Tarsal
Coalitions
A tarsal
coalition can be a congenital fibrous, cartilaginous or bony union
between two or more tarsal bones. The reported prevalence varies,
but is said to be around 1% of the general population.
Most
Frequent occurring coalitions:
Medial
talocalcaneal
Calcaneonavicular
Posterior talocalcaneal
Talonavicular
Multiple
fusions of the tarsal bones
Classification
Three
types:
1.
Synostosis: a bony fusion
2.
Synchondrosis: a cartilaginous fusion
3.
Syndesmosis: a fibrous fusion
Or
a combination of any of the above.
They
can be:
1.
Complete
2.
Incomplete
3.
Rudimentary
Xray
Many
coalitions are readily seen on plain radiographs (foot series),
apart from the:
Calcaneonavicular
(seen with a 45° medial oblique view)
Talocalcaneal
coalitions are to difficult to observe from a plain xray
CT
is useful to help diagnose coalitions which cannot be seen on plain
xray.
Secondary
xray signs
Talar
beaking: due to loss of motion at subtalar joints
Narrowing
of the posterior talocalcaneal joint space
Broadening
of the lateral process of the talus
Ball
and socket tibiotalar articulation
Absence
of the middle facets of anterior subtalar joint
Concave
undersurface of the talar neck
|
A
talocalcaneal coalition: note the bar above
A
CT or Harris and Beath View would confirm whether the coalition
is intra or extra articular.
|
For
an excellent example of a calcaneonavicular coalition, click
here
