In the lateral malleolar ankle fracture without talar shift there is much uncertainty regarding the diagnosis of deltoid ligament injury severe enough to require surgical treatment. The current study evaluated the mechanical integrity of the ankle using a novel gravity-stress mortise radiographic view, which is practical for clinical use. Eight cadaveric lower extremities were tested under the following conditions: (1) intact ankle, (2) distal fibular oblique osteotomy, (3) plated fibula after osteotomy, (4) transection of the superficial deltoid with fibula osteotomized or plated, and (5) all possible combinations of deep deltoid transection with superficial deltoid transected or repaired and fibula osteotomized or plated. For each condition, a mortise radiograph was taken of the specimen while it was mounted horizontally, lateral side down. Fibular osteotomy with or without transection of the superficial deltoid did not alter the mortise radiograph appearance of the ankles. With combined deep and superficial deltoid transection and fibular osteotomy, the talus always (eight of eight specimens) showed a lateral shift of 2 mm or greater and a valgus tilt of 15° or more. The gravity stress view of the ankle was found to reproducibly document destabilizing deltoid ligament damage.