Elaine Chan, Cynthia Chang, Alex Gordon, Eric Vu, Peter Yang · The Osteonexus: Actively Dynamized...
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The Osteonexus: Actively Dynamized Fracture Healing Elaine Chan, Cynthia Chang, Alex Gordon, Eric Vu, Peter Yang Department of Bioengineering, Rice University, [email protected] TSGC Design Challenge 2005-2006 2005-2006 GORDON CHANG CHAN VU YANG Rice University Figure 1. The Osteonexus prototype. Limits movement to the axial direction Lined with linear bushings to minimize friction Guide Shafts Attached to motor Crankshaft attached to inset ballbearing Moves the crankshaft at each revolution Revolving Plate Crankshaft Attached off-center to revolving plate to create axial displacement The Osteonexus Active Dynamizer produces healing-enhancing, axial micromovements at the fracture site that simulate physiological loading. Secure the device into the bone Pins ACKNOWLEDGEMENTS CONCLUSIONS REFERENCES POWER FEEDBACK FINITE ELEMENT ANALYSIS THE OSTEONEXUS ACTIVE DYNAMIZER PROTOTYPE EVALUATION INTRODUCTION OBJECTIVE Figure 3. Average power consumption as a function of spring constant. Motor power draw can be correlated to fracture site strength to monitor the healing process. b) Static Fixation Figure 2. Stress distribution in tibia a) with active dynamization fracture fixation under 1 mm displacements. b) with static fracture fixation under weight bearing conditions of a 70 kg man. a) Osteonexus Active Dynamization Stresses at fracture site are reduced under static fixation in comparison to active dynamization. Stresses on the order of magnitude of 1 MPa have been correlated to osteocyte differentiation and endochondral ossification 4,5 . Maximum stress at fracture site: 1.3 MPa The Osteonexus is expected to provide a faster healing response than current static fracture fixation methods. Maximum stress at fracture site: 0.3 MPa Fracture Site Fracture Site Develop a device which promotes fracture healing via actively induced, controllable axial micromovements at the fracture site directly beneficial for: Patients who are unable to sufficently amublate or load their bones Elderly, traumatized, or paraplegic Astronauts Patients in the general public desiring a quicker healing response Finite Element Analysis Stresses at fracture site modeled using ABAQUS TM : Active dynamization (1 mm displacment) Static fixation (300 N load on tibia) Tibia in early stages of fracture healing (0-4 weeks) modeled using 3 : Cortical shell elastic modulus, 17.4 GPa Fracture site elastic modulus, 8.7 GPa Bone Poisson's ratio, 0.39 Fixator properties: Steel elastic modulus, 210 GPa Steel Poisson's ratio, 0.28 All components modeled as isotropic materials. Power Feedback: Springs of varying stiffness: Used to induce mechanical resistance Positioned between two components of Osteonexus Calibrated using Instron 5565 system Voltage and current across motor measured using LabVIEW 7.1 and ELVIS data acquisition board Five seconds of data recorded for each spring Special thanks to Dr. Maria Oden, Dr. Michael Liebschner, Dr. Joseph Gugenheim, Dr. Roman Skoracki, Debbie Mullins, Tara Ruttley, Kevin Bowen, Eugene Koay, Ram Krishnamurthy, Matthew Wettergreen, and Kobie Williams. Funding provided by Texas Space Grant Consortium. 1. Aro HT, et al. The effects of physiologic dynamic compression on bone healing under external fixation. Clin Orthop. 1990; (256):260-273. 2. Kenwright J, et al. Controlled mechanical stimulation in the treatment of tibial fractures. Clin Orthop Relat Res. 1989; (241):36-47. 3. Vijayakumar V, et al. Load transmission through a healing tibial fracture. Clin Biomech. 2006; (21):49-53. 4. Gardner TN, et al. The influence of mechanical stimulus on the pattern of tissue differentiation in a long bone fracture - an FEM study. J Biomech. 2000; (33):415-425. 5. Gardner TN, et al. The biomechanical environment of a bone fracture and its influence upon the morphology of healing. Med Eng Phys. 2003. The Osteonexus is a unique dynamizing external fixator that actively induces controllable micromovements. Finite element analysis demonstrates that the Osteonexus design produces therapeutic stresses at the fracture site that would reduce healing time. Power consumption of the device provides the physician with a diagnostic tool to monitor fracture healing process. Fracture healing requires: Good fracture fixation Partial loading of fracture site Partial axial loading: Through micromovements of 1 mm at 0.5 Hz have been shown to speed fracture healing by 27% 1 Stimulates callus formation Accelerates remodeling of osteocytes late in the healing phase 2 The Osteonexus Active Dynamizer: Incorporates effective fixation Provides controlled micromovements to promote fracture healing Accommodates patients unable to load bones The stiffer the spring, the more motor power is required to induce micromovement. The relationship between average power consumption and stiffness can be used as a standard curve. y = 0.8776e 0.0887x R 2 = 0.9657 0.8 1 1.2 1.4 1.6 1.8 2 0 2 4 6 8 Spring Constant (N/mm) Average Power Consumption (W)
Transcript of Elaine Chan, Cynthia Chang, Alex Gordon, Eric Vu, Peter Yang · The Osteonexus: Actively Dynamized...
