摘要:

Study Design.A prospective analysis of 33 control and 39 surgical human lumbar disc specimens from the anulus was undertaken to assess disc cell extracellular matrix production and cell function. The authors of this study analyzed immunohistochemical distributions of Types I, II, III and VI collagen,in situlocalization of apoptotic disc cells, and tartrate-resistant acid phosphatase localization.Objectives.To quantify the incidence of apoptotic cell death in the anulus; examine the collagen distribution in the pericellular, territorial, and interterritorial matrix; examine matrix cell degeneration; and compare diseased tissue with normal tissue from control individuals.Summary of the Background Data.Previous studies of disc histopathology have focused on extracellular matrix morphology and on biochemical synthetic and degenerative changes, but little is understood about the cell populations within the disc that are responsible for these changes.Methods.In this study light microscopy, immunohistochemistry, enzyme histochemistry, andin situhybridization were used to examine 33 patient and 39 control specimens of human anulus obtained either via surgical procedures or from donors to the Cooperative Human Tissue Network.Results.The high incidence of apoptotic cell death was significantly greater in the control group (73.1 ± 5.1% [mean ± SEM]; n = 20) than among surgical specimens (53.5 ± 5.6%; n = 20;P< 0.001); this was probably a result of the significantly greater average age in the control population (57.2 ± 3.1 years) compared with that in the patient population (44.3 ± 3.2 years;P< 0.001). Immunohistochemistry yielded findings that led to an expanded appreciation of the greatly modified extracellular domains that surrounded disc cells during aging and degeneration in both study groups. Enzyme histochemistry revealed the presence of tartrate-resistant acid phosphatase activity in human disc cells.Conclusions.These findings reveal that there is a high incidence of apoptosis in the intervertebral disc. Surviving cells are not synthetically inactive but are, rather, producing inappropriate matrix products during aging and degeneration. In certain instances it appears that the matrix surrounding the cell may form an isolation barrier, which may influence individual cell activity and intercellular communication. These results point to the need to 1) more fully understand the cause of disc cell death via apoptosis and to determine whether this programmed cell death can be reversed or halted, and 2) more fully understand the dynamic relation between disc cells and the surrounding extracellular matrix, which they produce and remodel. The factors regulating extracellular matrix-disc cell homeostasis in the disc are unknown, as is the relation between extracellular matrix and disc cell functional modulation. The morphologic findings of this study suggest that these issues are important considerations in disc cell biology. The identification of tartrate-resistant acid phosphatase activity in disc cells allows for a new area of study of disc extracellular matrix remodelling. In summary, these new perspectives provide new parameters with which to assess disc cell health and function.

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Study Design.The Alpine goat model for multilevel anterior cervical discectomy and fusion was used to analyze the use of an intervertebral fusion device to promote an arthrodesis after anterior cervical discectomy. Comparisons were drawn with biomechanical, histologic, and radiographic data.Objectives.To analyze the use of an intervertebral fusion device, with and without a bone graft substitute, to promote an arthrodesis after anterior cervical discectomy.Summary of Background Data.In previous studies, the goat cervical spine has proven to be an excellent model for examining the healing of fusions using bone grafts, instrumentation, or bone substitutes.Methods.Three-level anterior cervical discectomies were performed on 21 mature Alpine goats. Three treatment groups of seven goats each were used. Group I used a standard titanium cervical BAK device filled with autogenous bone graft. Group II used a hydroxyapatite-coated BAK device filled with autogenous bone graft. Group III used a BAK device filled with recombinant human bone morphogenetic protein-2.Results.Radiographically, no cages became displaced. Lucencies were seen around 3 of the 21 cages in Group I, 4 cages in Group II, and none in Group III. Fluorochrome analysis revealed that the recombinant human bone morphogenetic protein-2-filled cages had an accelerated rate of bone growth around and through each cage-vertebral body interface at 3 weeks. A successful arthrodesis was also more likely with a recombinant human bone morphogenetic protein-2-filled cage (95%) than the hydroxyapatite-coated (62%) or the standard (48%) cage. Biomechanical stiffness testing did not reveal any statistically significant differences between the three groups. There was a tendency for successfully arthrodesed interspaces to be stiffer than those that were not.Conclusions.The use of a threaded intervertebral fusion cage, with or without hydroxyapatite coating, filled with autogenous bone graft provides a fusion rate that is slightly better than those previously reported using autogenous interbody bone grafts with or without plate stabilization. Recombinant human bone morphogenetic protein-2-filled cages resulted in a much higher arthrodesis rate and accelerated bone formation compared with either autogenous bone-filled BAK devices, or autogenous interbody bone grafts with or without plate stabilization.

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Study Design.Spinal kinematics after the implementation of rigid spinal instrumentation or the achievement of a solid fusion was studied using a sheep posterolateral spinal arthrodesis model.Objective.To investigate the effects of rigid spinal instrumentation or solid fusion on spinal kinematic parameters.Summary of Background Data.Numerous studies have attempted to define spinal instability in terms of kinematics. Recentin vitrostudies have documented the neutral zone, or a measure of spinal laxity, as more sensitive to spinal instability than the range of motion.Methods.Seven skeletally mature sheep underwent a single-level posterolateral lumbar arthrodesis using autologous bone graft augmented with transpedicular screw fixation. The animals were killed 4 months after surgery. The identical surgical procedures were performed in seven sheep cadaveric spines, which served as acute postoperative controls. Each functional spinal unit was tested biomechanically before and after hardware removal. The experimental control groups consisted of destabilized spines and spines that underwent transpedicular screw fixation alone, whereas the fusion groups included spines that underwent posterolateral fusion alone or posterolateral fusion with instrumentation.Results.Rigid instrumentation and solid fusion significantly decreased the neutral zone and range of motion in all testing modes. In axial rotation and lateral bending, solid fusion reduced the range of motion significantly more than transpedicular screw fixation alone. However, in all testing modes, the neutral zones showed no statistical difference between transpedicular screw fixation alone and fusion groups.Conclusions.The range of motion was an equivalent or better indicator of fixation or fusion stability compared with the neutral zone. Moreover, the immediate postoperative fixation stability, even if using transpedicular screw fixation, was less than the stability present after a solid fusion.

