Vertebral augmentation: vertebroplasty and kyphoplasty1

Vertebral Augmentation: Vertebroplasty and Kyphoplasty John A. Carrino, Roxanne Chan, and Alexander R. Vaccaro

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STEOPOROTIC COMPRESSION fractures can be associated with prolonged pain and possibly spinal deformity. Although conservative management may be adequate for pain management in a majority of the cases, some patients experience significant pain beyond 4 to 6 weeks. Furthermore, the ensuing spinal deformity from the collapsed vertebral body may result in a severe deterioration of the quality of life of elderly individuals. The application of traditional surgical techniques with conventional spinal instrumentation is often fraught with problems such as hardware migration, screw pullout, or lack of rigid stability because of the poor bone quality related to underlying osteoporosis. Therefore, the majority of patients are treated nonoperatively even in the presence of a progressive spinal deformity. Although many patients respond to nonoperative intervention, a subset will develop worsening or chronic severe pain, discomfort, and disability that adversely affect their overall level of function. Medical pain management is also associated with increased pharmacological side effects in this predominantly elderly population with a restricted physiological reserve. In addition, some patients go on to development a deformity that can compromise pulmonary and gastrointestinal functioning whether the fracture pain resolves or not. The limited traditional nonoperative treatment options and the risks of traditional spine instrumentation have been the impetus to seek novel minimally invasive treatment methods. Open surgery is usu-

From the Department of Radiology, Brigham and Women’s Hospital, Boston, MA; and Department of Orthopaedics-Spine Division, Rothman Institute, Thomas Jefferson University Hospital, Philadelphia, PA. This article is an instructional and educational vehicle that complements but does not replace the time, proctoring, and practical experience needed to perform vertebral augmentation. Familiarity with vertebral body bone biopsy techniques and basic spinal injection principles are valuable prerequisites. A hands-on workshop with cadavers or mini-fellowship is strongly recommended. Address reprint requests to John A. Carrino, MD, MPH, Harvard Medical School, Brigham and Women’s Hospital, Department of Radiology, 75 Francis Street, Boston, MA 02115. © 2004 Elsevier Inc. All rights reserved. 0037-198X/04/3901-0008$30.00/0 doi:10.1053/j.ro.2003.10.012 68

ally reserved for those patients with disabling symptomatic compression of their neural elements. Percutaneous vertebral augmentation has been advocated as a technique to address pain related to a compromised vertebra either from an osteoporotic fracture or neoplasm. The intravertebral injection of acrylic resin cement is believed to stabilize the fracture site and thus reduce pain. However, vertebroplasty does not aim at restoring height and ultimately preventing spinal deformity. The ideal minimally invasive intervention should be designed to not only treat the present pain and discomfort from the compressed vertebrae but also change the natural history of continued compression of the vertebrae and future compression of adjacent vertebrae from altered spinal biomechanics. This limitation has led to the development of kyphoplasty (balloon-assisted vertebroplasty), a percutaneous procedure in which an inflatable bone tamp is used to restore the lost vertebral body height before the injection of cement. There is also cadaveric evidence that kyphoplasty may restore the vertebral body stiffness to its original value.1 INDICATIONS

The primary indication for performing vertebral augmentation is to manage the pain related to nontraumatic benign or neoplasm associated vertebral fractures. In this context, the fundamental indications for vertebral augmentation are persistently (⬎4-6 weeks) painful fractures (osteoporosis or neoplasm related) despite appropriate medical treatment. The primary goal in osteoporosis management is pain relief, prevention of further deformity, and restoration of vertebral body height if possible. A secondary indication is the management of painful benign or malignant neoplasms involving the vertebrae (aggressive hemangioma, metastasis, and myeloma) or for vertebrae at risk of pathologic fracture because of tumor invasion. In this context, one may consider vertebral augmentation in the presence of osteolytic lesions undergoing chemotherapy or radiotherapy that may collapse if substantial tumor necrosis is achieved. Osteoporosis The patients with osteoporosis who seem to respond best to vertebroplasty are patients with only one or two fractures less than 12 months old Seminars in Roentgenology, Vol 39, No 1 (January), 2004: pp 68-84

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that are not severely compressed. Interestingly fractures greater than 12 months of age (chronic lesions) may also respond to cement augmentation. Patients who are likely to benefit have fracture(s) that show bone marrow edema on magnetic resonance imaging (MRI) or radiotracer uptake on a nuclear medicine bone scintigram. The patient should be in significant pain and the pain from the fracture should alter their lifestyle. Identifying the appropriate pain generator in the presence of multiple compression fractures of differing ages can be a challenging endeavor. Imaging plays an important role because some clinicians have found that lack of preoperative spinous process tenderness does not adversely affect clinical success of percutaneous vertebroplasty.2 Neoplasms: Benign The benign neoplasm most commonly treated with percutaneous cement augmentation are hemangiomas (a vascular tumor composed of endothelial cells). Although hemangiomas have a benign histology, they may exhibit an aggressive growth pattern and come to clinical attention because of axial pain or compressive neurologic symptoms (so called “aggressive hemangioma”). Vertebroplasty consolidates the vertebral body and reduces the risk of hemorrhage. Subsequent surgery may then be focused on relieving neural compression and epidural extension resection.3 In this fashion, vertebroplasty is another adjuvant treatment similar to intralesional sclerosis or preoperative embolotherapy. Neoplasms: Malignant Metastatic neoplasm. The malignant neoplasms most commonly treated with percutaneous cement augmentation are metastases (typically from adenocarcinomas). Vertebroplasty has been found to be effective in treating osseous vertebral metastases that result in pain or instability by providing immediate and long-term pain relief and spinal stabilization.4 Vertebral augmentation is not an ablative procedure. The resultant structural bone reinforcement most likely results in analgesia. The mechanism of pain relief is most likely related to vertebral strength and stiffness and not a thermal ablative phenomenon.5 A secondary role of vertebral augmentation has been to allow other therapies, such as radiotherapy or surgical resection and fixation, to ensue, while minimizing the risk of

