ACL Injury

Overview

Anterior cruciate ligament (ACL) injury is a tear or sprain of one of the four main ligaments in the knee. The ACL connects the thighbone (femur) to the shinbone (tibia) and provides stability to the knee. This ligament prevents the knee from moving excessively and ensures the joint stays in place especially during rotational movements.

ACL injuries usually occur during sports. They are very common in basketball, soccer, skiing, and other sports requiring sudden pivoting, stopping, or jumping. A "popping" sound is usually heard at the moment of injury and the knee swells suddenly. The person feels looseness in the knee and has difficulty bearing weight.

ACL injuries can be mild, moderate, or severe. In mild injuries, the ligament is stretched but not torn (sprain). In moderate injuries, the ligament is partially torn. In severe injuries, the ligament is completely ruptured. In complete ruptures, the ligament usually does not heal on its own and surgery may be required.

Treatment varies depending on the severity of the injury, the person's age, activity level, and general health condition. Some people can recover with physical therapy. Active athletes or young patients usually have surgery. The post-surgical rehabilitation process takes 6-12 months.

ACL injuries are very common in athletes. Women are 2-8 times more at risk than men. This difference is related to anatomical factors, hormones, and movement patterns.

Symptoms

ACL injury symptoms usually appear suddenly. Characteristic symptoms develop at the moment of injury or immediately after.

ACL injury symptoms include the following:

• "Popping" sound and sensation. A "pop" or "popping" sound is heard and felt in the knee at the moment of injury. This sound indicates the ligament has torn. The person themselves and people nearby can hear this sound. However, this sound may not occur in every ACL injury.
• Sudden and severe pain. Sharp and severe pain is felt in the knee at the moment of injury. The pain is so severe that the person cannot continue the activity. The pain may decrease somewhat within the first few hours but increases again when the knee is used.
• Rapid swelling. Within a few hours after injury (usually 2-6 hours), the knee swells noticeably. Swelling occurs due to bleeding (hemarthrosis) inside the knee joint. The knee feels warm and appears tense.
• Limited movement. Due to swelling and pain, inability to fully bend or straighten the knee occurs. Complete movement of the knee cannot be achieved. Especially full straightening of the knee becomes difficult.
• Instability and looseness sensation. The knee feels like it is "slipping" or "giving way." The person cannot trust their knee. Especially during turning movements or going down stairs, the knee may suddenly buckle. This instability sensation is one of the most characteristic symptoms of ACL injury.
• Difficulty bearing weight. Stepping on the injured leg is difficult or impossible. The person walks with a limp or cannot walk at all. Crutches may be needed.
• Tenderness at the joint line. There may be pain with touch on the inner or outer edges of the knee. This may also indicate meniscus injury because ACL injuries are frequently seen together with meniscus tears.

The severity of symptoms depends on the degree of injury. In partial tears, symptoms may be milder. In complete rupture, symptoms are very pronounced and the person becomes unable to play sports.

When to See a Doctor

ACL injury is a serious condition and must definitely be evaluated. Early diagnosis and treatment prevent long-term complications.

See a doctor urgently in the following situations:

• If severe pain and swelling develop after hearing a "popping" sound in the knee
• If you cannot move your knee
• If you cannot step on your injured leg at all
• If your knee feels like it is suddenly "giving way" or "coming out of place"
• If the knee is noticeably swollen
• If you have had a knee injury while playing sports

When ACL injury is suspected, it is important to see an orthopedic or sports medicine doctor within 24-48 hours. The initial evaluation determines the severity of the injury and shapes the treatment plan.

Causes

ACL injuries usually occur during sports activities. The ligament tears with sudden and powerful forces that exceed the knee's normal range of motion.

