Introduction

Osteoporosis is a major public health problem affecting an estimated 55% of people over 50 years of age. Every year in the United States more than 700,000 people suffer from vertebral compression fractures (VCFs), with osteoporosis being the main cause. Osteoporosis, the most common metabolic bone disorder, is typically a silent disease, but has the potential to cause debilitating back pain when VCFs occur. Other causes of vertebral fracture include trauma, benign lesions (e.g., hemangioma), and malignant lesions (e.g., multiple myeloma and metastatic cancer). Osteoporosis is characterized by decreased bone mineral density.

In a normal person, the vertebral bodies are composed of a porous structure, called trabecular or cancellous bone, encapsulated within a thin external cap of cortical (dense) bone. In a person with osteoporosis, the trabeculae that form the central porous bone become thinner and weaker. When this occurs, the vertebra can fracture and become deformed. This deformation of the vertebral bodies is classified into three types according to the shape: wedge, biconcave, and crush. As the vertebral bodies collapse, the natural curvature of the spinal column changes. These changes have mechanical effects on the paraspinal musculature and nerves, resulting in a wide range of symptoms, including pain, decreased sensitivity, tingling, and weakness. Multiple VCFs can produce kyphotic deformity, pulmonary dysfunction, loss of appetite, depression, and functional decline.

Until recently, the options for treatment of vertebral fractures were limited. Patients were confined to bed for prolonged periods and were given large doses of analgesics. Bracing was used but was usually not well tolerated by these typically elderly patients and has fallen out of favor. These palliative treatments do not restore the anatomy of the patient’s vertebral column to the alignment and morphology it had before the fracture. Treatment success, defined as relief of pain symptoms, depended on the individual’s capacity to heal the fracture. This physical change, along with forward angulation, can cause persistent deformity.

The traditional surgical techniques used to treat vertebral fractures or to maintain spinal stabilization are not as effective in the setting of osteoporosis, because the weakened bone is often not strong enough to support the metallic rods and screws. Because of the debilitating nature of the disease, many different procedures have been attempted. Among these, the procedure that has been the most successful is the injection of polymethyl methacrylate (PMMA) bone cement into the vertebral body to stabilize it. This procedure, known as vertebroplasty or kyphoplasty (when a balloon is first used to create a space in the vertebra) is performed in patients with painful fractures that fail to respond to conservative treatment.

A potentially devastating complication of vertebroplasty is the accidental escape (or leakage) of PMMA from the vertebral body, a problem known as cement extravasation. This problem can damage the vital structures, such as the spinal cord, or can contribute to the formation of emboli as a result of the flow of cement to the venous plexus. This can result in serious neurological complications or even death. Kyphoplasty was developed to help minimize cement extravasation by first introducing a balloon tamp to create a space for the cement and compact the surrounding bone. However, cement leakage is still possible with kyphoplasty, because the cement is only injected after removal of the balloon.

The Crosstrees PVA (percutaneous vertebral augmentation) pod is a device designed to percutaneously provide well-controlled delivery of PMMA during vertebral augmentation. The Crosstrees PVA System (Crosstrees Medical, Boulder, Colo.) is designed for use with Mendec Spine PMMA manufactured by Tecres S.p.a. (Verona, Italy), which is marketed with approved indications for use in the treatment of pathologic vertebral fracture. The pod device consists of a catheter for administering the cement into a releasable closed fabric barrier. Following delivery of a known volume of PMMA and expansion of the pod to a defined size, the fabric barrier is opened and removed from the vertebral body, leaving only the PMMA within the bony structure. A final volume of highly viscous PMMA can be added to the center of the initial bolus to provide additional interdigitation of PMMA to the cancellous bone. The system is novel in providing the ability to control the delivery of PMMA to the vertebral body and maintaining fracture reduction without the need for a permanent implant to remain within the patient.

Indications and Contraindications

Surgical treatment of VCFs with the Crosstrees PVA pod is indicated when debilitating back pain persists despite nonsurgical therapies (Table 42-1). MRI, the imaging study of choice for diagnosing VCF, typically shows increased signal on short T1 inversion recovery (STIR) sequences when a VCF is acute/subacute or if there is residual bony edema indicating incomplete healing. A nuclear medicine study (bone scan) is particularly useful when a MRI cannot be performed (e.g., when pacemaker is present).

TABLE 42-1 Relative Indications

In cases of chronic fracture, vertebral augmentation is not indicated. Other absolute contraindications to Crosstrees or any other PVA technique include pregnancy, coagulopathy, osteomyelitis, spinal instability, known allergy to PMMA, and previous augmentation with PMMA (Table 42-2). Relative contraindications (Table 42-3) include neurologic deficit (i.e., burst fracture with significant bony retropulsion, or fracture extending to the posterior cortical wall) and pathologic vertebral fracture related to primary or metastatic cancer; however, because the Crosstrees pod fully contains the cement during implantation and has a defined shape, it may be used more safely in these cases than current vertebroplasty or kyphoplasty techniques. Another relative contraindication is vertebra plana or greater than 60% loss of height.

TABLE 42-2 Absolute Contraindications

TABLE 42-3 Relative Contraindications