| [Objects] Monitoring and assessment of fracture healing have many potential applications, including (1) quantitative recommendations for progression from non-weight bearing to full weight bearing, to reduce the disuse osteoporosis, (2) the prediction of abnormal fracture healing such as delayed union or nonunion very early in the course of fracture treatment, to alter the fracture treatment plan, for example, mobilizing the fixator or early cancellous bone grafting of the facture, and (3) more precisely timing of fixation device removal. To date, the conventional method of assessing fracture healing is by a passive manipulation of the injured limb, to assess the strength of the fracture, together with radiographic examination to gauge the extent of callus formation. Although these criteria of healing assessment are helpful, they are subjective, insensitive, non-quantitative and inaccurate. Over the past decade, the need for an accurate and precise outcome measure in fracture healing has been highlighted and many people dedicate to find a quatitative measurement to monitor the rate of healing. There have been many noninvasive techniques available for evaluation of fracture healing including ultrasound technique, callus mechanical properties investigation, bone mineral changes monitoring, digital radiographic photodensito-metry and bony metabolic activity assessment. Bone healing is a course of rehabilitation of the bone structure and the biomechanical properties. The most important thing of fracture healing evaluation is prediction of the strength of the healing bone. Callus mechanical properties have high correlations with callus density. Assessment bone mineral density of fracture site would appear to have the most interesting clinical applications in fracture healing evaluation. The objectives of this research project are: (1)with the study on animal experiment of investigation the changes of bone mineral density at osteotomy gap and the biomechanical characteristics of healing bone during fracture healing, to explore the relationship between bone mineral density (BMD) of callus and the biomechanical characteristics of healing bone using statistical method and to evaluate the feasibility of dual energy X-ray absorptiometry (DEXA) in assessing fracture healing quantitatively. (2) with the study on clinical trial of investigation the changes of bone mineral density at fracture site during distal radius fracture healing, to analyze the effects of individual influences such as age, sex, height, weight and total body density status on the callus densitometry during fracture healing using statistical methods and find a method to reduce effect of these variables on bone mineral density assessment. [Material and methods] This study includes two parts. (1) Experimental research on correlation between bone mineral density and biomechanical properties. In 30 adult beagles, a right midshaft tibial osteotomy was performed and was stabilized with a 4-mm gap using a unilateral external fixator. A group of 5 animals were euthanized at 4, 6, 8, 10 and 12 weeks respectively after surgery. Both tibias were harvested and bone mineral densitometries were performed at 1 cm regions of interest of the osteotomy gap using DEXA. The intact contralateral tibia served as a control to normalize the data. Mechanical tests were performed on both tibias to determine biomechanical properties. The bending stiffness was determined with nondestructive three-point cantilever bending test. The torsional stiffness and the torsional strength were determined with torsional test. Curve estimation was used to analyze the relationships between BMD and biomechanical parameters, BMD ratio and biomechanical properties indexes and to explore whether linear correlation between bone mineral density and biomechanical properties can be established. (2) Clinical research on influences of individual factors on callus density assessment during fracture healing. 90 cases of distal radius fracture treated with closed reduction and splinting were enrolled in this research and were divided into three equal groups of 30 cases according to osteoporosis diagnostic definition proposed by the ChineseOsteoporotic Committee (lumber spine as a reference for diagnosing as BMD normal, osteopenia and osteoporosis). Bone mineral density of fracture site was determined by DEXA at 2, 4 and 6 weeks respectively after injury. The contralateral distal radius served as a control. Analysis of covariance and stepwise regression analysis were used to analyze whether individual influences such as age, sex, height, weight and total body density status affect the results of the BMD measurement and BMD ratio at fracture site. [Results] The main results are: 1. The animal experimental results of the curve estimate analysis show that there are goodness of fit between BMD and bending stiffness, torsional stiffness and torssional strength in Quadratic, Cubic, Compound, Linear and Power model. But statistics of five models are not significantly different. Linear relationships can be affirmed. There were high correlations between BMD determined by DEXA and biomechanical parameters (R2=0.789, 0.745, 0.655). 2. Using parameters of the contralateral limb as a control, the result of the curve estimate analysis shows that there are goodness of fit between BMD ratio and bending stiffness ratio, torsional stiffness ratio and torsional strength ratio in Quadratic, Cubic, Compound, Linear and Power model. But statistics of five models are not significantly different. Linear relationship can be affirmed. There were high correlations between BMD ratio and biomechanical parameter indexes (R2=0.837, 0.824, 0.807). 3. The results of clinical trial show that age, sex, weight and total body density status can affect BMD values. Only total body density status affects BMD ratio. Other factors have no effect on BMD ratio. [Conclusions] From our research, conclusions can be drawn as follow: (1) bone mineral density and biomechanical properties (bending stiffness, torsional stiffness and torsional strength) of callus increase over time during fracture healing. Statistical analyses show that a positive linear relationship is presented between bone mineral density and biomechanical parameters respectively. These associations lend credibilityto the use of callus BMD determined by DEXA to quantify the extent of mineralization at the fracture site, which could be useful in predicting the healing potential. (2) Using the normal contralateral limb as a control, a positive linear relationship is presented between bone mineral density ratio and biomechanical parameter indexes respectively. BMD ratio is a valid and reliable method to quantify bone mineral accretion of the fracture healing instead of direct BMD measurement, with better correlations between BMD ratio and biomechanical characteristic indexes at fracture site. (3) Statistical analyses in clinical research show that individual influences such as age, sex, height, weight and total body density status affect BMD measurement. Only total body density status has effect on BMD ratio which has more potential benefit in clinical application. Bone mineral density only accounts for 80% to 90% of the measured variation in ultimate strength of intact bone. Many variables have an effect on the fracture healing process, including the gap of fracture site, stability of fracture, injury of soft tissues around the bone, vascular supply to the fracture site, fracture mechanical environment. Moreover, close attention should be paid to false positive outcome once abnormal bone healing occurs, such as noneffective, exuberant callus formation in hypertrophic nonunion which have viable bone ends and sclerous bone ends. The use of DEXA as a precise, quantitative method to monitor fracture healing warrants further investigation clinically.
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