Anterior cruciate ligament injury passes in front of another ligament, the posterior cruciate ligament (PCL). The cruciate ligaments get their name from the fact they form a cross within the knee as they run in different directions from the thigh to the shin bone. Along with the other ligaments in your knee, your ACL keeps your knee stable and prevents your thigh and shin bones moving out of place.
When your knee ligaments are stretched but not torn, they’re called a sprain. Knee ligament injuries are given different grades depending on how severe they are. Around half of all people with an ACL injury will have injuries to other parts of their knee as well, such as a meniscus tear.
Anatomy of knee
Where is the ACL located in the anatomy of the knee?
The ACL is one of four main ligaments in the knee that attach the thigh bone (femur) to the shin bone (tibia). The kneecap (patella) located in the front of the knee, protects the ACL and other knee ligaments. The ACL and another ligament called the posterior cruciate ligament (PCL) run through the center of the knee. These ligaments prevent the shin bone from sliding too far forward or backward under the thigh bone.
Two other ligaments run along either side of the knee, the medial collateral ligament (MCL) and lateral collateral ligament (LCL). These ligaments prevent the knee from bending too far to either side of the leg. The meniscus provides padding and shock absorption for the knee. There are two menisci in each knee. Without these wedge-shaped pieces of cartilage, the thigh bone and shin bone would rub painfully against each other.
The ACL injury grading system
An ACL injury may be diagnosed when the ligament is overstretched or torn. The tear may be partial or complete; a complete tear of the ACL is also known as an ACL rupture.
- Grade I tears refer to a slightly stretched ACL. Symptoms are typically mild. The ligament can still keep the knee stable.
- Grade II tears refer to stretching of the ACL to the point of looseness. These injuries are often referred to as “partial” tears. Symptoms are more severe than Grade I tears. Range of motion may be restricted and the knee may occasionally feel unstable (the knee feels like it is “giving out”).
- Grade III tears (ligament rupture) are complete tears (the ACL has been split in two). Grade III tears may also be referred to as an ACL rupture. A person may not be able to bear weight on the injured leg.
ACL tears can produce a range of symptoms, which can make it difficult to diagnose without further examination from a doctor.
Risk factors of Anterior cruciate ligament injury
There are a number of factors that increase your risk of an ACL injury, including:
- Being female possibly due to differences in anatomy, muscle strength and hormonal influences
- Participating in certain sports, such as soccer, football, basketball, gymnastics and downhill skiing
- Poor conditioning
- Using faulty movement patterns, such as moving the knees inward during a squat
- Wearing footwear that doesn’t fit properly
- Using poorly maintained sports equipment, such as ski bindings that aren’t adjusted properly
- Playing on artificial turf
ACL injuries can be caused by:
- Stopping suddenly while running
- Slowing down while running
- Changing directions rapidly while running
- Jumping or landing incorrectly
- Contact injuries, such as a football tackle
- Overuse of the leg from repetitive impact activity such as jumping, running, twisting or pivoting
Anterior cruciate ligament injury symptoms
Symptoms of an acute ACL injury include:
- Feeling or hearing a pop in the knee at the time of injury.
- Pain on the outside and back of the knee.
- The knee swelling within the first few hours of the injury. This may be a sign of bleeding inside the knee joint. Swelling that occurs suddenly is usually a sign of a serious knee injury.
- Limited knee movement because of pain or swelling or both.
- The knee feeling unstable, buckling, or giving out.
After an acute injury, you will probably have to stop whatever you are doing because of the pain, but you may be able to walk.
The main symptom of chronic ACL deficiency is the knee buckling or giving out, sometimes with pain and swelling. This can happen when an ACL injury is not treated.
Some complications it may cause include:
- Risk of developing knee osteoarthritis
- Deterioration of joint cartilage
- Less range of motion
Diagnosis and test
Your doctor will want to hear exactly how you injured your knee. They’ll look at both knees to see if the sore one looks different. They may also order any of the following:
Tests: Your doctor may ask you to lie on your back and bend your hips and/or your knees at certain angles. They’ll then place their hands on different parts of your leg and gently shift you around. If any of your bones move in a way that isn’t normal that could be a sign that your ACL is damaged.
X-ray: Soft tissues like the ACL don’t appear on X-rays, but your doctor may want to rule out broken bones.
MRI or ultrasound: These exams can show both soft tissue and bone. If you have a damaged ACL, it should appear on the images.
Arthroscopy: This literally means to “look within the joint.” During the exam, an orthopedic surgeon makes a small cut in your skin. They insert a pencil-sized tool that contains a lighting system and lens (arthroscope) into the joint. The camera projects an image of the joint onto a TV screen. Your doctor can see what type of injury you have and repair or correct it, if needed.
Treatment of anterior cruciate ligament injury
Treatment for an ACL tear will vary depending upon the patient’s individual needs. For example, the young athlete involved in agility sports will most likely require surgery to safely return to sports. The less active, usually older, individual may be able to return to a quieter lifestyle without surgery.
A torn ACL will not heal without surgery. But nonsurgical treatment may be effective for patients who are elderly or have a very low activity level. If the overall stability of the knee is intact, your doctor may recommend simple, nonsurgical options.
Bracing: Your doctor may recommend a brace to protect your knee from instability. To further protect your knee, you may be given crutches to keep you from putting weight on your leg.
Physical therapy: As the swelling goes down, a careful rehabilitation program is started. Specific exercises will restore function to your knee and strengthen the leg muscles that support it.
Rebuilding the ligament: Most ACL tears cannot be sutured (stitched) back together. To surgically repair the ACL and restore knee stability, the ligament must be reconstructed. Your doctor will replace your torn ligament with a tissue graft. This graft acts as scaffolding for a new ligament to grow on.
Grafts can be obtained from several sources. Often they are taken from the patellar tendon, which runs between the kneecap and the shinbone. Hamstring tendons at the back of the thigh are a common source of grafts. Sometimes a quadriceps tendon, which runs from the kneecap into the thigh, is used. Finally, cadaver graft (allograft) can be used.
There are advantages and disadvantages to all graft sources. You should discuss graft choices with your own orthopaedic surgeon to help determine which is best for you.
Because the regrowth takes time, it may be six months or more before an athlete can return to sports after surgery.
Procedure: Surgery to rebuild an anterior cruciate ligament is done with an arthroscope using small incisions. Arthroscopic surgery is less invasive. The benefits of less invasive techniques include less pain from surgery, less time spent in the hospital, and quicker recovery times.
Whether your treatment involves surgery or not, rehabilitation plays a vital role in getting you back to your daily activities. A physical therapy program will help you regain knee strength and motion.
If you have surgery, physical therapy first focuses on returning motion to the joint and surrounding muscles. This is followed by a strengthening program designed to protect the new ligament. This strengthening gradually increases the stress across the ligament. The final phase of rehabilitation is aimed at a functional return tailored for the athlete’s sport.
Prevention of anterior cruciate ligament injury
Many ACL injuries can be prevented if the muscles that surround the knees are strong and flexible.
Prevention focuses on proper nerve and muscle control of the knee. Exercises aim to increase muscle power, balance, and improve core strength and stability.
The following training tips can reduce the risk of an ACL injury:
- Train and condition year round.
- Practice proper landing technique after jumps.
- When you pivot, crouch and bend at the knees and hips. This reduces stress on the ACL.
- Strengthen your hamstring and quadriceps muscles. The hamstring muscle is at the back of the thigh; the quadriceps muscle is at the front. The muscles work together to bend or straighten the leg. Strengthening both muscles can better protect the leg against knee injuries.