Biomedical subjects

Bryan W Cunningham

Publications and source records attributed to Bryan W Cunningham.

32 records · Page 2Linked to original sources

PubMed2003

SB Charité disc replacement: report of 60 prospective randomized cases in a US center.

Sixty patients with one-level discogenic pain confirmed by plain radiography, magnetic resonance imaging, and provocative discography for degenerative disc disease were randomized: one-third BAK anterior interbody fusion and two-thirds anterior SB Charité artificial disc replacement. The mean age was 40.3 years (range 21-56 years). Nineteen cases were at L4-L5 and 41 cases were at L5-S1. Nineteen cases had BAK anterior interbody fusion and 41 cases were randomized as SB Charité disc replacement. The length of surgery was mean 88.4 minutes (range 54-137 minutes) for both groups. The estimated blood loss was mean 289.5 mL (range 50-1800 mL). The length of hospital stay was a mean of 3.03 days (range 2-6 days). Oswestry Disability Index scores for the SB Charité disc (aggregate study group) were 50.0 +/- 14.3 preoperatively and 25.0 +/- 20.1 at 1-3 years' follow-up (P < 0.001). This is the first study that shows improvement of functional outcome measures in a prospective randomized design with disc arthroplasty treating primarily mechanical back pain and achieving comparable successful results to lumbar fusion-interbody fusion cage and BMP or interbody autograft and pedicle screw instrumentation.

Adult↗

PubMed2002

Biomechanical comparison of lumbosacral fixation techniques in a calf spine model.

STUDY DESIGN: biomechanical testing of the strength and stability of lumbosacral fixation constructs. OBJECTIVES: The purpose of this study was to quantify and compare the biomechanical properties of five different lumbosacral fixation constructs and determine the benefit of adding supplementary fixation to S1 screws. SUMMARY OF BACKGROUND DATA: Extension of long fusions to the sacrum remains a difficult clinical challenge. Only a limited number of biomechanical studies have evaluated the different fixation methods available, and none has included both nondestructive and load to failure testing of these fixation methods. METHODS: Six fresh-frozen calf spines were prepared and tested for each construct. The five constructs tested included the following: S1 screws alone, S1 screws and S2 proximally directed screws, S1 screws and S2 distally directed screws, S1 screws and intrasacral rods, and S1 screws and iliac screws. Nondestructive, multidirectional flexibility analyses included four loading methods followed by a destructive flexural load to failure. Lumbosacral peak range of motion (millimeters or degrees) and ultimate failure load (Nm) of the five reconstruction techniques were statistically compared using a one-way analysis of variance combined with a Student-Newman-Keuls post hoc test. RESULTS: S1 screw strain tested in flexion-extension was significantly reduced by the addition of any second point of distal fixation. There was no significant difference between any of the different sacral fixation constructs (P > 0.05). In axial compression, only the addition of iliac screws significantly reduced S1 screw strain. In destructive testing under flexion loading, only iliac screws statistically increased the load at failure (P = 0.005). CONCLUSION: This study demonstrates the effectiveness of adding a second fixation point distal to the S1 screws in reducing S1 screw strain. Iliac fixation is more effective than secondary sacral fixation points but may not be necessary in all clinical situations. Only iliac fixation effectively increased the load to failure under catastrophic loading conditions. Supplementary sacral fixation failed to significantly protect against catastrophic failure. These findings support the clinical observation that iliac fixation is least likely to fail in high-risk, long fusions. Whether testing range of motion, screw strain, or load to failure, no benefit could be demonstrated for intrasacral rod placement when compared with other supplementary sacral fixation techniques. Intrasacral rod placement was equal to a second sacral screw in reducing S1 screw strain during flexion-extension loading. It was not as effective as iliac fixation in reducing screw strain or preventing catastrophic failure. When choosing fixation methods in long fusions to the sacrum, this study supports the use of iliac fixation as the method least likely to loosen or pull out. A second point of sacral fixation also offers biomechanical advantages when compared with S1 fixation alone and may be an appropriate choice in less "high risk" fusions to the sacrum.

