An unusual flexor of the little finger and ulnar nerve entrapment : a case report

Introduction The classic description of the flexor digitorum superficialis (FDS) muscle states that, it arises by two heads, humero-ulnar and radial heads respectively and divides into four muscle bundles in the distal third of the forearm. The muscle bundles then form four separate tendons above the wrist and get inserted to the sides of the shaft of the middle phalanx of the medial four digits [1,2]. Barker [3], Austin [4], and Stein [5] et al demonstrated that a few individuals are absolutely superficialis deficient in the little finger. Thompson et al [6] found only 2% of his study population had absolute superficialis deficiency in the little finger (6 unilateral, 4 bilateral). In the absence of the fourth belly of the muscle to the little finger, its place may be taken by a muscle arising from the medial collateral ligament of ulna, the deep flexor, the transverse carpal ligament and palmar aponeurosis or the ligament alone or the lumbricals [7]. Macalister [8] found the medial two FDS tendons arising separately, with a condyloid origin. Carr et al [9] reported that FDS tendon to the little finger was absent and replaced by an unusual digastric flexor arising from the medial epicondyle of the right humerus, much similar to our findings.