Posterior tibial tendon
dysfunction (PTTD), also known as posterior tibial tendonitis, is one of
the leading causes of acquired flatfoot in adults. The
onset of PTTD may be slow or abrupt. An abrupt
onset is typically linked to some
form of trauma, whether it be simple (stepping down off a curb or
ladder) or severe (falling from a
height or automobile accident). PTTD is seldom seen in children and
increases in frequency with age.
The characteristic finding
of PTTD include;
Loss of
medial arch height
Edema (swelling) of the medial ankle
Loss of the ability to resist force to abduct or push the foot out from
the midline of the body
Pain on
the medial ankle with weight bearing
Inability to raise up on the toes without pain
Too many toes sign
Lateral subtalar joint (outside of the ankle) pain
A common test to evaluate
PTTD is the 'too many toes sign'. The 'too many toes sign' is a test
used to measure abduction (deviation away from the midline of the body) of
the forefoot. With damage to the posterior tibial tendon, the
forefoot will abduct or move out in relationship to the rest of the
foot. In cases of PTTD, when the foot is viewed from behind, the
toes appear as 'too many' on the outside of the foot due to abduction of
the forefoot.
In advanced cases of PTTD,
in addition to the pain of the tendon itself, pain will also be noted in the
subtalar joint and sinus tarsi. The sinus tarsi refers to a small tunnel or divot
on the outside of the subtalar joint that can actually be felt. This tunnel
is the entry to the subtalar joint. The subtalar joint is the
joint that controls the side to side motion of the foot, motion that
would occur with uneven surfaces or sloped hills. As PTTD
progresses and the ability of the posterior tibial tendon to support the
arch becomes diminished, the arch will collapse overloading the subtalar
joint. As a result, there is increased pressure applied to the
joint surfaces of the lateral aspect of the subtalar joint, resulting in
pain.
There have
been many proposed explanations for PTTD over the years since this
condition was first described by Kulkowski in 1936. The most
contemporary explanation refers to an area of hypovascularity (limited
blood flow) in the tendon just below the ankle. Tendon derives
most of its' nutritional support from synovial fluid produced by the
outer lining of the tendon. Extremely small blood vessels also
permeate the tendon sheath to reach tendon. This makes all tendon
notoriously slow to heal. In the case of the posterior tibial
tendon, this problem is exacerbated by a distinct area of poor blood
flow (hypovascularity). This area is located in the posterior
tibial tendon just below or distal to the inside ankle bone (medial
malleolus).
Tendon is also most susceptible
to fatigue and failure at an area where the tendon changes
direction. As the posterior tibial tendon descends the leg and
comes to the inside of the ankle, the tendon follows a well defined
groove in the back of the tibia (bone of the inside of the ankle).
The tendon then takes a dramatic turn towards the arch of the
foot. If the tendon is put into a situation where significant load
is applied to the foot, the tendon responds by pulling up as the load of
the body (in addition to gravity) pushes down. At the location
where the tendon changes course, the tibia acts as a wedge and may apply
enough force to actually damage or rupture the tendon.
Equinus is also a
contributing factor to PTTD. Equinus is the term used to describe
the ability or lack of ability to dorsiflex the foot at the ankle (move
the toes towards the shin). Equinus is usually due to tightness in the
calf muscle, also known as the gastroc-soleal complex (a combination of
the gastrocnemius and soleus muscles). Equinus may also be due to
a bony block in the front of the ankle. The presence of equinus
forces the posterior tibial tendon to accept additional load during
gait.
Additional contributing
factor to the onset of PTTD may include obesity, hypertension, diabetes,
peripheral neuropathy, smoking or arthritis.
PTTD is a progressive condition, meaning to say, that if
left untreated, PTTD will become worse. The progression of PTTD
begins with tendonitis and progresses to partial tears of the tendon and
finally a complete tendon
rupture. Several classifications have been developed to describe
PTTD. The classification as described by Johnson and Strom is most
commonly used today.
