The term calcar femur refers to a specific structure within the femur, or thigh bone, located near the hip joint. It is not a separate bone but rather a thickened, strong plate of bone integral to the femur itself. This area of increased density provides internal reinforcement. The term is often heard in discussions of hip health and injury, as its condition can have significant implications.
Anatomical Location and Structure
The calcar femorale is situated on the inner and rear-facing side (posteromedial aspect) of the upper femur. It lies at the junction where the femoral neck, the angled segment connecting to the hip socket, joins the main vertical shaft of the bone. It is an internal, vertically oriented plate of dense cortical bone, which makes it substantially stronger than the surrounding cancellous, or spongy, bone tissue. This structure extends from the posteromedial femoral cortex laterally toward an area near the greater trochanter. It is thickest on its medial side and gradually becomes thinner as it spreads outward.
Biomechanical Importance
The primary function of the calcar femorale is to manage the mechanical forces that travel through the hip joint. During daily activities such as walking, standing, or running, the hip is subjected to pressure. The calcar provides support to the femoral neck, an area particularly susceptible to stress. It plays a part in distributing stress from the femoral head—the “ball” of the ball-and-socket joint—down into the strong, cylindrical shaft of the femur. This internal plate of bone is positioned to counteract compressive forces that push down on the hip and also resists tensile forces that pull and stretch the bone. By managing these loads, the calcar helps maintain the structural integrity of the proximal femur.
Role in Hip Fractures
The condition of the calcar femorale becomes particularly relevant when a hip fracture occurs, specifically in the region between the femoral neck and the lesser trochanter (intertrochanteric fractures). The integrity of this structure is a primary determinant of whether a fracture is considered “stable” or “unstable.” An unstable fracture pattern often involves significant damage to or comminution (breaking into multiple pieces) of the calcar. This compromises the bone’s inherent ability to support itself.
When the calcar femorale remains intact during a fracture, it provides a solid wall of bone that can help resist collapse and displacement of the broken pieces. A fracture that disrupts this structure removes a point of medial support. This loss of support can lead to a varus deformity, where the angle of the hip decreases, causing instability and complicating the healing process.
Surgical Implications
In orthopedic surgery, the calcar femorale serves as a landmark and a foundation for repairing hip fractures and performing hip replacements. Surgeons rely on its strength and location to anchor fixation devices such as plates, screws, and intramedullary nails. The calcar’s integrity directly influences the choice of surgical implant and technique, as stable fixation often depends on leveraging this dense bone.
During a total hip arthroplasty (hip replacement), the prosthetic femoral stem is inserted into the hollowed-out canal of the femur. Certain implant designs, known as “calcar-bearing” or “calcar-guided” stems, are specifically engineered to rest upon the calcar. This allows for the transfer of body weight from the prosthesis to this strong bone structure, promoting stability and proper load distribution. Reconstructing or bypassing a damaged calcar is a consideration in complex fracture surgeries to ensure a stable outcome.