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.
The femoral head-neck-shaft angle is used in the diagnosis and therapeutic or rather surgical planning of several pathological conditions including the following :
- 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 (NSA) angle is influenced by femoral rotation, which might lead to measurement errors if not considered .
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 .
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) .
A known normal range of the caput-collum-diaphyseal (CCD) angle is generally considered 125°-135° , with a global mean of 126.4° and standard deviations are approximately 5.6° measured with a 360° goniometer in anatomical studies . But global median values apparently vary in respect to climate and population being about 125° in the Americas up to 130° in Asians .
Widely considered cut-off values are the following :
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 .