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further vertebral collapse or fracture. Primary Neoplasm (Myeloma) Myeloma is a plasma cell dyscrasia and is the most common primary bone neoplasm in patients over 40 years of age. The myeloma cells physically displace the bony architecture, as well as secrete a chemical that destroys the bone. This bone destruction results in bone pain, bone fractures, and hypercalcemia. There are several musculoskeletal manifestations seen in the setting of multiple myeloma. A common spinal manifestation is a slow progressive thoracolumbar kyphosis. Unfortunately, early signs of focal vertebral marrow lesions detected with MRI have not been correlated with the potential or degree of spinal collapse often seen with multiple myeloma. The painful spine deformities that result from multiple vertebral compressions may be arrested and possibly reversed (kyphoplasty) with vertebral cement augmentation. CONTRAINDICATIONS

Absolute contraindications for vertebral cement augmentation in the setting of an osteoporotic compression fracture include (1) the presence of an asymptomatic stable fracture, (2) a patient showing substantial symptomatic improvement with time, and (3) the presence of severe osteoporosis without a fracture in a patient not undergoing reconstructive spinal surgery. Absolute contraindications for vertebral cement augmentation in both osteoporotic and neoplastic conditions include infection, uncorrectable coagulopathy, and allergy to any component required for the procedure. Acute traumatic fractures of a nonosteoporotic vertebra are also considered a contraindication. Relative contraindications include a compression fracture with a minor degree of axial pain with or without radicular pain, retropulsion of fracture fragment(s) causing substantial spinal canal compromise, and the presence of neoplastic tissue extending into the epidural space with substantial spinal canal compromise. Marked vertebral body compression (ie, the vertebral body height is smaller than the sagittal pedicle height) and vertebra plana (height loss greater than two thirds of the original vertebral body height) make it technically challenging to place a needle, and therefore some clinicians believe these fracture types should be considered a

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Fig 1. Vertebroplasty: treatment of vertebra plana using a single-needle transpedicular approach. (A) Lateral fluoroscopic image shows needle tip projected in the mid portion of a severely collapsed vertebra. (B) Lateral fluoroscopic image shows a horizontal lucent plane (arrows) reflecting a pseudarthrosis. Applying gentle distraction and extension under fluoroscopy may create this phenomenon. (C) Lateral fluoroscopic image shows cement filling the pseudarthrosis.

relative contraindication to cement augmentation. However, there is evidence from some case series that symptomatic fractures with severe collapse may still be treated effectively with vertebroplasty and should not necessarily be excluded from treatment.6 Needle placement in this scenario does require some additional expertise. Smaller diameter needles (13 gauge) and judicious cement injection is advocated because pain relief is not necessarily correlated with amount of cement or proportion of vertebral filling. In patients that have a fracture pseudarthrosis as manifested by an intravertebral vacuum cleft,7 some advocate complete filling of the cleft with cement to maximize stabilization of the fracture fragments8 (Fig 1).

Attempting to obtain some cephalocaudal vertebral filling is also believed to be important. The end result, regardless of the technique chosen, is to minimize complications to protect the surrounding soft-tissue integrity. Preprocedural Imaging Evaluation Pre-evaluation imaging should show the morphologic characteristic of the compromised vertebra and clearly shows physiologically an incompletely healed (ie, “active”) fracture. Other goals of imaging include the delineation of neoplastic involvement as well as the degree of associated degenerative disease. Radiography is useful for showing the degree of

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collapse. MRI should be performed for all candidates, unless contraindicated, using a specific protocol employing sagittal T1-weighted conventional spin echo, sagittal T2-weighted fast spin echo, or turbo spin echo with fat saturation and axial T2 fast spin echo through areas of abnormality. If fat suppression is not available for the T2-weighted images (either in a magnet with poor homogeneity or in a low-field strength system) then a short tau inversion recovery sequence should be substituted. The fluid sensitive sequences (T2 with fat suppression or short tau inversion recovery images) are necessary for determination of the level of “acuity” of the compression fracture. Although the causes of bone marrow edema are legion, in the context of compression fractures and appropriate clinical symptoms, it often indicates a potential source of pain (pain generator). The age of the compression fracture is less important then the presence of bone marrow edema on MRI and is relevant for people who have had symptoms for months or years. If MRI is contraindicated, then scintigraphy can be used as a substitute to show physiologic activity related to an incompletely healed fracture. There are data showing that increased activity (if localized to the vertebral body) is highly predictive of a positive clinical response to vertebroplasty.9 Computed tomography (CT) imaging is useful in neoplasms to delineate areas of osteolysis, to show cortical interruption, and to quantify the degree of osseous retropulsion. Pain Assessment Concordant pain evaluation has been considered an important aspect for determining those patients with benign fractures that will respond to cement augmentation. A physical examination under fluoroscopy may be performed to determine if the patient’s symptoms are concordant with the level of the suspected compression fracture on MRI. This has been found to be more useful for osteoporotic compression fractures rather than fractures caused by neoplasms. Under fluoroscopy, the back is palpated over the spinous processes marking the areas of tenderness. The patient is also asked to assume any position which may elicit pain that can be identified and marked. If the pain corresponds to the fractured level (usually within 1 vertebral level above or below), then the symptoms are likely to be amenable to treatment at that vertebral level. Today many clinicians are finding fluoroscopy too

