PubMed Health⌕ Search

Biomedical subjects

Bryan W Cunningham

Publications and source records attributed to Bryan W Cunningham.

At least 19 recordsLinked to original sources
PubMed2005

Frontal impact causes ligamentous cervical spine injury.

STUDY DESIGN: Whole cervical spine model with muscle force replication was subjected to simulated frontal impacts of increasing severity, and resulting injuries were evaluated via flexibility testing. OBJECTIVES: To identify and quantify cervical spine soft tissue injury and the injury threshold acceleration due to frontal impact. SUMMARY OF BACKGROUND DATA: Cervical spine instability may result from automotive collisions. No previous studies have quantified soft tissue injuries due to frontal impact. METHODS: Six human cervical specimens (occiput-T1) with muscle force replication were subjected to frontal impacts of 4, 6, 8, and 10 g. Before frontal impact, baseline flexibility data were collected following a 2 g simulation. Flexibility parameters of total (flexion plus extension) neutral zone (NZ), flexion NZ, total range of motion (ROM), and flexion ROM were obtained following each impact and compared with baseline flexibility. Injury was a significant increase (P < 0.05) in intervertebral flexibility due to frontal impact over baseline. Injury threshold was the lowest T1 peak acceleration that caused injury. RESULTS: The injury threshold acceleration was 8 g, as determined by significant increases of 12.6 to 51.4% over the baseline flexibility, in the C4-C5 total NZ, and the C6-C7 total NZ, flexion NZ, total ROM, and flexion ROM. Following 10 g, significant increases in flexibility parameters were observed at C2-C3, C3-C4, C4-C5, C6-C7, and C7-T1. CONCLUSIONS: Middle (C2-C3 to C4-C5) and lower (C6-C7 and C7-T1) cervical spine were at risk for injury during frontal impacts, for the experimental conditions studied.

Acceleration↗
PubMed2005

Adjacent level intradiscal pressure and segmental kinematics following a cervical total disc arthroplasty: an in vitro human cadaveric model.

STUDY DESIGN: In vitro investigation of cervical adjacent level intradiscal pressures (IDPs) following a total disc replacement arthroplasty. OBJECTIVES: The current in vitro study was undertaken to compare adjacent level IDPs and operative level kinematics following a cervical arthroplasty versus an arthrodesis procedure. SUMMARY OF BACKGROUND DATA: Clinical data indicate the incidence of symptomatic transition syndrome to be as high as 3% annually following a cervical interbody arthrodesis. Recent developments in the motion preservation technology should, in theory, minimize transition syndrome at the adjacent levels. METHODS: A total of 10 human cadaveric cervical spines were used in this investigation. Following intact analysis, all specimens were sequentially reconstructed at C5-C6 with 1) total disc replacement (TDR), 2) allograft dowel, and 3) allograft dowel + anterior cervical plate. Testing was performed in displacement control under axial rotation, flexion/extension, and lateral bending loading modes. IDPs were recorded at C4-C5 and C6-C7 whereas peak range of motion (ROM) and NZ were monitored at C5-C6 level. RESULTS: Similar IDPs were recorded between the intact condition and a TDR reconstruction at both adjacent levels under all loading modes (P > 0.05). However, the C4-C5 IDP values produced under flexion/extension testing for both arthrodesis treatments were significantly higher than the means obtained for the intact and disc replacement groups (P < 0.05). Similar intergroup differences were observed at the C6-C7 level; however, statistical significance was achieved during all three loading methods (P < 0.05). C5-C6 ROM analysis indicated a significantly lower ROM for both arthrodesis constructs compared with intact and TDR groups during flexion/extension testing (P < 0.05). No differences were recorded between the intact and the total disc replacement group under any loading conditions (P > 0.05). CONCLUSION: This is a first study to document that a cervical disc replacement arthroplasty procedure maintains adjacent level IDPs and reconstruction level kinematics near the preoperative values. Consequently, total disc replacement may provide an alternative to conventional surgical management of cervical discogenic pathology decreasing the incidence of symptomatic transition syndrome.

Arthroplasty, Replacement↗
PubMed2005

The indications for interbody fusion cages in the treatment of spondylolisthesis: analysis of 120 cases.

