Between December 1997 and December 1999, three elite athletes (four
ankles) were referred to the senior author (M.S.) with disabling symptoms of
pain in the posterior aspect of the ankle related to activity. The mean age at
the time of presentation was 21.6 years (fourteen, twenty, and thirty-one
years), and the mean duration of symptoms before tertiary referral was 16.3
months (nine, sixteen, and twenty-four months). The average duration of
follow-up was thirty-seven months (twenty-four, thirty-nine, and forty-eight
months). All patients had a positive posterior impingement test on
examination. All three patients had been treated prior to referral with
prolonged courses of physiotherapy, anti-inflammatory medications, orthotic
inserts, and cortisone injections.
In all patients, the initial magnetic resonance imaging study as read by
nonmusculoskeletal radiologists did not identify the anomalous muscles.
Further investigation at our institution by a dedicated musculoskeletal
radiologist subsequently recorded the presence of anomalous muscles. In all
three patients, abnormal fluid collection was noted in the tendon sheath
directly associated with the anomalous muscle
(Fig. 1). This area of fluid
was injected with local anesthetic and steroid under ultrasound control, and
the temporary relief of symptoms suggested that these muscles were indeed the
source of the
symptoms2.
All operations were carried out with the patient under general anesthesia
and lying prone, with the leg exsanguinated and under tourniquet control. The
surgical approach chosen depended on magnetic resonance imaging findings.
Postoperatively, a soft compression bandage was applied, the patient was
allowed to bear full weight immediately, and, after suture removal, a
graduated return to full sports activities was encouraged. The average time to
return to full sports activities was 7.7 months (five, six, and twelve
months). Our patients were informed that data concerning the cases would be
submitted for publication.
Cases 1 and 2. A fourteen-year-old top-level male
rugby player presented with a twenty-four-month history of pain in both ankles
associated with training. The patient reported that he had no previous ankle
trauma.
Magnetic resonance imaging on the left side revealed marked fluid
distension of the flexor hallucis longus tendon sheath above the fibro-osseous
tunnel without adjacent ankle or subtalar joint effusions. In both ankles, an
accessory muscle was noted to be arising at the posterolateral aspect of the
flexor hallucis longus muscle, coursing along the lateral margin of the flexor
hallucis longus tendon within the tendon sheath, and inserting onto the distal
aspect of the medial margin of the sustentaculum tali. The anomalous muscle
belly was noted to extend distally to the level of the ankle joint
(Fig. 2). This muscle was
reported to be consistent with a peroneocalcaneus
internus9.
At the operation, excision of the peroneocalcaneus internus muscle was
performed bilaterally through posterolateral incisions preserving the sural
nerve. The deep fascia was released, and the anomalous muscle was identified
within the flexor hallucis longus tendon sheath, adjacent to but separate from
the flexor hallucis longus tendon. Its origin was traced to the lower aspect
of the fibula and the insertion was into the undersurface of the sustentaculum
tali. The muscles had caused a moderate mass effect in the flexor hallucis
longus tendon sheath at the posterior aspect of the ankle and subtalar
joints.
The patient had no postoperative complications and began a gradual
rehabilitation program after the sutures were removed. By six months the
patient had no complaints of stiffness, swelling, or pain with training and
returned to full sports activities.
Case 3. A thirty-one-year-old professional male basketball
player presented with a sixteen-month history of pain in the right ankle
associated with training. On evaluation at our center, it was determined that
the symptoms and findings on examination were not consistent with tarsal
tunnel syndrome16.
A magnetic resonance imaging examination identified a lesion on the medial
aspect of the talar dome, and the patient underwent arthroscopy and curettage
of the lesion. The patient subsequently had improvement, but he was unable to
resume elite-level play because of pain in the posterior and posteromedial
aspect of the ankle. A repeat magnetic resonance imaging scan showed that the
talar dome lesion was quiescent, and an anomalous muscle was identified.
On magnetic resonance imaging, a prominent accessory flexor muscle was
identified posterior to the tibial neurovascular structures. It extended
distally to insert on the quadratus plantae muscle. Fluid was noted in the
midfoot region of the flexor digitorum longus tendon sheath. This muscle was
reported to be consistent with the long accessory to the quadratus
plantae9.
At the operation, a medial incision was performed directly over the tarsal
tunnel, and the calcaneal branches of the tibial nerve were identified and
protected. The deep fascia was released, and the fleshy fibers of the
anomalous muscle were identified in the tarsal tunnel. The muscle was adherent
to the neurovascular bundle and was carefully dissected away before being
excised. The origin was from the gastrocnemius-soleus complex, and the
insertion was into the quadratus plantae. The muscle belly caused a moderate
mass effect at the posteromedial part of the ankle.
The patient had no postoperative complications and began a basketball
training program at two months. For nonmedical reasons, the patient did not
fully return to play until twelve months after the operation, but he was able
to play with slight pain on activity that did not interfere with his
performance.
Case 4. A twenty-year-old Olympic-level female hurdler
experienced a severe (grade-III) sprain of the right ankle and underwent
standard treatment and rehabilitation for such a sprain. After nine months,
the patient had continued pain in the posterolateral aspect of the ankle
without instability and presented to our tertiary center.
On magnetic resonance imaging, a muscle was identified with its
midsubstance extending distal to the level of the ankle and subtalar joints
(Fig. 3-A) and inserting onto
the lateral aspect of the calcaneus. The muscle was medial to the peroneus
brevis and longus and adjacent to the flexor hallucis longus, consistent with
the previously reported peroneus
quartus9.
