Nikolaus Aebli

Fat embolism and acute hypotension during vertebroplasty: an experimental study in sheep.

Study Design. An experimental study of cardiovascular complications that arise during vertebroplasty was conducted. Objective. To investigate the sequential occurrence of fat embolism and hypotension during vertebroplasty. Summary of Background Data. Vertebroplasty, the augmentation of vertebrae with polymethylmethacrylate, is a technique for treating osteoporotic compression fractures and achieving prophylactic stabilization of osteoporotic vertebral bodies at risk of fracture. However, there is concern that fat embolism and acute hypotension could occur as in a variety of other orthopedic procedures. Methods. In six sheep, 6 mL of polymethylmethacrylate was injected unilaterally into L1. Transesophageal echocardiography monitored the pulmonary artery for echodense particles. Heart rate, arterial and venous pressures, and blood gas values were recorded before and for 25 minutes after injection. The lungs were subjected to postmortem histologic evaluation and compared with lung specimens from two sheep that had not undergone vertebroplasty. Results. Injection of cement elicited a very rapid decrease in heart rate (within 2 ± 1 seconds) and a rapid increase in venous pressure (within 3 ± 1 seconds), which was followed by a fall in arterial pressure (within 5 ± 2 seconds) (phase 1). Thereafter, showers of echogenic material appeared (within 6 ± 1 seconds) and lasted for 138 ± 36 seconds. A second more severe fall in arterial pressure was observed beginning at 18 ± 2 seconds (phase 2). The injection resulted in an increase in partial pressure of carbon dioxide and a decrease in pH. The histology showed intravascular fat globules and bone marrow cells in lung tissue. Conclusions. The results suggest that immediately after cement injection, there was a reflex fall in heart rate and arterial pressure. The second fall in arterial pressure was a consequence of fat emboli passing through the heart and getting trapped in the lungs.

Influence of different commercial scaffolds on the in vitro differentiation of human mesenchymal stem cells to nucleus pulposus-like cells

IntroductionCell-based therapies for regeneration of the degenerated intervertebral disc (IVD) are an alternative to current surgical intervention. Mesenchymal stem cells (MSCs), in combination with a scaffold, might be ideal candidates for regenerating nucleus pulposus (NP), the pressure-distributing part of the IVD. While the use of growth factors for MSCs differentiation currently receives major attention, in this study we compare the performance of sponge-like matrixes in supporting cell differentiation into NP-like cells.Materials and methodsFour types matrixes approved as medical devices for other applications were tested as scaffolds for MSCs: two made of equine or porcine collagen, one of gelatin and one of chitosan. Bone marrow-derived human MSCs were seeded in these scaffolds or embedded in alginate, as a three-dimensional control. After five weeks in culture, NP-like differentiation of the cell-scaffold constructs was analyzed by qRT-PCR, histology, total DNA quantification, proteoglycan accumulation and immunohistochemistry.ResultsMSCs in collagen matrixes and gelatin produced more mRNA and proteins of the chondrogenic markers collagen type I, collagen type II (COL2) and aggrecan (ACAN), when compared with cells embedded in alginate or chitosan. Proteoglycan accumulation and cell survival were also higher in collagen and gelatin matrixes. Gene expression results were also confirmed by histological and immunohistochemical staining. In contrast to alginate control, the gene expression of the undesired bone marker osteopontin was lower in all tested groups. In porcine collagen supports, MSC expression ratio between COL2/ACAN closely resembled the expression of nucleus pulposus cells, but gene expression of recently described NP markers keratin19, PAX1 and FOXF1 was lower.ConclusionsCollagen supports provide a readily available, medically approved and effective scaffold for chondrogenic differentiation in vitro, but the phenotype of differentiated MSCs is not yet completely equivalent to that of NP cells.

In vivo temperature profile of intervertebral discs and vertebral endplates during vertebroplasty - An experimental study in sheep

Study Design. Experimental study of temperature profiles during vertebroplasty. Objectives. To define accurate temperature profiles during vertebroplasty in an in vivo animal model. Summary of Background Data. Controversy still exists whether vertebroplasty achieves its analgesic effect by stabilizing fracture fragments or due to thermal damage of sensory nerves inside the vertebral body. Furthermore, the energy release during cement polymerization may cause thermal injury to the spinal cord or intervertebral discs. Methods. A total of 4.0 mL PMMA was injected into three lumbar vertebrae of four skeletally mature mixed-bred ewes. Nine separate K-type thermocouples were placed into 12 vertebrae and their adjacent intervertebral discs. Temperature changes were recorded continuously before, during, and after the injection. Results. The highest peak temperatures were measured at the cranial endplate (mean 42.4 ± 8.8 C) and in the center of the vertebral body (mean 43.3 ± 6.9 C). Temperatures stayed above 40 C for approximately 2.5 minutes. Peak temperatures in the discs and at the dorsal wall (closest to spinal cord) did not exceed 41 C and 47 C and stayed above 40 C for approximately 1.5 minutes. Conclusions. The intervertebral discs and the spinal cord do not seem to be in danger of thermal damage during vertebroplasty. The measured energy does not seem to be sufficient for the palliative effect achieved by vertebroplasty.

