Vertebroplasty and Kyphoplasty: Indications and Techniques

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Chapter 173 Vertebroplasty and Kyphoplasty

Indications and Techniques

Clifford J. Eskey

Vertebroplasty and kyphoplasty are minimally invasive, percutaneous procedures in which a fast-setting polymer is injected into a pathologic vertebral body with the goal of relieving pain or disability. These treatments have been applied to painful osteoporotic compression fractures, painful neoplasms, and structurally compromised vertebrae. They represent an evolving set of technologies for treating a common and important problem with limited medical and open surgical treatments. The remarkable anecdotal success of the procedures has spurred rapidly increasing clinical use. Scientific investigation of these treatments is just beginning to improve our understanding of best practices and expected outcomes.

Before the introduction of vertebroplasty and kyphoplasty, treatment of compression fractures consisted of bed rest, pain control (with nonsteroidal anti-inflammatory medications, calcitonin, and narcotics), and back bracing.¹ This regimen is often effective, and most people eventually find relief from their pain as the fracture heals. However, a substantial number fail to heal within 3 to 6 weeks. These people often suffer persistent back pain and a risk of gradually worsening kyphotic deformity. Even in those whose compression fractures heal over time, the recovery period is time consuming, requiring at least several weeks. The experience is often profoundly unpleasant and can be marked by periods of insufficient pain control, delirium, and constipation. Such patients are sometimes bedridden, with the attendant risks of deep venous thrombosis, pulmonary embolism, and pneumonia. The prolonged immobility accelerates bone resorption and predisposes the patient to additional injury. Finally, the long-term effects of even a healed fracture may be substantial: kyphotic deformity, decreased lung capacity, and altered forces on intervertebral discs and facet joints.

The vertebroplasty procedure was introduced in France in 1984 by a group that used the technique to treat symptomatic vertebral hemangiomas.² They found that the “internal casting” provided by polymethyl methacrylate (PMMA) injected into the pathologic vertebral body provided substantial pain relief. This success led to expansion of the procedure to the treatment of pain from myeloma and metastatic neoplasms of the vertebrae³; these indications remain the most common ones for the use of vertebroplasty in Europe. In 1993, the technique was introduced in the United States,⁴ where its chief use has been to treat the pain from osteoporotic compression fractures. Kyphoplasty was introduced in 1999 as the proprietary technology of Kyphon Inc. Kyphoplasty differs from vertebroplasty by adding the insertion and inflation of a balloon before cement delivery. It has the added goal of restoring vertebral body height and spine alignment.⁵ Both procedures are now practiced throughout the world, with the number of procedures and practitioners (including radiologists, orthopedic surgeons, neurosurgeons, and anesthesiologists) growing rapidly.

Indications

The primary indication for vertebroplasty and kyphoplasty is a painful, unhealed compression fracture. These fractures may be the result of osteoporosis, hematopoietic or lymphoid neoplasm (e.g., leukemia or multiple myeloma), or hematogenous metastasis. People with no fracture but pain resulting from lytic metastatic neoplasm or the rare symptomatic hemangioma are also candidates for vertebroplasty. People with chronically nonhealing traumatic fractures (e.g., osteonecrosis) may be candidates. In all these circumstances, there should be congruent historical, physical, and imaging findings. Vertebroplasty can also be performed prophylactically to stabilize a weakened vertebra before planned surgery.

Contraindications

There are a few absolute contraindications to vertebroplasty and kyphoplasty. These contraindications are (1) recent systemic or spinal infection, (2) uncorrected bleeding diathesis, (3) insufficient cardiopulmonary health to tolerate sedation or general anesthesia, and (4) fracture-related compromise of the spinal canal sufficient to result in myelopathy or radiculopathy. In addition, these procedures are generally not performed for fractures that are painless or have already healed.

In addition, specific fracture features do not represent absolute contraindications but substantially increase the risk or technical difficulty of the procedure. Disruption of the posterior cortex increases the risk of posterior cement leakage and therefore the risk of spinal cord or nerve root compression; this feature is rare in osteoporotic compression fractures but frequent in burst fractures and metastatic neoplasm. Substantial canal narrowing (without clinical evidence of myelopathy or radiculopathy) increases the risk that even a small amount of cement leakage will produce neurologic compromise. Marked loss of vertebral body height makes the procedure more difficult since there may be little space for needle placement. Poor visualization of osseous structures on fluoroscopy increases the risk of improper needle placement and symptomatic cement leakage but can be overcome with the use of computed tomography (CT). Treatment of patients whose fractures have these features should only be performed by the most experienced practitioners.

Preprocedure Evaluation

A thorough preprocedure evaluation is necessary for patients being considered for vertebroplasty or kyphoplasty. The pain of an acute fracture can be difficult to distinguish from the many other sources of pain in the back. Most people with osteoporotic vertebral compression fractures are elderly, and they often suffer from more than one painful pathology. A combination of careful history, physical examination, and advanced imaging is needed to make sure (1) the patient is likely to benefit from treatment, (2) vertebroplasty or kyphoplasty is the best alternative, (3) all pathologic vertebrae suitable for treatment are identified, and (4) the treatment is performed safely. The excellent outcomes reported with these procedures are grounded in the careful selection of appropriate candidates.