Animals↗

PubMed2002

Biomechanical evaluation of lumbosacral reconstruction techniques for spondylolisthesis: an in vitro porcine model.

STUDY DESIGN: Biomechanical evaluation of lumbosacral fixation using a porcine model. OBJECTIVES: The primary objective of the current study was to quantify and compare the changes in lumbosacral range of motion produced by four different methods of surgical stabilization, as well as comparing the relative effects of the four constructs in destructive testing. SUMMARY OF BACKGROUND DATA: The lumbosacral junction continues to be a difficult region to obtain a successful spinal arthrodesis and is one of the primary regions for construct failure. METHODS: Twenty-four fresh-frozen porcine lumbosacral spines were used in this investigation. Following intact analysis, the specimens were radically destabilized at the lumbosacral junction and randomized into four treatment groups based on reconstruction: 1) L7-S1 pedicle screws alone (n = 6); 2) L7-S1 pedicle screws and interbody cage (titanium mesh) (n = 6); 3) L7-S1 pedicle screws and iliac screws (n = 6); and 4) L7-S1 pedicle/iliac screws and interbody cage (n = 6). Nondestructive, multidirectional flexibility analyses included four loading methods and fatigue component followed by a destructive flexural load to failure. Lumbosacral peak range of motion (millimeters or degrees) and ultimate failure load (Nm) of the four reconstruction techniques were statistically compared using a one-way analysis of variance combined with Fisher's PLSD. RESULTS: 1) Axial compression: There were no differences in lumbosacral flexibility among the four treatment groups (P > 0.05). 2) Axial rotation: Iliac screw constructs, with or without cages, decreased flexibility at the lumbosacral junction compared with pedicle screws alone (P < 0.05). However, interbody cage reconstructions did not significantly reduce motion. 3) Flexion-extension: Iliac screws with interbody cages reduced segmental motion about the lumbosacral junction, which was significantly different from the remaining treatments (P < 0.05). 4) Lateral bending: The iliac screw constructs afforded significantly less lumbosacral motion compared with bothpedicle screw constructs (with or without cages). With destructive testing, pullout for L7-S1 constructs occurred at the sacrum, whereas failure for the L7-S1/iliac screw, with and without cages, occurred at the proximal adjacent level. CONCLUSION: Iliac screw constructs reduced lumbosacral flexibility levels in three of four loading methods (axial rotation, flexion-extension, and lateral bending) compared with pedicle screw reconstructions. The addition of interbody cages decreased lumbosacral motion for the iliac screw treatments under flexion-extension loading and pedicle screw constructs under axial rotation but did not protect the sacral screws in destructive testing as the iliac screws did. Based on evaluation using an porcine model, both iliac screws and interbody cages effectively reduce the multidirectional flexibility properties of the lumbosacral junction; however, iliac screws are more restrictive of motion (at the lumbosacral joint) and protective of the S1 screws.

Animals↗

PubMed2002

The effect of titanium particulate on development and maintenance of a posterolateral spinal arthrodesis: an in vivo rabbit model.

