Bone ingrowth in retrieved Bryan Cervical Disc prostheses

STUDY DESIGN

Explant analysis for bone ingrowth of retrieved cervical disc prosthesis in chimpanzees and humans.

OBJECTIVES

To assess the bone ingrowth into retrieved Bryan Cervical Discs.

SUMMARY OF BACKGROUND DATA

Bone ingrowth in cervical disc prosthesis has not been documented in the literature.

METHODS

Chimpanzee: Two chimpanzees underwent placement of the Bryan disc at C3-C4 and 3 months later had explantation and interbody fusion. Human: Two patients had removal of their Bryan disc and interbody fusion for failure to resolve symptoms at 8 and 10 months. The explants were analyzed for bone ingrowth.

RESULTS

Chimpanzee: Histologic analysis showed bony ingrowth through the interstices of the porous coating and apposition ranging from 10% to 50% of toluidine blue-stained sections. New ingrowth, rather than bony impaction, was confirmed with fluorochrome-labeled sections Human: Bone ingrowth was a mean of 30.1% (12% SD). No difference was observed between peripheral, intermediate, or central locations.

CONCLUSIONS

Adequate bony apposition was found in all primate device-to-vertebral body interfaces. Human retrievals also demonstrated significant ingrowth in all four surfaces. This compares with hip and knee arthroplasty percent ingrowth rates of 10% to 30%. All implants had stable fixation judged by radiographs and at the time of implant removal.

Thoracolumbar injury classification and severity score: a new paradigm for the treatment of thoracolumbar spine trauma

BACKGROUND

Contemporary understanding of the biomechanics, natural history, and methods of treating thoracolumbar spine injuries continues to evolve. Current classification schemes of these injuries, however, can be either too simplified or overly complex for clinical use.

METHODS

The Spine Trauma Group was given a survey to identify similarities in treatment algorithms for common thoracolumbar injuries, as well as to identify characteristics of injury that played a key role in the decision-making process.

RESULTS

Based on the survey, the Spine Trauma Group has developed a classification system and an injury severity score (thoracolumbar injury classification and severity score, or TLICS), which may facilitate communication between physicians and serve as a guideline for treating these injuries. The classification system is based on the morphology of the injury, integrity of the posterior ligamentous complex, and neurological status of the patient. Points are assigned for each category, and the final total points suggest a possible treatment option.

CONCLUSIONS

The usefulness of this new system will have to be proven in future studies investigating inter- and intraobserver reliability, as well as long-term outcome studies for operative and nonoperative treatment methods.

The ponticulus posticus: implications for screw insertion into the first cervical lateral mass

BACKGROUND

The arcuate foramen is an important osseous anomaly of the first cervical vertebra (the atlas) that must be taken into consideration during placement of lateral mass screws into the atlas.

METHODS

The prevalence of this anomaly in our patient population was determined through a retrospective review of 464 lateral radiographs of the neck. The anatomy of the arcuate foramen was identified in a study of cadavers.

RESULTS

Seventy-two arcuate foramina, complete or incomplete, were identified on the 464 lateral radiographs of the neck; thus, the prevalence was 15.5% in our patient population.

CONCLUSIONS

Although the arcuate foramen is a common anomaly, it is often not recognized. Proper identification of this anomaly on preoperative lateral radiographs should alert the surgeon to avoid using the ponticulus posticus as a starting point for a lateral mass screw in order to not injure the vertebral artery.

A new classification of thoracolumbar injuries: the importance of injury morphology, the integrity of the posterior ligamentous complex, and neurologic status

STUDY DESIGN

A new proposed classification system for thoracolumbar (TL) spine injuries, including injury severity assessment, designed to assist in clinical management.

OBJECTIVE

To devise a practical, yet comprehensive, classification system for TL injuries that assists in clinical decision-making in terms of the need for operative versus nonoperative care and surgical treatment approach in unstable injury patterns.

SUMMARY OF BACKGROUND DATA

The most appropriate classification of traumatic TL spine injuries remains controversial. Systems currently in use can be cumbersome and difficult to apply. None of the published classification schemata is constructed to aid with decisions in clinical management.

METHODS

Clinical spine trauma specialists from a variety of institutions around the world were canvassed with respect to information they deemed pivotal in the communication of TL spine trauma and the clinical decision-making process. Traditional injury patterns were reviewed and reconsidered in light of these essential characteristics. An initial validation process to determine the reliability and validity of an earlier version of this system was also undertaken.

