The effect of osteoporotic vertebral fracture on predicted spinal loads in vivo
- 304 Downloads
The aetiology of osteoporotic vertebral fractures is multi-factorial, and cannot be explained solely by low bone mass. After sustaining an initial vertebral fracture, the risk of subsequent fracture increases greatly. Examination of physiologic loads imposed on vertebral bodies may help to explain a mechanism underlying this fracture cascade. This study tested the hypothesis that model-derived segmental vertebral loading is greater in individuals who have sustained an osteoporotic vertebral fracture compared to those with osteoporosis and no history of fracture. Flexion moments, and compression and shear loads were calculated from T2 to L5 in 12 participants with fractures (66.4 ± 6.4 years, 162.2 ± 5.1 cm, 69.1 ± 11.2 kg) and 19 without fractures (62.9 ± 7.9 years, 158.3 ± 4.4 cm, 59.3 ± 8.9 kg) while standing. Static analysis was used to solve gravitational loads while muscle-derived forces were calculated using a detailed trunk muscle model driven by optimization with a cost function set to minimise muscle fatigue. Least squares regression was used to derive polynomial functions to describe normalised load profiles. Regression co-efficients were compared between groups to examine differences in loading profiles. Loading at the fractured level, and at one level above and below, were also compared between groups. The fracture group had significantly greater normalised compression (p = 0.0008) and shear force (p < 0.0001) profiles and a trend for a greater flexion moment profile. At the level of fracture, a significantly greater flexion moment (p = 0.001) and shear force (p < 0.001) was observed in the fracture group. A greater flexion moment (p = 0.003) and compression force (p = 0.007) one level below the fracture, and a greater flexion moment (p = 0.002) and shear force (p = 0.002) one level above the fracture was observed in the fracture group. The differences observed in multi-level spinal loading between the groups may explain a mechanism for increased risk of subsequent vertebral fractures. Interventions aimed at restoring vertebral morphology or reduce thoracic curvature may assist in normalising spine load profiles.
KeywordsOsteoporosis Vertebral fracture Spine loading Biomechanics Optimization
The authors gratefully acknowledge the assistance of Associate Professor David Pearsall (McGill University, Canada) with providing additional trunk inertial data and the Medical Imaging department at St. Vincent’s Hospital, Melbourne, Australia.
Funding: seeding grant 013/05: Physiotherapy Research Foundation (Australia).
- 2.Alexeeva L, Burckhardt P, Christiansen C et al (1994) Report of a World Health Organization study group. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. WHO, GenevaGoogle Scholar
- 4.Briggs A, Wark J, Phillips B et al (2005) Subregional bone mineral density characteristics in the lumbar spine: an in vivo pilot study using dual energy X-ray absorptiometry. Annual scientific meeting of the Australian and New Zealand bone and mineral society, Perth, Australia, 7–9 September 2005Google Scholar
- 6.Briggs AM, Tully EA, Adams PE et al (2005) Vertebral centroid and Cobb angle measures of thoracic kyphosis. Intern Med J 35:A96Google Scholar
- 11.Dieën JHv, Kingma I (2005) Effects of antagonistic co-contraction on differences between electromyography based and optimization based estimates of spinal forces. Ergonomics 48:411–426Google Scholar
- 40.Motulsky H, Christopoulos A (2003) Fitting models to biological data using linear and non-linear regression: a practical guide to curve fitting. GraphPad Software Inc., San DiegoGoogle Scholar
- 49.Winter DA (1990) Biomechanics and motor control of human movement, 2nd edn. Wiley, New YorkGoogle Scholar