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    Related Topics

    From Musculoskeletal System

    Acromioclavicular Ligament
    Ligament that connects the acromion to the clavicle.
    Coccyx
    Tailbone, the remnant of the tail in humans.
    Sternum
    Breastbone located in the center of the chest.
    Radius
    Forearm bone on the thumb side.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Ischium
    Part of the pelvis that supports weight while sitting.
    Pubis
    Part of the pelvis that joins with the opposite side to form the pubic symphysis.
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Cranial Bones
    Bones of the skull that protect the brain.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Gliding (Plane) Joints
    e.g., between carpals
    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).
    Diaphragm
    Primary muscle for breathing.
    Brachioradialis
    Muscle responsible for forearm flexion.
    Ulna
    Forearm bone on the pinky side.
    Patella
    Knee cap, protecting the knee joint.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Mandible
    Lower jawbone that houses the teeth.
    Deltoid
    Shoulder muscle responsible for arm abduction.

    Anterior Cruciate Ligament (ACL)

    Reviewed by our medical team

    Knee ligament that stabilizes the joint.

    1. Overview

    The Anterior Cruciate Ligament (ACL) is one of the key ligaments of the knee joint, providing critical stability during dynamic movements. It connects the femur (thigh bone) to the tibia (shin bone) and is primarily responsible for preventing anterior translation and excessive rotation of the tibia. The ACL is frequently injured in athletes and active individuals, often requiring surgical intervention and extensive rehabilitation. It plays a crucial role in maintaining joint integrity during running, jumping, pivoting, and decelerating activities.

    2. Location

    The ACL is located within the knee joint capsule, in the center of the knee:

    • Origin: Posteromedial aspect of the lateral femoral condyle.

    • Insertion: Anterior intercondylar area of the tibia, just medial to the tibial eminence.

    • It courses inferiorly, anteriorly, and medially from femur to tibia, crossing with the Posterior Cruciate Ligament (PCL) to form an "X" shape.

    The ACL resides intra-articularly but extra-synovially, meaning it is inside the joint capsule but outside the synovial lining.

    3. Structure

    The ACL is a dense, fibrous connective tissue composed mainly of Type I collagen fibers, giving it tensile strength:

    • Length: ~32–38 mm

    • Width: ~7–12 mm

    • Two functional bundles:

      • Anteromedial (AM) bundle: Tight in flexion; controls anterior translation.

      • Posterolateral (PL) bundle: Tight in extension; controls rotational stability.

    • Blood supply: Mainly from the middle genicular artery.

    • Innervation: Provided by branches of the tibial nerve; includes mechanoreceptors for proprioception.

    4. Function

    The ACL provides essential mechanical and dynamic stabilization of the knee:

    • Prevents anterior translation of the tibia relative to the femur, especially during deceleration.

    • Limits internal rotation of the tibia on the femur.

    • Restricts hyperextension and valgus stress in certain positions.

    • Supports joint proprioception, allowing coordinated muscular responses to loading.

    5. Physiological role(s)

    Beyond simple restraint, the ACL contributes to:

    • Dynamic neuromuscular control: Works with hamstrings and quadriceps to maintain functional stability during motion.

    • Proprioceptive feedback: Mechanoreceptors within the ACL detect stretch and position changes, signaling the central nervous system to activate stabilizing muscles.

    • Joint congruency: Maintains optimal alignment of articular surfaces under load-bearing activities.

    • Injury prevention: Acts as a first-line defense against excessive anterior and rotational knee forces in high-impact sports.

    6. Clinical Significance

    ACL injuries are among the most common and debilitating injuries in sports and orthopedic practice:

    • ACL tear/rupture:

      • Usually non-contact, caused by sudden deceleration, pivoting, or landing awkwardly from a jump.

      • Symptoms: Popping sensation, rapid swelling, knee instability, and pain with weight-bearing.

      • Diagnosis: Clinical tests (Lachman test, anterior drawer, pivot shift), MRI for confirmation.

    • ACL reconstruction:

      • Common surgical procedure using autograft (hamstring, patellar tendon) or allograft.

      • Postoperative rehab is extensive—typically 6–12 months before return to high-impact sports.

    • ACL injury risk factors:

      • Female athletes are at higher risk due to anatomical, hormonal, and neuromuscular factors.

      • Other risks: poor landing mechanics, muscle imbalances, weak hip/knee control.

    • Chronic ACL deficiency:

      • Can lead to recurrent instability, meniscal tears, and early-onset osteoarthritis if not addressed properly.

    • Preventive strategies:

      • Neuromuscular training programs to enhance landing, cutting, and jumping mechanics can reduce injury risk.

    Did you know? The coccyx is the remnant of the tailbone in humans.