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Biomedical subjects

W C Hutton

Publications and source records attributed to W C Hutton.

At least 55 records · Page 3Linked to original sources
PubMed1996

Can variations in intervertebral disc height affect the mechanical function of the disc?

STUDY DESIGN: The finite element method was used to investigate the effect of variations in disc height on the mechanical behavior of the intervertebral disc. OBJECTIVES: The effect of disc height on the mechanical behavior of a human lumbar spine segment in terms of axial displacement, intradiscal pressure, posterolateral disc bulge, tensile stress in the peripheral anulus fibers, and longitudinal stress distribution at the end plate-vertebra interface was evaluated. SUMMARY OF BACKGROUND DATA: Disc height varies with individuals, disc level, abnormal conditions, and clinical management. METHODS: A three-dimensional finite element model of L2-L3 disc body unit was developed. Parametric studies were undertaken by studying discs of three different heights: 8 mm, 10 mm, and 12 mm, whereas disc cross sectional area, finite element mesh density, and all other parameters were kept constant. The model accounted for geometric nonlinearity but assumed that the material properties were linear. RESULTS: Variations in disc height had a significant influence on the axial displacement, the posterolateral disc bulge, and the tensile stress in the peripheral anulus fibers, but the effect on the intradiscal pressure and the longitudinal stress distribution at the endplate vertebra interface was minimal. CONCLUSIONS: Variations in disc height may compromise the general conclusions reached from experimental work and analytic studies in which geometric parameters (especially disc height and disc cross-sectional area) are not taken into consideration.

Biomechanical Phenomena↗
PubMed1996

Strength of fixation of anterior vertebral body screws.

STUDY DESIGN: The technique of hole preparation and the placement or orientation of anterior transvertebral screws in relation to the endplates were the subject of two experiments. OBJECTIVES: Experiment 1--to determine if anterior transvertebral body screws have higher pull-out strengths after unicortical predrilling compared with a bicortical predrilling; Experiment 2--to determine the effect of the screw's orientation in the vertebral body on its resistance to loosening. SUMMARY AND BACKGROUND DATA: There are a variety of surgical techniques for using anterior transvertebral screws in the vertebral body without any clear guidelines as to which techniques optimize the strength of fixation. METHODS: In experiment 1, 31 cadaveric vertebral bodies were tested for pull-out strength of transvertebral body screws placed after unicortical predrilling compared with bicortical predrilling. In experiment 2, 48 cadaveric vertebral bodies were tested with transvertebral screws inserted using four different screw orientations. RESULTS: There is no statistically significant difference in pull-out strength of anterior transvertebral body screws inserted after unicortical compared with bicortical predrilling (Experiment 1). The resistance to loosening is greatest when transvertebral screws are oriented in the "superior oblique" position (Experiment 2). CONCLUSIONS: Experiment 1--preparation of the far cortex by predrilling is not necessary. Experiment 2--transvertebral screws should be obliquely oriented so that the forces applied to the screws are resisted by both of the endplates.

Aged↗
PubMed1996

Is it important to secure the horns during lateral meniscal transplantation? A cadaveric study.

The purpose of this investigation was to determine if secure attachment of the horns of the lateral meniscus during transplantation affects the load-bearing function of the meniscus. Six knee joints were loaded in compression (310 N) and the interarticular contact pressure in the joint measured using pressure-sensitive film inserted into the joint. Each knee was tested first with the original intact meniscus and then after each of the following surgical procedures involving the original lateral meniscus: (1) total meniscectomy; (2) meniscal transplantation with a tibial bone bridge; (3) meniscal transplantation with neither horn secured; (4) meniscal transplantation with the anterior horn secured; (5) meniscal transplantation with the posterior horn secured; and (6) meniscal transplantation with both horns secured. The results are as follows. (1) The intact joint gave the largest contact area and the smallest peak contact pressure. The joint with the total meniscectomy gave the smallest contact area and the largest peak contact pressure. (2) A meniscal transplantation with either a tibial bony bridge or with both horns secured gave results similar to those for the intact joint. (3) A meniscal transplantation with only one horn secured gave results somewhere in between those for the intact joint and those for the joint without a meniscus. A meniscal transplantation with neither horn secured gave results similar to those for a joint without a meniscus.

Aged↗
PubMed1996

Treatment of screw hole defects using bone graft materials: a histologic and biomechanic study.

