Sonographic Features of a Medial Subtalar Coalition and Implications for Diagnosis and Treatment.

Abstract

A 21-yr-old man presented with progressive right medial foot pain. Symptoms began 1 yr prior and were described as aching, stiffness, worse after prolonged standing, but improved with rest. There was no associated weakness, numbness, or inciting mechanical trauma. Physical examination of the right foot showed mildly reduced eversion and inversion and moderately reduced pronation and supination. The medial foot was tender to palpation without evidence of swelling. Strength and sensation were intact along the L2-S1 distributions. Foot radiographs suggested a subtalar coalition (Fig. 1A). This was confirmed on computerized tomography (Figs. 1B, C). Ultrasound was used to visualize the right subtalar joint (Fig. 2A). A contralateral comparison was also obtained (Fig. 2B). Kenalog (40 mg/ml) was injected with excellent arthrogram effect via a sonographically guided, out of plane, posterior to anterior walk down technique. One-month after injection, the patient reported 80% relief in pain.FIGURE 1: A–C, Lateral ankle radiograph, computerized tomography, and 3D reconstruction of the right subtalar joint. Relevant bony structures are identified and include the talus (abbreviated as “tal”), calcaneus (“cal”), and tibia (“tib”). Lateral ankle radiograph demonstrates subtle irregularity along the middle subtalar joint with small, hypertrophic bone formation. Computerized tomography and 3D reconstruction of the right subtalar joint demonstrate evidence of a fibrous or cartilaginous coalition associated with mild to moderate degenerative subchondral cystic change and sclerosis.FIGURE 2: A, Ultrasound image in the coronal plane with a GE Logiq E device using a linear (13–5 MHz) array transducer revealed a reduced right medial subtalar joint with an irregular, pointed joint line appearance consistent with a subtalar coalition. B, A normal contralateral comparison of the left talocalcaneal joint was obtained for comparison.The subtalar joint normally permits foot pronation and supination. Due to closed chain kinetics, the leg normally internally rotates when the foot is in stance and externally rotates during toe-off. In subtalar coalition, this torque converter movement is lost because of joint rigidity, increasing stress on neighboring structures.1,2 Patients may present with rigid pes planus and medial foot pain during periods of increased physical activity. Plain radiographs are first line for evaluation, but direct visualization is difficult because of the complex anatomy of the joint.3,4 Computed tomography has a limited ability to assess adjacent soft tissues. Ultrasound provides excellent resolution of periarticular soft tissue, minimizes exposure to radiation, and maximizes patient comfort. In fibrous coalition, ultrasound demonstrates reduced medial joint space with irregular, hypoechoic tissue.5,6 In osseous coalition, ultrasound demonstrates a smooth, continuous, hyperechoic structure representing disappearance of the joint space.5,6 Ultrasound can confirm suspicion of coalition and allows for dynamic evaluation and therapeutic intervention. LEARNING POINTS Subtalar coalition should be considered as a cause of medial ankle and foot pain in adolescents with restricted ankle motion and flat feet. Direct visualization of the subtalar joint via standard foot radiographs can be difficult, and ultrasound can be especially helpful for dynamic evaluation and therapeutic intervention.