I'm not a doctor, nor did I stay at a holiday inn express last night, but it sounds like a meniscus problem.
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In Brief: Meniscal tears are very common sports injuries. Typical symptoms include pain, catching, and buckling. Signs on physical exam include joint-line tenderness, effusion, and, possibly, a click when the knee is taken through full range of motion. MRI is often needed to confirm tears and differentiate pain from that caused by other injuries such as articular cartilage damage. Treatment comprises physical therapy and rest, partial meniscectomy, or, in special instances, surgical repair. Therapeutic goals, which are often achieved, are to restore a high level of pain-free function and to prevent premature joint degeneration.
Knee meniscal tears are among the most common injuries seen in sports medicine. Twisting motions with the knee flexed, which are common in sports, place high stresses on the menisci. Many times the injury occurs when the athlete attempts a pivot; contact with another player typically does not occur, nor does lunging or landing awkwardly. A single "wrong step" is sufficient.
Meniscal tears among active patients are clinically significant on two counts. First, they cause pain, mechanical symptoms such as catching or
locking, and effusion. Even if athletes can continue to play, they are rarely at top form with a tear. Second, healthy menisci are needed to prevent damage and degeneration of the joint. Thus, even if the patients are able to ignore symptoms, they should be dissuaded from doing so, especially if the tear is repairable. (emphasis added)
I apologize if this was already covered.