We surgically applied compression plates, secured with cortical screws, to the anterolateral surface of each radius in 20 dogs. Five weeks later, the plates and screws were removed. The dogs were then divided into four groups of 5, and each group had the screw holes in the left radii filled with a different form of bone graft material. The screw holes in the right radii received no graft material and served as controls. Five weeks later the dogs were euthanized, and the radii were removed and torqued to failure. All bones failed through a previous screw hole. An analysis of variance comparing all grafted radii to the ungrafted controls revealed no significant difference in torque to failure. This suggests that both grafted and ungrafted screw holes still increase stress at 5 weeks, and any period of protection after plate removal should be longer than 5 weeks. However, histology revealed that the holes filled with graft material had, in every case, more bone in the screw holes than did the holes in the ungrafted controls.

Animals↗
PubMed1996

Morphology of the lumbar intertransverse process fusion mass in the rabbit model: a comparison between two bone graft materials--rhBMP-2 and autograft.

We used computed tomography and the rabbit model to seek an explanation for the biomechanical superiority of recombinant human bone morphogenetic protein-2 (rhBMP-2) as compared with autogenous iliac bone in lumbar intertransverse process fusions, i.e., the rhBMP-2 fusions demonstrated significantly higher strength and stiffness. The results show that the fusion masses using rhBMP-2 have higher volume, and higher minimum contact area of fusion mass attachment to the transverse process. For both bone graft materials there was a correlation between site of failure and the fusion mass quadrant that contained the minimum contact area of attachment to the transverse process. The ideal graft material would be one that produced strong, mature, early fusions that failed along their length at random positions, rather than failing with high frequency at the transverse process. The fusions using rhBMP-2 were nearer to the ideal than those using autograft: These were stronger, more mature, and only 6 of 9 rhBMP-2 failed in the quadrant that contained the minimum contact area of attachment to the transverse process, as opposed to 11 of 12 for autograft.

Animals↗
PubMed1996

Do diurnal changes in loading affect the interpretation of MRI scans of the lumbar spine?

We tested the hypothesis that the visual interpretation of magnetic resonance imaging (MRI) scans of the asymptomatic lumbar spine are affected by diurnal changes in fluid exchange in the intervertebral discs. Ten male subjects carried a 20-kg backpack in the intervening 3-h period between two MRI scans of the lumbar spine. After the subjects arrived at the MRI center (within 45 min of awakening), they lay on a bed for 45 min. The first set of MRI scans were obtained. Each subject was then fitted with a 20-kg backpack. After they walked for 3 h, the pack was removed, and a second set of MRI scans were obtained immediately. The sets of MRI scans were reviewed by three radiologists: none of the three radiologists found differences in the interpretation of the MRI scans. On the basis of these results, diurnal changes in fluid exchange in the asymptomatic intervertebral disc (exaggerated in our case by the backpack) are undetectable by visual reading of MRI scans.

Adult↗
PubMed1996

Transfacet screws with lumbar interbody reconstruction: biomechanical study of motion segment stiffness.

In a biomechanical study using nine cadaveric lumbar motion segments, we evaluated the effect that the insertion of transfacet screws had on stiffness, after the implantation of a threaded spine cage to simulate anterior lumbar interbody arthrodesis. Each motion segment was tested according to a biomechanical loading sequence, which consisted of compression, flexion, extension, right lateral bending, and left lateral bending. This was applied to each motion segment four times as follows: (a) the intact intervertebral joint; (b) after the insertion of an interbody threaded spine cage; (c) after the additional insertion of transfacet screws; and (d) after the removal of the transfacet screws (with the cage still inserted). At each step in the loading sequence, a load-deformation curve was obtained, and from this curve a stiffness value was calculated. The most important finding was the increase in stiffness of the motion segment, particularly in extension, after the insertion of the transfacet screws. This finding suggests that transfacet screws may be useful for stabilizing segments reconstructed with bone graft or cages.

Aged↗
PubMed1995

1995 Volvo Award in basic sciences. The use of an osteoinductive growth factor for lumbar spinal fusion. Part I: Biology of spinal fusion.