RESULTS

A new classification system called the Thoracolumbar Injury Classification and Severity Score (TLICS) was devised based on three injury characteristics: 1) morphology of injury determined by radiographic appearance, 2) integrity of the posterior ligamentous complex, and 3) neurologic status of the patient. A composite injury severity score was calculated from these characteristics stratifying patients into surgical and nonsurgical treatment groups. Finally, a methodology was developed to determine the optimum operative approach for surgical injury patterns.

CONCLUSIONS

Although there will always be limitations to any cataloging system, the TLICS reflects accepted features cited in the literature important in predicting spinal stability, future deformity, and progressive neurologic compromise. This classification system is intended to be easy to apply and to facilitate clinical decision-making as a practical alternative to cumbersome classification systems already in use. The TLICS may improve communication between spine trauma physicians and the education of residents and fellows. Further studies are underway to determine the reliability and validity of this tool.

A blinded assessment of radiographic criteria for atlanto-occipital dislocation

STUDY DESIGN

Blinded comparison of 5 methods to diagnose atlanto-occipital dislocation (AOD) on plain radiographs and computerized tomography (CT) of the cervical spine.

OBJECTIVE

To determine the best method to diagnose AOD.

SUMMARY OF BACKGROUND DATA

Several methods are proposed for the diagnosis of AOD, including the Power's ratio, X-line method, basion-dens interval, condylar gap, and Harris method. No blinded comparison of the results of these methods has been compared to patient outcome, and there is no information available regarding the accuracy of these methods applied to CT scans.

METHODS

Plain lateral radiographs and CTs of the cervical spine were reviewed in 104 patients, including 6 with AOD. Images underwent a blinded review by a board certified neurosurgeon (D.K.R.), orthopedist (P.A.A.), radiologist (J.C.), and emergency physician (D.B.B.). Each diagnostic method for AOD was applied for determination of sensitivity, specificity, and positive and negative predictive values. The ability to identify relevant anatomic landmarks was also tabulated.

RESULTS

Average values for sensitivities, specificities, positive and negative predictive values for each method applied to plain radiographs are: 0.4625-1.0, 0.8933-0.9725, 0.2775-0.45, and 0.975-1.0, respectively. These values for each method applied to CT scans are: 0.7075-1.0, 0.8725-0.9775, 0.3175-1, and 0.98-1.0, respectively. Identification of relevant anatomic landmarks occurred 99.75% of the time when these methods were applied to CT scans compared to 39% to 84% of the time on plain radiographs.

CONCLUSIONS

Sensitivity, specificity, positive and negative predictive values of these methods improve when applied to CT scans because of better visualization of anatomic landmarks. This result suggests CT scans of the cervical spine may be warranted in all trauma patients suspected of having cervical spine injury.

The thoracolumbar injury severity score: a proposed treatment algorithm

OBJECTIVE

Significant controversy exists regarding the optimal management of thoracolumbar injuries. This is in part due to the lack of understanding of the natural history of various injury subtypes and the absence of a universally accepted classification scheme that facilitates communication among care providers and assists in directing treatment. The Spine Trauma Study Group has developed an injury severity score based on three major variables: the mechanism of injury determined by radiographic appearance, the integrity of the posterior ligamentous complex, and the neurologic status of the patient. By systematically assigning specific point values within each category based on the severity of injury, a final severity score may be generated that can be used to help direct treatment. The goal of this work is to present a proposal of a detailed treatment algorithm to assist in the nonoperative or operative management of thoracolumbar injuries.

METHODS

A detailed review of the world's spinal literature was performed to ascertain predictors of instability following thoracolumbar trauma. With use of known biomechanical and clinical outcome measures, an arbitrary assignment of point values to various injury descriptors was performed. The assessment of the validity of the severity score was compared retrospectively with a variety of selected cases representing the typical injury patterns under the three major injury groups: compression, translational/rotational, and distraction injuries.

CONCLUSIONS

The proposed treatment algorithm is an attempt to assist physicians using best-evidence medicine in managing thoracolumbar spinal injuries. The final point flow chart with graduated treatment recommendations is only preliminary and needs to be validated through prospective cohort analysis. In addition, the importance of the chosen variables determining spinal stability must also be verified.

Chemical activation of MgH2; a new route to superior hydrogen storage materials

We report the discovery of a new, chemical route for 'activating' the hydrogen store MgH2, that results in highly effective hydrogen uptake/release characteristics, comparable to those obtained from mechanically-milled material.

Intervertebral disc arthroplasty

STUDY DESIGN

Review article of current knowledge of disc arthroplasty.

OBJECTIVES

To review the rationale for disc replacement, the general principles of design, and early clinical results.