STUDY DESIGN: This study retrospectively examines outcomes of unilateral transforaminal lumbar interbody fusion (TLIF) with posterior fixation using anterior carbon fiber cages and 360 degrees fusion in spondylolisthesis. OBJECTIVES: The goals were to examine the outcomes and perioperative complications of using anterior column support in the treatment of various types of spondylolisthesis. SUMMARY OF BACKGROUND DATA: In 2000, Brantigan et al reported the Brantigan interbody fusion cage used as a posterior lumbar interbody fusion in the US IDE clinical trial. This is the largest series to date of TLIF cages specifically used in the treatment of spondylolisthesis. METHODS: A comprehensive long-term follow-up study was conducted to evaluate the fusion success and morbidity following implantation with an anterior column support and posterior pedicle screw fixation. The 120 patients with spondylolisthesis were comprised by 11 cases, dysplastic; 58 cases, degenerative; and 51 cases, isthmic-acquired spondylolisthesis. Anterior column support was either a rectangular carbon fiber/PEEK device or a cylindrical carbon fiber/PEEK device. Twenty-eight cases (23%) were revisions. RESULTS: There were no pseudarthrosis, instrumentation failures, or significant subsidence at the TLIF level. The disc space height and foraminal height were restored as part of the surgical procedure. Disc height, as measured from the posterior edge of the superior vertebral body, increased from a mean of 5.6 mm before surgery to a mean of 9.3 mm after surgery. Although reduction of the slip was not the primary goal during the surgical procedure for the 120 cases with spondylolisthesis (isthmic-acquired = 51, degenerative = 58, and dysplastic = 11), the 23% slip reduction achieved at surgery was maintained at follow-up. Mean operative time was 143 +/- 33 minutes (range, 70-255 minutes) for all cases. Mean blood loss was 724 +/- 431 mL (range, 300-2,500 mL). There were seven incidental durotomies and three infections. One patient with Grade I degenerative spondylolisthesis required revision of the carbon fiber cage for posterior migration secondary to a traumatic event 3 months after surgery. Fusion success was 98% using the criteriaof Lenke for the posterior fusion and Brantigan and Steffee for the TLIF graft incorporation. CONCLUSIONS: Interbody cages in spondylolisthesis are useful to increase neuroforaminal height, to facilitate reduction, and to improve the chances of achieving a successful 360 degrees fusion.

Adolescent↗
PubMed2005

Multidirectional flexibility analysis of cervical artificial disc reconstruction: in vitro human cadaveric spine model.

OBJECT: This in vitro experimental study was conducted to investigate the initial biomechanical effect of artificial intervertebral disc replacement in the cervical spine. The multidirectional flexibility of replaced and adjacent spinal segments were analyzed using a cadaveric cervical spine model. METHODS: The following three cervical reconstructions were sequentially performed at the C5-6 level after anterior discectomy in seven human cadaveric occipitocervical spines: anterior artificial disc replacement with a bioactive three-dimensional (3D) fabric disc (FD); anterior iliac bone graft; and anterior plate fixation with iliac bone graft. Six unconstrained pure moments were applied with a 6-df spine simulator, and 3D segmental motions at the operative and adjacent segments were measured with an optoelectronic motion measurement system. The 3D FD group demonstrated statistically equivalent ranges of motion (ROMs) when compared with intact values in axial rotation and lateral bending. The 45% increase in flexion-extension ROM was demonstrated in 3D FD group; however, neutral zone analysis did not reach statistical significance between the intact spine and 3D FD. The anterior iliac bone graft and iliac bone graft reconstructions demonstrated statistically lower ROMs when compared with 3D FD in all loading modes (p < 0.05). The adjacent-level ROMs of the 3D FD group demonstrated nearly physiological characteristics at upper and lower adjacent levels. Excellent stability at the interface was maintained during the whole testing without any device displacement and dislodgment. CONCLUSIONS: The stand-alone cervical 3D FD demonstrated nearly physiological biomechanical characteristics at both operative and adjacent spinal segments in vitro, indicating an excellent clinical potential for cervical artificial disc replacement.

Bone Plates↗
PubMed2004

Soft tissue injury threshold during simulated whiplash: a biomechanical investigation.

