When a physical trauma involves the structure of the knee, the result is a minor strain, a sprain, or a tear of the anterior cruciate ligament (ACL).  Such injuries are categorized into different grades of sprains. Here are the three grades and some products that can help control pain and aid in rehabilitation:

Grade I Sprain
The fibers of the ACL ligament are stretched, but there is no tear in the fibers. There is a little tenderness and swelling. Weight bearing and walking are still possible. The knee does not feel unstable or give out during activity. Grade 1 sprains can usually be contained by using ice, bracing and exercise of the quadriceps - simple quad contractions working toward quad squats and knee extensions.

Grade II sprain
The fibers of the ACL ligament are partially torn. There is tenderness and moderate swelling. Walking feels uncomfortable, and you may need to limp. The joint may feel unstable or give out during activity. It is recommended that you consult your doctor for full evaluation. Grade II sprains can also heal on their own. Although some ligament laxity may still exist which can produce degenerative conditions in later years and leave the knee susceptible to further injury. To reduce symptoms, use ice, exercise and a compressive knee brace for 2-3 weeks.

Grade III sprain
The fibers of the ACL ligament are completely torn (ruptured) and there is usually a lot of pain at the time of rupture, though it lessens in time. There may be a little or a lot of swelling. The ligament cannot hold the knee in place properly, and the knee feels unstable and may give out at certain times. Walking usually is not possible, and the use of crutches is recommended. This type of injury requires a visit to the doctor and can require surgical intervention.

Avulsion of the ACL occurs when the ligament is torn away from either the upper leg bone or lower leg bone and a piece of the bone is broken off.

NOTE: More information on ACL injuries