STUDY DESIGN: The histology of lumbar intertransverse process spinal fusion was studied in an experimental model in rabbits. OBJECTIVES: To qualitatively and quantitatively analyze the sequential histology of spinal fusion using a previously validated animal model. SUMMARY OF BACKGROUND DATA: Few previous studies have described the sequential histology during the posterolateral spinal fusion healing process using autogenous bone, and a basic understanding of the biology of this repair process is lacking. METHODS: Fourteen adult New Zealand white rabbits underwent single-level posterolateral lumbar intertransverse process arthrodesis with autogenous iliac bone graft. Animals were killed 1-10 weeks after surgery, and the fusion masses were analyzed histologically and quantitated using a semiautomated image analysis system. RESULTS: Three distinct phases of healing were identified (inflammatory, reparative, and remodeling) and occurred in sequence but in a delayed fashion in the central zone of the fusion mass compared with the outer transverse process zones. Membraneous bone formation, evident first at the ends of the fusion eminating from the decorticated transverse processes, was the predominant mechanism of healing. The central zone was somewhat different in that there was a period of endochondral bone formation during weeks 3 and 4 in this zone where cartilage formed and was converted to bone. Remodeling in the central zone had equilibrated with the transverse process zones by 10 weeks. CONCLUSIONS: Lumbar intertransverse process spinal fusion is a complex process from a spatial and temporal standpoint. When autogenous bone is used as the graft material, this process critically depends on a variety of factors from the decorticated host bone and exposed marrow. The persistence of a central cartilage zone may be related to some types of nonunions and deserves future investigation. This enhanced understanding of the biology of spinal fusion with autogenous bone graft will provide a foundation for optimizing the use of osteoinductive bone growth factors in this healing process.

Animals↗
PubMed1995

1995 Volvo Award in basic sciences. The use of an osteoinductive growth factor for lumbar spinal fusion. Part II: Study of dose, carrier, and species.

STUDY DESIGN: Efficacy of a bovine-derived osteoinductive growth factor was studied in a rabbit model and in a nonhuman primate model of posterolateral lumbar spinal fusion. OBJECTIVES: To determine the minimum effective dose of growth factor and the influence of different carrier material on the outcome of intertransverse process lumbar fusion. SUMMARY OF BACKGROUND DATA: Bone morphogenetic proteins and related growth factors are becoming increasingly available in purified extract or genetically engineered forms and are capable of inducing new bone formation in vivo. Osteoinductive growth factors to enhance lumbar spinal infusion have not been well studied in models of posterolateral intertransverse process fusion. Because of the diminished potential of bone regeneration in primates (including humans) compared with phylogenetically lower animals, extrapolations regarding dose and efficacy cannot be made directly from results obtained in experiments performed on phylogenetically lower animals. Experiments on non-human primates are a critical step before attempting to use these growth factors on humans. METHODS. One hundred fifteen adult New Zealand white rabbits and 10 adult rhesus macaques underwent single level posterolateral intertransverse process lumbar spinal arthrodesis to evaluate different doses and carrier materials for a bovine-derived osteoinductive bone protein extract. Rabbit fusion masses were evaluated 5 weeks after arthrodesis by manual palpation, radiography, biomechanical testing, and light microscopy. Monkey fusion masses were evaluated 12 weeks after arthrodesis by radiography and light microscopy. RESULTS: Successful posterolateral intertransverse process spinal fusions were achieved in the rabbit models using an osteoinductive growth factor with three different carriers (autogenous iliac bone, demineralized allogeneic bone matrix, and natural coral). There was a dose-dependent response to the osteoinductive growth factor in the rabbit model, indicating that a threshold must be overcome before bone formation is induced. The methodology for biologic enhancement of spinal fusion developed in the rabbit model transferred successfully to the rhesus monkey, where the use of the osteoinductive growth factor with a demineralized bone matrix carrier resulted in spinal fusion in 12 weeks. CONCLUSION: These experiments provide an essential building block in the understanding of the biology of spinal fusion and the use of osteoinductive growth factors to enhance a posterolateral intertransverse process spinal fusion. The achievement of posterolateral spinal fusion in the rhesus monkey using an osteoinductive growth factor is a significant step toward the biologic enhancement of spinal fusion in humans.

Animals↗
PubMed1995

The effect of nicotine on incorporation of cancellous bone graft in an animal model.

