摘要:

Study DesignHistologic changes in the intervertebral disc were evaluated by light and electron microscopy after an intradiscal injection of methylprednisolone acetate.ObjectiveTo evaluate the histologic changes that occur in the disc after an intradiscal injection of corticosteroids.Summary of Background DataSeveral orthopedic surgeons have managed lumbar disc herniation with intradiscal steroid injection. Few studies have addressed the histologic changes after this treatment.MethodsThirty rabbits were surgically treated. Rabbits were divided into two groups. Group A: 25 rabbits underwent intradiscal steroid injections. Methylprednisolone acetate was injected into the L3-L4 disc, whereas methylprednisolone sodium succinate was injected into the L4-L5 disc. Physiologic saline was injected into the L5-L6 disc as a control. Groups of five rabbits were killed 1 day, 1, 4, 12, and 24 weeks after the injection and subjected to microscopic evaluation. Group B: Another five rabbits underwent an injection of polyethylene glycol 4000, a vehicle for methylprednisolone acetate, into the L3-L4 and L4-L5 discs. All five rabbits were killed 24 weeks after the injection and subjected to microscopic evaluation.ResultsGroup A: Light microscopic evaluation showed tissue in the nucleus pulposus, and the inner layer of the anulus fibrosus had degenerated in the methylprednisolone acetate group killed 24 weeks after the injection. Matrix vesicles, an indication of primary tissue calcification, were observed by electron microscopy. In the methylprednisolone sodium succinate group and saline group, however, no histologic changes were observed. Group B: Degeneration of the nucleus pulposus and primary tissue calcification were observed in the discs of all rabbits.ConclusionsMethylprednisolone acetate and its vehicle polyethylene glycol cause degeneration and primary calcification in discs.

