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Biomedical subjects

T C Ryken

Publications and source records attributed to T C Ryken.

At least 37 records · Page 2Linked to original sources
PubMed2002

Treatment of subaxial cervical spinal injuries.

UNLABELLED: SUBAXIAL CERVICAL FACET DISLOCATION INJURIES: STANDARDS: There is insufficient evidence to recommend treatment standards. GUIDELINES: There is insufficient evidence to recommend treatment guidelines. OPTIONS: Closed or open reduction of subaxial cervical facet dislocation injuries is recommended. Treatment of subaxial cervical facet dislocation injuries with rigid external immobilization, anterior arthrodesis with plate fixation, or posterior arthrodesis with plate or rod or interlaminar clamp fixation is recommended. Treatment of subaxial cervical facet dislocation injuries with prolonged bedrest in traction is recommended if more contemporary treatment options are not available. SUBAXIAL CERVICAL INJURIES EXCLUDING FACET DISLOCATION INJURIES: STANDARDS: There is insufficient evidence to recommend treatment standards. GUIDELINES: There is insufficient evidence to recommend treatment guidelines. OPTIONS: Closed or open reduction of subluxations or displaced subaxial cervical spinal fractures is recommended. Treatment of subaxial cervical spinal injuries with external immobilization, anterior arthrodesis with plate fixation, or posterior arthrodesis with plate or rod fixation is recommended.

Cervical Vertebrae↗
PubMed2002

Management of acute central cervical spinal cord injuries.

STANDARDS: There is insufficient evidence to support treatment standards. GUIDELINES: There is insufficient evidence to support treatment guidelines. OPTIONS: Intensive care unit (or other monitored setting) management of patients with acute central cervical spinal cord injuries, particularly patients with severe neurological deficits, is recommended. Medical management, including cardiac, hemodynamic, and respiratory monitoring, and maintenance of mean arterial blood pressure at 85 to 90 mmHg for the first week after injury to improve spinal cord perfusion is recommended. Early reduction of fracture-dislocation injuries is recommended. Surgical decompression of the compressed spinal cord, particularly if the compression is focal and anterior, is recommended.

Acute Disease↗
PubMed2002

Management of vertebral artery injuries after nonpenetrating cervical trauma.

DIAGNOSTIC STANDARDS: There is insufficient evidence to support diagnostic standards. GUIDELINES: There is insufficient evidence to support diagnostic guidelines. OPTIONS: Conventional angiography or magnetic resonance angiography is recommended for the diagnosis of vertebral artery injury after nonpenetrating cervical trauma in patients who have complete cervical spinal cord injuries, fracture through the foramen transversarium, facet dislocation, and/or vertebral subluxation. TREATMENT STANDARDS: There is insufficient evidence to support treatment standards. GUIDELINES: There is insufficient evidence to support treatment guidelines. OPTIONS: Anticoagulation with intravenous heparin is recommended for patients with vertebral artery injury who have evidence of posterior circulation stroke. Either observation or treatment with anticoagulation in patients with vertebral artery injuries and evidence of posterior circulation ischemia is recommended. Observation in patients with vertebral artery injuries and no evidence of posterior circulation ischemia is recommended.

Evidence-Based Medicine↗
PubMed2001

Ultrasonographic guidance for spinal extracranial radiosurgery: technique and application for metastatic spinal lesions.

OBJECT: The relatively stationary anatomy of the intracranial compartment has allowed the development of stereotactic radiosurgery as an effective treatment option for many intracranial lesions. Difficulty in accurately tracking extracranial targets has limited its development in the treatment of these lesions. The ability to track extracranial structures in real time with ultrasound images allows a system to upgrade and interface pretreatment volumetric images for extracranial applications. In this report the authors describe this technique as applied to the treatment of localized metastatic spinal disease. METHODS: The extracranial stereotactic system consists of an optically tracked ultrasonography unit that can be registered to a linear accelerator coordinate system. Stereotactic ultrasound images are acquired following patient positioning, based on a pretreatment computerized tomography (CT) simulation. The soft-tissue shifts between the virtual CT-based treatment plan and the actual treatment are determined. The degree of patient offset is tracked and used to correct the treatment plan. The ultrasonography-based stereotactic navigation system is accurate to within an approximate means of 1.5 mm based on testing with an absolute coordinate phantom. A radiosurgical treatment was delivered using the system for localization of a metastatic spinal lesion. Compared with the virtual CT simulation, the actual treatment plan isocenter was shifted 12.2 mm based on the stereotactic ultrasound image. The patient was treated using noncoplanar beams to a dose of 15.0 Gy to the 80% isodose shell in a single fraction. CONCLUSIONS: A system for high-precision radiosurgical treatment of metastatic spinal tumors has been developed, tested, and applied clinically. Optical tracking of the ultrasonography probe provides real-time tracking of the patient anatomy and allows computation of the target displacement prior to treatment delivery. The results reported here suggest the feasibility and safety of the technique.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2001