History

The classic symptoms from an acute vertebral compression fracture include deep pain with sudden onset, midline location, and exacerbation by motion and standing. These fractures may occur with little or no trauma. The pain often diminishes little in the first week and then fades gradually over the next several weeks to 3 months.¹ Lateral radiation may be present, but persistent radiation of the pain in a radiculopathic pattern is rare. When there is substantial kyphosis, patients may also suffer from difficulty breathing, anterior chest wall pain, and gastrointestinal discomfort.

In addition to evaluating the nature of the pain, the interview should include assessment of the effect of the pain on activities of daily living and sense of well-being. The practitioner may choose to quantify these factors using such questionnaires as the Oswestry Disability Questionnaire, Roland-Morris Disability Questionnaire, and Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Such indices can be used in conjunction with a visual analogue pain scale to follow the success of treatment.

The physician should evaluate ongoing or potential treatment of the underlying disease process. For osteoporotic patients, the interview is an opportunity to make sure that appropriate treatment of the osteoporosis is under way. The severity of osteoporosis and the use of antiosteoporosis medications substantially alter the risk of additional fractures. For patients with neoplasm, timing of the treatment may be affected by ongoing chemotherapy and radiation.

The physician should evaluate the patient’s general health and coexisting medical problems to perform the procedure safely. This evaluation allows the practitioner to determine the feasibility and the safest and most effective means of performing the procedure. Consultation with an anesthesiologist may be warranted. The physician should search for possible contraindications to the procedure (e.g., use of warfarin) and for allergies to planned pharmaceutical use (e.g., prophylactic antibiotic).

Physical Examination

The practitioner should perform a directed physical examination. This examination includes inspection of the back, palpation for focal areas of tenderness, and correlation of the site of pain with anatomic landmarks. In difficult cases, examination of the sites of pain and tenderness can be performed with fluoroscopic assistance to localize the pain to specific anatomic structures. Although point tenderness at the spinous process of the fractured vertebra is the typical finding in unhealed compression fractures, the absence of typical focal tenderness does not preclude the presence of such a fracture. Imaging is a more reliable test than this portion of the physical examination.⁶ Assessment of lower extremity neurologic function is especially important in patients with symptoms suggestive of myelopathy, radiculopathy, or spinal stenosis. Evaluation of the heart and lungs is necessary for the safe use of sedation for the procedure.

Imaging

Imaging of the spine is undertaken in all cases to confirm the clinical diagnosis and to plan the procedure. Radiographs are the imaging study of choice for the initial imaging evaluation (Fig. 173-1). Anteroposterior (AP) and lateral views should be obtained. This study allows the practitioner to confirm the presence of fracture, determine the location of fractures, assess the degree of height loss and kyphosis, and identify anatomic variants. Whenever possible, comparison to prior studies is valuable. A single radiograph almost never allows the practitioner to distinguish a new or unhealed fracture from a chronic, healed fracture. With prior radiographs (“old gold”) for comparison, new compression fractures can be identified. If serial radiographs taken several weeks apart show a new compression fracture in a patient with classic history and symptoms, no further imaging may be necessary. However, since back pain is a difficult diagnostic problem, most patients benefit from advanced imaging.

FIGURE 173-1 Lateral radiograph of the lumbar spine. The loss of height and wedge deformity signal compression fractures at L1 to L4. It is not possible to determine the age of these fractures from a single radiograph.

Magnetic resonance imaging (MRI) is the test of choice for this additional evaluation. The main goals of MRI are to (1) distinguish new or unhealed fractures from healed fractures, (2) identify other causes of pain, and (3) evaluate the risk of symptomatic cement leakage during the procedure. For these purposes, the most useful sequence is a T2-weighted sequence with fat suppression. We prefer using inversion recovery (i.e., a short tau inversion time recovery, or STIR, sequence) to achieve the fat suppression, since it is less prone to artifact than frequency-selective fat saturation techniques. On these MRI sequences, recent or unhealed fractures show a hyperintense signal within the bone marrow (Fig. 173-2). This signal may be present in poorly marginated areas filling much of the vertebral body or as discrete curvilinear fracture clefts. In contrast, healed fractures have a marrow signal similar to that of unfractured vertebra. These sequences also provide an adequate evaluation of the spinal canal and show most alternative causes of pain that might mimic fracture. Additional imaging with a sagittal T1-weighted sequence and axial T1- and T2-weighted images may be helpful. In most patients with a typical clinical history and physical examination for osteoporotic compression fracture, the STIR sequence alone is adequate, and the practitioner can reserve the full set of MRI sequences for patients whose pain is atypical or who have STIR abnormalities that require clarification. We have found value in obtaining an additional MRI shortly before the procedure when either (1) there has been worsening of the patient’s pain since the initial evaluation or (2) the imaging study used for the initial evaluation is more than 3 months old.⁷

FIGURE 173-2 MRI with a sagittal STIR sequence. The hyperintense signal in the T7 vertebral body is consistent with an unhealed compression fracture. While there is also wedge deformity at T11 and T12, the absence of marrow signal abnormality identifies these compression fractures as old and healed.

