If a joint effusion occurs after a sports injury, you should rest immediately, elevate the affected limb, apply pressure and apply ice, which can constrict blood vessels and reduce swelling and pain in the joint. Cold packs can be applied to acute inflammation of the joint and to the effusion immediately following an injury.
Hot compresses dilate the blood vessels and speed up the local blood flow, mainly by taking away the local pain and inflammatory factors, so they are usually applied during the chronic, remission and recovery phases of joint pathology.