STUDY DESIGN: A newly developed biofidelic whole cervical spine (WCS) model with muscle force replication (MFR) was subjected to whiplash simulations of varying intensity, and the resulting injuries were evaluated through changes in the intervertebral flexibility. OBJECTIVES: To identify the soft tissue injury threshold based on the peak T1 horizontal acceleration and the association between acceleration magnitude and injury severity resulting from simulated whiplash using the WCS + MFR model. SUMMARY OF BACKGROUND DATA: Whiplash has been simulated using mathematical models, whole cadavers, volunteers, and WCSs. The measurement of injury (difference between prewhiplash and postwhiplash flexibilities) is possible only using the WCS model. METHODS: Six WCS + MFR specimens (C0-T1) were incrementally rear-impacted at nominal T1 horizontal maximum accelerations of 3.5, 5, 6.5, and 8 g, and the changes in the intervertebral flexibility parameters of neutral zone and range of motion were determined. The injury threshold acceleration was the lowest T1 horizontal peak acceleration that caused a significant increase in the intervertebral flexibility. RESULTS: The first significant increase (P <0.01) of 39.8% occurred in the C5-C6 extension neutral zone following the 5 g acceleration. At higher accelerations, the injuries spread among the surrounding levels (C4-C5 to C7-T1). CONCLUSIONS: A rear-end collision is most likely to injure the lower cervical spine by intervertebral hyperextension at a peak T1 horizontal acceleration of 5 g and above. These results may aid in the design of injury prevention systems and more precise diagnoses of whiplash injuries.

Aged↗
PubMed2004

Endoscopic instrumented posterolateral lumbar fusion with Healos and recombinant human growth/differentiation factor-5.

OBJECTIVE: The goal of this study was to use a minimally invasive endoscopic surgical technique in a sheep model to evaluate the efficacy of an osteoinductive growth factor, recombinant human growth/differentiation factor-5 (also designated MP52), and an osteoconductive matrix formulation (Healos; DePuy AcroMed, Inc., Mountain View, CA) for inducing and facilitating bone formation. METHODS: Twelve mature sheep underwent bilateral posterolateral lumbar fusion and pedicle screw fixation via a posterior endoscopic approach. Each sheep received two different types of graft material, autogenous iliac crest bone, or a bone graft substitute (MP52 with Healos), inserted into the right and left sides of the spine in an alternating fashion. Groups of four sheep were killed at 2, 4, and 6 months postoperatively for manual, radiographic, and histological evaluation. RESULTS: No neurological impairments, infections, or other complications were observed. After 2 months, partial fusion on both sides was observed, but radiographic evaluation showed greater bone growth on the side that received the bone graft substitute. Solid posterolateral fusion was observed in both autograft and bone graft substitute sites at 4 and 6 months, and autograft and Healos MP52 fusion sites were essentially the same at histological examination. There was no abnormal overgrowth of new bone from either of these two materials. CONCLUSION: Endoscopic posterolateral lumbar arthrodesis and instrumentation is feasible, safe, and effective in a sheep model. Healos is a useful bonding agent that mimics natural bone in posterolateral intertransverse fusion sites. Combined with MP52, it produced fusion comparable to that of autogenous bone graft. Minimally invasive techniques and bone graft substitutes could eliminate morbidity and increase the likelihood of successful fusion.

Animals↗
PubMed2003

General principles of total disc replacement arthroplasty: seventeen cases in a nonhuman primate model.