STUDY DESIGN: The current study was undertaken to determine if the presence of titanium wear particulate deleteriously influences early osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass. OBJECTIVES: Using an in vivo animal model to evaluate the effect(s) of titanium wear particulate on a posterolateral spinal arthrodesis based on serologic, histologic, and immunocytochemical analyses. SUMMARY OF BACKGROUND DATA: The effect of unintended wear particulate resulting from micromotion between the interconnection mechanisms in spinal instrumentation remains a clinical concern. METHODS: Thirty-four New Zealand White rabbits were randomized into two groups based on postoperative time periods of 2 months (Group 1, n = 14) and 4 months (Group 2, n = 20). Group 1 underwent a posterolateral arthrodesis at L5-L6 using tricortical iliac autograft or tricortical iliac autograft + titanium particulate. Group 2 received iliac autograft at the initial surgery and were reoperated on after 8 weeks and treated with posterolateral arthrodesis exposure alone or titanium particulate. Postoperative analysis included serologic quantification of systemic cytokines. Postmortem microradiographic, immunocytochemical, and histopathologic assessment of the intertransverse fusion mass quantified the extent of osteolysis, local pro-inflammatory cytokines, osteoclasts, and inflammatory infiltrates. RESULTS: Serologic analysis of systemic cytokines indicated no significant differences in cytokine levels (P > 0.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of local cytokines (tumor necrosis factor-alpha) at the titanium-treated posterolateral arthrodesis sites at both time periods (P < 0.05). Osteoclast cell counts and regions of osteolytic resorption lacunas were higher in the titanium-treated versus autograft-alone groups (P < 0.05), and the extent of cellular apoptosis was markedly higher in the titanium-treated sites at both time intervals. Electron microscopy indicated definitive evidence of phagocytized titanium particles and foci of local, chronic, inflammatory changes in the titanium-treated sites. CONCLUSION: Titanium particulate debris introduced at the level of a spinal arthrodesis elicits a cytokine-mediated particulate-induced response favoring pro-inflammatory infiltrates, increased expression of intracellular tumor necrosis factor-alpha, increased osteoclastic activity, and cellular apoptosis. The presence of titanium particulate debris, secondary to motion between spinal implants, may serve as the impetus for late-onset inflammatory-infectious complications and long-term osteolysis of an established posterolateral fusion mass in the clinical setting.

Acid Phosphatase↗

PubMed2002

Total disc replacement arthroplasty using the AcroFlex lumbar disc: a non-human primate model.

Using a non-human primate model, the current study was undertaken to investigate the efficacy of the AcroFlex lumbar disc as an intervertebral disc prosthesis, based on biomechanical, histopathologic and histomorphometric analyses. A total of 20 mature male baboons (Papio cynocephalus, mean weight 30 kg) were randomized into two equal groups based on post-operative time periods of 6 (n=10) and 12 months (n=10). Each animal underwent an anterior transperitoneal surgical approach to the lumbar spine, with intervertebral reconstructions performed at L3-L4 and L5-L6 using the following techniques: (1) tricortical iliac autograft and (2) AcroFlex lumbar disc. The two treatments were equally randomized between the non-contiguous operative lumbar levels. Post-mortem analysis included histopathologic assessment of the systemic reticuloendothelial tissues, multi-directional flexibility testing of the operative functional spinal units and quantitative histological analysis of trabecular bone coverage at the prosthesis endplates. Data were statistically compared using a one-way ANOVA with the Student-Newman-Keuls test. All animals survived the operative procedure and post-operative interval without significant intra- or peri-operative complications. Histopathologic analysis of the paraffin-embedded systemic reticuloendothelial tissues indicated no significant pathologic changes at the 6- or 12-month intervals. Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Biomechanical testing of the 6-month autograft, reconstructions with AcroFlex lumbar disc and non-operative control (n=10) intact motion segments indicated no significant differences in peak range of motion (ROM) in axial compression. However, axial rotation produced significantly lower ROM for the autograft treatment compared to the intact and AcroFlex groups (P<0.05). The most significant differences in peak ROM were noted between all treatment groups under flexion/extension and lateral bending loading modalities (P<0.05). By 12 months, the intact condition indicated significantly more motion in all bending modes compared to the AcroFlex and autograft treatments, which were not statistically different from each other (P>0.05). Gross histopathologic analysis of the AcroFlex disc prosthesis demonstrated excellent ingrowth at the level of the implant-bone interface, without evidence of fibrous tissue or synovium. BioQuant histomorphometric analysis at the metal-bone interface (bone contact area/total endplate area) indicated the mean ingrowth was 54.59+/-13.24% at 6 months and 56.79+/-5.85% at 12 months. Radiographic analysis showed no lucencies or loosening of the AcroFlex vertebral endplate. Based on multi-directional flexibility testing, motion was preserved in axial rotation, but significantly diminished in the other bending modalities, particularly at the 12-month interval. This effect may be secondary to the limited surface area of device-vertebral endplate contact. Histomorphometric analysis of porous ingrowth coverage at the vertebral bone-metal interface was more favorable for total disc arthroplasty compared to historical reports of cementless femoral components. This project serves as the first comprehensive in vivo investigation into the AcroFlex disc prosthesis, and establishes an excellent research model in the evaluation of total disc replacement arthroplasty.

