Estimate of Muscle Contribution to Spinal Loads During Continuous Passive Motion for Low Back Pain



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This research is a first approximation model for determining the active loads in the lumbar spine during continuous passive motion (CPM) in the prone position. The study consisted of two groups' five healthy subjects and four subjects with the diagnosis of mechanical low back pain (LBP) at L4/L5/S1. Solutions to the issues in this investigation were sought in three stages. First was the introduction and synchronization of a number of sensors for making valid, time-linked observations of kinematic variables during CPM. Second, a root mean square myoelectric signal (RMS-MES) model was needed to calibrate muscle activation levels during feasible standardized tasks to be performed by low back pain patients. Such a model must be able to partition passive and active load components acting on the lumbar spine and to estimate equivalent muscle loads from activity observed during CPM. Finally, biomechanical models are necessary for estimating the passive, active and total loads transmitted through the trunk during CPM. Testing consisted of three calibration stances: upright, weighted holding 3lb weights in hands extended 90?? the shoulder and CPM at intermediate speed 11.5 degrees, fast speed 11.5 degrees, and intermediate speed at 20 degrees. Measurements recorded: 8 myoelectric signals (MES) of paired muscles (latissimus dorsi, multifidus, gluteus maximus, and hamstring femoris), 4 Polhemus Fastrak electromagnetic positioning sensors (lumbar, sacrum, 10cm posterior to center of knee, and table), linear accelerometer, uniaxial load cell, and modified treatment table with AMTI force plate. Results demonstrate consistent repeatable measurements from the instrumented treatment table. The active loads created during CPM are minimal in comparison to the passive loads for both groups and therefore the muscle loads are not counteracting the implied therapy.

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