The treatment of osteoporotic fractures is one of the current orthopaedic challenges because of the reduced bone mass and weakened strength of the fracture site, the difficulty of repositioning and firm internal fixation, the tendency of the implantation of artificial materials to loosen and lead to failure, and the relatively poor quality of bone scab healing, so the fracture reoccurrence rate is extremely high. Therefore, in addition to surgical treatment, the treatment of osteoporotic fractures with primary osteoporosis can help to improve the fracture healing rate. rhPTH1-34 is one of the most important peptide hormones that regulate calcium and phosphorus metabolism and maintain calcium balance in the body. rhPTH1-34 has the same receptor binding ability and biological activity as whole molecule PTH, and has fewer side effects than whole molecule PTH. It has been widely used to study the structure and function of PTH with fewer side effects than whole molecule PTH. Although many animal and clinical studies now suggest that PTH is a new approach to increase bone mass, improve bone quality, and treat osteoporosis, it is worth exploring whether PTH can be used to treat osteoporotic fractures in a way that both increases bone density and improves bone biomechanical properties, promotes fracture healing, and reduces the incidence of re-fracture. I. Materials and methods 1. Establishment of osteoporotic fracture model Eighty 6-month-old rats weighing 260-300 g, female, clean SD rats were randomly divided into rhPTH1-34 group, estrogen group, control group and sham-operated group, 20 rats in each group. The first three groups were anesthetized under 10% chloral hydrate (0.3 g/kg) intraperitoneal injection and underwent bilateral ovariectomy, while the sham-operated group was exposed without ovariectomy and the incision was sutured. After 3 months of rearing, a fracture model was established under the same anesthesia, i.e., the middle segment of the right femur was severed with a wire saw, and retrograde internal fixation of the medullary cavity was performed with a Kirschner pin (2 mm in diameter). Both surgical procedures were performed under strict aseptic conditions, and postoperative penicillin (2 million μ/kg) was used to prevent infection for three days, after which the animals were released to their cages for free movement and feeding. 2. Drug administration methods and specimen collection and treatment From the first day after the establishment of the experimental model of fracture, rhPTH1-34 was injected subcutaneously into the rhPTH1-34 group three times/week at 20 μg/kg; estradiol benzoate was injected subcutaneously into the estrogen group three times/week at 0.1 mg/kg; equal amount of saline was injected subcutaneously into the control and sham-operated groups three times/week. Two rats in each group were executed at 8 weeks after internal fixation of the fracture, and the right femur was removed intact, soft tissues were removed, rinsed with saline, immediately placed in 10% neutral formaldehyde (formalin) solution, fixed for 24 hours, labeled in groups, and histological examination of bone scabs was performed. After 9 weeks of treatment with medication after right femur fracture internal fixation, the rats were executed by over-anesthesia, the right femur and lumbar 3 vertebrae were removed, the soft tissues attached to the bone were removed, the internal fixation was removed, wrapped in saline-soaked gauze and placed in plastic bags, labeled in groups, stored in a refrigerator at -20°C, and prepared for the three-point bending test and the lumbar 3 vertebrae recess test. The following measurements or examinations were performed: BMD measurements: 10 rats in each group were selected, and BMD values of the 4th and 5th lumbar vertebrae and the right femur fracture were measured in vivo before ovarian removal, 12 weeks after ovarian removal, and 9 weeks after drug treatment, BMD values of the 4th and 5th lumbar vertebrae were measured in vivo using a bone densitometer, and the right femur was removed intact after execution of the rats, and the soft tissue was removed. BMD values were measured at the right femoral fracture site. Radiographic examination: Right femur radiographs were taken from pre-labeled rats at 4 and 8 weeks after internal fixation of the fracture to compare and observe the growth of bone scabs in each group. Histopathological examination of bone scabs at the fracture site: 2 rats were executed in each group at 8 weeks after internal fixation of the fracture, and the bone scabs at the fracture site were taken for histopathological observation to compare the fracture healing of each group. Biomechanical measurement: After 9 weeks of treatment, rats were executed, and the right femur and lumbar 3 vertebrae were taken, and the three-point bending test of the femur and the concavity test of the lumbar vertebrae were performed by using the MTS-858 biomaterials experimental instrument. 3, statistical processing: SPSS11.0 statistical software was used for statistical analysis, and the results were expressed as ± s. One-way ANOVA was used to compare the means of four groups in the same time period, and the difference was significant at P<0.05. II. RESULTS 1. Radiological detection The comparative observation of radiographs at 4 and 8 weeks after internal fixation of fracture revealed that continuous bone scabs were seen in the rhPTH1-34 group through the fracture line, with bone scabs wrapped around the fracture line and blurred fracture line, and only a few reactive bone scabs were seen in the estrogen group, control group and sham operation group at the same period, with no bone scabs wrapped around the fracture line and clear fracture line. 2. Histological examination of bone scabs At week 8, cartilaginous bone scabs were gradually replaced by bony bone scabs, among which the bone trabeculae in the rhPTH1-34 group were thicker and denser, aligned with the stress direction, with good ossification, and the cartilaginous bone scabs were converted into bony bone scabs. In the control group, more cartilaginous bone crusts were still visible, and the transformation to bony bone crusts was slow, with more chondrocytes, finer bone trabeculae, larger gaps, disorganized structure and laxity. 3. Measurement of bone mineral density Before treatment (3 months after ovariectomy), the BMD values of lumbar 4 and 5 vertebrae and right femur of rhPTH1-34 group, estrogen group and control group rats were significantly lower than those of the sham-operated group, with significant differences (P<0.05), suggesting that OVX rats showed significant osteoporosis at 3 months after bilateral ovariectomy, indicating successful modeling (see Table 1). The BMD values of the right femur in the rhPTH1-34 and estrogen groups were significantly higher than those in the control group 9 weeks after subcutaneous injection of rhPTH1-34, with significant differences (P<0.05). The BMD values of the right femur in the sham-operated group were significantly higher than those in the control group, with a significant difference (P<0.05). The BMD values of the right femur in the rhPTH1-34, estrogen and sham-operated groups were not significantly different.