STUDY DESIGN: To investigate the biomechanical, histochemical, and biologic ingrowth characteristics of two different lumbar disc prostheses-AcroFlex (DePuy-AcroMed) and the SB Charitè (DePuy-AcroMed)-for total disc replacement arthroplasty. METHODS: A total of 17 mature baboons (n = 17, Papio cynocephalus) underwent L5-L6 total disc replacement procedures. The AcroFlex device (n = 10 levels) consisted of sintered titanium beaded ingrowth surfaces, bound together by a hexene-based polyolefin rubber core. The SB Charitè (n = 7 levels) device prosthetic vertebral end plates were cobalt chrome, covered by two layers of thin titanium with an electrochemically bonded hydroxyapatite coating and an ultra-high molecular weight polyethylene core. RESULTS: Following 6-month survival periods, the range of motion of the SB Charitè and intact nonoperative controls under axial compression, flexion-extension, and lateral bending showed no statistical difference (P > 0.05). However, both exhibited greater range of motion compared to the AcroFlex treatments (P < 0.05). Plain film radiographic analysis showed no lucencies or loosening of any metallic prosthetic vertebral endplate. Gross histopathologic analysis of the AcroFlex and SB Charité prosthesis demonstrated excellent ingrowth at the level of the implant-bone interface, without evidence of fibrous tissue or synovium. Histochemical assays showed no local or systemic accumulation of particulate wear debris (titanium, ultra-high molecular weight polyethylene, or cobalt chrome) nor cytokines (TNF-alpha, PGE2, IL-1, IL-2, or IL-6). Porous ingrowth calculations showed the mean ingrowth (linear apposition) ranging from 47.9% +/- 9.12 for the SB Charitè device and 54.59% +/- 13.24 for the AcroFlex device. CONCLUSIONS: The porous ingrowth, percentage pore ingrowth coverage at the bone-metal interface was more favorable for total disc replacement compared to that reported for cementless total joint components in the appendicular skeleton (range 10-30%). The reason for the improved degree of porous ingrowth in total disc replacement prostheses is probably due to ligamentotaxis causing sustained compression across the metal-bone interface. This project serves as the first comprehensive in vivo investigation comparing two different types of unconstrained disc prostheses with alternate in-growth surfaces and establishes an excellent research model in the evaluation of lumbar total disc replacement arthroplasty.

Animals↗
PubMed2003

Biomechanical evaluation of total disc replacement arthroplasty: an in vitro human cadaveric model.

STUDY DESIGN: This in vitro biomechanical study was undertaken to quantify the multidirectional intervertebral kinematics following total disc replacement arthroplasty compared to conventional stabilization techniques. OBJECTIVE: Using an in vitro human cadaveric model, the primary objective was to compare the multidirectional flexibility properties and map the center of intervertebral rotation of total disc arthroplasty versus conventional threaded fusion cages and cages augmented with transpedicular fixation for single-level spinal instrumentation. SUMMARY OF BACKGROUND DATA: The utilization of motion-preserving implants versus instrumentation systems, which stabilize the operative segments, necessitates improved understanding of their comparative biomechanical properties. METHODS: A total of eight human cadaveric lumbosacral spines (L2 to sacrum) were utilized in this investigation and biomechanically evaluated under the following L4-L5 reconstruction conditions: 1) intact spine; 2) SB Charitè disc prosthesis; 3) BAK cages; and 4) BAK cages + ISOLA pedicle screw/rod fixation (anteroposterior). The superior (L3-L4) and inferior (L5-S1) intervertebral levels remained uninstrumented to quantify adjacent level properties. Multidirectional flexibility included pure, unconstrained moments (+/-8 Nm) in axial rotation, flexion-extension, and lateral bending, with quantification of the operative and adjacent level range of motion and neutral zone, which were normalized to the intact spine condition. RESULTS: The SB Charitè prosthesis indicated an average percentage increase in axial rotation range of motion by 44% compared to the intact condition (P < 0.05), whereas the BAK and anteroposterior reconstructions decreased range of motion by 29% and 80%, respectively (P < 0.05). The SB Charitè was significantly different from BAK and combined anteroposterior reconstructions (P < 0.05). Flexion-extension indicated a minor increase in range of motion for the SB Charitè (3%) versus the intact disc (P > 0.05), whereas the BAK and anteroposterior stabilization groups resulted in significant decreases in range of motion (BAK = 57%, anteroposterior = 93%) (P < 0.05) when compared to the intact and SB Charitè conditions. Based on flexion-extension radiographs, the intervertebral centers of rotation were in the posterior one-third of the operative intervertebral disc only for the SB Charitè reconstruction and intact spine condition, with definitive evidence of physiologic intervertebral translation (intact 2.06 +/- 77 mm; SB III = 1.9 +/- 0.98 mm). CONCLUSIONS: Total disc arthroplasty serves as the next frontier in the surgical management of discogenic spinal pathology. The SB Charitè restored motion to the level of the intact segment in flexion-extension and lateral bending and increased motion in axial rotation. The anterior annular resection necessary for device implantation and unconstrained design of the prosthesis account for this change in rotation. The normal lumbar flexion-extension axis of rotation is an ellipse rather than a single point. Only disc replacement rather than pedicle instrumentation or BAK interbody instrumentation preserves the kinematic properties and normal mapping of segmental motion at the operative and adjacent intervertebral disc levels.

