe the muscle as arising by two heads, a long and a short head arising from the supraglenoid tubercle and coracoid process of scapula, respectively. The two heads form a common belly proximal to the elbow joint and insert as a rounded tendon at the posterior aspect of the radial tuberosity. This tendon has a broad and flat medial expansion, the bicipital aponeurosis, which is reinforced by the antebrachial fascia inserts on the upper part of the posterior ulnar border [1]. Contemporary anatomical research is replete of a spectrum of variations in the origin of biceps brachii muscle in context to its topography and supernumerary heads [2, 3]. Variations of the insertion pattern of the distal biceps tendon and its aponeurosis are rarely addressed in research works [4]. In this report we attempt to describe an extremely rare and unique deviation of the insertion pattern of biceps brachii muscle. In addition to its usual tendinous and aponeurotic insertion sites, the muscle presented an additional extension to join the extensor carpi radialis longus (ECRL) muscle. This anatomical variant is particularly significant in compression syndromes of the neighboring vessels and nerves and also in tendon repair surgeries.