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

Tips and tricks for using cement augmentation of pedicle screws and vertebral body replacements-A literature review supported by two case reports

BACKGROUND

The prevalence of osteoporosis is escalating alongside an aging global population, increasing the demand for spinal surgeries, including those necessitating cement augmentation for enhanced construct stability.

OBJECTIVE

This article delves into the nuanced application of cement augmentation techniques for pedicle screws and vertebral body replacements (VBR), aimed at optimizing surgical outcomes in osteoporotic spines.

METHOD

Drawing from a comprehensive literature review according to important clinical and biomechanical studies and the authors' clinical experiences, we elucidate strategies to mitigate complications and improve surgical efficacy.

RESULTS

Cement augmentation has shown promise in managing vertebral fractures and in securing pedicle screws within osteoporotic vertebrae, with the advent of polymethylmethacrylate (PMMA) bone cement marking a pivotal advancement in spinal surgery. We highlight intraoperative measures like the choice between pre-injecting cement and utilizing cannulated or fenestrated screws, emphasizing the importance of controlling cement viscosity to prevent leakage and embolism. Through two case reports, we demonstrate the practical application of endplate cementation following VBR.

CONCLUSION

While the use of cement augmentation poses certain risks, its judicious application-supported by evidence-based guidelines and surgical expertise-can substantially enhance the stability of spinal constructs in osteoporotic patients. This allows a reduction in instrumentation length by enhancing biomechanical stability concerning pullout, bending, and rotational forces. Furthermore, the incidence of endplate sintering following VBF can be significantly reduced. Future research, particularly on antibiotic-loaded PMMA, may further expand its utility and optimize its safety profile.

Tips and tricks for using cement augmentation of pedicle screws and vertebral body replacements-A literature review supported by two case reports

BACKGROUND

The prevalence of osteoporosis is escalating alongside an aging global population, increasing the demand for spinal surgeries, including those necessitating cement augmentation for enhanced construct stability.

OBJECTIVE

This article delves into the nuanced application of cement augmentation techniques for pedicle screws and vertebral body replacements (VBR), aimed at optimizing surgical outcomes in osteoporotic spines.

METHOD

Drawing from a comprehensive literature review according to important clinical and biomechanical studies and the authors' clinical experiences, we elucidate strategies to mitigate complications and improve surgical efficacy.

RESULTS

Cement augmentation has shown promise in managing vertebral fractures and in securing pedicle screws within osteoporotic vertebrae, with the advent of polymethylmethacrylate (PMMA) bone cement marking a pivotal advancement in spinal surgery. We highlight intraoperative measures like the choice between pre-injecting cement and utilizing cannulated or fenestrated screws, emphasizing the importance of controlling cement viscosity to prevent leakage and embolism. Through two case reports, we demonstrate the practical application of endplate cementation following VBR.

CONCLUSION

While the use of cement augmentation poses certain risks, its judicious application-supported by evidence-based guidelines and surgical expertise-can substantially enhance the stability of spinal constructs in osteoporotic patients. This allows a reduction in instrumentation length by enhancing biomechanical stability concerning pullout, bending, and rotational forces. Furthermore, the incidence of endplate sintering following VBF can be significantly reduced. Future research, particularly on antibiotic-loaded PMMA, may further expand its utility and optimize its safety profile.

Fatal fat embolism syndrome during posterior spinal fusion surgery: A case report and literature review

RATIONALE

Fat embolism syndrome (FES) is a rare but potentially lethal complication. Although serious FES is associated with long bone fractures and major joint surgery, the number of patients who develop fatal FES intraoperatively is probably higher than the described number. We herein report an extremely rare autopsy-confirmed case of fatal FES during posterior spinal fusion to enhance pedicle screw (PS) fixation with allograft bone augmentation.

PATIENT CONCERNS

A 74-year-old woman came to the hospital complaining of back pain, lower extremity pain and numbness, and intermittent claudication.

DIAGNOSIS

She was diagnosed with lumbar degenerative scoliosis and lumbar spinal canal stenosis based on imaging findings.

