Kirkham B. Wood

Magnetic Resonance Imaging of the Thoracic Spine. Evaluation of Asymptomatic Individuals (

We reviewed magnetic resonance imaging studies of the thoracic spines of ninety asymptomatic individuals to determine the prevalence of abnormal anatomical findings. This group included sixty individuals who had no history of any thoracic or lumbar pain and thirty individuals who had a history of low-back pain only. In addition, we reviewed imaging studies of eighteen patients who had an operatively proved herniation of a thoracic disc and studies of thirty-one patients who had been seen with thoracic pain. Sagittal T1-weighted spin-echo and axial multiplanar gradient refocused images at each disc level were interpreted by us (two neuroradiologists and two orthopaedic spine surgeons); we had no clinical information about the patients. Sixty-six (73 percent) of the ninety asymptomatic individuals had positive anatomical findings at one level or more. These findings included herniation of a disc in thirty-three subjects (37 percent), bulging of a disc in forty-eight (53 percent), an annular tear in fifty-two (58 percent), deformation of the spinal cord in twenty-six (29 percent), and Scheuermann end-plate irregularities or kyphosis in thirty-four (38 percent). This study documents the high prevalence of anatomical irregularities, including herniation of a disc and deformation of the spinal cord, on the magnetic resonance images of the thoracic spine in asymptomatic individuals. We emphasize that these findings represent roentgenographic abnormalities only, and any clinical decisions concerning the treatment of pain in the thoracic spine usually require additional studies.

Experimental measurement of ligament force, facet force, and segment motion in the human lumbar spine

Facet forces, longitudinal ligament loads, and vertebral body motion were experimentally measured in five fresh human lumbar spine segments, L1-L2. Strain gages on the bone surface were used to quantify facet loads. Buckle transducers were used to measure anterior and posterior longitudinal ligament loads. The three-dimensional motion of the motion segment was measured with an instrumented spatial linkage. The facets were found to carry no load in flexion, large loads during extension (205 N at a 10 Nm moment and a 190 N axial load), torsion (65 N at a 10 Nm moment and a 150 N axial load), and lateral bending (78 N at a 3 Nm moment and a 160 N axial load). The facet contact site on the inferior articular process of L1 was found to move inferiorly to a position of tip impingement near the lamina as extension moments increased. Impingement occurred in the range of 4-6 Nm extension. The posterior and anterior longitudinal ligaments were predominantly loaded in flexion and extension, respectively. No ligament loads occurred in lateral bending and torsion. A 1 cm strip of the anterior longitudinal ligament carried loads up to 130 N at the largest extension moment of 11.4 Nm. The posterior longitudinal ligament had a 60 N load at the largest flexion moment of 7.1 Nm. There was no pre-load in the ligament detectable with the buckle transducers (> 4 N). The facets and ligaments began carrying load immediately with applied load, without a lax region. The experimental technique developed and used provides a good tool for obtaining simultaneous facet joint loads, ligament loads, and vertebral body motion without altering the motion segment.

Rotational changes of the vertebral pelvic axis after sublaminar instrumentation in adolescent idiopathic scoliosis.

Study Design The authors studied the rotational effect of sublaminar wiring on the spinal pelvic axis on 20 patients who were being treated for adolescent idiopathic scoliosis. Objectives To determine if sublaminar wiring effectively derotates the scoliotic spine. Summary of Background Data The correction of the rotational deformity in adolescent scoliosis via sublaminar wiring is not well quantified in the literature. The derotation maneuver of Cotrel‐Dubousset has been shown to produce variable and unpredictable amounts of axial derotation. Methods Twenty patients who underwent posterior spine fusion for adolescent idiopathic scoliosis were evaluated using computed tomography scans and plain radiography before and after surgery and at a subsequent follow‐up examination (average time of follow‐up examination, 35 months after surgery). The degree of angle of vertebral rotation about the sagittal plane and that relative to the pelvis were measured before and after surgery and at a follow‐up examination. Results The primary thoracic curves were not derotated significantly relative to the pelvis with sublaminar wiring. Primary thoracolumbar curves instrumented on the convexity with pedicle screws were derotated significantly relative to the pelvis (P =.001). The average initial correction was 57%. On final follow‐up examination, the correction was 24% (18 of 20 twenty individuals lost axial correction by an average of 34%). In nine of 20 patients the spine was more rotated, relative to the pelvis, than it had been before surgery. No coronal or sagittal decompensation was seen in any curve type. Conclusions Coronal and sagittal plane correction of scoliotic curves may be achieved with sublaminar instrumentation. The ability to derotate axially the scoliotic spine appears to be variable, however, and, in most cases, curve‐type dependent. Over time, much correction appears to be lost, and in many patients the scoliosis actually becomes worse than it was before surgery. Nonetheless, the apical derotation that takes place appears to be reasonably true: the percent correction of angle of rotation about the sagittal plane and the percent correction of angle of rotation about the sagittal plain relative to the pelvis were closely correlated. Derotation forces applied to the instrumented spine do not appear to be transmitted to more distal segments.

