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    Related Topics

    From Musculoskeletal System

    Sartorius
    Longest muscle in the body responsible for hip flexion.
    Anterior Longitudinal Ligament
    Spinal ligament running along the front of the vertebral column.
    Rotator Cuff Tendons
    Tendons of the rotator cuff muscles.
    Iliolumbar Ligament
    Ligament connecting the ilium and lumbar vertebrae.
    Phalanges (14 bones)
    14 bones forming the toes.
    Lateral Collateral Ligament (LCL)
    Knee ligament that stabilizes the outer knee.
    Triceps Brachii
    Muscle responsible for elbow extension.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Saddle Joints
    e.g., thumb joint
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Posterior Longitudinal Ligament
    Spinal ligament running along the back of the vertebral column.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Wormian Bones
    Sutural bones in the skull.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Coccygeus
    Pelvic floor muscle supporting the coccyx.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Ligamentum Flavum
    Spinal ligament connecting the laminae of adjacent vertebrae.
    Masseter
    Muscle that elevates the mandible.
    Rectus Abdominis
    Abs muscle that flexes the trunk.
    Tibialis Anterior
    Muscle that dorsiflexes and inverts the foot.
    Nasal Bones
    Bones forming the bridge of the nose.
    Medial Collateral Ligament (MCL)
    Knee ligament that stabilizes the inner knee.
    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.

    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? Your skeleton is 5 times stronger than steel.