The complex function of the knee relies on many bones and ligaments working properly. Injured or sprained ligaments can create instability since the ligaments control the backwards, forwards and sideways motion of the knee. When the knee is forced sideways it can rupture the different soft tissues that provide support and stability. Swelling, pain and instability are main symptoms from an MCL tear.
Injuries can range from mild to severe and might require surgery. For more information visit the American Academy of Orthopaedic Surgeons website: https://orthoinfo.aaos.org/en/diseases–conditions/collateral-ligament-injuries/