Bones of the Lower Limb: Femur and Patella

The femur consists of a head that articulates with the hip bone, a neck below the head, a shaft in the middle, and condyles at the distal end. Rough projections called trochanters attach to hip and buttock muscles, while the linea aspera on the posterior surface provides attachment for thigh muscles. The condyles separate into lateral and medial structures divided by the intercondylar fossa.

The patella is a large sesamoid bone enclosed within the tendon of the quadriceps femoris muscle. It lifts the tendon away from the knee joint, increasing the leverage power of the quadriceps muscle as it acts across the knee. This unique positioning allows the patella to enhance muscle efficiency during knee extension movements like kicking, running, and jumping.

During knee extension, the patella glides across the femur's patellar groove in an up-and-down motion only. The quadriceps femoris muscle pulls the patella both superiorly and laterally, with the lateral pull being greater in women due to their larger Q-angle. This anatomical difference makes women more vulnerable to developing patellofemoral syndrome than men.

The patella is cartilaginous at birth and begins to ossify around ages 2 or 3. Ossification continues throughout childhood and completes at puberty. This developmental timeline reflects the gradual transformation of the kneecap from cartilage to bone as the skeleton matures.

The fovea capitis is a minor indentation on the medial side of the femoral head that serves as an attachment site for the ligament of the head of the femur. This weak ligament spans between the femur and acetabulum, providing support to the hip joint. Though not the primary stabilizer, it contributes to overall hip joint integrity.

The femoral neck is a common fracture site because it is a narrowed region below the femoral head with reduced bone density. The inclination angle between the neck and shaft, approximately 128 degrees, decreases with age, further compromising structural integrity. This anatomical vulnerability makes the neck susceptible to fractures from falls and trauma.

The greater trochanter is a large bony projection above the base of the neck to which multiple hip and thigh muscles attach, acting across the hip joint. The lesser trochanter is a smaller bony prominence just below the neck where a single muscle attaches. Both serve as attachment sites for muscles, but the greater trochanter accommodates more muscular attachments and bears greater functional load.