At the operation, a posterolateral approach was made, preserving the sural
nerve. The peroneus quartus was identified by its origin on the fibula
separate from the peroneal muscles. The muscle belly extended distal to the
level of the ankle joint and inserted onto the peroneal tubercle of the
calcaneus (Fig. 3-B). It was
completely excised.
The patient had no postoperative complications and began a gradual
rehabilitation program after the sutures were removed. By five months, the
patient had no symptoms and had returned to international competition.
Five different anomalous muscles around the ankle have been
described9. The
peroneus quartus is located posterolaterally, while the peroneocalcaneus
internus, long accessory to the long flexors or quadratus plantae,
tibiocalcaneus internus, and accessory soleus are located
posteromedially9.
The peroneus quartus muscle has been described by many names, including the
peroneus accessorius, peroneus calcaneus externus, and peroneus
externus9-12,14.
It most commonly arises from the peroneal brevis muscle and inserts into the
retrotrochlear eminence of the
calcaneus10. Other
variations include an origin on the peroneus longus or the fibula and
insertion onto the cuboid or the dorsal aspect of the base of the fifth
metatarsal9,10.
The prevalence of the muscle in normal ankles has been reported to range
between 7% and
22%9,10.
Isolated case reports have implicated this muscle as a cause of chronic ankle
pain following an ankle sprain; however, these reports predated magnetic
resonance imaging and the recognition of posterior impingement of the ankle as
a clinical
entity12,14,17.
It has been surmised that the symptomatic peroneus quartus caused a
"checkrein effect" on the peroneal tendons, thus only
necessitating a resection of the
tendon12,14.
Longitudinal split tears of the peroneus brevis have been found in 18% to 50%
of cadaver specimens with a peroneus
quartus10,11,
and our surgical dissection revealed that the muscle belly exerted a mass
effect on the adjacent tissues and ankle joint. Therefore, we resected the
anomalous structure completely.
The peroneocalcaneus internus muscle originates from the lower half of the
medial surface of the fibula, and its tendon travels distally and anteriorly,
coursing through the same compartment as the flexor hallucis
longus9. It inserts
onto the undersurface of the sustentaculum tali. It is bordered anteriorly by
the interosseous membrane, the tibiotalar joint, and the soleus; laterally by
the peroneal muscles; and medially by the flexor hallucis longus. The muscle
has been identified by magnetic resonance imaging in 1% of asymptomatic
volunteers18.
Testut, in 1884, was the first, as far as we know, to describe the flexor
digitorum accessorius longus, which has also been reported as the long
accessory of the long flexors, quadratus plantae, accessorius of Turner,
second accessorius of Humphrey, or long accessory flexor
muscle9,11.
It arises from varying portions of the tibia, fibula, and interosseous
membrane and may have a single or a double
head19. It courses
deep to or crosses the neurovascular bundle and inserts into the flexor
digitorum longus at various levels before the knot of
Henry20 or onto the
lateral head of the quadratus plantae
muscle21. Previous
studies involving anatomical dissection have shown that its prevalence is
between 1% and
8%21. It is the
most common muscle anomaly on the medial side of the ankle and second most
common to the peroneus quartus in the
ankle22. Because of
its proximity to the neurovascular bundle and its often fleshy consistency at
this level, it has been implicated as a cause for tarsal tunnel
syndrome13,15,19,23,24.
In one study, surgical release of the tarsal tunnel and excision of this
muscle resulted in a reduction of the symptoms in four of six patients,
although the results were not as good as those after surgery performed for
other space-occupying
lesions13. In
contrast, a review of the cases of seven patients with tarsal tunnel syndrome
secondary to anomalous muscles described the complete resolution of symptoms
in all of the patients at twelve months after excision of the anomalous
muscle15.
Because these anomalous muscles are relatively common in the general
population, it is unclear why the individuals in this series became
symptomatic; however, it may have been due to their high level of activity.
Clinically and at the time of surgical exploration, the symptoms appeared to
be the result of direct soft-tissue impingement from the anomalous muscle
bellies.
Hamilton et al. found a low-lying distal insertion of the muscle fibers of
the flexor hallucis longus in seven ballet dancers with posterior impingement
and speculated that this created a mass effect leading to tenosynovitis of the
tendon2. Ischemia
has also been suggested as the source of pain for the accessory
soleus25, but the
muscle bellies in the four ankles described in the present study were small
and not tightly invested in a fascial
sheath26. Tearing
and inflammation in the muscle
itself25 may cause
symptoms; however, this was not demonstrated on magnetic resonance imaging or
intraoperatively in our patients.
One important finding highlighted by this case report pertains to the fact
that the initial magnetic resonance imaging scans performed by nonspecialized
radiologists did not detect these anomalous muscles even though they were
subsequently identified on the original magnetic resonance imaging scan by a
musculoskeletal radiologist. The use of magnetic resonance imaging for the
diagnosis of abnormalities in the posterior aspect of the ankle is well
established3,5,27,
and such scans can be useful in differentiating accessory muscles from other
soft-tissue
masses20. Magnetic
resonance imaging was also helpful for determining the surgical approach and
for identifying the accessory muscles at the time of surgery.
Hamilton et al.2
and Hedrick and
McBryde1 recommended
a medial approach to release the tendon sheath of the flexor hallucis longus;
however, we have found that complete release can be attained through a
posterolateral approach with prone positioning of the patient and the use of
loupe magnification. An advantage of this approach is the avoidance of
postoperative scarring around the tibial nerve, which is particularly
important in elite athletes.
The cases described in the present report demonstrate that, although rare,
anomalous muscles about the ankle should be considered as a potential cause of
pain in the posterior aspect of the ankle. ?