Article

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: 1.84). 04/2011; 33(8):1001-7. DOI: 10.1016/j.medengphy.2011.04.002
Source: PubMed

ABSTRACT 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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