ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study Design.Animal scoliosis model associated with syringomyelia.Objective.To investigate the pathogenesis of scoliosis produced in dogs with kaolin-induced syringomyelia.Summary of Background Data.Kaolin injected into the cisterna magna produces basilar arachnoiditis, leading to hydrocephalus and syringomyelia. There have been no reports on scoliosis associated with kaolin-induced syringomyelia.Methods.Kaolin was injected percutaneously into the cisterna magna of 11 beagles 6-8 weeks after birth. Roentgenograms, computed tomography, and magnetic resonance imaging were obtained. The spinal cord and the paraspinal muscles were examined histologically. Structural changes of the vertebral column were analyzed with calcein and tetracycline labeling.Results.Hydrocephalus occurred in nine dogs. A communicating syringomyelia appeared in five dogs. Mild scoliosis developed in two dogs, and severe cervical scoliosis in one dog. In the syringomyelia cases, acute or subacute inflammatory changes were found in the spinal cord. Damage of the anterior and posterior horn cells was more marked in the scoliotic animals than in the nonscoliotic animals. In three of the syringomyelia cases, including two scoliosis cases, the paraspinal muscles revealed neurogenic changes. The deformed vertebrae appeared to diminish rather than to increase the deformity in severe scoliosis.Conclusion.The exact mechanism of the development of scoliosis could not be identified, although an etiologic relation with malfunction of the central nervous system was noted. This model may be useful to study scoliosis experimentally.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study Design.Surgical spinal cable and wire fixation systems were tested mechanically using standardized methodologies.Objectives.To compare the relative mechanical properties and biomechanical performances of the different commercially available spinal wire and cable fixation devices, and to provide information that will help in selecting different cables for different clinical applications.Summary of Background Data.Spinal cables have become extensively used for spinal fixation; however, there are few published accounts delineating their mechanical properties. No reports have compared the relative properties of different cable systems.Methods.Nine spinal cable and wire fixation systems were mechanically tested to compare their static tensile strength, stiffness, fatigue strength, creep, conformance, and abrasion properties. Titanium and stainless steel Codman cable, Danek cable, and AcroMed cable, polyethylene Smith & Nephew cable, and 20- and 22-gauge stainless steel monofilament Ethicon wire were tested using identical methodologies. The cable or wire was connected into loops with methods that simulatedin vivoclinical applications.Results.Under static tensile testing, titanium cables had 70% to 90% of the ultimate tensile strength of the comparable steel cables; the different cables were 100% to 600% stronger than monofilament wire; the ultimate strength of the polyethylene cable was similar to that of the strongest available steel cable. Fatigue testing delineated important differences among the different materials. For a given manufacturer, titanium cables were always more susceptible to fatigue than stainless steel cables of comparable diameter. Polyethylene cable withstood cyclical loading without breaking better than all of the metal cables and wires. The mechanisms of failure differed substantially among materials and types of tests. Polyethylene cables exhibited significant stretching or "creep" at loads that were much lower than the static failure loads. In contrast, no wire cable demonstrated creep. Monofilament wires demonstrated little creep. Polyethylene cables failed by elongating and loosening; wire cables failed by breaking. Monofilament wire and cables conformed least to a solid surface; polyethylene cable conformed the most and flattened out against solid surfaces. Abrasion properties depended on the surface characteristics of the implants. Polyethylene cable was abraded by (and eventually failed by wearing against) the simulated bone, a result that did not occur with any metal cables or wires. The steel and titanium cables and the monofilament wires all had an ability to abrade through simulated bone.Conclusions.Titanium, steel, and polyethylene cable systems all behave substantially differently mechanically compared with monofilament wire. The relative advantages and disadvantages of each particular product should be considered when selecting an implant for a specific clinical use.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study Design.Nondestructive flexibility testing was performed to quantify biomechanical parameters of human cadaveric thoracic spines before and after microdiscectomy.Objectives.To assess the biomechanical differences between the normal thoracic spine and the thoracic spine after microdiscectomy and to determine whether microdiscectomy results in spinal instability.Summary of Background Data.Previous studies have investigated thoracic disc properties and the biomechanical effects of thoracic ligament or bone trauma. No studies were found assessing the effects of thoracic discectomy.Methods.Eight motion segments (T4-T5 to T11-T12) from five human cadaveric thoracic spines were studied before and after microdiscectomy. Three-dimensional motion was recorded in response to nondestructive, nonconstraining pure moments. Parameters measured included the neutral zone, elastic zone, range of motion, rotational flexibility, and instantaneous axis of rotation.Results.The neutral zone, elastic zone, and range of motion increased a small but significant (averageP= 0.02 for range-of-motion increase) amount in all directions after thoracic microdiscectomy (mean bilateral range of motion increase, 2.1°; range, 0.5-4.2°). Flexibility increased slightly during lateral bending and flexion. The instantaneous axis of rotation location usually did not change, but sometimes shifted slightly away from the discectomy site after microdiscectomy.Conclusions.Thoracic microdiscectomy had small effects on the immediate mechanics and kinematics of the thoracic spine and did not overtly destabilize the motion segments.