An ACL sprain is a stretching or tearing injury to the anterior cruciate ligament in the knee joint.
Three bones make up the knee joint: the femur (thigh bone), the tibia (shin bone), and the patella, which is the kneecap. These bones are kept in position by ligaments, strong cords of fibrous connective tissue that attach bone to bone. Two of the four main ligaments are the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), which together form an ‘X’ shape inside the knee joint. The ACL is attached to the bottom of the femur at the back of the knee. It then passes through the joint diagonally and is attached to the top of the tibia at the front of the knee. Its purpose is to keep the joint stable by limiting the rotation and forward movement of the tibia underneath the femur. It is consequently very strong but not very flexible.
ACL sprains are graded according to the severity of the injury. A Grade I sprain causes pain, but there are only microscopic tears to the ligament and the joint remains stable. A Grade II injury means that the ligament has been partially torn, or stretched to the point of looseness in the joint. Grade III sprains are more severe; the ligament has been completely torn and the knee joint is unstable.
These injuries usually happen during sports. Only 20 per cent of such injuries are as a result of direct impact with another person or object; most happen without outside involvement. Examples of situations that might cause an ACL sprain are:
Along with the pain associated with an ACL sprain, there is often a loud ‘pop’ heard at the moment of injury. Depending on the severity of the sprain, there may be rapid and extensive swelling around the knee, caused by the rupture of a blood vessel that passes through the joint. There might be bruising with the swelling.
One of the strongest indicators of an ACL sprain is the sensation that the knee might ‘give out’ at any time. An old, unrepaired sprain might cause the sufferer to feel that the knee might give way during strenuous activity, particularly during twisting movements.
It is recommended that you seek medical assistance quickly, before any swelling makes diagnosis more difficult.
Your doctor will take a medical history from you and ask questions relating to:
A Lachman test might be performed to assess the amount of movement in the joint and the rigidity of the ligament. This test involves gentle pulling on the shin while the thigh is kept stable.
- The movement that caused the injury
- Any popping sound heard at the time
- The rapidity of the onset of swelling
- The severity of the pain
- Any feeling of instability in the knee joint
An x-ray might be needed to view the structure of the knee joint, and occasionally an MRI scan, which shows the soft tissues as well as bones, might be ordered.
The appropriate treatment for an ACL sprain depends on the severity of the injury. For milder sprains, rest and rehabilitation will be sufficient, but Grade III sprains will require surgery. Unfortunately, anterior cruciate ligaments cannot be sewn together so, if surgery is necessary, a ligament or tendon from another part of the leg will be removed and then attached to the femur and tibia to support the knee joint.
Self-help options if your injury is mild:
Your doctor or physiotherapist will develop an exercise routine to rehabilitate the knee when sufficient healing has taken place. These will help to reduce any stiffness, increase range of motion of the knee joint and build strength in the leg muscles. Strong leg muscles, particularly the quadriceps, which run from the hip to the knee, are important for knee joint stability.
- Limit your activity while the injury is in its acute phase.
- Apply ice, crushed in a bag and covered with a towel, to the knee several times a day for 15 minutes at a time.
- Wrap the knee with a compression bandage or wear a brace to help stabilize the joint.
- Use crutches to avoid placing weight on the injured knee.
- Elevate the knee above the level of the heart, when possible.
- Take over the counter pain medication such as acetaminophen (Tylenol) or anti-inflammatories such as ibuprofen (Advil), naproxen (Aleve) or aspirin.
Be guided by your physiotherapist before beginning any exercise regime and gradually build up the number of repetitions. Do not continue if any exercises cause pain in the knee joint. Always remember to warm up properly before starting. A heat pad on the knee for 15 minutes before exercise will help reduce stiffness.
Sitting down with legs stretched out, contract the thigh muscles (quads). Hold the stretch for 10 seconds. Release. Repeat 10 times for 1 set. Do 3 sets.
Prone hamstring curls:
Lying on the stomach, gently bend the injured knee so that the foot moves towards the buttocks. Hold for 5-10 seconds then slowly lower. Repeat 10 times for 1 set. Do 3 sets.
Standing in front of a chair, with the feet shoulder width apart, slowly bend the knees until your buttocks reach halfway to the chair. If you feel any pain before you reach that point, stop there. Slowly straighten the legs to a standing position. Repeat 10 times for 1 set. Do 3 sets.
Lying down on the back with the injured leg extended and the other bent at the knee, lift the straight leg until the heel is about 5 inches off the ground. Hold 5-10 seconds then lower. Repeat 10 times for 1 set. Switch legs and repeat. Do 3 sets.
Lying on the stomach with legs straight, tighten the quads and lift 1 leg as high as you can. Hold 5-10 seconds then slowly lower. Repeat 10 times for 1 set. Do 3 sets for each leg.
What to look for in a brace for an ACL sprain:
The purpose of wearing a knee brace is to protect the knee joint if you slip or fall, to allow the knee to rest while healing is taking place, and to keep the knee extended to avoid stretching the ligament further.
Your doctor will probably suggest a particular brace for you. In order to gain the maximum benefit, get the brace properly fitted and ensure that it feels comfortably supportive and secure.
ACL sprains are caused by accident so they are difficult to prevent, but taking care to always warm up and stretch properly before exercise may help to avoid injury. Athletes are particularly vulnerable to ACL sprains, so if your sport requires equipment, make sure it fits properly.
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