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    Hinge Joints
    e.g., elbow, knee
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Acetabulum
    The acetabulum is the pelvic socket that connects with the femoral head to form the hip joint, vital for stability, movement, and weight-bearing.
    Radius
    Forearm bone on the thumb side.
    Diaphragm
    Primary muscle for breathing.
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Clavicle
    Collarbone connecting the arm to the body.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Lateral Collateral Ligament (LCL)
    Knee ligament that stabilizes the outer knee.
    Annular Ligament
    The annular ligament is a strong fibrous band encircling the head of the radius, stabilizing the proximal radioulnar joint and allowing smooth rotation of the forearm.
    Adductors
    Muscles that bring the thighs toward the midline.
    Tarsals (7 bones)
    7 ankle bones.
    Brachioradialis
    Muscle responsible for forearm flexion.
    Rotator Cuff Tendons
    Tendons of the rotator cuff muscles.
    Occipital Bone
    Bone forming the back and base of the skull.
    Sacrum
    Triangular bone at the base of the spine.
    Pivot Joints
    e.g., atlanto-axial joint
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Flexor and Extensor Groups
    Muscles responsible for flexing and extending the hand and wrist.
    Nasal Bones
    Bones forming the bridge of the nose.
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Gastrocnemius
    Calf muscle responsible for plantarflexion of the foot.
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Lacrimal Bones
    Bones forming part of the eye socket and housing the tear ducts.

    Coccygeus

    Reviewed by our medical team

    Pelvic floor muscle supporting the coccyx.

    1. Overview

    The coccygeus muscle, also known as the ischiococcygeus, is a small triangular muscle that forms part of the pelvic diaphragm. It is located posteriorly within the pelvis and works closely with the levator ani muscles to support the pelvic organs. Although relatively minor in size compared to other pelvic muscles, the coccygeus contributes to the structural integrity of the pelvic floor and assists in voluntary and reflexive functions related to posture and defecation.

    2. Location

    The coccygeus muscle is located in the posterior part of the pelvic floor:

    • Origin: Ischial spine of the hip bone.

    • Insertion: Lateral borders of the sacrum and coccyx (S5 to the coccygeal vertebrae).

    • Position: Lies posterior to the levator ani and anterior to the sacrospinous ligament, with which it blends closely.

    It forms the posterior portion of the pelvic diaphragm and bridges the gap between the sacrum and ischial spine.

    3. Structure

    The coccygeus is a flat, triangular, skeletal muscle with the following structural features:

    • Muscle fiber orientation: Directed superomedially from the ischial spine to the sacrum and coccyx.

    • Innervation: Branches of the anterior rami of spinal nerves S4 and S5.

    • Associated structures: The muscle is tightly associated with the sacrospinous ligament, often indistinguishable from it in dissection.

    • Blood supply: Inferior gluteal artery and branches from internal pudendal artery.

    4. Function

    The coccygeus muscle serves the following functions:

    • Supports pelvic viscera: Contributes to the structural integrity of the pelvic floor along with the levator ani.

    • Pulls coccyx forward: Assists in returning the coccyx to its normal position after defecation or childbirth.

    • Stabilizes the sacroiliac joint: Through its attachments and muscle tone, it supports pelvic alignment during movement.

    5. Physiological role(s)

    The coccygeus contributes to multiple physiological functions despite its small size:

    • Pelvic floor integrity: Acts with levator ani to support pelvic organs and prevent prolapse.

    • Continence mechanisms: Provides secondary support to the anal and urogenital sphincters during increased intra-abdominal pressure (e.g., coughing, lifting).

    • Defecation and childbirth: Assists in posterior movement of the coccyx to widen the pelvic outlet, then helps restore its position.

    • Postural role: Helps maintain upright posture by supporting pelvic tilt and pelvic base alignment.

    6. Clinical Significance

    Although less frequently discussed than other pelvic muscles, the coccygeus has several clinical considerations:

    • Coccygodynia (coccyx pain):

      • Strain or spasm of the coccygeus may contribute to tailbone pain, especially after trauma or prolonged sitting.

    • Pelvic floor dysfunction:

      • Weakness or imbalance involving the coccygeus can be part of broader pelvic floor disorders, including prolapse or fecal incontinence.

    • Postpartum changes:

      • The coccygeus may become overstretched or damaged during vaginal childbirth, contributing to postpartum pelvic pain.

    • Surgical relevance:

      • Understanding its location is important in sacrospinous ligament fixation procedures for pelvic organ prolapse repair.

    • Palpation and therapy:

      • Can be accessed through internal pelvic floor therapy techniques to manage chronic pelvic pain or myofascial dysfunction.

    Did you know? Tendons attach muscles to bones.