Polymethylmethacrylate causes prolonged pulmonary hypertension during fat embolism: a study in sheep

Mechanical Cavity Creation with Curettage and Vacuum Suction (Q-VAC) in Lytic Vertebral Body Lesions with Posterior Wall Dehiscence and Epidural Mass before Cement Augmentation

Background and Objectives: We describe a novel technique for percutaneous tumor debulking and cavity creation in patients with extensive lytic lesions of the vertebral body including posterior wall dehiscence prior to vertebral augmentation (VA) procedures. The mechanical cavity is created with a combination of curettage and vacuum suction (Q-VAC). Balloon kyphoplasty and vertebral body stenting are used to treat neoplastic vertebral lesions and might reduce the rate of cement leakage, especially in presence of posterior wall dehiscence. However, these techniques could theoretically lead to increased intravertebral pressure during balloon inflation with possible mobilization of soft tissue tumor through the posterior wall, aggravation of spinal stenosis, and resultant complications. Creation of a void or cavity prior to balloon expansion and/or cement injection would potentially reduce these risks. Materials and Methods: A curette is coaxially inserted in the vertebral body via transpedicular access trocars. The intravertebral neoplastic soft tissue is fragmented by multiple rotational and translational movements. Subsequently, vacuum aspiration is applied via one of two 10 G cannulas that had been introduced directly into the fragmented lesion, while saline is passively flushed via the contralateral cannula, with lavage of the fragmented solid and fluid-necrotic tumor parts. Results: We applied the Q-VAC technique to 35 cases of thoracic and lumbar extreme osteolysis with epidural mass before vertebral body stenting (VBS) cement augmentation. We observed extravertebral cement leakage on postoperative CT in 34% of cases, but with no clinical consequences. No patients experienced periprocedural respiratory problems or new or worsening neurological deficit. Conclusion: The Q-VAC technique, combining mechanical curettage and vacuum suction, is a safe, inexpensive, and reliable method for percutaneous intravertebral tumor debulking and cavitation prior to VA. We propose the Q-VAC technique for cases with extensive neoplastic osteolysis, especially if cortical boundaries of the posterior wall are dehiscent and an epidural soft tissue mass is present.

First-time systematic postoperative clinical assessment of a minimally invasive approach for lumbar ventrolateral vertebroplasty in the large animal model sheep

BACKGROUND CONTEXT

Large animal models are highly recommended for meaningful preclinical studies, including the optimization of cement augmentation for vertebral body defects by vertebroplasty/kyphoplasty.

PURPOSE

The aim of this study was to perform a systematic characterization of a strictly minimally invasive in vivo large animal model for lumbar ventrolateral vertebroplasty.

STUDY DESIGN/ SETTING

This is a prospective experimental animal study.

METHODS

Lumbar defects (diameter 5 mm; depth approximately 14 mm) were created by a ventrolateral percutaneous approach in aged, osteopenic, female sheep (40 Merino sheep; 6-9 years; 68-110 kg). L1 remained untouched, L2 was left with an empty defect, and L3 carried a defect injected with a brushite-forming calcium phosphate cement (CPC). Trauma/functional impairment, surgical techniques (including drill sleeve and working canula with stop), reproducibility, bone defects, cement filling, and functional cement augmentation were documented by intraoperative incision-to-suture time and X-ray, postoperative trauma/impairment scores, and ex vivo osteodensitometry, microcomputed tomography (CT), histology, static/fluorescence histomorphometry, and biomechanical testing.

