Biomechanical analysis of bone healing in long bone fractures

The purpose of this research was to develop a non-invasive method of monitoring fracture healing that would not interfere with or disrupt the healing process. In the first study, a minimally-invasive method of vibration analysis was used to monitor fracture healing in the ulnae of two canines. One ulna in each subject was used as the control while the contralateral ulna received an osteotomy. Orthopedic screws were implanted 1.7 cm proximal and distal to the osteotomy site. The measurements were obtained with a needle fixture that penetrated the skin and soft tissues and rested in the hexagonal head of the cortical bone screw. The mechanical impedance at resonance obtained under transverse vibration was used to monitor the healing process. Vibration and radiographic analyses were performed prior to fracture and every week following fracture for a period of 20 weeks. The mechanical impedance values at resonance were found to show a significant variation between weekly measurements and an increasing trend as healing progressed. A simple beam model was analyzed using mechanical impedance methods to verify the use of vibration analysis in detecting changes in the stiffness of a healing bone. It was shown that simulated mechanical impedance curves were similar to those seen experimentally.;In the second study, a non-invasive vibration analysis method was used to monitor the healing of ulnar fractures. The frequency corresponding to the peak value in the mobility response curve obtained under transverse vibration was used to monitor the fracture healing process following an osteotomy in one ulna of fifteen mixed breed canines. The contralateral limb was used as a control. Vibration and radiographic analysis were performed prior to fracture, following fracture, and every two weeks thereafter. Five subjects were sacrificed at 6, 12, and 18 weeks. Mechanical testing was performed on the excised ulnae to determine the bending stiffness. The frequency values measured by vibration analysis were compared to stiffness values obtained from mechanical testing. Frequency values were compared to fracture gap widths measured from the radiographs. One fractured ulna healed, and this was confirmed from both vibration and radiographic analysis. The frequencies increased as healing progressed. The other 14 fractured ulnae exhibited a non-union or delayed union at the time of sacrifice. However, the variation between frequency values measured at different testing times was found to be significant for the fractured ulnae.;In the third study, a finite element model was developed to verify the use of vibration analysis to monitor fracture healing in the previous study. A finite element model was used to calculate the natural frequencies of an ulna containing a fracture as it progressed through the healing process. Beam elements with varying cross-sectional area and moment of inertia values were used to model the ulna. The fracture site was represented as an element with a varying elastic modulus to simulate fracture healing. The natural frequencies obtained from the finite element model for different stages of healing were compared to experimental results. (Abstract shortened by UMI.).