Mechanisms leading to ACL injury are as follows:

• Sudden change of direction and pivoting. This is the most common injury mechanism. When the body suddenly rotates while the foot is planted on the ground, the knee can turn inward and the ACL stretches. Common in sports like soccer, basketball, and tennis. Injury can occur when a person suddenly changes direction while running or turns to avoid an opponent.
• Sudden stopping. Suddenly stopping while running fast creates great stress on the ACL. If the foot is planted on the ground while the body's momentum continues, the knee can slide forward and the ligament can tear.
• Wrong landing. Landing incorrectly after jumping is a common cause of ACL injuries. Risk increases especially if landing is done with knees completely straight or turned inward. Common in volleyball and basketball players.
• Direct impact. Another athlete or object hitting the side of the knee can tear the ligament. Seen in soccer, rugby, and American football. However, most ACL injuries occur without contact.
• Hyperextension (excessive stretching). The knee extending backward more than normal can stretch or tear the ligament. Especially seen in skiing accidents.
• Valgus stress (inward bending). The knee collapsing inward and the foot turning outward creates stress on the ACL. This is an injury mechanism more commonly seen in women.

Approximately 70 percent of ACL injuries occur without contact, during the person's own movement. Usually multiple mechanisms come together (for example, sudden stopping and pivoting).

Risk Factors

Some people are at greater risk for anterior cruciate ligament injury. Knowing these factors enables taking preventive measures.

Risk factors for ACL injury are as follows:

• Sex. Women are 2-8 times more at risk than men. The reasons for this are as follows. Anatomical differences (wide hips, narrow notch, Q angle difference), hormonal factors (estrogen affects ligament flexibility), neuromuscular control differences (women land with less knee flexion), muscle strength and coordination differences.
• Type of sport. Sports containing sudden pivoting and jumping such as basketball, soccer, skiing, gymnastics, volleyball, and American football are high risk. Contact sports also increase risk.
• Weak muscle strength and imbalance. Especially hamstring (back thigh) muscles being weak compared to quadriceps (front thigh) muscles increases risk. Weakness of hip and core muscles also has an effect. Muscle fatigue raises injury risk.
• Poor movement technique. Knees collapsing inward, landing with straight knees, weak trunk control increase injury risk. Teaching correct movement patterns is protective.
• Previous injury history. Having had an ACL injury before increases new injury risk. There is risk for both the same knee and the opposite knee. Inadequate rehabilitation further increases risk.
• Surface and footwear. High-friction surfaces such as artificial turf or dry ground can cause the foot to get stuck. Inappropriate footwear also increases risk.
• Genetic factors. If there is a history of ACL injury in the family, risk increases slightly. Ligament structure and flexibility can be genetically influenced.
• Anatomical characteristics of the knee. Anatomical differences such as narrow intercondylar notch (the area where the ligament passes), increased tibial slope (shinbone inclination) can increase risk.

Diagnosis

Anterior cruciate ligament injury diagnosis is made with physical examination and imaging tests. An experienced doctor can diagnose most cases with physical examination.

The methods used in ACL injury diagnosis are as follows:

• Physical examination. The doctor evaluates the knee's range of motion, swelling, and tenderness. Special tests are performed. The Lachman test is the most reliable test for evaluating ACL integrity. While the patient lies on their back, the doctor checks the front-to-back mobility of the knee. The anterior drawer test is also applied similarly but is not as reliable as the Lachman. The pivot shift test evaluates the knee's stability during rotation. In these tests, more than normal movement and lack of a definite endpoint indicate ACL tear.
• Magnetic resonance imaging (MRI). This is the gold standard test in ACL injury diagnosis. It shows whether the ligament is torn, whether the tear is complete or partial, and accompanying injuries (meniscus, cartilage, other ligaments). MRI also provides valuable information for surgical planning.
• X-ray. Does not show ACL tear because ligaments are not visible on x-ray. However, it is taken to check for fractures. X-ray is important especially in young people because there may be avulsion fracture at the bone-ligament junction.
• Ultrasonography. Used in some centers but does not provide as detailed information as MRI. Can be useful in experienced hands.
• Arthroscopy. This is a direct viewing method by inserting a small camera into the knee. Generally not needed for diagnosis because MRI is sufficient. However, definitive diagnosis and treatment can be done together during surgery.

