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    From Musculoskeletal System

    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.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Phalanges (14 bones)
    14 bones forming the toes.
    Ligamentum Flavum
    Spinal ligament connecting the laminae of adjacent vertebrae.
    Rotator Cuff Muscles
    Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Ethmoid Bone
    Bone forming part of the nasal cavity and the orbit.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Tibialis Anterior
    Muscle that dorsiflexes and inverts the foot.
    Sacrum
    Triangular bone at the base of the spine.
    Tarsals (7 bones)
    7 ankle bones.
    Quadriceps
    Rectus Femoris, Vastus Medialis, Vastus Lateralis, Vastus Intermedius.
    Gastrocnemius
    Calf muscle responsible for plantarflexion of the foot.
    Clavicle
    Collarbone connecting the arm to the body.
    Posterior Longitudinal Ligament
    Spinal ligament running along the back of the vertebral column.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    Mandible
    Lower jawbone that houses the teeth.
    Occipital Bone
    Bone forming the back and base of the skull.
    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.

    Acromioclavicular Ligament

    Reviewed by our medical team

    Ligament that connects the acromion to the clavicle.

    1. Overview

    The acromioclavicular (AC) ligament is a small but critical ligament that supports the acromioclavicular joint—where the clavicle (collarbone) meets the acromion of the scapula. This ligament functions to stabilize the joint and limit horizontal movement of the clavicle. Though small in size, the AC ligament plays an important role in maintaining upper limb alignment and transmitting forces from the arm to the axial skeleton. Injury to this ligament is common in contact sports and is often referred to as a shoulder separation.

    2. Location

    The acromioclavicular ligament is located at the superior aspect of the shoulder:

    • Proximally: Attaches to the lateral end of the clavicle.

    • Distally: Connects to the medial margin of the acromion process of the scapula.

    • Forms the roof of the acromioclavicular joint and lies just deep to the skin and subcutaneous tissue in this region.

    It is part of a complex joint structure that includes the acromion, clavicle, and supporting capsule and ligaments.

    3. Structure

    The acromioclavicular ligament is composed of dense regular connective tissue and consists of two main parts:

    • Superior acromioclavicular ligament:

      • Stronger and more functionally important; provides horizontal stability.

      • Reinforced by the fibers of the deltoid and trapezius muscles.

    • Inferior acromioclavicular ligament:

      • Thinner and less developed; may assist in maintaining joint integrity.

    The ligament blends with the fibrous capsule of the acromioclavicular joint and provides static support against translational forces.

    4. Function

    The acromioclavicular ligament serves several vital mechanical functions:

    • Stabilizes the acromioclavicular joint: Maintains articulation between the clavicle and scapula.

    • Prevents excessive horizontal movement: Especially anterior and posterior displacement of the clavicle relative to the acromion.

    • Supports shoulder girdle integrity: Helps transmit loads from the upper limb to the axial skeleton.

    5. Physiological role(s)

    Beyond its static structural role, the acromioclavicular ligament contributes to:

    • Dynamic shoulder mechanics: Works in concert with the coracoclavicular ligaments and joint capsule to allow controlled movement of the scapula during arm elevation and rotation.

    • Force transmission: Transfers stresses from the limb during lifting, throwing, or pushing activities.

    • Proprioception: Contains mechanoreceptors that aid in joint position sense and muscular coordination during complex upper limb movements.

    6. Clinical Significance

    The acromioclavicular ligament is clinically significant due to its vulnerability in shoulder trauma:

    • AC joint sprain (shoulder separation):

      • Commonly caused by a fall onto the shoulder or direct impact; graded from Type I to Type VI based on ligament involvement and displacement.

      • Type I: Partial tear of AC ligament; no visible displacement.

      • Type II: Complete tear of AC ligament; partial injury to coracoclavicular ligaments.

      • Type III+: Complete disruption of both AC and coracoclavicular ligaments with visible deformity and instability.

    • Clinical signs:

      • Tenderness, swelling, a prominent “step-off” at the AC joint, and pain with shoulder movement.

    • Diagnosis:

      • Clinical exam with imaging (X-rays, sometimes MRI) to assess ligament integrity and joint displacement.

    • Treatment:

      • Type I–II injuries: Conservative (rest, ice, sling, physiotherapy).

      • Type III+: May require surgical reconstruction, especially in athletes or individuals with persistent dysfunction.

    • Degenerative changes:

      • Chronic overuse or minor injuries can lead to osteoarthritis of the AC joint, often seen in weightlifters and older adults.

    Did you know? The knee is the largest joint in the body.