The Effect of Fibular Malreduction on Contact Pressures in an Ankle Fracture Malunion Model*

BY DAVID B. THORDARSON, M.D.f, SOHEL MOTAMED, B.S4, THOMAS HEDMAN, PH.D.t, EDWARD EBRAMZADEH, PH.D.8, AND SAM BAKSHIAN, M.DJ, LOS ANGELES, CALIFORNIA

Investigation performed at the Department of Orthopaedic Surgery, University of Southern California, Los Angeles


ABSTRACT: Nine fresh-frozen cadaveric specimens were disarticulated through the knee, and the soft tissues, except for the interosseous ligaments and interosseous membrane, were removed to the level of the ankle. The subtalar joint was secured with screws in neutral position (approximately 5 degrees of valgus). Contact pressures in the tibiotalar joint were measured with use of low-grade pressure-sensitive film, which was placed through an anterior capsulotomy. For each measurement, 700 newtons of load was applied to the specimen for one minute. The film imprints were scanned, and the contact pressures were quantitated in nine equal quadrants over the talar dome. A fracture displacement device was secured to the distal end of the fibula; the device allowed for individual or combined displacements consisting of shortening, lateral shift, and external rotation of the fibula. The ankle was maintained in neutral flexion. The ligamentous injury associated with a pronation-lateral rotation fracture of the ankle was simulated by dividing the deep fibers of the deltoid ligament, the anterior-inferior tibiofibular ligament, and the interosseous membrane to a point that was an average of fifty-three millimeters proximal to the ankle joint. Baseline contact area and contact pressure in the joint were determined, followed by measurements after two, four, and six millimeters of shortening of the fibula; after two, four, and six millimeters of lateral shift of the fibula; and after 5,10, and 15 degrees of external rotation of the fibula. The three types of displacement were tested individually as well as in combination. 

 

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