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cumbersome and less useful and are relying more on cues from their physical examination. Patients who are not candidates for vertebral augmentation may still benefit from other spinal interventions such as an epidural injection for moderate pain relief. Technical Aspects Detailed technical descriptions are available elsewhere.10-15 Particularly useful in gaining a perspective on performing percutaneous vertebral augmentation are hands-on cadaver courses and mentorship programs. The technique for vertebral augmentation entails penetration of the involved vertebra(e), followed by injection of a cement or another reinforcing substance into the vertebral body. The cement may be injected with or without the creation of a void and some height restoration. Techniques that do not use a balloon for height restoration and void creation are referred to as vertebroplasty, whereas the technique that uses an inflatable balloon tamp is known as kyphoplasty or balloon-assisted vertebroplasty. Imaging modalities used for the procedure include either fluoroscopy or CT imaging, with or without CT fluoroscopy. Vertebral augmentation can adequately be accomplished with biplane fluoroscopy or with a high-quality single-plane (Carm) fluoroscopic unit that has rapid rotation capability such as the devices that are frequently available in interventional radiology suites. For single plane scenarios, it is imperative that an isocenter be established to facilitate rapid transitioning from lateral to anteroposterior projections and to avoid distortions. Many operators prefer biplanar fluoroscopy because of the time saving afforded by this configuration. Needle placement may be transpedicular or extrapedicular. Transpedicular placement is most often used for the lumbar spine and lower thoracic spine (below T7) because it provides a readily identifiable fluoroscopic target and is believed to reduce cement extravasation. The extrapedicular approach is frequently used in the middle to upper thoracic spine (Fig 2) with a readily identifiable target zone along the costotransverse process plane providing a safe pathway for access to the anterior vertebral body while avoiding the spinal canal and pleural space. The thoracic pedicles are smaller and more parasagittally oriented and thus do not readily facilitate needle entry toward the anterior

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Fig 2. Vertebroplasty: thoracic spine extrapediculate single-needle technique. (A) Oblique fluoroscopic image shows needle path (arrow) along a plane just posterior to the rib and anterior to the transverse process. The needle trajectory is toward the vertebral body center and was able to avoid the pedicle screws. (B) Anteroposterior fluoroscopic image from a different patient shows needle tips near the midline from an extrapedicular single-needle placement at T3 and T4. Note cement injection at T4 cross filling to the contralateral vertebral hemisphere.

central portion of the thoracic vertebra. This can be particularly problematic for a patient with “bulletshaped” thoracic vertebral bodies. Some clinicians use solely extrapedicular techniques for all lumbar levels, especially if placing the needles using CT guidance. Extrapedicular placement may be done under fluoroscopic guidance as well as with a posterolateral entry point into the vertebral body anterior to the transverse process and above the level of the exiting nerve root. This trajectory allows direct access to the anterior portion of the vertebral body in the lumbar region. Traditionally both vertebroplasty and kyphoplasty is performed with a 2-needle bilateral bipedicular technique. The rationale for this in vertebroplasty is to avoid the tendency for potentially suboptimal cement distribution. However, unipedicular or unilateral extrapedicular injections can also result in substantial vertebral reinforcement when adequate volumes of cement are injected that cross the midline of the vertebral body resulting in a similar cement distribution to bilateral injections. The ability to produce adequate cross filling is enhanced by using an extrapedicular posterolateral trajectory or a modified transpedicular approach (ie, an oblique targeting of the pedicle while visualizing a “Scotty Dog” projection) (Fig 3). Use of a unilateral approach in vertebroplasty allows

cross filling of vertebrae from a single puncture site with no significant difference in clinical outcome from that of bilateral vertebroplasty16 (Fig 3B). However, in the setting of vertebra plana in which there is a centrally depressed endplate, a bipedicular approach may be needed, placing the needle in a more lateral location to avoid transgression of the endplate and minimizing intradiscal and extraosseous cement injection17 (Fig 4). The rationale for using a bilateral technique with kyphoplasty is to provide symmetric endplate elevation and height restoration. However, for small thoracic vertebral bodies, some operators have used a single-balloon technique if the needle placement is centrally located under the depressed portion of the endplate. For vertebroplasty, the needles used are standard bone marrow biopsy type needles or variations thereof that have a Luer-Lock connection. Both beveled or pointed tips can be effectively used, and choice of needle is based largely on operator preference and experience. For lumbar levels, 10 or 11 gauge needles are used but for the thoracic levels 13 or 14 gauge needles are preferred. The needle tips should be placed in the anterior one fourth to one third of the vertebral body. This is to facilitate filling of the fracture area, which is typically anterosuperior and avoid injection into

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Fig 3. Vertebroplasty: lumbar spine unipedicular technique. This technique can be useful to minimize the number of needles placed. (A) Oblique fluoroscopic image shows needle trajectory along the eye of the “Scotty Dog,” which represents the pedicle. Note that the needle is centrally located in the ring shadow of the pedicle (arrowheads). (B) Lateral fluoroscopic image shows needle tips project in anterior third of vertebral body. (C) Anteroposterior fluoroscopic image shows tip near midline and cement crossing midline to fill a portion of the contralateral aspect of the vertebra. (D) Transaxial CT image shows a rounded deposit of cement located in the anterior central aspect of the vertebral body.

