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    From Musculoskeletal System

    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Masseter
    Muscle that elevates the mandible.
    Extensor Tendons
    Tendons that help extend the fingers and toes.
    Acromioclavicular Ligament
    Ligament that connects the acromion to the clavicle.
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Sternocleidomastoid
    Muscle that rotates and flexes the neck.
    Hinge Joints
    e.g., elbow, knee
    Saddle Joints
    e.g., thumb joint
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Radius
    Forearm bone on the thumb side.
    Tarsals (7 bones)
    7 ankle bones.
    Cranial Bones
    Bones of the skull that protect the brain.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.
    Sutures (in the skull)
    Fibrous joints between skull bones.
    Medial Collateral Ligament (MCL)
    Knee ligament that stabilizes the inner knee.
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    Ulna
    Forearm bone on the pinky side.
    Anterior Longitudinal Ligament
    Spinal ligament running along the front of the vertebral column.
    Temporalis
    Muscle involved in closing the jaw.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    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.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.

    Sacroiliac Ligaments

    Reviewed by our medical team

    Ligaments connecting the sacrum to the iliac bones.

    1. Overview

    The sacroiliac (SI) ligaments are a group of strong, fibrous structures that stabilize the sacroiliac joints—the articulations between the sacrum and the ilium of the pelvis. These ligaments are essential for maintaining pelvic integrity, distributing weight from the upper body to the lower limbs, and limiting excessive motion at the SI joint, which is mostly an immobile or slightly mobile joint.

    2. Location

    The sacroiliac ligaments are located in the posterior pelvis, surrounding the sacroiliac joints:

    • Connect: The sacrum (S1–S4 vertebrae) to the ilium of each hip bone.

    • Span: From the lateral sacral surface to the ilial auricular surface and iliac tuberosity.

    • Lie posterior to: The sacroiliac joint capsule and anterior pelvic organs.

    3. Structure

    There are several distinct sacroiliac ligaments, classified into anterior, interosseous, and posterior groups:

    • Anterior sacroiliac ligament:

      • A thin, broad band located on the anterior surface of the joint capsule.

      • Connects the anterior sacral ala to the ilium's auricular surface.

    • Interosseous sacroiliac ligament:

      • The strongest and deepest of the SI ligaments.

      • Occupies the space between the sacrum and the ilium posterior to the joint.

      • Provides the primary stabilization of the SI joint.

    • Posterior sacroiliac ligament:

      • Located on the dorsal surface of the sacrum and ilium.

      • Subdivided into short (horizontal) and long (oblique) portions.

      • Attaches from the sacral tubercles to the posterior superior iliac spine (PSIS) and iliac crest.

    These ligaments are composed of densely packed collagen fibers capable of resisting high tensile loads and shear forces.

    4. Function

    The sacroiliac ligaments provide essential structural and mechanical functions:

    • Stabilize the sacroiliac joint: Limit anterior and inferior movement of the sacrum relative to the ilium.

    • Distribute mechanical load: Transfer weight from the spine to the pelvic girdle and lower limbs.

    • Resist shear forces: Prevent displacement during twisting, lifting, or shifting motions.

    • Anchor pelvic structures: Support the connection between the axial and appendicular skeletons.

    5. Physiological role(s)

    Though passive in nature, sacroiliac ligaments contribute to:

    • Postural integrity: Maintain pelvic alignment during upright stance, walking, and load-bearing.

    • Shock absorption: Act as tension-bearing structures during spine and hip motion.

    • Pelvic movement regulation: Control minute joint glides (nutation and counternutation) needed for locomotion and childbirth.

    • Proprioception: Contain mechanoreceptors that help the nervous system regulate posture and movement.

    6. Clinical Significance

    Dysfunction or injury to the sacroiliac ligaments can lead to pain and mobility issues:

    • Sacroiliac joint dysfunction:

      • May result from ligamentous laxity, trauma, leg-length discrepancy, or poor biomechanics.

      • Presents as lower back or buttock pain, sometimes radiating to the thigh.

    • Sacroiliitis:

      • Inflammation of the SI joint, often involving the ligaments; associated with conditions like ankylosing spondylitis and other spondyloarthropathies.

    • Ligament strain or tear:

      • Can occur from sudden rotational forces, lifting injuries, or falls.

      • May cause acute localized pain, swelling, and tenderness over the SI joint.

    • Pregnancy-related pelvic pain:

      • Hormonal relaxation of the sacroiliac ligaments increases joint mobility, which can result in pain and instability.

    • Injection or surgical intervention:

      • SI joint injections target inflammation involving these ligaments.

      • Fusion surgery may be considered for chronic, treatment-resistant SI joint instability.

    Did you know? The human body has over 600 muscles.