Keywords:
Education and training, Congenital, Education, Plain radiographic studies, MR, CT, Musculoskeletal joint, Musculoskeletal bone, Anatomy
Authors:
R. Wheeler, A. Agahi, R. Berkeley, W. Tilden, J. B. Davies, D. Pefanis, S. G. Cross; London/UK
DOI:
10.26044/essr2019/P-0081
Imaging findings OR Procedure Details
The imaging features of tarsal coalition are varied.
There are broadly three subtypes of coalition; fibrous,
cartilaginous and osseous with progressive osseous changes occurring with increasing age. Tarsal coalitions are classified by the joint that is involved and also the type of coalition.
Non-osseous coalitions (fibrous and cartilaginous) are subtle with abnormal,
irregular joint space narrowing appearing degenerative on radiographs Fig. 1 .
CT features are similar to that of osteoarthritis with joint space narrowing,
sclerosis and subchondral cysts in an involved joint on a background of an otherwise normal foot Fig. 2 , Fig. 5 .
MRI also demonstrates irregular bony interfaces and bone marrow oedema Fig. 3 .
MRI of cartilaginous coalitions demonstrates intermediate T1 signal and intermediate to high T2 signal intensities similar to fluid or cartilage Fig. 4 whilst fibrous coalitions have low T1 and T2 signal intensities Fig. 6 .
Osseous coalitions will demonstrate a bone bridge or continuity of two or more tarsal bones on radiograph,
CT and MRI Fig. 9 Fig. 8 .
The subtalar joint is difficult to interpret on radiograph and numerous signs such as the talar beak Fig. 12 and C-sign Fig. 7 can be helpful indicators of the presence of a coalition.
As mentioned,
the imaging features of tarsal coalition are varied.
The radiologist needs awareness of anatomic variants such as congenital thickening of a normal ligament or thickening of the subtalar capsule which may resemble features of fibrous coalitions,
however,
the absence of bone marrow oedema is a hallmark of such variants.