When making the diagnosis, accompanying injuries are also investigated. Approximately 50 percent of ACL tears have accompanying meniscus tear, 10-30 percent have collateral ligament injury, and some have cartilage damage.

Treatment

Anterior cruciate ligament injury treatment is personalized. The severity of the injury, the person's age, activity level, occupation, and general health condition affect the treatment decision.

The methods used in ACL injury treatment are as follows:

First aid (RICE protocol). Applied immediately after injury. Rest (rest) do not use the injured leg, do not bear weight. Ice (ice) apply ice for 15-20 minutes every 2-3 hours for the first 48-72 hours. Compression (compression) wrap the knee with an elastic bandage, do not tighten too much. Elevation (elevation) raise the leg above heart level. This method reduces swelling and pain.

Conservative (non-surgical) treatment. Surgery is not performed in some patients. Older patients, people with low activity levels, partial tears, or those who do not accept surgery are monitored with conservative treatment. The physical therapy program focuses on increasing the knee's strength and stability.

Especially hamstring and quadriceps muscles are strengthened. Knee brace or support can be used. Activity modification is done (avoiding high-risk sports). Conservative treatment can be successful but chronic instability may remain in the knee and the risk of meniscus or cartilage damage increases in the future.

Surgical treatment (ACL reconstruction). This is rebuilding the ligament. The torn ligament is not sewn because it does not heal. Instead, a new ligament is created using another tendon (graft) taken from the body.

The most commonly used grafts are as follows.

• Hamstring tendon (semitendinosus and gracilis) is taken from the back of the leg, it is the most widely used graft in ACL reconstruction.
• Patellar tendon (kneecap tendon) is taken from under the kneecap, it is very strong but there is a risk of anterior knee pain. Quadriceps tendon is taken from above the kneecap.
• Cadaver graft (allograft) is tissue taken from a donor, it is an option for those who do not want to use their own tissue.

ACL surgery is performed arthroscopically (closed method). Camera and instruments are inserted into the knee through small incisions. The graft is passed through tunnels opened in the bones and fixed with screws. Surgery takes 1-2 hours and discharge is usually the same day.

Treatment of accompanying injuries. If there is a meniscus tear, it is repaired or removed. If there is collateral ligament injury, it is treated. If there is cartilage damage, necessary procedures are applied.

When making the surgery decision, the following are considered. Young and active patients usually have surgery. Professional or serious amateur athletes have surgery. Those with recurrent instability episodes in the knee are surgery candidates. If there is accompanying meniscus or cartilage injury, surgery is preferred.

Rehabilitation. It is critically important in both conservative and surgical treatment. The physical therapy program is applied in stages. Post-surgical rehabilitation usually takes 6-12 months.

• In the first phase (0-6 weeks), reducing swelling, gaining range of motion, and quadriceps activation are targeted.
• In the second phase (6-12 weeks), muscle strength is increased, walking returns to normal.
• In the third phase (3-6 months), running and agility work begins.
• In the fourth phase (6-12 months), sport-specific exercises and return-to-sport preparation are done.

The return-to-sport decision is made through joint evaluation by the doctor, physiotherapist, and athlete.

Complications

ACL injury and its treatment can lead to some complications. Early and appropriate treatment reduces risks.

Complications that may be seen in ACL injury are as follows:

