Kinematic determination of the line of loading in the sagittal plane relative to the human vertebral column

The main objectives of this research were to (1) develop a technique to accurately determine the exact location of the line of loading on the lumbar spine in the sagittal plane (LLSP) of the human subjects in this study, (2) determine how much the spine and the location of the LLSP distort with the alterations caused by standard sagittal plane X-ray techniques, and (3) provide an accurate account for the errors associated with performing the spine loading measurement technique developed for this study.In order to achieve the first and second objectives, i.e., establishing the technique and studying distortions from taking X-rays, an experiment aimed at studying the force distribution of the body during static standing postures in conjunction with radiographic imaging of the spine was conducted. Electromyography data was also collected to support and validate assumptions about the standing posture of the subjects while participating in the experiment.In order to achieve the third objective, an error analysis of the technique was conducted where all the major sources of error were identified and quantified. Correction factors were derived that may be used to adjust previous accounts of the location of the body\u27s LLSP.Lateral position data for the three dimensional location of critical landmarks on the body surface was determined using a motion monitoring device. By comparing these results with radiographic data, the exact location of the LLSP relative to the vertebral column was found to be located in the anterior section of the lumbar region of the vertebral column. The major errors associated with this measuring technique were found to be magnification errors across the X-ray field, body sways during force measurements and subject repositioning. The errors from the repositioning of subject for the X-ray and the distortions of the spine in the X-ray positions versus normal, relaxed standing were far greater than all other errors identified. Taking all errors into account, this procedure for locating the line of loading of the lumbar spine is accurate to +/-3mm