Animals↗

PubMed2002

An in vitro human cadaveric study investigating the biomechanical properties of the thoracic spine.

STUDY DESIGN: An in vitro human cadaveric study comparing the effects of anterior and posterior sequential destabilization conditions on thoracic functional unit mechanics was studied. OBJECTIVES: To investigate the biomechanical properties of the human thoracic spine. SUMMARY OF BACKGROUND DATA: Few studies have addressed the mechanical role of the costovertebral joints under torsion in the stability of the human thoracic spine. METHODS: Sixteen functional spinal units with intact costovertebral joints were obtained from six human cadavers and randomized into two groups based on destabilization procedures: Group 1, anterior to posterior sequential resection; and Group 2, posterior to anterior sequential destabilization. Biomechanical testing was performed after each destabilization procedure, and the range of motion under maximum load was calculated. RESULTS: Group 1: Under flexion-extension, lateral bending, and axial rotation loading, discectomy increased the range of motion by 193%, 74%, and 111%, respectively. Moreover, subsequent right rib head resection further increased the range of motion by 81%, 84%, and 72%, respectively. Group 2: Under all loading conditions laminectomy + medial facetectomy resulted in a 22-30% increase in range of motion. Subsequent total facetectomy led to an additional 15-28% increase in range of motion. CONCLUSION: The rib head joints serve as stabilizing structures to the human thoracic spine in the sagittal, coronal, and transverse planes. In anterior scoliosis surgery additional rib head resection after discectomy may achieve greater curve and rib hump correction. The lateral portion of the facet joints plays an important role in providing spinal stability and should be preserved to minimize postoperative kyphotic deformity and segmental instability when performing decompressive wide laminectomy.

Aged↗

PubMed2002

Microradiographic and histopathologic findings in a human cage explant after two-level corpectomy: a case report.

STUDY DESIGN: A case involving microradiographic and histopathologic analysis of an explanted human corpectomy mesh cage is reported. OBJECTIVE: To describe the clinical circumstance, the radiographic appearance, and the histopathologic assessment of a titanium mesh device explanted from a two-level corpectomy. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, no published microradiographic or histopathologic reports have described a retrieved human corpectomy cage. METHODS: The explanted device was stained using Osteochrome Villanueva bone stain and underwent routine decalcified histologic processing and embedding in polymethylmethacrylate. Midsagittal sections were prepared and polished to 100 microm for histologic and microradiographic analysis. RESULTS: Microscopic analysis demonstrated normal-appearing lamellar and woven trabecular bone in close contact with the titanium implant interface. Further analysis of serial sections indicated that, on the average, 35% (range, 30-40%) of the inner device region contained trabecular bone. CONCLUSION: Osteosynthesis and bone remodeling can occur within titanium corpectomy cages. METHODS: This study involved one titanium mesh device (Harms cage), 20 mm in diameter and 45 mm long, explanted from a two-level corpectomy clinical case. This device was retrieved, processed, and analyzed after informed patient consent and approval from the authors' institutional review board.

Adult↗

PubMed2002

Anterior BAK instrumentation and fusion: complete versus partial discectomy.

Beginning in January 1994, a prospective, clinical study was done comparing the effectiveness of complete anterior (Group 1) versus partial reamed channel discectomies (Group 2) in 100 consecutive patients who had anterior BAK instrumentation and fusion using autogenous iliac crest bone graft. At 2 or more years of followup, all patients in Group 1 who had complete operative disc removal achieved solid arthrodesis. There were no revision surgeries. However, in Group 2, there were seven patients who had a pseudarthrosis and an additional patient with early postoperative cage displacement, which resulted in eight patients in Group 2 requiring revision surgery. The differences in operative preparation of the disc space for BAK instrumentation surgery resulting in complications proved to be significant. The use of interbody titanium cages dramatically increases the biomechanical efficacy of anterior fusions. Original proponents of cages advocated removing a cylindrical channel of disc material using a drill. A prospective review of 100 patients who had complete versus partial discectomy revealed 14% of patients in Group 2 eventually had a pseudarthrosis develop.

