Hypoglossal Nerve Palsy After Anterior Cervical Spine Surgery: A Case Report and Literature Review.

CASE: A 37-year-old man was found to have hypoglossal nerve palsy after undergoing anterior cervical spine surgery at C3-C5, an injury that would cause him severe disability and further complications. CONCLUSION: Knowledge of the hypoglossal nerve is crucial for cervical spine surgery even at lower levels (C4-C7), including variations in its course and potential displacement during the induction of anesthesia.

Periprosthetic UHMWPE Wear Debris Induces Inflammation, Vascularization, and Innervation After Total Disc Replacement in the Lumbar Spine.

BACKGROUND: The pathophysiology and mechanisms driving the generation of unintended pain after total disc replacement (TDR) remain unexplored. Ultrahigh-molecular-weight polyethylene (UHMWPE) wear debris from TDRs is known to induce inflammation, which may result in pain. QUESTIONS/PURPOSES: The purpose of this study was to determine whether (1) periprosthetic UHMWPE wear debris induces immune responses that lead to the production of tumor necrosis factor-α (TNFα) and interleukin (IL)-1ß, the vascularization factors, vascular endothelial growth factor (VEGF) and platelet-derived growth factor-bb (PDGFbb), and the innervation/pain factors, nerve growth factor (NGF) and substance P; (2) the number of macrophages is associated with the production of the aforementioned factors; (3) the wear debris-induced inflammatory pathogenesis involves an increase in vascularization and associated innervation. METHODS: Periprosthetic tissues from our collection of 11 patients with contemporary TDRs were evaluated using polarized light microscopy to quantify UHMWPE wear particles. The major reason for revision (mean implantation time of 3 years [range, 1-6 years]) was pain. For control subjects, biopsy samples from four patients with degenerative disc disease with severe pain and autopsy samples from three normal patients with no history of back pain were also investigated. Immunohistochemistry and histology were used to identify secretory factors, macrophages, and blood vessels. Immunostained serial sections were imaged at ×200 magnification and using MATLAB and NIH ImageJ, a threshold was determined for each factor and used to quantify positive staining normalized to tissue sectional area. The Mann-Whitney U test was used to compare results from different patient groups, whereas the Spearman Rho test was used to determine correlations. Significance was based on p < 0.05. RESULTS: The mean percent area of all six inflammatory, vascularization, and innervation factors was higher in TDR tissues when compared with normal disc tissues. Based on nonparametric data analysis, those factors showing the most significant increase included TNFα (5.17 ± 1.76 versus 0.05 ± 0.03, p = 0.02), VEGF (3.02 ± 1.01 versus 0.02 ± 0.002, p = 0.02), and substance P (4.15 ± 1.01 versus 0.08 ± 0.04, p = 0.02). The mean percent area for IL-1ß (2.41 ± 0.66 versus 0.13 ± 0.13, p = 0.01), VEGF (3.02 ± 1.01 versus 0.34 ± 0.29, p = 0.04), and substance P (4.15 ± 1.01 versus 1.05 ± 0.46, p = 0.01) was also higher in TDR tissues when compared with disc tissues from patients with painful degenerative disc disease. Five of the factors, TNFα, IL-1ß, VEGF, NGF, and substance P, strongly correlated with the number of wear particles, macrophages, and blood vessels. The most notable correlations included TNFα with wear particles (p < 0.001, ρ = 0.63), VEGF with macrophages (p = 0.001, ρ = 0.71), and NGF with blood vessels (p < 0.001, ρ = 0.70). Of particular significance, the expression of PDGFbb, NGF, and substance P was predominantly localized to blood vessels/nerve fibers. CONCLUSIONS: These findings indicate wear debris-induced inflammatory reactions can be linked to enhanced vascularization and associated innervation/pain factor production at periprosthetic sites around TDRs. Elucidating the pathogenesis of inflammatory particle disease will provide information needed to identify potential therapeutic targets and treatment strategies to mitigate pain and potentially avoid revision surgery. LEVEL OF EVIDENCE: Level III, therapeutic study.

UHMWPE wear debris and tissue reactions are reduced for contemporary designs of lumbar total disc replacements.

