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Vertebral Body Augmentation Procedures: Vertebroplasty and Kyphoplasty
Compression fractures of vertebral bodies affect approximately 750,000 people each year in the United States and up to 25% of postmenopausal women. The leading cause of vertebral compression fractures is osteoporosis, a disease that affects 44 million Americans. Younger patients taking corticosteroids for medical problems such as lupus, asthma, and rheumatoid arthritis may also suffer from osteoporotic compression fractures. Other, less common causes of vertebral body compression fractures or deformities are severe trauma to healthy bone, metastatic or other neoplastic lesions, and prior, healed infections such as osteomyelitis or tuberculosis.
Patients with vertebral compression fractures often present with acute or chronic back pain. As a result of the pain, these patients often experience limited mobility that leads to osteoporosis and progressive vertebral body collapse. In the thoracic spine, significant sagittal kyphosis may lead to decreased vital capacity of the lungs, with increased respiratory difficulties. The first line of treatment for vertebral compression fractures is conservative therapy. This may include pain medication, calcium and vitamin D supplements, short-term bed rest (because prolonged inactivity can lead to further bone loss), external bracing, and physical therapy. Pain from the spinal fracture can last for several months, but if the fracture heals well with conservative treatment the pain will usually improve significantly within a few days or weeks.
Patients are typically evaluated with imaging studies that may include plain radiographs, CT, MRI, or radionuclide bone scintiscans. Lateral radiographs demonstrate the loss of vertebral body height resulting from the fracture and the sagittal alignment of the spine. Axial and sagittal reformatted CT images ( Fig. 24-1 ) demonstrate any retropulsed bone fragments in addition to the loss of vertebral height. Preoperatively, CT is helpful for assessing the integrity of the posterior cortex and for planning the needle trajectory. MRI provides excellent anatomic detail. T1-weighted and short tau inversion recovery (STIR) sequences show edema of acute fractures ( Fig. 24-2 ). MRI also reveals any other lesions or injuries that may contribute to the patient's back pain. In patients with no evidence of osteoporosis and otherwise unexplained compression of the vertebra, it is important to obtain both a noncontrast and a contrast-enhanced MRI to exclude malignancy. Radionuclide bone scans are useful for patients who are unable to have an MRI. A bone scan ( Fig. 24-3 ) will demonstrate activity in an acute fracture and in a chronic, nonhealed fracture. However, bone scans will not demonstrate activity in chronic, healed fractures. Bone scans are also useful for detecting the presence of occult metastases.
Axial ( A ) and sagittal ( B ) CT scans show an L1 compression fracture. Note the bony retropulsion with narrowing of the spinal canal on the axial view.
Sagittal STIR MR sequence shows characteristics suggestive of an acute compression fracture of T8. There does not appear to be an underlying neoplastic lesion. Note the retropulsed fragments and cord signal changes.
Bone scintigraphy demonstrates increased uptake of the L5 vertebral body ( arrows ), suggestive of an acute or unhealed fracture.
Vertebroplasty is an image-guided, minimally invasive, nonsurgical therapy used to strengthen a vertebral body that has been weakened by osteoporosis, malignant lesion, or treated infection. This procedure was initially developed in France in 1984 and was first introduced in the United States in 1994. The purpose of strengthening a compression deformity is to decrease pain, increase the patient's functional abilities, permit the patient to return to the previous level of activity, and prevent further vertebral collapse. Vertebroplasty is accomplished by injecting a cement mixture through a needle into the fractured bone under fluoroscopic or CT guidance. Kyphoplasty is a variant form of vertebroplasty that was introduced in 1998 to address several concerns posed by those performing simple vertebroplasty, specifically, the potential for cement to extravasate into the spinal canal, neural foramen, or venous plexus and the failure of vertebroplasty to restore the vertebra to normal height. In kyphoplasty, a balloon catheter is introduced into the fracture site and, under fluoroscopic guidance, is inflated until the fracture is reduced or until it is unsafe to continue. The cavity created by the inflated balloon is then filled with cement.
