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Anterior Cruciate Ligament (ACL) Injury

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An anterior cruciate ligament injury occurs when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn. The most common injury is a complete tear. Symptoms include pain, a popping sound during injury, instability of the knee, and joint swelling.

    Knee is responsible for absorbing shock and providing stability when in motion.

    Knee is stablises by medial collateral ligament, lateral collateral ligament, posterior cruciate ligament, and anterior cruciate ligament.

    Athletes that participate in highly demanding sports such as soccer, football, basketball, and netball are more likely to sustain an ACL injury.

    The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments. ACL crosses the posterior cruciate ligament to form an “X”. It is composed of strong, fibrous material and assists in controlling excessive motion.

    Women are at greater risk of ACL injury due to the gender specific changes that occur at the onset of puberty.

    Relevant anatomy of ACL

    The ACL arises from the anteromedial aspect of the intercondylar area on the tibial plateau and passes upwards and backwards to attach to the posteromedial aspect of the lateral femoral condyle. ACL which runs diagonally through the knee, from the lateral aspect of the femur to the medial tibia.The ACL ranges from 25 to 35 mm in length, approximately 10 mm in breadth, and 4 to 10 mm in width

    Anatomy of ACL

  1. Ligaments consist of fibroblast cells and the extracellular matrix (ECM).

  2. Fibroblasts are immature , Large, Flat, and Branched cells that have retained the ability to divide. and secrete collagen fibers and ground substance that constitutes the ECM.

  3. Collagen fibers are regularly arranged bundles of fibers in a parallel pattern. This arrangement provides mechanical resistance to pull force along the axis of fibers.

    Ground substance forms the matrix and has multiple functions such as storing water,serving as a medium for the exchange of materials between cells and blood and controls the overall metabolic activity of the tissue.

    Bundles of ACL

    ACL is composed of two principal parts: small anteromedial Band(AMB) and a larger bulky posterolateral Band (PLB)

  4. The AMB is responsible for the posterior translation of the femur at flexion, and the PLB resists hyperextension and prevents posterior translation of the femur in extension .

  5. Anteromedial bundle is tight in flexion, attaches to roof of intercondylar notch.

    Posterolateral bundle is tight in extension , attaches to wall of intercondylar notch.

    Injury of ACL

    A ligament is a tough, flexible and strong band of tissue that holds bones and cartilage together within your knee and tissue that help connect your thigh bone (femur) to your shinbone (tibia).

    It prevents the shin bone from sliding out in front of the thigh bone.as it resists anterior tibial translation and rotational loads.

    ACL Torn

    The anterior cruciate ligament (ACL) can be torn by hyperextension of the knee joint, or by the application of a large force to the back of the knee with the joint partly flexed.

    The ACL stabilizes your knee, so tearing it either partially or completely can cause pain and swelling.

    Younger athletes usually sustain growth plate injuries (avulsion fractures) rather than ligamentous injuries because of the relative weakness of the cartilage at the epiphyseal plate compared with the ACL.

    Mechanism of injury

    ACL injury occurs when an excessive tension force is applied on the ACL. A non‐contact ACL injury occurs when a person themselves generates great forces or moments at the knee that apply excessive loading on the ACL.

    70% of knee injuries are Non-Contact with knee in "Dynamic Valgus Position"

    Dynamic Valgus Position

    Anterior shear force at the proximal end of the tibia is a major contributor to ACL loading, whereas valgus, varus and internal rotation moments of the knee can increase ACL loading when an anterior shear force is applied to the proximal end of the tibia.

    According to these ACL loading mechanisms, a small knee flexion angle, a strong quadriceps muscle contraction or a great posterior ground reaction force can increase ACL loading.

    Why are Women more at risk of ACL injury ?

    More Riks of ACL in Woman

    Women are at greater risk of ACL injury due to the gender specific changes that occur at the onset of puberty. Due to the genetic bone structure, Females are predisposed to valgus forces at the knee due to their wider hips. It is also know that Female athletes are generally not as strong as their Male counterparts, who receive a dose of testosterone, ILGF and growth hormone during puberty that contributes to the increase in strength, and therefore dynamic knee stability.

