The femoral neck is an important part of the human femur, or thigh bone. It connects the spherical head of the femur to its elongated shaft. It is important for hip movement and supporting body weight, enabling mobility.
Anatomical Positioning of the Femoral Neck
The femoral neck is a short, flattened, constricted section. It connects the rounded femoral head (which articulates with the hip socket, or acetabulum) to the cylindrical femoral shaft. It projects superiorly and medially from the shaft, not in a straight line. Its lateral end is wider, narrowing towards its middle.
The femoral neck forms an angle with the femoral shaft, known as the angle of inclination. In adults, this angle ranges from 120 to 135 degrees (averaging 125-126 degrees). This angulation allows for efficient weight transfer and a broad range of motion at the hip joint. The angle varies with age and sex; it is wider in infancy, decreases during growth, and is slightly less in females due to pelvic width. Its anterior surface contains small openings for blood vessels, while the posterior surface is smoother.
Functional Importance and Structural Vulnerability
The femoral neck bears significant mechanical loads, transferring forces from the upper body to the lower limb through the hip joint. Its angled orientation and internal bone structures (trabeculae) distribute these forces effectively. Trabeculae align along lines of stress, reinforcing the bone to withstand high forces during activities like standing, walking, and running. During single-leg stance, for instance, the hip joint can experience forces up to two and a half times body weight, increasing to five times body weight during running.
Despite its adaptations for load bearing, the femoral neck’s unique angulation and relatively narrow structure make it susceptible to injury. This vulnerability arises because it acts as a lever arm, concentrating stress, especially during twisting movements or direct impacts. Leverage forces can exceed its structural capacity, leading to damage. While enabling mobility, this design also creates a point of mechanical compromise within the femur.
Common Injuries Associated with the Femoral Neck
Due to its load-bearing function and structural characteristics, the femoral neck is a common site for fractures. These fractures often result from low-energy falls in older adults, especially those with osteoporosis (reduced bone density). In younger individuals, fractures occur due to high-impact trauma, such as motor vehicle accidents.
A fracture can disconnect the femoral head from the rest of the femur, significantly impacting mobility and requiring medical intervention. The seriousness of fractures is compounded by disruption of blood supply to the femoral head, which travels along the femoral neck. Impaired blood flow can hinder healing and lead to complications like avascular necrosis (bone tissue death due to lack of blood supply).