After a direct blow to the medial aspect of the patella or, more commonly, without contact and only after a sudden twisting motion to the opposite side of an outward-pointing planted foot (with a powerful contraction of the quadriceps while the thigh is turning inward), the patient’s kneecap dislocates laterally. The patient, who is usually an adolescent, is brought in with the knee guarded and slightly flexed, in severe pain, with the patella situated lateral to the lateral femoral condyle, creating an obvious and dramatic lateral deformity (Fig. 122.1). Most often there will have been a spontaneous reduction, and the patient reports that the knee or kneecap “gave way” or “gave out” with pain and then slipped back into place. A patient with recurrent, acute dislocation is usually able to relate an appropriate history and usually knows exactly what happened.