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    Related Topics

    From Musculoskeletal System

    Anterior Scalene Muscle
    The anterior scalene muscle is a deep neck muscle that elevates the first rib during inspiration and aids in neck flexion and stability, located between key neurovascular structures.
    Frontal Bone
    Bone forming the forehead and upper part of the orbits.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Medial Collateral Ligament (MCL)
    Knee ligament that stabilizes the inner knee.
    Pubis
    Part of the pelvis that joins with the opposite side to form the pubic symphysis.
    Sesamoid Bones
    e.g., patella, some found in hands/feet.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Coccyx
    Tailbone, the remnant of the tail in humans.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Soleus
    Calf muscle responsible for plantarflexion of the foot.
    Ellipsoidal (Condyloid) Joints
    e.g., wrist
    Abductor Digiti Minimi Muscle
    The abductor digiti minimi muscle is a hypothenar muscle that abducts and flexes the little finger, aiding grip and precision in hand movements.
    Phalanges (14 bones)
    14 bones forming the toes.
    Sternocleidomastoid
    Muscle that rotates and flexes the neck.
    Ilium
    Uppermost and largest part of the hip bone.
    Fibula
    Smaller bone in the lower leg, located alongside the tibia.
    Tarsals (7 bones)
    7 ankle bones.
    Triceps Brachii
    Muscle responsible for elbow extension.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    Adductors
    Muscles that bring the thighs toward the midline.
    Biceps Tendon
    Tendon that attaches the biceps muscle to the bone.
    Ischium
    Part of the pelvis that supports weight while sitting.

    Carpals (8 bones)

    Reviewed by our medical team

    8 wrist bones.

    1. Overview

    The carpal bones are a group of eight small, irregularly shaped bones that form the wrist (carpus) and connect the forearm to the hand. These bones are arranged in two rows—proximal and distal—and articulate with each other, the radius, and the metacarpals. The carpal bones contribute to the flexibility and strength of the wrist and serve as a stable yet mobile base for hand movement. They are vital for transmitting forces and allowing a wide range of motion while maintaining wrist stability.

    2. Location

    The carpal bones are located in the wrist region, situated between the distal end of the radius and ulna proximally, and the metacarpal bones distally. They are organized into:

    • Proximal row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform

    • Distal row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate

    The mnemonic “Some Lovers Try Positions That They Can’t Handle” helps recall the order from lateral (thumb side) to medial (pinky side).

    3. Structure

    Each carpal bone is composed of cortical bone externally and cancellous (spongy) bone internally. The structural characteristics include:

    • Scaphoid: Boat-shaped; largest bone of the proximal row; articulates with the radius.

    • Lunate: Crescent-shaped; centrally located; articulates with the radius and capitate.

    • Triquetrum: Pyramid-shaped; articulates with lunate and pisiform.

    • Pisiform: Pea-shaped sesamoid bone lying over the triquetrum; embedded in the tendon of flexor carpi ulnaris.

    • Trapezium: Saddle-shaped; articulates with the first metacarpal; key to thumb mobility.

    • Trapezoid: Wedge-shaped; articulates with the second metacarpal.

    • Capitate: Largest carpal bone; centrally located; articulates with the third metacarpal.

    • Hamate: Characterized by a hook-like projection (hamulus); articulates with the fourth and fifth metacarpals.

    4. Function

    The carpal bones work collectively to:

    • Allow wrist movement: Facilitate flexion, extension, radial deviation, and ulnar deviation of the wrist joint.

    • Transmit force: Distribute loads from the hand to the radius and ulna during grip and weight-bearing activities.

    • Enable thumb opposition: Especially through the trapezium, allowing fine manipulation.

    • Support tendons: Serve as pulleys and surfaces for tendon gliding, especially within the carpal tunnel.

    5. Physiological role(s)

    The carpal bones contribute to broader functional systems in the upper limb:

    • Dexterity: Provide a mobile yet stable platform for finger movement and tool use.

    • Muscle attachment: Serve as anchor points for muscles controlling the wrist and hand.

    • Ligamentous integrity: Connect with strong ligaments (e.g., scapholunate, radiocarpal) for wrist stability.

    • Neurovascular protection: The concavity formed by the carpal arch creates the carpal tunnel, through which the median nerve and tendons pass.

    6. Clinical Significance

    The carpal bones are frequently involved in fractures, dislocations, and compressive syndromes:

    • Scaphoid fracture:

      • Most commonly fractured carpal bone; typically due to a fall on an outstretched hand (FOOSH).

      • Prone to avascular necrosis due to poor blood supply, especially to the proximal pole.

    • Lunate dislocation:

      • Can compress the median nerve and lead to carpal instability or acute carpal tunnel syndrome.

    • Carpal tunnel syndrome:

      • Compression of the median nerve beneath the transverse carpal ligament, often caused by swelling or structural narrowing involving carpal bones.

    • Arthritis:

      • Osteoarthritis or rheumatoid arthritis can affect intercarpal joints, reducing wrist mobility and causing pain.

    • Kienböck’s disease:

      • Avascular necrosis of the lunate, leading to progressive collapse and wrist dysfunction.

    • Hook of hamate fracture:

      • Often seen in sports (e.g., golf, baseball); may compress the ulnar nerve and affect grip strength.

    Did you know? The human body has over 600 muscles.