IS Case 274: Tarsal coalition
Imaging Sciences URMC 2009
Publication Date: 2009-07-29
Patient is a 34-year-old male presenting with left foot pain. Patient has had numerous imaging studies of the left foot dating back over ten years for similar presenting complaints of left foot pain, at times aggravated by suspected trauma.
Plain radiographs showed flat foot deformity, a prominent talar "beak" and dorsal osteophytes of the navicular bone. CT of the foot confirmed tarsal coalition with calcaneonavicular bar.
Tarsal coalition involves union of two adjacent bones of the hindfoot and frequently involves the calcaneus. Etiology may be either congenital, representing segmentation abnormality of developing structures, or acquired, representing the sequelae of trauma, infection, or hypertrophic degenerative disease. Patients most often present with pain and possible spastic / symptomatic pes planus, although some are asymptomatic with subclinical limitation of subtalar joint motion. Bilateral tarsal coalition is common.
Talocalcaneal and calcaneonavicular coalition are the most common forms of tarsal coalition, representing at least 90% of cases; talonavicular and cubonavicular are less common. Connections between involved structure may be in the form of extra-articular “bars”, or intra-articular “bridges”. The nature of the bridging tissue is also variable; “syndesmosis” refers to a non-articulating fibrous connection, “synchrondrosis” refers to cartilaginous connection, and “synostosis” refers to complete osseous coalition.
Multiple obliquities of joint spaces present imaging challenges, as does the variety of bridging tissues which may or may not be radio-opaque. Most tarsal coalitions may be diagnosed on plain radiographs in lateral, axial and 45 degree internal oblique projections designed to interrogate the posterior and middle facets and calcaneonavicular space respectively.
Multiplanar CT imaging and MRI are diagnostic modalities of choice. They are useful in clarifying complex anatomy. MR is the preferred imaging modality due to the ability to assess non-ossified coalitions and identification of associated marrow edema.
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