Improved Splines Fitting of Intervertebral Motion by Local Smoothing Variation

Knowledge of intervertebral motion provides important information about the level of stabilization of a single spine segment. By using X-ray fluoroscopy it is possible to screen spinal motion during spontaneous patient’s movement. Discrete-time experimental measurements can be interpolated by smoothing splines, which provide both noise reduction and continuous-time representation of joint motion. A patient, albeit trained, is unable to perform a spontaneous movement with such regularity to keep constant certain parameters such as the speed. Therefore, spontaneous motion can include different tracts performed at different speed. The use of a single smoothing parameter to fit the entire motion for spline fitting requires a compromise. Alternatively, smaller differences with the experimental data and more stable motion parameters can be obtained by appropriately varying the smoothing parameter: less smoothing is applied in higher velocity tracts. This concept has been applied to the analysis of cervical intervertebral motion as obtained by processing sequences of fluoroscopic images. Preliminary results showed more close representation of the experimental data without missing the regular progression of the joint movement.