RESULTS

Minimally invasive vertebroplasty resulted in short operation times (28±2 minutes; mean±standard error of the mean) and X-ray exposure (1.59±0.12 minutes), very limited local trauma (score 0.00±0.00 at 24 hours), short postoperative recovery (2.95±0.29 hours), and rapid decrease of the postoperative impairment score to 0 (3.28±0.36 hours). Reproducible defect creation and cement filling were documented by intraoperative X-ray and ex vivo conventional/micro-CT. Vertebral cement augmentation and osteoconductivity of the CPC was verified by osteodensitometry (CPC>control), micro-CT (CPC>control and empty defect), histology/static histomorphometry (CPC>control and empty defect), fluorescence histomorphometry (CPC>control; all p<.05 for 3 and 9 months), and compressive strength measurements (CPC numerically higher than control; 102% for 3 months and 110% for 9 months).

CONCLUSIONS

This first-time systematic clinical assessment of a minimally invasive, ventrolateral, lumbar vertebroplasty model in aged, osteopenic sheep resulted in short operation times, rapid postoperative recovery, and high experimental reproducibility. This model represents an optimal basis for standardized evaluation of future studies on vertebral augmentation with resorbable and osteoconductive CPC.

Cardiac Emboli Documented by Intraoperative Transesophageal Echocardiogram During Administration of a Topical Hemostatic Agent Prior to Pedicle Subtraction Osteotomy

STUDY DESIGN

This is a case report.

OBJECTIVE

Describe the occurrence of cardiac emboli recorded on transesophageal echocardiogram (TEE) after the injection of a topical hemostatic agent into a vertebra prior to performing a pedicle subtraction osteotomy (PSO).

SUMMARY OF BACKGROUND DATA

Hemostasis during spinal surgery is critical for adequate visualization and to reduce the risk of perioperative complications. Adult spinal deformity surgery can involve performing PSOs which are useful in cases of fixed spinal deformities and are associated with increased blood loss secondary to epidural and cancellous bleeding. Prior to performing a PSO, a topical hemostatic agent can be injected into the vertebra through the pedicle screw pilot holes in an attempt to decrease cancellous bleeding. Injected hemostatic agents can pressurize the vertebral body similar to cementation in vertebroplasty and during fracture reaming and prosthetic implantation in the femur. Patients with cardiac defects such as patent foramen ovale or atrial septal defect may be more prone to systemic embolic events resulting in morbidity or mortality.

METHODS

We injected a topical hemostatic matrix agent through the pedicle screw pilot holes into the L1 vertebral body prior to performing a PSO while simultaneously recording with TEE.

RESULTS

The TEE recorded large visible emboli traveling through the heart into the pulmonary vasculature. The patient remained stable throughout the remainder of the case and a postoperative spiral computed tomography (CT) scan was negative for filling defects. The patient had an uneventful hospital course.

CONCLUSION

Questions remain about the exact consistency of these emboli, when they are most likely to occur, how much cardiopulmonary insult can be tolerated without resulting in complications, or how to prevent their occurrence. Patients undergoing spinal surgery with the plan to inject hemostatic matrix agents into the vertebral body may benefit from a preoperative TEE to reduce the risk of complications associated with embolic events, especially in patients with undiagnosed patent foramen ovale or atrial septal defect.

LEVEL OF EVIDENCE

5.

Fat embolism syndrome following percutaneous vertebroplasty: a case report

BACKGROUND CONTEXT

Vertebroplasty is commonly performed for management of pain associated with vertebral compression fractures. There have been two previous reports of fatal fat embolism following vertebroplasty. Here we describe a case of fat embolism syndrome following this procedure, and also provide fluoroscopic video evidence consistent with this occurrence.

PURPOSE

The purpose of this study was to review the literature and report a case of fat embolism syndrome in a patient who underwent percutaneous vertebroplasty for compression fracture.

STUDY DESIGN/SETTING

The study design for this manuscript was of a clinical case report.

METHODS

A 68-year-old woman who developed sudden back pain with minimal trauma was found to have a T6 vertebral compression fracture on radiographs and bone scans. Percutaneous vertebroplasty of T5 and T6 was performed.

