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Paul C McAfee

Publications and source records attributed to Paul C McAfee.

18 recordsLinked to original sources
PubMed2004

Neurological complications of lumbar artificial disc replacement and comparison of clinical results with those related to lumbar arthrodesis in the literature: results of a multicenter, prospective, randomized investigational device exemption study of Charité intervertebral disc. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004.

OBJECT: Arthrodesis is the gold standard for surgical treatment of lumbar degenerative disc disease (DDD). Solid fusion, however, can cause stress and increased motion in the segments adjacent to the fused level. This may initiate and/or accelerate the adjacent-segment disease process. Artificial discs are designed to restore and maintain normal motion of the lumbar intervertebral segment. Restoring and maintaining normal motion of the segment reduces stresses and loads on adjacent level segments. A US Food and Drug Administration Investigational Device Exemptions multicentered study of the Charité artificial disc was completed. The control group consisted of individuals who underwent anterior lumbar interbody fusion involving BAK cages and iliac crest bone graft. This is the first report of Class I data in which a lumbar artificial disc is compared with lumbar fusion. METHODS: Of 304 individuals enrolled in the study, 205 were randomized to the Charité disc-treated group and 99 to the BAK fusion-treated (control) group. Neurological status was equivalent between the two groups at 6, 12, and 24 months postoperatively. The number of patients with major, minor, or other neurological complications was equivalent. There was a greater incidence of both major and minor complications in the BAK fusion group at 0 to 42 days postoperatively. Compared with data reported in the lumbar fusion literature, the Charité disc-treated patients had equivalent or better mean changes in visual analog scale and Oswestry Disability Index scores. CONCLUSIONS: The Charité artificial disc is safe and effective for the treatment of single-level lumbar DDD, resulting in no higher incidence of neurological complications compared with BAK-assisted fusion and leading to equivalent or better outcomes compared with those obtained in the control group and those reported in the lumbar fusion literature.

Biomechanical Phenomena↗
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

Biomaterial optimization in total disc arthroplasty.

STUDY: Knowledge gained through the clinical history of total joint replacement materials combined with the current promise of new biomaterials provides improved guidelines for biomaterial selection in total disc arthroplasty. OBJECTIVES: The following will detail: 1) current biomaterials technology; 2) how current designs of total disc arthroplasty seek to optimize implant performance through judicious biomaterial selection; and 3) what technical obstacles and clinical concerns remain. METHODS: Metals and polymers remain the central material components of state-of-the-art total joint arthroplasties. Polymers provide low friction surfaces for articulating bearings and some degree of shock absorption. Metals provide appropriate material properties such as high strength, ductility, fracture toughness, hardness, corrosion resistance, formability, and biocompatibility necessary for use in load-bearing roles required total disc replacement. There are three principal metal alloys used in orthopaedics and particularly in total joint replacement: 1) titanium based alloys; 2) cobalt based alloys; and 3) stainless steel alloys. Alloy specific differences in strength, ductility, and hardness generally determine which of these three alloys is used for a particular application or implant component. RESULTS: Current designs. Two examples of current lumbar (Charitè and Prodisc) and cervical (Bryan and Prestige) disc replacements are compared. The similarities and differences in the biomaterials used for each demonstrate prevailing consensus and some idea of how to best optimize implant performance through biomaterial selection. CONCLUSION: The primary factors governing total disc arthroplasty biomaterials are similar to those of all total joint arthroplasties: generation of wear debris is the primary source of implant degradation, and the subsequent tissue reaction to such debris is the primary factor limiting the longevity of joint replacement prostheses. Particulate debris generated by wear, fretting, or fragmentation induces the formation of an inflammatory reaction, which at a certain point promotes a foreign-body granulation tissue response that has the ability to invade the bone-implant interface. This commonly results in progressive, local bone loss that threatens the fixation of both cemented and cementless devices alike. All metal alloy implants corrode in vivo. When severe, the degradative process may reduce structural integrity of the implant, and the release of corrosion products is potentially toxic to the host. The corrosion resistance of implant alloys is primarily due to the formation of passive oxide films to prevent significant electrochemical dissolution from taking place. The result of this knowledge is a consensus of opinion as to which materials are best suited for use in current total disc arthroplasty designs, where most total disc replacement designs incorporate cobalt-chromium-molybdenum alloy endplates articulating internally on a relatively soft polymeric core and externally coated with titanium or titanium alloy for enhanced bone fixation.