the larger vascular sinuses of the basivertebral venous plexus, which may allow preferential flow into the epidural space. Vertebral venography has been advocated before bone cement injection when performing percutaneous vertebroplasty. The original rationale was to identify if the needle tip was in a major basivertebral venous branch. Although venography can document sites of potential leakage during subsequent cement application, the presence of a

stagnant contrast agent may render the cement injection more difficult to monitor. Cement flow viscosity is different than contrast and will not necessarily travel into a vessel that is demonstrated by venography. Based on a large retrospective case series, it has been shown that vertebroplasty can be performed safely without prior venographic evaluation.18 It is believed that venography does not significantly improve the effectiveness or safety of percutaneous vertebroplasty performed by quali-

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Fig 4. Vertebroplasty: lumbar spine bipedicular technique. This technique can be useful for moderately to severely compressed vertebrae that have a centrally depressed endplate. (A) Anteroposterior fluoroscopic image shows needles placed via each pedicle projected over the respective hemivertebra. Care should be made not to place the needle tips too far lateral else they could penetrate the anterolateral cortex. (B) Lateral fluoroscopic image shows needle tips projected in anterior third of vertebral body.

fied, experienced operators.19 Additional anecdotal experience is that the practice of precement injection venography has been largely abandoned because many practitioners did not substantially alter the injection pattern after assessing the results of the venogram. Kyphoplasty is a slightly more complicated technique than vertebroplasty. Initial entry into the vertebral body is via penetration with a bone biopsy-type needle similar to vertebroplasty. Once the needle is passed through or around the pedicle and the vertebral body is penetrated, a guide wire is placed through the bone biopsy needle into the posterior portion of the vertebral body. A blunt cannula is then placed over the guide wire followed by a 10-gauge working cannula. The inner cannula is removed, which allows placement of a handheld drill into the vertebral body. The path created by the drill is directed toward the anterior half of the vertebral body, allowing the delivery of an inflatable bone tamp (IBT). The purpose of the IBT is afferent to restore the vertebral body back toward its original height, while creating a cavity that can be filled with a highly viscous bone cement. The proper position of the inflatable bone tamp (balloon) is identified by distal and proximal radiographic markers (Fig 5A). The balloon should reside in the anterior half of the vertebral body. The balloon is then inflated, elevating the endplates

in an attempt to restore vertebral body height (Fig 5B and C). The contralateral balloon is placed before balloon inflation to allow for symmetric elevation of the vertebral endplates. Once both bone tamps are in place, an alternating slow filling of each balloon is undertaken. The balloon is filled using radiographic contrast medium to evaluate the size of balloon expansion. For patients with a history of a severe contrast allergic reaction, gadolinium should be substituted because of the possibility for balloon rupture during inflation and thus contrast leakage into the intravascular space via the basivertebral plexus. Currently, there are 2 sizes of balloons available: 15-mm and 20m-m length tamps (10-mm balloons are being developed). The endpoint of balloon inflation occurs when (1) adequate reduction of the compression fracture is accomplished, (2) pressure readings approach 220 psi, (3) cortical proximity of the bone tamp occurs based on orthogonal fluoroscopic images, or (4) maximum inflation volumes are achieved. Inflation volumes and pressure measurements are read from the syringe barrel connected to the inflation device (4 mL for the 15-mm length balloon and 6 mL for the 20-mm length balloon tamps). Factors that ultimately determine the final pressure and volume of the balloon tamp depend on the volume and density of the vertebral body

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Fig 5. Kyphoplasty: IBT placement and height restoration. (A) Lateral fluoroscopic image shows the inflatable bone tamp placed through working cannula. Radiopaque markers (arrows) denote the balloon’s longitudinal extent distally and proximally. (B) Lateral fluoroscopic image shows partial balloon inflation. (C) Lateral fluoroscopic image shows balloon inflation with endplate elevation and partial height restoration compared with images in A and B.

(trabecular microarchitecture), as well as the age (healing rate) of the compression fracture. Higher pressures are generally needed for more dense bone as well as for subacute fractures, whereas low pressures are commonly experienced in less dense bone and more acute fractures. The operator must be vigilant in detecting any evidence of a cortical breech or leakage of any contrast material from the balloon before the insertion of cement. Once the desired reduction is obtained or maximal pressure is achieved, the bone tamp is deflated and removed. For more acute fractures, the balloons may be deflated on only 1 side to prevent the loss of reduction. The cavity (or void) created by kypho-

plasty can often be identified as a lucent region on fluoroscopic imaging (Fig 6). Specific technical considerations for metastatic neoplastic lesions include needle placement, cement volume, and adjuvant therapy. Needle placement is similar to osteoporosis cases (transpedicular or parapedicular approach) and not necessarily altered based on lesion location. Often the needle is initially placed in normal nontumor infiltrated bone. Placement of the needle tip is directed toward the midline of the anterior portion of the vertebral body. The goal in cement application is to obtain craniocaudal filling (attempting to get superior to inferior endplate filling) that crosses the