SUMMARY OF BACKGROUND DATA

Disc arthroplasty is an emerging treatment for patients with disc degeneration. Its theoretical advantages are to maintain motion, decrease the incidence of adjacent segment degeneration, avoid complications related to fusion, and allow early return to function.

METHODS

Literature review of currently implanted prostheses or those undergoing investigation.

RESULTS

At this time, the theoretical advantages are unproven clinically but have been confirmed in biomechanical and kinematic investigations. Multicenter studies of both cervical and lumbar prostheses have shown short-term results equivalent to fusion. Neurologic complications and failures have been rare. Prosthetic subsidence and long-term wear will most likely be potential failure mechanisms. Thus far, with the exception of nucleoplasty, these problems have not been observed.

CONCLUSIONS

The early results are satisfactory, but the basic premise that motion preservation will diminish adjacent segment degeneration is yet unproven. Long-term results are unavailable and failure modes are unknown. Before implantation, the surgeon and patient must understand the experimental nature of the devices.

The Bryan Cervical Disc: wear properties and early clinical results

BACKGROUND CONTEXT

The rationale for motion preservation by disc replacement after anterior cervical discectomy is to diminish long-term morbidity secondary to adjacent segment degeneration. However, these disc prostheses will be subject to wear and its possible adverse consequences.

PURPOSE

Assess the in vitro and in vivo wear properties of the Bryan Cervical Disc and the early clinical results.

STUDY DESIGN

In vitro mechanical testing, caprine animal model and prospective European human trial.

OUTCOME MEASURE

In vitro mechanical testing used American Society for Testing and Materials standards to measure wear rates and debris. Caprine results were analyzed by histopathologic analysis by a blinded veterinary pathologist. Clinical outcomes were measured by Odoms's criteria, independent radiologic analysis and Short Form-36.

METHODS

In vitro wear testing in cervical spine simulator for up to 40 M cycles. Wear rates were determined and particles analyzed microscopically. The in vivo inflammatory response was studied in goats that had discectomy at C4-C5. They were sacrificed between 3 and 12 months and histopathologically were compared with controls who had fusions with titanium plates. A prospective clinical trial of 136 patients with minimum 1-year follow-up was analyzed using validated questionnaires and radiographs.

RESULTS

In vitro wear averaged approximately 1.76% by weight at 10 M cycles and 18% at 40 M cycles. Wear debris were present in the periprosthetic tissues in 4 of 11 animals without inflammatory response. The early clinical results were satisfactory in over 90% of patients.

CONCLUSION

The in vivo and in vitro wear properties are satisfactory for the expected duration of life of the prosthesis. The early clinical results are satisfactory and equal to fusion.

A comparison of simulator-tested and -retrieved cervical disc prostheses

Object. Total joint arthroplasties most commonly fail because the implant becomes worn and a host inflammatory response subsequently develops. Both the material response to the biological environment and the host response to the device must be thoroughly evaluated to establish the efficacy of cervical arthroplasty. Analyses of devices explanted in humans allow evaluation of both responses. Hypothetical wear rates can be determined by comparing in vivo wear with simulator-derived wear. The purpose of this study was to perform explant analyses involving the Bryan and Prestige discs and compare these results with those obtained using spine simulators.

Methods. Of the approximately 5500 patients treated with the Bryan disc, 11 have undergone explantation of the device. Six of these devices were analyzed for dimensional and chemical changes. Three of the approximately 300 implanted Prestige discs were retrieved, and two were examined microscopically. Histological specimens were assessed for wear particles and host inflammatory response. Additionally, the extent of simulator-produced wear was compared with that demonstrated in the retrieved specimens.

Conclusions. The simulator-generated results predict adequate wear-related characteristics for both the Bryan and Prestige prostheses for a minimum of 40 years. Comparison of data with those of the retrieved specimens indicates that the wear was more minimal than predicted in simulators by five- to 10-fold. In no instance did the revisions result from failure of the device due to a reaction to wear debris, fracture, polymer oxidation, or metal corrosion. The inflammatory response seen in the periprosthetic tissues was minimal and not characteristic of inflammatory responses in failed diarthrodial joint arthroplasties.

Probing the Location and Distribution of Paramagnetic Centers in Alkali Metal-Loaded Zeolites through 7Li MAS NMR

The nature and surroundings of lithium cations in lithium-exchanged X and A zeolites following loading with the alkali metals Na, K, Rb, and Cs have been studied through (7)Li solid-state NMR spectroscopy. It is demonstrated that the lithium in these zeolites is stable with respect to reduction by the other alkali metals. Even though the lithium cations are not directly involved in chemical interactions with the excess electrons introduced in the doping process, the corresponding (7)Li NMR spectra are extremely sensitive to paramagnetic species that are located inside the zeolite cavities. This sensitivity makes (7)Li NMR a useful probe to study the formation, distribution, and transformation of such species.

