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Musculoskeletal Imaging

Femoral neck

1. Anatomy

the portion of the femur between the femoral head and the shaft of the femur. The greater trochanter projects from the posterosuperior aspect of the femoral neck-shaft junction, and the lesser trochanter extends from the posteromedial aspect of the same junction. Also, see femoral neck.

2. Pathology

One of the radiographic measurements useful in assessing for hip disorders is the angle of anteversion of the femoral neck. In addition, the pattern of trabeculae in the upper end of the femur and femoral neck has been used as an index of osteoporosis (Singh index). Wards triangle, an area of loosely arranged trabeculae, may become more prominent after bone resorption.

In

osteoarthritis

, osseous and cartilaginous debris may become embedded in the synovium, particularly in the recesses associated with the capsular reflection on the femoral neck. Osteophytes may also develop in this location, where thickening of the medial femoral cortex characteristically occurs, termed buttressing. Buttressing may result from microfractures. On radiographs buttressing appears as a radiodense line of variable thickness along the femoral neck. Although this abnormality is frequent in osteoarthritis, it may also be seen in osteonecrosis, congenital subluxation of the hip, rheumatoid arthritis and ankylosing spondylitis.

Fractures

of the femoral neck may occur spontaneously, after minor or major trauma, after radiation therapy, or as a response to cumulative effects of prolonged stress (fatigue or insufficiency fracture) (Fig.1). Conventional radiographs may reveal nondisplaced fractures, although other imaging methods have shown better results. Fractures of the femoral neck in Gauchers disease are associated with coxa vara deformity. Bone scintigraphy and MR imaging (especially STIR images) hold the most promise in this regard. The MR imaging characteristics of a nondisplaced fracture of the femoral neck on T1-weighted spin-echo MR sequences include a well-defined linear zone of low signal intensity that may be surrounded by a broader and poorly defined zone of low signal intensity consistent with marrow oedema. On T2-weighted spin-echo MR images, the fracture line may remain of low signal intensity, but the oedematous zone demonstrates high signal intensity.

Post-traumatic osteolysis

may occur under some circumstances, with resorption and rotation at a fracture site sometimes producing a radiographic picture that may be mistaken for a malignant process. In the later stages of Legg Calv Perthes disease, one of the radiographic findings is widening and shortening of the femoral neck. Increased apposition of bone may occur over the length of the femoral neck. One or more patterns of premature closure of the longitudinal growth plate of the femoral neck may be present in this condition.

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Fig.1

a. AP radiograph of the hip demonstrates a fracture through the femoral neck. b. AP radiograph after fixation of the femoral neck fracture with three cannulated screws.
Femoral neck, Fig.1 (a)
Femoral neck, Fig.1 (b)