[MIRS-IR Vol III:6; 12/17/99]

Percutaneous Vertebroplasty

Jeffrey James Peterson, MD, Edward L. Siegel, MD, and Donald A. Eckard, MD

Introduction
Vertebral body compression fractures are a common cause of chronic back pain and disability. The leading etiology of vertebral compression fractures is osteoporosis, particularly in older individuals. Other causes include trauma, osteolytic metastatic vertebral lesions, aggressive vertebral hemangiomas, and vertebral body involvement by multiple myeloma.

Until recently, treatment of vertebral compression fractures has consisted of conservative measures including rest, analgesics, and dietary and medical regimens to restore bone density or prevent further bone loss. In some cases of malignant and aggressive hemangiomatous lesions, radiation therapy has been beneficial. In severe cases that have not responded adequately to conservative treatment, surgical stabilization has been advocated. However, in the last few years percutaneous vertebroplasty (PVP) has emerged as an important new tool for treating patients with painful vertebral compression fractures due to osteoporosis or aggressive bone lesions. The aim of PVP is to alleviate pain by stabilizing vertebral microfractures with methyl methacrylate cement. In addition to stabilizing the existing microfractures, the cement strengthens the vertebral body and may help to prevent further progression of disease.

The PVP procedure consists of a fluoroscopically guided percutaneous transpedicular puncture into the affected vertebral body. Methyl methacrylate cement is then injected directly into the vertebral body using sufficient pressure to force the cement into the fracture fissures. In some cases the entire vertebra can be filled with cement from a unilateral injection. More commonly, however, bilateral injections are necessary to insure adequate filling of the entire vertebral body. PVP is a relatively easy outpatient procedure that can be performed by most radiologists experienced in invasive radiological techniques.

Case Presentation
An 85-year-old man presented with severe chronic back pain. The patient had been seen by several physicians and had failed to respond to conservative measures. He was ultimately referred to our neurosurgery service for treatment. Conventional radiographs (figure 1) and magnetic resonance imaging (figure 2) were performed and demonstrated diffuse osteopenia and an osteoporotic compression fracture of the T12 vertebral body. After consideration of all available options the patient was referred to our interventional service for PVP.

Procedure / Technique
Conventional radiography, computed tomography, and magnetic resonance imaging studies are obtained prior to PVP to identify all levels of involvement, assess the extent of vertebral collapse, and evaluate the paravertebral tissues. When multiple compression fractures are present, correlation of imaging data with physical examination is necessary to limit treatment to the symptomatic lesions. PVP is performed under fluoroscopic guidance with general or local anesthesia. A 10 or 11 gauge needle is utilized for thoracic or lumbar vertebroplasty. We currently use an 11 gauge Manan® Bone Marrow Biopsy Needle (MD-Tech, Gainesville, FL). A transpedicular approach into the vertebral body is used to avoid potential injury to segmental spinal nerves and to decrease the risk of leakage of methyl methacrylate into the paravertebral tissue (1). The needle is advanced under fluoroscopic guidance through the pedicle (figure 3) and into the anterior one-third of the vertebral body (figure 4). Following entry into the vertebral body a biopsy can be performed coaxially through the existing needle if clinically indicated. Vertebral venography is then performed in the frontal (figure 5) and lateral (figure 6) projections to evaluate the paravertebral venous drainage and to assure that there is no direct filling of large veins. Although we routinely perform vertebral venograms, this is not the case at all centers. Some investigators believe that the information gained from the venogram is only of marginal value given the marked difference in the viscosity of contrast media and the methyl methacrylate cement.

We prepare the methyl methacrylate polymer using approximately 20 grams of polymethylmethacrylate powder, 7-10 ml of solvent (methyl methacrylate monomer) and 6 grams of sterile barium sulfate for radiographic visualization of the cement. Tantalum or tungsten powder can be substituted for the barium sulfate if desired. Polymerization begins as the solvent is added to the polymethylmethacrylate powder. When the mixture assumes a paste-like consistency, it is filled into 2-3 ml syringes and injected through the needle. Injection of the cement is monitored with continuous lateral fluoroscopy. If venous leakage is identified the injection is terminated immediately. Otherwise, the injection continues until the cement approaches the posterior vertebral body or firm resistance is met (figure 7). A total of 2-10 ml of cement is typically injected. At the conclusion of the injection AP and oblique fluoroscopy and/or spot films are used to assess the adequacy of vertebral body filling (figure 8). When filling is complete the needle is removed. In many cases a contralateral puncture will be necessary to achieve adequate filling of both sides of the vertebral body. The contralateral puncture and injection are performed as described above (figure 9). Upon completion of the injection(s), spot films are obtained in the frontal (figure 10) and lateral (figure 11) projections to document good filling and evaluate for extravasation of the methyl methacrylate cement. The entire procedure usually can be performed in 1-2 hours per vertebral body

Outcome
PVP was performed utilizing approximately 5 ml of methyl methacrylate per pedicle or 10 ml total. The procedure, which lasted approximately 90 minutes, was technically successful with no complications encountered. The patient reported immediate improvement in his symptoms following the procedure and, following monitoring for approximately 3 hours in our department, he was discharged home in satisfactory condition. The patient is scheduled to return for follow-up in 3 months.

Discussion
Early studies of PVP have indicated favorable outcomes with a majority of patients reporting marked reduction to near complete resolution of symptoms. A study by Jensen, Evans, et al reviewed 29 patients who underwent PVP for osteoporotic vertebral compression fractures. 26 patients (90%) reported significant pain relief immediately after treatment (3). A study by Cortet, Cotten, et al reviewed their results in 37 patients who underwent vertebroplasty. This series included 29 patients with bone metastases and 8 with multiple myeloma. 36 patients (97.3%) reported a decrease in pain 48 hours following the procedure. Five of these patients (13.5%) were completely free of pain, 20 (55%) were significantly improved, and 11 (30%) were moderately improved (4).

Patients with neurologic symptoms secondary to compression fractures should be treated cautiously to avoid leakage of cement that could potentially worsen symptoms. Vertebroplasty can be technically difficult in cases of severe vertebral collapse and/or vertebral body destruction. Potential complications of the procedure include epidural and foraminal leakage of cement that can lead to spinal compression or nerve root injury (1). Leakage into paravertebral veins should be aggressively avoided as this could lead to pulmonary embolism, although reported cases of this complication are rare. Because leakage of cement could potentially result in acute spinal cord compression, the procedure should be performed at a center with neurosurgical or orthopedic support available (2).

The mechanism of pain relief after vertebroplasty is poorly understood. Destruction of sensitive nerves secondary to chemical, mechanical, thermal, and vascular forces as well as reduction of mechanical forces and stabilization of microfractures probably combine to alleviate pain. Strengthening of the vertebral body by the methyl methacrylate polymer also serves to eliminate further progression of vertebral collapse. PVP has proved to be a simple yet efficacious alternative treatment for symptoms related to vertebral body pathology and can be performed as an outpatient procedure by most radiologists with experience in interventional radiological techniques.