STUDY DESIGN: A basic science study using a rabbit model of bone graft revascularization in the distal femoral metaphysis. OBJECTIVES: The goal of the present study was to determine the effect of nicotine on the revascularization and incorporation of autogenous iliac crest bone graft implanted in an orthotopic location. SUMMARY OF BACKGROUND DATA: Although nicotine is the major toxin in cigarettes, it has not been confirmed as the primary factor affecting bone metabolism, and although the effects of smoking on bone homeostasis have been well studied, the effect of nicotine on new bone formation and neovascularization in the setting of bone graft transplantation has not been well studied. METHODS: Twenty-four New Zealand white rabbits were randomly divided into two groups to be exposed to nicotine or saline control. A cancellous iliac crest bone graft was harvested and implanted in the lateral distal femur. Mini-osmotic pumps were used to deliver continuous serum levels of nicotine. The animals were killed at the following intervals: 1 week (n = 6), 2 weeks (n = 12), and 4 weeks (n = 6). The vascular tree was injected with Microfil silicone rubber solution, and the degree of revascularization was determined with a semiautomated image analysis system to determine the area of vascularization for each specimen. RESULTS: All seven of the control (no nicotine) animals harvested at 1 or 2 weeks had over 50% bony vascular ingrowth, whereas only four of the nine nicotine-exposed animals showed over 50% bony vascular ingrowth. These differences were statistically significant (P = 0.03) using the Fischer exact test. By the fourth week (after nicotine levels in experimental animals had diminished), the revascularization of the nicotine-exposed grafts was indistinguishable from that of grafts in the animals that were not exposed to nicotine. CONCLUSIONS: We conclude the following. 1) Uniform dosages of nicotine in the rabbit model decreases the vascular ingrowth into autogenous cancellous bone graft. 2) The inhibitory effect of nicotine varies between animals, suggesting predisposition in some. 3) The vascular effects are reversible within 2 weeks of elimination of nicotine, although late bony resorption continues beyond the time of high serum nicotine levels.

Animals↗
PubMed1995

The effect of nicotine on spinal fusion.

STUDY DESIGN: An animal model of posterior lateral intertransverse process fusion healing in the face of systemic nicotine. OBJECTIVES: To evaluate the effect of systemic nicotine on the success of spinal fusion and its effect on the biomechanic properties of a healing spinal fusion in an animal model. SUMMARY OF BACKGROUND DATA: Clinical observations suggested that cigarette smoking interferes with the healing of bony fusion. No direct link has been made to implicate nicotine as a cause for impaired healing of spinal fusions or fractures. METHODS: Twenty-eight adult female New Zealand white rabbits underwent single level lumbar posterior lateral intertransverse process fusion using autologous iliac bone graft. Animals were randomly assigned to either receive systemic nicotine or receive no nicotine. Animals were killed 35 days after surgery. Manual testing of the fusion mass was performed to determine the fusion status. Each fusion mass underwent biomechanic testing. RESULTS: Fifty-six percent of the control animals were judged to have solidly fused lumbar spines, and there were no solid fusions in the nicotine group (P = 0.02). The mean relative fusion strength in the control group was greater (P = 0.09) than in the nicotine group. For the comparable stiffness figures, the control group was greater than the nicotine group (P = 0.08). CONCLUSIONS: This animal model established a direct relationship between the development of a nonunion in the presence of systemic nicotine. The results suggested that bone formed in the face of systemic nicotine may have inferior biomechanic properties.

Animals↗
PubMed1995

The effect of different surgical releases on thoracic spinal motion. A cadaveric study.

STUDY DESIGN: Two separate experiments (A and B), each involving six human cadaveric torsos with intact rib cages and sternums, were done to determine the effect of two different sequences of surgical releases (at T8-T9) on thoracic spinal motion. OBJECTIVES: Experiment A was designed to test the effects of three releases in sequence from anterior to posterior, analogous to a two-stage operative treatment with anterior and posterior releases. Experiment B, which involved three releases, was designed to determine 1) if unilateral posterior total facetectomy alone allowed a significant increase in motion and 2) if rib head resection without discectomy allowed a significant increase in motion. SUMMARY OF BACKGROUND DATA: In the surgical treatment of thoracic spinal deformity, surgical release is often done to impart additional flexibility to the spine. Available releases include discectomy, rib head resection, and facetectomy. There is little work to date on the relative importance of the disc, rib head, and facet joint in the stability of the thoracic spine. METHODS: In experiment A and experiment B, the cadaveric torsos were mounted on a custom-made loading frame. Mechanical testing (using weights, pulleys, and digital goniometers) was done after each surgical release to measure the extent of angular rotation in the coronal plane (right lateral bending and left lateral bending) and in the sagittal plane (flexion and extension). RESULTS: The combination of rib head resection and radical discectomy provided the greatest increase in thoracic spinal motion. Standard discectomy alone did not allow a significant increase in motion. Rib head resection without discectomy did not allow a significant increase in motion. Unilateral posterior total facet excision did not allow a significant increase in motion. CONCLUSIONS: These experiments indicate that the combination of rib head resection and radical discectomy may be the optimal thoracic spinal release.

