Biomechanics of pathologic fractures.

The successful treatment of a patient with a tumor involves an estimate of weakening due to the tumor and a consideration of the probability of gross fracture through that defect. Weakening due to an open section defect usually results in fracture. Holes produce a stress concentration that is of concern to the orthopedist in reconstituting such fractures. The reconstitution itself must be such that the postoperative possibility of refracture is minimized. Surface-structured intramedullary devices and polymethylmethacrylate offer conversion of open sections into closed sections and minimize the stress risers to allow significant uniaxial bending and torsional loads to be carried by the reconstituted bone, which is usually of inadequate quality to allow reconstitution with screws, plates, and cement. Treatment of a pathologic fracture often involves extensive bony resection, necessitating reconstitution for mechanical stability and reduction of limb shortening. Several combinations of polymethylmethacrylate bone cement and standard metallic devices are satisfactory for reconstitution. Those combinations that offer the maximum cement-metal interface interactions should be chosen and used with proper cement preparation and delivery.