Medical Radiology - Lazar A.P. 2008

Radiation examination of bones and joints
Bones and joints in X-ray imaging

Bone tissue contains 50% Water, 28% organic matter, and 22% inorganic matter. The Inorganic Components of bone consist of Calcium and phosphorus salts (85%), potassium and carbon salts (10%), and magnesium (5%); they absorb X-rays effectively. The dense PARTS OF THE bone (bone trabeculae and spicules) are composed primarily of inorganic salts and show up clearly on radiographs, whereas soft-tissue structures (Cartilage, Bone Marrow, endosteum, periosteum, Blood Vessels, and nerves) consist mainly of organic matter and are not visible on radiographs.

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Fig. 30. Radiograph of the right hip joint region in the anteroposterior projection.

In tubular bones, the cortical layer appears as a homogeneous, dense shadow with smooth, even margins along the edge of the bone (Fig. 30). The radiolucency of the medullary cavity is visible between the two layers of cortical bone. A thick layer of cortical bone is observed along the diaphysis, tapering toward the epiphyses. The medullary cavity terminates at the metaphyseal level between the diaphysis and epiphysis, where the cortical layer transitions into a thin strip. Bony prominences on the epiphyses that serve as attachment sites for tendons and ligaments are referred to as apophyses.

Articular cartilage On the surface of the epiphysis absorbs virtually no X-radiation; therefore, the joint appears on a radiograph as a uniform radiolucent band known as the radiological joint space. The normal thickness of hyaline articular cartilage ranges from 0.2 to 6 mm. The thin layer of cortical bone outlining the radiological joint space is termed the subchondral bone plate (or articular end-plate) in radiology. This plate is thicker along the concave surfaces of the joint.

In the epiphyses and metaphyses of tubular bones, the orientation of bone trabeculae corresponds to the lines of resistance to compression (running vertically) and tension (arranged in arches). In the metaepiphyseal regions of tubular bones, the trabeculae form a fine-meshed reticular pattern. A similar fine-meshed bone pattern is also observed in flat bones. On radiographs where flat bones are positioned tangentially, their cortical layer appears as a thin margin-forming line.

Vascular and neural foramina and canals, when oriented tangentially to the path of the X-ray beam, appear as rounded radiolucencies with sharp, smooth margins. When positioned perpendicularly, they appear as branching linear shadows that correspond to the vascular network pattern. Without an anatomical understanding of their Location within the bones, these linear shadows can be mistaken for a fracture.