INTERVENTIONS

During posterior spinal fusion to enhance pedicle screw fixation with allograft bone augmentation, her blood pressure and oxygen saturation dropped significantly, so the operation was stopped, and cardiopulmonary resuscitation was performed. Chest computed tomography demonstrated bilateral diffuse alveolar infiltrates.

OUTCOMES

The patient died three days later due to fat embolism. The autopsy revealed diffuse myocardial ischemia and diffuse alveolar damage. Numerous fat emboli were observed at lung, kidney and spleen and small necrotic bone fragments, possibly derived from allograft bone debris, were found in the peripheral pulmonary artery.

LESSONS

Fatal FES associated to seemingly harmless isolated osteoporotic vertebral fractures-vertebroplasty and posterior spinal fusion has been reported. The mechanism was hypothesized to be that both vertebral fractures and spine surgery have the potential to involve bone marrow, thereby increasing intraosseous pressure, and this pressure dislodges fat and bone marrow and pushes them out into the venous circulation, causing systemic inflammation.This is the first report to show histological evidence that the allografted bone embolized to the lungs. Although several reports have indicated that inserting reinforcing materials into the tapped screw holes can enhance the pedicle screw fixation, this procedure may cause severe FES due to fat and debris of material augmentation (i.e. cement, hydroxyapatite, allograft bone). It is important for physicians, especially spinal surgeons, and anesthetists, to be aware of the potential for FES to occur during spinal surgery, which can cause serious complications in a small minority of patients.

Effect of cementing on pulmonary arterial pressure in vertebroplasty: A comparison of two techniques

BACKGROUND

Increase in intraosseous pressure and displacement of bone marrow contents leading to fat embolism and hypotension during cement injection in vertebroplasty (VP). We aimed to compare the effect of low and high viscosity cements during VP on pulmonary arterial pressure (PAP) with different cannula.

MATERIALS AND METHODS

Fifty-two patients having multilevel VP due to osteoporotic vertebral compression fractures were randomly treated either by a high viscosity cement (group A, n = 27 patients) and 2.8 mm cannula or a low viscosity cement (group B, n = 25 patients) injected through 4.2 mm cannula. PAP was measured by standard echocardiography and blood d-dimer values were recorded preoperatively, 24 h and third day after operation.

RESULTS

Mean age was 69 (62-87) years in group A and 70 (64-88) years in group B, and sex and comorbidities were similar. Average number of augmented levels was 5.4 in group A and 5.7 in group B. Preoperative mean PAP was 33 mm/Hg in group A, elevated to 41 mm/Hg on first day, and decreased to 36 mm/Hg on third day. The mean PAP in group B was 35 mm/Hg preoperatively, 51 mm/Hg on first day and 46 mm/Hg on third day (p < 0.05). The average blood d-dimer values in group A increased from 2.1 µg/mL to 2.3 µg/mL and in group B from 2.2 µg/mL to 4.2 µg/mL.

CONCLUSION

The finding of this study showed that high viscosity cement injected through a narrower cannula results in lesser PAP increase and d-dimer levels when compared to low viscosity cement injected through a wider cannula. Higher PAP and d-dimer level may show possible thromboembolism. This finding may give spine surgeons to reconsider their choice of cement type and cannula size.

The old sheep: a convenient and suitable model for senile osteopenia

INTRODUCTION

Existing osteoporosis models in sheep exhibit some disadvantages, e.g., challenging surgical procedures, serious ethical concerns, failure of reliable induction of substantial bone loss, or lack of comparability to the human condition. This study aimed to compare bone morphological and mechanical properties of old and young sheep, and to evaluate the suitability of the old sheep as a model for senile osteopenia.

MATERIALS AND METHODS

The lumbar vertebral body L3 of female merino sheep with two age ranges, i.e., old animals (6-10 years; n = 41) and young animals (2-4 years; n = 40), was analyzed concerning its morphological and mechanical properties by bone densitometry, quantitative histomorphometry, and biomechanical testing of the corticalis and/or central spongious region.

