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Effect of Obesity on Spinal Loads during Various Activities: A Combined in Vivo-Modeling Approach

Kazemi, Hossein | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49313 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Arjmand, Navid; Parnianpour, Mohammad
  7. Abstract:
  8. Obesity is a worldwide growing health challenge affecting ~30% of the world's population. Increased rate of disc degeneration and herniation, low back pain and surgery has been reported in obese individuals. Although obesity-related low back diseases have multifactorial etiology, presumably greater mechanical loads on the spine of heavier individuals during their daily activities may be considered as a risk factor. Likely larger trunk muscle sizes, disc sizes and thus passive stiffness in heavier individuals may however partly or fully offset the effect of their additional body weight on the spinal loads. In absence of in vivo approaches, the present study aims to construct subject-specific musculoskeletal models of five obese (BMI>30 kg/m2) and five normal-weight (BMI<25 kg/m2) individuals to investigate differences between their spinal loads during a number of loaded and unloaded static activities. A 3.0 Tesla Siemens MR machine was used to take images in the supine position from the T1-S1 spine of five healthy young male obese (average BMI≈34 kg/m2 and BW≈105 kg) and five age-and-height matched normal-weight subjects (average BMI≈23 kg/m2 and BW≈70 kg). The following parameters were determined from the images: Average cross-sectional area (ACSA), anterior-posterior (AP) and medio-lateral (ML) moment arms of the erector spinae (ES), quadratus lumborum (QL), iliopsoas (IP), rectus abdominus (RA), external oblique (EO) and internal+Transverse oblique (ITO) muscles at all lumbar disc levels (T12-L1 through L5-S1), masses and center of masses (CoM) of all trunk segments ( T1-L5) and CSAs of the lumbar discs (T12-L5). For each individual, a subject-specific musculoskeletal T1-S1 model was developed based on the foregoing measured parameters in The AnyBody Modeling SystemTM and spine loads were estimated in static upright and forward flexed postures. ACSAs of all muscles were larger in obese individuals as compared to normal-weight ones (p<0.05 except for RA and IP). At the L1-L5 levels, AP moment arms of abdominal muscles were larger in obese individuals while those of back muscles (ES, MF, and QL) were almost equal to those of normal subjects (p>0.05). Mass of all T1-L5 segments was significantly larger in obese individuals (p<0.05). Moment arm of CoMs with respect to the vertebrae were larger at all segments for obese individuals (up to 1.5 cm in some levels) but with no statistical significance (p>0.05). CSA of the L1-L5 discs were slightly larger in obese individuals (<10% in average, p>0.05). For obese individuals, disc heights were slightly larger only at the T12-L3 levels (p>0.05) while they were smaller at the L3-L5 levels (p>0.05). The model predicted considerably larger L4-S1 mean compression and AP shear loads for obese individuals. This was due to the larger BW and more anterior CoMs in obese individuals and almost identical AP moment arms of back muscles and disc sizes (and thus similar joint passive stiffness) for both groups
  9. Keywords:
  10. Spine ; Low Back Pain ; Biomechanical Models ; Optimization ; Functional Magnetic Resonance Imaging (FMRI) ; Obesity

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