Pressurization of vertebral bodies during vertebroplasty causes cardiovascular complications: an experimental study in sheep.

Study Design. An experimental study of cardiovascular complications arising during vertebroplasty (VP) of multiple levels in sheep. Objectives. To investigate the effect of pressurizing vertebral bodies during VP using different materials in the development of fat embolism (FE) and any associated cardiovascular changes. Summary of Background Data. Polymethylmethacrylate (PMMA) is the material of choice for VP. However, PMMA has several disadvantages, such as toxicity, exothermic curing, uncertain long-term biomechanical effects, and biocompatibility. Alternative materials are being developed for VP; however, there is the concern that an increase in intraosseous pressure and displacement of bone marrow contents could lead to FE and hypotension during VP regardless of what type of materials is used. Methods. In 20 sheep, four vertebral bodies were augmented either with PMMA or bone wax. Heart rate; arterial, central venous, and pulmonary artery pressure; cardiac output; and blood gas values were recorded. Postmortem the lungs were subjected to histologic evaluation. Results. The consecutive augmentation of four vertebral bodies with PMMA induced a cumulative FE that gradually deteriorated baseline mean arterial blood pressure (MABP) and blood gas values. The augmentation with bone wax resulted in similar cardiovascular changes and amount of intravascular fat in the lungs. Conclusion. There are potential cardiovascular complications during VP of multiple levels regardless of the augmentation material used. The deteriorating baseline MABP during VP is associated with the pressurization of the vertebral bodies rather than with the use of polymethylmethacrylate.

Influence of Bone Marrow Fat Embolism on Coagulation Activation in an Ovine Model of Vertebroplasty

BACKGROUND Intraoperative cardiovascular deterioration as a result of pulmonary embolization of bone marrow fat is a potentially serious complication during vertebroplasty. The release of fatty material and thromboplastin from the bone marrow cavity during vertebroplasty may activate the coagulation cascade resulting in thrombogenesis, and pharmacological prophylaxis may therefore prevent cardiovascular complications. Thus, the effects of bone marrow fat embolism on coagulation activation during vertebroplasty were investigated with use of an animal model. METHODS Polymethylmethacrylate was injected into three lumbar vertebrae of six sheep in order to force bone marrow fat into the circulation. Invasive blood pressures and heart rate were recorded continuously until sixty minutes after the last injection. Cardiac output, arterial and mixed venous blood gas parameters, and coagulation parameters were measured at selected time-points. Postmortem lung biopsy specimens were assessed for the presence of intravascular fat. RESULTS Embolization of bone marrow fat resulted in a sudden and dramatic increase in mean pulmonary arterial pressure and a decrease in mean arterial blood pressure. There were no significant changes in any coagulation parameter from before the injection to after the injection. Intravascular fat and bone marrow cells were present in all lung lobes. CONCLUSIONS Injection of polymethylmethacrylate into vertebral bodies caused embolization of bone marrow fat with subsequent transient cardiovascular deterioration, but no changes in coagulation parameters were observed. Thromboembolism did not contribute to the observed cardiovascular changes.

The Torg-Pavlov ratio for the prediction of acute spinal cord injury after a minor trauma to the cervical spine