In patients who cannot tolerate MRI (e.g., those with a pacemaker), bone scan is the test of choice. Bone scan does not provide any evaluation of the soft tissues or spinal canal, but it does allow the differentiation of healed and recent fractures. The recent fractures take up the injected technetium 99m–medronate tracer in much higher concentrations (Fig. 173-3). The relative sensitivity and specificity of bone scan and MRI for this purpose have not been established.

FIGURE 173-3 Bone scan. Areas of increased uptake in the L1 and L2 vertebrae represent bone turnover in recent or unhealed fractures.

CT is not necessary for most osteoporotic compression fractures but is useful for preprocedure evaluation of burst fractures and metastases. In these circumstances, there may be substantial loss of integrity of the posterior vertebral body cortex (Fig. 173-4). This loss increases the risk of the procedure, specifically the risk of posterior leakage of cement or posterior displacement of bone or tumor.⁸ CT provides the best means for assessing this cortex. CT is also the test of choice for postprocedure evaluation of unexpected symptoms (see the later section on risks).

FIGURE 173-4 Loss of posterior vertebral body integrity. A, MRI shows metastasis with a pathologic compression fracture at T1. B, CT scan demonstrates more clearly the extensive destruction of the posterior cortex.

Procedure: Vertebroplasty

Sedation

Analgesia is necessary to perform vertebroplasty and kyphoplasty safely and with minimal discomfort. This process begins with the informed consent. Fully informing the patient of what to expect in the operating room or procedure suite facilitates patient comfort, cooperation, and satisfaction. Satisfactory analgesia usually can then be achieved with local anesthetics and moderate sedation, but in some cases general endotracheal anesthesia is needed. Vertebroplasty has generally been performed with moderate sedation, while kyphoplasty has more commonly been performed with general anesthesia. At our institution, both are usually performed using moderate sedation with intravenous midazolam and fentanyl. Continuous patient monitoring is performed with electrocardiography, blood pressure measurement, and pulse oximetry. The drug delivery and monitoring are performed by certified nursing personnel. In patients with substantial preexisting respiratory or cardiac disease, an anesthesiologist is asked to evaluate the patient and determine whether monitored anesthesia care is warranted.

Patient Positioning

The ideal patient position for thoracic and lumbar procedures is prone. This position allows the practitioner to place the needle from either side and simplifies positioning of the biplane fluoroscopy unit or C-arm. Furthermore, this position and proper cushion support maximize extension of the fractured segments, promoting kyphosis reduction.⁹ Although the patient can be rotated slightly, substantial patient angulation can make this a more difficult procedure. A special table and cushions may be used to support the head and body, but good results can be achieved with a flat fluoroscopy table and careful placement of cushions. The patient’s arms should be placed sufficiently toward the head to keep them out of the path of the fluoroscope. Patients can usually be placed in the prone position despite their painful compression fracture. If necessary, moderate sedation can be initiated before the patient is moved. Care must be taken when transferring aged or osteoporotic patients, since transfer alone may cause new fractures.

Antibiotic Prophylaxis and Skin Preparation

The risk of infection is minimized with the meticulous use of operating room procedures for sterile preparation of the skin, draping, operator scrub, and sterile gowns, masks, and gloves. Antibiotic prophylaxis is usually provided. The most common form is the intravenous administration of cefazolin (or clindamycin for those with cephalosporin allergy) just before or during the procedure. Alternatively, tobramycin may be added directly to the PMMA.

Image Guidance

Imaging guidance is necessary to ensure the success and safety of vertebroplasty and kyphoplasty. Generally, needle placement and cement placement are performed with fluoroscopy, but in rare cases, CT may be necessary. Fluoroscopy has inherently lower contrast resolution and makes greater demands on imaging technique, on the operator’s knowledge of radiographic anatomy, and on the operator’s ability to integrate planar data into a three-dimensional picture. However, the compelling reasons for using fluoroscopy whenever possible are the lower radiation dose and the ability to monitor the cement infusion continuously as the injection proceeds.

There are no established minimum standards for the fluoroscopic equipment used in vertebroplasty. However, one key to avoiding complications in this procedure is the ability to see the needles, bone landmarks, and opacified cement at all times. At least one C-arm unit is necessary. A dedicated biplane fluoroscopy suite is optimal. The quality of these fluoroscopic systems varies widely, and many older C-arm systems used for general orthopedic work put the operator at a disadvantage. The newer image intensifiers and digital fluoroscopy systems available from numerous vendors provide the best image quality and lowest radiation exposure. Shielding to minimize operator exposure to scatter radiation is necessary if the practitioner performs this procedure routinely.