BACKGROUND: Lumbar total disc replacement (L-TDR) is a procedure used to relieve back pain and maintain mobility. Contemporary metal-on-polyethylene (MoP) L-TDRs were developed to address wear performance concerns about historical designs, but wear debris generation and periprosthetic tissue reactions for these newer implants have not been determined. QUESTIONS/PURPOSES: The purpose of this study was to determine (1) whether periprosthetic ultrahigh-molecular-weight polyethylene (UHMWPE) wear debris and biological responses were present in tissues from revised contemporary MoP L-TDRs that contain conventional cores fabricated from γ-inert-sterilized UHMWPE; (2) how fixed- versus mobile-bearing design affected UHMWPE wear particle number, shape, and size; and (3) how these wear particle characteristics compare with historical MoP L-TDRs that contain cores fabricated from γ-air-sterilized UHMWPE. METHODS: We evaluated periprosthetic tissues from 11 patients who received eight fixed-bearing ProDisc-L and four mobile-bearing CHARITÉ contemporary L-TDRs with a mean implantation time of 4.1 and 2.7 years, respectively. Histologic analysis of tissues was performed to assess biological responses and polarized light microscopy was used to quantify number and size/shape characteristics of UHMWPE wear particles from the fixed- and mobile-bearing devices. Comparisons were made to previously reported particle data for historical L-TDRs. RESULTS: Five of seven (71%) fixed-bearing and one of four mobile-bearing L-TDR patient tissues contained at least 4 particles/mm(2) wear with associated macrophage infiltration. Tissues with wear debris were highly vascularized, whereas those without debris were more necrotic. Given the samples available, the tissue around mobile-bearing L-TDR was observed to contain 87% more, 11% rounder, and 11% less-elongated wear debris compared with tissues around fixed-bearing devices; however, there were no significant differences. Compared with historical L-TDRs, UHMWPE particle number and circularity for contemporary L-TDRs were 99% less (p = 0.003) and 50% rounder (p = 0.003). CONCLUSIONS: In this preliminary study, short-term results suggest there was no significant influence of fixed- or mobile-bearing designs on wear particle characteristics of contemporary L-TDRs, but conventional UHMWPE has notably improved the wear resistance of these devices compared with historical UHMWPE.

Retrieval analysis of PEEK rods for posterior fusion and motion preservation.

INTRODUCTION: The purpose of this study was to analyze explanted PEEK rod spinal systems in the context of their clinical indications. We evaluated damage to the implant and histological changes in explanted periprosthetic tissues. METHODS: 12 patients implanted with 23 PEEK rods were revised between 2008 and 2012. PEEK rods were of the same design (CD Horizon Legacy, Medtronic, Memphis TN, USA). Retrieved components were assessed for surface damage mechanisms, including plastic deformation, scratching, burnishing, and fracture. Patient history and indications for PEEK rod implantation were obtained from analysis of the medical records. RESULTS: 11/12 PEEK rod systems were employed for fusion at one level, and motion preservation at the adjacent level. Surgical complications in the PEEK cohort included a small dural tear in one case that was immediately repaired. There were no cases of PEEK rod fracture or pedicle screw fracture. Retrieved PEEK rods exhibited scratching, as well as impressions from the set screws and pedicle screw saddles. PEEK debris was observed in two patient tissues, which were located adjacent to PEEK rods with evidence of scratching and burnishing. CONCLUSION: This study documents the surface changes and tissue reactions for retrieved PEEK rod stabilization systems. Permanent indentations by the set screws and pedicle screws were the most prevalent observations on the surface of explanted PEEK rods.

The Latest Lessons Learned from Retrieval Analyses of Ultra-High Molecular Weight Polyethylene, Metal-on-Metal, and Alternative Bearing Total Disc Replacements.

Knowledge regarding the in vivo performance and periposthetic tissue response of cervical and lumbar total disc replacements (TDRs) continues to expand. This review addresses the following four main questions: 1) What are the latest lessons learned from polyethylene in large joints and how are they relevant to current TDRs? 2) What are the latest lessons learned regarding adverse local tissue reactions from metal-on-metal, CoCr bearings in large joints and how are they relevant to current TDRs? 3) What advancements have been made in understanding the in vivo performance of alternative biomaterials, such as stainless steel and polycarbonate urethane, for TDRs in the past five years? 4) How has retrieval analysis of all these various artificial disc bearing technologies advanced the state of the art in preclinical testing of TDRs? The study of explanted artificial discs and their associated tissues can help inform bearing selection as well as the design of future generations of disc arthroplasty. Analyzing retrieved artificial discs is also essential for validating preclinical test methods.

Lumbar total disc replacement impingement sensitivity to disc height distraction, spinal sagittal orientation, implant position, and implant lordosis.