Adult↗

PubMed2002

The use of interbody cage devices for spinal deformity: a biomechanical perspective.

Spinal instrumentation has revolutionized the treatment of spinal deformities and offers a plethora of techniques and designs to surgically treat deformity conditions. The authors address the biomechanical properties afforded by various posterior and anterior spinal instrumentation mechanisms, with and without intervertebral reconstruction, and the principles associated with optimal reconstruction techniques. The integration of multiple strategies can improve anterior and posterior construct stiffness in the treatment of spinal deformities. Structural interbody support probably is the best method to minimize longitudinal rod and screw-bone interface strain. Moreover, anterior load-bearing structural grafts and interbody devices have been shown to increase construct stiffness, decrease the incidence posterior implant failure, permit the use of smaller diameter longitudinal rods, and may enhance the rate of successful spinal arthrodesis. From a biomechanical standpoint, treatment of medium to high-grade spondylolisthesis with stand-alone interbody or transvertebral cages, in the absence of supplemental posterior fixation, is contraindicated. Collectively, the included studies reinforce the principles of load sharing between the anterior and posterior spinal columns and affirm the biomechanical dominance of anterior column support in circumferential spinal arthrodesis.

Biomechanical Phenomena↗

PubMedDate not supplied

Basic scientific considerations in total disc arthroplasty.

BACKGROUND CONTEXT: Total disc arthroplasty serves as the next frontier in the surgical management of intervertebral discogenic pathology. PURPOSE: As we move from an era of interbody spinal arthrodesis to one in which segmental motion is preserved, this promising new technology offers increasing clinical and research challenges in the areas of spinal kinematics, histologic osseointegration at the prosthetic-bone interface and the effects of particulate wear debris. STUDY DESIGN: The primary focus of this paper is to provide a methodologic basis to investigate the spinal kinematics, histologic osseointegration and particulate wear debris after total disc arthroplasty by using in vitro and in vivo models. METHODS: Part I: Using an in vitro cadaveric model, multidirectional flexibility testing evaluated the functional unit kinematics under the following L4-L5 reconstruction conditions: 1) intact spine, 2) Charite disc prosthesis, 3) BAK cages, 4) BAK cages+ISOLA pedicle screw or rod fixation (anteroposterior). Part II: A total of 27 mature baboons (n=27, Papio cynocephalus) underwent L5-L6 total disk replacement procedures to investigate the biomechanical, histochemical and biologic ingrowth characteristics of two different lumbar disc prostheses (AcroFlex and Charite) for total disc arthroplasty. Functional spinal unit fusion status was assessed by using radiographic analysis, biomechanical testing, undecalcified histopathologic and histomorphometric analyses. Part III: Using a total of 50 New Zealand white rabbits, this investigation served to quantify the neural and systemic tissue histopathologic response, after epidural application of four different types of spinal instrumentation particulate wear debris: 1) sham (control) (n=10), 2) stainless steel 316LVM (n=10), 3) titanium alloy Ti-6AL-4V (n=10), 4) cobalt chrome alloy (n=10) and 5) ultrahigh molecular weight polyethylene (UHMWPE) (n=10). RESULTS: In vitro multidirectional flexibility testing demonstrates the operative and adjacent level motion-preserving properties of total disc arthroplasty versus interbody arthrodesis cages and pedicle screw spinal instrumentation. To this end, disc replacement preserves the normal centrode or locus of intervertebral rotation at the operative and adjacent intervertebral spinal levels compared with conventional stabilization implants. On the basis of nonhuman primate modeling in the current studies, porous titanium interface surfaces afforded the greatest percentage of trabecular ingrowth at the prosthesis-end plate interface. In vivo segmental motion under multidirectional testing was preserved with the Charite device and slightly diminished with the AcroFlex implants. The porous ingrowth coverage at the bone-metal interface was more favorable for total disk replacement (range, 40% to 50%) compared with that reported for cementless total joint components in the appendicular skeleton (range, 10% to 30%). Direct epidural application of spinal instrumentation particulate wear debris elicits a chronic histiocytic reaction localized primarily within the epidural fibrous layers. Moreover, particles have the capacity to diffuse intrathecally, eliciting a macrophage and cytokine response within the epidural tissues, cerebrospinal fluid and spinal cord itself. Overall, on the basis of the postoperative time periods evaluated, no evidence was observed of an acute neural or systemic histopathologic response to the materials included in the current project. CONCLUSION: The implementation of dynamic spinal stabilization systems for fusionless correction of spinal deformity, dynamic posterior stabilization and total disc arthroplasty necessitates improved understanding with regard to spinal kinematics, patterns and mechanisms of histologic osseointegration and the neurohistopathologic response to particulate wear debris. Collectively, the current studies provide a methodologic basis to comprehensively evaluate these three areas.

