12.4:
Bones of the Lower Limb: Femur and Patella
The weight-bearing lower limbs have thick bones that connect to strong muscles.
The thigh bone or the femur is the longest and heaviest bone in the body.
It has a head, a neck, a shaft, and condyles.
The head articulates with the hip bone, and rough projections called the greater and lesser trochanters attach to the hip and buttock muscles.
On the posterior surface, a rough crest called the linea aspera attaches to the thigh muscles.
Near the knee joint, it bifurcates into the supracondylar ridges that end in the lateral and medial condyles, separated by the intercondylar fossa.
The patella or the kneecap is a large sesamoid bone. It is surrounded by the tendon of the quadriceps femoris muscles that help straighten the knee during kicking, running, and jumping.
During such actions, the patella glides across the femur's patellar groove, allowing only up and down movement.
The patella is cartilaginous at birth and starts to ossify at the age of 2 or 3, completing ossification at puberty.
12.4:
Bones of the Lower Limb: Femur and Patella
The femur is the body's longest and strongest bone spanning the thigh region. Its head articulates with the acetabulum of the hip bone to form the hip joint. A minor indentation on the medial side of the femoral head, called the fovea capitis, serves as the site of attachment for the ligament of the head of the femur. This weak ligament spans the femur and acetabulum and supports the hip joint. The narrowed region below the head is the neck of the femur. The inclination angle between the neck and shaft is about 128 degrees, which decreases with age. The neck is a common area for fractures of the femur. Above the base of the neck is the large bony projection called the greater trochanter. Multiple muscles attach to this projection, acting across the hip joint.
Just below the neck of the femur is a small bony prominence called the lesser trochanter, to which a single muscle attaches. The roughened intertrochanteric line runs between the greater and lesser trochanters on the anterior side of the femur. The femoral shaft has a rough line called the linea aspera to which muscles of the hip and thigh regions attach. Distally the femur broadens and ends in the lateral and medial condyles, which articulate with the tibia to form the knee joint. Posteriorly, the medial and lateral condyles are separated by a deep depression called the intercondylar fossa. Anteriorly, the smooth surfaces of the condyles join together to form a wide groove called the patellar surface, which provides for articulation with the patella bone.
The patella, or the kneecap, is the most prominent sesamoid bone of the body. The patella is enclosed in the tendon of the quadriceps femoris muscle that attaches to the tibia. It articulates with the patellar surface of the femur. The patella lifts the tendon away from the knee joint, which increases the leverage power of the quadriceps femoris muscle, as it acts across the knee.
Patellofemoral syndrome, also known as the runner's knee, is the most common overuse injury among runners. During extension of the knee, the quadriceps femoris muscle pulls the patella both superiorly and laterally, with the lateral pull greater in women due to their large Q-angle. This makes women more vulnerable to developing patellofemoral syndrome than men.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 8.4: Bones of the lower limb.