BACKGROUND CONTEXT: It is estimated that up to 80% of the general population will experience at least one significant bout of low back pain in their lifetime. The leading known cause of low back pain is degenerative disc disease (DDD). Many established risk factors for low back pain and DDD are mechanical in nature and are often related to occupational activities, such as poor posture and frequent/heavy lifting. Altered mechanical loading in the spine has been shown to be a potential stimulus for disc degeneration. However, a link between occupational/environmental factors and intervertebral loading has never been demonstrated in vivo. We hypothesize that intervertebral loading is highly dependent on muscle activation and recruitment. These relationships are significant because they provide a potential connection between everyday activities and low back pain.
PURPOSE: The purpose of this study was to use a novel force-sensing interbody implant to measure in vivo loads in the disc space of the goat cervical spine in real time and analyze their dependence on activity, posture, rate of motion, and whole body compensation

Glennon, Joseph C.

Grabowsky, Mary Beth M.

Ledet, Eric H.

Wachs, Rebecca A.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnBiological Systems Engineering: Papers andPublications Biological Systems Engineering2012P95. In Vivo Loads in the Cervical Spine: APreliminary Investigation Using a Force-SensingImplantRebecca A. WachsRensselaer Polytechnic Institute, rebecca.wachs@unl.eduMary Beth M. GrabowskyRensselaer Polytechnic InstituteJoseph C. GlennonVeterinary Specialties Referral CenterEric H. LedetRensselaer Polytechnic Institute, ledete@rpi.eduFollow this and additional works at: http://digitalcommons.unl.edu/biosysengfacpubPart of the Bioresource and Agricultural Engineering Commons, Environmental EngineeringCommons, and the Other Civil and Environmental Engineering CommonsThis Article is brought to you for free and open access by the Biological Systems Engineering at DigitalCommons@University of Nebraska - Lincoln. Ithas been accepted for inclusion in Biological Systems Engineering: Papers and Publications by an authorized administrator ofDigitalCommons@University of Nebraska - Lincoln.Wachs, Rebecca A.; Grabowsky, Mary Beth M.; Glennon, Joseph C.; and Ledet, Eric H., "P95. In Vivo Loads in the Cervical Spine: APreliminary Investigation Using a Force-Sensing Implant" (2012). Biological Systems Engineering: Papers and Publications. 500.http://digitalcommons.unl.edu/biosysengfacpub/500Published in Proceedings of the NASS 27th Annual Meeting / The Spine Journal 12 (2012) 99S–165S Copyright © 2012 Elsevier. Used by permission. http://dx.doi.org/10.1016/j.spinee.2012.08.369   P95. In Vivo Loads in the Cervical Spine: A Preliminary Investigation Using a Force-Sensing Implant  Rebecca A. Wachs, MS1  Mary Beth M. Grabowsky2  Joseph Glennon, VMD3 Eric H. Ledet, PhD1  1 Rensselaer Polytechnic Institute, Troy, NY 2 Rensselaer Polytechnic Institute, Montclair, NJ 3 Capital District Veterinary Surgical Associates, New York, NY  BACKGROUND CONTEXT: It is estimated that up to 80% of the general population will experience at least one significant bout of low back pain in their lifetime. The leading known cause of low back pain is degenerative disc disease (DDD). Many established risk factors for low back pain and DDD are mechanical in nature and are often related to occupational activities, such as poor posture and frequent/heavy lifting. Altered mechanical loading in the spine has been shown to be a potential stimulus for disc degeneration. However, a link between occupational/environmental factors and intervertebral loading has never been demonstrated in vivo. We hypothesize that intervertebral loading is highly dependent on muscle activation and recruitment. These relationships are significant because they provide a potential connection between everyday activities and low back pain.  PURPOSE: The purpose of this study was to use a novel force-sensing interbody implant to measure in vivo loads in the disc space of the goat cervical spine in real time and analyze their dependence on activity, posture, rate of motion, and whole body compensation.  STUDY DESIGN/SETTING: In vivo large animal model.  METHODS: A novel force-sensing implant was developed to directly measure uniaxial compressive loads in the goat cervical disc space in vivo. Following IACUC approval, Alpine-Nubian cross bred goats underwent anterior cervical discectomy and implant placement at C4-C5. Postoperatively, the goat performed several prescribed activities while interbody forces were measured and activities were recorded to video. For flexionextension and walking trials, measured loads were correlated to factors including head position, neck position, rate of motion, and technique.  RESULTS: For each of the 125 flexion-extension trials, the change in force magnitude was substantial with a maximum shift of 179 N as the head and neck moved from full extension to full flexion. In all trials, peak loads corresponded to extensor muscle activation during deceleration of the head/neck. Data suggest that increasing extensor muscle activity causes increased interbody loading. Altering neck position, head position, or rate of motion strongly affected the magnitude of loading. A distinct pattern of forces was also observed for walking and running that coincided with the gait cycle. Like flexion/extension data, highest forces appeared to correspond with extensor muscle activity. Force magnitude was highly dependent on head position, rate of acceleration or deceleration, and gait speed (walking versus running).  CONCLUSIONS: Results from this study indicate a strong correlation between interbody force and activity, with substantial and repeatable changes in force observed for several motions. Although muscle recruitment was not specifically measured in this study, the highest force measurements consistently correlated to maximum head deceleration during neck flexion. These points likely correspond with maximum contraction of the primary neck extensors to decelerate the head and maximum contraction of the primary neck flexors to pull the head into flexion. Furthermore, slight alterations in the technique used to achieve motion caused significant differences in the resulting loads. These results imply that muscle forces are the major contributor to axial compressive spinal loads during motion, and may play a primary role in the development of low back pain.  FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.  

