I was at the gym this morning and I must have stepped wrong, severe pain on the left side of my leg just under the knee. Very tender to touch and it hurts like heck. Going up and down stairs does hurt. Knee cap and all is in one place. Could I have pulled something? Some pain does radiate down the leg and up the thigh.
In my opinion you are describing lateral meniscal injury, I recommend an MRI to confirm start on NSAIDs (alphinturn) 3 times a day till then, also wear a knee brace physical therapy can early fix the problem and help you avoid surgery Good Luck