Aged↗
PubMed1995

Experimental spinal fusion with recombinant human bone morphogenetic protein-2.

STUDY DESIGN: Lumbar intertransverse process arthrodesis using recombinant human bone morphogenetic protein-2 was performed in a previously established rabbit model for posterolateral spinal fusion and compared with fusions achieved using autogenous bone graft. OBJECTIVES: To qualitatively compare different recombinant human bone morphogenetic protein-2 dosages and carriers and to determine the efficacy of recombinant human bone morphogenetic protein-2 as a bone graft substitute to produce lumbar intertransverse process fusion in a validated rabbit model for posterolateral spinal fusion. SUMMARY OF BACKGROUND DATA: Autogenous bone was considered the most successful bone graft material used for spinal arthrodesis. Problems with its use may occur in 25-30% of patients and prompted the search for and investigation of bone graft substitutes and osteoinductive growth factors, such as bone morphogenetic proteins. Recombinant human bone morphogenetic protein-2 was used successfully in orthotopic sites to generate bone in animal mandibular and long bone defect models. METHODS: Posterolateral intertransverse process arthrodeses were performed at L5-L6 in 56 rabbits using recombinant human bone morphogenetic protein-2 or autogenous bone graft. Rabbits were killed either 5 weeks later to qualitatively compare fusions achieved using different recombinant human bone morphogenetic protein-2 dosages and carriers or 4 weeks later to compare the efficacy of recombinant human bone morphogenetic protein-2 in achieving spinal fusion compared with using autogenous bone graft. Inspection, manual palpation, radiography, histology, and biomechanic testing were used to assess the fusion. RESULTS: All rabbits implanted with recombinant human bone morphogenetic protein-2 achieved solid spinal fusion by manual palpation and were fused radiographically, whereas only 42% of the autograft control fusions were solid. More mature fusions with greater trabecular bone formation were shown radiographically and histologically in rabbits implanted with the high-dose recombinant human bone morphogenetic protein-2 than with the low-dose recombinant human bone morphogenetic protein-2. Fusions achieved using recombinant human bone morphogenetic protein-2 delivered in the collagen carrier were more remodeled and homogeneous compared with using recombinant human bone morphogenetic protein-2 delivered in autograft +/- collagen carrier. Fusions achieved with recombinant human bone morphogenetic protein-2 were biomechanically stronger and stiffer than fusions achieved using autogenous bone graft. CONCLUSIONS: Recombinant human bone morphogenetic protein-2 successfully and reliably achieved lumbar intertransverse process fusion in a validated rabbit model for posterolateral spinal fusion. Radiographically and histologically, greater and more rapid bone formation, consolidation, and remodeling were shown with recombinant human bone morphogenetic protein-2 compared with autogenous bone graft. Fusions achieved with recombinant human bone morphogenetic protein-2 were biomechanically stronger and stiffer than autograft fusions.

Animals↗
PubMed1995

An experimental lumbar intertransverse process spinal fusion model. Radiographic, histologic, and biomechanical healing characteristics.

OBJECTIVE: The purpose of this investigation was to develop, characterize, and validate an animal model for lumbar intertransverse process fusion. STUDY DESIGN: This study used a rabbit model to characterize the radiographic, histologic, and biomechanical properties of the intertransverse process spinal fusion healing process. METHODS: Sixty adult New Zealand white rabbits underwent bilateral posterolateral spinal fusion at L5-L6 using autogenous iliac bone graft. Four of the rabbits were used as negative controls: two received bone graft without decortication of the transverse process, and two underwent decortication without bone grafting. Rabbits were killed at 2, 3, 4, 5, 6, or 10 weeks and the spinal fusions were analyzed by radiography, manual palpation, and uniaxial tensile mechanical testing or light microscopy. RESULTS: Overall the nonunion rate was 33% in animals 4 or more weeks from surgery. Biomechanical strength and stiffness of the fusions became statistically different from the adjacent unfused control levels after the third week (P < 0.05). Tensile strength of the nonunions (1.4 times unfused control levels) was statistically less (P < 0.05) than that of the solidly fused levels (1.8 times unfused controls) in weeks 4, 5, 6, and 10. Fusion was not achieved in any of the control animals with omission of decortication or bone grafting. Light microscopic analysis showed three distinct and reproducible phases of spinal fusion healing. CONCLUSIONS: This animal model overcomes the limitations of previous models by more closely replicating the human procedure in surgical technique, graft healing environment, and outcome (i.e., a nonunion rate similar to that seen in humans). This model provides an opportunity to explore questions relevant to the biology of intertransverse process fusion and to investigate the coupling of the membranous and endochondral mechanisms of bone formation during spinal fusion.

