![]() The 45° axially angulated Harris-Beath projection of the heel is the most commonly performed supplemental examination to see sustentaculum tali fracture or subtalar coalition. ![]() Lateral foot radiographs in maximum plantar flexion and maximum dorsiflexion may help in assessing rigidity of foot deformity as well as subtalar motion. In addition to the standard AP, lateral, and oblique views of the foot, several other views may be helpful in specific cases. ĭedicated radiographic techniques for imaging the subtalar joints are useful in some circumstances, although definitive diagnosis of hindfoot pathology generally requires CT or MRI. More recent studies have suggested that a surgical corrective approach to limb length discrepancies and malalignment in the setting of ball-and-socket ankle may prevent chronic osteoarthrosis and pain. However, its association with leg length discrepancy and other congenital abnormalities makes it important to recognize. Regardless of etiology, this entity may not become symptomatic during childhood. Two major hypotheses have been proposed to explain the mechanical development: one postulates a secondary adaptation in shape to permit inversion and eversion in an ankle that has been limited by congenital tarsal fusions the other states that the ball-and-socket ankle may be a characteristic component of a complex malformation with both deleted and fused foot bones. Congenital and acquired etiologies of ball-and-socket ankle have been suggested (Table 15.1). The ball-and-socket ankle is characterized by a hemispheric configuration of the articular surface of the talus on both frontal and lateral radiographs, with corresponding congruent concavity of the distal tibial articular surface (Fig. Many consider stress radiography of the ankle unreliable and instead utilize clinical examination and dynamic imaging by ultrasound to directly evaluate the ligamentous structures. Studies have shown that a 10° difference in inversion stress angulation between the two ankles is a specific but insensitive indicator of ligamentous injury. Comparison views of both ankles can be obtained to look for asymmetry. With such marked change on inversion stress possible in normals, caution must be observed when using this to test for abnormal ligamentous laxity. With inversion the average obtainable tilt of the talar surface is 7°, with a normal range of up to 27°. When stress is applied to the heel during eversion (whether by gravity or force), there should be no tilt of the talar dome in relation to the tibial plafond. When there is an acute injury, stress views in children are quite painful and may require sedation. Radiography performed with stress applied to the ankle may be useful when chronic ligamentous injury or intrinsic malalignment is suspected. By age 12, most will have fused with the main ossific epiphysis, but 1–2 % remain separate through adulthood-especially at the fibula these eventually become persistent ossification centers. Generally appearing between ages 7 and 8, they usually unite with the main epiphysis 1–1.5 years after initial ossification. They are bilateral in more than two thirds of patients and more frequently so in girls. These secondary centers are encountered in 17–24 % of boys and in up to 47 % of girls. At the ankle, these are usually seen inferior to the tip of the medial malleolus. In contrast, secondary ossification centers will usually coalesce with other epiphyseal or apophyseal centers, eventually contributing to adult bone contours (Fig. Examples at the ankle include the os subtibiale and os subfibulare. They will not fuse with the adjacent bone and thus persist into adulthood. Accessory centers may be single or multiple and are visualized adjacent to or slightly separated from the main epiphyseal center (Fig. Many differentiate between these centers, labeling them either secondary or accessory centers of ossification. Additional ossification centers are often encountered at the distal ends of the medial and lateral malleoli in children and are especially common medially.
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