Needle Placement

Once the patient is properly positioned in the fluoroscopy unit, the needle trajectory can be planned. There are two principal approaches for needle placement: transpedicular and parapedicular. The transpedicular approach takes the needle directly through the full length of the pedicle. It has the advantage of a long intraosseous path protecting the nerve roots and blood vessels from direct injury and protecting the soft tissues from cement leakage along the tract. However, in pedicles that have a long axis parallel to the sagittal plane, this approach limits the practitioner’s ability to achieve a final needle tip position near the midline. A parapedicular approach may then be the technique of choice. Here, the needle is directed along the lateral cortex of the pedicle, and then additional angulation is applied as the needle pierces the cortex at the junction of the pedicle and vertebral body.

For either approach, there are two image guidance strategies. The “end-on” approach uses fluoroscope angulation to place the barrel of the pedicle cortex over the target site in the vertebra body. This view simplifies trajectory planning and is the simplest way of preventing the needle from violating the medial cortex of the pedicle. Alternatively, the AP approach may be used. This view may be easier to achieve with some fluoroscopy systems and in some cases provides superior delineation of the pedicle margins. Once an approach has been selected, the skin is anesthetized with a small amount of subcutaneous lidocaine or bupivacaine. Following the planned needle trajectory, the periosteum is anesthetized in a similar fashion. The planned trajectory can be assessed and adjusted from fluoroscopic views of this smaller needle at the bone surface. A small nick is made in the skin, and an 11- or 13-gauge needle is placed.

End-on Technique

For the end-on technique, the operator rotates the fluoroscopy unit into an ipsilateral oblique view that places the fluoroscopy beam and needle tract perfectly parallel to each other (Fig. 173-5). The image intensifier is first rotated to a true AP position, aligning the spinous process midway between the pedicles. The craniocaudal angulation is changed to bring the pedicles to the midportion of the vertebral body. The image intensifier is then rotated to bring the ipsilateral pedicle so that its medial cortex is at the middle third of the vertebral body. This rotation can only be continued as long as the medial cortex of the pedicle remains clearly visible. The needle is placed so that it is “end on” to the image intensifier and appears as a small circle or ellipse. Once the needle has been advanced to the bone surface, small corrections in the craniocaudal angulation can be made using a true lateral view (care is needed to angle this view so that the pedicles project over each other). The needle is then advanced through the pedicle, maintaining the end-on appearance of the needle. Once the needle has traversed the pedicle, it is advanced using the lateral view to the junction of the anterior and middle thirds of the vertebral body.

FIGURE 173-5 Needle placement with end-on approach. A, Initial AP view. B, Craniocaudal angulation to place the pedicle at the vertical middle of the vertebral body. C, Ipsilateral oblique view to place the pedicle over the medial aspect of the vertebral body. D, Ipsilateral oblique view with the needle (black circle) in proper alignment. This view is maintained as the needle is advanced through the pedicle. Care is taken to avoid the medial cortex of the pedicle. E and F, Lateral and AP views with final needle location.

AP Technique

For the AP technique, the craniocaudal angulation is adjusted to bring the vertebral body end plates perpendicular to the image (Fig. 173-6). The skin entry site is placed about 1 cm superior and lateral to the center of the pedicle but must be adjusted for the thickness of the posterior paraspinal soft tissues. The needle is advanced anteriorly, medially, and caudally. By the time it reaches the bone surface, the tip should project over the upper outer cortex of the pedicle. Again, small corrections in the craniocaudal angulation can be made using a true lateral view. The needle is advanced so that its tip projects over the center of the pedicle on both AP and lateral views. The tip should project over the medial pedicle cortex as the needle traverses the posterior third of the vertebral body. The final position is again adjusted on the lateral view.

FIGURE 173-6 Needle placement with the AP approach. A, AP view with the site of skin entry (black dot). B, Needle appearance as it enters the posterior pedicle surface. C, Needle appearance when it has been advanced to the midpoint of pedicle on the lateral view. If the needle tip is more medial at this point, there is risk for traversing the medial pedicle cortex.

The image guidance for a parapedicular approach is quite similar. The needle is placed lateral and superior to the lateral cortex of the pedicle and enters the vertebral body at its junction with the pedicle. The position at which bone is encountered (i.e., at the junction of the pedicle and vertebral body) is more anterior on the lateral view.

The advance of the large needle is achieved with either using a drilling motion or tapping with a small hammer. The needle position should be checked frequently in the oblique (or AP) view for two reasons. First, it is important to ensure that the needle does not violate the medial cortex of the pedicle. Second, needle trajectory cannot be markedly altered once the needle has passed beyond a small distance into the pedicle. Accurate placement is also aided by positioning the needle centrally in the field of view to avoid inaccuracies from parallax.

