THE SPONDYLOLYTIC VERTEBRA AND ITS ADJACENT SEGMENT - MOBILITY MEASURED BEFORE AND AFTER POSTEROLATERAL FUSION

Study Design. By using roentgen stereophotogram metric analysis in six patients having tantalum indicators implanted at a preoperative exter nal fixation lest, the mobility in the spondylolytic lumbosacral level and its adjacent segment could be studied before fusion and during th e course of postoperative fusion consolidation. Objective. To study th e mobility effects on the segment adjacent to a lumbar fusion over tim e from the preoperative situation until fusion healing as defined by r oentgen stereophotogrammetric analysis. Summary of Background Data. In vitro studies indicate that the altered biomechanical situation after lumbar fusion increases the intradiscal pressure and changes the kine matics in the juxta-fused segment. Methods. Six patients with low grad e spondylolysis-olisthesis were scheduled for fusion of the spondyloly tic lumbosacral segment after a preoperative external fixation test. T he latter procedure also included implantation of tantalum markers for spinal roentgen stereophotogrammetric analysis. Each patient was exam ined by roentgen stereophotogrammetric analysis at four separate occas ions: before fusion (2 months after removal of the external frame) and 3, 6, and 12 months after surgery. The translatory movements of the L 5 vertebra in relation to sacrum and of the L4 vertebra in relation to the L5 vertebra were calculated at each examination. Results. For the juxtafused L4-L5 level, increased and decreased mobility patterns cou ld be identified. Transformation of the preoperative mobility in the l umbosacral segment to the adjacent segment during fusion consolidation was verified in two patients but was not a general phenomenon. Conclu sion. Fusion of the lumbosacral segment can alter the kinematics of th e adjacent segment, redistributing the mobility toward relative hyperm obility in the juxtafused segment.