Diagnosis

Fibrous Calcaneonavicular and Talocalcaneal Coalition

Case Discussion

Tarsal coalitions are an abnormal congenital bridging between two or more tarsal bones. They may be osseous, or non-osseous (cartilaginous or fibrous).

The most common type of tarsal coalition is the calcaneonavicular (CN) bar, followed by the middle facet coalition of the talocalcaneal (TC) joint. Onset of symptoms typically coincides with the onset of ossification: CN around 8-12 years and TC around 12-15 years. Patients with coalitions typically present with a painful and rigid flat foot.

MRI findings depend on whether the coalition is osseous, cartilaginous, or fibrous in nature. In osseous coalitions, the marrow signal will continue across the coalition and is similar to anatomic marrow with high signal intensity on T1 weighted images and low signal intensity on T2-weighted fat-suppressed images. Non-osseous coalitions demonstrate narrowing of the affected joint space, cortical irregularity and often stress related bone marrow edema and cyst formation surrounding the coalition. Cartilaginous coalitions appear similar to anatomic fluid and/or cartilage with intermediate signal on T1 and intermediate-to-hyperintense T2 signal. Fibrous coalitions demonstrate lower-signal intensity on all sequences. 

Two tip-offs to the diagnosis of calcaneonavicular and talocalcaneal coalition non-bony are:

  1. Anterior process of the calcaneus is too wide and doesn’t taper;
  2. Isolated subtalar posterior facet and middle facet arthrosis with no explanation in a young patient.

Key Images

Non-osseous calcaneonavicular coalition and talocalcaneal middle facet coalition in a 51-year-old man complaining of Achilles pain for 2 weeks with no inciting event.

A. Sagittal T1 image of the right ankle shows nonosseous (fibrous) calcaneonavicular coalition with irregularity (red arrow).
B. Sagittal STIR image of the right ankle shows posterior talocalcaneal arthropathy with marginal spurring and osteophyte formation (yellow arrow). There is also non-osseous calcaneonavicular coalition with irregularity at the anterior process articulation (red arrow).
C. Sagittal STIR image of the right ankle shows non-osseous middle facet coalition of the talocalcaneal joint (red arrow) with surrounding reactive/stress related osteoedema and cyst formation (yellow arrows)
D. Coronal T2 SPAIR image of the right ankle shows non-osseous talocalcaneal middle facet coalition with mild surrounding marrow edema (green arrow).

References

  1. Crim JR, Kjeldsberg KM. Radiographic diagnosis of tarsal coalition. American Journal of Roentgenology 2004; 182:323-328
  2. Newman JS, Newberg AH. Congenital tarsal coalition: Multimodality evaluation with emphasis on CT and MR imaging. RadioGraphics 2000; 20:321-332