The planning for the lateral position of the tip should be adjusted for the procedure to be performed and the shape of the vertebral body. Vertebroplasty for osteoporotic vertebral compression fractures was initially performed using two needles and a bipedicular approach. This technique allows reliable filling of both halves of the vertebral body, independent of the precise lateral position of the needle tip within its half of the vertebral body. However, some practitioners have adopted a unipedicular approach. This technique requires a single needle and decreases the risk and time associated with needle placement. For the unipedicular approach, a near-midline position of the needle tip provides more reliable filling of the vertebral body. In my experience, both techniques work well, and my colleagues and I base our approach on the number of levels to be treated and the configuration of the fractured vertebra. For example, in a severely collapsed vertebra, there is often substantially more marrow space at the lateral aspects of the vertebral body. In this circumstance, a bipedicular approach with lateral positioning of the needle tip provides reliable bilateral filling with little risk of symptomatic cement leakage.¹⁰ With more lateral tip positions, it is important to remember that the vertebral body is round and that the anterior cortex of the vertebra along the needle trajectory is posterior to the radiopaque line of anterior cortex on the fluoroscopic image.

Cement Placement

Both vertebroplasty and kyphoplasty currently employ PMMA cements. These cements either contain or must be modified with sterile barium sulfate powder to provide sufficient radiopacity. The barium sulfate is necessary to improve the visibility of the cement on fluoroscopy, making the procedure safer. Further alteration of the cement may be introduced by adjusting proportions of the PMMA powder and liquid monomer. The desired consistency of the cement, when ready for injection, is roughly similar to that of toothpaste. Working time varies from 10 to 20 minutes. There are a variety of delivery systems available for the cement. These systems vary from a few 1-ml syringes, a spatula, and a mixing bowl to self-contained, integrated, mixing and delivery devices. The syringe or delivery system is connected to the needle cannula, and the cement is slowly injected.

As the cement flows from the needle cannula, careful fluoroscopic monitoring helps ensure that the cement remains within the target zone or vertebra. While both AP and lateral views are important, the lateral is most valuable, since it allows the operator to evaluate the posterior position of the cement relative to the neural foramina and spinal canal. This view also shows venous or intradiscal leakage to good advantage. Some practitioners have advocated fluoroscopic monitoring of an injection of iodinated contrast before the cement instillation,⁴ but this practice is not necessary for the safe placement of cement.¹¹

The endpoints for cement injection are (1) leakage of cement beyond the marrow space, (2) cement reaching the posterior quarter of the vertebral body, and (3) cement filling the vertical expanse of the vertebra and extending across the midline. Injection stops when any of these criteria is met (Fig. 173-7). Since the cement tends to follow any pathway of least resistance, it is rare to achieve a complete vertebral body cast. It is tempting to inject until a “pretty” fluoroscopic picture is achieved. However, filling until the practitioner has achieved a complete cast of the vertebra is not necessary to provide pain relief or stability,^12,¹³ and when taken to extremes, this approach leads to higher rates of cement leakage and clinical complications.¹⁴ Even with these guidelines, however, there is substantial variation in philosophy and practice among practitioners regarding the optimum amount and pattern of cement deposition.¹⁵

FIGURE 173-7 Vertebroplasty. A and B, Final needle positions for a bipedicular technique shown on lateral and AP radiographs, respectively. C and D, Cement filling at end of the procedure on lateral and AP radiographs, respectively. Installation was stopped when the cement reached the posterior quarter of the vertebral body.

Postprocedure Monitoring

Manual compression is applied to the puncture sites, and sterile bandages are placed. Postprocedure radiographs are obtained. The patient is gently returned to the supine position. The patient is monitored for 1 to 2 hours with standard postanesthesia monitoring and neurologic assessment. The patient is then allowed to attempt supervised ambulation. As long as there is no increased pain or disability, the patient is allowed to return home with postprocedure instructions that include 3 days of limited activity and monitoring of the puncture sites. If there is worsening of the patient’s pain or if there are new symptoms, the patient is assessed by a physician and usually undergoes CT of the treated area.

Procedure: Kyphoplasty

Much of the kyphoplasty procedure follows steps and guidelines similar to those described for vertebroplasty. Patient preparation, sedation, positioning, and image guidance are largely the same. Kyphoplasty has traditionally been performed with general anesthesia. There is justification for this difference: The procedure time is longer, larger cannulas are used, and there is greater manipulation of osseous structures. However, many institutions have been able to overcome these obstacles for most patients, and the procedure is performed with moderate to deep sedation with success.^5,¹⁶

The key differences between kyphoplasty and vertebroplasty are the cannula introducer system, the balloon tamp and pressurization system, and the details of cement delivery. These features add slightly to the time and complexity of the procedure but decrease the incidence of cement leakage.