P95. In Vivo Loads in the Cervical Spine: A Preliminary Investigation Using a Force-Sensing Implant

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Biological Systems Engineering: Papers and
Publications Biological Systems Engineering
2012
P95. In Vivo Loads in the Cervical Spine: A
Preliminary Investigation Using a Force-Sensing
Implant
Rebecca A. Wachs
Rensselaer Polytechnic Institute, rebecca.wachs@unl.edu
Mary Beth M. Grabowsky
Rensselaer Polytechnic Institute
Joseph C. Glennon
Veterinary Specialties Referral Center
Eric H. Ledet
Rensselaer Polytechnic Institute, ledete@rpi.edu
Follow this and additional works at: http://digitalcommons.unl.edu/biosysengfacpub
Part of the Bioresource and Agricultural Engineering Commons, Environmental Engineering
Commons, and the Other Civil and Environmental Engineering Commons
This Article is brought to you for free and open access by the Biological Systems Engineering at DigitalCommons@University of Nebraska - Lincoln. It
has been accepted for inclusion in Biological Systems Engineering: Papers and Publications by an authorized administrator of
DigitalCommons@University of Nebraska - Lincoln.
Wachs, Rebecca A.; Grabowsky, Mary Beth M.; Glennon, Joseph C.; and Ledet, Eric H., "P95. In Vivo Loads in the Cervical Spine: A
Preliminary Investigation Using a Force-Sensing Implant" (2012). Biological Systems Engineering: Papers and Publications. 500.
http://digitalcommons.unl.edu/biosysengfacpub/500
Published in Proceedings of the NASS 27th Annual Meeting / The 
Spine Journal 12 (2012) 99S–165S 
Copyright © 2012 Elsevier. Used by permission. 
http://dx.doi.org/10.1016/j.spinee.2012.08.369 
 
 
P95. In Vivo Loads in the Cervical Spine: 
A Preliminary Investigation Using a 
Force-Sensing Implant 
 
Rebecca A. Wachs, MS1  
Mary Beth M. Grabowsky2  
Joseph Glennon, VMD3 
Eric H. Ledet, PhD1 
 
1 Rensselaer Polytechnic Institute, Troy, NY 
2 Rensselaer Polytechnic Institute, Montclair, NJ 
3 Capital District Veterinary Surgical Associates, New York, NY 
 
BACKGROUND CONTEXT: It is estimated that up to 80% of the 
general population will experience at least one significant bout of low 
back pain in their lifetime. The leading known cause of low back pain 
is degenerative disc disease (DDD). Many established risk factors for 
low back pain and DDD are mechanical in nature and are often related 
to occupational activities, such as poor posture and frequent/heavy 
lifting. Altered mechanical loading in the spine has been shown to be 
a potential stimulus for disc degeneration. However, a link between 
occupational/environmental factors and intervertebral loading has 
never been demonstrated in vivo. We hypothesize that intervertebral 
loading is highly dependent on muscle activation and recruitment. 
These relationships are significant because they provide a potential 
connection between everyday activities and low back pain. 
 
PURPOSE: The purpose of this study was to use a novel force-sensing 
interbody implant to measure in vivo loads in the disc space of the 
goat cervical spine in real time and analyze their dependence on 
activity, posture, rate of motion, and whole body compensation. 
 
STUDY DESIGN/SETTING: In vivo large animal model. 
 
METHODS: A novel force-sensing implant was developed to directly 
measure uniaxial compressive loads in the goat cervical disc space in 
vivo. Following IACUC approval, Alpine-Nubian cross bred goats 
underwent anterior cervical discectomy and implant placement at C4-
C5. Postoperatively, the goat performed several prescribed activities 
while interbody forces were measured and activities were recorded 
to video. For flexionextension and walking trials, measured loads 
were correlated to factors including head position, neck position, rate 
of motion, and technique. 
 RESULTS: For each of the 125 flexion-extension trials, the change in 
force magnitude was substantial with a maximum shift of 179 N as 
the head and neck moved from full extension to full flexion. In all 
trials, peak loads corresponded to extensor muscle activation during 
deceleration of the head/neck. Data suggest that increasing extensor 
muscle activity causes increased interbody loading. Altering neck 
position, head position, or rate of motion strongly affected the 
magnitude of loading. A distinct pattern of forces was also observed 
for walking and running that coincided with the gait cycle. Like 
flexion/extension data, highest forces appeared to correspond with 
extensor muscle activity. Force magnitude was highly dependent on 
head position, rate of acceleration or deceleration, and gait speed 
(walking versus running). 
 
CONCLUSIONS: Results from this study indicate a strong correlation 
between interbody force and activity, with substantial and repeatable 
changes in force observed for several motions. Although muscle 
recruitment was not specifically measured in this study, the highest 
force measurements consistently correlated to maximum head 
deceleration during neck flexion. These points likely correspond with 
maximum contraction of the primary neck extensors to decelerate the 
head and maximum contraction of the primary neck flexors to pull 
the head into flexion. Furthermore, slight alterations in the technique 
used to achieve motion caused significant differences in the resulting 
loads. These results imply that muscle forces are the major 
contributor to axial compressive spinal loads during motion, and may 
play a primary role in the development of low back pain. 
 
FDA DEVICE/DRUG STATUS: This abstract does not discuss or include 
any applicable devices or drugs. 
 


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P95. In Vivo Loads in the Cervical Spine: A Preliminary Investigation Using a Force-Sensing Implant

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