Initial clinical experience with frameless stereotactic radiosurgery: analysis of accuracy and feasibility.

PURPOSE: To report on preliminary clinical experience with a novel image-guided frameless stereotactic radiosurgery system. METHODS AND MATERIALS: Fifteen patients ranging in age from 14 to 81 received radiosurgery using a commercially available frameless stereotactic radiosurgery system. Pathologic diagnoses included metastases (12), recurrent primary intracranial sarcoma (1), recurrent central nervous system (CNS) lymphoma (1), and medulloblastoma with supratentorial seeding (1). Treatment accuracy was assessed from image localization of the stereotactic reference array and reproducibility of biteplate reseating. We chose 0.3 mm vector translation error and 0.3 degree rotation about each axis as the maximum tolerated misalignment before treating each arc. RESULTS: The biteplates were found on average to reseat with a reproducibility of 0.24 mm. The mean registration error from CT localization was found to be 0.5 mm, which predicts that the average error at isocenter was 0.82 mm. No patient treatment was delivered beyond the maximum tolerated misalignment. The radiosurgery treatment was delivered in approximately 25 min per patient. CONCLUSION: Our initial clinical experience with stereotactic radiotherapy using the infrared camera guidance system was promising, demonstrating clinical feasibility and accuracy comparable to many frame-based systems.

Adolescent↗
PubMed2001

Tumor Fas (APO-1/CD95) up-regulation results in increased apoptosis and survival times for rats with intracranial malignant gliomas.

OBJECTIVE: The cellular "death" receptor Fas has been proposed to be a potential specific target for anti-glioma therapy. However, little is known regarding the effects of Fas expression on glioma viability in vivo. The goal of this study was to clarify the relationships among Fas expression, apoptosis, and survival rates for high-grade astrocytomas. METHODS: Fas expression was measured in several human glioblastoma multiforme cell lines and a malignant rat glioma cell line (36B10), before and after Fas up-regulation by gene transfer. Expression was correlated with the degree of Fas-mediated cytotoxicity and apoptosis induced after Fas activation. Subsequently, rats underwent intracranial implantation of either wild-type or genetically altered 36B10 cell lines, for study of the effects of Fas up-regulation on survival rates. RESULTS: Low levels of cell surface Fas expression in glioblastomas multiforme were correlated with their limited susceptibility to Fas-mediated cytotoxicity. Through Fas receptor up-regulation, relationships among increased Fas expression, Fas-mediated cytotoxicity, and apoptosis were demonstrated. The percentage of cells undergoing apoptosis after exposure to a Fas ligand-producing cell line increased from 4% in the sham-transfected line (36B10-) to 27% in the Fas-transfected line (36B10-Fas). After intracranial implantation of these tumors into rats, the median survival time increased significantly from 14 days (36B10 and 36B10-) to 24.5 days (36B10-Fas), which represents a 75% increase in the survival time for the greater Fas-expressing group (P = 0.0005). CONCLUSION: It seems that the overall low rate of apoptosis in high-grade astrocytomas is related to low levels of cell surface Fas expression. With increases in cellular Fas expression, rates of Fas-mediated apoptosis and survival rates were increased.

Animals↗
PubMed2000

Evidence-based analysis of odontoid fracture management.

