An improved technique for measuring in vivo intervertebral motion in the canine

Study Design. An experimental animal study using an established technique for measuring in vivo motion in canines was designed to improve measurement techniques and to eliminate the effects of the instrument mounting technique on the tissue and subsequently on the motion being measured. Objectives. The purpose of this study was to improve a technique for measuring in vivo intervertebral motion in canines, so that the measuring technique did not affect the motion being measured. Summary of Background Data. Biplanar radiography has been used to measure in vivo intervertebral motion, but involves radiation exposure and expensive equipment. Electromechanical devices have been used more recently but have had significant effects on the motion over extended time periods. Methods. Intervertebral motion was measured using an instrumented spatial linkage in eight adult canines divided into two groups that differed regarding the method of "mounting pin" placement. Group I had open surgical placement of the pins and Group II had pins placed into the spinous processes. After pin implantation, the instrumented spatial linkage was attached and motion data were recorded during walking. This testing sequence was repeated 3 weeks later. Animals were killed and intervertebral and facet motion were calculated from the experimental data and compared statistically. Results. Facet motion decreased 1 to 3 weeks after pin implantation for animals of group I (3.4 ± 0.2 mm to 1.1 ± 0.3 mm), whereas the facet excursion of animals in Group II showed no change (3.0 ± 0.2 mm and 3.1 ± 0.3 mm). Conclusions. A new method of measuring in vivo intervertebral motion in canines has been developed and shown to have no significant affect on the segment mechanics.