RESULTS

In comparison with young sheep, old animals showed only marginally diminished bone mineral density of the vertebral bodies, but significantly decreased structural (bone volume, - 15.1%; ventral cortical thickness, - 11.8%; lateral cortical thickness, - 12.2%) and bone formation parameters (osteoid volume, osteoid surface, osteoid thickness, osteoblast surface, all - 100.0%), as well as significantly increased bone erosion (eroded surface, osteoclast surface). This resulted in numerically decreased biomechanical properties (compressive strength; - 6.4%).

CONCLUSION

Old sheep may represent a suitable model of senile osteopenia with markedly diminished bone structure and formation, and substantially augmented bone erosion. The underlying physiological aging concept reduces challenging surgical procedures and ethical concerns and, due to complex alteration of different facets of bone turnover, may be well representative of the human condition.

Effect of unilateral pulsed jet lavage prior to vertebroplasty on the intravertebral pressure and cement distribution

Background

Percutaneous vertebroplasty is the most common treatment for osteoporotic vertebral compression fracture. However, the morbidity of vertebroplasty-related complications, such as cement leakage, remains high. We tested a new technique of unilateral pulsed jet lavage and investigated its effect on the intravertebral pressure and bone cement distribution.

Methods

Thirty lumbar vertebrae (L1-L5) from six cadaver spines were randomly allocated into two groups (with and without irrigation). Prior to vertebroplasty, pulsed jet lavage was performed through one side of the pedicle by using a novel cannula with two concentric conduits to remove the fat and bone marrow of the vertebral bodies in the group with irrigation. The control group was not irrigated. Then, standardized vertebroplasty was performed in the vertebral bodies in both groups. Changes in the intravertebral pressure during injection were recorded. Computed tomography (CT) was performed to observe the cement distribution and extravasations, and the cement mass volume (CMV) was calculated.

Results

During cement injection, the average maximum intravertebral pressure of the unirrigated group was higher than that of the irrigated group (4.92 kPa versus 2.22 kPa, P < 0.05). CT scans showed a more homogeneous cement distribution with less CMV (3832 mm³ vs. 4344 mm³, P < 0.05) and less leakage rate (6.7% vs. 46.7%, P < 0.05) in the irrigated group than in the control group.

Conclusions

Unilateral pulsed jet lavage can reduce intravertebral pressure and lower the incidence of cement leakage during vertebroplasty. An enhanced bone cement distribution can also be achieved through this lavage system.

Local osteo-enhancement of osteoporotic vertebra with a triphasic bone implant material increases strength-a biomechanical study

PURPOSE

The aim of this study was to assess the biomechanical properties of intact vertebra augmented using a local osteo-enhancement procedure to inject a triphasic calcium sulfate/calcium phosphate implant material.

METHODS

Twenty-one fresh frozen human cadaver vertebra (Th11-L2) were randomized into three groups: treatment, sham, and control (n = 7 each). Treatment included vertebral body access, saline lavage to displace soft tissue and marrow elements, and injection of the implant material to fill approximately 20% of the vertebral body by volume. The sham group included all treatment steps, but without injection of the implant material. The control group consisted of untreated intact osteoporotic vertebra. Load at failure and displacement at failure for each of the three groups were measured in axial compression loading.

RESULTS

The mean failure load of treated vertebra (4118 N) was significantly higher than either control (2841 N) or sham (2186 N) vertebra (p < 0.05 for: treatment vs. control, treatment vs. sham). Treated vertebra (1.11 mm) showed a significantly higher mean displacement at failure than sham vertebra (0.80 mm) (p < 0.05 for: treatment vs. sham). In the control group, the mean displacement at failure was 0.99 mm.

CONCLUSIONS

This biomechanical study shows that a local osteo-enhancement procedure using a triphasic implant material significantly increases the load at failure and displacement at failure in cadaveric osteoporotic vertebra.

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.

The effect of mechanical aspiration of the vertebral body on pulmonary arterial pressure before cement injection in the vertebroplasty procedure

PURPOSE

The aim of this study is to compare the efficacy of the mechanical aspiration technique just prior to cement application in the standard vertebroplasty (VP).