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Fig 6. Kyphoplasty: Cavity creation. (A) Lateral fluoroscopic image shows the IBT placed through working cannula. Radiopaque markers (arrows) denote the balloon’s longitudinal extent distally and proximally. (B) Lateral fluoroscopic image shows balloon inflation with contrast material. (C) Lateral fluoroscopic image shows a lucent region (arrowheads) corresponding to the balloon configuration from b reflecting the creation of a void within the vertebra. (D) Lateral fluoroscopic image shows cement instillation filling the previously created void.

midline transversely providing a cement strut. The cement may fill part of the tumor. However, attempting to fill the whole tumor is not advised. This may be difficult or impossible to accomplish, and there is a risk that the neoplastic tissue may be displaced into the canal causing a symptomatic stenosis, which may make surgical debulking more difficult. In addition, it is controversial as to whether the cement is in itself toxic to the tumor. It is generally believed that tumor cells are killed

only within 2 mm of the cement because of the exothermic curing reaction. Thus, filling of the tumor is not the critical aspect of the procedure. However, it is vital that adjuvant therapy (surgery, chemotherapy or radiotherapy) be performed (or at least considered) in addition to the vertebroplasty so that tumor kill can be attempted. For cases involving malignant neoplasm, there is the possibility of vascular tumor seeding as the cement enters areas of hypervascularity and neovascularity

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displacing tumor into the vascular system. Although there is no literature regarding this issue, it is believed to be a nontrivial risk. In addition, tumor patients may also need to be admitted overnight (23-hour stay) for pain control and the potential for tumor necrosis syndrome. Anesthesia considerations revolve around the patient’s physiological status. However, vertebral augmentation may be accomplished with neuroleptic anesthesia (conscious sedation), monitored anesthesia, or general anesthesia. Kyphoplasty is most often performed under general anesthesia, although the authors have performed kyphoplasty using monitored anesthesia. Intravenous antibiotics (cephalosporin such as cefazolin or clindamycin if penicillin allergy) are typically given as infection prophylaxis. CEMENT CONSIDERATIONS

The common ingredient to almost all vertebral augmentation procedures is the use of acrylic resin cement. Current issues include the type of agent, how much to use, and how to apply it. The bone cement most commonly used is some form of polymethylmethacrylate (PMMA). The US Federal Drug Administration treats bone cement as a device, and there is currently no PMMA specifically approved for injection (however trials are underway). The most salient considerations for choice of an agent include ability to increase vertebral strength and stiffness, visibility under fluoroscopy, ease of cement flow, and simplicity of use. Kyphoplasty creates a void within the vertebral body whether endplate elevation occurs or not, and this allows the use of a more viscous, thicker form of cement, whereas vertebroplasty requires the use of a less viscous, thinner form of cement to interdigitate between trabecula. In this context, kyphoplasty is considered a “low-pressure” injection and vertebroplasty is considered a “highpressure” injection technique. The application of cement during kyphoplasty is done via a bone filler device and not through a syringe or injector system. Cement is loaded into the nozzle and pushed into the cavity with the inner rod. There are several types of mixing and delivery (injector) systems already available for vertebroplasty, and this is another area of intense development. Two of the more popular PMMA preparations used are Cranioplastic Type I- Slow Set (Codman, Johnson & Johnson Medical Ltd, Berkshire, UK)

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and Simplex P (Stryker-Instruments, Kalamazoo, MI). These preparations (mixed according to the package insert) produce cement that is difficult to inject and poorly visualized by fluoroscopy. Thus, the addition of an opacifying agent (sterile barium, tantalum, or tungsten) is required. Sterile barium preparations are available from Parallax Medical, Inc. (Mountainview, CA) or Bryan Corporation (Woburn, MA). It has been determined that PMMA mixtures containing approximately 25% to 30% by weight of barium sulfate will provide opacification sufficient for the performance of fluoroscopically guided vertebroplasty.20 The authors prefer the Simplex P for kyphoplasty because it is a commonly used orthopedic cement that has a fairly quick setup and polymerization time providing a consistency suitable for pushing through a large cannula. In addition, there is the availability of a sealed vacuum container, Advanced Cement Mixing System (Stryker Instruments, Kalamazoo, MI), for mixing the polymer and monomer to reduce exposure to fumes. However, at least 1 study has shown that for typical vertebroplasty working conditions, the methylmethacrylate vapor concentrations measured are well below the recommended maximum exposure.21 The authors prefer cranioplastic for vertebroplasty because it has a slower polymerization time and hence a longer working time (10-15 minutes). Parallax Medical, Inc. offers 2 products that are simple to combine and use together: SECOUR cement and TRACERS Imaging Particles sterile barium opacifying agent. The challenge for vertebroplasty has been to obtain suitable working times for injection especially for multilevel cases. This goal is accomplished by prolonging the polymerization phase. Some operators add the liquid monomer to a modified powder (PMMA with barium) until it reaches a desired consistency. There are descriptions of various “recipes,” which likely change the cement’s material properties; however, it is unknown whether there is a difference in clinical therapeutic efficacy.22 Some advocate that rather than altering the monomer to copolymer ratio, one may manipulate thermal factors (ie, refrigerating the cement components for 24 hours before use and keeping the cement in an iced bath) to prolong the working time of the cement.23 The cement flow needs to be carefully monitored, and the injection should cease if there is

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Fig 7. Vertebroplasty: cement extravasation. (A) Lateral fluoroscopic image from a 2-level thoracic vertebroplasty (T7 and T8) shows cement extravasation in the retroperitoneum (arrow) and the intervertebral disc (arrowhead). (B) Lateral fluoroscopic image from a 2-level thoracic vertebroplasty (T3 and T4) shows cement extravasation in the epidural space as a thin opaque line (arrows). The injection was terminated and the patient was asymptomatic from this leak.

