Bilateral Absence of Flexor Digitorum Superficialis Tendon of the Little Finger: Clinical Significance

Abstract

The flexor digitorum superficialis (FDS/sublimis) is a flexor of the digits of the hand and has been reported to have varying degrees of agenesis. During routine cadaveric dissection for undergraduates at SRMS-IMS Bareilly, India, we observed bilateral absence of the FDS tendon to little finger in the upper limbs of a 45-year-old male cadaver. The muscle was normally supplied by a branch of median nerve in the forearm. Variants of the FDS muscle of the little finger have been reported in the literature. Proper knowledge of muscular variations is essential not only for anatomists but also for orthosurgeons, plastic surgeons and neurologists especially when evaluating possible tendon laceration/dysfunction. The FDS has been used as a motor for a wide variety of tendon transfer operations in the hand. CASE REPORTDuring routine dissection of the front of the forearm for undergraduate teaching in the Department of Anatomy, SRMS-IMS, Bareilly, India, we observed bilateral absence of the FDS tendon to the little finger in the upper limbs of a 45-year-old male cadaver. The muscles of the flexor compartment of both limbs were carefully dissected using Cunningham's Manual of Anatomy. After stepwise dissection of the front of forearm, we found the normal origin of the muscle by two heads, viz., humero-ulnar and radial head. A branch of median nerve supplied the muscle. The FDS divided distally into 3 tendons (instead of 4) for the ring, middle and index fingers. Relationship with neighbouring structures was found normal and no other associated abnormalities were noticed. Also, no other variation was noted in the course and insertion of the remaining FDS tendons [Table/ Fig-1 and 2]. The Flexor digitorum profundus (FDP) tendon for the little finger remains interconnected with ring and middle finger tendon (except for index finger tendon which seperates early) in the forearm. In the palm, it passes normally through perforated FDS tendon and is inserted to the base of terminal phalanx.

Bilateral Congenital Absence of Small Finger Flexor Digitorum Superficialis Tendons in a Trauma Patient

“…There are many described variations of the FDS [1,3,5,[7][8][9][10], and suspicion of these variations preoperatively and identification intraoperatively is important for accurate diagnosis and tendon repair. The FDS independent variation, where the small finger FDS tendon inserts on to the middle phalanx of the small finger independently without direct connections to the ring finger tendon, is the most common variant of the FDS [2,5,8,9].…”

“…The primary action of FDS is to flex the middle phalanx at the proximal interphalangeal (PIP) joints and can also flex the metacarpal phalangeal (MCP) joints and wrist joint with sustained action [1,3]. This allows the human hand to make skilled, grasping movements necessary for fine motor skills [3][4]. For instance, Gupta and Kumar found that the independent function of the FDS tendons was essential for high caliber, professional musicians [3].…”

“…This allows the human hand to make skilled, grasping movements necessary for fine motor skills [3][4]. For instance, Gupta and Kumar found that the independent function of the FDS tendons was essential for high caliber, professional musicians [3]. However, Austin et al suggested that a common variant of a shared distal FDS tendon to the ring and small fingers limits independent PIP flexion of the small finger [5].…”

“…The origin of these muscles migrated proximally to establish the present separate forearm and intrinsic hand muscle arrangements, giving the organism more control over hand movements [4]. The evolutionary role of the FDS tendon to the small finger warrants further investigation, as its small structure has limited functional consequence [1,6] and its absence may represent evolutionary progression with improved independent flexion of the ring and small finger PIP joints [1,3,6].…”

“…Anatomical variations of the forearm flexor muscles are common [2], and there are several documented variations of the FDS [1,3,5,7]. Variations in the FDS are clinically important for the assessment of injuries and pre-surgical planning for harvesting the small finger FDS tendon [3]. The purpose of this case report is to discuss a variant of congenital absence of bilateral small finger FDS tendons that was found on exploration of traumatic injuries.…”