METHODS

Forty patients were included in the study. In group A, mechanical aspiration of the cavity was done just before the cement injection and in group B aspiration of vertebral body did not perform, VP was done with the same size cannula, same injection force, same injection speed and same cement viscosity. Pulmonary arterial pressures (PAPs) and blood d-dimer values were recorded preoperatively, 24 h and 3 days after the procedure. The PAP and d-dimer data were statistically compared with Student's t-test.

RESULTS

The mean age was 71 (62-87) in A and 70 (64-88) in B. The augmented level was 6.7 in A and 6.9 in B. Cement leakage was present in four in A and six in B. Acute hypotension was observed immediately after cement injection in one patient in A and four patients in B. The preoperative mean PAP in A was 35mm/Hg and elevated to 48 mm/Hg on the first postoperative day and decreased to 42 mm/Hg on the third postoperative day. The mean PAP in B was 36 mm/Hg preoperatively, 71 mm/Hg on the first day, and 58 mm/Hg on the third day ( p < 0.05). The d-dimer values revealed a difference between groups, the PAP values significantly changed between before and after the operation in both groups ( p < 0.005).

CONCLUSION

Aspiration of the vertebral body can easily be used to decrease the risk of cement leakage and the migration of fatty particles into the pulmonary circulation.

Percutaneous Vertebral Body Augmentations: The State of Art

Osteoporotic compression fractures of the vertebral body can result in pain and long-term morbidity, including spinal deformity, with increased risk of mortality resulting from associated complications. Conservative management includes opioids and other analgesics, bed rest, and a back brace. For patients with severe and disabling pain, vertebral augmentation (vertebroplasty and kyphoplasty) is often considered, with these procedures endorsed by multiple professional societies, and provides immediate structural support, and stabilizes and reinforces the weakened bone structure. The purpose of this article is to review the vertebral biomechanics, indications and contraindications, and techniques of performing successful vertebral augmentation.

Vertebral Body Lavage Reduces Hemodynamic Response to Vertebral Body Augmentation With PMMA

STUDY DESIGN

Retrospective comparative study.

OBJECTIVES

To assess the effect of vertebral body lavage (VBL) on (1) systemic blood pressure, (2) heart rate, and (3) oxygen saturation following cement augmentation procedures for acute vertebral compression fractures (VCFs).

METHODS

A total of 145 consecutive patients undergoing cement augmentation for acute VCF (mean age 74 ± 12 years, age range 42-96 years; 70% female; 475 levels treated) were allocated to the "lavage group" (n = 61 patients; VBL prior to cement application) and to the "control group" (n = 84 patients, no VBL). Mean arterial blood pressure (MAP), heart rate, and oxygen saturation were monitored immediately prior and 3 minutes after cement injection. Logistic regression analysis was performed with ΔMAP ≥10 mm Hg before and after cement injection as the dependent outcome variable and demographic, radiographic, and procedural factors as independent variables.

RESULTS

MAP decreased by mean 3 ± 7.3 mm Hg before and after cement injection in the "lavage group" and 9 ± 10.5 mmHg in the control group (P < .001). There were no significant differences in terms of heart rate and oxygen saturation before and after cement application within each group, or between the 2 groups. Multivariate logistic regression analyses revealed VBL as an independent factor influencing MAP (adjusted odds ratio: 3.49 [confidence interval, 1.16-10.50], P = .03).

CONCLUSION

VBL prior to cement augmentation procedures reduces the hemodynamic response, most likely resulting from decreased amounts of bone marrow substance displaced into the circulation thereby decreasing the risk of pulmonary fat embolism syndrome.

Percutaneous vertebroplasty: a new animal model

BACKGROUND CONTEXT

Percutaneous vertebroplasty (PVP) is a minimally invasive surgical procedure and is frequently performed in humans who need surgical treatment of vertebral fractures. PVP involves cement injection into the vertebral body, thereby providing rapid and significant pain relief.

PURPOSE

The testing of novel biomaterials depends on suitable animal models. The aim of this study was to develop a reproducible and safe model of PVP in sheep.