OBJECT: The management of odontoid fractures remains controversial. Evidence-based methodology was used to review the published data on odontoid fracture management to determine the state of the current practices reported in the literature. METHODS: The Medline literature (1966-1999) was searched using the keywords "odontoid," "odontoid fracture," and "cervical fracture" and graded using a four-tiered system. Those articles meeting selection criteria were divided in an attempt to formulate practice guidelines and standards or options for each fracture type. Evidentiary tables were constructed by treatment type. Ninety-five articles were reviewed. Five articles for Type I, 16 for Type II, and 14 for Type III odontoid fractures met selection criteria. All studies reviewed contained Class III data (American Medical Association data classification). CONCLUSIONS: There is insufficient evidence to establish a standard or guideline for odontoid fracture management. Given the extent of Class III evidence and outcomes reported on Type I and Type III fractures, a well-designed casecontrolled study would appear to provide sufficient evidence to establish a practice guideline, suggesting that cervical immobilization for 6 to 8 weeks is appropriate management. In cases of Type II fracture, analysis of the Class III evidence suggests that both operative and nonoperative management remain treatment options. A randomized trial or serial case-controlled studies will be required to establish either a guideline or treatment standard for this fracture type.

Evidence-Based Medicine↗
PubMed2000

Treatment of Down syndrome-associated craniovertebral junction abnormalities.

OBJECT: Operative intervention for craniovertebral junction (CVJ) instability in patients with Down syndrome has become controversial, with reports of a low incidence of associated neurological dysfunction and high surgical morbidity rates. The authors analyzed their experience in light of these poor results and attempted to evaluate differences in management. METHODS: Medical and radiographic records of 36 consecutive patients with Down syndrome and CVJ abnormalities were reviewed. The most common clinical complaints included neck pain (15 patients) and torticollis (12 patients). Cervicomedullary compression was associated with ataxia and progressive weakness. Hyperreflexia was documented in a majority of patients (24 cases), and 13 patients suffered from varying degrees of quadriparesis. Upper respiratory tract infection precipitated the presentation in five patients. Four patients suffered acute neurological insults after a minor fall and two after receiving a general anesthetic agent. Atlantoaxial instability was the most common radiographically observed abnormality (23 patients), with a rotary component present in 14 patients. Occipitoatlantal instability was also frequently observed (16 patients) and was coexistent with atlantoaxial dislocation in 15 patients. Twenty individuals had bone anomalies, the most frequent of which was os odontoideum (12 patients) followed by atlantal arch hypoplasia and bifid anterior or posterior arches (eight patients). Twenty-seven patients underwent surgical procedures without subsequent neurological deterioration, and a 96% fusion rate was observed. In five of 11 patients basilar invagination was irreducible and required transoral decompression. Overall, 24 patients enjoyed good or excellent outcomes. CONCLUSIONS: The results of this series highlight the clinicopathological characteristics of CVJ instability in patients with Down syndrome and suggest that satisfactory outcomes can be achieved with low surgical morbidity rates.

Adolescent↗
PubMed1999

Co-expression of Fas and Fas ligand in human non-astrocytic glial tumors.

The study of Fas (APO-1/CD95) and Fas ligand (FasL) expression in human glial neoplasms has been primarily restricted to astrocytomas. Using immunohistochemistry, we analyzed 35 non-astrocytic glial neoplasms (12 WHO grade II ependymomas, 15 grade II oligodendrogliomas, and 8 grade III oligodendrogliomas) for these factors. A significant correlation was found between Fas and FasL expression within the same tumors (P = 0.001). Western blotting was used to corroborate these findings in 7 of these tumors (3 ependymomas and 4 oligodendrogliomas). Theoretically, the co-expression of Fas and FasL should render gliomas susceptible to suicidal and fratricidal elimination. Their progressive nature, however, suggests that gliomas have acquired mechanisms to prevent Fas-mediated apoptosis. Expression of the anti-apoptotic protooncogene bcl-2 is one potential way in which Fas/FasL-bearing gliomas can escape this fate. Although expression of Bcl-2 protein was found in 6 of 12 (50%) grade II ependymomas, 5 of 15 (33%) grade II oligodendrogliomas, and 6 of 8 (75%) grade III oligodendrogliomas, no correlation between Fas/FasL co-expression and Bcl-2 production could be demonstrated, indicating that protection from Fas-mediated apoptosis probably involves other mechanisms.

