Bone strength is the sum of bone mass and bone quality. Clinically the bone mass and osteoporosis are usually measured by bone mineral density (BMD) . Distal radius is one of the commonly used parts to measure bone mineral density. The radius is located in lateral forearm, which is consisted of radial head and neck, shaft and distal radius. Its main function includes rotation and elbow flexion and extension. Different parts of Radial show different forms of anatomy. The main stem epiphyseal end on both sides is consisted of cancellous bone, while the radial shaft is composed of cortical bone. Previous literature studied the stability at the bottom of radial by means of biomechanics, but the description and contrast research of the bone mechanical property of different anatomical parts of radical was not found. The concept and measurement method of bone microhardness is proposed for the first time in 1954. It can detect bone mineral content and bone structure performance directly at the level of organization. This study measures the microhardness of different parts of radial bone via vickers hardness method (vickers hardness, HV) . Through the analysis of hardness distribution, our study discusses its relationship with the fracture characteristics of epidemiology and the fracture treatment.

I. Specimen preparation: This experiment was approved by the ethic committee of Third Hospital of Hebei Medical University and was recorded in the center of international clinical experiment platform . This research adopted the radial specimens from 3 fresh frozen corpse (male, 62 years old; male, 58 years old; female, 45 years old) , and X-way was done on all samples to exclude the related diseases that might affect the quality of bone. The right side of radial was taken respectively from the 3 bodies specimen. After careful removing of soft tissue, the radius was divided into 3 segments including radial proximal, shaft, and distal radius based on the AO anatomical principle. Then, 3 mm bone tissue slice vertical to the long axis of each segment was taken using high precision slow saw (the music companies in the United States, BUEHLER11-1280-250) . 3 pieces of bone tissue slice were taken from radial head, radial neck and radial tuberosity of the radical proximal; 9 pieces of bone tissue slice were taken from the shaft in proximal to distal manner; 2 slices were taken from distal radius. During the process of slow saw operation, condensate was used to continue lowering the temperature of bone surface in order to prevent tissue degeneration caused by high temperature. The bone tissue slice was fixed on slide and marked, which was then polished by the mesh sand papers with silicon carbide grain in the order of 800, 1000, 1200, 2000 and 4000 before frozen in the refrigerator of -20℃. 2. Microhardness measurement: Before hardness measurement, the specimen was soaked in physiological saline for 1 hour to restore the bone tissue changes due to dehydration. This research adopted the Germany KB -5 vickers hardness measuring instrument to press vickers microhardness probe to the wet surface of bone. Through the measurement of the length of indentation diagonal line, the hardness value of each part of the body was calculated. The unit of hardness was represented by HV or kgf/mm². Five points at the before, after, inside and outside of each piece of bone tissue slices (a total of 20 points) were selected for examination. According to the previous literature, the hardness value was measured by 50 g force loaded for 12 s. All valid values were recorded, and the data with the indentation diagonal length difference of greater than 10% were dropped. 3. statistics analysis: With SPSS19.0 software data processing, radial bone hardness values accord with normal distribution, variance with ±s. Each part microscopic bone hardness difference compared with single factor analysis of variance. Multiple comparison, the variance of the group by T test, P<0.05 the difference was statistically significant.

In this study, 840 measurement points on five parts of radical including radial head, radial neck, radial tuberosity, shaft and distal radius from three radical specimens were taken to measure the bone hardness. The distribution characteristics of radial bone hardness are as follows: the distribution of radical overall hardness is (19.10-60.40) HV with an average of 39.70 HV. The area with maximum hardness value is located at the lower shaft segment, and the hardness value is 43.82 HV. The area with minimum hardness value is located at the radial head, and the hardness value is 33.31 HV. In the three radial specimens, the overall hardness of shaft bone is the highest (42.54 HV) , which is higher than that of proximal radius (34.15 HV) and that of distal radius (35.24 HV) , and the difference is statistically significant (P<0.001) . The bone hardness of proximal and distal radius is almost the same, and there is no statistically significant difference (P>0.05) . There is no statistically significant difference in the internal and external hardness values between proximal radius, shaft and the area around distal radius.

This study demonstrates that the shaft of radius is the bone fragment with a significant higher value of micro-hardness compared with the two ends of radius. The difference of micro-hardness value between proximal radius and distal radius is not significant. The difference of micro-hardness value among the four areas of radius (before, after, inside and outside) is not significant. This study reveals the rule of the micro-hardness distribution of radius and provides data support for the preparation of radial head prosthesis with human physiological characteristics through 3D printing.