The initial needle placement is similar to that of vertebroplasty, but the cannula is only advanced to the posterior aspect of the vertebral body. The stylet or introducer is then exchanged for a hand-operated drill bit. This drill is carefully advanced to the anterior aspect of the vertebral body, 3 to 4 mm posterior to the anterior cortical margin (Fig. 173-8). In general, a near-midline position of the needle tip on the AP view is desired. The drill or introducer is removed, and the space thus created is smoothed with a blunt stylet. A deflated balloon tamp is advanced into this small cavity so that the posterior balloon marker is sufficiently anterior to the cannula tip. A second system is then placed from the other side in a similar manner. Once both balloons are in place, each balloon tamp, attached to a locking syringe with a digital manometer, is slowly inflated with iodinated contrast. The inflation is performed synchronously and is monitored with the pressure transducer and intermittent fluoroscopy. Inflation continues slowly until (1) the kyphotic deformity is corrected, (2) the balloon tamp reaches one of the cortical margins, or (3) the system reaches maximum pressure or maximum balloon volume. The balloon is then deflated. Cement is prepared and placed into tubular bone fillers. Sufficient time is allowed for the cement to reach the desired consistency, often with a greater viscosity than that many practitioners use for vertebroplasty. The loaded bone filler is placed through the cannula into the cavity, and the cement is slowly hand injected under fluoroscopic guidance. The cement fills the cavity, matching or slightly exceeding the volume of the inflated balloon tamp.

FIGURE 173-8 Kyphoplasty. A, Lateral view with the cannula at the posterior aspect of the vertebral body and the drill advanced to the anterior aspect of the vertebral body. B, Balloons in place before inflation. C, Balloons inflated. D, Final view after cement deposition.

Kyphoplasty has traditionally been performed with bilateral needle and balloon placements, but unilateral balloon placement has also been used with success.^5,¹⁷ Several balloon sizes and configurations improve the ability of the system to achieve vertical expansion of the vertebral body before inflation must end. An available curette allows the operator to focally disrupt the integrity of the osseous matrix before full balloon inflation, improving chances for height gain and kyphosis reduction.

Risks

Vertebroplasty and kyphoplasty are minimally invasive procedures with only small risks of morbidity and mortality. However, careful attention to technique and first-rate imaging equipment are necessary, since the practitioner is working near the spinal cord and aorta with large needles and a liquid polymer. With such care, the overwhelming majority of complications should be minor. The overall incidence of clinically evident complications for the procedures ranges from 1% to 5%.^18,¹⁹

The most common complication reported for vertebroplasty and kyphoplasty is rib fracture. In the largest case series, the reported incidence is 3%.^20,²¹ These fractures presumably result from even minor trauma to the osteoporotic skeleton during transfer of the patient or needle placement. Since such fractures can occur in these patients with even normal movement, they may be difficult to prevent entirely.

Passage of cement beyond the confines of the vertebra is a complication unique to these procedures. The cement is injected, and filling of the vertebra depends on a small pressure gradient between the needle tip and the cement’s destination. The cement flows along pathways of least resistance. These pathways include fracture clefts and venous channels. The incidence of such leakage varies substantially in reported series and is a function of the procedure chosen (vertebroplasty vs. kyphoplasty), operator experience, and approach to cement filling (see the earlier section on cement placement). In most circumstances, a small amount of extraosseous cement produces no symptoms or long-term morbidity. These leaks include those that occur along the anterior and lateral surfaces of the vertebral body and those into the intervertebral disc. However, even small amounts of cement adjacent to a nerve root can produce radicular pain. The large vertebroplasty case series published by experienced operators reported a risk of symptomatic cement leakage about the vertebral body that varies from 0% to 1% for the treatment of osteoporotic fractures ^11,^20,²¹ and is up to 4% to 8% for the treatment of metastases.^8,²² For kyphoplasty, the overall risk of leakage is less.¹⁸ Kyphoplasty permits greater control of cement instillation through the creation of a cavity into which a predetermined volume of cement is placed and the use of more viscous cement. The incidence of any leakage with kyphoplasty is about 14%, and symptomatic leakage is rare.¹⁸

When radiculopathy is produced by cement leakage, the pain usually can be treated with a short course of intravenous or oral steroids or nerve root block. In some cases, there is sufficient foraminal cement to cause frank root compression; in these cases, surgical decompression may be the treatment of choice.²² In rare cases, sufficient cement has been placed in the spinal canal to cause cord compression or cauda equina syndrome; surgical decompression is then warranted.²³

If cement passes into perivertebral veins, it can be carried to the lungs and produce symptomatic pulmonary embolism. The incidence of small pulmonary cement emboli is probably higher than once thought, with a recent CT study uncovering the phenomenon in 23% of treatment sessions.²⁴ However, most such emboli produce no symptoms or changes in oxygenation.^24,²⁵ Although the morbidity is usually mild,^20,²⁶ substantial cement embolization has occurred, necessitating endovascular or surgical intervention. Paradoxical embolization, including cerebral embolization and stroke, has been reported.²⁷ Most cases of embolism have been unrecognized during cement placement; good cement opacification, high-quality equipment, vigilant fluoroscopic monitoring, and meticulous patient monitoring keep these risks to a minimum.

