Ligaments are often strained because of exercise and are commonly sports-related injuries. A knee ligament strain happens when one or more ligaments in the knee are suddenly stretched or torn. Ligaments are what hold bones together. Ligaments support the knee and keep the joint and bones in the correct position. They help you walk, twist and turn. There are four ligaments that help support the knee. It is important that a professional assess and determines which of the ligaments in the knee were sprained at the time of injury. 
Recommended rehab exercise: Return to sport should be gradual. Focus on balance and comprehensive knee strengthening. Exercises for the quadriceps, hamstrings and calf muscles are very important. Deep Heat can be applied to reduce pain and assist in the warming of the muscles around the knee. Estimated time of recovery: Treatment and recovery time depend on the type and cause of the knee strain. Recovery usually takes around a month, but it can vary. How to prevent this injury from recurring:  Strapping and taping can be used to prevent the injury from reoccurring. Rehabilitation with a Biokineticist is recommended to ensure the knee is as stable and strong as possible.