Effects of posterior instrumentation on axial rotation of the lumbar spine: an in vitro biomechanical study.
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Biomechanical Phenomena↗
Biomedical subjects
W C Hutton
Publications and source records attributed to W C Hutton.
Nicotine on the revascularization of bone graft. An experimental study in rabbits.
STUDY DESIGN: In 24 rabbits, the authors transplanted autologous cancellous bone to the anterior chamber of the eye. Half of the rabbits received nicotine and half received placebo (albumin) from mini-osmotic pumps that were implanted subcutaneously. Revascularization of the bone graft was evaluated postoperatively using ophthalmology slit-lamp and fluorescein angiography, and after sacrifice using microvascular silicone injection and histology. OBJECTIVES: The hypothesis that nicotine inhibits the revascularization of bone graft because of its pharmacologic action on the microvasculature was tested. SUMMARY OF BACKGROUND DATA: Pseudoarthrosis after spinal fusion occurs more frequently in smokers as compared with nonsmokers. METHODS: Observations of the bone graft were made regarding the time after implantation when vessels within the graft were noted and the pattern of these vessels. Revascularization of the graft was graded based on the observed percent area of fluorescence after injection of fluorescein. Serum levels of nicotine were measured weekly. Colored silicone was injected at sacrifice to fix the vasculature of the bone graft. Histologic analysis of undecalcified sections was performed. RESULTS: Nicotine, as compared with placebo, was associated with delayed revascularization within the graft, a smaller percent area of revascularization, and a larger number of grafts showing necrosis. CONCLUSIONS: Nicotine inhibits, but does not prevent, the revascularization of cancellous bone grafts. Inhibition of early revascularization by nicotine is proposed as the pathophysiologic mechanism by which smoking may adversely affect the healing of spinal fusions.
Animals↗
Optimal graft fixation--the effect of gap size and screw size on bone plug fixation in ACL reconstruction.
In reconstruction of the anterior cruciate ligament (ACL), using central one-third patellar tendon graft, an early weak link is the bone plug junction. To study this, we carried out experiments to determine the relationship between gap size, screw size, and pullout force of patellar bone plugs inserted in the femur of the porcine model. Forty-nine porcine knees were obtained. Holes 11 mm in diameter were drilled in the intercondylar notch of the femur. Bone plugs fashioned from the patella were made to fit the holes with gap sizes of 1, 2, 3, or 4 mm. The bone plugs were inserted into the holes in the femur and secured by means of 20-mm-long screws (either 7- or 9-mm diameter). The bone plugs were then pulled out using a tensile testing machine and the pullout force was measured. The results suggest that a 7-mm (or a 9-mm) diameter screw can be used for gaps of 1 and 2 mm, and a 9-mm diameter screw should be used for gaps of 3 and 4 mm.
Animals↗
Correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws.
The bone-screw interface is critical in the use of spinal instrumentation. The purpose of these experiments described here was twofold. First, to determine whether a correlation existed between torque generated during screw insertion and the pullout strength. Second, to determine how differing surgical methods of screw hole preparation influenced torque of insertion and screw pullout strength. A series of experiments were carried out in which screws were inserted into synthetic bone (experiment 1) and into calf vertebrae (experiment 2). The method of screw hole preparation (i.e., diameter of entrance hole and pilot hole) was varied while the resulting torque of insertion and the pullout strength of the screw was measured in each case. A torque screwdriver was used to measure the torque of insertion of the screws. Screw pullout strength was measured using a materials testing machine. Two important results emerged from these experiments. First, a higher torque of insertion correlated with a higher screw pullout force. This correlation may be useful intraoperatively in evaluating fixation. Second, torque of insertion and pullout force were more influenced by cortex over-drill diameter than pilot hole diameter. These experiments show the importance of the dorsal cortex in pedicle screw fixation.
Animals↗
Determination of the compartment pressure threshold of muscle ischemia in a canine model.