Rheumatoid arthritis of the cervical spine

BACKGROUND CONTEXT

Rheumatoid arthritis affects over 2 million patients in the United States. It is the most common inflammatory disorder of the cervical spine. The natural history is variable. Women tend to be more commonly involved than men. Atlantoaxial instability is the most common form of cervical involvement and may occur either independently or concomitantly with cranial settling and subaxial instability. Cervical spine involvement can be seen in up to 86% of patients and neurologic involvement in up to 58%. Myelopathy is rare but when present portends a poor prognosis. What is frustrating for clinicians treating these patients is that pain cannot be equated with instability or instability with neurologic symptoms. The goal is to identify patients at risk before the development of neurologic symptoms. Both radiographic and nonradiographic risk factors play an important role in the surgical decision-making process.

PURPOSE

We will describe the current concepts in rheumatoid arthritis of the cervical spine. Emphasis is placed on the natural history, anatomy, pathophysiology and decision-making process.

STUDY DESIGN

A review of the current concepts of rheumatoid arthritis of the cervical spine.

METHODS

MEDLINE search of all English literature published on rheumatoid arthritis of the cervical spine.

RESULTS

Rheumatoid arthritis of the cervical spine was first described by Garrod in 1890. The prevalence has been estimated to be 1% to 2% of the world's adult population. Despite its prevalence, the etiology of rheumatoid arthritis remains unknown. Because of its potentially debilitating and life-threatening sequelae in advanced disease, rheumatoid arthritis in the cervical spine today remains a high priority to diagnose and treat.

CONCLUSIONS

Many aspects of the natural history and pathophysiology of the rheumatoid spine remain unclear. The timing of operative intervention in patients with radiographic instability and no evidence of neurologic deficit is an area of considerable controversy. Continued surveillance into the natural history of the rheumatoid spine is required.

An ordered array of cadmium clusters assembled in zeolite A

We report the assembly of a cubic array of cationic cadmium clusters encapsulated in zeolite A, and its characterization through Rietveld analysis of powder synchrotron X-ray diffraction data and high resolution transmission electron microscopy.

Rubidium doped zeolite rho: structure and microwave conductivity of a metallic zeolite

Large crystallites of high purity zeolite rho were synthesized by controlled monitoring of the aging and heating period of the mother gel. The microwave conductivity of Rb-rho doped with up to 20 Rb atoms per unit cell was measured over the temperature range 15-300 K, and the structures of three of the samples were examined through Rietveld analysis of powder neutron diffraction data. At low concentrations of rubidium dopant the observed microwave responses were dominated by polarization effects. In the sample Rb(17)/Rb-rho a strongly temperature-dependent electronic contribution to the conductivity was observed above approximately =150 K. In Rb(20)/Rb-rho, conductivities in the range 1.5-2.3 Sm(-1) were observed between 15 and 300 K. This residual conductivity at 15 K, unprecedented in a zeolite, indicates that the sample is indeed metallic; however, the values of conductivity measured are low in comparison to conventional metals and comparable to those of doped semiconductors. The evolution of the conducting behaviour is discussed in relation both to observed structural and to possible electronic changes occurring within the samples on metal doping.

Wear analysis of the Bryan Cervical Disc prosthesis

STUDY DESIGN

In vitro wear testing of the Bryan Cervical Disc prosthesis was performed in a cervical spine simulator. The biologic response was assessed in chimpanzee and goat animal models.

OBJECTIVE

Determine the wear characteristics of the Bryan disc.

SUMMARY OF BACKGROUND DATA

Large joint arthroplasties fail most commonly by wear and consequent formation of particulate material, which induces an inflammatory response. Therefore, measuring the wear characteristics of the new spinal disc replacements is important.

METHODS

Six prosthetic assembles were tested to 10 or 40 million cycles by load and motion and 3 additional assemblies were tested by load only in a cervical spine simulator. Any debris was examined using ASTM standards. The local biologic response to the prosthesis was examined in two chimpanzees. Nine goats were used to assess the biologic response in both local and distant tissues. Arthrodesis was performed on three additional control goats that received an allograft and an anterior cervical plate.