  6. Female athletes had a higher incidence of ACL injuries compared with their male counterparts. the incidence in female athletes is two to eight times higher than in males in soccer, basketball and volleyball.
  7. Risk Factor

    Most ACL injuries occur when an anterior force is applied to the tibia.

    Injuries to the anterior cruciate ligament (ACL) are immediately disabling and are associated with long-term consequences, such as posttraumatic osteoarthritis..

    There are a number of factors that increase your risk of an ACL injury, including:

    Risk Involving games

    1. Being female: The rate of ACL injuries is higher in female athletes than in males possibly due to differences in anatomy, muscle strength and hormonal influences.
    2. Participating in certain sports: Commonly occur in sports such as basketball, soccer, football, volleyball, downhill skiing, lacrosse, and tennis. These sports require frequent and sudden deceleration, such as cutting, pivoting, or landing on one leg.
    3. Previously torn ACL
    4. Age: ACL tears are most common between the ages of 15 and 45, mostly due to the more active lifestyle and higher participation in sports.
    5. Using faulty movement patterns
    6. Wearing unfit clothes during playing, may cause uncomforatbly.

    When the ACL is torn, vessels that feed the ligament can fill the joint space with blood in a condition known as hemarthrosis. This causes the swelling as well as redness, warmth, bruising, and a bubbling sensation in the joint.

    Biomechanism of Knee Joint in Stair Climbing

    • Level walking involves up to 30° flexion at the knee joint but during stair climbing, the knee flexion angle varies from 60° to 135°, depending on the height of each stair and Quadriceps contract eccentrically during knee flexion.

    • The center of rotation (CoR) of the knee joint varies with respect to the angle of flexion. For the first 30° of flexion, femoral condyle undergoes minimal anterior translation. Between 30° and 135°, the femoral condyle undergoes larger anterior translation.

    Biomechanism of Knee joint

    Hamstring muscle force (HAMS), Gastrocnemius muscle force (GAS), Patellar tendon muscle force (PT), Tibiofemoral force (TF)

    Hamstring muscles are attached behind the knee and therefore apply a posterior shear force on the tibia and this force depends upon the magnitude and direction of the individual forces. The highest shear forces at ACL occur during hyperextension (−5° of flexion) of the knee joint.

    Hamstring muscles are attached behind the knee. The shear force due to the patellar tendon (high quadriceps force) has the largest share in determining the total shear force and occurs during the contralateral toe off (CTO).

    Symptoms of ACL Injury

    • A "popping" sound at the time of injury).

    • Knee swelling within 6 hours of injury).

    • Pain, especially when you try to put weight on the injured leg).

    • Difficulty in continuing with your sport).

    • Reduced range of motion).

    • Joint tenderness).

    • Initial inability to weight bear, which improves in a short period).

    • Knee felt to "gives way" especially during pivoting movement).

    What causes ACL injuries?

    ACL injuries typically happen while playing sports. Athletic moves that strain the knee include:-
    • Changing direction rapidly
    • Stopping suddenly while speedly running
    • Faulty landing
    • Participating in high demand game with reletively poor condition
    • Slowing down or stopping suddenly
    • Jumping and landing
    • Contact and collisions


    Grades 1 ACL Injury

    • The ACL ligament is pulled, No tear.
    • No joint instability.
    • The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.

    Grades Sprains

    Grades 2 ACL Injury

    • Less than 50% fibres of the ACL are torn: Partial tear.
    • Minimal joint instability.
    • A Grade 2 Sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament.

    Grades 3 ACL Injury

    • 50-100% fibres of ACL are torn: Complete tear
    • Joint is unstable. Giving away sensation may be present
    • This type of sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces, and the knee joint is unstable.
    • As grade 3 tears involve complete disruption of the integrity of the ligament, people often feel a sudden sharp pain initially. It occurs most commonly with a popping sound.

    Diagnostic Procedure

    Physical Examination

    This type of assessment is probably the first evaluation you will undergo if you suspect an ACL tear.

