the human thumb is opposable and prehensile , making it the most unique digit of the hand , responsible for hand functions , grasp , manual dexterity , and fine motor skills .
the thenar eminence constitutes the intrinsic muscles of the hand that are responsible for complex movements of the thumb .
congenital anomaly of the thumb and/or of the thenar muscles can be quite a disabling condition . in 1979 , arminio was the first to report congenital absence of the flexor pollicis longus ( fpl ) tendon . since then , many cases have been published with congenital absence of the fpl tendon with or without associated anomalies of the thumb and thenar muscles . most of the reports have documented unilateral absence of fpl tendon ; bilateral absence is extremely rare .
only three cases of bilateral congenital absence of fpl tendon have been reported so far ; no thenar atrophy was seen in these cases .
we present a case of a 9-year - old female child with bilateral congenital absence of fpl tendon and associated thumb hypoplasia and thenar eminence atrophy .
a 9 year old female child presented to our hospital with difficulty in performing tasks like writing or holding an object .
there was absence of flexion movement at interphalangeal ( ip ) joints of bilateral thumbs .
local examination revealed minor hypoplasia of the thumbs and absence of dorsal wrinkles [ figure 1a ] and flexion creases [ figure 1b ] at the ip joints of both the thumbs .
minor hypoplasia of both the thumbs and absence of dorsal wrinkles are seen ( arrows ) .
( b ) palmar surface of the hands show absent flexion creases ( arrows ) of bilateral thumbs .
( c ) functional limitation in holding a pen ; note the absence of active flexion of the interphalangeal joints of both the thumbs radiograph of hands showed mild skeletal and soft tissue hypoplasia of bilateral thumbs [ figure 2 ] .
radiograph of both hands shows mild skeletal and soft tissue hypoplasia of bilateral thumbs magnetic resonance imaging ( mri ) of hands showed absence of bilateral fpl muscles .
in addition , there was absence of flexor pollicis brevis ( fpb ) and abductor pollicis brevis ( abpb ) muscles and hypoplasia / atrophy of bilateral opponens pollicis ( op ) muscles .
bilateral adductor pollicis brevis ( adpb ) muscles appeared normal in morphology [ figure 3 ] .
t1w coronal image of both the hands shows absence of bilateral flexor pollicis longus ( fpl ) tendons .
normally , fpl tendon is seen between the lateral head of flexor pollicis brevis ( fpb ) and the oblique head of adductor pollicis brevis ( adpb ) muscles , and is inserted into the base of the distal phalanx of thumb ( see inset images ) .
bilateral flexor pollicis brevis ( fpb ) and abductor pollicis brevis ( abpb ) muscles were also absent .
bilateral adpb muscles appeared normal in morphology after pre - anesthetic checkup , the patient was planned for fpl reconstruction in bilateral thumbs .
two - staged surgery was planned ; in the first stage , flexor pulley was reconstructed , and 2 months later , fpl reconstruction was done using flexor digitorum superficialis ( fds ) tendon to the ring finger .
postoperative physiotherapy was done to increase the range of motion ( rom ) of the ip joints of both thumbs . at this moment , the patient has achieved ~20 of flexion at the ip joints bilaterally .
congenital inability to flex the ip joint of the thumb may be due to several causes , including congenital absence of fpl , anomalous insertion of fpl , congenital tenovaginitis of the flexor tendon sheath , partial anterior interosseous nerve paralysis , traumatic rupture of the fpl , and anomalous connection between the tendons . among these , congenital absence of the fpl is extremely rare . absence of fpl may occur with or without associated anomalies of the thumb and thenar muscles .
thumb hypoplasia with congenital absence of the fpl tendon , but without hypoplasia of the thenar muscles is the rarest variation
. congenital absence of thenar muscles ( e.g. fpb and abpb ) without absence of fpl has also been reported in literature .
most cases are reported in the pediatric age group and only a few are described in adults .
clinically , the affected thumb shows absent or less evident dorsal wrinkles and flexion creases .
skeletal and soft tissue hypoplasia of thumb may be present . according to blauth et al .
, thumb hypoplasia may be classified as isolated minor hypoplasia ( type 1 ) , associated with thenar hypoplasia and metacarpophalangeal ( mcp ) joint instability ( type 2 ) , musculotendinous / osseous deficiency with absent active motion at mcp or ip joint ( type 3 ) , floating thumb ( type 4 ) , and complete absence of the thumb ( type 5 ) .
imaging may show absence ( agenesis ) , hypoplasia , or atrophy of the muscles and tendons .
ultrasonography ( usg ) is a low - cost , safe , non - invasive , and rapid method of evaluating musculoskeletal system .
it is indicated in patients with cardiac pacemakers and metal implants where mri is contraindicated . computed tomography ( ct ) and mri
may be used to confirm and support the usg findings . surgical reconstruction followed by rigorous rehabilitation
the preferred surgical technique is one- or two - staged tendon transfer using the fds tendon of the ring finger .
the range of flexion achieved at ip joint after the surgery varies between 20 and 35. following surgery , planned physiotherapy is a must to obtain satisfactory results .
this case is unique as it demonstrates bilateral congenital absence of fpl tendon in association with thumb hypoplasia and thenar atrophy in a child .
thenar atrophy was due to selective absence of bilateral fpb and abpb , and hypoplasia / atrophy of op .
 congenital absence of flexor pollicis longus with or without associated anomalies of thenar muscles and thumb is of rare occurrence . 
 inability to flex the interphalangeal joint of the thumb and absent dorsal wrinkles and flexion creases of the thumb are important clues to the diagnosis . 
 routine radiography and cross - sectional imaging help to confirm and document the condition . 
 this article presents an extremely rare case of bilateral congenital absence of flexor pollicis longus tendon with thumb hypoplasia and thenar atrophy . 
Introduction
Case Report
Discussion