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Study Design.Surface electromyographic activities were recorded from bilateral trunk muscles as test participants maintained a 50% maximum, voluntary, isometric, lateral bend contraction to volitional exhaustion.Objectives.To challenge the trunk with a prolonged lateral bend task and observe the responses of the agonist and antagonist muscles to the resulting fatigue.Summary of Background Data.Lateral bend exertions of the trunk have been identified as a risk factor for injury to spine tissues. However, little is known about the response of spine muscles to fatigue and the subsequent implications for spine stability, joint loading, and tissue injury. Surface electromyography provides a window on muscle loading and progressive fatigue.Methods.Eleven male participants performed a set of maximum lateral bend exertions at the start of the trial, then maintained an upright standing posture while resisting 50% of the maximum moment until volitional exhaustion, then performed another set of maximum contractions. All contractions were isometric. Measurements were made, throughout each contraction, of the lateral bend moment and abdominal and trunk extensor electromyographic activities at six bilateral surface electromyography sites. Electromyographic amplitude and mean power frequency were calculated with 500-millisecond segments recorded serially every 800 milliseconds. Mean values were calculated with data from the first and last 5% of the trial durations. Statistics determined if fatigue had a significant effect on maximum moment and the electromyographic statistics for each muscle site.Results.Fatigue resulted in a significant decrease in maximum lateral bend moment and increase in moment variability. Decreases in mean power frequency, indicating fatigue, were observed in three agonists (the trunk extensors) and one antagonist muscle. Unfatigued agonist electromyographic amplitudes correlated well with the mechanical advantage of muscles to generate lateral bend moments. Unfatigued antagonist activities were low except for the thoracic erector spinae. The agonists and antagonists demonstrated average increases of 17% and 8%, respectively, when pooled across muscles. Much of this change was predicted to have been associated with increases in co-contracting muscle forces.Conclusions.The trunk responded to a prolonged, lateral bend contraction by increasing co-contraction as agonist trunk muscles fatigued. It was proposed that the fatigue compromised neural coordination and that the co-contraction served to maintain spine stability.

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Study Design.This was a prospectivein vitrostudy comparing titanium alloy and stainless steel alloy in transpedicular spine implants from two different manufacturers.Objective.To compare the multicycle mechanical performance of these two alloys, used in each of two different implant designs.Summary of Background Data.Transpedicular spine implants primarily have been manufactured from stainless steel, but titanium alloy offers imaging advantages. However, the notch sensitivity of titanium alloy has caused concern regarding how implants made from this material will compare in stiffness and fatigue life with implants made from stainless steel.Methods.Twenty-four implants (two alloys, two designs, six implants per group) were mounted in machined polyethylene wafers and repetitively loaded (up to 1 million cycles) from 80 N to 800 N using a 5-Hertz sinusoidal waveform. Load and displacement data were automatically and periodically sampled throughout the entire test.Results.Implant stiffness increased with cycle load number, reached a steady state, then declined just before fatigue failure. Stiffness varied less in titanium transpedicular spine implants than in their stainless counterparts. All stainless steel implant types were stiffer (steady-state value,P< 0.0001) than their titanium alloy counterparts. One titanium implant design failed with fewer (P< 0.05) load cycles than its stainless steel counterpart, whereas a stainless steel implant of another design failed with fewer (P= 0.002) load cycles than its titanium counterpart. Overall, fatigue life,i.e.,the total number of load cycles until failure, was related to implant type (P< 0.0001), but not to implant material.Conclusions.A transpedicular spine implant's fatigue lifetime depends on both the design and the material and cannot be judged on material alone. Stainless steel implants are stiffer than titanium alloy implants of equal design and size; however, for those designs in which the fatigue life of the titanium alloy version is superior, enlargement of the implant's components can compensate for titanium's lower modulus of elasticity and result in an implant equally stiff as its stainless steel counterpart. Such an implant made from titanium alloy would then be clinically preferable because of titanium's previously reported imaging advantages.

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Study Design.A prospective study to determine the long-term outcome of traumatically induced vertebral artery injuries. Magnetic resonance angiography was performed at the time of cervical injury and at a follow-up office visit.Objective.To determine the long-term outcome in terms of arterial flow competency of traumatically induced vertebral artery injuries.Summary of Background Data.Vertebral artery injury associated with cervical spine trauma has been well documented; however its healing or nonhealing potential has not been elucidated.Methods.During the 7-month period from July 1993 to January 1994, all patients admitted to the authors' institution with cervical spine injuries underwent magnetic resonance imaging and magnetic resonance angiography of the cervical spine to determine the patency of their vertebral arteries. Magnetic resonance angiography was performed at the time of injury and at a follow-up office visit. Twelve of 61 patients were found to have a lack of signal flow within one of their vertebral vessels during this study period.Results.Eighty-three percent of the patients (five of six) who were available for follow-up observation in this study did not manifest flow reconstitution of their vertebral arteries after an average 25.8-month follow-up period.Conclusions.According to these data, most patients with vertebral artery injuries after nonpenetrating cervical spine trauma do not reconstitute flow in the injured vertebral arteries. This lack of flow must be considered if future surgery in this region of the cervical spine is contemplated.

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1998

数据来源: OVID