ABSTRACT
Objective To measure the range of motion (ROM) of the lumbar pedicle screw entrance point (LPSEP) in vivo during unrestricted motion under physiological weight bearing.Methods Eleven healthy volunteers aged 45-60 years underwent MRI scans in a supine position.Three-dimensional (3D) models of L2-5 were constructed.Next,each volunteer was asked to stand and was positioned in the following sequence:standing,45° flexion,maximal extension,maximal left-right twisting,while two orthogonal fluoroscopic images were taken simultaneously at each position.The MRI models were matched to the osseous outlines of the images from the two orthogonal views to determine the position of the vertebrae in 3D at each position.Coordinate systems were established to study the ROM of the LPSEP.Results The predominant translations were along anteroposterior and craniocaudal axis from supine to standing position (average,2.44mm and 2.35 mm).Rotation of the LPSEP occurred mainly around the mediolateral axis(average,3.91 °).During flexion-extension movements of the trunk,the predominant translation were along anteroposterior and craniocaudal axis and rotation were around mediolateral axis.During lateral bending and twisting,ROM of LPSEP did not rotate or translate in one dominant direction.Instead,the resulting motion represented a combination of rotation and translation in different directions.There was no significantly difference in translation and rotation between the three axis in L4,5segment (P＞0.05).Conclusion The kinematic behaviors of the LPSEP of the upper lumbar spine (L2,3 and L3,4) are similar which are different from that of the lower lumbar spine (L4,5).