Biceps brachii muscle attached to the extensor carpi radialis brevis muscle: an unreported anatomical variation in humans.

We report a new muscular variation in humans. It consisted of a biceps brachii muscle attached to the extensor carpi radialis brevis muscle by means of an accessory fasciculus. It was a trapezoid tendinous connection band that arose from the terminal tendon of the biceps brachii muscle and ended in the internal margin of the extensor carpi radialis brevis muscle. This intermuscular connection band was the external slip of the insertion tendon of the biceps brachii muscle, which was also attached by means of two other fascicles to the radial tuberosity (intermediate slip) and the flexor digitorum superficialis muscle (internal slip). This variation was observed in only one of the sixty upper limbs examined.

Accessory fasciculi of the human pronator teres muscle: incidence, morphological characteristics and relation to the median nerve.

The purpose of this study is to determine the incidence of the accessory fasciculi of the pronator teres muscle and to evaluate the predispositional role of its morphological characteristics to median nerve entrapment. The accessory fasciculi of the pronator teres muscle have been found in 8.3% of 60 upper extremities which were studied. These fasciculi arose from the tendon of the brachialis muscle (5.0%), from the radial tendon of the biceps brachii muscle (3.3%), from the Gantzer's muscle (1.6%) or from the flexor digitorum superficialis muscle (1.6%). They were slips of origin of the deep head of the pronator teres muscle. They represented the deep head, when there was no other origin slip, or they were additional origin slips when the deep head also had a coronoid origin. Only the accessory fasciculi that represented the deep head and the accessory fasciculi located inside to the coronoid fasciculus were related directly to the median nerve. Three characteristics of these accessory fasciculi adjacent to the median nerve could be considered to be factors that predispose to the nerve entrapment: 1) the location dorsal to the superficial head of the pronator teres muscle, because it increases the area of contact with the median nerve; 2) the location between the superficial head and the coronoid fasciculus, because it reduces the space occupied by the median nerve; and 3) the tendinous nature of considerable segments of short accessory fasciculi because they are less extensible.

Variations of the pronator teres muscle: predispositional role to median nerve entrapment.

The variability of the human pronator teres muscle is studied in 60 upper limbs. The humeral head was present in all cases and was double in 3 cases (5.0%). The ulnar head was present in 47 cases (78.3%). The ulnar head was muscular in 11 cases, tendinous in 6 cases, and mixed in 30 cases. The collateral branches of the median nerve destined to the pronator teres muscle were found to be arranged in three main patterns: arising directly from the median nerve, arising from the superficial flexor antebrachial muscles nerve, and mixed type. Special reference is made to the influence of variations in the pronator teres muscle on the compression or the entrapment of the median nerve (pronator syndrome). The proposed determinant variations are: short and tendinous ulnar head, ulnar head joined to the arch of the flexor digitorum superficialis muscle, ulnar head with triple origin slips, and humeral head perforated by the median nerve.