STUDY DESIGN

This study used ex vivo and in vivo large animal model study (Merino sheep).

METHODS

Ex vivo vertebroplasty was performed through a bilateral modified parapedicular access in 24 ovine lumbar hemivertebrae, divided into four groups (n=6). Cerament (Bone Support, Lund, Sweden) was the control material. In the experimental group, a novel composite was tested-Spine-Ghost-which consisted of an alpha-calcium sulfate matrix enriched with micrometric particles of mesoporous bioactive glass. All vertebrae were assessed by micro-computed tomography (micro-CT) and underwent mechanical testing. For the in vivo study, 16 sheep were randomly allocated into control and experimental groups (n=8), and underwent PVP using the same bone cements. All vertebrae were assessed postmortem by micro-CT, histology, and reverse transcription-polymerase chain reaction (rt-PCR). This work has been supported by the European Commission under the 7th Framework Programme for collaborative projects (600,000-650,000 USD).

RESULTS

In the ex vivo model, the average defect volume was 1,275.46±219.29 mm³. Adequate defect filling with cement was observed. No mechanical failure was observed under loads which were higher than physiological. In the in vivo study, cardiorespiratory distress was observed in two animals, and one sheep presented mild neurologic deficits in the hind limbs before recovering.

CONCLUSIONS

The model of PVP is considered suitable for preclinical in vivo studies, mimicking clinical application. All sheep recovered and completed a 6-month implantation period. There was no evidence of cement leakage into the vertebral foramen in the postmortem examination.

Lavage prior to vertebral augmentation reduces the risk for cement leakage

PURPOSE

This study aimed at assessing the cement leakage rate and the filling pattern in patients treated with vertebroplasty, kyphoplasty and stentoplasty with and without a newly developed lavage technique.

STUDY DESIGN

Retrospective clinical case-control study.

METHODS

A newly developed bipedicular lavage technique prior to cement application was applied in 64 patients (45.1 %) with 116 vertebrae, ("lavage" group). A conventional bipedicular cement injection technique was used in 78 patients (54.9 %) with 99 levels ("controls"). The outcome measures were filling patterns and leakage rates.

RESULTS

The overall leakage rate (venous, cortical defect, intradiscal) was 37.9 % in the lavage and 83.8 % in the control group (p < 0.001). Venous leakage (lavage 12.9 % vs. controls 31.3 %; p = 0.001) and cortical defect leakage (lavage 17.2 % vs. controls 63.3 %; p < 0.001) were significantly lower in the lavage group compared to "controls," whereas intradiscal leakages were similar in both groups (lavage 12.1 % vs. controls 15.2 %; p = 0.51). For venous leakage multivariate logistic regression analysis showed lavage to be the only independent predictor. Lavage was associated with 0.33-times (95 % CI 0.16-0.65; p = 0.001) lower likelihood for leakage in compared to controls.

CONCLUSIONS

Vertebral body lavage prior to cement augmentation is a safe technique to reduce cement leakage in a clinical setting and has the potential to prevent pulmonary fat embolism. Moreover, a better filling pattern can be achieved.

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.

Intraoperative PEEP-ventilation during PMMA-injection for augmented pedicle screws: improvement of leakage rate in spinal surgery

BACKGROUND

Within the last two decades the use of polymethylmethacrylate (PMMA) in the treatment of osteoporotic vertebral fractures has been established widely. Several techniques of cement application in spinal surgery have been described. Besides classical vertebroplasty, kyphoplasty and related techniques that reinforce stability of the fractured vertebral body itself, augmentation of pedicle screws became an issue in the past 10 years. Aim of this technique is strengthening of the implant-bone-interface and the prevention of loosening and failure of posterior instrumentation in limited bone quality due to osteoporosis. PMMA use in spinal surgery always bears the risk of cement leakage and cement embolism. There are only few publications dealing with cement leakage in pedicle screw augmentation. We examined our cohort concerning incidence and type of leakage in comparison to the literature. In particular, we evaluated a possible role of intrathoracic pressure during cementation procedure.

