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    Related Topics

    From Musculoskeletal System

    Masseter
    Muscle that elevates the mandible.
    Patella
    Knee cap, protecting the knee joint.
    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.
    Mandible
    Lower jawbone that houses the teeth.
    Cranial Bones
    Bones of the skull that protect the brain.
    Lacrimal Bones
    Bones forming part of the eye socket and housing the tear ducts.
    Sphenoid Bone
    Bone forming part of the base of the skull and sides of the orbits.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Ilium
    Uppermost and largest part of the hip bone.
    Occipital Bone
    Bone forming the back and base of the skull.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    Flexor and Extensor Groups
    Muscles responsible for flexing and extending the hand and wrist.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Ulna
    Forearm bone on the pinky side.
    Facial Bones
    Bones forming the structure of the face.
    Lateral Collateral Ligament (LCL)
    Knee ligament that stabilizes the outer knee.
    Diaphragm
    Primary muscle for breathing.
    Gliding (Plane) Joints
    e.g., between carpals
    Deltoid
    Shoulder muscle responsible for arm abduction.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Coccygeus
    Pelvic floor muscle supporting the coccyx.
    Patellar Tendon
    Tendon connecting the patella to the tibia.
    Tarsals (7 bones)
    7 ankle bones.

    Pivot Joints

    Reviewed by our medical team

    e.g., atlanto-axial joint

    1. Overview

    A pivot joint, also known as a trochoid joint, is a type of synovial joint that allows rotational movement around a single axis. It functions like a mechanical axle, enabling one bone to rotate around another. Pivot joints are essential for motions such as head rotation and forearm pronation and supination. Though limited in range, they play a vital role in daily motor activities.

    2. Location

    There are two primary pivot joints in the human body:

    • Atlantoaxial joint (cervical spine): Located between the first (atlas) and second (axis) cervical vertebrae; allows head rotation side-to-side (e.g., "no" movement).

    • Proximal radioulnar joint (forearm): Located near the elbow, between the head of the radius and the radial notch of the ulna; enables pronation and supination of the forearm.

    3. Structure

    A pivot joint consists of a rounded or pointed bone that rotates within a ring formed by another bone and a ligament:

    • Bone component: One bone has a bony process (e.g., the dens of the axis or the radial head).

    • Ring or sleeve: This may be bony (e.g., atlas) or ligamentous (e.g., annular ligament of the radius).

    • Joint capsule: A fibrous capsule encloses the joint, allowing synovial fluid to lubricate and reduce friction.

    • Ligaments: Support and limit the range of motion; examples include the transverse ligament of the atlas and annular ligament in the elbow.

    4. Function

    Pivot joints allow uniaxial rotation around a central axis:

    • Rotation: The only permitted motion; no flexion, extension, abduction, or adduction.

    • Example in neck: Rotation of the head left and right via the atlantoaxial joint.

    • Example in forearm: Pronation (palm down) and supination (palm up) movements via the proximal radioulnar joint.

    5. Physiological role(s)

    Pivot joints are essential for specific physiological tasks and functional mobility:

    • Vision and awareness: The atlantoaxial pivot joint allows the head to rotate and track visual or auditory stimuli.

    • Tool manipulation: The radioulnar pivot enables rotational forearm movement, allowing gripping, turning, and writing.

    • Neuromuscular coordination: Smooth rotational movement supports coordinated motor skills in upper limb and neck.

    6. Clinical Significance

    Though small, pivot joints are subject to specific injuries and disorders:

    • Atlantoaxial instability:

      • May be congenital (e.g., Down syndrome) or acquired (e.g., rheumatoid arthritis), posing a risk for spinal cord compression.

    • Rotational subluxation:

      • Occurs when the atlas and axis misalign; can lead to torticollis or restricted head movement.

    • Radial head dislocation (nursemaid’s elbow):

      • Common in young children; results from sudden traction on the forearm causing the radial head to slip out of the annular ligament.

    • Fractures:

      • Radial head fractures can impair pronation and supination; dens fractures affect cervical rotation and may compromise neural structures.

    • Rheumatoid arthritis:

      • Chronic inflammation may erode ligaments or bones, especially in the cervical spine, destabilizing the pivot joint.

    Did you know? The adult human body contains around 60,000 miles of blood vessels.