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study Design.In this retrospective study, a 5-year series of a pediatric population undergoing Chiari decompressions is reviewed.Objectives.To review the experience with children treated with suboccipital craniectomy and uni- or multi-level cervical laminectomy for Chiari malformation, to determine the incidence of kyphosis and to identify factors predictive of cervical instability.Summary of Background Information.Upper cervical laminectomy in the pediatric population has a significant risk of postoperative kyphosis. To decrease the incidence of this complication, a concerted effort was made to avoid violation of the facet joint during cervical laminectomy.Methods.Thirty-two patients (mean age 4.9 years, range 1 day to 18 years) had surgical decompression of Chiari I or II malformations throughout a 5-year period (1989-1994). Radiographs and operative records were analyzed to determine the number of cervical levels decompressed and extent of laminectomy.Results.Mean follow-up was 3.7 years (range 9 months to 7 years). Only one patient had clinical and radiographic evidence of kyphosis and required C2-C3 fusion. Two others had radiographic signs of mild cervical kyphosis but remained asymptomatic. These three patients had two-level complete laminectomies. Twentynine patients had no clinical or radiographic evidence of cervical instability. A mean of three cervical levels were decompressed (range 0-4), including partial laminectomies, complete laminectomies, and one osteoplastic laminotomy to drain a lower cervical syrinx. The overall frequency of kyphosis in this series (9%) was substantially lower than in previous reports. Although the number of cervical levels decompressed did not correlate with cervical instability, the one patient with clinical instability had inadvertent violation of the facet joint, suggesting that overaggressive laminectomy may be a critical factor that predisposes patients to postoperative kyphosis.Conclusion.Cervical kyphosis after Chiari decompression is a recognized complication of cervical laminectomy in children, the frequency of which may be decreased by careful attention to operative technique.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study Design.This study analyzes the effects of a new anterior spinal instrumentation system and the results of use in 50 patients with scoliosis.Objectives.Anterior spine systems are reviewed. The principles of a new anterior spinal instrumentation system allowing for postoperative care without external support are discussed.Summary of Background Data.Numerous different implants have been presented in the literature for anterior spinal surgery. Nevertheless, a primary stable anterior instrumentation was not available for multisegmental procedures until now, and the restoration of lordosis in the lumbar spine was very difficult with the common devices. The development of more stable devices that also allow a restoration of lordosis in combination with derotation and compression is discussed.Methods.Fifty patients with scoliosis of different etiologies (neuromuscular: n = 33; idiopathic: n = 16; congenital: n = 1) underwent anterior spinal surgery at the thoracic, thoracolumbar, and lumbar spine. During follow-up, no revision operation was necessary after the monosegmental and multisegmental application of this method, and there were no vessel complications. The results were controlled with a mean follow-up of 26.6 (range, 12-41) months.Results.Clinical and radiologic follow-up and complications are reported. Statistical data obtained show a different average blood loss and operation time depending on the different etiology of the scoliotic deformity. The mean corrections for the scolioses by etiology are as follows: myelomeningocele (MMC) (mean preoperative angle 89°, mean correction 54%); neuromuscular (81°, 46%); and idiopathic (55°, 69%). The mean lordosis of the lumbar spine was 29.2° (measured between T12-S1) and could be corrected to 45.2° depending on the etiology of the curvature, whereas the angle of the thoracic kyphosis did not show an essential change. The segmental measurement in idiopathic scoliosis did not show a kyphosization in the lumbar spine. Derotation of the apical vertebra in 15 patients in relation to the sagittal plane was 37%.Conclusions.The study shows the effect of a new anterior device allowing the application of three-dimensional correction forces to the spine. Particularly in scoliosis derotation, compression and restoration of lordosis are possible. Primary stability is obtained by anchoring the implants with a new wedge-locking technique, which makes postoperative external support unnecessary.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study Design.The three-dimensional (3-D) interrelations in the correction of the spine and rib cage produced by the Boston brace were analyzed in a group of adolescents with idiopathic scoliosis.Objectives.To investigate the coupling movements between the spine and rib cage initiated by brace wear (i.e.,the displacements of the spine that take place in other directions than the ones generated by brace pressures on the thorax).Summary of Background Data.The effects of thoraco-lumbo-sacral orthosis in the frontal plane have been well documented, but they have never been studied in terms of 3-D coupled movements between the spine and rib cage.Methods.The spine and rib cage of 36 adolescents with idiopathic scoliosis with and without their Boston brace were reconstructed in 3-D using a stereo-radiographic technique. Several geometric indices were evaluated on the trunk, and the relative motions of the spine and rib cage resulting from brace wearing were compared by means of Studentttests, Pearson correlation matrices, and linear regressions.Results.Rib cage transverse plane translations resulting from brace pressures are related to those of the spine. Coupled movements between the spine and rib cage were found to alter substantially the expected 3-D correction of the trunk. Significant anterior displacements of the thorax were observed and were statistically associated with lateral displacements of the spine and with an increase of spinal thoracic curvatures in the frontal and sagittal planes.Conclusion.Brace loads are not applied in an optimal way to correct the 3-D deformities associated with thoracic idiopathic scoliosis. Loads applied on the posterior rib hump should be reequilibrated to reduce anterior displacement of the trunk.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID