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Research Papers

Development of a Force-Driven Distractor for Distraction Osteogenesis

[+] Author and Article Information
Jinyong Wee, Rahamim Seliktar

School of Biomedical Engineering,  Drexel University, Philadelphia, PA 19104

Robert E. Akins, William G. Mackenzie

 Alfred I. duPont Hospital for Children, 1600 Rockland Road, Wilmington, DE 19803

David G. Levine, Dean W. Richardson

Widener Hospital,  The University of Pennsylvania School of Veterinary Medicine, 382 West Street Road, Kennett Square, PA 19348

George R. Dodge

Department of Orthopaedic Surgery,  University of Pennsylvania, 424 G Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104-6081

Tariq Rahman1

 Alfred I. duPont Hospital for Children, 1600 Rockland Road, Wilmington, DE 19803

1

Corresponding Author: Tariq Rahman, Ph.D., Center for Orthopedic Research and Development, Alfred I. DuPont Hospital for Children, P.O. Box 269, Wilmington, DE 19899, e-mail: trahman@nemours.org

J. Med. Devices 5(4), 041004 (Nov 14, 2011) (5 pages) doi:10.1115/1.4005321 History: Received April 06, 2011; Revised October 04, 2011; Published November 14, 2011

Distraction osteogenesis is a routine surgical procedure to lengthen a long bone. A fixed lengthening rate is typically used. We investigate measuring forces continuously and producing a variable distraction rate. A motorized distractor was instrumented with a load cell to measure the forces developed in a limb during distraction osteogenesis. The motor moves 2.6 μm at each step, with a variable frequency depending on the distraction rate. The forces were measured every 15 s and used to change the rate on the autodistractor. The autodistractor, load cell, data logger, controller, and battery pack were all mounted on a monolateral rail fixator, which was tested on a sheep that underwent tibial lengthening. Results show the feasibility of continually recording forces in vivo. The lengthening rate changed automatically, based around a threshold force of 300 N. Findings indicate that force readings are feasible and practical with a simple device. Force determination may provide an additional means to evaluate tissue integrity in real-time and away from the clinic. An automatic variable rate device could improve limb lengthening.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diagram of the distraction environment with the unilateral fixator. The force measured at the distractor is composed of muscle forces, Fmuscle , forces due to the callus, Fcallus , and the ground reaction forces, FGRF .

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Figure 2

The load cell was inserted inside the autodistractor. This structure allowed the transmission of force to the load cell and also minimized dimensions. The force feedback controller/data logger was specifically designed for this application.

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Figure 3

(a) Load cell, (b) Memory, (c) Micro-controller, (d) Force-feedback controller circuit board

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Figure 4

Flow diagram of the force feedback control scheme implemented on the autodistractor. Drate is the distraction rate.

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Figure 5

Autodistractor and controller shown attached to the hind left tibia of the sheep

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Figure 6

Distraction force (compressive) shown for sheep undergoing limb lengthening at a variable distraction rate. The dark line shows the average of the force values. The stepped line at the bottom is the distraction rate, which starts at 1 mm/day and increases in increments of 0.25 mm/day.

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Figure 7

Radiographs taken (a) the first day of distraction, (b) day 9, (c) day 16, (d) day 23, and (e) the end of lengthening (day 31). The distraction zone shows gradual callus formation during lengthening.

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