Arthroplasty, Replacement↗
PubMed2003

Experimental design of total disk replacement-experience with a prospective randomized study of the SB Charitè.

STUDY DESIGN: Prospective randomized clinical trial. OBJECTIVES: To determine if a prospective randomized study of patients with symptomatic degenerative disc disease treated with disc arthroplasty could be safely completed. METHODS: Sixty patients with one-level discogenic pain confirmed by plain radiography, magnetic resonance imaging, and provocative discography for degenerative disc disease were randomized comparing 1/3 BAK anterior interbody fusion and 2/3 anterior SB Charitè artificial disc replacement. RESULTS: 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 Charitè 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 cc (range 50-1800 cc). The length of hospital stay was a mean of 3.03 days (range 2 to 6 days). Oswestry Disability Index for the BAK control group was 45.9 +/- 10.4 before surgery and 23.5 +/- 17.2 at follow-up (P < 0.001). The corresponding ODI scores for the SB Charitè disc were 50.0 +/- 14.3 before surgery and 25.0 +/- 20.1 at a mean of 2 years' follow-up (P < 0.001). CONCLUSIONS: This is the first study that shows improvement of functional outcome measures in a prospective randomized design treating primarily mechanical back pain and achieving comparable successful results to lumbar spinal stenosis decompression.

Adult↗
PubMed2003

Analysis of porous ingrowth in intervertebral disc prostheses: a nonhuman primate model.

STUDY DESIGN: A study was conducted to investigate the biomechanical, histochemical, and biologic ingrowth characteristics of the most widely used total disc prosthesis, the hydroxyapatite-coated SB Charité prosthesis. OBJECTIVE: To compare the porous ingrowth, linear apposition, or bony ingrowth in total disc replacement with published reports of porous ingrowth prostheses in the appendicular skeleton. METHODS: Seven mature baboons (Papio cynocephalus) underwent L5-L6 total disc replacement through an anterior transperitoneal approach. The SB Charité prosthetic vertebral endplates (n = 14) were cobalt-chrome covered by two layers of thin titanium with a hydroxyapatite coating, which was electrochemically bonded to the implant surface. RESULTS: At 6 months after surgery, the range of motion exhibited by the SB Charité and the nonoperative control subjects under axial compression, flexion-extension, and lateral bending showed no statistical difference (P > 0.05). Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Gross histopathologic analysis of the hydroxyapatite-coated SB Charité prosthesis demonstrated excellent ingrowth at the level of the implant-bone interface, without evidence of fibrous tissue or synovium. Histochemical assays showed no accumulation of particulate wear debris (no titanium, ultrahigh molecular weight polyethylene, or cobalt-chrome) nor cytokines (tumor necrosis factor-alpha, prostaglandin E2, interleukin-1, -2, or -6). Total endplate area showed a mean ingrowth (volume fraction) of 47.9% +/- 9.12% and a total ingrowth range of 35.5% to 58.8%. CONCLUSIONS: The porous ingrowth (percentage of pore ingrowth coverage at the bone-metal interface) was more favorable for total disc replacement than for cementless total joint components in the appendicular skeleton (range, 10-30%). The reason for the improved degree of porous ingrowth in total disc replacement prostheses probably is that ligamentotaxis causes sustained compression across the metal-bone interface.

Animals↗
PubMed2003

Classification of heterotopic ossification (HO) in artificial disk replacement.

There is currently no structured classification system to quantitate heterotopic bone formation after artificial disk replacement procedures. The purpose of this work was to develop a method of classifying heterotopic bone formation that is reliable between investigators with different levels of training and easy to remember with only five gradations of severity. One hundred one radiographs of clinical patients and 17 microradiographs from nonhuman primates having undergone various types of disk replacement were classified by seven independent reviewers. The kappa statistics were calculated for interobserver variation between the seven participants with various levels of spinal training and the intraobserver error based on two assessments made at least 2 months apart. The interobserver reliability correlation coefficient for seven raters calculated using the intraclass kappa correlation coefficient and the Kish rho was r = 0.9683 (P < 0.0001). The intraobserver reliability based on readings at two time intervals at a minimum of 2 months apart was r = 0.8949 (P = 0.01). This classification of heterotopic ossification, periannular calcification, and ectopic bone formation associated with total disk arthroplasty proved to be highly reliable and reproducible.

Animals↗
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↗