INDICATIONS
Indications for treating patients with spinal augmentation procedures, vertebroplasty, or kyphoplasty include failure of conservative therapy, prolonged immobility, and progressive kyphotic deformity on serial imaging studies. Specific types of fractures respond poorly to conservative therapy and may be better treated with augmentation early on. These include thoracolumbar junction fractures, burst fractures, and significant anterior wedge compression fractures. Such fractures can heal in compressed or flattened wedge shape, precluding later treatment by minimally invasive spinal augmentation procedures. Thus, they should be treated early, before the spinal deformity becomes irreparable.
Vertebral augmentation may also be an alternative to more extensive surgery. Spinal instrumentation/fusion surgery requires prolonged general anesthesia and may be accompanied by substantial blood loss. Postoperative complications include infection, instrumentation failure, prolonged pain from the surgery itself and consequently prolonged immobility, and the attendant complications of deep vein thrombosis, pulmonary embolus, and pneumonia. A patient with multiple comorbidities and/or advanced age may not be able to tolerate such prolonged surgery and should be considered for minimally invasive vertebral body augmentation instead. Similarly, in patients with severe diffuse osteoporosis or destructive metastases the residual weakened vertebrae may not be able to support the mechanical constructs used for spinal instrumentation, so these patients should also be considered for minimally invasive vertebral augmentation to prevent further collapse of their vertebral bodies.
Patients with metastatic lesions may also be treated with vertebroplasty or kyphoplasty for palliative pain control. Vertebral augmentation is now being performed before chemotherapy or radiation therapy. It has the advantage of relieving pain rapidly and adding structural support to the weakened bone. Additionally, the cement does not interfere with subsequent chemotherapy or radiation therapy. As with osteoporotic fractures, identifying and treating the symptomatic lesion is paramount. Lesions confined to the vertebral body often result in localized back pain at that level. Radicular symptoms, myelopathy, or focal weakness should raise suspicion of epidural or foraminal extension of the lesion and necessitate neurosurgical consultation. Any mass lesion, unusual-appearing compression fracture, or fracture in a patient with a history of cancer should be sampled during the procedure. In addition to their role in treating metastatic lesions, vertebroplasty and kyphoplasty have been shown to be effective in treating painful hemangiomas and fractures from multiple myeloma.
A patient with a history of treated infection, osteomyelitis, or tuberculosis may develop progressive kyphosis leading to increased back pain. In such patients, active infection should first be ruled out by CT, MRI, or radionuclide bone scan. However, a biopsy and culture should still be performed at the time of the procedure. In osteomyelitis, the disc space is often involved and there may be subsequent anterior subluxation of one vertebral body over another. This situation may necessitate surgical correction of sagittal alignment and internal stabilization.
Avascular necrosis is another cause of painful fracture deformity. This unstable lesion most commonly results from prior infection, chronic corticosteroid use, alcoholism, and radiation therapy. Imaging studies typically demonstrate a collapsed vertebral body with an intravertebral vacuum cleft or fluid collection ( Fig. 24-4 ). Such a cleft is a good prognostic sign, indicating that vertebroplasty is highly likely to relieve the patient's pain.
CONTRAINDICATIONS
Contraindications to these procedures include an uncorrectable coagulation disorder, active infection in the area (including the overlying skin, prevertebral soft tissues, and vertebral body or disc), spinal cord compression, and posterior vertebral body fracture with cortical disruption (which allows the cement to leak into the spinal canal). The relative weight of these contraindications is under debate. Other relative contraindications include vertebral body collapse greater than 75%, epidural extension of disease with more than 20% involvement of the spinal canal diameter, and preoperative radiculopathy. Recent literature does not substantiate the fear that cement may leak into the spinal canal from a compression or burst fracture with posterior vertebral cortical disruption.
EQUIPMENT
Vertebroplasty and kyphoplasty should be performed in an interventional radiology suite or in an operating room. The room should contain fluoroscopy equipment (biplane preferable), an adjustable table, and viewing monitors. Typically, vertebroplasty or kyphoplasty kits with all the necessary equipment are used for the procedure. They include 11-gauge bone needles, cement (polymethyl methacrylate [PMMA]), and the cement delivery device. PMMA comes as separate liquid and powder components that must be mixed before use. In vertebroplasty kits, the cement delivery device consists of a rotating syringe-like apparatus that allows for controlled delivery of the cement into the vertebral body. Kyphoplasty kits also contain balloon catheters that are inflated with an insufflator to create the cavity within the vertebral body. Thereafter, the cement is usually delivered through a hand plunger system, which is also provided in the kit.
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