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Within the scope of this chapter, the sacrum, innominates (including the acetabulum), and proximal femur are discussed. Features of the proximal femur are of particular interest because of their frequent pathologic involvement. The femoral head comprises approximately two-thirds of a sphere with an orientation medially, superiorly, and anteriorly to articulate with the acetabulum. The surface of the femoral head is covered with articular cartilage with the exception of the fovea. The cartilage is thickest centrally and is slightly attenuated peripherally; the fovea is devoid of articular cartilage. Connecting the head and the shaft of the femur is the neck extending inferolaterally. The femoral neck has considerable variability in morphology and forms an angle of approximately 130° with the femoral diaphysis, which is an important angle of reference. Surrounding the femoral neck are the circumflex arteries, which give rise to much of the blood supply to the femoral head. From the medial femoral circumflex artery arises the lateral epiphyseal artery, which provides the majority blood supply to the femoral head.1
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The acetabular labrum is attached at the periphery of the acetabulum and to the transverse ligament. The morphology of the labrum is triangular in cross section and thinner along the superoanterior aspect than the posteroinferior aspect. The joint capsule connects the acetabulum to the base of the labrum and has three ligamentous condensations comprising the iliofemoral, pubofemoral, and ischiofemoral ligaments. The zona orbicularis is that portion of the capsule in which the fibers encircle the femoral neck midpoint.1,2
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The pelvis includes the two innominates and the sacrum, forming a strong ring-like structure. Included in this ring are the synchondrotic pubic symphysis and the two sacroiliac joints, which are a combination of synovial and syndesmotic joints. The ring-like structure is of particular functional importance as injury in one area of the ring will tend to cause disruption in another.
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Radiography remains the entry-level imaging option for many patients presenting with suspected hip or pelvic girdle pathologies, or regional manifestations of systemic disorders. After trauma, radiography is usually undertaken as the initial imaging of choice owing to the ability to obtain rapid, accurate information to guide emergent care for possible fractures or dislocations.1,3
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Basic landmarks guide the assessment of skeletal integrity. Shenton line is a curve of the lower border of the superior pubic ramus and the inferior aspect of the neck of the femur, forming a smooth arc. This arc is an important reference when considering the alignment of the femoral head and neck with the acetabulum. Ward triangle is a radiographically lucent zone of the femoral neck located between the primary or medial compressive trabeculae, secondary or lateral compressive trabeculae, and the principal tensile group of trabeculae. Also in reference to the acetabulum is the identification of four fundamental osseous landmarks: iliopectineal line, ilioischial line, anterior rim ...