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    From Musculoskeletal System

    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Diaphragm
    Primary muscle for breathing.
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Lacrimal Bones
    Bones forming part of the eye socket and housing the tear ducts.
    Quadriceps Tendon
    Tendon that connects the quadriceps to the patella.
    Lateral Collateral Ligament (LCL)
    Knee ligament that stabilizes the outer knee.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Occipital Bone
    Bone forming the back and base of the skull.
    Deltoid
    Shoulder muscle responsible for arm abduction.
    Pectoralis Major
    Chest muscle responsible for shoulder movement.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.
    Sternum
    Breastbone located in the center of the chest.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Sutures (in the skull)
    Fibrous joints between skull bones.
    Radius
    Forearm bone on the thumb side.
    Skull
    Bony structure of the head that encases the brain.
    Anterior Longitudinal Ligament
    Spinal ligament running along the front of the vertebral column.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Ischium
    Part of the pelvis that supports weight while sitting.

    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? Tendons attach muscles to bones.