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    From Musculoskeletal System

    Masseter
    Muscle that elevates the mandible.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Gliding (Plane) Joints
    e.g., between carpals
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Iliolumbar Ligament
    Ligament connecting the ilium and lumbar vertebrae.
    Temporal Bones
    Bones forming the lower sides of the skull and housing the ears.
    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Biceps Tendon
    Tendon that attaches the biceps muscle to the bone.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    Frontal Bone
    Bone forming the forehead and upper part of the orbits.
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Patellar Tendon
    Tendon connecting the patella to the tibia.
    Triceps Brachii
    Muscle responsible for elbow extension.
    Saddle Joints
    e.g., thumb joint
    Sartorius
    Longest muscle in the body responsible for hip flexion.
    Rotator Cuff Muscles
    Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Tarsals (7 bones)
    7 ankle bones.
    Phalanges (14 bones)
    14 bones forming the toes.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Vomer Bone
    Bone forming the nasal septum.
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    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.
    Tibia
    Shin bone, the larger bone in the lower leg.

    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 pelvic girdle consists of the ilium, ischium, and pubis.