Encyclopedia / K / Knee Sprains

Knee Sprains


By definition, a knee sprain is an injury to a knee ligament. The sprain may vary in severity from a slight stretch to a complete tear of the ligament.

A mild, or grade 1, sprain simply stretches the ligament and causes pain and swelling. A moderate, or grade 2, sprain partially tears the ligament and is much more disabling. A severe, or grade 3, sprain is a complete rupture and often needs surgical repair.


Most ligament injuries of the knee involve a tearing of either the medial collateral ligament (MCL) on the medial side of the knee (medial means toward the midline of the body, and lateral means away from the midline), the anterior cruciate ligament (ACL) deep inside the joint, or both ligaments. The posterior cruciate ligament (PCL) is much less likely to sustain an injury than the ACL.


The most commonly sprained ligament is the medial collateral ligament (MCL). This ligament can be sprained by a blow to the outside of the knee, particularly if your foot is planted on the ground when you are hit. The blow causes the knee to move toward the inside of the body and stretches the ligament. You will feel tenderness and pain on the inside of the knee, and the knee will feel like it may buckle or give way to the inside. Anything more than minimal pain should be treated by a doctor.

A sprain on the outside of the knee, the lateral collateral ligament, is caused by a blow to the inside of the knee, which forces the knee to the outside. This is much less common than an MCL sprain because it is hard to get hit on the inside of the knee. Usually, your leg gets in the way and takes the blow.

Athletic or occupational trauma is usually the cause of an ACL injury. Sports that involve sudden acceleration and deceleration, such as basketball, soccer, field hockey, football and skiing, are frequently associated with ACL injuries. Nevertheless, ACL injuries can occur in any sport if the knee undergoes acceleration-rotation-type movement. Disability may be immediate because of pain and (frequently) swelling, which sometimes appears as soon as 1 to 4 hours after injury. However, immediate disability does not suggest the degree or severity of a particular type of injury. Patients may report that the knee "gave way" or became unstable; an audible "pop" raises the specter of an ACL tear.

A good rule of thumb for these injuries is: if you receive a blow to the knee and the pain is on the same side of the knee that was hit, it is probably just a bruise, and the pain will go away rapidly. If the pain is on the opposite side of the knee, consider this a serious injury that needs careful treatment.


Surgery is needed for patients who fall into the high or moderate risk category based on job, recreational, and/or athletic demands. Surgery may be considered for patients who are not at high risk but who experience symptoms during everyday activities, such as walking on uneven surfaces and performing simple twisting maneuvers. Before surgery, it is necessary to establish whether there is a full range of motion in the knee; if there is significant atrophy of the quadriceps and hamstrings, an intensive retraining period should be instituted before surgery.

It is not uncommon for patients with ACL-deficient knees to have had multiple procedures to remove articular or meniscal cartilage fragments. With the loss of these secondary restraints, the knee becomes more unstable, and the patient may become a surgical candidate based on overall knee instability. Physical therapy may help enhance balance and proprioception.


If the MCL sprain is a mild one, an early rehabilitation program using a stationary bicycle and leg extension and curl exercises is all you need. Begin by riding the bicycle for 20 minutes. Keep the seat high so that the range of motion is minimal. Do not put any drag on the bike; you are simply interested in moving the knee. In the very beginning, you may not be able to pedal all the way around. Just pedal back and forth until you can come over the top.

Do the leg extension while seated at a bench or a table. Once you lift the weight, hold at full extension for three seconds, and then very slowly lower your leg. Concentrate on the slow movement down, which is the most important part of the lift. Muscle contraction against weight while the muscle is lengthened builds the most strength. Ten lifts make a set. Do five sets of this exercise and rest for 30 seconds or more, if needed, after each set.

Do the leg curl while lying on your stomach. Do 10 lifts per set for five sets. If you are using a weight machine, you should hold for three seconds with the leg bent. If you are using free weights, this is not necessary.

The purpose of these exercises is to strengthen the quadriceps muscles in the front of the thigh (leg extensions) and the hamstring muscles in the back of the thigh (leg curls). These muscles control the knee and must be restrengthened.

If you have a problem doing the leg extensions, that is, if your range of motion is too limited or you find it too painful, then do isometric quadriceps exercises first.


Where is the sprain located and how severe is it?

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Will surgery be recommended?

Can conservative treatment be tried first?

Will the knee ligaments be permanently weak or susceptible to injury?

The immediate treatment for a sprained knee is the standard RICE formula. This is an acronym for Rest, Ice, Compression, and Elevation. These steps will help reduce swelling and pain, and speed the healing process. Rest the knee while it aches and ice it intermittently several times a day. Wrap it in an elastic bandage in between icings, and keep it elevated as much as possible.