Kyphoplasty Technique

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CHAPTER 33 Kyphoplasty Technique

Amir H. Fayyazi, Frank M. Phillips

INTRODUCTION

Pathologic vertebral compression fractures (VCFs) are a leading cause of disability and morbidity in patients with osteoporosis, multiple myeloma, and bone metastases.1–4 The consequences of these fractures include pain and often progressive vertebral collapse with resultant spinal kyphosis. Osteoporotic VCFs have been shown to adversely affect quality of life, physical function, mental health, and survival.4–6 These effects are related to the severity of the spinal deformity and are, in part, independent of pain.4,5 In recent years, researchers have highlighted the reduced quality of life, functional limitations, and impaired pulmonary function associated with spinal kyphotic deformity from osteoporotic VCFs.3,4,7–9 Kyphosis can lead to reduced abdominal space with poor appetite and resultant nutritional problems.4,10 By shifting the patient’s center of gravity forward, kyphotic deformity not only increases the risk of additional fractures,11 but also may lead to poor balance which potentially increases the risk of accidental falls.12,13

The ideal surgical treatment of VCFs should address both the fracture-related pain and the kyphotic deformity. It should be accomplished in a minimally invasive fashion without subjecting the patient to inordinate risks or excessive surgical trauma. Over the past decade, percutaneous vertebroplasty, involving the injection of polymethylmethacrylate (PMMA) into a fractured vertebral body, has been popularized. Substantial alleviation of pain has been reported in a majority of patients treated with vertebroplasty for osteopenic VCF.14–22 Although effective at relieving vertebral fracture pain, vertebroplasty is not designed to address the associated sagittal plane deformity.

Kyphoplasty involves the penetration of the vertebral body with a trochar followed by insertion of an inflatable balloon tamp (IBT). Inflation of the balloon tamp restores the vertebral body back towards its original height, while creating a cavity to be filled with bone void filler. This technique was first performed in 1998. Early results of kyphoplasty suggest significant pain relief as well as the ability to improve the collapsed vertebral body’s height.23–29

The kyphoplasty procedure was designed to address vertebroplasty’s shortcomings such as high rates of cement leakage, although they rarely manifest with symptoms, and inability to correct fracture deformity. As the balloon tamp is inflated in the fractured vertebral body, the vertebral endplates are pushed apart reducing the fracture, and cancellous bone is pushed away from the balloon creating a cavity surrounded by compacted cancellous bone.30–32 The creation of an intravertebral cavity may decrease the potential for cement leakage by allowing for low-pressure, controlled placement of ‘doughy’ cement into the cavity and by creating a dam effect by densely compacting bone around the cavity.

PMMA has been the most common bone void filler used in both vertebroplasty and kyphoplasty. This acrylic cement has a long history of clinical use for the fixation of metal and plastic joint replacements and for the fixation of pathological fractures.33,34 When used to treat vertebral compression fractures, PMMA is usually modified (for example, addition of more barium sulfate, addition of antibiotics, alteration of monomer to powder ratio), in part to attain a viscosity that allows percutaneous insertion into vertebrae while minimizing risk of extravertebral leaks. In April, 2004, the United States FDA approved a formulation of PMMA for use in kyphoplasty procedures.

KYPHOPLASTY PATIENT SELECTION

Indications and contraindications

The main indications for kyphoplasty are painful or progressive osteoporotic or osteolytic vertebral compression fractures. Contraindications include systemic pathologies such as sepsis, prolonged bleeding times, or cardiopulmonary conditions that would preclude the safe completion of the procedure. In certain vertebra plana fracture configurations with height loss greater than 80% of the prefracture height, kyphoplasty may be technically difficult. The feasibility of the procedure should be assessed on the merits of the case. Patients with true burst fractures or fractures associated with neurologic findings are not candidates for percutaneous vertebral augmentation procedures. Generally, we do not advocate cementing more than three vertebral levels in one procedure because of the potential for deleterious cardiopulmonary effects related to pulmonary embolization (fat or cement) or to cement monomer.

Surgical timing

The optimal timing of kyphoplasty treatment is uncertain. In a patient with an acute VCF and relatively minor vertebral collapse, the senior author (F.M.P.) will attempt a trial of conservative care during which serial radiographs are obtained. Kyphoplasty is recommended if there is progressive collapse of the vertebral body, if the pain attributed to the VCF is incapacitating, or if the pain attributed to the VCF does not respond to a reasonable period of conservative care.

