Prospective Cohort Study Of Risk Factors For Stress Fracture In Male Infantry Recruits In China

Background: Stress fracture is also called the fatigue fracture which is a kind of bone damage caused by excessive use. Stress fracture is common in soldiers, athletes and dancers. With the strength and difficulty of the military training increasing, the incidence of the stress fracture is always high. It has affected the army’s fighting force to a large extent. Stress fracture is usually misagnosed because of insidious onset, nonspecific signs and symptoms, and lack of the early diagnosis ways. And once the treatment on the stress fracture was delayed, there will be a significant impact on patients. Therefore, it is crucial to find out the risk factors of the stress fracture and draw out a corresponding plan to screen high risk soldiers for stress fractures. In this way, the incidence of stress fractures can be effectively reduced.METHODS: With the method of prospective cohort study, we choosed all the military recruits enlisted in the summer of 2013 from three units sampled randomly from the troops stationed in Luo Yang as the object of study. Baseline surveys were conducted via questionnaire. Blood samples were used for analyzing the variables of bone turnover biomarkers and genetic factors. After all the stress fracture cases were collected, analyze the summarized data and compare the distributional differences between the case group and the health group and explore the potential risk factors of stress fractures.RESULTS:1. By comparing the demographic characteristics, personal body measurement data, prior fracture history and training work between the groups with and without stress fractures,the result showed that there were significant differences in the distribution of the following six variables between the two groups. They are education, registered residence of the recruit, exercise level prior to enlistment, prior fracture history,subjective feeling of the military training and long distance running scores and the OR value was 0.661、0.756、0.692、1.596、1.665、0.518 respectively. Among them, the registered residence of the recruit showed no significance in the multivariate logistic regression analysis, but it still provided as an indicator of the risk factor for stress fractures.2. The participants’ serum level of BALP, OC, CTX-Ⅰ and 25(OH)D were tested by ELISA methods. After comparing these variables between the recruits with and without stress fractures, the serum average concentration of 25(OH)D in the stress fracture group was 43.3±11.8 nmol/L which was significantly lower than that in the no stress fracture group which was 54.8±10.4 nmol/L, P=0.02. And there were no significant differences in the serum level of BALP, OC and CTX-Ⅰ between the two groups.3. Genomic DNA was isolated from peripheral venous blood leucocytes using standard procedures. Genotyping was conducted through DNA sequencing according to the manufacturer’s instructions(ABI 3730 DNA analyzer, Applied Biosystems, USA). The result showed that the T and C allelic frequency of GDF-5 rs143383 in the stress fracture group were 299(79.1%)and 79(20.9%)respectively and that were 1653(68.3%)and 765(31.7%)in the no stress fracture group. A significant difference existed between the two groups(P(27)0.001), and the T allele was identified as a risk factor for stress fractures. Significant findings were also observed under the conditions of dominant and recessive models, as well as the co-dominant model(OR value was2.91, 1.18, 1.76 respectively).CONCLUSION:1. The pathogenesis of stress fractures was complex and multiple factors involved. We can draw a conlusion based on our study that little education, rural population, lower level of exercise prior to the enlistment, prior fracture history, bad feeling of the military training and lower scores of long distance running can be considered as early warning indicators for stress fractures.2. The lower baseline serum level of 25(OH)D before military training can be considered as a risk factor for stress fractures. There were no significant differences in the serum level of BALP, OC and CTX-Ⅰ between the two groups. But this conclusion needed further investigation on the biomarkers at different time points.3. The T allelic frequency of GDF-5 rs143383 in the stress fracture recruits was significantly higher than the no stress fracture recruits. The T allele can be considered as a risk allele for stress fractures.