Morphology and clinical implication of the extra-head of biceps brachii muscle

The biceps brachii muscle is present in the anterior aspect of the arm. Its morphological variations have great clinical significance for surgeons, orthopaedic surgeons, anaesthetists, neurologists and anatomists. This study aimed to describe the incidence and morphology of the extra-heads of the biceps brachii muscle. Hundred upper limbs of 50 adult human cadavers (30 men and 20 women) were used in this study after the approval of the medical ethical committee. These cadavers were obtained from the Anatomy Department, Faculty of Medicine, King Abdul-Aziz University. The incidence of anatomical variations of biceps muscle was equal in both male and female cadavers (10%) with predominance of the left side (7%). The 3-headed biceps brachii muscle was noticed in 7% (4% male and 3% female), while the 4-headed biceps was seen in 2 (2%) left limbs, 1 male and 1 female. The third head of the biceps muscle arose from the anteromedial aspect of humerus, between the coracobrachialis insertion and the brachialis origin, in 6% and from middle of the medial border of humerus in 3%. While the fourth head originated from the articular capsule of shoulder joint in 1 (1%) limb and from the coracoid process of scapula in the other limb. The biceps common tendon of insertion received the supernumerary heads in 7% of the limbs. However, the extra-head fused with the long head in 2 (2%) limbs and united with the short head in 1 (1%) limb. The mean of the third head length was 118.8±10.9 in all limbs, where it was 121.8±12.3 in male and 113.5±8.1 in female cadavers. The third head length/arm length ratio was 38.4±2.6 in all, 38.3±3.4 in male and 38.8±1.8 in female cadavers. The length of the extra-head was extremely significant with those of the corresponding limb in all, male and female cadavers (p<0.0001). Knowledge of the morphological variations of biceps muscle provides better pre-operative evaluation, safe surgical intervention within the arm and better postoperative outcomes.