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    From Musculoskeletal System

    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Saddle Joints
    e.g., thumb joint
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Acromioclavicular Joint
    The acromioclavicular joint connects the clavicle and scapula at the top of the shoulder, enabling smooth scapular motion and stability during arm movements.
    Temporal Bones
    Bones forming the lower sides of the skull and housing the ears.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Extensor Tendons
    Tendons that help extend the fingers and toes.
    Achilles Tendon
    Tendon connecting the calf muscle to the heel bone.
    Posterior Cruciate Ligament (PCL)
    Knee ligament that stabilizes the joint.
    Mandible
    Lower jawbone that houses the teeth.
    Interspinous Ligament
    Spinal ligament between adjacent vertebral spinous processes.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Temporalis
    Muscle involved in closing the jaw.
    Thoracic Cage
    Ribs and sternum forming the protective cage for the heart and lungs.
    Patella
    Knee cap, protecting the knee joint.
    Sternum
    Breastbone located in the center of the chest.
    Ellipsoidal (Condyloid) Joints
    e.g., wrist
    Frontal Bone
    Bone forming the forehead and upper part of the orbits.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Pelvic Floor Muscles
    Muscles that support pelvic organs.
    Tarsals (7 bones)
    7 ankle bones.
    Buccinator
    Muscle that helps with chewing and blowing air out.

    Coccyx

    Reviewed by our medical team

    Tailbone, the remnant of the tail in humans.

    1. Overview

    The coccyx, commonly known as the tailbone, is the terminal portion of the vertebral column. It is a small, triangular bony structure composed of 3 to 5 fused vertebrae, usually four. The coccyx is considered a vestigial structure, the remnant of a tail in humans, but it still plays important roles in posture, muscle attachment, and weight-bearing when sitting. Despite its small size, injury or dysfunction of the coccyx can lead to significant pain and discomfort.

    2. Location

    The coccyx is located at the inferior end of the vertebral column:

    • Superiorly: Articulates with the sacrum at the sacrococcygeal joint.

    • Inferiorly: Ends in an apex that may be slightly curved or pointed.

    • Posteriorly: Lies just beneath the skin at the base of the spine.

    In seated posture, it is positioned anterior to the gluteal cleft and can be palpated externally.

    3. Structure

    The coccyx is typically made up of four small fused vertebrae (Co1–Co4), though variation exists:

    • Co1: The largest and most prominent segment, often retains rudimentary transverse processes and may articulate with the sacrum.

    • Co2–Co4: Progressively smaller; lack true pedicles, laminae, and spinous processes.

    • Sacrococcygeal joint: A fibrocartilaginous joint (sometimes synovial) between the sacrum and coccyx; may become fused with age.

    • Ligamentous support: Includes the anterior and posterior sacrococcygeal ligaments and the intercornual ligament connecting the sacral and coccygeal cornua.

    4. Function

    The coccyx serves several biomechanical and support functions:

    • Supports weight in sitting: Helps bear body weight when seated, especially when leaning backward.

    • Muscle and ligament attachment: Serves as an anchor for several pelvic floor muscles and ligaments.

    • Shock absorption: Acts as a slight buffer or flex point during falls or sudden seating pressure.

    5. Physiological role(s)

    Despite being vestigial, the coccyx plays important physiological roles:

    • Pelvic floor support: Provides attachment for muscles such as the levator ani, coccygeus, and external anal sphincter, which support pelvic organs and control continence.

    • Postural balance: Contributes to distribution of pressure and posture during sitting and dynamic movement.

    • Parturition (childbirth): May move slightly backward to increase the pelvic outlet during vaginal delivery.

    6. Clinical Significance

    The coccyx can be a source of clinical concern, especially in cases of trauma or dysfunction:

    • Coccydynia (tailbone pain):

      • Pain in the coccygeal region, often from falls, prolonged sitting, childbirth, or idiopathic causes.

      • May involve inflammation, dislocation, or spasm of surrounding muscles (e.g., coccygeus, levator ani).

    • Fracture or dislocation:

      • Results from direct trauma (e.g., falling onto a hard surface); can be very painful and slow to heal.

    • Hyper- or hypomobility:

      • Excessive or restricted movement at the sacrococcygeal joint may cause chronic pain or functional limitations.

    • Surgical consideration:

      • In rare, refractory cases of coccydynia, coccygectomy (surgical removal of the coccyx) may be considered.

    • Referred pain:

      • Pelvic floor dysfunction or nerve entrapment in the region may mimic coccygeal pain and require differential diagnosis.

    Did you know? The metatarsals are the bones in the feet that connect to the toes.