STUDY DESIGN: A 3-dimensional finite element model of 2 lumbar motion segments (L4-L5 and L5-S1) was used to evaluate the sensitivity of lumbar total disc replacement (TDR) impingement to disc height distraction, spinal sagittal orientation, implant position, and implant lordosis. The models were implanted with a mobile-bearing TDR and exposed to simulated sagittally balanced erect posture. OBJECTIVE: The objective of this study was to determine the sensitivity of TDR impingement to disc height distraction, implant lordotic angle, implant anterior-posterior position, and spinal orientation relative to the horizon. SUMMARY OF BACKGROUND DATA: TDR has the potential to replace fusion as the "gold standard" for treatment of painful degenerative disc disease. However, complications after TDR have been associated with device impingement and accelerated polyethylene wear. METHODS: A previously developed finite element model of the lumbar spine was altered to include implantation of a mobile-bearing TDR. A series of sensitivity analyses was performed to determine impingement risk. Specifically, spinal orientation, disc height distraction, footplate lordotic angle, and anterior-posterior position were evaluated. RESULTS: Generally, TDR tended to result in an increase in extension rotation and facet contact force during simulated erect posture when compared with the intact models. Impingement risk was sensitive to all of the tested parameters. CONCLUSION: The data from this study indicate that lumbar mobile-bearing TDR impingement is sensitive to disc height distraction, anterior-posterior position, implant lordosis, and spinal sagittal orientation. TDR impingement risk can be minimized by choosing an implant with an appropriate amount of lordosis, not overdistracting the disc space, and taking care not to place the implant too far anterior or posterior.

Biomechanical evaluation of a spherical lumbar interbody device at varying levels of subsidence.

BACKGROUND: Ulf Fernström implanted stainless steel ball bearings following discectomy, or for painful disc disease, and termed this procedure disc arthroplasty. Today, spherical interbody spacers are clinically available, but there is a paucity of associated biomechanical testing. The primary objective of the current study was to evaluate the biomechanics of a spherical interbody implant. It was hypothesized that implantation of a spherical interbody implant, with combined subsidence into the vertebral bodies, would result in similar ranges of motion (RoM) and facet contact forces (FCFs) when compared with an intact condition. A secondary objective of this study was to determine the effect of using a polyetheretherketone (PEEK) versus a cobalt chrome (CoCr) implant on vertebral body strains. We hypothesized that the material selection would have a negligible effect on vertebral body strains since both materials have elastic moduli substantially greater than the annulus. METHODS: A finite element model of L3-L4 was created and validated by use of ROM, disc pressure, and bony strain from previously published data. Virtual implantation of a spherical interbody device was performed with 0, 2, and 4 mm of subsidence. The model was exercised in compression, flexion, extension, axial rotation, and lateral bending. The ROM, vertebral body effective (von Mises) strain, and FCFs were reported. RESULTS: Implantation of a PEEK implant resulted in slightly lower strain maxima when compared with a CoCr implant. For both materials, the peak strain experienced by the underlying bone was reduced with increasing subsidence. All levels of subsidence resulted in ROM and FCFs similar to the intact model. CONCLUSIONS: The results suggest that a simple spherical implant design is able to maintain segmental ROM and provide minimal differences in FCFs. Large areas of von Mises strain maxima were generated in the bone adjacent to the implant regardless of whether the implant was PEEK or CoCr.

In vivo deformation, surface damage, and biostability of retrieved Dynesys systems.