resistance or if the cement approaches the posterior vertebral margin. If any extraosseous cement is identified, that injection should be terminated. For vertebroplasty, the needle may be repositioned if additional cement needs to be injected. Alternatively, one may wait for additional solidification (formation of a cement plug) and then proceed with the remainder of the injection. For kyphoplasty, under low-pressure injection force, the PMMA is delivered through the cannula into the created void under continuous fluoroscopic monitoring and the volume of cement used normally exceeds the volume of balloon inflation by 1 mL. Once cement injection is completed, the stylet should be replaced when possible being cognizant that there is some cement (about 0.7 mL) along the needle “dead space” that will be pushed into the vertebral body. This technique prevents the complication of a cement “spike” that could cause soft-tissue irritation. Most commonly only 1 or 2 levels are done at a time. The risk of doing numerous levels simultaneously is that the PMMA can cause significant fat emboli because of marrow displacement. A final anteroposterior and lateral image is obtained to document cement location and endplate elevation. Several investigations have also shown no correlation between cement volume injected and the degree of pain relief. Thus, the trend has been to

place smaller volumes of cement rather than trying to fill the entire vertebral body and increase the risk of cement leak. Based on cadaveric models, guidelines for cement use include 4 to 6 mL of cement in the thoracic vertebrae and 6 to 8 mL of cement in the lumbar vertebrae to restore both strength and stiffness.24 INFORMED CONSENT AND COMPLICATIONS

The informed consent process should be a comprehensive discussion of the risks, benefits, and alternatives to cement augmentation. Risks include bleeding, infection, allergic reaction to the PMMA components, fracture (pedicle or rib), and cement extravasation. Pneumothorax is also a potential risk for thoracic levels. In the United States, informed consent must be obtained in compliance with state law. Fortunately, major complications of vertebral augmentation are uncommon. Minor nonclinically significant complications do occur and are most often related to extraosseous cement leakage (Fig 7). The potential complications for kyphoplasty and vertebroplasty are similar and include cement extravasation and pulmonary embolism. Epidural leakage of PMMA after percutaneous vertebroplasty is noted to be dose dependent. The incidence of epidural leakage is related to the amount of injected cement and vertebral level with a higher

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incidence of leakage when more cement is injected and when injecting vertebrae above T-725 (Fig 7B). The clinical significance of extravasation is less important than previously believed. Small to moderate amounts of cement may extravasate from the vertebrae with no significant effect on therapeutic success.26 Overall, there is a high technical success rate reported for accomplishing vertebral augmentation with minimal complications by experienced operators. The most common significant complication reported for vertebroplasty is radicular pain caused by migration of cement into the epidural venous plexus. Paralysis has been reported but is exceptional and less likely to occur if the procedure is performed in a controlled image guided fashion. Also noted have been rib, pedicle, or transverse process fractures. In most patients, intradiscal and paravertebral leaks of cement have no clinical importance.27 One of the theoretical and realized advantages of kyphoplasty is the reduced cement extravasation rate. One investigation showed less vascular and transcortical extravasation of injected contrast with kyphoplasty than with vertebroplasty, although the leakage of contrast may not necessary correlate with cement leakage.28 Nonetheless, there are case reports of severe neurologic complications that underscores the need for appropriate safeguards as outlined previously.29 There are also case reports of pulmonary embolism caused by acrylic cement.30 Adjacent level vertebral fracture is reported to be a potential complication with cement augmentation because the treated vertebral level often becomes stronger than the adjacent remaining osteoporotic bones. There are mixed data regarding this issue. One confounding factor is that the natural history of spinal osteoporosis is for the development of additional fractures once the threshold has been reached for the initial fracture event. For vertebroplasty, there has been documented a slight but significantly increased risk of vertebral fracture in the vicinity of a cemented vertebra.31 Another investigation found that a substantial (12.4%) number of patients with osteoporosis develop new fractures after undergoing percutaneous vertebroplasty and that 75% of these new fractures occur in vertebrae adjacent to those previously treated.32 In 1 kyphoplasty investigation, 2% of treated patients returned for additional augmentation procedures, which was not statisti-

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cally greater than adjacent fractures in untreated patients.33 POSTVERTEBRAL AUGMENTATION MANAGEMENT

Postprocedure care includes keeping the patient in bed without substantial head elevation for approximately 2 hours followed by bed rest with head of bed elevated less than 45° for several hours. This additional recovery period consists of 1 to 3 hours of observation depending on the patient’s status. The operator or other qualified staff member should supervise initial ambulation of the patient. If any new severe pain or new neurologic symptoms develop, a CT scan should be done immediately to evaluate the distribution of cement. Some advocate CT whenever leakage occurs to document cement location. The discharge plan should include postprocedure pain management in conjunction with the referring provider. Written discharge instructions are given to the patient with a plan for pain management, especially for the first few days, related to the morbidity of needle placement. The goal is to start tapering narcotic usage at 1 to 2 weeks after procedure. A decrease in analgesic use is encouraged to an “as needed” basis, so that assessment of pain reduction can be made. Patients are encouraged to have a gradual return to activity with or without a short course of physical therapy. Short-term bracing may also be useful. All osteoporotic patients should be in a medical therapy program for treating the underlying metabolic condition. Careful coordination and communication should be maintained with the referring provider regarding patient rehabilitation progression. Postdischarge follow-up involves either a telephone call 24 to 48 hours postprocedure or an office visit to assess the clinical progress of the patient. CLINICAL EXPERIENCE