    While diagnostic anatomical assesment are essential, they often rely on subjective factors such as the experience of the physician, muscle relaxation, and underlying knee variability. Physical diagnosis is particularly difficult in older patients and in patients with severe injury and soft-tissue swelling and guarding.

    The Lachman test is the most accurate test for detecting ACL injury, followed by the anterior drawer test and the pivot shift test.

    • Arthrometer / Laximeters
    • Radiography
    • MRI
    • Arthroscopy

    Note: The Lachman's Test is the most accurate test for detecting an ACL tear.

    Treatment Option



    Athletes who attempt nonoperative management and continue to play sports with a chronic ACL tear frequently develop persistent knee instability which presents as a shifting sensation.

    Your physical therapist will work with you to restore your muscle strength, agility, and balance, so you can return to your regular activities. Your physical therapist may teach you ways to modify your physical activity in order to put less stress on your knee. If you decide to have surgery your physical therapist can help you before and after the procedure.

    By undertaking a Rehabilitation program, it is possible to function normally without having surgery to reconstruct a torn ACL.

    Physical therapy before surgery

    In nonsurgical treatment, progressive physical therapy and rehabilitation can restore the knee to a condition close to its pre-injury state and educate the patient on how to prevent instability.

    Nonsurgical management of isolated ACL tears is likely to be successful or may be indicated in patients:-

    • With partial tears and no instability symptoms
    • With complete tears and no symptoms of knee instability during low-demand sports who are willing to give up high-demand sports
    • Who do light manual work or live sedentary lifestyles
    • Whose growth plates are still open

    Before any treatment, encourage strengthening of the quadriceps and hamstrings, as well as range of motion (ROM) exercises. Performance of ROM helps reduce the amount of effusion and helps the patient regain motion and strength.It may include treatments such as gentle electrical stimulation applied to the quadriceps muscle.

    The rehab program consisted of single- and multiple-joint exercises; open and closed kinetic chain exercises; and concentric, eccentric, and isometric exercises with 3 to 4 sets and 6 to 8 repetitions per exercise. Plyometric exercises were gradually progressed.

    A trial of conservative management may be considered if the patient has few giving-way episodes, near normal range of motion on knee extension, minimal or no meniscal damage on magnetic resonance imaging, strong quadriceps femoris.

    Treatment After Surgery

    Icing and compression

    Immediately following surgery, your physical therapist will control your swelling with a cold application, such as an ice sleeve, that fits around your knee and compresses it.


    Some people with a damaged ACL can get by with wearing a brace on their knee when they run or play sports. It provides extra support.nSome surgeons will give you a brace to limit your knee movement (range of motion) following surgery. Your physical therapist will fit you with the brace and teach you how to use it safely. Some athletes will be fitted for braces as they recover and begin to return to their sports activities.

    Knee Brace

    Bearing weight

    You will use crutches to walk. The amount of weight you are allowed to put on your leg and how long you use the crutches will depend on the type of reconstructive surgery you have received. Your physical therapist will design a treatment program to meet your needs and gently guide you toward full weight bearing.

    Supportive Walker

    Movement exercises

    Movement exercises help with increasing blood flow, which also helps reduce swelling.your physical therapist will help you begin to regain motion in the knee area, and teach you gentle exercises you can do at home. The focus will be on regaining full movement of your knee.

    Electrical stimulation

    Your physical therapist may use electrical stimulation to help restore your thigh muscle strength, and help you achieve those last few degrees of knee motion.

    Strengthening exercises

    Your physical therapist will help you increase your ability to put weight on your knee, using a combination of weight-bearing and non-weight-bearing exercises. The exercises will focus on your thigh muscles (quadriceps and hamstrings) and might be limited to a specific range of motion to protect the new ACL.

    Balance exercises 

    Your physical therapist will guide you through exercises on diffrent surfaces to help restore your balance and coordination. Initially,by the exercises you will learn how to shift weight on to the surgery leg.

    To prevent ACL injuries

    Athletes should participate in neuromuscular and proprioceptive strengthening and conditioning programs. These should include plyometric exercises and coaching regarding proper positioning while landing.

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