Development of Ex Vivo Femoral Head Deformity Model to Test Restorative Surgical Techniques

Legg-Calve-Perthes disease (LCPD) is a childhood ischemic hip disorder which produces femoral head deformity due to weakened bone structure. The femoral head deformity causes pain, stiffness, and debilitating osteoarthritis; if left untreated, a total hip replacement is eventually required. Currently there is no reliable ex-vivo deformity model to develop and test the efficacy of new surgical devices and methods to improve the deformity and to restore the round shape. We hypothesize that a reliable model of deformity comparable to LCPD can be created using porcine cadaver bone by applying compressive force methods. Due to the availability of porcine humeral heads in the lab, we performed our preliminary studies using the humeral heads. We tested four mechanical approaches. Our first approach involved the application of static and cyclic compressions to mature humeral heads. However, the method failed to deform the heads due the high compressive strength of the mature bone. Our second approach involved drilling into the mature heads to create stress risers before applying the compression forces. This resulted in undesirable fracture of the bone. Our third approach used juvenile porcine humeral heads with cyclic compressions which resulted in deformity, but was inconsistent in the number of cycles required to achieve the appropriate deformity. Finally, we successfully achieved a reliable deformity model resembling LCPD by mounting juvenile humeral heads in a specific orientation and applying successive increases in static compression force at 50, 100, 150, 200, and 250 lbs using a Bose Electroforce 3330 test instrument. The amount of collapse after each static compression was measured using calipers. Identical measurements were taken after each compression test, up to 250lbs of force. This method created a 2 mm collapse of the humeral head which was reproducible. In summary, we developed a novel ex-vivo model of deformity which will facilitate the development of new restorative surgical devices and techniques to improve the femoral head deformity of LCPD.