Blotting, Western↗
PubMed1999

Human astrocytomas co-expressing Fas and Fas ligand also produce TGFbeta2 and Bcl-2.

Human astrocytomas frequently co-express Fas (APO-1/CD95) and Fas ligand (FasL), yet do not appear to be overly susceptible to suicidal, fratricidal and immune-mediated elimination. This suggests that these gliomas have acquired mechanisms to prevent Fas-mediated apoptosis from occurring. Candidates for such a role include transforming growth factor-beta2 (TGFbeta2) and B-cell lymphoma/leukemia-2 (Bcl-2). TGFbeta2 effectively functions by hiding tumor cells from the immune system. This may potentially prevent the delivery of FasL from cytolytic T cells to Fas bearing astrocytomas. Bcl-2 works by rendering gliomas resistant to Fas-mediated apoptosis. Using immunohistochemistry, we analyzed seventy-six human astrocytomas (11 World Health Organization (WHO) grade I, 17 grade II, 17 grade III, and 31 grade IV) for the expression of Fas, FasL, TGFbeta2 and Bcl-2 in vivo. Positive immunoreactivity was found to significantly increase with increasing tumor grade for Fas (p < 0.0002), FasL (p < 0.0001), TGFbeta2 (p < 0.001) and Bcl-2 (p < 0.01). In addition, Fas/FasL co-expression, a counter-intuitive combination of factors in regards to glioma survival, also increased with WHO grade. Forty-five of 76 (59%) astrocytomas co-expressed Fas and FasL. Of those co-expressing Fas and FasL, 44 of 45 (98%) produced TGFbeta2, and 26 of 45 (58%) expressed Bcl-2. We found a significant positive correlation between Fas/FasL co-expression and TGFbeta2 (p < 0.002) and Bcl-2 (p < 0.005) production. We conclude that Fas and FasL are frequently co-expressed in human astrocytomas and these tumors are likely to produce other immunosuppressive and antiapoptotic factors such as TGFbeta2 and Bcl-2.

Astrocytoma↗
PubMed1998

Evidence-based review of the role of reoperation in the management of malignant glioma.

Using an evidence-based approach to available clinical studies, the authors examined the role of reoperation in the management of malignant glioma. A review of 1270 Medline-referenced articles spanning the period from 1966 through March 1998 was undertaken using the key words "glioblastoma" and "astrocytoma." Using an evidence-based four-tiered grading system, the authors found only 14 articles that met their inclusion criteria. Of these, 11 were graded as Class III (retrospective case series) and three as Class II (prospective nonrandomized studies). There were no Class I reports (randomized clinical trials), and all Class IV reports (opinion reports) were excluded. The authors of 10 Class III and one Class II articles supported the role of reoperation in increasing survival time or quality of life in selected patients; however, the results of multivariate analysis in two Class II and one Class III article did not support prolonged survival. The authors conclude that there was insufficient evidence to support either a standard or a guideline for reoperation in malignant glioma given the current status of the literature. Selection bias was a major factor in these studies. With continued interest in clinical trials for recurrent malignant glioma, the role of reoperation needs to be addressed in case-controlled or randomized fashion to establish either standards or guidelines on this commonly debated issue.

Journal Article↗
PubMed1997

Assessment of primary and salvage lateral mass screw insertion torque in a cadaveric model.

This study was performed to determine the insertion torques of three types of lateral mass screws and to explore their relationship to bone mineral density (BMD). The peak insertion torque of primary articular screws was measured, and the holes were then stripped by overtightening. Larger diameter "salvage" screws were placed in the stripped holes, and peak insertion torque was measured. Peak primary screw insertion torque and BMD were positively correlated (r = 0.48, p = 0.00001). The ratio of salvage to primary screw insertion torque varied significantly among the systems (p = 0.0003). The positive correlation between BMD and primary screw peak insertion torque confirms the importance of bone density for satisfactory screw purchase. The large variation in the ratio of salvage to primary screw insertion torque among systems may be due to differences in primary and salvage screw design.

Bone Density↗
PubMed1996

Effect of specimen fixation method on pullout tests of pedicle screws.

