Tarsal tunnel syndrome (TTS) refers to an
entrapment of the posterior tibial nerve as it descends from the leg to
the foot. This condition was first described by Keck and Lam in
1962. The terminal aspect of the posterior tibial nerve (L4-S1
nerve distribution) supplies the motor function to the muscles of the
foot and the sensory innervation to the bottom of the foot.
Varying degrees of entrapment of this nerve may effect either motor
function, sensory function or both.
There's no universal agreement between clinicians and
surgeons as to why tarsal tunnel syndrome occurs.
Contributing factors that may cause tarsal tunnel syndrome include trauma
to the tarsal canal, varicose veins, bone spurs and soft tissue tumors such as ganglionic
cysts. Other contributing factors include biomechanical instability of
the foot caused by pronation (flattening of the arch) and supination
(high arch). Each of these contributing factors ultimately results
in compression of the posterior tibial nerve. The site where the
nerve is compressed is also called an entrapment.
Testing for tarsal tunnel syndrome with EMG (electromyography) is
often imprecise and misleading. The most reliable method
assessing tarsal tunnel syndrome is percussion of the nerve. This test is
called a Tinel's sign. Two fingers are used to briskly tap the medial
ankle just behind the ankle bone (medial malleolus). An electrical shock
sensation is called a positive Tinel's sign and indicates the location of the
entrapment. The pictures to the left show the location of the posterior
tibial nerve (in green) as it descends the leg behind the inside ankle bone
(medial malleolus). Two common areas of entrapment are found as the
posterior tibial nerve passes beneath the lacinate ligament (in pink) and/or the
upper margin of the abductor hallucis muscle (dotted line). The posterior
tibial nerve passes deep to the muscle at the dotted line. This is the
most common location for entrapment of the posterior tibial nerve.
The posterior tibial nerve splints into three branches at the
level of the medial ankle. A positive Tinel's sign may be
positive for all three branches or just one isolated branch. This
variation in the Tinel's sign depends upon the level of the entrapment and
whether the entrapment is proximal or distal to the triforcation (split) of the
nerve into its' three branches.
An alternative method of nerve conduction testing proposed by Lee
Dellon, MD, of Baltimore MD, uses a device called a
pressure specified sensory device or PSSD. This method incorporates
two point discrimination and pressure testing to quantify sensory loss due to
nerve entrapments. My personal experience with PSSD is that it is
difficult to duplicate findings between providers, and may therefore lead to
misrepresentation in testing data.
Treatment of tarsal tunnel
care for tarsal tunnel syndrome includes injectable cortisone, and most importantly, support of the
arch. Many studies have shown that the pronated or flat foot is
much more prone to tarsal tunnel syndrome.
Arch support has
been shown to decrease strain on many of the structures (nerve and
tendon) that pass from the leg to the foot through the tarsal
Tarsal tunnel syndrome may be treated
surgically with a release of the lacinate ligament and exploration of
the tarsal canal with decompression of the posterior tibial nerve.
Most peripheral nerves are slow to
respond to surgical procedures. The recovery period for patients
undergoing tarsal tunnel surgery may vary from 3 months to 18
months. The outcome of the procedure varies and seems to depend
upon the nature of the entrapment and the damage that the posterior tibial
nerve had sustained prior to surgery.
The pictures below show the steps involved in a tarsal tunnel
release. Image 1 shows the planned incision line running behind the medial
ankle to a level just distal to the upper margin of the abductor hallucis
muscle. Dissection is carried down through the subcutaneous space where in
Image 2 we see the lacinate ligament identified. Image 3 shows the
lacinate ligament released and direct visualization of the posterior tibial
nerve and associated vein and artery. Image 4 shows the posterior tibial
nerve isolated. The nerve and surrounding soft tissue is inspected for any
visual defect including tumors or evidence of trauma. Image 5 shows the
dissection Baxter's nerve. And Image 6 shows the fibrous tissue that
invests the abductor hallucis muscle. The fibrous tissue surrounding the
abductor hallucis extends into the porta pedis. A tarsal tunnel release
requires dissection of this fibrous tissue into the porta pedis to insure a
The calcaneal branch of the posterior
tibial nerve may become selectively entrapped as it descends from the tarsal canal
to supply sensory innervation to the bottom of the heel. This
condition is called a
Baxter's nerve entrapment and is an important differential diagnosis in treating heel pain
and should always be considered a possibility when treating plantar
Other Nerve Entrapments of the Foot
Tarsal tunnel syndrome and
Neuroma are by far and away the two most common peripheral nerve
entrapment found in the foot. There are other areas of the foot
where peripheral nerves may be entrapped by bone or soft
tissue structures, or by external factors such as shoes.
Each of these additional locations of peripheral nerve entrapment
require specialized care with either shoe modifications, injections or
surgical decompression of the nerve at the level of the entrapment.
Entrapment of the deep peroneal nerve is another common
peripheral nerve entrapment of the foot. The deep peroneal nerve is found on the top of the foot (anterior or dorsal foot).
A deep peroneal nerve entrapment is often found in conjunction with a small bump
of bone at the metatarsal cuneiform joint. This bump of bone is
called a saddle bone deformity or met-cuneiform exostosis.
A deep peroneal nerve entrapment is an entrapment of the nerve as it descends over the top of the
bone deformity. Compression of the deep peroneal nerve occurs when
we wear shoes that apply pressure to the saddle bone deformity.