Efforts to standardize the reporting of pain

In an effort to develop a method for standardizing patients reports of pain intensity, we tested seven different approaches to employing patients ratings of four consistent types of pain as a means of correcting their reports (the average of the four standard pain measures, the average of the greater pains--finger in a door and tooth drilling, the average of the lesser pains--blister and leg cramp, the predicted back pain VAS from a regression of the standard pains, a conversion to the same scale based on population mean, the difference between individual mean and population mean of the four standard pain measures, and the difference between individual range and population range of the four standard pain measures). None of the adjustments proved to be a substantial improvement over the unstandardized approach. The best adjuster was the approach that used the average of the greater pain scores.

Description and application of instrumented staples for measuring in vivo bone strain

In vivo bone strain measurements using strain gages cemented to bony surfaces with cyanoacrylate polymers are limited in duration due to debonding of the gages from bone. As an alternative to the bone bonded strain gages, a technique was developed in which strain gages were first bonded to miniature staples and then the staples embedded into bone. The instrumented staples may be calibrated so that staple strain is directly proportional to bone strain. The method was first validated by comparing the staple output with cemented surface strain gages. Comparison of instrumented staples to cemented strain gages revealed only a 3% deviation from linearity during longitudinal bending; the staples were insensitive to transverse loading. The instrumented staples were then applied to the in vitro canine lumbar spine to determine L2-3 facet loads. Load testing, repeatibility of facet calibration, and validity testing of the in vitro instrumented staples were found to be comparable to that of the previous cemented strain gage techniques. In vivo facet joint application of the instrumented staples for periods of greater than 5 weeks gave load measurements comparable to our previous short-term in vivo studies obtained with cemented strain gages. The advantages of the instrumented staples are a more secure bonding to the bone, and less traumatic surgery for fixation.

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° 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°) with suitable accuracy such that it is a useful tool in documenting the in vivo response of a motion segment to surgical procedures.

Validation, reliability, and complications of a tethering scoliosis model in the rabbit

This study was conducted to refine a small animal model of scoliosis, and to quantify the deformities throughout its growth period. Subcutaneous scapula-to-contralateral pelvis tethering surgery was selected due to its minimally invasive nature and potential applicability for a large animal model. The procedure was performed in 7-week-old New Zealand white rabbits. Group A animals (n=9) underwent the tethering procedure with a suture that spontaneously released. Group B animals (n=17) had the identical procedure with a robust tether and pelvic fixation, which was maintained for 2xa0months during growth. All animals developed immediate post-operative scoliosis with a Cobb angle of 23° (range, 6–39°) in group A and 59° (range, 24–90°) in group B animals. During the 2xa0month post-tethering, group A animals lost their tether and scoliosis resolved, whereas all animals in group B maintained their tether until scheduled release at which time the mean scoliosis was 62°. Immediately after tether release, group B scoliosis decreased to a mean 53°. Over the following 4xa0months of adolescent growth, the scoliosis decreased to a mean of 43° at skeletal maturity; the decrease usually occurred in animals with less than 45° curves at tether release. Radiographs revealed apical vertebral wedging (mean 19°) in all group B animals. Sagittal spinal alignment was also assessed, and for group B animals, the scoliotic segment developed mild to moderate kyphosis (mean 28°) and torsional deformity, but the kyphosis resolved by 4xa0months after tether-release. Complications specific to this technique included a high rate of transient scapulothoracic dissociation and cases of cor pulmonale. In conclusion, this tethering technique in immature rabbits consistently produced scoliosis with vertebral wedging when the tether was intact through the first 2xa0months of the protocol. The transient exaggeration of kyphosis suggests that the production of scoliosis is not necessarily dependent on lordosis in this model. Because this technique does not violate thoracic or spinal tissues, it may be useful in the investigation of secondary physiologic effects of mechanically-induced scoliosis, and may be scalable to larger animal species.

Lumbar intervertebral cages: Limitations and complications

Threaded cylindrical titanium intervertebral cages have become exceedingly popular as a means of achieving lumbar arthrodesis. The complication rate, however, remains considerable. There is a risk of vascular, urologic and neurologic injury from both anterior and posterior surgical approaches. Complications directly related to the cages include misplacement or migration, neurologic injury, and pseudarthrosis, probably the most common complication of all.

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 intervertabral 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 1 (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.

P10. Multisurgeon assessment of thoracolumbar fractures: reproducibility and repeatability of the AO and Denis classification systems

P10. Multisurgeon assessment of thoracolumbar fractures: reproducibility and repeatability of the AO and Denis classification systems Kirkham Wood, MD, Alexander Vacarro, MD, David Polly, MD, Amir Mehbod, MD, G. Khanna, MD, Jill Wroblewski, MS; University of Minnesota, Minneapolis, MN, USA; Rothman Institute, Philadelphia, PA, USA; Walter Reed Medical Center, Chevy Chase, MD, USA; Twin Cities Spine Center, Minneapolis, MN, USA