Alloys↗
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

Cervical disc replacement-porous coated motion prosthesis: a comparative biomechanical analysis showing the key role of the posterior longitudinal ligament.

STUDY DESIGN: Benchtop cadaveric biomechanical comparative testing and caprine animal model in vivo implantation. OBJECTIVE: To evaluate the role of the posterior longitudinal ligament in cervical arthroplasty and to understand the relative contribution of this ligament in nonfusion applications. SUMMARY OF BACKGROUND DATA: Rauschning refers to the posterior longitudinal ligament as "The Kleenex Ligament" due to its apparent anatomic insignificance. White and Panjabi found the posterior longitudinal ligament ranked only fourth in importance in tensile load-to-failure biomechanical testing. In the postoperative situation following anterior cervical diskectomy fusion, posterior longitudinal ligament integrity is overlooked by physicians because the entire disc space usually fuses into a homogeneous block of bone. PURPOSE: This biomechanical study was undertaken to determine the relative importance of the posterior longitudinal ligament following two different degrees of anterior decompression, anterior disc replacement, and anterior arthrodesis procedures. METHODS: A total of seven fresh frozen human cadaveric cervical spines (C3-C7) (mean age 68 +/- 19 years) were used for biomechanical testing. Each vertebra was equipped with three non-colinear light emitting diodes designed for detection by an optoelectronic motion measurement system (3020 Optotract System). To determine the multidirectional flexibility, six pure moments (flexion, extension, right + left lateral bending, right + left axial rotation) and axial compression were applied using a servohydraulic 858 Bionix testing device configured with a six-degree-of-freedom spine simulator. Range of motion was defined as the peak displacement from the initial neutral position to the maximum load, whereas the neutral zone represents the motion from the initial neutral position to the unloaded position at the beginning of the third cycle. Seven groups of (N = 7 each) constructs at C5-C6 were: 1) intact "native" C5-C6 level; 2) anterior diskectomy (posterior longitudinal ligament intact); 3) a Low Profile Porous Coated Motion cervical disc replacement; 4) posterior longitudinal ligament resected; 5) Porous Coated Motion cervical disc replacement fixed with anterior flanges and screws; 6) tricortical structural allograft; and 7) an anterior cervical translational plate + allograft. The caprine model was evaluated for suitability as an animal model with 12 goats undergoing C3-C4 anterior cervical Porous Coated Motion disc replacement. RESULTS: Group 2 (anterior diskectomy alone) was significantly more stable than Group 4 (anterior diskectomy + posterior longitudinal ligament resection) in flexion-extension, 18.7 +/- 4.76 degrees versus 24.8 +/- 4.42 degrees (P < 0.05) and in lateral bending, 5.9 +/- 1.79 degrees versus 10.7 +/- 2.8 degrees (P < 0.05). The comparison for the two conditions for axial rotation, 10.4 +/- 13.9 degrees versus 13.9 +/- 2.7 degrees, and axial compression, 1.19 +/-.98 degrees versus 1.52 +/- 1.14 degrees, showed the same trend. Twelve goats undergoing porous coated motion cervical disc replacement had no evidence of prosthesis loosening, neurologic complications, or experienced inflammatory reactions from particulate wear debris after 6 months of implantation. DISCUSSION: This study confirms the pivotal role of the posterior longitudinal ligament in postsurgical stability of the cervical spine following anterior diskectomy. This is because the lateral anulus, uncovertebral ligaments, and lateral capsular ligaments are stretched and plastically deformed in the surgical distraction process of restoring the disc space height following anterior surgical decompression. There should be a separate determination of the range of motion of cervical disc replacements depending of the integrity and the amount of the posterior longitudinal ligament that has been resected. CLINICAL RELEVANCE: There are two basic types of total knee replacements, posterior cruciate ligament-preserving and posterior cruciate ligament-sacrificing designs. In the cervical spine, an analogous situation exists biomechanically depending on whether the posterior longitudinal ligament needs to be removed in its entirety as part of the spinal cord decompression part of the procedure--it may be helpful to conceptually differentiate between posterior longitudinal ligament-preserving and posterior longitudinal ligament-sacrificing total cervical disc replacements.

Aged↗
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

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

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↗
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↗