Accessory flexor carpi ulnaris and bilaterally variant vascular anatomy of upper limb: An unusual presentation

Abstract

We report a rare combination of variations in the upper limb of a human cadaver. Accessory flexor carpi ulnaris with absent palmaris longus was observed in the left forearm during routine dissection of a male cadaver. Variant vascular pattern was observed bilaterally. Brachial artery bifurcated at a higher level. Ulnar artery gave rise to persistent median artery (PMA) which pierced the median nerve and accompanied it deep into flexor retinaculum to terminate as two common palmar digital arteries. Superficial palmar arch was not formed as the PMA did not anastomose with either the radial or ulnar artery. Radial artery was small and deep palmar arch was mainly contributed by the deep branch of ulnar artery. Awareness of these coexistent variations in the forearm and hand is anatomically as well as clinically important in reconstructive hand surgeries.

Notes on the Accessory Flexor Carpi Ulnaris Muscle: A Rare Supernumerary Variation

“…Clinically, the presence of supernumerary or abnormally large muscles on the forearm may be the cause of neurovascular bundle compression. [3][4][5]7,12,15,16 The length, girth, width and the relations of the aFCUM reported herein could predispose an individual to develop compressive neuropathies of the UN not only on the Guyon's canal, but in the whole forearm instead. In addition, the distal insertion on the flexor retinaculum by the aFCUM could compromise the median nerve as well.…”

“…Development of the muscles starts with segmentation of the paraxial mesoderm into somites. Each somite has two portions: the sclerotome (which gives origin to bones and cartilages of the thorax and vertebral column) and the dermomyotome (which will form the muscles) 5,8,9 The myotomes give origin to myoblasts, which go through extensive migration in order to originate the limb muscles. This process starts during the fifth week of development.…”

“…The ventral mass forms the flexors and pronators, while the dorsal mass forms the extensor and supinator muscles of the forearm. 5,8,9 Through apoptotic mechanisms and growth factors, each muscle begins to take its shape and current appearance. The presence of supernumerary muscles is usually caused by an increase of cell stimuli, which causes proliferation of muscle tissue and the lack of apoptotic stimuli to cease its growth.…”

“…The presence of supernumerary muscles is usually caused by an increase of cell stimuli, which causes proliferation of muscle tissue and the lack of apoptotic stimuli to cease its growth. 5,8,9 The FCUM is a fairly consistent muscle that rarely varies (0.02% of all flexor compartment variations). Aberrant origin or insertion, additional slips, partial muscle belly, split tendon, fusion with palmaris longus muscle and the presence of an aFCUM are among reported variations of the FCUM.…”

“…1,3 Although variations of the FCUM are rare, it is a clinically significant muscle, as it can cause compression of the UN, and it can be used as a muscle flap for soft tissue reconstruction. [4][5][6] Accessory muscles of the forearm can also mimic neuromas or soft tissue tumors, and can contribute to the onset of thrombosis and syndromes such as carpal tunnel. Knowledge of these variations are important to surgery, as most of them are discovered intraoperatively 5,7 The present work reports the presence of an accessory flexor carpi ulnaris muscle (aFCUM) in a male cadaver and discusses its clinical significance.…”