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Posted by firstname.lastname@example.org, 11/25/03 at 8:52:56 AM.
What is it?
Tarsal coalition is an abnormal union between tarsal
bones. The union can be osseous, fibrous, or
cartilaginous. This causes abnormal articulation within the mid
and hind foot which produces accelerated degenerative
osteoarthritis of the hindfoot and midfoot. The frequency of
tarsal coalition is approximately 1% and occurs in males more than
females. It is bilateral in 25% of cases. These numbers are
generally accepted and based on symptomatic groups. Recent
post-mortem exams have been performed to attempt to discover the "true"
incidence of tarsal coalition. Solomon, et al, report an
incidence of non-osseous coalitions as high as 12.7%!
How does it happen?
Etiologies can be congenital or acquired. Congenital tarsal
coalition is the most common and results from a failure of normal
tarsal segmentation. Congenital tarsal coalition classically
presents in the 2nd or 3rd decade of life as a painful flatfoot
deformity also known as "peroneal spastic flatfoot." Acquired
tarsal coalition can follow infection, trauma, surgery or inflammatory
Which bones are involved?
The calcaneus, talus, navicular and cuboid are commonly
affected. A frequent written boards question asks: Which is
the most common tarsal coalition? The answer depends on
who you ask. Resnick lists them in this order with the most
- 1. Calcaneo-navicular
- 2. Talo-calcaneal, middle facet
- 3. Talo-navicular
- 4. Calcaneo-cuboid
MSK Requisites lists them this way:
- 1. Talo-calcaneal, middle facet
- 2. Calcaneo-navicular
- 3. Talo-navicular
- 4. Calcaneo-cuboid
In general, calcaneo-navicular and talo-calcaneal are far more common than talo-navicular or calcaneo-cuboid.
What are the imaging findings?
Plain films classically demonstrate a number of bony abnormalities. These include:
1. The ant-eater sign: elongation of the
anterior calcaneal process on the lateral view of the foot. This
represents the bony bridging of calcaneo-navicular coalition.
And you thought you would never see another plain film tomogram again (circa 5/3/72):
2. Talar beaking: dorsal beaking of the
talar head may indicate underlying tarsal coalition, most commonly
talo-calcaneal. However, it can also indicate Rheumatoid
arthritis, DISH and acromegaly.
3. Ball-and-socket mortise joint: spherical remodeling
of the talar dome. This occurs when the mortise joint gradually
takes responsibility for abduction and adduction that is lost when the
subtalar joint is fused in talo-calcaneal coalition.
4. Subchondral sclerosis, cortical irregularity and joint
space narrowing: These are all indirect findings of fibrous or
Link to "Absent middle facet" AJR article on coalition, 2003.
What are the imaging strategies?
Calcaneo-navicular: A special 45 degree medial oblique
projection will generally provide a clear view of the ant-eater
sign in a complete osseous coalition. It will also show joint
space narrowing, irregularity and sclerosis in a cartilaginous or
Cartilaginous or fibrous coalition:
Talo-calcaneal: The Harris-Beath view, a penetrated posterior
oblique image (aka, the penetrated axial view), with the patient
standing on the cassette and the beam angled between 35 and 45 degrees
to the cassette, is designed to reveal coalition between the
sustentaculum and the talus at the middle facet.
CT is usually definitive. It will clearly show any osseous
coalition. It will also demonstrate the joint space narrowing,
sclerosis and irregularity of cartilaginous or fibrous coalition.
Bone scan is sensitive but less specfic. It will show uptake
in multiple elements of the hindfoot and midfoot because of
altered mechanics and weight-bearing.
What difference does it make? What can we do about it?
Most patients with tarsal coalition have a fixed hindfoot
valgus of varying severity and some loss of the normal longitudnal
arch. Peroneal muscle tightness develops and the patient complains
of vague dorsolateral foot pain centered on the sinus tarsi, difficulty
walking on uneven surfaces, foot fatigue and occasionally a painful
There are three common therapeutic options for calcaneo-navicular coalition.
- Interval casting: The least invasive approach
consists of 4 - 6 week periods of casting to relieve symptoms without
surgical intervention. If this doesn't work then an operation may
- Resection of the calcaneo-navicular bar: Resection is
followed by fat or muscle inerposition to prevent re-unification.
Various degrees of success have been reported. Approximately 70%
report complete or near complete resolution of symptoms and do not need
further intervention (Campbell's Operative Orthopedics). But
there is one more option for the other 30%.
- Arthrodesis: Standard triple arthrodesis, including
subtalar, talo-navicular and calcaneo-cuboid joints, is performed as
the definitive therapy.
And the therapies for talo-calcaneal coalition:
- Interval casting can also relieve symptoms for this type of coalition.
- Triple arthrodesis.
Campbell's operative orthopedics. Canale ST, Campbell WC, eds. 10th ed. Mosby, 2002.
Musculoskeletal imaging: the requisites. Manaster BJ, et al. 2nd ed. Mosby, 2002.
Diagnosis of bone and joint disorders. Resnick, D, 4th ed, WB Saunders, 2002.
Liu PT et al; Absent middle facet sign: a sign on unenhanced radiography of subtalar joint coalition. AJR;181(6):1565-1572.
Solomon LB et al; A dissection and computer tomograph study of tarsal coalitions in 100 cadaver feet. J Orthop Res. 2003 Mar;21(2):352-8.
Many images courtesy of Dr. Melvin Figley's University of Washington teaching file.