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 DesignWater content of fresh human lumbar intervertebral discs (with adjacent endplates) was assessed in three studies: 1) after each of seven specimen preparation steps, 2) during exposure to either saline spray or a saline bath, and 3) during exposure to a saline bath and 445 N axial compression, either without or with previous exposure to the bath and no compression (“free swelling”).ObjectiveTo assess the effect on disc hydration of various aspects of specimen preparation and testing environments.Summary of Background DataWater content is an important determinant of disc behavior. Specimen preparation method and testing environments may be important determinants of water content, yet no work appears to have been reported specifically on this topic.MethodsEndplate-disc-endplate specimens were prepared from refrigerated cadavers within 24 hours of death by transverse sectioning of adjacent vertebral bodies. Water content change was determined by specimen weight change across each time interval of interest.ResultsSpecimen preparation (including multiple freeze-thaw cycles) produced no water content change. Saline spray and plastic film wrap resulted in no change, but saline bath exposure resulted in a 24% increase over 7 hours, 44% of which occurred in the first 0.5 hour. A subsequent 7 hours of 445 N compression reduced the overall increase to 10%. This was not significantly different from the 8% increase that resulted from initial exposure to saline bath and compression.ConclusionsSpecimen preparation as typically performed and specimen exposure to saline spray and plastic film wrap do not result in hydration change. Exposure to saline bath results in substantial swelling, which can either be reversed or prevented by axial compression in the physiologic range. Whether discs exposed to saline spray and wrap without compression and those exposed to saline bath with compression behave the same and which of these more closely mimics thein vivocondition are important issues for the experimentalist to test.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignA finite element parametric analysis to investigate the relative load carrying roles of the shell and centrum in the lumbar vertebral body.ObjectiveTo address the issue of the structural role of the vertebral shell and clarify some of the contradictions raised by previous studies.Summary of Background DataA number of experimental and finite element studies have attempted to quantify the relative structural roles of the shell and centrum, but these studies support no consensus on the relative contribution of the shell to vertebral body strength.MethodsThe authors developed finite element models to predict the fraction of the total compressive force acting on the lumbar vertebral body that is carried by the shell. Parametric variations were investigated to determine how the fraction of shell force was affected by changes in shell thickness, shell and centrum modulus, centrum anisotropy, and loading conditions.ResultsThe fraction of compressive force carried by the shell increased from approximately 0 at the endplate to approximately 0.2 at the mid-transverse plane for a typical case. The shell force was highly sensitive to the degree of anisotropy of the trabecular centrum but was relatively insensitive to changes in shell thickness and the ratio of shell-to-centrum elastic modulus.ConclusionsThe conflicting conclusions of previous studies about the structural roles of the vertebral shell and centrum can be explained by differences in their methods. Our findings support the claims that the shell accounts for only approximately 10% of vertebral strengthin vivoand that the trabecular centrum is the dominant structural component of the vertebral body.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignLumbar motion segments were testedin vitroto examine biomechanical changes after posterior fixation by a flexible device.ObjectivesTo assess changes in load distribution and conformation of vertebral structures after a flexible stabilization. This should provide the foundations for a scientific understanding of the immediate effects of this surgical procedure.MethodsHooks were placed over the proximal spinous process and the distal laminas of a motion segment and connected by a polyester braid. Tension applied to the braid then generated a compression of the posterior elements. The force between the articular facets, the displacement of the posterior anulus fibrosus of the intervertebral disc, and the change in the relative position of the adjacent vertebrae were measured as the applied tension was increased.ResultsFacet joint force, disc bulge, and vertebral angulation increased with applied tension until a position of “locking” was achieved, apparently when the bony margin of the superior half of the facet joint contacted the inferior pars interarticularis. A tension of between 50 to 100 N in the braid was required for this. Facet joint force was less than 40% of this, and disc bulge was only 0.15 mm. The extension of the motion segment was between 2° and 8°.ConclusionsThe results suggest that if such a system is applied surgically, stabilization is produced by compaction of the bony margins of the facet joints. Only a relatively small proportion of the posteriorly applied load is carried by the facet joints themselves, and little angulatory change is expected with minimal disc bulge.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignA direct method for three-dimensionalin vivospine kinematic studies was developed and used to measure segmental motion patterns in healthy subjects.ObjectivesTo validate the new method, and to study the L3-L4 segmental motion patterns for complex dynamic movements.Summary of Background DataConventional two-dimensional and three-dimensional radiographic methods have been used in the past to study spine kinematics. Few studies provided a direct approach to study segmental kinematics. No dynamic recordings of three-dimensional segmental motion patterns have been reported previously.MethodsIn 16 healthy men, Kirschner wires were inserted in the spinous processes of L3 and L4. Electromagnetic tracking sensors were attached to the pins. Motion data recorded during ranging exercises were used with biplanar radiographs to calculate L3-L4 segmental motion patterns. Errors resulting from pin deformation and the dynamic accuracy of the tracking system were investigated thoroughly.ResultsThe average range of motion for flexion-extension was 16.9°, for one side lateral bending 6.3°, and for one side axial rotation 1.1°. Large intersubject variation was found in flexion-extension with values ranging from 7.1 to 29.9°. Coupled motion patterns were found to be consistent among subjects in active lateral bending and inconsistent for active axial rotation.ConclusionsThis new method offers dynamic recording capabilities and a measurement error comparable with stereo radiographic methods. Repetitive ranging experiments are highly reproducible. The range of motion for axial rotation seems overestimated in previous cadaveric studies. Coupling patterns show large variations between individuals.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThis biomechanical study analyzed the axial pull-out strength of tappedversusuntapped pilot holes for bicortical screws in the anterior cervical spine.ObjectiveTo determine which pilot hole preparation method was mechanically better.Summary of Background DataTapping pilot holes in the lumbar spine was previously shown significantly to reduce pull-out strength of pedicle screws. No study was found investigating the effect of tapping on pilot holes for anterior cervical bicortical screws.MethodsTwenty-five unembalmed human cadaveric cervical vertebrae (C3-C7) were tested. Two identical pilot holes were drilled into each vertebra: one pilot hole was tapped, and the control pilot hole was not tapped. A fully threaded cortical bone screw was inserted into each pilot hole. Screw pull-out strength was determined using a servocontrolled hydraulic materials testing system and an axial load cell. Force-deformation and failure curves were obtained.ResultsThere were no statistically significant differences between the axial pull-out strength of tapped and untapped pilot holes at any vertebral level. Mean force-to-failure was 386 ± 42 N in the untapped pilot holes and 397 ± 48 N in the tapped pilot holes.ConclusionsTapping a pilot hole for bicortical screws of the anterior cervical spine neither weakens nor strengthens the axial pull-out strength of fully threaded cortical bone screws. Tapping may be unnecessary; however, it may be desirable in patients with dense bone to cut the thread profile into the bone or if the screws have dull tips and threads.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThe authors measured and compared the stiffness of cadaveric lumbar spines stabilized with several anterior interbody fusion devices. The information obtained provides a foundation for determining how methods of anterior lumbar fixation can maximize rigidity and promote development of bony fusion.ObjectivesTo compare the utility of three anterior spinal instrumentation systems for stabilizing the lumbar spine.Summary of Background DataAnterior spinal instrumentation is used to prevent progressive spinal deformity and maintain correction after spinal fusion surgery. Newer instrumentation systems developed for anterior interbody fusions can be inserted by minimally invasive procedures. The stability of these systems has not been tested adequately in human cadaveric specimens.MethodsFusion constructs were evaluated in 12 human cadaveric specimens sequentially loaded in axial compression and torsion, flexion and extension, and lateral bending. The fusion constructs used were 1) two anterior bilateral threaded interbody fusion devices, 2) lateral hollow interbody screws (Texas Scottish Rite Hospital-B screws), and 3) femoral allograft and conventional anterior Texas Scottish Rite Hospital instrumentation.ResultsThe construct with Texas Scottish Rite Hospital-B screws connected by a rod produced stiffness comparable with that produced by conventional Texas Scottish Rite Hospital instrumentation with femoral ring allografts. The threaded interbody fusion device stiffness tested in axial rotation was comparable with that achieved with Texas Scottish Rite Hospital instrumentation.ConclusionsOur data demonstrate the effectiveness of threaded interbody fusion device and the Texas Scottish Rite Hospital-B screw in immobilizing the L3-L4 and L4-L5 disc spaces. Rigidity of fixation in the lumbar spine may aid in the maintenance of lordosis.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignA prospective study with independent clinical and radiologic review.ObjectiveTo assess whether regression of cervical intervertebral disc herniations accompanied and correlated with clinical improvement in patients recovering from cervical radiculopathy without undergoing surgical intervention.Summary of Background DataThe study subjects were 13 consecutive patients, nine men (69%) and four women (31%), presenting with cervical radiculopathy. All patients but one had objective neurologic signs. All patients had large posterolateral cervical intervertebral disc herniations demonstrated by magnetic resonance imaging.MethodsPain was controlled by serial periradicular and epidural corticosteroid injections. Patients were finally examined and discharged from care because of sustained pain control at an average of 6 months (range, 2-12 months). They were interviewed subsequently over the telephone by an independent clinician and rescanned at an average of 12 months (range, 4-31 months). The scans were reviewed by an independent radiologist masked to the sequence of the scans.ResultsRegression of cervical disc herniations was demonstrated in 12 of the 13 patients. All patients had made a satisfactory clinical recovery, but the one with the herniation that had not regressed suffered from persistent minor symptoms.ConclusionsMost cervical disc herniations regress with time and without the need for surgical resection. Thus, surgical intervention can be avoided with adequate pain control, allowing the herniation time to regress.

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