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    Related Topics

    From Musculoskeletal System

    Flexor Tendons
    Tendons that help flex the fingers and toes.
    Cranial Bones
    Bones of the skull that protect the brain.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Ilium
    Uppermost and largest part of the hip bone.
    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.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Gliding (Plane) Joints
    e.g., between carpals
    Ischium
    Part of the pelvis that supports weight while sitting.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Sternum
    Breastbone located in the center of the chest.
    Skull
    Bony structure of the head that encases the brain.
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Femur
    Thigh bone, the longest and strongest bone in the body.
    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.
    Ulna
    Forearm bone on the pinky side.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Gastrocnemius
    Calf muscle responsible for plantarflexion of the foot.
    Clavicle
    Collarbone connecting the arm to the body.
    Radius
    Forearm bone on the thumb side.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Nasal Bones
    Bones forming the bridge of the nose.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.

    Saddle Joints

    Reviewed by our medical team

    e.g., thumb joint

    1. Overview

    A saddle joint, also known as a sellar joint, is a type of synovial joint characterized by articulating surfaces that are concave in one direction and convex in the other—resembling a saddle. This unique structure allows movement in two planes, including flexion/extension and abduction/adduction, with a small degree of axial rotation. Saddle joints offer greater mobility than hinge joints but less than ball-and-socket joints.

    2. Location

    The most notable and functionally significant saddle joint in the human body is the first carpometacarpal (CMC) joint of the thumb:

    • Located between: The trapezium (a carpal bone) and the base of the first metacarpal (thumb).

    • Additional example: The sternoclavicular joint is sometimes functionally classified as a saddle joint.

    3. Structure

    Saddle joints are biaxial synovial joints with reciprocally concave and convex articular surfaces:

    • Joint surfaces: Each surface is shaped like a rider sitting on a saddle—concave in one direction and convex in the perpendicular direction.

    • Synovial membrane: Lines the joint capsule and secretes synovial fluid for lubrication.

    • Joint capsule: Encloses the articulating surfaces, providing support and mobility.

    • Ligaments: Surround and reinforce the joint—especially the anterior oblique, dorsoradial, and intermetacarpal ligaments in the thumb CMC joint.

    4. Function

    Saddle joints enable biaxial movement—allowing motions in two primary planes:

    • Flexion and extension: Bending and straightening movements.

    • Abduction and adduction: Moving away from and toward the central axis of the body or hand.

    • Opposition (in thumb): Unique movement combining flexion, abduction, and rotation, allowing the thumb to touch other fingertips.

    This functionality makes the thumb highly versatile, playing a key role in gripping and manipulating objects.

    5. Physiological role(s)

    Saddle joints contribute to essential hand functions and upper limb dexterity:

    • Fine motor skills: The CMC joint of the thumb enables precise movements required for writing, pinching, and tool use.

    • Opposability: Allows thumb to oppose fingers, a trait unique to humans and some primates.

    • Load distribution: Transfers force during grasping and weight-bearing through the upper limb.

    • Functional versatility: The combination of mobility and stability allows for complex hand postures and tool manipulation.

    6. Clinical Significance

    Due to their high mobility and mechanical load, saddle joints are prone to wear and pathology, especially in the thumb:

    • Osteoarthritis (thumb CMC joint):

      • Degeneration of the articular cartilage from repetitive use; most common cause of thumb base pain in older adults, especially postmenopausal women.

      • Symptoms include pain, stiffness, swelling, and decreased grip strength.

    • Joint instability:

      • Ligament laxity or trauma can lead to subluxation or instability of the joint, affecting thumb positioning and grip.

    • De Quervain’s tenosynovitis:

      • Although not directly a saddle joint issue, this inflammatory condition affects tendons crossing near the CMC joint and may cause confusion in diagnosis.

    • Surgical interventions:

      • For severe arthritis, options include trapeziectomy, ligament reconstruction, tendon interposition, or joint replacement.

    • Rehabilitation:

      • Conservative treatments include splinting, NSAIDs, corticosteroid injections, and physical therapy to strengthen surrounding muscles and reduce joint strain.

    Did you know? The largest muscle in the body is the gluteus maximus, responsible for hip extension.