STUDY DESIGN: Experimental axial pullout tests of a new type of pedicle screw were done on cadaveric lumbar vertebrae. The manner in which specimens were secured in the testing apparatus was varied to determined influence of specimen fixation method on the maximum pedicle screw pullout force. OBJECTIVES: To determine the appropriateness of embedding (i.e., potting) spinal specimens in polymer resin (e.g., bone cement or Plastic Padding [Plastic Padding Ltd., High Wycombe, Buckinghamshire, England]) for axial pullout tests of pedicle screws. Several different specimen fixation methods were examined to make recommendations for the standardization of future experimental testing protocols. SUMMARY OF BACKGROUND DATA: Axial pullout of transpedicular screws, although not a likely clinical mode of failure, is a popular experimental testing mode for evaluating screw-bone biomechanics. A wide variety of techniques for securing a vertebral specimen to counter the axial pullout force has been reported (including the use of polymer resin) with a correspondingly wide range in the resulting axial pullout strengths. The possible influence of the specimen fixation method on pedicle screw axial pullout strength has not been addressed previously. METHODS: Axial pullout tests of pedicle screws (DDS, Plus Endoprothetik, Rotkreuz, Switzerland) from the pedicles of 21 isolated lumber vertebral bodies were done using a Model 810 MTS Universal Testing Machine (MTS Systems, Inc., Minneapolis, Minnesota). The specimens were secured in a custom-made vise fixture either as is or after the vertebral bodies were potted in Plastic Padding up to the pedicle origin. Some of the potted specimens were wrapped first in latex to prevent polymer resin intrusion, and the others were unprotected. Pullout tests were attempted on both the left and right pedicles of each specimen, and the maximum pedicle screw pullout force was recorded. Measurement of bone mineral density by means of dual energy x-ray absorptiometry, in addition to macroscopic and scanning electron microscopy histologic analyses, microradiography, and energy dispersive X-ray spectroscopy, was done post-test to assist in the interpretation of the data. RESULTS: The maximum pedicle screw pullout force was found to be dependent on both the bone mineral density and the mode of fixation of the vertebrae. Embedding in polymer resin without protection of the specimen (i.e., latex wrapping) led to several instances of well-documented polymer resin intrusion; in these specimens, mean maximum pedicle screw pullout force was significantly greater than that of specimens secured without polymer resin and that of embedded specimens for which intrusion did not occur. CONCLUSIONS: Polymer resin intrusion can have a significant effect on the biomechanical characteristics of the bone-pedicle screw interface. When polymer resins are used to secure vertebral specimens for in vitro biomechanical tests of the bone-pedicle screw interface, it is important to either prevent intrusion (e.g., with a latex wrapping) or document post-test (e.g., through the methods described in this article) that intrusion did not occur for the specimens included in the analysis.

Aged↗
PubMed1996

Biomechanical evaluation of Caspar and Cervical Spine Locking Plate systems in a cadaveric model.

There exist two markedly different instrumentation systems for the anterior cervical spine: the Cervical Spine Locking Plate (CSLP) system, which uses unicortical screws with a locking hub mechanism for attachment, and the Caspar Trapezial Plate System, which is secured with unlocked bicortical screws. The biomechanical stability of these two systems was evaluated in a cadaveric model of complete C5-6 instability. The immediate stability was determined in six loading modalities: flexion, extension, right and left lateral bending, and right and left axial rotation. Biomechanical stability was reassessed following fatigue with 5000 cycles of flexion-extension, and finally, the spines were loaded in flexion until the instrumentation failed. The Caspar system stabilized significantly in flexion before (p < 0.05) but not after fatigue, and it stabilized significantly in extension before (p < 0.01) and after fatigue (p < 0.01). The CSLP system stabilized significantly in flexion before (p < 0.01) but not after fatigue, and it did not stabilize in extension before or after fatigue. The moment needed to produce failure in flexion did not differ substantially between the two plating systems. The discrepancy in the biomechanical stability of these two systems may be due to differences in bone screw fixation.

Adult↗
PubMed1995

Assessment of unicortical and bicortical fixation in a quasistatic cadaveric model. Role of bone mineral density and screw torque.

