The prediction of lumbar spine geometry: method development and validation.

OBJECTIVES To develop and validate a new method of predicting the neutral lumbar spine curve from external (non-invasive electrogoniometer) measurements. BACKGROUND Non-invasive techniques for lumbar spine geometry prediction suffer from a lack of a complete geometry description, problems with applicability to field conditions, or both. METHODS The study consisted of three steps. First, utilizing lateral imaging (MRI and X-ray pictures) of the lumbosacral junction, the torso geometry was described using measures of lumbar lordosis via the Cobb method. Second, the relationship between imaging based measurement of lumbar spinal curvature and externally measured torso flexion angle in the sagittal plane using a goniometer was determined. Finally, method validation was performed with an independent set of nine subjects. The predicted lumbar spine curve was determined and the prediction errors were analyzed against the measured curves from digitized lateral X-ray images of the lumbosacral junction. RESULTS The shape of the lumbar curve was described as function of three externally measured parameters. The lumbar spine Cobb angle, segmental centroid positions (S(1)-T(12)), and segmental orientations were predicted from the external lumbar motion monitor measurements, with average precisions of 5.8 degrees , 4.4 mm, and 3.9 degrees , respectively. CONCLUSIONS The position and orientation of each segment (vertebrae and disc), along with the lumbar spine lordosis, can be predicted in the neutral posture using data from back angular measurements. RELEVANCE The consideration of the spine as a curve is necessary to accurately quantify and describe the forces acting along the (lumbar) vertebral column for any given loading. The method could be a very useful prediction tool for industrial and laboratory experiments, as well as analytical models.