A canine model was used to test the hypothesis that critical intracompartmental pressure leading to ischemic muscle necrosis is linked to diastolic blood pressure. Twenty adult dogs were subjected to an infusion of autologous plasma into the anterolateral muscle compartment of the left hindlimb to create an elevation in compartment pressure. There were four experimental groups of five dogs each. In group I, the compartment pressure (CP) was maintained at the animals' diastolic blood pressure (DBP); in group II, at 10 mm Hg less than the DBP; in group III, at 20 mm Hg less than the DBP; and in group IV, at 30 mm Hg. The pressure was measured continuously in the proximal, central, and distal segments of the compartment during an 8-hour period. Immediately postoperatively, and, on the first, fourth, seventh, and fourteenth days one animal from each group was killed. The tibialis cranialis muscle was then removed and analyzed using light and electron microscopy. The critical pressure threshold for ischemic muscle necrosis was found to be 20 mm Hg less than the diastolic blood pressure.
Analysis of Variance↗
Increase of motion between lumbar vertebrae after excision of the capsule and cartilage of the facets. A cadaver study.
Seventeen fresh segments of cadaveric lumbar spines were tested in flexion, extension, and axial rotation. The resulting angular rotations were measured with the use of a goniometer and a three-dimensional system of video analysis. Measurements of flexibility were made, in order, in the intact spine; after decompression (bilateral total laminectomies, partial medial facetectomies, and foraminotomies); after excision of the capsule and cartilage of the facets; and after cancellous bone had been packed into the facet defects. Decompression resulted in a slight increase in the sagittal and axial ranges of motion. Subsequent excision of the capsule and cartilage of the facets, as in preparation for an arthrodesis of the facets, resulted in a significant increase in both the sagittal (5.7 +/- 2.9 degrees, mean and standard deviation) (p < 0.001) and the axial (1.4 +/- 0.9 degrees) (p < 0.01) ranges of motion compared with the motion in the intact specimen and with the motion in the specimen after only decompression had been done (p < 0.01 and p < 0.05, respectively). Packing of bone in the facets did not significantly reduce motion. It was calculated that the increase in the sagittal range of motion after excision of the capsule and cartilage of the facets would increase the tensile strain in a graft between the transverse processes of the fourth and fifth lumbar vertebrae (18 +/- 1 per cent tensile strain [mean and 95 per cent confidence interval] for the intact vertebrae and 25 +/- 1 per cent for the vertebrae in which the facets had been excised).
Biomechanical Phenomena↗
The effect of surgical floor mats in prolonged standing: an EMG study of the lumbar paraspinal and anterior tibialis muscles.
The purpose of this study was to determine whether or not surgical floor mats affect low back and leg muscle activity during prolonged standing. The EMG activity was measured continuously using surface electrodes on the paraspinal muscles of the low back and on the anterior tibialis muscles; the subjects were normal and stood on two different surfaces. Six male subjects were each instructed to stand for two hours on a specially designed surgical floor mat and then, on a separate day, to stand for two hours on a linoleum-covered concrete surface. Six other subjects carried out the same procedure, but stood on the linoleum first. There was no difference in EMG activity obtained from the anterior tibialis muscles and paraspinal muscles of the low back when the subjects stood on the surgical mat, as compared with the linoleum-covered concrete.
Adult↗
Posterior pelvic fixation using a transiliac 4.5-mm reconstruction plate: a clinical and biomechanical study.
Operative management of unstable pelvic fractures is directed toward stabilization of the posterior lesion. We describe a technique of posterior pelvic fixation that uses a 4.5-mm reconstruction plate as a transiliac tension band. The plate is inserted through the posterior superior iliac spines with screw fixation to the ilium. Our initial clinical experience was gained using this technique in 15 patients who had unstable pelvic ring injuries with sacral fractures. Stable fixation was achieved in all patients with this low-profile plate. There were no infections, no wound complications, and no failures of fixation. Comparative biomechanical testing using cadaveric and artificial pelvises demonstrated that the strength of the transiliac plate method was equal to that of other techniques of posterior pelvic fixation.
