EFFECT OF LOW-POWER LASER IRRADIATION ON THE MECHANICAL-PROPERTIES OFBONE-FRACTURE HEALING IN RATS

Background and Objective: Low-power laser irradiation (LPLI) has been found to have a positive effect on bone fracture healing in animal mod els, based on morphogenic, biochemical, roentgenographic, and electron microscopic measurements. We investigated the effect of LPLI on bone fracture healing in rats using biomechanical methods. Study Design/Mat erials and Methods: Two groups of male Wistar rats, divided in a rando mized block design in a blinded fashion, each consisting of 25 animals , were subjected to anesthesia and tibial bone fracture with internal fixation. The first group was treated with LPLI (HeNe laser 632.8 nm, 35 mW), applied transcutaneously over 30 minutes to the area of the fr acture daily for 14 days. The second group served as a control. After 4 weeks, the tibia was removed and tested at tension up to failure (by a Lloyd LR 50K testing apparatus, U.K.) in 16 rats from group I and 1 5 from group II. The maximal load at failure, the structural stiffness of the tibia (callus stiffness), and the extension maximal load were measured. Results: The maximal load at failure and the structural stif fness of the tibia were found to be elevated significantly in the irra diated group (P = .014 and P = .0023, respectively), whereas the exten sion maximal load was reduced (P = .015). In addition, gross non-union was found in four fractures in the control group, compared to none in the irradiated group. Conclusion: These results suggest that LPLI tre atment may play a role in enhancing bone healing. (C) 1998 Wiley-Liss, Inc.