RESULTS

Fluoroscopic imaging during the procedure demonstrated compression and rarefaction of the fractured vertebra associated with changes in intrathoracic pressure. Immediately after the procedure, the patient's back pain resolved and she was discharged home. Two days later, she developed increasing respiratory distress, confusion, and chest pain. A petechial rash on her upper arms also appeared. No evidence of bone cement leakage or pulmonary filling defects were seen on computed tomography-pulmonary angiography. Brain magnetic resonance imaging demonstrated hyperintensities in the periventricular and subcortical white matter on T2/fluid-attenuated inversion recovery sequences. A diagnosis of fat embolism syndrome was made, and the patient recovered with conservative management.

CONCLUSIONS

Percutaneous vertebroplasty is a relatively safe and simple procedure, reducing pain and improving functional limitations in patients with vertebral fractures. This case demonstrates an uncommon yet serious complication of fat embolism syndrome. Clinicians must be aware of this complication when explaining the procedure to patients and provide prompt supportive care when it does occur.

No difference in mortality between cemented and uncemented hemiprosthesis for elderly patients with cervical hip fracture. A prospective randomized study on 334 patients over 75 years

INTRODUCTION

Laboratory and human mechanical studies indicated that chemical substances in bone cement had toxic and prothrombotic effects. Impaction of cement added a mechanical trauma to the reaming and broaching procedure and contributed to a substantial local and systemic thrombin generation. Case reports and materials have indicated bone cement as the immediate trigger of cardiorespiratory and vascular dysfunction, occasionally fatal, and described as the bone cement implantation syndrome. In spite of this knowledge, bone cement has gained popularity and is widely used for prosthesis fixation, possibly due to a lack of clinical evidence supporting the basic science indicating bone cement as a mortality risk factor.

METHOD

This is a prospective, randomized study comparing cemented and non cemented hemiprosthesis on patients suffering a dislocated cervical hip fracture. Perioperative characteristics and 1 year mortality differences between the groups were estimated.

PATIENTS

Hundred and thirty-four patients over 75 years were enrolled from two hospitals in Norway. Average age was 84 years, 75 % were female and 60 % had symptomatic comorbidities.

RESULTS

We find no difference in mortality between cemented and uncemented hemiprosthesis up to 1 year (HR 0.77, 95 % CI 0.51-1.18, p = 0.233). However, statistically significant reduced operation time and blood loss were found in the non-cemented group. (mean difference of 13 min, 95 % CI 4-22, p = 0.004 and 92 ml 95 % CI 3-181, p = 0.043, respectively).

CONCLUSION

Installation of non-cemented hemiprostheses in elderly with hip fracture may have benefits perioperatively regarding operation time and bleeding, and do not seem to influence 1 year mortality relative to cemented implants.

Fat embolism syndrome in a child with dystonia musculorum deformans

A 16-year-old boy with dystonia musculorum deformans underwent an operation for removal of femoral implants and excision of the prominence at the greater trochanter of the left hip. He was found to have fat embolism syndrome at postoperative day 1 as evidenced by confusion, respiratory symptoms, chest radiograph changes, raised erythrocyte sedimentation rate, thrombocytopenia and fat in the urine and sputum.

Cardiovascular changes after PMMA vertebroplasty in sheep: the effect of bone marrow removal using pulsed jet-lavage