BACKGROUND CONTEXT Acute cervical spinal cord injury (SCI) has been observed in some patients after a minor trauma to the cervical spine. The discrepancy between the severity of the trauma and the clinical symptoms has been attributed to spinal canal stenosis. However, to date, there is no universally established radiological parameter for identifying critical spinal stenosis in these patients. The spinal canal-to-vertebral body ratio (Torg-Pavlov ratio) has been proposed for assessing developmental spinal canal stenosis. The relevance of the Torg-Pavlov ratio for predicting the occurrence and severity of acute cervical SCI after a minor trauma to the cervical spine has not yet been established. PURPOSE To investigate the Torg-Pavlov ratio values of the cervical spine in patients suffering from acute cervical SCI after a minor trauma to the cervical spine and the use of the Torg-Pavlov ratio for identifying patients at risk of cervical SCI and predicting the severity and course of symptoms. STUDY DESIGN/SETTING Retrospective radiological study of consecutive patients. PATIENT SAMPLE Forty-five patients suffering from acute cervical SCI and 68 patients showing no neurologic symptoms after a minor trauma to the cervical spine. OUTCOME MEASURES Midvertebral sagittal cervical spinal canal diameter and the sagittal vertebral body diameter. Calculation of the Torg-Pavlov ratio values. METHODS Conventional lateral radiographs of the cervical spine (C3-C7) were analyzed to determine the Torg-Pavlov ratio values. Receiver operating characteristic curves were calculated for evaluating the classification accuracy of the Torg-Pavlov ratio for predicting SCI. RESULTS The Torg-Pavlov ratio values in the SCI group were significantly (p<.04) smaller compared with that in the control group. A Torg-Pavlov ratio cutoff value of 0.7 yielded the greatest positive likelihood ratio for predicting the occurrence of SCI. However, there were no significant differences in the Torg-Pavlov ratio values between the different American Spinal Injury Association Impairment Score groups and between patients with complete, partial, and no recovery of symptoms. CONCLUSIONS Developmental cervical spinal canal stenosis assessed by the Torg-Pavlov ratio was characteristic for patients suffering from acute cervical SCI after a minor trauma to the cervical spine. Patients at risk of SCI after a minor trauma to the cervical spine can be identified by applying a Torg-Pavlov ratio cutoff value of 0.7. Other factors in addition to the spinal canal-to-vertebral body ratio affect the severity and course of symptoms as a result of cervical SCI.

Predicting the risk and severity of acute spinal cord injury after a minor trauma to the cervical spine

BACKGROUND CONTEXT Acute spinal cord injury (SCI) after a minor trauma to the cervical spine has been reported in patients without preceding neurologic symptoms. Spinal canal stenosis may be the reason for the discrepancy between the severity of the injury and that of the trauma. The spinal canal to vertebral body ratio is often used to assess canal stenosis on conventional radiographs. However, the ratio does not appraise soft-tissue stenosis and canal narrowing at the level of the intervertebral disc. Parameters measured on magnetic resonance (MR) images may thus be more meaningful. The relevance of MR image parameters for predicting the risk and severity of acute SCI in patients after a minor trauma to the cervical spine has not yet been established. PURPOSE To investigate MR image parameters of the cervical spine in patients suffering from acute SCI after a minor trauma to the cervical spine. To investigate the use of these parameters for predicting the risk and severity of acute cervical SCI after a minor trauma to the cervical spine. STUDY DESIGN/SETTING Retrospective radiological study of consecutive patients. PATIENT SAMPLE Fifty-two patients suffering from acute cervical SCI and 131 patients showing no neurologic deficits after a minor trauma to the cervical spine. OUTCOME MEASURES On sagittal MR images: vertebral body diameter, midvertebral canal diameter, disc-level canal diameter, and spinal cord diameter. On lateral conventional radiographs: vertebral body diameter and midvertebral canal diameter. METHODS Conventional lateral radiographs and sagittal T2-weighted MR images of the cervical spine (C3-C7) were analyzed. The following calculations were performed using measurements from MR images: the spinal canal to vertebral body ratio, the space available for the cord, and the canal-to-cord ratio. Using measurements from conventional radiographs, the spinal canal to vertebral body ratio was determined. Receiver-operating curves were calculated for evaluating the classification accuracy of the different parameters for predicting the risk, severity, and course of SCI. RESULTS All investigated MR image parameters in the SCI group were significantly (p<.001) smaller compared with the control group. However, there was no significant (p>.9) difference in any parameter among the different American Spinal Injury Association impairment score groups. A cutoff value of 8.0 mm for the minimal sagittal disc-level canal diameter yielded the largest positive predictive value and likelihood ratio for predicting SCI. CONCLUSIONS Patients at risk of acute SCI after a minor trauma to the cervical spine can be identified by applying a disc-level canal diameter cutoff value (measured on MR images) of 8 mm. Additional factors to the radiological characteristics of the spinal canal affect the severity of acute SCI after a minor trauma to the cervical spine.