PATIENTS AND METHODS

In this retrospective study 42 patients were included. Mean age was 74 (57-89) years. 311 fenestrated, augmented screws were analyzed postoperatively concerning leakage and subsequent pulmonary embolism of cement particles. Overall, there was a leakage rate of 38.3 %, and 28.6 % of patients showed pulmonary embolism of PMMA. During surgery, patients were in part ventilated with a positive end-expiratory pressure (PEEP) of 15 cmH2O during cement injection. These individuals showed significantly less leakage locally as well as less PMMA-emboli in the pulmonary circulation in contrast to patients ventilated without increased PEEP.

CONCLUSION

PEEP elevation during administration of PMMA via fenestrated pedicle screws is reducing the leakage rate in spinal surgery. These beneficial effects warrant further evaluation in prospective studies.

Acrylic bone cement: current concept review

Acrylic bone cement has had for years an important role in orthopedic surgery. Polymethylmethacrylate (PMMA) has been extended from the ophthalmological and dental fields to orthopedics, as acrylic cement used for fixation of prosthetic implants, for remodeling osteoporotic, neoplastic and vertebral fractures repair. The PMMA bone cement is a good carrier for sustained antibiotic release in the site of infection. Joint prostheses chronic infection requires surgical removal of the implant, in order to eradicate the infection process. This can be performed in the same surgical time (one-stage procedure) or in two separate steps (two-stage procedure, which involves the use of an antibiotic-loaded cement spacer). The mechanical and functional characteristics of the spacers allow a good joint range of motion, weight-bearing in selected cases and a sustained release of antibiotic at the site of infection. The improvement of fixation devices in recent years was not accompanied by the improvement of elderly bone quality. Some studies have tested the use of PMMA bone cement or calcium phosphate as augmentation support of internal fixation of these fractures. Over the past 20 years, experimental study of acrylic biomaterials (bone cement, bioglass ceramic, cement additives, absorbable cement, antibiotic spacers) has been of particular importance, offering numerous models and projects.

Percutaneous cement augmentation techniques for osteoporotic spinal fractures

Minimally invasive vertebral augmentation-based techniques have been used for the treatment of spinal fractures (osteoporotic and malignant) for approximately 25 years. In this review, we try to give an overview of the current spectrum of percutaneous augmentation techniques, safety aspects and indications. Crucial factors for success are careful patient selection, proper technique and choice of the ideal cement augmentation option. Most compression fractures present a favourable natural course, with reduction of pain and regainment of mobility after a few days to several weeks, whereas other patients experience a progressive collapse and persisting pain. In this situation, percutaneous cement augmentation is an effective treatment option with regards to pain and disability reduction, improvement of quality of life and ambulatory and pulmonary function.

Development of an in vivo experimental model for percutaneous vertebroplasty in sheep

INTRODUCTION

Several studies have described 'open' approach techniques for cementation of sheep and goat vertebrae; however, no percutaneous technique has been developed so far for use in non-primates. The aim of this study was to develop an animal model for percutaneous vertebroplasty under clinical conditions.

METHODS

In a pilot study with dissected cadaveric ovine vertebrae, the technique and instruments as well as the optimal needle position were determined. In an in vivo animal study using 33 lumbar vertebrae of 11 sheep, a percutaneous vertebroplasty was performed under general anaesthesia. Needle position and cement volume were evaluated from high resolution, quantitative computed tomography imaging.

RESULTS

The percutaneous technique for vertebroplasty was applicable to the vertebral bodies (L1 to L5) of the ovine lumbar spine without any related adverse effects for the animals. The procedure showed a steep learning curve represented by the reduction of the distance between the actual and planned needle positioning (7.2 mm to 3.7 mm; median value) and shorter surgery times (21.3 min to 15.0 min, average) with progression of the study.

CONCLUSION

The described technique is feasible and repeatable under clinical conditions. This is the first percutaneous vertebroplasty technique for non-primates and we conclude that the sheep is a valid animal model to investigate the effects of cement augmentation in vivo.