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- Discussion:
     - tunnel radiograph of knee provides an angled PA projection of knee;
           - patient is prone with the knee flexed at 40 deg;
           - central beam directed caudally toward the knee joint at a 40 deg angle from the vertical;
     - clinical relevance:
           - displays profile of intercondylar notch;
           - profiles of posteriorsuperior articular surfaces of medial & lateral condyles;
           - profiles the notch on the lateral surface of lateral femoral condyle from which popliteus originates
    - clinical correlation: Osteochondritis Dissecans