Abstract
Study design:
Cross-sectional observation.
Objectives:
To explore the association between muscle size and function, and indices of bone strength among a sample of adults with chronic spinal cord injury (SCI).
Setting:
Ontario, Canada.
Methods:
Sixty-five participants (n=47 men) with chronic SCI (C1-T12 American Spinal Injury Association Impairment Scale (AIS) A–D) were recruited, mean±s.d. age 49.4±12.8 years and years post-injury 14.3±10.7. Muscle cross-sectional area (CSA) and indices of bone strength at the distal tibia and tibia shaft were measured by peripheral quantitative computed tomography. Muscle CSA was multiplied by tibia length to obtain muscle-bending moment (MBM), a surrogate of torque. Plantar flexor components of the lower-extremity motor scores (pf-LEMS) were used as clinical measures of muscle function. Pearson's correlations (r) were used to determine the strength of relationships.
Results:
Correlations were found between MBM and indices of bone strength at the distal tibia and tibia shaft (r=0.44–0.56), as well as between pf-LEMS and indices of bone strength at the distal tibia and tibia shaft (r=0.37–0.71). pf-LEMS had a stronger association with bone variables at the distal tibia compared with MBM (r=0.6 vs r=0.4). All relationships between muscle and bone remained significant when controlling for the duration of injury.
Conclusion:
It appears that lower limb muscle size and function are more strongly correlated with bone strength indices at the distal tibia than at the tibia shaft among individuals with SCI. The relationships between muscle and bone are clinically important, as muscle CSA and strength (motor scores) are potentially amenable to rehabilitation intervention(s).
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Acknowledgements
This material was based on work supported partially by the Ontario Graduate Scholarship, Canadian Institute for Health Research Frederick Banting and Charles Best Canada Graduate Scholarship, and Ontario Neurotrauma Foundation (ONF), Grant ONF-SCI-2006-WAVE-445. J O Totosy de Zepetnek was the recipient of an Ontario Graduate Scholarship and the Canadian Institute for Health Research, Frederick Banting and Charles Best Canada Graduate Scholarship Master’s Award. We acknowledge the support of the Toronto Rehabilitation Institute, which receives funding under the provincial rehabilitation research program from the Ministry of Health and Long-Term Care in Ontario. We thank Jude Delparte and Dr David Gonzalez for their help with data analysis.
Author contributions: Study concept: JO Totosy de Zepetnek, LM Giangregorio, BC Craven; acquisition of data: JO Totosy de Zepetnek, LM Giangregorio, BC Craven; interpretation of data: JO Totosy de Zepetnek, LM Giangregorio, BC Craven; drafting of manuscript: JO Totosy de Zepetnek; critical revision of manuscript for important intellectual content: LM Giangregorio, BC Craven; obtained funding: JO Totosy de Zepetnek, LM Giangregorio, BC Craven.
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de Zepetnek, J., Craven, B. & Giangregorio, L. An evaluation of the muscle-bone unit theory among individuals with chronic spinal cord injury. Spinal Cord 50, 147–152 (2012). https://doi.org/10.1038/sc.2011.99
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DOI: https://doi.org/10.1038/sc.2011.99
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