Vertebroplasty: Current Concepts and Outlook

	Ajeya P. Joshi, MD Orthopaedic Surgeon Beth Israel Deaconess Medical Center Boston, MA, USA
	Paul A. Glazer, MD Assistant Clinical Professor, Department of Orthopaedic Surgery Harvard University Boston, MA, USA

Introduction

Percutaneous vertebroplasty is a procedure which augments a weakened vertebra by injecting a substance through a percutaneous, fluoroscopically guided needle placed into the vertebral body. The injected compound, typically polymethylmethacrylate (PMMA) cement restores some of the mechanical properties of the vertebra, thereby helping to stabilize the spine and relieve the patient of pain.

Growing clinical experience with vertebroplasty has increased our understanding of the proper indications and our awareness of the procedure's limitations and contraindications. Reported complications underscore the high level of risk associated with this procedure, and the technical aspects of vertebroplasty continue to be refined. The mechanism of action underlying vertebroplasty has been studied but remains under debate, despite basic science studies which have addressed this question.

We will review the procedure itself, as well as the clinical indications, and the basic science behind vertebroplasty. We will also describe current applications of the technique and the clinical results, and suggest further areas of investigation to improve vertebroplasty and safely broaden its use.

Initial Development

Vertebroplasty was first developed in France, with preliminary reports in 1987. ¹ The earliest procedures were through an open surgical exposure. In these first cases, vertebroplasty was used to treat benign, aggressive hemangiomata which were destroying the vertebral body and producing pain secondary to pathological microfracture or over fracture. Shortly afterward, the technique was developed percutaneously. ^{1, 2}

Subsequently, vertebroplasty was used for pain relief or spinal stabilization of osteolytic tumor foci. Currently, the two most common conditions treated with vertebroplasty are osteoporotic compression fractures and metastases. ^3-5

Procedure

Percutaneous vertebroplasty may be performed to augment weakened vertebrae at the cervical level, though most clinical experience is in the thoracolumbar region. The approach is anterolateral with the patient supine for a cervical procedure, and posterolateral or transpedicular with the patient prone for thoracolumbar injections.

Sedation along with local anesthesia allow for intraprocedure monitoring of neurological status; alternatively, general anesthesia may be used. ⁶ Imaging consists of biplanar fluoroscopy⁶ in most cases, and occasionally CT and fluoroscopy together.⁵ A 10-12 gauge needle is used to enter the lumbar vertebral body under fluoroscopic guidance (12-13 ga. Ðthoracic, 15 ga. Ðcervical spine). When needle position is satisfactory, the injectable compound (such as PMMA) is prepared and mixed with radio-opaque barium sulfate or tantalum powder to increase fluoroscopic visibility. Because of the high viscosity of PMMA, it is necessary to inject the material via several small (1-2 cc) syringes. The material is injected into the vertebral body, under continuous fluoroscopic monitoring. The lateral view is especially important because one risk of the procedure is leakage of cement into the spinal canal or neural foramina. Leakage may occur through venous channels, lytic posterior body wall lesions, or an iatrogenically perforated medial pedicle wall. Injection is stopped when cement reaches the posterior wall on a lateral view, or when it is seen to enter parts of the vertebral venous plexus, where venous embolism to the lungs is a theoretical concern. Deramond et al. ⁷ have described a second injection through the other pedicle if filling is <50 % on fluoroscopy (Figure 1). Pre-procedure CT scanning helps to identify anatomical features predisposing leakage, such as lytic cortical defects. Leakage through endplates into the disk space has been noted be asymptomatic and inconsequential.^6-9 Leakage into the paravertebral soft tissues potentially threatens the femoral nerve in the lumbar region, and the intercostals nerves in the thoracic region.

Injection may be uni- or bi-pedicular, and typically up to 2-3 levels are treated in one session. Afterward, the patient is positioned supine and observed carefully for 24 hours. Immediate post-procedure CT scan and plain films are reviewed for leakage. Common side effects include post-procedure fever, which is thought to be an inflammatory response to the cement, and is treated with non-steroidal medications. Transient exacerbation of pain, also thought to be mediated by inflammation, can also occur. New paresthesias or partial motor deficits on post-procedure exam are treated with steroids in the absence of obvious physical compression of the nerve roots or spinal cord by cement leakage. If any leakage associated with a neurological change or deficit is detected during or after the procedure, a stand-by orthopedic or neurosurgical team must be available to decompress the neural elements and remove the leaked cement. There have been a few reported instances of this serious complication.^8-10

Initial hospitalization averaged 4 days,⁸ although this has decreased to 1-2 days. Patients are allowed to get out of bed and bear full weight the day after the procedure.

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