Animals↗

PubMedDate not supplied

Prospective randomized study of the Charite artificial disc: data from two investigational centers.

BACKGROUND CONTEXT: For decades there has been a desire to restore motion of a painful degenerated spinal segment. Artificial discs have been used in Europe for almost 20 years. In the few reports available in the literature, the results have been promising. However, there have been no prospective randomized studies comparing artificial discs with spinal fusion. PURPOSE: The purpose of this study was to determine if patients with symptomatic degenerative disc disease treated with Charite artificial disc (DePuy Spine, Raynham, MA) arthroplasty would show significant improvement in functional outcome measures and to compare these results to fusion. STUDY DESIGN/SETTING: This was a prospective randomized clinical trial comparing total disc replacement with anterior lumbar interbody fusion using cages. The data reported were collected from two spine specialty centers participating in a Food and Drug Administration regulated trial. METHODS: A consecutive series of 144 patients were randomized using a 2:1 ratio of Charite versus BAK (Zimmer Spine, Minneapolis, MN). All patients were being treated for single-level discogenic pain confirmed by plain radiography, magnetic resonance imaging and provocative discography. Data were collected at designated follow-up periods for up to 24 months. RESULTS: The mean age was 40.1 years (range, 21 to 56 years). Forty-four cases had BAK anterior interbody fusion, and 100 cases were randomized to Charite disc replacement. The mean operating time was 76.2 minutes (range, 54 to 137 minutes) for the Charite cases. The mean estimated blood loss was 196.2 cc (range, 50 to 1,800 cc). Most patients were discharged in 1 to 2 days with a soft corset and returned to normal activities within 3 weeks if they underwent the disc replacement. The mean Oswestry Disability Index score for the BAK group was 69.6+/-12.8 preoperatively and 27.5+/-26.4 at 24-month follow-up (p<.001) The corresponding mean Oswestry score for the Charite disc patients was 70.9 preoperatively and 30.0 at 24-month follow-up (p<.001). CONCLUSIONS: In this prospective randomized study, both surgical groups improved significantly. Complications of total disc replacement were similar to those encountered with anterior lumbar interbody fusion. Total disc replacement appears to be a viable alternative to fusion for the treatment of single-level symptomatic disc degeneration unresponsive to nonoperative management.

Adult↗

PubMedDate not supplied

Osseointegration of autograft versus osteogenic protein-1 in posterolateral spinal arthrodesis: emphasis on the comparative mechanisms of bone induction.