The result is that the deep peroneal nerve is compressed between the
shoe and bone. We'll often see a deep peroneal nerve entrapment in
skiers, those who wear clogs or folks who lace their shoe very tightly.
In each case, the direct pressure from the shoe compresses the nerve
over the bump of bone. A Tinel's sign can be elicited at the top
of the foot with a positive Tinel's sign resulting in electrical shock
sensation to the first and second toes.
Treatment of a deep peroneal nerve entapment can be accomplished
by avoiding the reasons for direct
compression of the deep peroneal nerve. If the compression is due to shoe
laces that are laced too tight, loosen the shoe or skip and eyelet of the shoe.
An easy way to eliminate pressure to the deep peroneal nerve is to use a
modified tongue pad. Split the
tongue pad longitudinally (from heel to toe) and place the adhesive backed pad
on the under side of the tongue of the shoe. Use the pad to create a gap
so that direct pressure to the deep peroneal nerve is decreased. Tongue
pads also work well in clogs and ski boots.
The following images show the steps used to perform a surgical
decompression of the deep peroneal nerve. Image 1 shows the planned incision overlying the 1st metatarsal
cuneiform joint. Image 2 shows dissection through the subcutaneous space.
The extensor retinaculum is underscored by a pair of Metzenbaum scissors.
Image 3 shows the complete release and the deep peroneal nerve. Image 4
shows final closure of the incision. This procedure is performed in a
surgery center of hospital using a local anesthetic. The procedure takes
approximately 45 minutes to complete. Patients are able to walk on the
foot for short distanced immediately following surgery.
The sural nerve, on the outer portion of
the foot may also become entrapped. Symptoms of a sural nerve
entrapment include numbness of the outside of the foot and small toe.
The most common location of sural nerve entrapment is at the lateral
heel, just below the lateral ankle bone (fibula or lateral malleolus) at
the peroneal tubercle. Percussion to this site may elicit a
positive Tinel's sign with distribution of a shock sensation to the
It is not uncommon for the sural nerve to be injured during
surgery. The sural nerve is often in the center of an incision for
flatfoot procedures or ankle fracture repairs. Exposure to the air and
retraction of the nerve during surgery may cause temporary loss of sensation in
the lateral (outside) foot to the 5th toe. Return of normal sensation may
take up to a year following surgery.
Lacinate Ligament - A broad thin band
running from the tibia to the calcaneus that keeps each of the tendon
and neurovascular structures of the ankle in place as they descend from
the leg to the foot. Without the lacinate ligament, these structures
would have a tendency to bowstring or displace as the ankle moved.
Surgical decompression of a peripheral
nerve - a surgical procedure used to release any adhesion, scar tissue
or soft tissue structure that may inhibit the normal function of the
Tarsal tunnel syndrome
occurs on the inside of the ankle, just behind the ankle bone.
Many of the structures that govern the function of the foot pass through
a tunnel in this area referred to as the porta pedis or tarsal canal. These
structures include arteries, veins, nerves and multiple tendons.
As these structures round the inside of the ankle, they are held in
place by a broad ligament known as the lacinate ligament. The
purpose of the lacinate ligament is to prevent these vital structures from
bowstringing or popping out of position with motion such as walking or
The posterior tibial nerve
is the primary nerve that passes through the porta pedis. The
posterior tibial nerve is susceptible to problems as it passes deep to the
lacinate ligament and abductor hallucis muscle. If for any reason pressure is applied to the
posterior tibial nerve, symptoms of tarsal tunnel will occur.
The flexible flatfoot has been discussed
in many papers as a contributing biomechanical factor in cases of
TTS. The flexible flatfoot, or pronated foot, is considered by many to be a poorly
functioning foot due to its' inability to bear load effectively.
As the arch of the foot decreases, pressure within the tarsal canal
increases. Also, as the height of the medial arch decreases, the
structures on the inside of the arch are required to traverse a longer
distance subsequently placing tension on many of the structures of the
medial foot, including the posterior tibial nerve.
Diagnosing tarsal tunnel syndrome can be difficult due to the vague symptoms described by patients. Many patients describe a dull, achy
sensation in the medial ankle and the plantar foot. The pain is
described as vise like and is not relieved by short periods of rest. Pain
does not occur with the first step on the foot, but rather increases with the
duration of time spent on the foot. Tarsal tunnel syndrome occurs most commonly
in one foot but can be found in both feet at the same time.
The Tinel's sign, as previously described, is the most specific
test used to determine the extent and location of the entrapment.
often makes the diagnosis tarsal tunnel syndrome more challenging is the fact that the posterior tibial nerve
trifurcates, or splits into three parts at the level of the lacinate ligament. The
two main branches of the posterior tibial nerve continue on to supply
sensation to the medial (inside) and lateral (outside) aspects of the
bottom the foot, while the third branch travels to the bottom of the heel. Therefore, depending on the level of the
triforcation of the nerve, the symptoms can vary and include only a part
or all of the bottom of the foot. The picture at left shows the
course of the posterior tibial nerve as it descends into the foot
(red). The black dotted circle describes an area of the medial
ankle that is often painful for those with TTS. The blue shaded
area details a focal entrapment of the calcaneal branch of the posterior
tibial nerve. This isolated entrapment of the calcaneal branch is called
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