What is Femoral Neck-Shaft Angle

Femoral neck-shaft angle is an Angle between the neck of the femur and the shaft of the femur. It is widest at birth and diminishes with age till adolescence.This Angle is 160° in young children and ranges from 110° to 140° in adults. Greater than 140° is a valgus, and less than 110° is a varus.

What is Femoral Neck Anteversion

Femoral neck anteversion (FNA) describes the normal torsion or twist present in the femur. Femoral neck anteversion is the angle between the axis of the femoral neck and the frontal surface of the femur (ie, the coronal plane of the human body). In adults without pathology, the femur is twisted so the head and neck of the femur are angled forward between 15 and 20 degrees.

Femoral neck anteversion sometimes is called “medial femoral torsion.” It is thought to result from medial (internal) rotation of the limb bud in early intrauterine life. In postnatal development, a reduction of the FNA angle usually occurs during growth. In the newborn, the average FNA angle is 31 degrees.The average FNA angle is 26 degrees by 5 years of age, 21 degrees by 9 years of age, and 15 degrees by 16 years of age.The FNA angle, therefore, diminishes about 1.5 degrees a year until about 15 years of age. In the adult, average femoral head and neck torsion forward of the body’s frontal plane is about 15 degrees, a little less in men (less than 15°) and a little more in women (18°) Femoral neck anteversion angle is typically symmetrical from the left side to the right side.

Related Lower Extremity Diseases

Assessing passive hip medial and lateral rotation can be a useful guide in determining if an increased or decreased FNA angle exists. An increased or a decreased FNA angle has been linked to many different lower- extremity problems, including osteoarthritis of the hip, coxa plana, slipped capital femoral epiphysis, congenital hip dysplasia, acetabular labral tears, and in-toeing and out-toeing of the lower extremities.Moreover, asym- metries in hip joint rotation also have been associated with low back and regional pain in the sacroiliac joint.

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