Clinically, the displacement of intravertebral fat into the circulation during vertebroplasty is reported to lead to problems in elderly patients and can represent a serious complication, especially when multiple levels have to be treated. An in vitro study has shown the feasibility of removing intravertebral fat by pulsed jet-lavage prior to vertebroplasty, potentially reducing the embolization of bone marrow fat from the vertebral bodies and alleviating the cardiovascular changes elicited by pulmonary fat embolism. In this in vivo study, percutaneous vertebroplasty using polymethylmethacrylate (PMMA) was performed in three lumbar vertebrae of 11 sheep. In six sheep (lavage group), pulsed jet-lavage was performed prior to injection of PMMA compared to the control group of five sheep receiving only PMMA vertebroplasty. Invasive recording of blood pressures was performed continuously until 60 min after the last injection. Cardiac output and arterial blood gas parameters were measured at selected time points. Post mortem, the injected cement volume was measured using CT and lung biopsies were processed for assessment of intravascular fat. Pulsed jet-lavage was feasible in the in vivo setting. In the control group, the injection of PMMA resulted in pulmonary fat embolism and a sudden and significant increase in mean pulmonary arterial pressure. Pulsed jet-lavage prevented any cardiovascular changes and significantly reduced the severity of bone marrow fat embolization. Even though significantly more cement had been injected into the lavaged vertebral bodies, significantly fewer intravascular fat emboli were identified in the lung tissue. Pulsed jet-lavage prevented the cardiovascular complications after PMMA vertebroplasty in sheep and alleviated the severity of pulmonary fat embolism.

Fat embolism

Fat embolism refers to the presence of fat droplets within the peripheral and lung microcirculation with or without clinical sequelae. The pathologic consequences of fat embolism are well recognized. Fat embolism is most often associated with trauma and orthopedic injuries. Fat embolism syndrome (FES) is a serious manifestation of fat embolism that involves a cascade of clinical signs such as petechial rash, deteriorating mental status, and progressive respiratory insufficiency, usually occurring within 24 hours of injury. This article reviews the definition, epidemiology, etiology, pathophysiology, clinical presentation, diagnosis, management, and prognosis of FES.

Histopathological and biochemical changes following fat embolism with administration of corn oil micelles

Several experimental models have been used to produce intravascular fat embolism. We have developed a simple technique to induce fat embolism using corn oil emulsified with distilled water to form fatty micelles. Fat embolism was produced by intravenous administration of these fatty micelles in anaesthetised rats, causing alveolar oedema, haemorrhage and increased lung weight.

Histopathological examination revealed fatty droplets and fibrin thrombi in the lung, kidney and brain. The arteriolar lumen was filled with fatty deposits. Following fat embolism, hypoxia and hypercapnia occurred. The plasma phospholipase A2, nitrate/nitrite, methylguidanidine and proinflammatory cytokines were significantly increased. Mass spectrometry showed that the main ingredient of corn oil was oleic acid.

This simple technique may be applied as a new animal model for the investigation of the mechanisms involved in the fat embolism syndrome.

Monitoring and controlling intramedullary pressure increase in long bone instrumentation: a study on sheep

Intramedullary reamed nailing causes elevation in intramedullary pressure and extravazation of intramedullary contents into the venous blood system. This study investigated the effect of an intramedullary suction system, recently developed in our laboratory, on the pressure and fat extravazation in isolated bovine bone and a sheep model. During reaming, the pressure with and without suction was recorded at each step of the procedure. Hemodynamic parameters of mean arterial blood pressure, pulmonary artery pressure, pulmonary arterial CO(2) (PaCO(2)), heart rate, and oxygen saturation were monitored. Blood and lung tissue samples were collected for the examination of medullary fat intravazation. The increases of intramedullary pressure were dramatically reduced in the suction group (p < 0.05) in both in vitro and in vivo experiments. PaCO(2) was significantly lower in the suction group than nonsuction group (32 vs. 40 mmHg, respectively, p = 0.02), while oxygen saturation was higher in the suction group (99 vs. 91 mmHg, respectively, p = 0.009). Histological data revealed a significant higher count of fat emboli in sheep lung tissue in the nonsuction group. Total lipids in lung specimens was lower in the suction group (7.6 mg/g tissue) than in the nonsuction group (13.6 mg/g, p = 0.04). The suction system appears to control the surge in intramedullary pressure and therefore prevent fat embolism.

