A 38-year-old man has pain and stiffness of his right knee. This began 2 weeks ago after he fell while skiing. On two occasions he had the sense that his knee was locked in a semiflexed position for a few seconds. He has noted a popping sensation when he bends his knee. On examination there is tenderness over the medial joint line of the knee. Marked flexion and extension of the knee are painful. The Lachman test (anterior displacement of the lower leg with the knee at 20° of flexion) and the anterior drawer test are negative. What is the most likely diagnosis?
A. Medial meniscus tearThis patient has a medial meniscus tear. This may occur after trauma, but sometimes occurs spontaneously. Patients complain of pain, stiffness, and a popping sensation. A sensation of locking is very characteristic. On examination patients frequently have tenderness at the joint line and pain on flexion and extension. Routine x-rays are usually negative and the diagnosis is made by MRI scanning. Osteoarthritis usually occurs in patients older than age 50 unless the patient is very obese. OA pain typically comes on gradually, and physical examination may reveal patellofemoral crepitance. An anterior cruciate tear usually results from a twisting injury. It is a common injury in female soccer and basketball players. Frequently a large effusion occurs acutely. Chondromalacia patella is a common problem in runners. The pain typically worsens when the patient walks down stairs. The physical examination demonstrates lateral displacement of the patella with knee extension. Pathology in the back and hip may be referred to the knee, but is not associated with physical examination abnormalities localized to the knee.