Obesity and spinal loads; a combined MR imaging and subject-specific modeling investigation

Epidemiological studies have identified obesity as a possible risk factor for low back disorders. Biomechanical models can help test such hypothesis and shed light on the mechanism involved. A novel subject-specific musculoskeletal-modelling approach is introduced to estimate spinal loads during static activities in five healthy obese (BMI > 30 kg/m(2)) and five normal-weight (20 < BMI < 25 kg/m(2)) individuals. Subjects underwent T1 through S1 MR imaging thereby measuring cross-sectional-area (CSA) and moment arms of trunk muscles together with mass and center of mass (CoM) of T1-L5 segments. MR based subject-specific models estimated spinal loads using a kinematics/optimization-driven approach. Average CSAs of muscles, moment arms of abdominal muscles, mass and sagittal moment arm of CoM of T1-L5 segments were larger in obese individuals (p < 0.05 except for the moment arm of CoMs) but moment arms of their back muscles were similar to those of normal-weight individuals (p > 0.05). Heavier subjects did not necessarily have larger muscle moment arms (e.g., they were larger in 64 kg (BMI = 20.7 kg/m(2)) subject than 78 kg (BMI = 24.6 kg/m(2)) subject) or greater T1-L5 trunk weight (e.g., the 97 kg (BMI = 31 kg/m(2)) subject had similar trunk weight as 109 kg (BMI = 33.3 kg/m(2)) subject). Obese individuals had in average greater spinal loads than normal-weight ones but heavier subjects did not necessarily have greater spinal loads (117 kg (BMI = 40.0 kg/m(2)) subject had rather similar L5-S1 compression as 105 kg (BMI = 34.7 kg/m(2)) subject). Predicted L4-L5 intradiscal pressures for the normal-weight subjects ranged close to the measured values (R-2 = 0.85-0.92). Obese individuals did not necessarily have greater IDPs than normal-weight ones. (C) 2017 Elsevier Ltd. All rights reserved.