Other rare complications reported in the larger case series for these procedures include transient fever, transient hypotension, unexplained pain exacerbation, hematoma, pedicle fracture, noninfectious discitis, and spinal infection. Death has occurred in a few patients in the periprocedure period, generally from cardiovascular complications of uncertain etiology.²⁸

It has been proposed that the presence of the intravertebral PMMA creates stresses that can lead to fractures in adjacent vertebrae. Additional fractures occur in 8% to 27% of patients treated with PMMA augmentation.²⁹ Suspicion that fracture risk is increased by the procedures arises from retrospective analyses showing a substantially greater risk of fracture at levels adjacent to treated vertebrae.^30,³¹ However, there are other explanations for this phenomenon. Regional variation in stresses and in bone integrity at baseline could explain increased fracture risk in adjacent vertebrae.²⁹ In the one prospective, randomized trial sufficiently powered to detect differences in fracture rates, no difference was observed.³²

Benefits

Pain Relief and Activity

The primary goal of both vertebroplasty and kyphoplasty is pain relief. This pain relief is often immediate (as soon as the patient has reached the recovery room) and sometimes complete. Most practitioners have had bedridden patients in severe pain leave the same day, smiling and pain free. Most patients are able to stop or reduce their use of analgesic medications and resume activities of daily living. This experience has been borne out in case series that testified to the marked pain relief and improved function in about 90% of patients.³³

Until recently, data on the efficacy of these procedures chiefly consisted of large case series. For vertebroplasty, case series have reported the results in hundreds of patients with osteoporosis. Most of these studies consistent of patients treated after a 4- to 6-week trial of conservative management. These studies have uniformly shown long-standing benefits of reduced pain and improved function in patients treated.^20,^21,^30,^34,³⁵ One small prospective, randomized trial compared vertebroplasty with medical management in patients within 8 weeks of fracture and found that patients who received vertebroplasty had substantially better pain control at 24 hours than those hospitalized for narcotic analgesia and bed rest.³⁶ Consistent with the known natural history of patients with compression fractures (i.e., those not subjected to a trial of conservative management), follow-up at 3 months showed no significant benefit.

In 2009, the results of two double-blinded, randomized, controlled studies were reported. Each included a control group that underwent a sham procedure simulating vertebroplasty. Neither of the studies showed a major benefit for vertebroplasty. Buchbinder et al.³⁷ randomized 78 patients and used as the primary endpoint a score for overall pain at 3 months postprocedure. The study was powered to have an 80% chance of finding a 2.5 in 10 difference in this score. Kallmes et al.,³⁸ randomized 131 patients and used as primary endpoints the modified Roland-Morris Disability Questionnaire and an average 24-hour back pain scale at 1 month postprocedure. The study did not meet initial enrollment targets but ultimately had an estimated 80% chance of detecting a 3-point difference on the disability measure and a 1.5-point difference on the pain scale.

Kyphoplasty has shown a similar ability to reduce pain in smaller series.³⁹^–⁴³ One larger, multicenter, prospective series of 155 patients showed a mean decrease in a visual analogue pain scale of 4.5 in 10, significant improvement in patient activity, and substantial improvements in most SF-36 physical and mental subdomains.⁴⁴ Recently, the results of a multicenter, prospective, randomized trial were published for kyphoplasty. In this study, 300 patients with compression fractures were randomized to either kyphoplasty or medical management. The SF-36 physical component summary scale and other measures showed significantly greater improvement in the kyphoplasty group at 1 month.³² The positive effects persisted over 1 year, though differences between treatment and control groups slowly diminished as scores in the control group improved.

The pain resulting from neoplasm and hemangioma frequently responds to vertebroplasty or kyphoplasty. For hemangiomas, pain relief is nearly uniform and long lasting.⁴⁵ For neoplasms, pain relief is achieved in many patients but results are slightly less impressive than those for patients with osteoporotic fractures.^3,⁴⁶ One recent prospective, uncontrolled study of kyphoplasty showed marked, immediate, and durable pain relief in such patients,⁴⁷ and no clinical adverse events occurred.

Fracture Stabilization

Stabilization of the vertebral body is usually a secondary goal of vertebroplasty and kyphoplasty. Many vertebrae that have compression fractures continue to lose height over time as they undergo additional fractures. Vertebroplasty and kyphoplasty prevent this additional pain and additional deformity in almost all cases. Case series with long-term follow-up have generally not reported any recurrent fractures at treated levels.^22,³⁴ However, a small incidence of repeat fracture in treated vertebrae has been reported in the setting of osteoporosis.⁴⁸ In patients with metastatic neoplasm, vertebroplasty has been performed for stabilization of pathologic but unfractured vertebrae. In this setting, no fracture has been reported in short-term follow-up.³

Height Restoration and Kyphosis Correction

Kyphoplasty has the added goal of restoring or improving vertebral body height and mechanical alignment at the fracture. The height loss and kyphosis associated with compression fractures can lead to decreased pulmonary capacity and quality of life. Furthermore, it has been proposed that the kyphotic deformity alone may predispose patients to chronic pain and the risk of additional injury. There are clearly cases in which marked height restoration and kyphosis reduction can be achieved with kyphoplasty (Fig. 173-9). There is anecdotal evidence of patients for whom kyphoplasty provides substantial relief of not only pain but also breathing difficulty and deformity. However, this feature has been de-emphasized in recent years and was not assessed in the industry-sponsored Fracture Reduction Evaluation (FREE) trial.

