The effect of protein malnutrition and nutritional support on the mechanical properties of fracture healing in the injured rat.

Abstract

We investigated the effect of different nutritional regimens on fracture healing in the injured rat model. Four groups, each consisting of 12 male rats (307 +/- 16 g), were subjected to anesthesia, laparotomy (injury), and tibial osteotomy with internal fixation. Group I received 23% protein, group II received 23% protein and high caloric feed, group III received 5% protein, and group IV received 38% protein. After 8 weeks, calluses were x-rayed and the tibia was removed, fixed in a special block of methyl-metacrylate, and tested at tension up to failure in a mechanical testing apparatus. The distraction force at failure was measured, and callus stiffness and energy absorbed to failure were calculated. The low protein diet resulted in significantly lower tensile strength and stiffness of calluses compared to the other three dietary regimens, this despite adequate caloric intake. In addition, the low protein diet resulted in a callus with "rubbery" mechanical properties compared to the "rigid" calluses of the other three groups. The high protein diet did not result in any significant improvement in fracture healing. These results gain clinical significance in the face of a high incidence of protein calorie malnutrition in injured orthopedic surgery patients.