Femoral neck-shaft angle

The femoral neck-shaft angle (NSA) or caput-collum-diaphyseal (CCD) angle is one of the most frequently applied measurements to assess hip morphology, in particular, the relation of the femoral shaft to the femoral head-neck axis.

Usage

The femoral head-neck-shaft angle is used in the diagnosis and therapeutic or rather surgical planning of several pathological conditions including the following ¹:

• proximal femoral fractures
• hip osteoarthritis
• developmental dysplasia of the hip
• cerebral palsy
• femoroacetabular impingement
• Perthes disease
• slipped capital femoral epiphysis

The femoral head-neck-shaft angle is influenced by femoral rotation, which might lead to measurement errors if not considered ^1,2.

Measurement

The angle between the longitudinal femoral shaft axis and the femoral head-neck axis is measured. The axis of the femoral neck is defined by a line bisecting the femoral neck through the center of the femoral head. The longitudinal femoral shaft axis is determined by two bisections of the femoral shaft at different locations ¹.

Due to the susceptibility of angle measurements to rotation and to account for the usual femoral anteversion an internal rotation of the feet of 15°-20° is recommended for the standardized acquisition of the pelvis (AP view) ¹.

Interpretation

A known normal range of the caput-collum-diaphyseal (CCD) angle is generally considered 125°-135° ³, with a global mean of 126.4° and standard deviations are approximately 5.6° measured with a 360° goniometer in anatomical studies ⁴. But global median values apparently vary in respect to climate and population being about 125° in the Americas up to 130° in Asians ⁴.

Widely considered cut-off values are the following ³:

• coxa valga: >140°
• coxa vara: <120°

Potential measurement errors

Potential measurement errors radiographically caused by external rotation of the femur can cause a change of >10° in the apparent femoral neck-shaft angle with as little as 7° of external rotation of the femur ².