Overall, postvertebral augmentation patients with osteoporosis have done well with respect to pain management and this therapeutic phenomenon has led to the popularity of these procedures.34 Several studies have been performed and uniformly report good pain relief, reduced requirements for analgesics, and improved functional mobility following vertebroplasty.35-37 Literature reviews are available summarizing the reports of numerous case series supporting that these proce-

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dures are associated with pain relief in 67% to 100% of cases.38 Prospective noncontrolled trials also support that the pain benefit is achievable in a high proportion of patients in the short term39 and in the longer term (15-18 months) with high patient satisfaction.40 In a nonrandomized trial, when compared with conservative therapy, percutaneous vertebroplasty results in prompt pain relief and rapid rehabilitation within 24 hours but similar clinical outcomes at 6 weeks and 6 to 12 months.41 There is also evidence that for kyphoplasty, the pain benefits persist at 1-year posttreatment.42 Satisfaction results have been documented after vertebroplasty up to 4 years postprocedure.43 Long-term pain management and mechanical and physiologic benefits have not yet been shown. Short-term complications are mainly the result of extravasation of cement and include increased pain because of heat damage neural compression. Rarely is decompressive surgery required. Longterm complications are unknown but potentially include a granulomatous response (foreign-body reaction) at the cement-bone interface similar to joint arthroplasties. Vertebroplasty has also been shown to be effective in the management of painful chronic compression fractures (benefit is not fracture age dependent).44 The growing consensus is that kyphoplasty and vertebroplasty are believed to be safe and effective and have a useful role in the treatment of painful osteoporotic vertebral compression fractures that do not respond to conventional treatments.45 Vertebroplasty cannot correct curvature (kyphosis) of the spine caused by osteoporosis but may help to prevent worsening deformity and the ensuing thoracoabdominal complications. Kyphoplasty is designed to relieve pain by vertebral fracture stabilization and possibly through fracture reduction and restoration of vertebral height and proper spinal biomechanics. The outcomes after kyphoplasty are also limited, but data are slowly accruing. A phase I study treating 70 fractures in 30 patients showed no major complications related directly to this technique or with the use of the inflatable bone tamp. Forty-seven percent of lost height in 70% of vertebral bodies46 was restored. The amount of vertebral height restoration because of prone positioning versus endplate elevation with the balloon tamp is not clear. Medical Outcomes Study short form self-assessment testing (SF-36)

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showed significant improvement in 6 of 8 SF-36 scales: bodily pain, physical function, role, vitality, mental health, and social functioning. General health and role emotional scales did not show significant improvement. Cement leakage occurred at 6 levels (8.6%), which entered the epidural space in 1 case, the disc space in 2 cases, and the paraspinal tissues in 3 cases with no long-term sequelae. Additional retrospective investigations have shown that kyphoplasty was efficacious in restoring vertebral body height in 26 patients (41 fractures) who were monitored for 1 year after treatment.47 At present, an ongoing industry sponsored study has gathered data on greater than 1,000 compression fractures (unpublished data). Ninety percent of the patients in this study have experienced significant pain relief, and 90% of patients were able to return to their normal activities of daily living. A complication rate of less than 2% was found, and none were related to the balloon used in the procedure. Preliminary analysis from a multicenter study of over 2,194 fractures (1,439 patients) concluded kyphoplasty is a safe and effective treatment option for patients with painful vertebral compression fractures secondary to osteopenia and provided most effective height restoration if the procedure was performed within 3 months of a fracture.48 The current North American experience with minimally invasive percutaneous vertebral augmentation has focused on the treatment of benign osteoporotic compression fractures. Vertebral augmentation has been more widely adopted for use in neoplastic vertebral lesions in Europe.49 Malignant lesions can be more challenging. Vertebroplasty has been shown to be beneficial as part of the treatment for osteolytic metastases and multiple myeloma lesions.27 There is a growing body of evidence that these procedures are safe and efficacious for painful vertebral body fractures in cancer patients.50 Vertebroplasty provides spinal stabilization in patients with neoplasm but does not produce consistent pain relief.51,52 Interestingly, the clinical results of pain management are not correlated to the extent of vertebral body filling.53 Pain relief is likely related to factor related to the genesis of tumor pain beyond the mechanics of a fracture. The initial experience of kyphoplasty for use in myeloma patients with multiple fractures has been favorable. In 18 patients with mean length of symptoms equal to 11 months who underwent

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55 levels of kyphoplasty, there were no major complications at a mean follow-up time of 7.4 months. Asymptomatic cement leakage was identified in 4% (2/55) of levels. An average of 34% of height lost at the time of fracture treatment was restored. There was also significant improvement in several SF-36 subscores of bodily pain (23.255.4, P ⫽.0008), physical function (21.3-50.6, P ⫽.0010), vitality (31.3-47.5, P ⫽ .010) and social functioning (40.6-64.8, P ⫽.014).54 Nevertheless, although the principle of vertebral augmentation remains encouraging, data to support widespread use has been primarily retrospective and the exact indications are yet to be firmly established. Studies have not addressed the “placebo effect.” That is, a patient willing to undergo an invasive procedure has a powerful motivation to feel better after the procedure. The strongest type of study design for evidenced based medicine, randomized control trials of vertebroplasty, and kyphoplasty have not been reported. To date, there are no studies that randomly assign patients to the procedure or a “sham-procedure” so that the patient is not aware of the actual treatment received. It is difficult to recruit patients who are not able to choose their own treatment, but randomization is believed to be the best methodology to minimize bias. There is a small but definitive risk of anesthesia exposure, the potential for bleeding, or infection associated with percutaneous needle placement irrespective of cement injection or balloon inflation. No studies have addressed the issue of whether vertebroplasty without or with balloon assistance for restoring or partially correcting spinal alignment makes a difference in function and outcomes. Certainly, more controlled trials are needed to determine both short-term and long-term safety and efficacy of vertebroplasty and kyphoplasty. Industry and government sponsored prospective clinical trials are underway. Vertebroplasty Versus Kyphoplasty: How to Decide? There are no accepted criteria as to when to perform 1 type of vertebral augmentation over another. Both vertebroplasty and kyphoplasty are undergoing technical developments and improvements. It is likely that both techniques and probably new ones will have a role in vertebral and other bone augmentation applications. What follows is a

