摘要:

Study Design.Descriptive, microdissection study.Objective.To determine the morphology of the human adult cervical intervertebral disc and its ligaments.Summary of Background Data.Some studies indicate that the cervical disc is distinctly different from the lumbar intervertebral disc, yet most clinical and anatomic texts appear content with extrapolating data from the lumbar spine. A detailed three-dimensional description of the cervical intervertebral disc and its surrounding ligaments is currently unavailable.Methods.Whole cervical spinal columns were freed from 12 human adult embalmed cadavers, and the posterior elements and soft tissues were removed. Using microdissection, the longitudinal ligaments and the fibrous components of 59 cervical intervertebral discs were resected systematically. The orientation, location, and attachments of each stripped bundle of collagen were recorded photographically and in sketches.Results.The cervical anulus fibrosus does not consist of concentric laminae of collagen fibers as in lumbar discs. Instead, it forms a crescentic mass of collagen thick anteriorly and tapering laterally toward the uncinate processes. It is essentially deficient posterolaterally and is represented posteriorly only by a thin layer of paramedian, vertically orientated fibers. The anterior longitudinal ligament covers the front of the disc, and the posterior longitudinal ligament reinforces the deficient posterior anulus fibrosus with longitudinal and alar fibers.Conclusions.The three-dimensional architecture of the cervical anulus fibrosus is more like a crescentic anterior interosseous ligament than a ring of fibers surrounding the nucleus pulposus.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.A study on the efficacy of recombinant human bone morphogenetic protein 2 (rhBMP-2) in a nonhuman primate anterior interbody fusion model.Objectives.To investigate the efficacy of rhBMP-2 with an absorbable collagen sponge carrier to promote spinal fusion in a nonhuman primate anterior interbody fusion model.Summary of Background Data.RhBMP-2 is an osteoinductive growth factor capable of inducing new bone formationin vivo.Although dosage studies using rhBMP-2 have been performed on species of lower phylogenetic level, they cannot be extrapolated to the primate. Dosage studies on nonhuman primates are essential before proceeding with human primate application.Methods.Six female adult Macaca mulatta (rhesus macaque) monkeys underwent an anterior L7-S1 interbody lumbar fusion. All six sites were assigned randomly to one of two fusion methods: 1) autogenous bone graft within a single freeze-dried smooth cortical dowel allograft cylinder (control) or 2) rhBMP-2-soaked absorbable collagen sponges within a single freeze-dried smooth cortical dowel allograft cylinder also soaked in rhBMP-2. The animals underwent a baseline computed tomography scan followed by 3- and 6-month postoperation scans. Anteroposterior and lateral radiographs of the lumbosacral spine were performed monthly. After the monkeys were killed, the lumbar spine fusion sites were evaluated. Histologic evaluation of all fusion sites was performed.Results.The three monkeys receiving rhBMP-2-soaked collagen sponges with a freeze-dried allograft demonstrated radiographic signs of fusion as early as 8 weeks. The control animals were slower to reveal new bone formation. The computed tomography scans revealed extensive fusion of the L7-S1 lumbar vertebrae in the group with rhBMP-2. A pseudarthrosis was present in two of the control animals.Conclusions.This study was able to document the efficacy of rhBMP-2 with an absorbable collagen sponge carrier and a cortical dowel allograft to promote anterior interbody fusion in a nonhuman primate model at a dose of 0.4 mg per implant site (1.5 mg/mL concentration). The rate of new bone formation and fusion with the use of rhBMP-2 and cortical dowel allograft appears to be far superior to that of autogenous cancellous iliac crest graft with cortical dowel allograft.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.A rabbit model of posterolateral intertransverse process spine arthrodesis was used.Objective.To determine the efficacy of two new formulations of demineralized bone matrix.Summary of Background Data.The flowable gel form of Grafton (Osteotech, Eatontown, NJ) demineralized bone matrix has been shown to have osteoinductive properties in various models and currently is used clinically as bone graft material in posterolateral lumbar spine arthrodesis. Two new formulations of Grafton, one made of flexible sheets (Flex) and the other made in a malleable consistency (Putty), have improved handling characteristics compared with the gel form.Methods.In this study, 108 New Zealand white rabbits underwent bilateral posterolateral intertransverse spine arthrodesis at L5-L6 using autogenous iliac crest bone graft alone (control), one of the new forms of demineralized bone matrix (DBM; made from rabbit bone) alone or in combination with autogenous iliac crest bone. Rabbits were killed 6 weeks after surgery. The lumbar spines were excised, and fusion success or failure was determined by manual palpation and radiography. Specimens also were processed for undecalcified histologic analysis.Results.Manual palpation