Review of the role of bone-SPECT/CT in tarsal coalitions

Tarsal coalition (TC) is a congenital abnormal connection (fibrous, cartilaginous, or osseous) between two or more bones in the hind and midfoot, mostly consisting of calcaneonavicular or talocalcaneal coalition, and is often asymptomatic. However, TCs may result in foot motion limitation and pain with or without flatfoot (pes planus), arising in adolescents and young adults. Appropriate imaging is needed to pinpoint foot pain in the (suspected) TC, starting with plain radiographs. Still, normal radiographs do not exclude TCs. Computed tomography (CT) and MRI are frequently used advanced imaging techniques. CT alone has known limited sensitivity in cartilaginous and fibrous TCs and correlation between CT abnormalities and pain may be challenging, as solely anatomical changes in TCs are often asymptomatic. MRI can depict soft tissue abnormalities in TC with high accuracy. Nonetheless, after the implantation of metallic osteosynthesis material, MRI is often limited due to image distortion, signal loss, and misregistration. Bone scintigraphy with [99mTc]Tc-diphosphonate single photon emission computed tomography/CT (bone-SPECT/CT) is a known sensitive tool to detect osteoblastic bone pathology. However, the literature concerning bone-SPECT/CT in TC patients is limited. This article reviews bone-SPECT/CT patterns in TCs, how it complements other imaging techniques and their relation to clinical complaints. Bone-SPECT/CT excels in accurate bone pathology characterization in TC, confidently excluding synchronous lesions elsewhere, and offering optimal insight into osseous structures and 3D-localization of bone metabolism for surgery planning. Furthermore, even with implanted osteosynthesis material, bone-SPECT/CT can pinpoint the culprit pain generator, where MRI is either contra-indicated or considerably hampered.