STUDY DESIGN: Retrospective retrieval analysis. OBJECTIVE: To evaluate wear, deformation and biodegradation within retrieved polycarbonate urethane (PCU) components of Dynesys systems. SUMMARY OF BACKGROUND DATA: The Dynesys Dynamic Stabilization System (Zimmer Spine) consists of pedicle screws (Ti alloy), polycarbonate urethane (PCU) spacers, and a polyethylene-terephthalate cord. METHODS: Seventeen retrieved (mean implantation: 2.5 years, range: 0.7-7.0 years) and 2 exemplar implant systems were available. Reasons for revision were persistent pain (16/17), infection (1/17), and/or screw loosening (11/17), with 1/17 case of implant migration. Optical microscopy, microCT, and scanning electron microscopy were conducted to evaluate PCU spacer wear and deformation. Attenuated total reflectance Fourier transform infrared spectroscopy was used to assess spacer surface chemical composition. RESULTS: Retrieved spacer components exhibited permanent bending deformation (mean: 4.3°, range: 0.0°-15.8°). We observed evidence of PCU spacer contact with pedicle screws, cords, and surrounding bony structures (74/75, 69/75, and 51/75 spacers, respectively). Relatively infrequent damage modes included PCU fracture (1/75 spacers) or cracking (2/75 spacers), as well as pedicle screw fracture (3/103 screws). PCU degradation products were identified in 10/75 spacers, which represented retrievals having significantly longer implantation times (mean: 4.3 years, range: 1.0-7.0 years). Of these spacers, 8/10 had degradation peaks identified along the side of the spacer where the material would have been in contact with bodily fluid. CONCLUSION: PCU spacers from retrieved Dynesys systems exhibited permanent deformation, focal regions of in vivo wear and surface damage. Chemical changes associated with PCU biodegradation were associated with longer-term retrievals. The most frequently observed complication was pedicle screw loosening, with 3 incidences of screw breakage in 2 patients. These retrieval data provide a crucial basis for developing in vitro tests to simulate in vivo damage and degradation of posterior dynamic motion preservation implants. Longer-term retrievals, as well as retrievals that include more recent design features (e.g., HA coating), will be useful to provide a greater context for the clinical implications of our short-term observations.

National revision burden for lumbar total disc replacement in the United States: epidemiologic and economic perspectives.

STUDY DESIGN: Retrospective cohort study using a nationally representative inpatient database. OBJECTIVE: To quantify the national revision burden for lumbar total disc replacements (TDRs) in the United States following Food and Drug Administration approval, for comparison with lumbar fusion and other common orthopedic procedures, including hip and knee replacement. SUMMARY OF BACKGROUND DATA: Previous studies of revision lumbar TDR surgery have been based on IDE studies. The epidemiology and costs of TDR revision surgery from a national perspective have not yet been reported. METHODS: The Nationwide Inpatient Sample was used to identify primary and revision TDR and anterior fusion procedures in 2005 and 2006. Surgeries were identified in the Nationwide Inpatient Sample using ICD9-CM codes. The prevalence of TDR and fusion surgery was calculated as a function of age, gender, race, census region, primary payer class, and type of hospital. Average length of stay and total hospitalization costs were also computed for each type of procedure. RESULTS: During the study period, there was a national total of 7172 TDR and 62,731 anterior fusion surgeries, including both primary and revisions. Overall, TDR patients were younger and had less comorbidity than fusion surgery patients. The average revision burden for lumbar TDR and anterior fusion was 11.2% and 5.8%, respectively. The average length of stay for primary lumbar TDR was significantly shorter compared to revision TDR, primary anterior fusion, and revision anterior fusion (P < 0.0001). Both the primary and the revision surgery using the TDR surgery involved significantly lower total hospital costs relative to anterior fusion surgery (P < 0.0001). Including revision, the average costs per TDR procedure were lower than anterior and posterior lumbar fusion. CONCLUSION: Although the revision burden for TDR was significantly higher than fusion surgery, the TDR revision burden fell within the revision burden range of hip and knee replacement, which are generally considered successful and cost-effective procedures. Economically, the higher revision burden for TDRs was offset by lower costs for both the primary as well as the revision procedures relative to fusion.

The natural history of polyethylene oxidation in total disc replacement.

STUDY DESIGN: This study is an evaluation of wear and oxidation in retrieved total disc replacements (TDRs). Forty-eight CHARITE TDRs were retrieved from 41 patients after 7.8 years of average implantation. All implants were removed because of intractable back pain and/or facet degeneration. Three unimplanted implants served as controls. OBJECTIVE: Our aim was to determine whether gamma-sterilized polyethylene components implanted in the spine oxidize in vivo, and if so, whether polyethylene oxidation has clinical relevance for the long-term performance of TDRs. SUMMARY OF BACKGROUND DATA: The natural history of polyethylene oxidation following gamma sterilization and long-term implantation in the spine has not yet been investigated. METHODS: Oxidation and oxidation potential were measured at the rim and dome of 47 components using Fourier transform infrared spectroscopy. The wear patterns of each retrieved polyethylene core were analyzed at the rim and dome. RESULTS: Oxidation was significantly higher at the rim, as compared with the dome of the cores. Hydroperoxide index was also significantly higher at the rim, as compared with the dome. Dome penetration rate was negatively correlated to implantation time (P < 0.0001) but not correlated to oxidation or hydroperoxide index (P > 0.05). Implants with evidence of chronic rim loading had higher rim oxidation. CONCLUSION: The data support our hypothesis that, for the historical packaging methods employed by the manufacturer, polyethylene oxidation and oxidation potential were significantly higher at the rim as opposed to the dome. The mechanism is governed by access to oxygen in vivo and may be accelerated under certain combined modes of repeated rim loading. Our findings have clinical significance in cases of chronic impingement, when the rim has to support repeated loading for the lifetime of the implant.