RESULTS

Wear results: cervical spine simulators that applied the loads and motions associated with activities of daily living produced wear particulate at a rate of 1.2 mg per million cycles. Device height decreased 0.02 mm per million cycles with approximately 77% of this decrease due to gradual creep of the nucleus under the constant compressive load. Particles generated were granular in shape with a mean feret diameter of 3.9 microm. All animals tolerated placement of the Bryan disc. Wear debris was present in the periprosthetic and epidural spaces in some animals. However, no significant inflammatory response was observed. No wear material was found distant from the implant in draining lymph tissue, the liver, or the spleen.

CONCLUSIONS

The Bryan disc has satisfactory wear characteristics and does not produce a significant inflammatory response.

Comparison of anterior and posterior approaches in cervical spinal cord injuries

This study reports the results of 52 patients with unstable cervical spine injuries and associated spinal cord injuries randomized to either anterior or posterior stabilization and fusion. All patients had achieved reduction and had unstable injuries that were thought to require surgical stabilization. Patients requiring a specific approach for either reduction or decompression were not included. Frankel grades and ASIA motor index scores were followed in each patient as well as fusion status, changes in alignment, and pain at final follow-up. Neurologic improvement was noted in each group with no significant differences. In the anterior group, 70% improved at least 1 Frankel grade and 57% improved 1 Frankel grade in the posterior group. There were two nonunions in the anterior group (90% fusion) and none in the posterior group (100% fusion), although this was not statistically different. Seven patients in each group complained of pain at the final follow-up. There were no significant differences in fusion rates, alignment, neurologic recovery, or long-term complaints of pain in patients treated with either anterior or posterior fusion and instrumentation.

Cerebral spinal fluid pressure: effects of body position and lumbar subarachnoid drainage in a canine model

STUDY DESIGN

This study used in vivo an model of subarachnoid cerebrospinal fluid pressure measurement.

OBJECTIVES

To examine the relation between subarachnoid cerebrospinal fluid pressure in the cervical and lumbar spine and varying body positions, and to test the hypothesis that increasing body inclination and lumbar subarachnoid drainage decreases cervical cerebrospinal fluid pressures.

SUMMARY OF BACKGROUND DATA

Cerebrospinal fluid leaks are a recognized complication of anterior or posterior cervical surgery. Conflicting opinion exists regarding the benefits of postoperative patient positioning and lumbar subarachnoid drainage.

METHODS

Subarachnoid cerebrospinal fluid pressure of 7 beagles was monitored via two angiocatheters attached to pressure transducers inserted into the subarachnoid space through laminectomies at C3 and L4. Pressure measurements were taken when body position was inclined to 30 degrees, 60 degrees, and 90 degrees. A lumbar durotomy was performed to simulate the effects of lumbar subarachnoid drainage. The body was repositioned to 90 degrees, and pressure was measured.

RESULTS

As inclination increased from 0 degrees to 90 degrees, the mean cervical cerebrospinal fluid pressure significantly decreased. The mean lumbar subarachnoid pressure significantly increased as inclination increased from 0 degrees to 90 degrees. Lumbar durotomy plus repositioning to 90 degrees resulted in a significant reduction in cervical cerebrospinal fluid subarachnoid pressure, with pressures dropping by 46%. Lumbar cerebrospinal fluid subarachnoid pressure dropped to zero after lumbar durotomy plus repositioning to 90 degrees.

CONCLUSIONS

Cerebrospinal fluid pressures in the subarachnoid space of both the cervical and lumbar spines are affected by changes in body position. Both patient positioning and lumbar drainage may be important in reducing cervical cerebrospinal fluid pressure, and may reduce the occurrence of cerebrospinal fluid leaks after primary dural repair in the neck.

Cervical myelopathy. current diagnostic and treatment strategies

Cervical myelopathy is a varied clinical syndromes resulting from spinal cord dysfunction. Underlying causes are numerous, but spondylosis at one or more levels is the most common etiology. Natural history studies have demonstrated a variable clinical course with gradual neurologic deterioration in a majority of patients. While prospective clinical comparisons are limited, existing literature suggests that operative management reliably arrests the progression of myelopathy and may lead to functional improvement in a majority of patients. The selection of surgical procedures must be carefully individualized based on specific clinical and radiographic factors. Whereas anterior decompression and fusion procedures at one or two motion segments have predictable results, procedures involving three or more levels are associated with increased morbidity. Newer techniques for the treatment of multilevel cervical myelopathy include anterior decompression with 360-degree fusion, hybrid corpectomy/anterior cervical discectomy and fusion techniques and the use of dynamic anterior cervical plates. An alternative technique for patients with a lordotic sagittal alignment is laminoplasty, which has a proven track record of long-term good to excellent results.