Age / Sex : 59 / F

Chief complaint: right plantar tingling sensation for 2 months
                          

Tarsal tunnel syndrome due to talocalcaneal coalition

Discussion

Findings:

Right ankle lateral radiograph: C-sign (incomplete)

MR: Narrowing and irregularity of talocalcaneal joint

Protrusion of sustentaculum tali

Adjacent soft tissue edema (tarsal sinus, flexor retinaculum, around tibial nerve)

Differential Diagnosis:

C sign on lateral radiograph

DDx: pes planus without coalition

Diagnosis: talocalcaneal coalition inducing tibial nerve compression

Discussion:

 1) Tarsal coalition

Coalition can be osseous, cartilaginous or fibrous union and complete or partial union

between two or more bones in midfoot and hindfoot

Developmental fusion rather than acquired

calcaneonavicular (53%), talocalcaneal (37%)

Acquired coaliation is associated with arthritis, infection, trauma, and neoplasia.

Tarsal coalition is the most common cause of peroneal spastic flat foot.

Osseous; bony bar bridges

Nonosseous; joint space narrowing, cartilaginous or fibrous coalitions

Subchondral cyst or bone marrow edema

Combined findings

tarsal tunnel syndrome, ganglion, peroenal tendon spasticity, pes planus, secondary osteoarthritis

2) Talocalcaneal coalition

  Anterior, middle and posterior facet can be involved.

 Usually associated with overgrowth of the medial aspect of the talus an abnormal morphology of the sustentaculum tali (middle facet)

  Plain radiograph (best on lateral)

C-sign -- posterior continuity of the talus and sustentaculum tali

Talar beak sign -- prominent beak at the anterior aspect of the talus

 Coronal image on CT or MR scans is most important

References:

1. Stoller DW, Ferkel RD. The ankle and foot. In stoller DW ed. Magnetic resonance imagings in orthopedics and sports medicine, 3rd ed. Philadelphia: Lippincott Williams and Wilkins, 2007:733-1050

2. 최윤선, 전동진. 발과 발목. In 강흥식, 홍성환, 강창호 ed. 근골격 영상의학, 1st ed. 서울: 범문 에듀케이션, 2013:745-798