A flatfoot is a subjective
term that describes a foot with a decreased or absent arch. In the majority of flatfoot cases,
the primary problem is
an inherited tendency to have no arch. There's a number of
biomechanical and developmental reasons why this occurs, but in most cases, the
condition is benign and will never really have significant impact on that
patient over the course of their lives. Occasionally though we see specific
types of flatfeet that are real trouble makers. One of those conditions is
called a tarsal coalition.
There are a number of specific congenital (from birth)
deformities that we see that result in flatfeet. The most common of
these conditions is called a tarsal coalition. Tarsal refers to the bones of
the rear
portion of the foot and coalition refers to a bridge. What
happens in cases of tarsal coalition is that a coalition or bridge of
bone forms between two bones, limiting the range of motion of the joints
of the foot. The end result is a rigid, painful flatfoot. The initial
diagnosis of a tarsal coalition can be difficult to make. The challenge lies in the fact
that the symptoms of a tarsal coalition don't become evident until the late teens. Part
of the diagnostic challenge lies in the fact that the bridge of bone in
young children is made of fibrous material and cannot be seen on
x-ray. As the patient matures, the fibrous tarsal coalition begins to ossify
(turn to bone). As this ossification progresses, the foot becomes
markedly rigid and painful.
Tarsal coalitions can form at several different locations in the
foot. The most common tarsal coalition forms between the calcaneus and navicular
(shown in the x-rays on this page). The second most common tarsal coalition forms
in the subtalar joint and is subsequently called a talo-calcaneal coalition.
The third most common tarsal coalition forms at the talo-navicular joint. The
etiology of tarsal coalitions is unclear, but most clinicians assume that the
coalition forms as the result of an incomplete separation of the developing
bones while in utero.
Treatment of tarsal coalitions
The initial diagnosis of a tarsal coalition is based upon clinical
findings of a fixed, rigid foot. Although X-rays don't show any specific
location of the early fibrous tarsal coalition, they do show early changes in the bone
that are secondary to the limited range of motion. These changes include
dorsal spurring of the talo-navicular joint and a halo of increased bone density
surrounding the subtalar joint. This density is one of the radiographic
signs of the early onset of osteoarthritis in the subtalar joint. A
definitive diagnosis of a tarsal coalition can be made with an MRI.
Tarsal coalitions can be managed conservatively from the onset of
symptoms until the late teens. Prescription
orthotics and
ankle bracing can
help to relieve a bit of pain but won't help to delay formation of the
tarsal coalition. The usual and customary treatment of tarsal coalitions is surgical
resection of the coalition with or without fusion of the affected joint space.
Generally speaking, calcaneo-navicular (C-N) coalition resections are quite
successful. Resection of a C-N coalition would typically be performed with
an interposition of soft tissue or muscle to inhibit regrowth of the coalition.
Talo-calcaneo coalition resections are not quite as successful as an isolated
procedure and are often performed in conjunction with a fusion of the joint
between the talus and calcaneus (subtalar joint). The determination of
whether fusion is indicated is often dictated by the amount of degenerative
change of the subtalar joint seen during the surgery.
When should a tarsal coalition be corrected? From one
perspective, the earlier the better is true. If a tarsal coalition is
allowed to remain unaddressed, the foot will become rigid and progressively
undergo adaptive change during the second and third decades of the patient's
life. These changes will become fixed and can only be repaired with a
salvage fusion procedure called a triple arthrodesis. But it's also
important to allow for skeletal maturity. Most children reach skeletal
maturity between the ages of 16 and 19 years old. Therefore, the best time
for correction of a tarsal coalition is after the child reaches skeletal
maturity.
