Logo

    Related Topics

    From Musculoskeletal System

    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Masseter
    Muscle that elevates the mandible.
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Saddle Joints
    e.g., thumb joint
    Clavicle
    Collarbone connecting the arm to the body.
    Sacrum
    Triangular bone at the base of the spine.
    Sartorius
    Longest muscle in the body responsible for hip flexion.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Lateral Collateral Ligament (LCL)
    Knee ligament that stabilizes the outer knee.
    Gliding (Plane) Joints
    e.g., between carpals
    Quadriceps
    Rectus Femoris, Vastus Medialis, Vastus Lateralis, Vastus Intermedius.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Cranial Bones
    Bones of the skull that protect the brain.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Lacrimal Bones
    Bones forming part of the eye socket and housing the tear ducts.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Deltoid
    Shoulder muscle responsible for arm abduction.
    Phalanges (14 bones)
    14 bones forming the toes.
    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.
    Vomer Bone
    Bone forming the nasal septum.
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Carpals (8 bones)
    8 wrist 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? Bones become stronger when stressed by exercise.