Logo

    Related Topics

    From Musculoskeletal System

    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Wormian Bones
    Sutural bones in the skull.
    Radius
    Forearm bone on the thumb side.
    Medial Collateral Ligament (MCL)
    Knee ligament that stabilizes the inner knee.
    Adductors
    Muscles that bring the thighs toward the midline.
    Tibialis Anterior
    Muscle that dorsiflexes and inverts the foot.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Pivot Joints
    e.g., atlanto-axial joint
    Acetabulum
    The acetabulum is the pelvic socket that connects with the femoral head to form the hip joint, vital for stability, movement, and weight-bearing.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Skull
    Bony structure of the head that encases the brain.
    Posterior Cruciate Ligament (PCL)
    Knee ligament that stabilizes the joint.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Flexor and Extensor Groups
    Muscles responsible for flexing and extending the hand and wrist.
    Quadriceps
    Rectus Femoris, Vastus Medialis, Vastus Lateralis, Vastus Intermedius.
    Annular Ligament
    The annular ligament is a strong fibrous band encircling the head of the radius, stabilizing the proximal radioulnar joint and allowing smooth rotation of the forearm.
    Cranial Bones
    Bones of the skull that protect the brain.
    Coccygeus
    Pelvic floor muscle supporting the coccyx.
    Iliolumbar Ligament
    Ligament connecting the ilium and lumbar vertebrae.
    Flexor Tendons
    Tendons that help flex the fingers and toes.
    Mandible
    Lower jawbone that houses the teeth.
    Thoracic Cage
    Ribs and sternum forming the protective cage for the heart and lungs.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.

    Sesamoid Bones

    Reviewed by our medical team

    e.g., patella, some found in hands/feet.

    1. Overview

    Sesamoid bones are small, rounded bones embedded within tendons, typically near joints. Unlike other bones that are connected to other bones via joints, sesamoid bones form within tendons due to mechanical stress and friction. Their primary role is to protect tendons, reduce wear, and enhance muscle leverage. The most well-known sesamoid bone is the patella (kneecap).

    2. Location

    Sesamoid bones are usually found in areas where tendons cross over joints, especially in the hands, feet, and knee:

    • Patella: Largest sesamoid bone, located within the quadriceps tendon at the knee.

    • First metatarsophalangeal joint (big toe): Typically two sesamoid bones embedded in the tendons of the flexor hallucis brevis.

    • First metacarpophalangeal joint (thumb): Usually two sesamoids found in the tendons of the flexor pollicis brevis and adductor pollicis.

    • Other locations: May be present in the hand, wrist (e.g., pisiform), foot, or even knee joint capsule depending on individual variation.

    3. Structure

    Sesamoid bones are round or oval in shape and vary in size:

    • Tissue composition: Consist of compact bone surrounding a core of spongy bone.

    • Surrounded by: Fibrous connective tissue of the tendon or joint capsule.

    • Development: Form through endochondral ossification within tendons subjected to repetitive stress and compression.

    • Vascularity: Relatively poor, particularly in smaller sesamoids, which can affect healing after injury.

    4. Function

    Sesamoid bones perform several biomechanical and protective functions:

    • Enhance mechanical leverage: Increase the moment arm of tendons to boost muscle efficiency (e.g., patella improves quadriceps force).

    • Reduce tendon friction: Act as a pulley to redirect the force of tendon pull, reducing stress and wear.

    • Protect tendons: Shield tendons from compressive forces at high-pressure joints.

    5. Physiological role(s)

    Though small, sesamoid bones have broader physiological importance:

    • Aid in joint movement: Help stabilize tendons and support joint articulation, especially in weight-bearing or highly mobile joints.

    • Contribute to proprioception: Their location within tendons allows them to influence sensory feedback and neuromuscular control.

    • Absorb impact: Act as shock absorbers at high-stress points such as the forefoot or knee.

    6. Clinical Significance

    Sesamoid bones, especially those in the foot and knee, are prone to injury and pathology:

    • Sesamoiditis:

      • Inflammation of the sesamoid bones and surrounding tendons, usually due to overuse or repetitive trauma (common in runners, dancers).

      • Pain localized under the first metatarsal head; worsens with pressure or motion.

    • Fracture:

      • Can be acute (from trauma) or stress-related; particularly affects the sesamoids under the big toe or the patella.

      • Healing may be delayed due to poor blood supply.

    • Osteoarthritis:

      • Degeneration of the joint surrounding sesamoid bones (e.g., patellofemoral arthritis).

    • Patellar tracking disorders:

      • Due to malalignment, the patella (a sesamoid) may dislocate or track abnormally, leading to pain or instability.

    • Accessory sesamoids:

      • Extra sesamoid bones may be present and mistaken for fractures on imaging (e.g., bipartite patella).

    • Surgical consideration:

      • Severe or chronic sesamoid problems may require surgical excision (e.g., sesamoidectomy), especially in the foot.

    Did you know? The skull is made up of 22 bones.