BACKGROUND CONTEXT: Recent studies have documented increased fusion success afforded by bone morphogenetic proteins versus autogenous graft for posterolateral spinal arthrodesis. PURPOSE: The current study was designed to investigate the time-course maturation processes of lumbar posterolateral arthrodeses performed with Osteogenic Protein-1 (Stryker Biotech, Inc., Hopkinton, MA, USA) (rhOP-1) versus "gold standard" autograft. STUDY DESIGN: The primary focus of this study was to compare the histologic mechanisms of posterolateral osseointegration produced by "hot topic" growth factors. METHODS: A total of 36 coonhounds were equally divided into one of four postoperative time periods of 4, 8, 12 and 24 weeks (nine animals per period). Posterolateral arthrodesis treatments included 1) autograft alone, 2) autograft plus rhOP-1, or 3) rhOP-1 alone. The treatments and animals were divided such that a value of n=6 was obtained for each treatment group per time period and no one animal received the same treatment at both operative sites. Functional spinal unit (FSU) fusion status was assessed using radiographic analysis, biomechanical testing and undecalcified histopathologic and histomorphometric analyses. RESULTS: Radiographic differences in fusion maturation between the treatment groups were evident as early as the 4-week time interval and continued through the 24-week time period. The Osteogenic Protein-1 treatments demonstrated an accelerated rate of radiographic fusion by 4 weeks, which plateaued after the 8-week time period (22% autograft, 88% autograft/rhOP-1 and 66% rhOP-1). In contradistinction, the so-called "gold standard" autograft alone treatments reached a maximum of 50% fusion by the 6-month interval. Biomechanical testing of the FSUs indicated lower flexion-extension and axial rotation range of motion levels for both rhOP-1 treatments versus autograft alone at the 8- and 12-week time periods, respectively (p<.05). Histomorphometric analysis yielded no difference in the posterolateral trabecular bone area (mm(2)) between the three treatments (p>.05), and histopathology indicated no significant histopathologic changes. The most distinctive finding in this study deals with the mechanisms of posterolateral ossification. Based on plain and polarized light microscopy, bone induction and development for the rhOP-1 treatments, with and without autograft, was the result of intramembranous ossification, whereas the process of osseointegration for autograft alone was endochondral bone formation. By the 24-week interval, no discernable differences in trabecular histomorphology were evident based on the different mechanisms of ossification. CONCLUSIONS: This serves as the first study to document the mechanisms of bone induction and fusion maturation between posterolateral arthrodeses treated with autograft versus rhOP-1. The histological data served to corroborate the radiographic and biomechanical findings, because the rhOP-1 treatments consistently demonstrated increased fusion rates and lower range of motion levels compared with the autograft group, particularly at the 8-week postoperative time period. The improvements in these fusion criteria for Osteogenic Protein-1 versus autograft were considered secondary to the differing mechanisms of bone induction. When implanted for posterolateral arthrodesis, rhOP-1 induces an intramembranous healing response, obviating the need for the cartilage intermediate phases found in endochondral bone development. The mechanism of increased speed and incidence of fusion using growth factors (rhOP-1) is delineated by this comprehensive study of preferential intramembranous ossification.

Animals↗

PubMedDate not supplied

The effect of spinal instrumentation particulate wear debris. an in vivo rabbit model and applied clinical study of retrieved instrumentation cases.

