Thesis (M.Sc.)--Chulalongkorn University, 2008

Objective : To evaluate the relation between bone mineral density measured by calcaneal quantitative ultrasound and stress fractures among Thai army recruits during basic military training and to use this device for predicting stress fracture of lower extremities and to study the incidence and risk factors of stress fracture. Study design : Prospective cohort study Setting : 10 army battalions around Phramongkutklao hospital Research methodology : 1,263 new army recruits were enrolled from different 10 battalions in Bangkok. Before 10-week basic military training, their heels were measured by calcaneal QUS and risk factor questionnaires were replied. During training, their musculoskeletal injury was monitored especially stress fracture by military units trainers and researchers. Radiographic examination or either bone scintigraphy were performed in suspect of stress fracture. At the end of training, they informed another questionnaires and took physical examination. Results : The cumulative incidence of stress fracture was 6.57% (95% CI:5.27,8.08) and the incidence rate was 1.22 per 1,000 person-days (95% CI: 0.97,1.51). The Cox proportional hazards model showed that the bone mineral density measured by calcaneal QUS had relationship to stress fracture significantly. The lowest quartile (Q1) of speed of sound (SOS) was significantly related to stress fracture (Hazard ratio (HR) = 3.42; 95%CI: 1.74,6.75 ; p-value<0.001), history of fracture (HR=2.20; 95%CI: 1.15,4.21; p-value=0.017) , heavy smoker (HR=2.08; 95% CI: 1.23,3.50 ; p-value=0.006). The area under the ROC curve of SOS was 61.05% (95% CI: 54.70,67.39). Conclusion : The bone mineral density measured by calcaneal QUS was significantly related to stress fracture. SOS measurement, especially of the lowest (Q1) group including the high risk factors can identify the new army recruits who had the highest risk of stress fracture. The incidence of stress fracture may be reduced by the application for adaptive basic military training to the high risk recruits of stress fracture.