Aging and low back pain among exercise participants: a follow-up study with psychological adaptation factors.

This study is a follow-up to a study previously published in this journal that reported the moderating function of exercise exertion amid the relationship between age and low back pain (LBP) among consistent exercise participants. The current study analyzed factors of psychological adaptation as potential mediators within the age--LBP relationship. Measures of psychological adaptation included psychological vulnerability, avoidant coping, resilient coping, and perceived resilience. The sample reported slightly moderate psychological vulnerability; a moderate extent of avoidant coping and resilient coping; and high resilience. Age inversely correlated with psychological vulnerability and avoidance coping. LBP correlated inversely with avoidant coping. Avoidant coping positively mediated (enhanced) age's effect on LBP. Results from this follow-up analysis highlight the importance of understanding and testing psychological factors in models with age and a physical health outcome.

Retrieval analysis of motion preserving spinal devices and periprosthetic tissues.

This article reviews certain practical aspects of retrieval analysis for motion preserving spinal implants and periprosthetic tissues as an essential component of the overall revision strategy for these implants. At our institution, we established an international repository for motion-preserving spine implants in 2004. Our repository is currently open to all spine surgeons, and is intended to be inclusive of all cervical and lumbar implant designs such as artificial discs and posterior dynamic stabilization devices. Although a wide range of alternative materials is being investigated for nonfusion spine implants, many of the examples in this review are drawn from our existing repository of metal-on-polyethylene, metal-on-metal lumbar total disc replacements (TDRs), and polyurethane-based dynamic motion preservation devices. These devices are already approved or nearing approval for use in the United States, and hence are the most clinically relevant at the present time. This article summarizes the current literature on the retrieval analysis of these implants and concludes with recommendations for the development of new test methods that are based on the current state of knowledge of in vivo wear and damage mechanisms. Furthermore, the relevance and need to evaluate the surrounding tissue to obtain a complete understanding of the biological reaction to implant component corrosion and wear is reviewed.

What is the correlation of in vivo wear and damage patterns with in vitro TDR motion response?

STUDY DESIGN: This study combined the evaluation of retrieved total disc replacements (TDRs) with a biomechanical study using human lumbar spines. Thirty-eight CHARITE TDRs were retrieved from 32 patients after 7.3 years average implantation. All implants were removed because of intractable back pain and/or facet degeneration. In parallel, 20 new implants were evaluated at L4-L5 and L5-S1 in an in vitro lumbar spine model. OBJECTIVE: The purpose of this study was to correlate wear and damage patterns in retrieved TDRs with motion patterns observed in an in vitro lumbar spine model. We also sought to determine whether one-sided wear and motion patterns were associated with greater in vivo wear. SUMMARY OF BACKGROUND DATA: The comparison of polyethylene wear in TDRs after long-term implantation to those tested using an in vitro model had not yet been investigated. METHODS: The wear patterns of each retrieved PE core was analyzed at the rim and dome. Thirty-five cores were further analyzed using MicroCT to determine the penetration symmetry. For the in vitro study the implants were tested under physiologic loads using a validated cadaveric model. Motion patterns of the in vitro-tested implants were tracked using sequential video-fluoroscopy. RESULTS: Fifteen of 35 retrieved cores (43%) displayed one-sided wear patterns. Significant correlations were observed between implantation time and penetration and penetration rate. In the in vitro study, there was evidence of motion at both articulations, motion at both articulation but predominantly at the top articulation, and solelyat the top articulation. Core entrapment and pinching was observed and associated with visual evidence of core bending or deformation. CONCLUSION: This is the first study to directly compare the long-term PE wear and damage mechanisms in TDR retrievals with the motion patterns generated by a validated in vitro cadaveric testing model. The retrievals exhibited wear patterns consistent with the in vitro testing.

Complications of Lumbar Artificial Disc Replacement Compared to Fusion: Results From the Prospective, Randomized, Multicenter US Food and Drug Administration Investigational Device Exemption Study of the Charité Artificial Disc.