• Chronic knee instability. In untreated or inadequately treated ACL injuries, the knee remains chronically unstable. During daily activities, the knee "gives way" and the person may fall. Sports become impossible to play.
• Meniscus tear. In an unstable knee, the risk of meniscus injury increases over time. ACL deficiency causes abnormal movement of the knee and places excessive load on the meniscus.
• Early osteoarthritis (degenerative joint disease). In people who have had ACL injury, the risk of developing knee arthritis increases within 10-20 years. Risk exists in both non-surgical and surgical patients but is higher if there is meniscus or cartilage damage. Joint cartilage wears away over time, pain and stiffness develop.
• Post-surgical complications. Infection is a rare but serious complication. Graft failure is the surgery being unsuccessful and the ligament tearing again. Knee stiffness is the range of motion remaining limited after surgery. Anterior knee pain can especially be seen in those who use patellar tendon graft. Nerve or vessel damage is very rarely seen. Deep vein thrombosis can develop due to immobility after surgery.
• Re-injury. In people who return to sports after ACL reconstruction, there is a risk of new injury. The same knee or opposite knee can be injured. Risk increases especially if return to sport is early, rehabilitation is inadequate, or protective programs are not applied.
• Psychological effects. Having a serious injury and a long rehabilitation process is psychologically challenging. Fear of returning to sport (kinesiophobia) can develop. The person may not return to their former performance due to fear of re-injury.

Living with ACL Injury

ACL injury can be a life-changing experience. However, with appropriate treatment and rehabilitation, most people return to normal or near-normal activity levels.

Post-Surgical Recovery Process

The first days immediately after surgery are the hardest. Pain, swelling, and limited movement are normal. Use pain relievers regularly. Ice application reduces swelling. Keep the leg above heart level.

Crutches are used in the first weeks. Your doctor will tell you when you can bear full weight. Usually full weight can be borne within 2-6 weeks. Use of a knee brace or support is recommended.

Do not miss your physical therapy appointments. Do your home exercise program regularly. Rehabilitation is the key to success. Do not rush, complete each stage.

Return to Sport

The return-to-sport process takes 6-12 months. Rushing increases the risk of re-injury. Return-to-sport criteria are as follows. There should be no pain and swelling. Full range of motion should be gained. Muscle strength should be at least 90 percent of the healthy leg. Functional tests (single-leg jump, agility tests) should be successful. There should be psychological readiness.

Return to sport gradually. First light training, then full training, finally games. Use a protective knee brace for the first 6-12 months. Do proper warm-up and cool-down. Continue neuromuscular training programs.

Protecting the Opposite Knee

After having an ACL injury, the opposite knee is also at risk. Preventive exercise programs (such as FIFA 11+, PEP program) should be applied for both legs. These programs focus on muscle strength, balance, and correct movement patterns.

Lifestyle Changes

You may need to avoid high-risk activities. Low-risk activities such as swimming, cycling, or running may be preferred instead of sports containing cutting and pivoting movements like basketball and soccer. However, many people return to their former sport after appropriate rehabilitation.

Weight control is important. Excess weight places extra load on the knee and increases arthritis risk. Eating healthy and exercising regularly is also beneficial for general health.

Long-Term Care

Regular follow-up after ACL surgery is important. Checkups every 3-6 months in the first year, then annual checkups are recommended. If new pain, swelling, or instability develops in the knee, see a doctor immediately.

Continue exercising throughout your life to protect knee health. Especially keeping hamstring and quadriceps muscles strong is important. Do balance and proprioception (joint position sense) work.

Prefer low-impact exercises to reduce the risk of developing arthritis. Consume anti-inflammatory foods such as omega-3 that support joint health.

Preparing for Your Appointment

What you can do:

• Note in detail how the injury happened (which movement, what was heard, what was felt)
• Record the onset and development of symptoms
• Mention knee injuries you have had before
• Explain your sports and activity level
• List medications you use
• Write your questions down in advance

Questions you can ask your doctor are as follows:

• How severe is my ACL injury?
• Do I need to have surgery?
• Do I have a non-surgical treatment option?
• Which graft type is most appropriate for me?
• What will the post-surgical recovery process be like?
• When can I return to sport?
• What should I do for my opposite knee?
• What is my future arthritis risk?

Questions your doctor may ask you are as follows:

• How did the injury happen?
• Did you hear a "popping" sound?
• When did the knee swell?
• Do you feel instability in your knee?
• Can you step on your injured leg?
• Have you had a knee injury before?
• What sports do you play?
• What is your occupation?
• How have your daily activities been affected?