Kyphoplasty. A treatment for osteoporotic vertebral compression fractures

Patients experience more than 700,000 osteoporotic vertebral compression fractures each year in the United States, primarily because of bone brittleness and the inability of the vertebrae to resist increased forces applied to them. Patients diagnosed with this type of fracture are given the option of conservative or operative treatment approaches. Although a typical compression fracture generally heals in 6 to 12 weeks, patients may be offered the kyphoplasty procedure, which reduces the fracture and stabilizes it with cement. Although this procedure is not without risk, it is deemed a safe and effective treatment option. This article reviews the indications, implications, and care provided to patients pursuing kyphoplasty after osteoporotic vertebral compression fracture.

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.

Vertebral augmentation in osteoporotic fractures

Osteoporotic vertebral compression fractures result in an enormous medical, social and economic burden to society. Here, we review osteoporotic vertebral compression fractures, focusing on both their diagnosis and the treatment options, particularly vertebral augmentation.

Plasma levels of endothelin-1 after a pulmonary embolism of bone marrow fat

BACKGROUND

During orthopedic surgery, embolization of bone marrow fat can lead to potentially fatal, intra-operative cardiovascular deterioration. Vasoactive mediators may also be released from the bone marrow and contribute to these changes. Increased plasma levels of endothelin-1 (ET-1) have been observed after pulmonary air and thrombo-embolism. The role of ET-1 in the development of acute cardiovascular deterioration as a result of bone marrow fat embolization during vertebroplasty was therefore investigated.

METHODS

Bone cement 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 60 min after the last injection. Cardiac output, arterial and mixed venous blood gas parameters and plasma ET-1 concentrations were measured at selected time points. Post-mortem, lung biopsies were taken for analysis of intravascular fat.

RESULTS

Cement injections resulted in a sudden (within 1 min) and severe increase in pulmonary arterial pressure (>100%). Plasma concentrations of ET-1 started to increase after the second injection, but no significant changes were observed. Intravascular fat and bone marrow cells were present in all lung lobes.

CONCLUSION

Cement injections into vertebral bodies elicited fat embolism resulting in subsequent cardiovascular changes that were characterized by an increase in pulmonary arterial pressure. Cardiovascular complications as a result of bone marrow fat embolism should thus be considered in patients undergoing vertebroplasty. No significant changes in ET-1 plasma values were observed. Thus, ET-1 did not contribute to the acute cardiovascular changes after fat embolism.

Sildenafil Prevents Cardiovascular Changes after Bone Marrow Fat Embolization in Sheep

Background:

Sudden, intraoperative cardiovascular deterioration as a result of pulmonary embolization of bone marrow fat is a potentially fatal complication during total hip and knee arthroplasty, intramedullary nailing, and spine surgery. Anesthetic management is challenging in the presence of increased right ventricular afterload due to pulmonary hypertension. Selective pulmonary vasodilation may be an appropriate prophylactic or therapeutic measure. The effect of sildenafil (phosphodiesterase inhibitor) on cardiovascular deterioration after bone marrow fat embolization was therefore investigated.

Methods:

Bone cement (polymethylmethacrylate) was injected into three lumbar vertebrae in 12 sheep. Invasive blood pressures and heart rate were recorded continuously until 60 min after the last injection. Cardiac output and arterial and mixed venous blood gas variables were measured at selected time points. Before the first cement injection, 6 animals received a bolus injection (0.7 mg/kg) of sildenafil, with continuous infusion (0.2 mg · kg−1 · h−1) thereafter. Postmortem lung and kidney biopsies were taken for semiquantitative analysis of intravascular fat.

Results:

Fat embolism was associated with a transient increase (21 ± 7mmHg) in pulmonary arterial pressure. A transient decrease in arterial blood pressure and temporary increases in central venous pressure and dead space were also observed. No significant changes in any cardiovascular variable were observed after fat embolism in the sildenafil group. There was significantly (P &lt; 0.05) less intravascular fat in the lungs of the sildenafil (median count of 5 emboli per microscopic view) compared with the control group (median count of 1).

Conclusions:

Administration of sildenafil prevented the acute cardiovascular complications after bone marrow fat embolism in sheep.