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    From Musculoskeletal System

    Sternum
    Breastbone located in the center of the chest.
    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Soleus
    Calf muscle responsible for plantarflexion of the foot.
    Biceps Tendon
    Tendon that attaches the biceps muscle to the bone.
    Sternocleidomastoid
    Muscle that rotates and flexes the neck.
    Masseter
    Muscle that elevates the mandible.
    Pectoralis Major
    Chest muscle responsible for shoulder movement.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Interspinous Ligament
    Spinal ligament between adjacent vertebral spinous processes.
    Pivot Joints
    e.g., atlanto-axial joint
    Extensor Tendons
    Tendons that help extend the fingers and toes.
    Ligamentum Flavum
    Spinal ligament connecting the laminae of adjacent vertebrae.
    Cranial Bones
    Bones of the skull that protect the brain.
    Ilium
    Uppermost and largest part of the hip bone.
    Anterior Longitudinal Ligament
    Spinal ligament running along the front of the vertebral column.
    Nasal Bones
    Bones forming the bridge of the nose.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    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.
    Saddle Joints
    e.g., thumb joint
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Sphenoid Bone
    Bone forming part of the base of the skull and sides of the orbits.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Occipital Bone
    Bone forming the back and base of the skull.

    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 clavicle is the only bone in the body that connects the arm to the body trunk.