With advanced kyphosis at the time of presentation after a VCF, immediate kyphoplasty treatment may be considered to improve sagittal alignment. In the authors’ experience, earlier kyphoplasty may also be warranted for fractures at the thoracolumbar junction, fractures due to steroid-induced osteoporosis, and fractures occurring in vertebra with extremely low bone mineral density (i.e. a T score of ≤ 4 SD), which are predisposed to progressive collapse and deformity.

To improve reliability and the extent of fracture reduction, one might consider performing kyphoplasty soon after fracture. Some studies suggest improved fracture reduction when kyphoplasty is performed earlier.24,26 However, the appropriate duration of nonoperative treatment prior to consideration of kyphoplasty has not yet been established.

Preoperative evaluation

Before proceeding with kyphoplasty, the physician must confirm that the patient’s back pain is indeed caused by a VCF. This determination requires careful correlation of the patient’s history and clinical examination with radiographic documentation of an acute or nonhealed VCF. The possibility of other spinal pathologies such as tumors or degenerative spondylosis must be considered as potential causes of back pain and deformity. A thorough neurologic examination is essential to rule out neurologic compromise. Pain radiating around the trunk in a dermatomal manner may accompany VCFs. Pulmonary function should be evaluated in those patients in whom advanced kyphosis may have led to respiratory difficulty.

Preoperative planning for kyphoplasty includes imaging studies to confirm the fracture, estimate the duration of the fracture, and define the fracture anatomy. Lateral radiographs are particularly useful to plan the trajectory for any percutaneous procedure. Magnetic resonance imaging (MRI) can visualize bony edema, which indicates acute fracture, as well as help rule out infection or tumor involvement. Malignant causes of VCF are usually characterized by an ill-defined margin, signal enhancement, and pedicle involvement as well as by paravertebral soft tissue mass.35 Sagittal MRI images with short tau inversion recovery (STIR) sequences highlight the marrow edema changes associated with acute VCFs. STIR sequence MRI has proven useful in determining the acuteness of a VCF.

SURGICAL ANATOMY

Understanding the anatomy of the spinal column and correlating spinal anatomy with intraoperative fluoroscopic images is essential to performing kyphoplasty. The mediolateral pedicle diameter is significantly smaller than the superior–inferior diameter. In the thoracic spine, the pedicle diameters are smallest in the midthoracic region especially at T5–7. The pedicle size appears to decrease as one descends from the upper thoracic segment to the middle segment and later increases in the lower segments. In the lumbar spine, the pedicle diameter increases gradually in the caudal segments. Also, in the majority of patients, the L1 pedicle diameter is smaller than the T11 or T12 pedicle diameter.

The orientation of the pedicle is important in planning an appropriate trajectory for kyphoplasty. The medial inclination in the transverse plane appears to be greatest in the upper thoracic segments (T1–3), and becomes a straight anterior trajectory in the middle to lower thoracic spinal segments (Fig. 33.1). In the lumbar spine, the medial orientation of the pedicles increases slightly from L1 to L5. In the thoracic spine, the attachment of the ribs to the corresponding vertebral body (i.e. costovertebral joint) protects the lateral side of the pedicle allowing cannulation through an extrapedicular approach. Despite the smaller size of the thoracic pedicle, the costovertebral attachment results in a much larger effective pedicle size (Fig. 33.2)

image

Fig. 33.1 In the thoracic spine, the pedicles have less of a medial inclination (arrows), so that an extrapedicular approach will allow for better medialization of the IBTs.

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Fig. 33.2 The costovertebral attachment results in a much larger effective pedicle size in thoracic vertebrae.

KYPHOPLASTY SURGICAL TECHNIQUE

Anesthesia

Although the procedure may be performed under conscious sedation, the authors prefer to use general anesthesia for patients undergoing kyphoplasty. Advantages of general anesthesia include easier airway management, elimination of patient discomfort during the procedure, and elimination of patient motion that might impair fluoroscopic imaging.

Intraoperative positioning

The patient is positioned prone on a table in the operating room or on a spinal frame with cushioned bolsters in the radiology suite. We prefer to use a Jackson frame which enhances the natural extension of the spine and also allows for biplane fluoroscopy. Alternatively, the patient can be placed on a radiolucent table with rolls placed beneath the chest and hips. The face, elbows, and legs should be well padded.

