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    Related Topics

    From Musculoskeletal System

    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Masseter
    Muscle that elevates the mandible.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Hinge Joints
    e.g., elbow, knee
    Skull
    Bony structure of the head that encases the brain.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Nasal Bones
    Bones forming the bridge of the nose.
    Occipital Bone
    Bone forming the back and base of the skull.
    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Fibula
    Smaller bone in the lower leg, located alongside the tibia.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Tibialis Anterior
    Muscle that dorsiflexes and inverts the foot.
    Cranial Bones
    Bones of the skull that protect the brain.
    Deltoid
    Shoulder muscle responsible for arm abduction.
    Vomer Bone
    Bone forming the nasal septum.
    Wormian Bones
    Sutural bones in the skull.
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Tarsals (7 bones)
    7 ankle bones.
    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 ischium is the part of the pelvis you sit on.