Animals↗
PubMed1995

A biomechanical comparison between the central one-third patellar tendon and the residual tendon.

The purpose of this study was to compare the tensile strength of the central one third patellar tendon--as used for reconstruction of the anterior cruciate ligament--to that of the residual patellar tendon. Ten matched pairs of human cadaveric knees were used for this study, each specimen consisting of an intact patella-patellar tendon-proximal tibial unit. One knee from each pair was randomly selected for removal of both the medial and lateral one third of the patellar tendon, leaving the central one third intact. The contralateral knee of each pair underwent removal of the central one third of the patellar tendon, leaving the residual two thirds intact. Each specimen was then mounted in a materials testing machine and tensile tested to failure at a strain rate of 100%.s-1. The most important result to emerge from these experiments was that there was no significant difference in maximum force to failure for the residual patellar tendon compared to the central one third. Thus any thought that removal of the central one third as a graft still leaves a tendon twice as wide and therefore twice as strong as a graft is dispelled by these experiments.

Adult↗
PubMed1995

Lumbar intertransverse-process spinal arthrodesis with use of a bovine bone-derived osteoinductive protein. A preliminary report.

The use of a bovine bone-derived osteoinductive protein extract as a bone-graft substitute was evaluated in a rabbit model of intertransverse process arthrodesis of the lumbar spine. Forty-five adult New Zealand White rabbits had arthrodesis between the fifth and sixth lumbar vertebrae with use of one of three graft materials: autogenous iliac-crest bone, osteoinductive protein delivered in an allogeneic demineralized bone matrix/collagen carrier, or demineralized bone matrix/collagen carrier or demineralized bone matrix/collagen carrier without osteoinductive protein. Fusion was assessed by manual palpation, radiography, biomechanical testing, and light microscopy at two and five weeks after the operation. At two weeks, light microscopic analysis of the arthrodesis site in which osteoinductive protein had been used showed that most of the demineralized bone matrix was still present, with small amounts of membranous and endochondral bone formation at the peripheral margins of the implant. Light microscopic analysis of the five-week specimens showed increased new-bone formation and a more homogeneous and mature fusion mass with the osteoinductive bone protein than with the autogenous bone graft. At five weeks, the fusions with the osteoinductive protein extract were characterized by more secondary spongiosa, with formation of bone marrow centrally and a cortical rim peripherally. Of the thirty-five rabbits that were examined at five weeks, all ten in the group that had received osteoinductive bone protein had a solid fusion, but the rate of fusion was significantly less in the other two groups: eight of thirteen rabbits (p = 0.05) in the group that had received autogenous bone graft and two of twelve rabbits (p = 0.0001) in the group that had received demineralized bone matrix/collagen carrier without osteoinductive bone protein. The use of osteoinductive bone protein resulted in stronger (p = 0.02) and stiffer (p = 0.005) fusions compared with those obtained with the use of autogenous iliac-crest graft.

Animals↗
PubMed1995

Effects of posterior instrumentation on axial rotation of the lumbar spine: an in vitro biomechanical study.

We tested the hypothesis that instrumentation applied across two levels of the lumbar spine inhibits rotation at these levels and that this inhibition is accompanied by more rotation at the levels above and below. The rotation in the transverse plane of each of the five lumbar vertebrae of 10 cadaveric lumbar spines was produced by dead weights applied to a torsion bar attached at T12. The lumbar spines were first measured without instrumentation being applied. Three different types of instrumentation were then applied in turn across two levels of each lumbar spine: AO internal fixation from L2 to L4, lumbosacral Louis plates from L4 to S1, and Cotrel-Dubousset (CD) pedicular screws and rods from L2 to L4 and then from L4 to S1. For each of these four, a set of measurements of rotation in the transverse plane was taken. The Louis plates allowed less rotation across L4-S1 than CD, although the result was not significant. The AO fixator applied across L2-L4 allowed significantly less rotation across L2-L4 than CD. The AO fixator was compared with the spine with no instrumentation to determine if less rotation across L2-L4 was associated with more rotation across L1-L2 and L4-L5; the differences were significant (p < 0.05).

Biomechanical Phenomena↗