BACKGROUND: Previous reports of lumbar total disc replacement (TDR) have described significant complications. The US Food and Drug Administration (FDA) investigational device exemption (IDE) study of the Charité artificial disc represents the first level I data comparison of TDR to fusion. METHODS: In the prospective, randomized, multicenter IDE study, patients were randomized in a 2:1 ratio, with 205 patients in the Charité group and 99 patients in the control group (anterior lumbar interbody fusion [ALIF] with BAK cages). Inclusion criteria included confirmed single-level degenerative disc disease at L4-5 or L5-S1 and failure of nonoperative treatment for at least 6 months. Complications were reported throughout the study. RESULTS: The rate of approach-related complications was 9.8% in the investigational group and 10.1% in the control group. The rate of major neurological complications was similar between the 2 groups (investigational = 4.4%, control = 4.0%). There was a higher rate of superficial wound infection in the investigational group but no deep wound infections in either group. Pseudarthrosis occurred in 9.1% of control group patients. The rate of subsidence in the investigational group was 3.4%. The reoperation rate was 5.4% in the investigational group and 9.1% in the control group. CONCLUSIONS: The incidence of perioperative and postoperative complications for lumbar TDR was similar to that of ALIF. Vigilance is necessary with respect to patient indications, training, and correct surgical technique to maintain TDR complications at the levels experienced in the IDE study.

A prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part II: evaluation of radiographic outcomes and correlation of surgical technique accuracy with clinical outcomes.

STUDY DESIGN: A prospective, randomized, multicenter, Food and Drug Administration-regulated, investigational device exemption clinical trial. OBJECTIVES: To compare the safety and effectiveness of lumbar total disc replacement (TDR) with the CHARITE artificial disc (DePuy Spine, Raynham, MA) to anterior lumbar interbody fusion for the treatment of single-level degenerative disc disease from L4-S1 unresponsive to nonoperative treatment. In addition, to evaluate the radiographic outcomes of lumbar artificial disc replacement at either L4-L5 or L5-S1 with the CHARITE artificial disc as compared to anterior lumbar interbody fusion with cylindrical cages and iliac crest bone graft; and to determine if a correlation exists between clinical outcomes and surgical accuracy of TDR placement within the disc space. SUMMARY OF BACKGROUND DATA: Prior investigators have reported excellent radiographic results with the CHARITE artificial disc for the treatment of lumbar degenerative disc disease. These encouraging results are the product of retrospective reviews without a control. Very few studies have reported on the segmental motion of an intervertebral level implanted with an artificial disc, and no studies have reported a correlation of radiographic and clinical outcomes. METHODS: A prospective, randomized, multicenter, US Food and Drug Administration, investigational device exemption study with 24-month follow-up was performed at 14 centers throughout the United States. A total of 304 subjects were randomized in a 2:1 ratio, with 205 in the investigational group (TDR with the CHARITE artificial disc) and 99 in the control group (anterior lumbar interbody fusion with BAK cages and iliac crest bone graft). A total of 71 TDR training cases were performed (up to 5 at each site) before randomization beginning at each site. Plain radiographs were analyzed for each subject in both groups regarding range of motion (ROM) in flexion/extension, restoration of disc space height, and subsidence. Prosthesis placement in the coronal and midsagittal planes was analyzed for the 276 patients with TDR. Correlations were performed between prosthesis placement and clinical outcomes. RESULTS: Patients in the investigational group had a 13.6% mean increase, and those in the control group an 82.5% decrease in mean flexion/extension ROM at 24 months postoperatively compared to baseline. Patients in the investigational group had significantly better restoration of disc height than the control group (P < 0.05). There was significantly less subsidence in the investigational group compared to the control group (P < 0.05). The surgical technical accuracy of CHARITE artificial disc placement was divided into 3 groups: I, ideal (83%); II, suboptimal (11%); and III, poor (6%), and correlated with clinical outcomes. The flexion/extension ROM and prosthesis function improved with the surgical technical accuracy of radiographic placement (P = 0.003). CONCLUSIONS: Preoperative ROM in flexion/extension was restored and maintained in patients receiving a TDR. TDR with the CHARITE artificial disc resulted in significantly better restoration of disc space height, and significantly less subsidence than anterior interbody fusion with BAK cages. Clinical outcomes and flexion/extension ROM correlated with surgical technical accuracy of CHARITE artificial disc placement. In the majority of cases, placement of the CHARITE artificial disc was ideal.