Bilateral symmetrical supernumerary heads of biceps brachii with rare pectoralis major insertion

Abstract

During a routine dissection of a 51-year-old Caucasian male cadaver, bilateral symmetrical supernumerary heads (SH) of the biceps brachii muscles with insertion into the pectoralis major (PM) muscles were discovered. Multiple case reports have documented supernumerary heads for the biceps brachii; however, none have shown bilateral insertion into the pectoralis major. This study describes a previously undocumented variation of the SH that has potential for clinical impact. Healthcare providers could be confounded by patients presenting with shoulder pain or muscle tears as a result of the anomaly. Furthermore, MRI studies on patients with possible shoulder muscle tears could reveal unexpected results. Such cases would warrant consideration of SH anomaly and treatment should be adjusted accordingly. The significant bulk and angle of the SH insertion on the PM we observed changes force vectors which would have an unknown effect in performance, surgical interventions and pain syndromes. A second biceps brachii anomaly was observed on the left brachium in addition to the bilateral SH. We postulate that these variants provide the potential for clinical complications regarding muscular injury to these aforementioned muscle groups.

Five-headed biceps brachii muscle with a rare origin from the tendon of pectoralis major muscle

“…Even though the embryological explanation of the accessory heads of BB was well described, the supernumerary head originating from the pectoralis major described herein has rarely been described to the best of our knowledge. The supernumerary head in this cadaver is likely the result of some minor failure of some of the complex regulation system that acts in concert to ensure proper placement of myogenic cell groups during limb development, as previously suggested (Fraser et al 2014). Taken together, such dysgenesis including the division of origin and the anomalous insertion into the pectoralis major could explain the development of this case.…”

“…Macalister (1875) reported the 48 variations of BB, among which only 2 cases were related to the pectoralis major: a slip to the short head from the tendon insertion of pectoralis major and an instance of the origin of the long tendon of the BB from the tendon of pectoralis major. This variant has recently been reported in two cases, unilaterally (Sargon et al 1996) or bilaterally (Fraser et al 2014). Previous works showed the presence of a supernumerary head originated from the pectoralis major, but we report herein three supernumerary heads associated with a rare origin from the pectoralis major muscle with the other two supernumerary heads documented with the most common form originating from the humerus.…”

“…The presence of a supernumerary head of the BB, however, is known to affect the course and branching of the musculocutaneous nerve (Kosugi et al 1992), which could cause compression of surrounding neurovascular structures. Moreover, the significant bulk of the supernumerary head associated with the pectoralis major muscle may lead to variation of normal mechanical actions including flexion and supination of the forearm, as previously suggested (Fraser et al 2014). There was no additional variation of the musculocutaneous nerve, but there was significant bulk of the 3rd head associated with the pectoralis major muscle in this case, which might lead to variation of normal action without clinical manifestations.…”

Morphological variations of biceps brachii muscle in eastern indian population: A cadaveric study

“…Bilateral SH of BB having origin from the pectoralis major muscle, as reported earlier, is also seen in the present study. 10 These extra/supernumerary fibers of biceps originating from pectoralis major tendon are prone to rupture or tear in young healthy athletes undergoing strenuous exercises.…”

Anomalous Third Head of Biceps Brachii Muscle and its Variant Insertion Compresses Surrounding Neurovascular Structure: A Rare Case Report

“…According to Emeka and Emmanual (2009), unilateral occurrence of third head of biceps brachii muscle together with its abnormal origin of short head from the acromion and from the supraglenoid tubercle. Recent findings from Fraser et al (2015) also observe the clinical importance of supernumerary head of biceps brachii inserted at pectoralis major muscle. While Kopuz and co-workers (1999) observed that the third head of BB commonly begin from the anterior surface of the humerus distal to the insertion of the coracobrachialis muscle.…”