FIGURE 173-9 Restoration of vertebral body height and reduction of kyphosis after kyphoplasty. A, Preprocedure. B, Balloon inflation.

(Courtesy of Eric Truumees, MD, Southfield, MI.)

The restoration of vertebral body height following kyphoplasty has been quantified in several case series. Height improvement is achieved to some degree in 80% of patients,⁴⁴ and complete or near-complete height restoration is achieved in 10% to 20%.^40,⁴² Greater degrees of height restoration appear to be achieved when kyphoplasty is performed earlier.⁴¹ One study found small immediate improvement in height but observed that this diminished to baseline over 1 year.⁴⁷

The restoration of alignment following kyphoplasty has been studied in only a few reports. Phillips et al.⁴³ found 58% of fractures treated with kyphoplasty to be partially reducible; in the reducible fractures, the mean Cobb angle correction was 14 degrees. The mean for all levels was 9 degrees. Theodorou et al.¹⁶ reported substantially improved kyphosis with a mean angle correction for all fractures of about 10 degrees, representing a 62% reduction of the deformity. This improvement may also be transient.⁴⁷

Vertebroplasty also appears to result in partial restoration of vertebral body height and alignment in some cases. Teng et al.⁹ showed small but significant improvement in vertebral height and kyphosis, with these improvements present in all but a few patients. Pitton et al.⁴⁹ found durable height restoration (average 1.5 mm) and decreased wedge deformity (average 3.4 degrees) at 1 year, but these benefits were limited to patients with marked preprocedure wedge deformity. Hiwatashi et al.⁵⁰ found an average 2 mm increase in vertebral body height and 3 degree decrease in wedge deformity. Furthermore, they found no significant difference for these parameters between kyphoplasty and vertebroplasty.

Future Directions

Technical Innovation

Vertebroplasty and kyphoplasty continue to evolve. Innovation proceeds in instrumentation, cement materials, and hybrid procedures. New instruments have been designed to improve cement containment and height restoration. Percutaneously placed curettes of several forms can now be used to disrupt trabeculae and form a cavity for cement placement. One device provides a polyethylene terephthalate semiporous balloon that is expanded by the infused cement. Another replaces the balloon tamp with permanently implanted, stacked, plastic wafers. These devices are released for use but have not yet undergone rigorous evaluation of added benefit.

There are several PMMA formulations available, and they have different setting and mechanical properties.⁵¹ There has been considerable interest in development of higher-viscosity cements, again with the hope of providing superior vertebral filling and decreased leakage.⁵² One approach includes extracorporeal radiofrequency heating of the PMMA and controlled high-pressure cement injection. PMMA has been mixed with radioactive materials in a form of brachytherapy for spine metastases.⁵³

Bioactive cement materials may one day replace PMMA. The advantage of these materials is that they more closely match the physical properties of native bone and remodel over time. Early results with these materials have been mixed. While they appear to be capable of providing similar pain relief,^54,⁵⁵ there have been problems with cement stability and fracture.⁵⁶

Vertebroplasty and kyphoplasty are also being combined with other procedures for the treatment of neoplasm or trauma. For metastases, the procedures have been safely performed after the use of radiofrequency ablation or cyroablation.⁵⁷ For burst fractures, the procedures have been combined with posterior instrumented decompression.⁵⁸

Vertebroplasty versus Kyphoplasty

One of the chief controversies in the treatment of compression fractures revolves around the relative merits of vertebroplasty and kyphoplasty and their variants. Each of the procedures has some advantages. Vertebroplasty has the advantages of simplicity and lower cost. The procedure requires about half the time of kyphoplasty.⁵ The materials are less expensive by a factor of 5 to 10. Both procedures can be performed with moderate sedation, but the procedure time, larger cannulas, and balloon inflation of kyphoplasty make greater demands on the analgesia. Kyphoplasty has the advantage of providing better control of the infused cement, and this results in a lower incidence of extraosseous passage of PMMA and related adverse events.⁵⁹

The two procedures seem to provide similar levels and duration of pain relief. Meta-analyses have shown little difference in the clinical effectiveness between the two procedures.^59,⁶⁰ There are two ongoing randomized, controlled trials with primary objectives of comparing the effectiveness or safety of the two procedures. The industry-sponsored Kyphoplasty and Vertebroplasty in the Augmentation and Restoration of Vertebral Body Compression Fractures trials randomized patients with osteoporotic compression fractures to one of the two procedures. Their results may be available in 2012.

The proposal that one procedure is superior to the other may be overly simplistic. These may be complementary procedures whose use can be based rationally on patient and fracture characteristics. For example, patients with recent fractures may see substantial additional benefit from kyphoplasty, whereas those with older fractures may not. One prospective study used fracture age and morphology to select the procedure performed,⁶¹ with good result.