Adult↗
Intracompartmental pressure measurements in the normal forearm.
In 20 normal subjects, intracompartmental pressure measurements were made at three different sites in the volar forearm: half the distance between the medial epicondyle and ulnar styloid and at points 4 cm proximal and 4 cm distal. The pressure measurements were made using a hand-held digital compartment pressure monitor. The study demonstrated that in the uninjured volar compartment, clinically significant (5 mm Hg) intracompartmental pressure differences exist over distances as little as 4 cm.
Adult↗
Transverse ligament failure: a biomechanical study.
We investigated the biomechanical properties of the transverse ligament by simulating an anteroposterior shear injury mechanism. The ligament was tested in isolation. All secondary restraints and any interference from articular mass geometry were eliminated. In all, 13 specimens were tested. Eleven failed within the substance of the ligament, and two failed by bone avulsion. The mean load to failure was 692 N (range, 220-1590 N). The displacement to failure was 6.7 mm (2-14 mm). The measured values of load to failure agree with previous reports; however, the displacement to failure exhibited a broader range than expected.
Biomechanical Phenomena↗
Role of the capsulo-ligamentous structures in rotation and combined flexion-rotation of the lumbar spine.
We carried out experiments on whole cadaveric lumbar spines in order to determine the role that each of the capsulo-ligamentous structures play in axial rotation in the neutral position and in the flexed position. Eight specimens were first tested intact, then after division of all the apophyseal joint capsules between L1 and the sacrum. Another five specimens were also first tested intact, then after division of the supra- and interspinous ligaments and yellow ligament, and finally after cutting the posterior longitudinal ligament and posterior annulus at each level as well. The results show that there is considerable variation in the axial rotation of the lumbar vertebrae within the same spine and across different spines. The apophyseal joint capsules limit rotation both in neutral and flexed positions. In flexion, the amplitude of rotation in the lumbar spine is reduced. Of the capsulo-ligamentous structures, it is the posterior annulus and the posterior longitudinal ligament that seem to play the more important role in limiting axial rotation while the spine is flexed.
Adult↗
The force exerted by the halo pin. A study comparing different halo systems.
Seven different halo systems were evaluated biomechanically to compare the force exerted by the halo pin in each system. In three different experiments torque values of 2, 4, 6, 7, and 8 in lb were applied to the halo pin, and the force at the skull end of the halo pin was measured using a load cell. In the first experiment, the threads on the halo pin were dry, in the second experiment saline was applied to the threads on the pin, and in the third experiment cadaveric bone from the skull was interposed between the pin and the load cell. The results showed that for a given value of applied torque to the pin, the force exerted by the pin end varied widely according to the halo system and whether or not the pin was "lubricated."
Adult↗
Tests on hypotheses about osteoarthritis and hip joints.
Hypotheses suggesting that hip joints which develop osteoarthritis are congruent, have a single area of peak pressure, and have peak pressure which exceeds normal values were tested. Of 100 hip joints examined on necropsy; two showed an early stage of osteoarthritis and the geometry and pressure distribution under load were assessed in these joints. One joint was congruent, in agreement with the hypotheses, but the other was incongruent. In both joints there were several areas of high pressure, the number and location of which depended on the orientation of the joint. The measured values of pressure in the congruent joint exceeded values found previously in normal hip joints. In the incongruent hip joint the peak pressures were within normal limits.
Aged↗
Conformationally restricted polysubstituted biphenyl derivatives with angiotensin II receptors antagonist properties.