Fluoroscopic imaging

The authors have found simultaneous biplanar fluoroscopy to be advantageous by allowing orthogonal visualization without having to move the C-arm. The ability to visualize the pedicles in both anteroposterior (AP) and lateral views is essential to performing the procedure. Fluoroscopic images confirming the patient’s anatomy must be obtained prior to initiating vertebral cannulation. In the AP view, the superior and inferior endplates are parallel to the fluoroscopic beam and are each visualized as a single cortical shadow, the spinous process is centered in the vertebral body, and the pedicles are symmetric and positioned in the upper half of the vertebral body (Fig. 33.3A). In the lateral view, the endplates are also parallel and the pedicles are superimposed (Fig. 33.3B), Alternatively, the fluoroscope can be rotated 10–20° for a pedicle en-face view, the view down the path of the pedicle (Fig. 33.3C) In this position, the pedicle is visualized directly and can be cannulated by paralleling the pathway of the X-ray beam.

image

Fig. 33.3 (A) In a centered AP view, each endplate is visualized as a single cortical shadow, the spinous process is centered in the vertebral body, and the pedicles are symmetrical and positioned in the upper half of the vertebral body. (B) In a centered lateral view, the endplates are parallel, and the pedicles are superimposed. (C) When the fluoroscope is rotated 10–20°, a pedicle en-face view, the view down the path of the pedicle, is visualized.

Figures A and B courtesy of Kyphon Inc., Sunnyvale CA, USA.

Surgical approaches

Bilateral transpedicular and extrapedicular approaches have been described for accessing the vertebral body during kyphoplasty. Most kyphoplasty procedures are performed by accessing the vertebral body through a transpedicular approach. In the upper and midthoracic spine, the transpedicular route may not allow for adequate medial placement of the instruments, which may limit optimal IBT inflation. The extrapedicular approach is an alternative that may allow for better medialization of the tools. The extrapedicular approach takes advantage of the costovertebral complex and allows entry through a more lateral starting point. An alternative far lateral approach to the lumbar vertebra has also been described; however, this technique has not been widely adopted.

Surgical technique

Starting position

When using the transpedicular approach, the initial instrument should dock on the lateral aspect of the facet joint overlying the lateral aspect of the pedicle on the AP fluoroscopic image (Fig. 33.4). With the extrapedicular approach, the initial instrument is docked at the junction of the transverse process, rib head, and lateral pedicle wall (Fig. 33.5). The tip of the instrument appears outside of the lateral pedicle wall on the AP image. Unless an appropriate starting point is chosen, the balloon tamps cannot be positioned correctly, decreasing the success of the reduction. Once the docking position is selected on the AP view, the position of the starting point must be checked on the lateral view to confirm the appropriate trajectory toward the collapsed vertebral body.

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Fig. 33.4 With the transpedicular approach, the initial instrument should dock on the lateral aspect of the facet joint overlying the lateral aspect of the pedicle on the AP view (center). Lateral and axial views are shown (top and bottom, respectively).

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Fig. 33.5 With the extrapedicular approach, the initial instrument is docked at the junction of the transverse process, rib head, and lateral pedicle wall. Lateral, AP, and axial views are shown (top, center, and bottom, respectively).

Pedicle cannulation

During a transpedicular approach, the Jamshidi needle is advanced down the pedicle and into the posterior aspect of the vertebral body. At first, resistance to the passage of the needle is noted because of the cortical bone of the facet. As the needle enters the cancellous bone of the pedicle, the resistance decreases. Orthogonal fluoroscopic views are required as the needle advances through the pedicle.

With both transpedicular and extrapedicular approaches, as the needle is advanced, the tip should remain lateral to the medial pedicle wall on the AP image until it reaches the posterior aspect of the vertebral body on the lateral image (Fig. 33.6). This technique ensures that the instrument remains outside of the spinal canal. Once the vertebral body is entered, the tip of the instrument may be medialized as is appropriate but should not cross the midline. The Jamshidi needle should be advanced 1–2 mm past the posterior vertebral body margin.

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Fig. 33.6 With both transpedicular and extrapedicular approaches, as the needle is advanced (Midpedicle), the tip should remain lateral to the medial pedicle wall on the AP image (center) until it reaches the posterior aspect of the vertebral body on the lateral image (Final position, top). Axial views are also shown (bottom).

Placement of working cannulae

The inner stylet is removed from the introducer needle, and a guide wire is placed into the vertebral body. After the working cannula is advanced over the guide wire into the posterior aspect of the vertebral body under biplanar fluoroscopic guidance, the guide wire is removed (Fig. 33.7). It is important to limit the number of passes through the pedicle as multiple attempts at cannulation create potential paths for cement leakage.