Stage I
Tendon status - attenuated
(lengthened) with tendonitis but no rupture
Clinical findings - palpable pain in the medial
arch. Foot is supple, flexible with too many toes sign
X-ray/MRI - mild to moderate tenosynovitis on MRI, no X-ray changes
Stage II
Tendon status - attenuated with
possible partial or complete rupture
Clinical findings - pain in arch. Unable to raise
on toes. Too many toes sign present
X-ray/MRI - notes tear in tendon. X-ray noting abduction of forefoot, collapse of
talo-navicular joint
Stage III
Tendon status - severe
degeneration with likely rupture
Clinical findings - rigid flatfoot with
inability to raise up on toes
X-ray/MRI - shows tear in tendon. X-ray noting abduction of forefoot,
collapse of talo-navicular joint
An additional consideration in planning for PTTD
surgery and diagnosing PTTD pain is the presence of an accessory bone called an
os tibiale externum. The os tibiale externum, or what is frequently called
and accessory navicular, is a small bone that resides
within
the body of the PT tendon. The os tibiale externum functions to facilitate
motion around the navicular. The os tibiale externum functions much in the
same way that the knee cap (patella) works to guide the quadraceps tendon around
the knee as it bends. The os tibiale externum can undergo degenerative
wear called chondromalacia. The os tibiale externum also can fracture.
Therefore, the os tibiale externum must also be considered when diagnosing PT
tendon pain and planning surgery for PTTD. Excision of the os tibiale
externum during PT tendon correction is common. This procedure is called a
modified
Kidner procedure.
Treatment of posterior
tibial tendon dysfunction and posterior tibial tendonitis
Treatment
for PTTD is dependant upon the clinical stage and the health status of
the patient. It is important to recognize that PTTD is a
mechanical problem that requires a mechanical solution. This means
that treating PTTD with medication alone is fraught with failure.
Prompt introduction of some form of mechanical support is imperative.
PTTD is a condition that
increases in frequency with age and the prevalence of poor health
indicators such as diabetes and obesity. As a result, many patients
with PTTD are poor surgical candidates for correction of PTTD.
Prosthetics such as an ankle foot orthotic (AFO), Arizona
Brace or other bracing may be
very helpful to control the symptoms of PTTD.
Surgical procedures which
focus on primary repair of the posterior tibial tendon have been very unsuccessful.
This is due to the fact that tendon heals slowly following injury and
cannot be relied upon as a sole solution for PTTD cases. Surgical
success is usually achieved by stabilization of the rearfoot (subtalar
joint) which significantly reduces the work performed by the posterior
tibial tendon.
Stage I may respond to rest,
such as a walking cast. Pain and inflammation may be controlled
with anti-inflammatory medications. It is important to be sure
that Stage I patients realize that the use of shoes with additional arch
support and heel elevation, for the rest of their lives, is
imperative. Arch support, whether built into the shoe or added as
an orthotic,
helps support the posterior tibial tendon and decrease its' work.
Elevation of the heel, reduces equinus, one of the most significant
contributing factors to PTTD. If Stage I patients return to low heels
without arch support, PTTD will recur.
Stage II patients, or Stage
I patients that do not respond to rest and support, require surgical
correction to stabilize the subtalar joint prior to further damage to
the
posterior tibial tendon. Subtalar arthroeresis is a
procedure used to stabilize the subtalar joint. Arthroeresis is a
term that means the motion of the joint is blocked without fusion.
Subtalar arthroeresis can only be used in cases of Stage I or II where mild to moderate
deformation of the arch has occurred and MRI findings show the tendon to
be only partially ruptured. Subtalar arthroeresis is typically performed in
conjunction with an Achilles tendon lengthening procedure or endoscopic
gastrocnemius recession to correct
equinus. These procedures require casting for a period of weeks
following the procedure.
Stage III patients require
stabilization of the rearfoot with procedures that fuse the primary
joints of the arch and foot. These procedures are salvage
procedures and require prolonged casting and disability following
surgery. A common procedure for Stage III is called triple arthrodesis
which is a technique used to fuse the subtalar joint, the talo-navicular
joint and the calcaneal cuboid joint (picture at left).