The synthesis and in vitro activity of new nonpeptide angiotensin II antagonists is presented. Compared to previously reported biphenyl compounds, the new analogues 8 and 9 have reduced conformational freedom derived from steric hindrance. Methyl 4'-methyl-2',6'-dimethoxy[1,1'-biphenyl]-2-carboxylate 4 has been synthesized by a Von Pechmann condensation of orcinol with oxocyclohexane-2-carboxylate followed by dehydrogenation. This scheme provided the carbon skeleton of the biphenyl potentially substituted on the 2-, 2'-, 4'-, and 6'-positions. Elaboration of the subsituents led to a biphenyl derivative used to alkylate a 2-n-butyl-4-chloro-5-(hydroxymethyl)imidazole. After coupling with the imidazole two regioisomers were separated and identified by 1H NMR. NOESY experiments were useful to establish regiochemistry of the final products that have angiotensin II blocking activity. Their affinity for angiotensin II receptors was established in a binding assay experiment and in an isolated organ test. The presence of 2',6'-dimethoxy substituent on the biphenyl moiety of the antagonist was found to significantly decrease affinity for the receptor.
Angiotensin II↗
Diurnal changes in spinal mechanics and their clinical significance.
Diurnal changes in the loads acting on the spine affect the water content and height of the intervertebral discs. We have reviewed the effects of these changes on spinal mechanics, and their possible clinical significance. Cadaveric lumbar spines subjected to periods of creep loading show a disc height change similar to the physiological change. As a result intervertebral discs bulge more, become stiffer in compression and more flexible in bending. Disc tissue becomes more elastic as its water content falls, and its affinity for water increases. Disc prolapse becomes more difficult. The neural arch and associated ligaments resist an increasing proportion of the compressive and bending stresses acting on the spine. Observations on living people show that these changes are not fully compensated for by modified muscle activity. We conclude that different spinal structures are more heavily loaded at different times of the day. Therefore, the time of onset of symptoms and signs, and any diurnal variation in their severity, may help us understand more about the pathophysiology of low back pain and sciatica.
Back Pain↗
Physical activity and the strength of the lumbar spine.
The cadaveric lumbar spines of nine young men killed in road accidents were subjected to a range of mechanical tests, and the results compared with the men's occupational and recreational histories. It was found that the compressive strength of the spines tended to increase with the level of physical activity in life, but the increase was significant only in the eight spines aged 18 or over. Compressive failure usually occurred in the vertebral body, but in three cases, the disc prolapsed into the vertebral canal; these discs came from three of the four most physically active individuals. It is concluded that physical activity strengthens both the vertebrae and the discs. A high level of activity can cause vertebral strength to exceed that of the discs.
Adolescent↗
Commonly adopted postures and their effect on the lumbar spine.
The activity of the erector spinae muscles and the changes in lumbar curvature were measured in 11 subjects in a range of commonly adopted postures to see if there were any consistent trends. Surface electrodes were used to measure back muscle activity and lumbar curvature was measured using electronic inclinometers. The results showed that many commonly adopted postures reduced the lumbar lordosis when compared with erect standing or sitting, even at the expense of increasing the back muscle activity.
Adult↗
The lumbar spine in backward bending.
Cadaveric lumbar motion segments were loaded to simulate backward bending (extension) movements of the lumbar spine. The motion segments' resistance was measured initially, and after the spinous processes and apophyseal joints had been cut through in turn. Compression tests were then performed on the discs while they were wedged in full extension. The results showed that extension is resisted mainly by the disc and spinous processes, and that, in hyperextension, damage usually occurs first in the spinous processes (or the soft tissue squashed between them). However, if the spinous processes are particularly widely spaced, then the apophyseal joints can become damaged first. The protection offered the disc by the neural arch is greater in young people, and after the disc height has been reduced by creep loading. The disc can be damaged in hyperextension if the spine is subjected to high compressive forces at the same time. A sudden application of compressive force can cause an anterior disc prolapse, while a cyclic (fatigue) compressive force can increase the posterior bulging of the lamellas in the posterior annulus.
Humans↗