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    Related Topics

    From Musculoskeletal System

    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Mandible
    Lower jawbone that houses the teeth.
    Patella
    Knee cap, protecting the knee joint.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Occipital Bone
    Bone forming the back and base of the skull.
    Sphenoid Bone
    Bone forming part of the base of the skull and sides of the orbits.
    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Quadriceps Tendon
    Tendon that connects the quadriceps to the patella.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Rectus Abdominis
    Abs muscle that flexes the trunk.
    Anterior Longitudinal Ligament
    Spinal ligament running along the front of the vertebral column.
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Vomer Bone
    Bone forming the nasal septum.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Masseter
    Muscle that elevates the mandible.
    Gastrocnemius
    Calf muscle responsible for plantarflexion of the foot.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Medial Collateral Ligament (MCL)
    Knee ligament that stabilizes the inner knee.
    Ulna
    Forearm bone on the pinky side.
    Ligamentum Flavum
    Spinal ligament connecting the laminae of adjacent vertebrae.
    Soleus
    Calf muscle responsible for plantarflexion of the foot.
    Flexor Tendons
    Tendons that help flex the fingers and toes.

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