STUDY DESIGN: The stabilizing potential of the Caspar Trapezial Osteosynthetic Plate was studied using unicortical and bicortical screw placement in cadaveric cervical spines. OBJECTIVE: To determine if Caspar plates secured with unicortical screws provide the same degree of stability as those anchored with unlocked bicortical screws. SUMMARY OF BACKGROUND DATA: Previous work has demonstrated that bicortical cervical vertebral screws are superior to unicortical screws in terms of pullout strength and decreased wobble. However, these two methods of plate fixation have not been directly compared in a clinically relevant cadaveric model. METHODS: The immediate and post-fatigue stabilizing potential of Caspar plates secured with unicortical or bicortical screws was assessed using a model of complete segmental instability. RESULTS: Unicortical screw placement resulted in inadequate stabilization in half of the cervical specimens. CONCLUSIONS: Our results suggest that, for the Caspar screw, bicortical fixation provides greater flexion-extension stability.

Biomechanical Phenomena↗
PubMed1995

Craniocervical intradural neurenteric cysts.

Neurenteric cysts are rare lesions of the central nervous system that are lined by epithelium of intestinal nature. They result from abnormal separation of germ cell layers in the 3rd week of embryonic life, leading to persistence of entodermal elements in the spinal canal. The common location is cervical and ventral to the spinal cord. The lesions have been recognized as being entodermal in origin by such markers as vertebral anomalies, gut cysts, bowel reduplication and the presence of keratin markers. Three unusual cases of childhood craniocervical intradural neurenteric cysts in patients aged 4-8 years are described. These cysts were located in the ventral aspect of the spinal canal ranging from the craniocervical junction to the C6 level and were associated with bony anomalies such as a bifid clivus, hemivertebrae and blocked vertebrae. Two patients presented with signs of cervical cord compression and 1 with recurrent meningitis. One child with an anterior cervicomedullary region mass had undergone unsuccessful transoral transpalatal exploration and subsequently required excision with a dorsolateral approach. The second patient, after two successful attempts at drainage via laminectomies, required myelotomy of the spinal cord to allow excision. Thus the patient with the lesion from C4 through C6 underwent vertebrectomy and anterior excision with a C4 through C7 strut graft fusion. There were bony and vascular anomalies which would have complicated a dorsal approach. Pathological diagnosis of neurenteric cysts was based on the findings of nonciliated mucin producing small cuboidal or columnar epithelium lining a cystic cavity. Neurenteric cysts are uncommon congenital anomalies which may become symptomatic in the pediatric population.(ABSTRACT TRUNCATED AT 250 WORDS)

Cervical Vertebrae↗
PubMed1995

Cytotoxicity of cis-parinaric acid in cultured malignant gliomas.

The cytotoxic effects of cis-parinaric acid, a plant-derived 18-carbon polyunsaturated fatty acid, were assessed in vitro on normal and neoplastic glia. After being incubated for 24 hours in the presence of 12 mumol/L cis-parinaric acid, 36B10 glioma cultures demonstrated nearly 90% toxicity (unpaired Student's t test, P < 0.001). Similar results were obtained after the exposure of C6 rat glioma cultures, A172 human glioma cultures, and U-937 human monocytic leukemia cultures to cis-parinaric acid. In contrast, fetal rat astrocytes incubated with 12 mumol/L cis-parinaric acid demonstrated no significant toxicity (3% reduction, P = 0.12); fetal rat astrocytes showed only 20% toxicity after exposure to 40 mumol/L cis-parinaric acid (P = 0.001). The cytotoxic effects of cis-parinaric acid were antagonized with the addition of equimolar concentrations of alpha-tocopherol. Enzyme immunoassay of treated 36B10 glioma supernatant fluid for 8-isoprostane (a known oxidative metabolite) demonstrated a 10-fold increase of 8-isoprostane over 24 hours (123.0 +/- 10.3 versus 10.0 +/- 0.7 pg/ml for control, P < 0.001). These studies indicate that cis-parinaric acid may be significantly cytotoxic to malignant glioma cells in concentrations that spare normal astrocytes and that the mechanism of cytotoxicity is related to an oxidative process. The selective cytotoxic effect of cis-parinaric acid we describe represents the first step in the development of new chemotherapeutic agents for gliomas; these new agents act by preferentially enhancing lipid peroxidation in neoplastic cells.

Animals↗