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Distal fibula8/31/2023 The outer margin of the bone is its external architecture, and the remainder is its internal architecture. These shadows represent cortex, trabeculae, and superimposed osseous landmarks in the adult skeleton and constitute the architecture of the bone. Occasionally, focal areas of increased density are seen.Įach bone has its own characteristic shadows. More commonly, this appears as a relative radiolucency or decreased density. ![]() Variants of density can mimic abnormal or pathologic processes. Positional changes are predictable, however, and the experienced interpreter can recognize these alterations and correlate them to normal radiographic anatomy. Angle and base of gait positioning provide a means for minimizing the technical variation that may occur (described in Chapter 4). Varying forms may also be encountered in weight-bearing studies secondary to pronation and supination (internal and external leg rotation, respectively refer to Figure 5-1). For example, the navicular bone frequently appears rectangular in a pes cavus foot but wedge shaped in a pes planus foot. Other variants of form can be attributed to the position of the foot or ankle bones relative to each other and/or the image receptor. Synostosis/coalition is also a variation of form. Variants of form concern the girth, length, and contour of a bone. Most variations of existing bones are variants of form. 2 Variations of position can predispose for future pathology. In the two-dimensional radiograph, this position can vary considerably among patients and depends heavily on foot type and the degree of pronation or supination during weight-bearing stance in angle and base of gait. The axis of each bone has a characteristic position relative to the axes of adjacent bones. Variations Involving Normally Existing Bones Supernumerary bones include duplication of phalanges, metatarsals, and tarsal bones.īOX 6-1 Expression of Variants in the Foot Although rare, bipartite medial cuneiform and navicular bones may be encountered. Bipartite sesamoids, for example, are common. Variants of number include partite bones, supernumerary bones, and absence of bones. Accessory ossicles, in addition to the existing 30 bones, are not uncommon. Examples of variations involving normally existing bones include variants of number, position, form (shape and size), density, and architecture. Variations can be expressed in several ways ( Box 6-1). Also note that although all sesamoid bones are ossicles, not all ossicles are sesamoid bones. The terms partite, supernumerary, and accessory bone in the following discourse are differentiated thus: Partite can pertain to either a normally existing bone or an accessory bone that is subdivided supernumerary pertains to anomalous duplication of a normally existing bone and accessory bone refers to those ossicles (not anomalous duplication) that are found in addition to the normally existing bones. Variant: something that differs in some characteristic from the class to which it belongs, as a variant of a disease, trait, and so forth. ![]() Synostosis: the osseous union of two bones that are normally distinct. Supernumerary: in excess of the regular or normal number. Sesamoid: a small, nodular bone embedded in a tendon or joint capsule. Os: bone a general term that is qualified by the appropriate adjective to designate a specific type of bony structure or a specific segment of the skeleton. Their definitions are as follows (from Dorland’s Illustrated Medical Dictionary 1):Īccessory: supplementary to another similar and generally important thing.Īnomaly: marked deviation from the normal standard, especially as a result of congenital defects. Several words are frequently used when referring to variations of the skeleton. More common examples of the latter include the accessory navicular and tarsal coalition. Variations typically are incidental findings and asymptomatic, although symptomatology or pathology may occur secondary to a skeletal variation. However, variations in their appearance are not uncommon. (This number includes the distal tibia and fibula and the two sesamoids at the first metatarsophalangeal joint.) The previous chapter described the expected radiographic appearance of each bone in the many views available. Thirty bones compose the foot and ankle complex.
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