Spinal imaging and intervention: 1998.

Imaging of the lumbar spine is the most common application of magnetic resonance (MR) imaging in many radiologic practices. MR imaging has replaced computed tomography (CT) and CT myelography as the primary mode of spinal imaging and has relegated myelography to a secondary role in the evaluation of lumbar spinal disorders. At the same time, however, it has become evident that the correlation between gross anatomic findings as depicted on MR images and the clinical signs and symptoms detected by the clinician may be lacking. Defining the precise anatomic source of patients' complaints on the basis of imaging studies must be approached judiciously because a significant proportion of the population has disc disease as depicted on imaging studies, yet many have no clinical findings.

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.

Sacral screw loads in lumbosacral fixation for spinal deformity.

Fixation to the sacrum and pelvis is a problem in the operative treatment of spinal deformity. Previous testing of pedicle screws address axial pull-out strength, yet how screws are loaded in vivo remains unknown. The goals of this study were to determine the loads experienced by sacral screws when loaded as part of Cotrel-Dubousset (CD) sacral instrumentation and whether different anterior grafting methods would effect screw loads. Sacral screws were modified to become transducers capable of measuring axial and bending loads. The screw transducers were incorporated into the sacral fixation of CD instrumentation in seven calf spines. Specimens were loaded to simulate flexion. The sacral screws carried axial loads (1.1 N/[Nm of load]) and bending moments (1.1 Nm/[Nm of load]). The results suggest bending of the sacral screws may be important in their failure, and screw loading was not dependent on graft types used.

In vivo analysis of canine intervertebral and facet motion.

Using an instrumented spatial linkage, a method for measuring intervertebral motion in vivo was developed and used on six dogs. The segmental motion was recorded as the animals were exercised in routine functions. The standing posture was found to be a repeatable position. During walking, the average excursion between opposing facets was 3.4 +/- 1.3 mm, as the L2-L3 motion segment moved into 2.3 degrees of kyphosis with respect to the standing position. This method has the ability of measuring facet motion (+/- 0.7 mm), vertebral body motion (+/- 0.5 mm), and vertebral body rotations (+/- 0.6 degrees) with suitable accuracy such that it is a useful tool in documenting the in vivo response of a motion segment to surgical procedures.