Testing the mechanostat theory: the relationship between CT bone and muscle variables in mid-thigh in elderly men and women and association with incident lower limb fractures
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1
University of Iceland, Iceland
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2
Icelandic Heart Association, Iceland
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3
Icelandic Heart Association, Iceland
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4
University Hospital, Sweden
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5
Landspitali-University Hospital, Iceland
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6
National Institute on Aging, United States
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7
University of California, United States
Background: The mechanostat theory suggests a fixed ratio between bone and muscle as an adaptation to mechanical loading explaining the loss of bone and increasing fracture risk with age by sarcopenia.{BR}Methods and study group: In this cross-sectional study we investigated the relationship between muscle and bone parameters in mid-thigh in elderly men and women using computed tomography (CT). Additionally we have studied the association of these variables with incident low trauma lower limb fractures. A total of 3546 elderly individuals (1786 women, 1760 men) age 67-93 years, participants in a population-based study, the Age, Gene/Environment Susceptibility-Reykjavik Study (AGES-Reykjavík) were studied and of those 109 women and 64 men sustained a fracture during follow-up of 4.2 years. We used a single axial CT section through the mid-thigh (cross-sectional muscular area, medullary area, cortical area and thickness, buckling ratio, the ratio of bone radius to cortical thickness). Associations between variables were estimated by Pearson's correlations. The predictive power of these measures for fractures was tested by Cox proportional hazards regression.{BR}Results: The muscular area declined with 10 years in age similarly in both sexes. The increment in medullary area in mid femur with age was fourfold greater in women than in men. The cortical thickness declined significantly in both sexes but twofold more in women. Cortical area was positively associated with muscular area in both sexes and remained significant after adjustment for body size and age (r=0.16, p<0.001), explaining less than 5% of variability in cortical area. The association between muscular area and medullary area was minimally significant in women but not in men after correcting for body size and age. Small muscular area, large medullary area and high buckling ratio were significant predictors of fractures after adjustment for age and BMI in both sexes. The muscular area conferred significant protection against fracture independently of buckling ratio and meduallary area.{BR}Conclusion: The findings suggest that there are only weak correlations between muscles in mid-thigh and bone parameters which predict lower limb fractures after adjusting for body size. However, muscle parameters seem to be protective against fractures indirectly, independent of bone parameters.
Keywords:
Bones,
Bone Research
Conference:
2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society, Cambridge, United Kingdom, 27 Jun - 29 Jun, 2011.
Presentation Type:
Oral
Topic:
Abstracts
Citation:
Johannesdottir
F,
Aspelund
T,
Siggeirsdottir
K,
Jonsson
B,
Mogensen
B,
Sigurdsson
S,
Harris
T,
Lang
T,
Gudnason
V and
Sigurdsson
G
(2011). Testing the mechanostat theory: the relationship between CT bone and muscle variables in mid-thigh in elderly men and women and association with incident lower limb fractures.
Front. Endocrinol.
Conference Abstract:
2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society.
doi: 10.3389/conf.fendo.2011.02.00030
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Received:
30 Sep 2011;
Published Online:
30 Sep 2011.
*
Correspondence:
Ms. FJ Johannesdottir, University of Iceland, Reykjavik, Iceland, fjolajo@hi.is