Using distraction forces to drive an autodistractor during limb lengthening
School of Biomedical Engineering, Drexel University, Philadelphia, PA 19104, USA.Medical Engineering & Physics (Impact Factor: 1.83). 04/2011; 33(8):1001-7. DOI: 10.1016/j.medengphy.2011.04.002
Distraction osteogenesis can result in high forces developing in the limb. To determine and control the distraction forces (DF), a motorized distractor driven by feedback from DF was developed and used to lengthen the tibiae of 6 sheep undergoing distraction osteogenesis. The forces were measured continually, and, in 4 of the sheep, a force threshold was set, above which an increase in rate was initiated. The rate kept increasing to a set limit if forces remained above the threshold; otherwise, the rate was decreased. Radiographs were acquired biweekly, and muscle samples were analyzed from both the operated and contralateral limbs upon termination of the experiment. Results demonstrated a drop in DF associated with increased lengthening rate, attributed to separation of the callus as indicated by radiography. Histological evidence of muscle damage generally correlated with higher DF levels. There was a significant decrease in muscle fiber diameter in lengthened relative to contralateral limbs. Collectively, the results demonstrated the use of a force-driven distraction system and support the need for considering force data in regulating distraction rates to achieve optimal clinical outcomes.
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ABSTRACT: The load bearing characteristics of the intervened limb over time in vivo are important to know in distraction osteogenesis and bone healing for the characterization of the bone maturation process. Gait analyses were performed for a group of sheep in which bone transport was carried out. The ground reaction force was measured by means of a force platform, and the gait parameters (i.e., the peak, the mean vertical ground reaction force and the impulse) were calculated during the stance phase for each limb. The results showed that these gait parameters decreased in the intervened limb and interestingly increased in the other limbs due to the implantation of the fixator. Additionally, during the process, the gait parameters exponentially approached the values for healthy animals. Corresponding radiographies showed an increasing level of ossification in the callus. This study shows, as a preliminary approach to be confirmed with more experiments, that gait analysis could be used as an alternative method to control distraction osteogenesis or bone healing. For example, these analyses could determine the appropriate time to remove the fixator. Furthermore, gait analysis has advantages over other methods because it provides quantitative data and does not require instrumented fixators.
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ABSTRACT: Knowing the evolution of callus stiffness is very important in distraction osteogenesis and bone healing. It allows the characterization of the bone maturation process and the assessment of the moment to retire the fixator. A new distractor device that monitors the callus axial stiffness is presented in this study. It quantifies the callus stiffness during the bone transport process with some advantages over previous methods to assess stiffness during simple distraction and bone healing. This device avoids a misalignment between bone segments, uses real load conditions, monitors forces continuously, does not involve radiation for patients, and allows the study of the complete distraction process, i.e., the distraction and consolidation phases. The device was calibrated in vitro simulating different real bone load conditions depending on the stage of the process. The stiffness of the callus could be estimated for values between 4.2 N/mm and 9066.8 N/mm. The average relative error in measurements carried out in in vitro calibration tests was 7.8% during the distraction phase and 9.5% during the consolidation phase. These results improve the accuracy and increase the callus stiffness range of estimation with respect to other devices in the literature. In addition, the device was used successfully in vivo in a preliminary experiment. Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
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