STUDY DESIGN: The current study was undertaken to determine if the presence of spinal instrumentation wear particulate debris deleteriously influences early osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass. OBJECTIVES: Using an in vivo animal model, the first phase (basic science) of this study was to evaluate the effect(s) of titanium wear particulate on a posterolateral spinal arthrodesis based on serological, histological and immunocytochemical analyses. The second phase (clinical) was to perform the same analysis of soft tissue surrounding spinal instrumentation in 12 symptomatic clinical patients. SUMMARY OF BACKGROUND DATA: The effect of unintended wear particulate resulting from micromotion between the interconnection mechanisms in spinal instrumentation remains a clinical concern. METHODS: Thirty-four New Zealand White rabbits were randomized into two groups based on postoperative time periods of 2 months (Group 1, n=14) and 4 months (Group II, n=20). Group I underwent a posterolateral arthrodesis (PLF) at L5-L6 using tricortical iliac autograft or tricortical iliac autograft plus titanium particulate. Group 2 all received iliac autograft at the initial surgery and were reoperated on after 8 weeks and treated with PLF exposure alone or titanium particulate. Postoperative analysis included serological quantification of systemic cytokines. Postmortem microradiographic, immunocytochemical and histopathological assessment of the intertransverse fusion mass quantified the extent of osteolysis, local proinflammatory cytokines, osteoclasts and inflammatory infiltrates. Clinical aspect of study: Over the last 2 years, 12 patients more than 0.4 years after spinal instrumentation presented with painful paraspinal inflammation. At surgical exploration, the cultures were negative for infection and the surrounding soft tissue was examined for cytokine reactions. There was loosening of implants and osteolysis in the location of the wear debris in 8 of 12 patients. RESULTS: Basic science phase: serological analysis of systemic cytokines indicated no significant differences in cytokine levels (p>.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of local cytokines: TNF-alpha at the titanium-treated PLF sites at both time periods (p<.05). Osteoclast cell counts and regions of osteolytic resorption lacunae were higher in the titanium-treated versus autograft-alone groups (p<.05), and the extent of cellular apoptosis was markedly higher in the titanium-treated sites at both time intervals. Electron microscopy indicated definitive evidence of phagocytized titanium particles and foci of local, chronic inflammatory changes in the titanium-treated sites. Clinical aspect: Eleven of 12 clinical cases demonstrated elevated TNF-alpha levels and an increased osteoclastic response in the vicinity of wear debris caused by dry frictional wear particles of titanium or stainless steel. Osteolysis most commonly involved loose transverse connectors. Resection of the wear debris and surrounding fibroinflammatory glycocalyx resulted in resolution of clinical symptoms in all 12 cases. CONCLUSIONS: Titanium particulate debris introduced at the level of a spinal arthrodesis elicits a cytokine-mediated particulate-induced response favoring proinflammatory infiltrates, increased expression of intracellular TNF-alpha, increased osteoclastic activity and cellular apoptosis. This is the first basic scientific study and the first clinical study demonstrating associations of spinal instrumentation particulates wear debris and increased cytokines and increased osteoclastic activity. Osteolysis is the number one cause of failure of orthopedic implants in the appendicular skeleton. Spinal surgeons need to increase their awareness of this destructive process.

Acid Phosphatase↗

PubMedDate not supplied

Anterior thoracic scoliosis constructs: effect of rod diameter and intervertebral cages on multi-segmental construct stability.

BACKGROUND CONTEXT: Many studies have reported on the use of anterior instrumentation for thoracolumbar scoliosis and more recently thoracic scoliosis. However, the optimal construct design remains an issue of debate. PURPOSE: To optimize construct design and enhance implant survival until a successful spinal arthrodesis is achieved. STUDY DESIGN: This study evaluated the effect of rod diameter and intervertebral cages on construct stiffness and rod strain using a long-segment, anterior thoracic scoliosis model with varying levels of intervertebral reconstruction. METHODS: Sixteen fresh-frozen calf spine specimens (T1 to L1) were divided into two groups based on rod diameter reconstruction (4 mm and 5 mm). Testing included axial compression, anterior flexion, extension and lateral bending with variations in the number and level of intervertebral cage reconstructions: apical disc (one), end discs (two), apical and end discs (three), all seven levels (seven). Multisegmental construct stiffness and rod strain were determined and normalized to the intact specimen for analysis. RESULTS: The seven-level intervertebral cage construct showed significantly greater stiffness in axial compression for both the 4-mm (366% increased stiffness) and 5-mm (607% increased stiffness) rod groups (p<.001). The remaining constructs were not significantly different from each other (p>.05). In flexion, similar results were obtained for the 4-mm construct (p<.001) but not the 5-mm construct, because the reconstruction-alone, one-, two- and three-cage constructs were all significantly stiffer than the intact specimen (p<.05). Multisegmental construct stiffness under extension loading, as well as right and left lateral bending, also exhibited significant differences between the seven-level interbody cage reconstructions and the remaining constructs. Apical rod strain for both the 4-mm-rod and 5-mm-rod groups were significantly higher for the two cage constructs (a cage at either end but not the apex where the strain gauges were located) as compared with the other constructs (p<.05). These differences were more pronounced in the 4-mm-rod group. Similar results were obtained in anterior flexion, extension and lateral bending. CONCLUSIONS: Intervertebral cages at every level significantly improved construct stiffness compared with increasing rod diameter alone. Moreover, cages markedly decreased rod strain, and when structural interbody supports were not used, axial compression created the greatest rod strain.

Animals↗