Vertebral Augmentation

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Chapter 19 Vertebral Augmentation

Chapter Overview

Chapter Synopsis: The spine is susceptible to vertebral compression fractures (VCFs), which can arise from osteoporosis and various types of bone growths and tumors. The downstream consequences of VCF can be significant and go hand in hand with increased mortality, particularly in the aging population. Two minimally invasive procedures to treat VCF are percutaneous vertebroplasty (PV) and percutaneous kyphoplasty (PK). In PV, a substance called polymethylmethacrylate (PMMA), also known as bone cement, is injected into the vertebral body. PK is similar but involves the placement of a balloon, called a tamp, into the vertebral body. The tamp is then inflated and deflated repeatedly to create a space for injection of PMMA. Similar to many axial and mechanical sources of spinal pain, VCF pain abates with rest and can be exacerbated by activity after a fracture. This chapter considers technical aspects and the risks of complications with the injection procedures. As with any spinal injection technique, PV and PK require an intimate understanding of spinal anatomy. Patient selection requires special attention, and the details of the procedure should be specialized to each patient. The data largely support PV and PK as effective measures against pain after VCF.

Important Points:

Clinical Pearls:

Clinical Pitfalls:

Introduction

Vertebral compression fractures (VCFs) can result from a variety of conditions, which include but are not limited to osteoporosis, primary or metastatic spine neoplasms, and some benign bone tumors such as vertebral hemangiomas. Especially with the aging population, osteoporosis remains the most common cause of VCFs.1 Direct care costs of osteoporotic VCFs have been estimated between $12.2 and $17.9 billion a year. VCFs are associated with significant morbidity and mortality, including impairment of daily activities and psychosocial performance. The kyphotic deformities caused by VCFs are associated with pulmonary dysfunction, constipation, and imbalance. Compared with age-matched control subjects, patients with VCFs have a higher mortality rate, increasing with the numbers of fractures as well as the duration of follow-up.14

Vertebroplasty and kyphoplasty are minimally invasive techniques used to treat painful VCF. Vertebroplasty is the percutaneous injection of a vertebral body (VB) with bone cement, generally polymethylmethacrylate (PMMA). PMMA has been used in orthopedics since the late 1960s.5 Percutaneous vertebroplasty (PV) was first reported by a French group in 1987 for the treatment of painful hemangiomas. This case was a “stunner” of a C2 hemangioma, according to the authors. It was painful and got better after cement injection.6,7 Since then, the indications for PV have expanded to include osteoporotic compression fractures, traumatic compression fractures, and painful vertebral metastasis.8,9 Kyphoplasty is a modification of PV. It involves the percutaneous placement of balloons (called “tamps”) into the VB with an inflation and deflation sequence to create a cavity before the cement injection. Percutaneous kyphoplasty (PK) may restore some of the VB height and reduce the kyphotic angulation of the compression fracture before PMMA injection.10

Ideal candidates for PV or PK have activity-related axial pain corresponding to the level of a recent compression fracture. This pain lessens or abates completely with recumbency, sitting still, or both. A complete neurological examination and recent radiographic imaging are mandatory to rule out spinal cord compromise or retropulsed bony fragments in the canal. Magnetic resonance imaging (MRI) shows an increased T2-weighted signal caused by bone edema at the level with a recent fracture. Bone scan has also been used to target the most recent fracture(s) in patients with multiple fractures because uptake of radiotracer has been associated with a higher rate of excellent pain relief compared with PV without correlation with scintigraphy.11,12 Spinal cord compression on MRI (in the absence of neurological findings) is a relative contraindication. There may be cases in which the procedure is still indicated in a patient with a “tight canal” such as this, but the margin of error is very small, so if a small amount of PMMA extrudes, neurological deficits may ensue. If a posterior cortical fracture is suspected on MRI, a computed tomography scan will reveal the bony architecture more precisely.

Procedural Overview and Complication Avoidance

Standards for the safe practice of these techniques have been published by the Society of Interventional Radiology (SIR) in 2003 and recently updated by the Cardiovascular and Interventional Radiological Society of Europe; highlights of this document can be found in Box 19-1.13,14

Before the procedure, the patient should be taken off all anticoagulants, and the coagulation profile should be normal. The platelet count should be at least 50,000 per microliter at the time of the procedure, although no data exist to clearly define a “cut-off” platelet count. In the cancer population, we are asked, “How high do we want the number,” and there have been cases reported of hemorrhage requiring open surgery. We have had patients with prolonged “oozing” after the procedure with marginal coagulation status. There may be instances when the risk-to-benefit ratio favors performing these procedures in patients with lower platelet counts. Active infection and sepsis are contraindications. We recommend waiting at least 2 weeks after treatment of an infection to minimize the risk of infection.

Informed consent should include lack of pain relief, osteomyelitis, fracture of the vertebra or pedicle, extravasation of cement into the spinal canal or neural foramen, paralysis or nerve root damage, and venous embolism. Rare but fatal anaphylaxis to PMMA has been reported in four cases. Also, the rare but potential need for open surgery should be discussed with the patient.

Vertebroplasty and kyphoplasty require the clinician to be trained in spinal anatomy, fluoroscopic imaging, and the use of these techniques to perform interventional procedures. The procedure should be performed in a sterile operating room suite that allows fluoroscopic imaging of the thoracolumbar spine. Biplanar or C-arm fluoroscopy of good quality is mandatory for maximal procedural safety. A radiolucent table is mandatory, as is appropriate padding for prone slightly flexed positioning. Other procedural materials needed include local anesthetic solution (the authors use a 50:50 mixture of 1% lidocaine with 0.25% bupivacaine), PMMA material, and barium or other radio-opacification material, although most cements now come opacified by the manufacturer. Eleven- or 13-gauge bone biopsy needles with connection tubing and cement injection syringes are needed. Numerous commercial “kits” are available.

General anesthesia or monitored anesthesia care (MAC) can be used. If MAC is used, the surgeon must use generous amounts of local anesthetic, especially injected onto the periosteum, where much nociception occurs. Some patients experience discomfort with advancement of the trocars across the posterior cortical margin with balloon inflation (in the case of kyphoplasty) and with PMMA injection. The anesthesiologist must be prepared to “deepen” the MAC during these phases of the procedure. Patient selection is important with consideration to the anesthesia choice. Very anxious or nervous patients may have a better experience with a general anesthetic. Careful consideration must be given to padding the pressure points of this fragile group of patients. After uni- or bipedicular VB access has been obtained, some clinicians proceed directly with injection of PMMA, but others prefer to do venography before cement injection. In theory, venography provides anatomical knowledge of large venous channels’ proximity to the trocar. This information is used to more carefully inject the PMMA. For example, if a small amount of contrast injection reveals a direct spread into a venous channel, the operator may move the trocar before injection or carefully inject relatively solidified PMMA to embolize the large vein before injecting more PMMA into the VB. The literature reveals variable efficacy of the use of venography.15,16 Most groups no longer use venography.

PMMA injection into the VB is undertaken after careful imaging confirming location of the trocar or trocars into the anteromedial portion of the VB. The PMMA should be opacified and beginning to harden to the consistency of toothpaste before injection. Injection can be done by small syringes filled with PMMA or one of several commercially available kits. The injection must be done under live lateral or biplanar fluoroscopic guidance. If PMMA begins to go into a blood vessel or toward the posterior cortical margin, it must be halted immediately. The authors halt cement injection when it spreads to the posterior third of the VB. To minimize PMMA leakage, several groups recommend the use of high-viscosity cement and relatively small volume injection (Fig. 19-1).1719