of the harvested lumbar spines revealed that the fusion rates of the Flex-DBM/Auto group (9/9, 100%) and Putty-DBM/Auto group (10/10, 100%) were superior (P< 0.01) to those of the Auto/control group (3/9, 33%). As a stand-alone graft substitute, Flex-DBM performed superiorly with a fusion rate of 11/11 (100%) compared with that of Putty-DBM (10/12, 83%) and Gel-DBM (7/12, 58%). The devitalized version of Flex-DBM had a fusion rate of 4/11 (36%), which was comparable with the devitalized Putty-DBM rate of 4/12 (33%). Both were superior (P< 0.05) to the devitalized Gel-DBM rate of 0/12 (0%). More mature fusions with greater amounts of trabecular bone were present radiographically and histologically in rabbits that received all forms of demineralized bone matrix than in those in which autograft was used.Conclusions.The new flexible sheet and malleable putty forms of demineralized bone matrix were effective as graft extender and graft enhancer in a model of posterolateral lumbar spine fusion. These newer formulations of Grafton appear to have a greater capacity to form bone than the gel form or autogenous bone graft alone in this model.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.An assessment of the value of external fixation with or without percutaneous discectomy for the management of scoliosis in young rabbits with induced progressive thoracic scoliosis.Objectives.To investigate in an experimental setting the effect of external fixation with or without percutaneous discectomy for the management of scoliosis, as a preliminary study to precede clinical consideration.Summary of Background Data.External fixation of the spine using percutaneous transpedicular screws has been used clinically for cases of traumatic spinal injury, infectious spine, or chronic low back pain caused by a disc lesion. Percutaneous discectomy for the management of scoliosis has been reported.Methods.Thirty-two young rabbits underwent partial resection of the right lower ribs. Nine rabbits were not treated after production of scoliosis and were followed as controls. At 4-6 weeks after production of scoliosis, in 23 animals, Kirschner wires were inserted percutaneously into the T9-T10 and L1-L2 disc space, and both ends were attached to an external fixator after correction of the scoliosis. In 8 of those 23 animals, percutaneous discectomy was also performed at the apex of the caudal compensatory curvature.Results.In these 23 animals, the initial correction by fixation of the caudal vertebrae was accompanied by a derotation in the apex. Five animals treated with external fixation only and four treated with combined percutaneous discectomy survived with external fixation until the age of 17 weeks and were followed to the natural cessation of the curve progression, at which the fixation was removed and a final assessment was made. The mean progression of curvature was 15.8° in the group of five animals with external fixation only, and 33.8° in the controls. In the group of four animals treated with supplementary percutaneous discectomy, however, the treated disc space became rigid, and the mean progression of curvature after removal of the fixation was only 5.3°.Conclusions.The results of the current study suggest the potential for external fixation to allow for derotation and, when combined with percutaneous discectomy, to offer a feasible method of managing scoliosis in the human adolescent. This study was a preliminary experimental study; further experimental studies are planned to develop this novel technique.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.An In vitro biomechanical load-to-failure test.Objectives.To determine the comparative axial pullout strengths of pedicle screwversustransverse process screws in the upper thoracic spine (T1-T4), and to compare their failure loads with bone density as seen on computed tomography.Summary of the Background Data.The morphology of the upper thoracic spine presents technical challenges for rigid segmental fixation. Though data are available for failure characteristics of cervical lateral mass screws, analagous data are wanting in regard to screw fixation of the upper thoracic spine.Methods.Ten fresh-frozen human spines (T1-T4) were quantitatively scanned using computed tomography to determine trabecular bone density at each level. The vertebrae were drilled and tapped for the insertion of a 3.5-millimeter-diameter cortical bone screw in either the pedicle or the transverse process position. A uniaxial load to failure was applied.Results.The mean ultimate load to failure for the pedicle screws (658 N) was statistically greater than that of the transverse process screws (361 N;P< 0.001). The T1 pedicle screw sustained the highest load to failure (775 N). No significant difference was found between load to failure for the pedicle and transverse process screws at T1. A trend toward decreasing load to failure was seen for both screw positions with descending thoracic level. Neither pedicle dimensions nor screw working length correlated with load to failure.Conclusions.Upper thoracic pedicle screws have superior axial loading characteristics compared with bicortical transverse process screws, except at T1. Load behavior of either of these screws was not predictable based on anatomic parameters.