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Fig. 33.7 The working cannula is advanced over the guide wire into the posterior aspect of the vertebral body under biplanar fluoroscopic guidance, and the guide wire is removed.

Courtesy of Kyphon Inc., Sunnyvale CA, USA.

Vertebral body preparation

A drill or bone tamp is used to prepare the vertebral body for placement of the IBTs. Under lateral fluoroscopy, the drill or tamp should be advanced to within 2–4 mm of the anterior cortex without perforating the cortex (Fig. 33.8). On the AP view, the tip of the drill should approach the middle of the vertebral body (Fig. 33.9). Once the drill is removed, a dull guide pin can be used to palpate the anterior cortex to confirm that there is no perforation. The vertebral body is now ready for expansion.

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Fig. 33.8 Under lateral fluoroscopy, the drill (A) or tamp (B) should be advanced to within 2–4 mm of the anterior cortex without perforating the cortex.

Courtesy of Kyphon Inc., Sunnyvale CA, USA.

image

Fig. 33.9 On the AP view, the tip of the drill should approach the middle of the vertebral body but not cross midline.

Courtesy of Kyphon Inc., Sunnyvale CA, USA.

Inflatable balloon tamp inflation

The bilateral IBTs are placed anteriorly in the vertebral body. To create a cavity within the vertebra and to reduce the fracture deformity, the IBTs are inflated in 0.5 cc increments while using visual (radiographic), volume, and pressure controls (digital manometer). Inflation continues until vertebral body height is restored, the IBT contacts a vertebral body cortical wall, the IBT reaches the maximal pressure rating without spontaneous decay, or maximal balloon volume is reached (Fig. 33.10). Four- or six-millimeter-sized balloons are available. We prefer to use 6 mm balloons in larger vertebral bodies (T12–L5) and 4 mm balloons in the midthoracic spine.

image

Fig. 33.10 Inflation continues (A–C) until vertebral body height is restored, the IBT contacts a vertebral body cortical wall, the IBT reaches maximal pressure rating without spontaneous decay, or the maximal balloon volume is reached.

Courtesy of Kyphon Inc., Sunnyvale CA, USA.

Cement application

After the IBTs are withdrawn, a bone filler cannula is used to place partially cured PMMA into the cavity within the fractured vertebral body. To minimize the risk of cement extravasation, the authors allow the cement to become quite viscous prior to placement in the vertebral body. The bone filler device (BFD) filled with cement is positioned anteriorly in the intravertebral cavity created by IBT inflation. As the plunger is advanced, cement is expelled and fills the intravertebral cavity in a retrograde fashion. Cementing should be discontinued if extravertebral extravasation occurs or when cement reaches the posterior 25% of the vertebral body. The cement volume should approximate the volume of the intravertebral cavity. The judicious use of live fluoroscopic imaging is critical during cementing (Fig. 33.11). If cement extravasation occurs, usually through a fractured endplate or vertebral cortex, placing a small amount of viscous cement into the cavity and reinflating the balloon can salvage this situation. This maneuver will line the cavity walls with cement, effectively preventing further extravasation when the remainder of the cavity is filled with cement.

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Fig. 33.11 The cement volume should approximate the volume of the intravertebral cavity. The judicious use of live fluoroscopic imaging is critical during cementing.

Courtesy of Kyphon Inc., Sunnyvale CA, USA.

Postoperative care

Postoperatively, the authors prefer to keep patients prone until they are alert. Once the patients have recovered from the anesthesia, they are mobilized by first sitting on the side of the bed and ambulating later that evening. Most patients are discharged home within a day of the procedure.

COMPLICATIONS AND PREVENTIVE MEASURES

Errors in patient selection

Poor clinical outcomes may be predicted for kyphoplasty unless careful attention is given to patient screening and work-up. Treating old, healed VCFs is unlikely to affect the patient’s symptoms. The VCF must be confirmed as the likely pain generator if either vertebroplasty or kyphoplasty is being considered. This determination usually requires a combination of clinical findings suggestive of fracture pain and confirmatory imaging studies. VCF pain often increases with weight-bearing activities and eases with recumbency. On history, the presence of abrupt onset of pain that is aggravated by activity or changing positions and that is localized to the area of the radiographically documented fracture suggests the fracture to be responsible for the patient’s symptoms. In contrast to acute fracture pain, the back pain of chronic kyphosis typically worsens as the patient remains erect for periods of time and is not typically exacerbated by changes in position.

