Accessory FDL causing Tarsal Tunnel Symptoms in a 15 Year Old Girl: A Case Study
Ali Rahnama DPM, Tara Stock DPM FACFAS
Detroit Medical Center
Discussion:
Abstract:
The presence of an accessory flexor digitorum longus (FDAL) has been
sparsely reported in the foot and ankle literature. This makes for a particularly
challenging diagnosis for the practitioner, especially without more advanced
imaging modalities present. The current case presents a 15 year old track and
field runner who presented with tarsal tunnel symptoms only when running at
which point she had to stop due to increased pain that would subside with a
short period of rest. Ultimately she was found to have an FDAL which was
resected operatively at which point she was able to return to full physical
activity at the competitive level.
Introduction:
Tarsal tunnel syndrome can have many etiologies and is a relatively
common pathology that presents to the Foot and Ankle Surgeon. The basic
premise being that the tibial nerve has little room for compensation being
enclosed in the flexor retinaculum and is therefore vulnerable to changes in
the volume of the “tarsal tunnel”. Possible etiologies include tumor,
tenosynovitis, varicosities, bone spur, valgus foot type as well as the
presence of accessory muscles (1).
The presence of an accessory flexor digitorum longus (FDAL) has an
incidence as high as twelve percent in the population (2). The sparsity in
reporting this anatomic variant in the Foot and Ankle literature may
contribute to a difficulty in pinpointing it as a pathological source for the
patients tarsal tunnel syndrome (TTS) without more advanced imaging (3).
The current case report is of a case of TTS in an adolescent runner
whose symptoms resolved with surgical resection of the FDAL.
Case Presentation:
A 15 year old female cross country runner presented to the Foot and
Ankle clinic with a two month history of pain with shooting into the plantar
aspect of the right foot with a sharp nature when running. She reported
that the pain subsided with a short rest period. Her past medical history
was noncontributory and her mother reported a full term birth with no
complications.
On physical exam the patient has a positive Tinnel sign with mild pain
on palpation over the posterior tibial nerve. X-ray revealed no abnormality
and it was elected to obtain an MRI (Figure 1) due to the patients young
age and odd onset of symptoms (i.e. with moderate to intense physical
activity with a resolution of symptoms with little rest). MRI revealed an
accessory FDL tendon/muscle to the right lower extremity with a low lying
muscle belly into the tarsal canal. We hypothesized that the low lying
muscle belly was the cause of the pain. The muscle likely had little effect
on the nerve at rest but with activity if likely increased in volume with
increased blood flow to the muscle and that was when the patient
experienced her symptoms. It was elected after discussion with the
patient and her mother that she would need surgical intervention for
resolution of her symptoms.
The patient was placed on the operating table in the supine position
with her right leg in the frog leg position. Careful dissection was carried
down, the flexor retinaculum or lanciniate ligament was incised and the
accessory muscle with its tendon were identified just inferior to the flexor
digitorum longus tendon and superior to the neurovascular bundle (Figure
2). The muscle belly could be traced proximally about 2-3 cm proximal to
the medial malleolar tip and distally about 2 cm proximal to the navicular
tuberosity. While the adjoining slips of the accessory tendon were also
excised (Figure 3), ultimately we elected to leave the small slips left
behind after our resection of the muscle belly (Figure 4).
The patient tolerated this procedure well without complications. We
followed her weekly for wound check for one month at which point she
returned to full activity. She reported complete resolution of symptoms
and is asymptomatic at almost one year with a full return to cross country
running.
Tarsal tunnel syndrome is a common pathology known to the foot and
ankle surgeon that often requires surgical intervention for resolution of
symptoms (4). While there are many etiologies, once diagnosed
appropriately, the treatment options are few in number and often gravitate
towards surgery. While there are many possible etiologies for tarsal
tunnel syndrome, Cimino and colleagues reported that 34% were
idiopathic (5). This suggests that the involvement of more advanced
imaging modalities or techniques such as MRI may help the practitioner
reach a definitive diagnosis more quickly (6-9).
Conclusion:
The current case represents a 15 year old runner with TTS secondary
to an accessory FDL muscle. The Patient had complete resolution of
symptoms at almost one year follow up with no complications following
surgical resection.
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