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matter of opinion based on the current available information and the authors’ experience. In the osteoporotic patient population, both techniques seem to do equally well for pain management. Kyphoplasty has better success of height restoration for fractures less than 3 to 6 months old. In patients with a subacute fracture localized to 1 or 2 vertebral levels with loss of vertebral height up to about 40% to 50%, kyphoplasty may be beneficial because relatively acute fractures have the most potential to change their alignment. Vertebroplasty is probably the technique of choice in chronic symptomatic compression fractures greater than 6 months old, especially if there is severe vertebral height loss. Vertebra plana lesions are unlikely to gain much height, and these are best managed with vertebroplasty if necessary. When the vertebral height is less than the pedicle dimension, it can be difficult to access and place a balloon catheter using the current kyphoplasty equipment available and therefore vertebroplasty is the technique of choice in this setting. Midthoracic fractures significantly increase the potential for spinal kyphosis as compared to lower lumbar fractures.56 These fractures may be better suited for kyphoplasty because of the potential for vertebral height restoration for thoracic spine fractures. In the tumor population, pain management is important, but there are additional considerations. For metastatic neoplasms with only minimal height loss vertebroplasty seems a reasonable option to reinforce the existing bone while facilitating adjuvant treatment. Vertebroplasty is less demanding technically and can be performed more expeditiously and with less depth of anesthesia sedation requirement. This is an important consideration for cancer patients, the extreme elderly, and other patients with a diminished physiologic reserve. Vertebroplasty has the advantage of being relatively quick and inexpensive. For myeloma patients with multiple-wedged vertebral bodies contributing to a deformity without discreet destructive lesions, kyphoplasty appears to be a reasonable option. The desired restoration of spinal alignment and enhanced vertebral stability will theoretically improve spinal biomechanics therefore reducing pain from altered sagittal alignment. CONCLUSION

The decision to perform vertebral augmentation should be made by a multidisciplinary team be-

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cause the choice between vertebroplasty, kyphoplasty, surgery, radiation therapy, medical treatment, or a combination thereof depends on a number of factors. Vertebral augmentation should be viewed as only 1 component of a comprehensive program to manage symptomatic spinal osteoporosis and neoplastic disease and therefore the resulting sequelae and the complications of these common disorders affecting the axial skeleton. Of course, medical evaluation and treatment are paramount. The cement augmentation of vertebral bodies that have already fractured because of osteoporosis or osteolytic lesions is likely to prove useful by reducing pain, improving function, and preventing further collapse and deformity. Initial reports indicate that kyphoplasty affords a significant height gain of approximately 50% of the original height lost in appropriately selected cases. Vertebroplasty has also shown its usefulness in the symptomatic management of spinal metastatic disease. However, this is a different disease entity than osteoporotic compression fractures and with somewhat different treatment goals. In this clinical context, stabilization is the primary goal with pain management as a secondary goal with the role of

cement injection as an adjuvant therapy to surgery, chemotherapy, and/or radiotherapy. Kyphoplasty has been successfully applied to multiple myeloma and is an attractive option for assisting in the correction of multiple anterior wedging deformities to which these patients are prone. The complication rate of cement augmentation procedures is low and does not significantly differ between the 2 main types of vertebral augmentation procedures when performed by trained operators. The exact role and techniques for vertebral augmentation procedure continues to evolve, but both vertebroplasty and kyphoplasty will likely continue to play an important role in the treatment of symptomatic vertebral compression lesions. STANDARDS

The American College of Radiology has a standard for the performance of vertebroplasty, which was developed a by a consensus panel consisting of neuroradiologists, musculoskeletal radiologists, neurologic surgeons, and orthopedic surgeons. This document is available from the American College of Radiology’s web site (www.acr.org) as a portable document file.

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52. Weill A, Chiras J, Simon JM, et al: Spinal metastases: Indications for and results of percutaneous injection of acrylic surgical cement. Radiology 199:241-247, 1996 53. Cortet B, Cotten A, Boutry N, et al: Percutaneous vertebroplasty in patients with osteolytic metastases or multiple myeloma. Rev Rhum Engl Ed 64:177-183, 1997 54. Dudeney S, Lieberman IH, Reinhardt MK, et al: Kyphoplasty in the treatment of osteolytic vertebral compression fractures as a result of multiple myeloma. J Clin Oncol 20:2382-2387, 2002 55. Cortet B, Roches E, Logier R, et al: Evaluation of spinal curvatures after a recent osteoporotic vertebral fracture. Joint Bone Spine 69:201-208, 2002