The existence of multiple fractures may complicate the diagnosis, so that advanced imaging studies such as MRI or computed tomography (CT) with bone scans are usually required to identify recent fractures. Sagittal T1-weighted MR sequences can distinguish acute or nonhealed fractures from healed fractures. Edema associated with acute VCFs produces low signal intensity, whereas more chronic fractures tend to produce signals that are similar to those of nonfractured vertebrae. As mentioned in the Preoperative Evaluation section, sagittal STIR (heavily T2-weighted) MRI sequences are the most sensitive way to distinguish marrow fat from marrow edema. In STIR-MR images, edema in acute fractures produces high-intensity signal.36–38 On bone scan analyses, recently fractured vertebrae show an increased uptake of 99mTc compared to nonfractured vertebrae. CT plus bone scans may be used when MR images cannot be obtained.

Vertebral body access complications

With either the transpedicular or the extrapedicular approach, care must be taken to avoid injuring surrounding tissues while accessing the vertebral body. The risk of injury to the neural elements increases if the medial pedicle wall is breached. Accessing the vertebral body caudal to the pedicle may place the segmental vessels and nerve roots at risk. Anterior or lateral perforation of the vertebral cortices with instruments may result in vascular injury or injury to structures in the thoracic or retroperitoneal spaces. Multiple attempts at cannulating the vertebral body should be avoided because of the increased risk of cement leaks through these additional tracts.

Cement complications

The majority of complications reported for vertebral augmentation procedures relate to extravertebral cement extravasation. Cement may leak out of the vertebral body directly through deficiencies in the vertebral body cortex or via the venous system. If PMMA extravasates outside of the vertebral body, complications related to mechanical or thermal injury of adjacent anatomic structures may occur. The risk of local cement leakage is likely affected by cement injection pressure and cement viscosity as well as the ability of the bone, particularly the vertebral body cortex, to resist cement leakage. In addition to the risks of local cement leakage, systemic exposure to cement has been associated with cardiovascular collapse.39,40 It has been hypothesized that pressurization of PMMA into cancellous bone predisposes to embolization of cement, methylmethacrylate monomer, and bone marrow contents to the lungs with resulting adverse cardiopulmonary sequelae.39–42 This theorized result is certainly a cause for concern during vertebral augmentation procedures when high-pressure PMMA injection into vertebral bodies is performed.

Extravertebral cement extravasation commonly occurs during vertebroplasty with reported leak rates of up to 65%;14 however, clinical sequelae of the leakage have been infrequently reported. In contrast, the reported rate of cement extravasation with kyphoplasty is typically less than 10%.23,26–29,43 With kyphoplasty, the creation of an intravertebral cavity surrounded by compacted bone allows for the placement of higher-viscosity cement under lower pressure compared to the injection conditions needed for vertebroplasty.

Failure of reduction

The deleterious effects of spinal kyphosis on physical function, mental, respiratory, and gastrointestinal health are well established.3–5,9,44–46 Kyphoplasty attempts to reduce the fracture and associated deformity in a reliable and predictable fashion. Some degree of fracture reduction has been achieved in more than 60% of treated fractures.27,28 Factors that seem to limit reduction achieved with kyphoplasty include partial healing of bone, suboptimal placement of the IBT, and collapse of vertebral endplates after IBT removal and before cement placement. In cases where healed bone limits IBT expansion and fracture reduction, high IBT pressures at low balloon volumes and distorted IBT inflation shapes will be observed.

To improve reduction of partially healed bone, the authors have developed a technique combining kyphoplasty with percutaneous osteotomy. Regarding positioning, if the IBT is placed too far laterally in the vertebral body, balloon contact with the lateral vertebral body cortex early during inflation limits the surgeon’s ability to continue inflation and optimize vertebral endplate elevation. This difficulty may be salvaged by the use of directional balloon tamps that preferentially inflate in a medial direction; however, this situation is best prevented by creating an appropriate channel for IBT placement. In cases where loss of endplate reduction occurs with balloon deflation, it may be possible to maintain reduction with unilateral bone tamp inflation elevating the endplate while placing cement on the opposite side.

SUMMARY

Kyphoplasty is a technically demanding procedure offering a much needed treatment option for patients with symptomatic VCFs that do not respond to medical therapy or that are associated with progressive kyphosis. Rapid pain reduction, improved quality of life, and often fracture reduction have been observed in several consecutive case series.23,25–28,43,47 Further study is required to determine the optimal time for surgical intervention, to refine the patient selection criteria, and to delineate specific long-term effects of correcting vertebral deformity.

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