| Background: Delayed union and nonunion is the late or terminate course of fracture healing. The foreign data reported that fracture caused by various reasons take 5%～7% in all catagmatic patients. So delayed union and nonunion is an important problem in orthopedics territory. The shaft fracture of lower limbs includes shaft fractures of femur, tibia and tibiofibular. That fractures did not heal well had a bad effect on patients' daily life and load of lower limbs. So, lots of methods are being used to treat delayed union and nonunion in our country and outland at present, such as medicines, bone growth factor, electromagnetic field, shock wave, et al. But all these methods can not apply necessary stress to the fracture ends and always cause osteoporosis and other complications because of long-term bed and immobilization. Lots of scholars observed the course of fracture healing in different stress environment since the Law of Wolff that mechanical pressure can intercede the bone structure was put forward in 1892. There were many study support that the stress environment control the course of fracture healing. This result also extended the traditional Chinese medicine theory of dynamic and static combination. Many basic study and clinical study confirmed that micro-movement at the fracture ends could accelerate the callus formation and calcification. That Stress is used to stimulate fracture healing is a non-invasive treatment which is accepted widely. According to the theory that mechanical stress could stimulate the fracture healing and the theory of dynamic and static combination, a rap instrument of stress stimulation was developed in the prophase experiment of this scientific research project. The rap compressive stress that produced by rap instrument of stress stimulation could provide necessary stress environment to accelerate fracture healing. The instrument had been used in clinic, it could accelerate the fracture healing.Objective: To study the relation between the stress of fracture ends of lower limbs and the rap compressive stress produced by rap instrument of stress stimulation which was developed in the prophase experiment of this scientific research project.Methods: There were 5 adult cadavers (10 specimens of lower limbs). To make horizontal fracture in the middle of shaft of femur, tibia and tibiofibular artificially in order to measure expediently. There were 3 groups including femur fracture and tibia fracture and tibiofibular fracture. Fixed the fractures with steel plates and inter-locking intramedullary nails and external fixations respectively in every group, and left a clearance, 10mm, to fix the pressure sensor at the fracture ends. In order to make use of specimen well, to measure the femur fracture first, then tibia fracture and tibiofibular fracture. Then using the rap instrument of stress stimulation to rap heel of the specimen in different group. To increase the rap stress from 50N to 350N and add the stress 50N every time. Every specimen were rapped 6 times again and again. Then recorded the rap stress produced by rap instrument of stress stimulation and the compressive stress at the fracture ends. To analyze the data by statistics system and observe the results.Results: A linetype variation relation was observed between stress of fracture ends of lower limbs and rap stress produced by rap instrument of stress stimulation. The stress at the fracture ends among the different groups and different fixation had significant difference (p<0.05). The stress at the fracture ends: tibiofibular group > tibia group > femur group; external fixation > steel plate > inter-locking intramedullary nail.Conclusions: There is a variation relation between stress of fracture ends of lower limbs and rap stress, and the stress at the fracture ends are different in three groups and in three fixation methods. The results applies a good condition for popularization and use of the rap instrument of stress stimulation.
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