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.A comparison between femoral ring and fibular strut allografts in anterior lumbar interbody arthrodesis, as assessed by biomechanical analysis.Objectives.To assess the difference in stability and rigidity provided by the femoral ring allograftversusthat provided by fibular strut allograft.Summary of Background Data.Two commonly used techniques for spinal arthrodesis at L4-L5 include the femoral ring allograft and the fibular strut allograft. The postoperative stability has not been evaluated biomechanically.Methods.An anterior lumbar interbody fusion on seven cadaveric specimens was performed using femoral ring and fibular strut allografts. Biplanar radiography was used to measure the 6° of motion of L4 with respect to L5 during a range of loading maneuvers.Results.When an extension moment was applied, the femoral ring allograft extended 4.2° more than the intact specimen, compared with 1.6° with the fibular strut allograft (P= 0.18). When the flexion moment was imposed, lateral bending increased by 2.2° with the femoral ring, compared with 0.7° with the fibular strut allograft (P= 0.06). During lateral bending, increased lateral translation was observed to be 0.9 mm with the fibular strut allograft compared with 1.4 mm with the femoral ring allograft (P= 0.06).Conclusions.Although not statistically significant, the fibular strut allograft creates a more rigid construct immediately after surgery during flexion-extension, lateral bending angulations, and lateral translation. One should consider using the fibular strut allograft over the femoral ring allograft, as it is a more stable and rigid construct in the immediate postoperative period.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.An analysis of the geometric data of the lumbar spine in Chinese men. Lateral radiographs were obtained of 16 men in the upright position to a trunk flexion of 90° in 30° increments.Objectives.To establish reference data concerning the geometry of the lumbar spine for various degrees of trunk flexion.Summary of Background Data.In previous studies, the morphometry and alignment of the lumbar spine have been investigated. Reports of systematic analyses of the lumbar spine in trunk flexion have lacked adequate radiographic data. Moreover, few studies have focused on measuring lumbar spine geometric data in Chinese individuals.Methods.A total of 67 landmarks on each radiograph were identified. They were marked by investigators and digitized using a HyperSpace digitizing system (V.17; Mira Imaging Inc., Salt Lake City, UT). The geometric configuration of the vertebrae and discs then was derived from the digitized points.Results.The dimensions of the vertebrae and disc on the lumbar spine obtained in this study were similar to those of previous studies. The motion of the lumbosacral spine had the greatest contribution in trunk flexion, approximately 90% (i.e.,rotating at the rate of 9° for each 10° of trunk flexion) when the trunk was flexed from 30° to 60°. After that, the hips were dominant in accomplishing the trunk flexion from 60° to horizontal. This motion pattern may be useful for making clinical diagnoses of lumbar function in Chinese men.Conclusions.No obvious interracial differences were found in the geometric data found in this study, which suggests that morphometric data obtained from Caucasian individuals may be applied to Chinese patients for clinical purposes.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Study Design.An analysis of the change in strain distribution of intervertebral discs present after anterior cervical decompression and fusion by an original method. The analytical results were compared to occurrence of herniation of the intervertebral disc on magnetic resonance imaging.Objectives.To elucidate the influence of anterior cervical decompression and fusion on the unfused segments of the spine.Summary of Background Data.There is no consensus regarding the exact significance of the biomechanical change in the unfused segment present after surgery.Methods.Ninety-six patients subjected to anterior cervical decompression and fusion for herniation of intervertebral discs were examined. Shear strain and longitudinal strain of intervertebral discs were analyzed on pre- and postoperative lateral dynamic routine radiography of the cervical spine. Thirty of the 96 patients were examined by magnetic resonance imaging before and after surgery, and the relation between alteration in strains and postsurgical occurrence of disc herniation was examined.Results.In the cases of double- or triple-level fusion, shear strain of adjacent segments had increased 20% on average 1 year after surgery. Thirteen intervertebral discs that had an abnormally high degree of strain showed an increase in longitudinal strain after surgery. Eleven (85%) of the 13 discs that showed an abnormal increase in longitudinal strain had herniation in the same intervertebral discs with compression of the spinal cord during the follow-up period. Relief of symptoms was significantly poor in the patients with recent herniation.Conclusion.Close attention should be paid to long-term biomechanical changes in the unfused segment.

ISSN:0362-2436    

出版商:OVID    

年代:1999

数据来源: OVID