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    Related Topics

    From Musculoskeletal System

    Phalanges (14 bones)
    14 bones forming the toes.
    Saddle Joints
    e.g., thumb joint
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Sartorius
    Longest muscle in the body responsible for hip flexion.
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
    Radius
    Forearm bone on the thumb side.
    Lacrimal Bones
    Bones forming part of the eye socket and housing the tear ducts.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Nasal Bones
    Bones forming the bridge of the nose.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Flexor and Extensor Groups
    Muscles responsible for flexing and extending the hand and wrist.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Biceps Tendon
    Tendon that attaches the biceps muscle to the bone.
    Cranial Bones
    Bones of the skull that protect the brain.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Sesamoid Bones
    e.g., patella, some found in hands/feet.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Vomer Bone
    Bone forming the nasal septum.
    Adductors
    Muscles that bring the thighs toward the midline.
    Tibia
    Shin bone, the larger bone in the lower leg.

    Ischium

    Reviewed by our medical team

    Part of the pelvis that supports weight while sitting.

    1. Overview

    The ischium is one of the three bones that fuse to form the os coxae (hip bone), alongside the ilium and pubis. It forms the posteroinferior part of the pelvis and contributes to the formation of the acetabulum, the socket of the hip joint. The ischium plays an essential role in supporting body weight while sitting and serves as a major site of muscle and ligament attachment in the pelvic region.

    2. Location

    The ischium is located in the posterior and inferior part of the pelvis:

    • Inferiorly: Forms the lower and back portion of the hip bone.

    • Laterally: Contributes to the acetabulum, articulating with the femoral head.

    • Posteriorly: Forms the prominent bony structure of the buttocks (ischial tuberosity).

    • Medially: Bordered by the pubis and contributes to the boundary of the obturator foramen.

    3. Structure

    The ischium is composed of three main parts:

    • Body of the ischium: The thick upper portion that contributes to the acetabulum and supports the femoral head.

    • Superior ramus: Extends upward and forward from the body to help form the acetabulum.

    • Inferior ramus: Projects forward and joins the inferior ramus of the pubis, forming part of the pubic arch.

    Key anatomical landmarks include:

    • Ischial tuberosity: Large, roughened area that bears body weight during sitting; attachment site for hamstring muscles.

    • Ischial spine: Sharp bony projection between the greater and lesser sciatic notches; attachment point for the sacrospinous ligament.

    • Lesser sciatic notch: Below the ischial spine; forms part of the pathway for neurovascular structures entering the perineum.

    4. Function

    The ischium contributes to the pelvis both structurally and functionally:

    • Supports sitting posture: The ischial tuberosities support the body’s weight when seated.

    • Forms part of the acetabulum: Participates in forming the socket for the hip joint, allowing articulation with the femur.

    • Serves as an attachment site: Several important muscles (e.g., hamstrings, adductor magnus) and ligaments attach to the ischium.

    • Assists in pelvic stability: Provides structural support to the lower pelvis during movement and weight-bearing activities.

    5. Physiological role(s)

    Though a bony structure, the ischium indirectly supports several physiological processes:

    • Locomotion: As a part of the pelvis and hip joint, it transmits muscular force and supports lower limb movement.

    • Weight distribution: Distributes the body’s weight when seated and during movement via the pelvic girdle.

    • Muscle coordination: Anchors muscles involved in walking, running, and posture maintenance.

    • Childbirth (in females): The ischial spines are important obstetric landmarks for determining pelvic outlet size.

    6. Clinical Significance

    The ischium is clinically significant in multiple conditions and anatomical assessments:

    • Ischial bursitis:

      • Also known as “weaver’s bottom,” results from prolonged sitting or trauma over the ischial tuberosity, leading to inflammation of the bursa.

    • Pelvic fractures:

      • High-impact trauma (e.g., motor vehicle accidents) can cause fractures of the ischium, especially in conjunction with acetabular or pubic fractures.

    • Hamstring avulsion:

      • Forceful contraction of hamstring muscles may avulse their origin from the ischial tuberosity, especially in athletes.

    • Pressure ulcers:

      • Common in immobilized patients due to prolonged pressure on the ischial tuberosities while seated or bedridden.

    • Obstetric assessments:

      • Ischial spines are used to assess fetal descent during labor, as they form the narrowest diameter of the pelvic outlet.

    Did you know? Your spinal cord is protected by the vertebral column.