The Effect Of Low-intensity Ultrasound On Healing Of Osteoporotic Fracture In Rabbit

Osteoporosis is a skeletal disorder "characterized by low bone mass and microarchitectural deterioration of the bone tissue, leading to the increased bone fragility and the resultant increase in fracture risk". With the increasing proportion of the elderly in the population, more and more osteoporosis individuals are suffering from low-energy fracture-osteoporotic fracture (OPF). OPF at the distal part of radius, hip. vertebral body and rib is at high risk. Though the healing mechanism of OPF is not thoroughly clear, most researchers agree that OPF healing is more difficult than the traumatic fracture healing, so OPF causes severe health and economic problem to the victims and the society as well. At the same time, how to accelerate OPF healing is a big issue to be solved.Low intensity pulsed ultrasound (LIPU) is one kind of mechanical stimuli and may produce the bio-effects to the organisms. There are a few experimental studies and clinical observations on the accelerating traumatic fracture healing with LIPU. But there is no study on the effect of LIPU onthe OPF healing, to our knowledge.In this study, we investigated to see if LIPU could accelerate OPF healing in a osteoporosis rabbit radius fracture model. Sixty-nine OPF rabbits were randomly divided into five time groups-1W, 2W, 4W, 6W and 9W after operation. Exterior LIPU exposure was made to the right radius OPF site with intensity of 30mW/cm2 for 20 minutes daily and the sham exposure was made to the left radius as control. The effects of LIPU on OPF healing were systemically observed with X-ray film, histological examination, biomechanical testing, quantitative determination of blood flow at fracture site, microangiography, immunohistochemical staining and in situ hybridization.The main results and conclusions were as follows:1. X-ray films showed the callus formation and bony callus modeling in the LIPU treated side were earlier than that in the control side. Outer callus and blurring fracture line in the experimental side and periosteum reaction only in the control side were found at the end of the second week. Disappearance of fracture line and bony union in the experimental side and remaining blurring fracture line in the control side were found at the end of the sixth week. Recanalization of bone marrow cavity in the experimental side and disappearance of fracture line with uncanalizedbone marrow cavity obstruct in the control side were found at the end of the ninth week. The callus assessment with X-ray film indicated the healing process in the experimental side was earlier than that in the control side (P < 0.05). Histological findings in the experimental side included, active proliferation of osteoblast, fibrous connection and newly formed trabeculae between fracture fragments at the end of the second week, increased osteoblast, mainly woven bone at the fracture side at the end of the fourth week, bony callus bridged two fragments at the end of sixth week and excellent remodeling of callus with lamellar bone, recanalization of bone marrow cavity at the end of ninth week. But histological findings in the control side mainly included granulation tissue which was not completely replaced by fibrous tissue at the end of the second week, a lot of cartilage tissue at the end of the fourth week, increased woven bone at the end of the sixth week and mainly woven bone filled up the fracture site at the end of the ninth week. X-ray film and histological findings indicated that LIPU accelerated QPF healing by enhancing the process of inflammation absorb, callus formation and callus modeling.2. The bone mineral density (HMD) and ash content (mg% dry weight) of callus in the experimental side at 2 weeks, 6 weeks and 9 weekspostoperatively were respectively higher than that in the control side (P< 0.05). Biomechanical test of three-point bending showed the peak load, peak stress, elastic modulus and peak absorbed energy in the experimental side at 4 weeks and 9 weeks postoperatively were significantly higher than that in the control...