Definition
Calcaneo-navicular coalition.
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Radiographic Appearance
Oblique view:
calcaneonavicular coalition is most clearly seen on the oblique
view, although visible on both AP and Lateral views, the coalition is
much more difficult to recognize in these projections, lateral view often has signs suggestive of coalition, blunting of subtalar process, elongation of anteior calcaneal
process, narrowing
of posterior subtalar joint, & talar beaking;
MRI findings, perhaps most patients with calcaneonavicular coalition should have
an MRI or CT scan to rule out concomitant talocalcaneal coalition;
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Pathology
Types of tarsal coalition:
calcaneonavicular bar is most common, followed by middle facet of
the talocalcaneal joint;
ossification occurs between 8 and 12 years;
coalition between calcaneus & navicular is usually seen in pts
between 8-12 years of age when
cartilaginous coalition that results from embryologic failure of
tarsal segmentation undergoes ossification;
Clinical Manifestations:
rigid flatfoot with contracture of the peroneal tendons;
symptoms occur because the ossification limits subtalar motion,
which is required for normal walking;
when foot is placed on ground in normal gait, sub-talar joint
rotates externally to compensate for internal rotation
of tibia on femur w/ full extension at knee;
if subtalar motion is restricted, navicular is displaced dorsally on talus
& calcaneus is forced into valgus position with each step;
peroneus longus and brevis tendons adaptively shorten;
when inversion of foot is attempted, the shortened peroneal tendons
contract, pulling the foot into eversion;
this contraction of the tendons also protects the subtalar area when
it is painful;
limited subtalar motion and peroneal tendon shortening contribute to
rigid flatfoot;
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Treatment:
Non Operative Treatment:
symptomatic tarsal coalitions are initially be treated
conservatively;
immobilization followed by orthotic support is often sufficient;
symptomatic lesions often are treated initially by immobilization
for 3 to 6 weeks, followed by an orthosis;Indications for
Surgery:
If symptoms persist, then surgical intervention may be indicated;
calcaneonavicular bars are amenable to resection, w/ most patients
doing well;
talar beaking is not considered absolute contraindication to bar
resection;
pts w/ degenerative arthritis in tarsal joints undergo arthrodesis;
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Images 1
Xray and MRI or Calcaneo-navicualr bar
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