Age / Sex : 19 / M

Age / Sex: 19 / M

Chief complaint: Pain
of the right ankle joint

Talocalcaneal coalition

Discussion

Findings:

1) Plain radiography

- Lateral
radiograph of the right ankle joint shows narrowing of the middle subtalar
joint.

2) CT

- Axial CT image
shows narrowing and reactive hypertrophic changes of the middle subtalar joint.

- Coronal
reformatted CT image shows abnormal downward sloping of the sustentaculum tali.

Differential Diagnosis: None

Diagnosis: Talocalcaneal coalition

Discussion:

Talocalcaneal fusion most commonly involves the
middle facet at the level of the sustentaculum tali. Cartilaginous, fibrous, or bony bridges
may be identified. Cartilaginous coalitions are usually associated with marked
narrowing of the joint, whereas fibrous coalitions, which typically involve the
most posterior part of the sustentaculum tali, may lead to only subtle
diminution in interosseous space.

A number of secondary radiographic signs of talocalcaneal coalition have
been described, including a talar beak, narrowing of the posterior subtalar
joint, rounding of the lateral talar process, concave undersurface of the talar
neck and asymmetry of the talocalcaneonavicular joint, failure of visualization
of the “middle” subtalar joint, continuous C-sign, and ball-and-socket ankle
joint.

Talocalcaneal
coalitions are best depicted on coronal CT scans. In osseous coalition, a bony
bar bridges the middle facet of the subtalar joint. Involvement of the
posterior and anterior facets is variable, and abnormal narrowing or even
fusion of the posterior facet may be observed in advanced cases. In nonosseous
coalition, the middle facet of the subtalar joint may be narrowed with reactive
cystic and hypertrophic changes of the underlying bone.

References:

1. Resnick D. Diagnosis of bone and joint disorders. Saunders, 2002, 4^th ed. p4593-4599

2. Newman JS and Newberg AH. Congenital
tarsal coalition: multimodality evaluation with emphasis on CT and MR imaging.
Radiographics 2000;20:321-332