Development of a screening tool predicting the transition from acute to chronic low back pain for patients in a GP setting: protocol of a multinational prospective cohort study

BackgroundLow back pain (LBP) is by far the most prevalent and costly musculoskeletal problem in our society today. Following the recommendations of the Multinational Musculoskeletal Inception Cohort Study (MMICS) Statement, our study aims to define outcome assessment tools for patients with acute LBP and the time point at which chronic LBP becomes manifest and to identify patient characteristics which increase the risk of chronicity.MethodsPatients with acute LBP will be recruited from clinics of general practitioners (GPs) in New Zealand (NZ) and Switzerland (CH). They will be assessed by postal survey at baseline and at 3, 6, 12 weeks and 6 months follow-up. Primary outcome will be disability as measured by the Oswestry Disability Index (ODI); key secondary endpoints will be general health as measured by the acute SF-12 and pain as measured on the Visual Analogue Scale (VAS). A subgroup analysis of different assessment instruments and baseline characteristics will be performed using multiple linear regression models.This study aims to examine1. Which biomedical, psychological, social, and occupational outcome assessment tools are identifiers for the transition from acute to chronic LBP and at which time point this transition becomes manifest2. Which psychosocial and occupational baseline characteristics like work status and period of work absenteeism influence the course from acute to chronic LBP3. Differences in outcome assessment tools and baseline characteristics of patients in NZ compared with CH.DiscussionThis study will develop a screening tool for patients with acute LBP to be used in GP clinics to access the risk of developing chronic LBP. In addition, biomedical, psychological, social, and occupational patient characteristics which influence the course from acute to chronic LBP will be identified. Furthermore, an appropriate time point for follow-ups will be given to detect this transition. The generalizability of our findings will be enhanced by the international perspective of this study.Trial registration[Clinical Trial Registration Number, ACTRN12608000520336]

Characteristics and surgical management of neuropathic (Charcot) spinal arthropathy after spinal cord injury

BACKGROUND CONTEXT Neuropathic (Charcot) spinal arthropathy (CSA) is a rare but progressive and severe degenerative disease that develops in the absence of deep sensation, for example, after spinal cord injury. The diagnosis of CSA is often delayed as a result of the late onset or slow progression of the disease and the nonspecific nature of the reported clinical signs. Considering risk factors of CSA in combination with the common clinical signs may facilitate timely diagnosis and prevent severe presentation of the disease. However, there is a lack of data concerning the early signs and risk factors of CSA. Furthermore, the complications and outcomes after surgical treatment are documented insufficiently. PURPOSE To investigate the early signs and risk factors of CSA after spinal cord injury, as well as the complications and outcome after surgical treatment. STUDY DESIGN Retrospective case series from a single center. PATIENT SAMPLE Twenty-eight patients with 39 Charcot joints of the spine. OUTCOME MEASURES Clinical signs, radiological signs, risk factors, and complications. METHODS The case histories and radiological images of patients suffering from CSA were investigated. RESULTS The first clinical symptoms included spinal deformity, sitting imbalance, and localized back pain. Long-segment stabilization, laminectomy, scoliosis, and excessive loading of the spine were identified as risk factors for the development of the disease. Postoperative complications included implant loosening, wound healing disturbance, and development of additional Charcot joints. All patients were able to return to their previous levels of activities. CONCLUSIONS Radiological follow-up of the entire thoracic and lumbar spine should be performed in paraplegic patients. Risk factors in combination with typical symptoms should be considered to facilitate early detection. Functional restoration can be achieved with appropriate surgical techniques.

Cardiovascular Changes after Pulmonary Cement Embolism: An Experimental Study in Sheep

BACKGROUND AND PURPOSE: Most cement leaks during vertebroplasty are asymptomatic, but pulmonary cement embolism has been reported to cause cardiovascular disturbances and even death. Adding hydroxyapatite (HA) to polymethylmethacrylate (PMMA) cement to reduce the quantity of barium may aggravate cardiovascular deterioration in the event of cement embolism by activating coagulation. Thus, we investigated the cardiovascular changes after pulmonary cement embolism of PMMA with and without HA. MATERIALS AND METHODS: In 13 sheep, cement (2.0 mL) was injected into the pulmonary trunk. Two different cements were used: 1) standard PMMA and 2) PMMA with 10% HA (PMMA & HA). Arterial, central venous and pulmonary arterial pressures, heart rate, and cardiac output were monitored continuously until 60 minutes after the injection. Blood gases and coagulation parameters (antithrombin, D-dimer) were measured before and after injection. RESULTS: Mean pulmonary arterial pressure had increased by approximately 9% (PMMA) and 14% (PMMA & HA) 1 minute after injection and stayed elevated. There were no significant differences between the groups. No evidence of thromboembolism was detected. CONCLUSION: Cement embolism did not result in clinically significant pulmonary arterial hypertension. Adding HA to PMMA cement did not cause more severe cardiovascular changes.