Patella is the largest sesamoid bone, shielding the knee and enhancing quadriceps leverage.
The patella, commonly known as the kneecap, is a flat, triangular sesamoid bone embedded within the tendon of the quadriceps femoris muscle. It plays a critical role in the biomechanics of the knee joint, aiding in force transmission and protecting underlying structures. As the largest sesamoid bone in the human body, the patella has a unique anatomical form and function, essential for proper locomotion and knee stability.
The patella has a broad superior end called the base and a pointed inferior end known as the apex. The anterior surface is convex, roughened for ligament attachment, and subcutaneous, making it easily palpable. The posterior surface is smooth and divided into medial and lateral facets, which articulate with the femoral condyles.
The patella is situated anterior to the distal femur and embedded within the quadriceps tendon. It lies within the anterior compartment of the knee joint and is subcutaneous, making it easily accessible for clinical palpation and examination. Its posterior surface articulates with the trochlear surface of the femur, forming the patellofemoral joint.
The patella begins to ossify between the ages of 3 to 6 years. Ossification starts from multiple centers that gradually fuse into a single bony structure. Incomplete fusion of these centers may result in a bipartite patella, often discovered incidentally in imaging studies.
The patella forms a synovial joint with the femur called the patellofemoral joint. This articulation is part of the knee complex and is critical for flexion and extension. During movement, the patella glides along the trochlear groove of the femur.
Articulating Bone | Joint Type | Movement |
---|---|---|
Femur | Synovial (plane-type) | Gliding during knee flexion and extension |
The patella receives its vascular supply primarily from the genicular branches of the femoral, popliteal, and anterior tibial arteries. These vessels form a periarticular anastomosis around the knee, ensuring consistent blood flow even during movement.
Innervation of the patella and surrounding structures comes from the femoral nerve (via branches to the quadriceps) and contributions from the saphenous nerve. These nerves carry both proprioceptive and pain-related fibers.
The patella is clearly visible on standard anteroposterior (AP) and lateral knee X-rays. Special views like the sunrise (skyline) view are used to evaluate patellofemoral alignment and cartilage surface. CT and MRI provide detailed information about tracking, soft tissue injury, or cartilage integrity.
Due to its superficial location, the patella is easily palpated. The base can be felt superiorly, while the apex lies inferiorly near the tibial tuberosity. Medial and lateral movement can be appreciated during physical examination, especially during flexion and extension of the knee.