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The Osteonexus: Actively Dynamized Fracture HealingElaine Chan, Cynthia Chang, Alex Gordon, Eric Vu, Peter Yang
Department of Bioengineering, Rice University, [email protected] Design Challenge
2005-20062005-2006
GORDONCH
ANG
CHAN
VU
YANG
Rice University
Figure 1. The Osteonexus prototype.
Limits movement to the axial directionLined with linear bushings to minimize friction
Guide Shafts Attached to motorCrankshaft attached to inset ballbearingMoves the crankshaft at each revolution
Revolving Plate
CrankshaftAttached off-center to revolving plate to create axial displacement
The Osteonexus Active Dynamizer produces healing-enhancing, axial micromovements at the fracture site that simulate physiological loading.
Secure the device into the bone
Pins
ACKNOWLEDGEMENTS
CONCLUSIONS
REFERENCES
POWER FEEDBACK
FINITE ELEMENT ANALYSIS
THE OSTEONEXUS ACTIVE DYNAMIZER
PROTOTYPE EVALUATION
INTRODUCTION
OBJECTIVE
Figure 3. Average power consumption as a function of spring constant.
Motor power draw can be correlated to fracture site strength to monitor the healing process.
b) Static Fixation
Figure 2. Stress distribution in tibia a) with active dynamization fracture fixation under 1 mm displacements. b) with static fracture fixation under weight bearing conditions of a 70 kg man.
a) Osteonexus Active Dynamization
Stresses at fracture site are reduced under static fixation in comparison to active dynamization.Stresses on the order of magnitude of 1 MPa have been correlated to osteocyte differentiation and endochondral ossification4,5.
Maximum stress at fracture site:
1.3 MPa
The Osteonexus is expected to provide a faster healing response than current static fracture fixation methods.
Maximum stress at fracture site:
0.3 MPa
Fracture Site Fracture Site
Develop a device which promotes fracture healing via actively induced, controllable axial micromovements at the fracture site directly beneficial for:
Patients who are unable to sufficently amublate or load their bones
Elderly, traumatized, or paraplegicAstronauts
Patients in the general public desiring a quicker healing response
Finite Element AnalysisStresses at fracture site modeled using ABAQUSTM :
Active dynamization (1 mm displacment)Static fixation (300 N load on tibia)
Tibia in early stages of fracture healing (0-4 weeks) modeled using3:
Cortical shell elastic modulus, 17.4 GPaFracture site elastic modulus, 8.7 GPaBone Poisson's ratio, 0.39
Fixator properties:Steel elastic modulus, 210 GPaSteel Poisson's ratio, 0.28
All components modeled as isotropic materials.
Power Feedback:Springs of varying stiffness:
Used to induce mechanical resistancePositioned between two components of OsteonexusCalibrated using Instron 5565 system
Voltage and current across motor measured using LabVIEW 7.1 and ELVIS data acquisition boardFive seconds of data recorded for each spring
Special thanks to Dr. Maria Oden, Dr. Michael Liebschner, Dr. Joseph Gugenheim, Dr. Roman Skoracki, Debbie Mullins, Tara Ruttley, Kevin Bowen, Eugene Koay, Ram Krishnamurthy, Matthew Wettergreen, and Kobie Williams. Funding provided by Texas Space Grant Consortium.
1. Aro HT, et al. The effects of physiologic dynamic compression on bone healing under external fixation. Clin Orthop. 1990; (256):260-273.2. Kenwright J, et al. Controlled mechanical stimulation in the treatment of tibial fractures. Clin Orthop Relat Res. 1989; (241):36-47. 3. Vijayakumar V, et al. Load transmission through a healing tibial fracture. Clin Biomech. 2006; (21):49-53.4. Gardner TN, et al. The influence of mechanical stimulus on the pattern of tissue differentiation in a long bone fracture - an FEM study. J Biomech. 2000; (33):415-425.5. Gardner TN, et al. The biomechanical environment of a bone fracture and its influence upon the morphology of healing. Med Eng Phys. 2003.
The Osteonexus is a unique dynamizing external fixator that actively induces controllable micromovements.Finite element analysis demonstrates that the Osteonexus design produces therapeutic stresses at the fracture site that would reduce healing time.Power consumption of the device provides the physician with a diagnostic tool to monitor fracture healing process.
Fracture healing requires:Good fracture fixationPartial loading of fracture site
Partial axial loading:Through micromovements of 1 mm at 0.5 Hz have been shown to speed fracture healing by 27%1
Stimulates callus formationAccelerates remodeling of osteocytes late in the healing phase2
The Osteonexus Active Dynamizer:Incorporates effective fixationProvides controlled micromovements to promote fracture healingAccommodates patients unable to load bones
The stiffer the spring, the more motor power is required to induce micromovement.The relationship between average power consumption and stiffness can be used as a standard curve.
y = 0.8776e0.0887x
R2 = 0.9657
0.8
1
1.2
1.4
1.6
1.8
2
0 2 4 6 8
Spring Constant (N/mm)
Ave
rage
Pow
er C
onsu
mpt
ion
(W)
