Introduction

The Centers for Disease Control and Prevention (CDC) reports that there were 36.8 million U.S. residents older than 65 years in 2005. That number is predicted to grow to over 70 million by 2030.¹ Presently, it is estimated that 25% of women older than 50 years, 40% of women older than 80 years, and 33% of men reaching 75 years of age will sustain an osteoporotic compression vertebral fracture (OCVF).² Although many OCVFs appear to go clinically undetected, up to 30% of symptomatic fractures remain unresponsive to conservative management and are considered candidates for surgical intervention.^3,4 Considering these statistics along with the general effectiveness of vertebral augmentation in treating chronic pain from OCVFs, it is easy to understand the expected steady increase in frequency of procedures performed to treat this disease process.

Originally developed in France during the mid-1980s to treat vertebral hemangiomas and later introduced in the United States in 1994 in the treatment of symptomatic OCVFs, the percutaneous injection of bone cement, polymethyl methacylate (PMMA), has gained widespread use by physicians who treat OCVFs. Vertebroplasty and kyphoplasty have consistently demonstrated the ability to improve patient function and quality of life through excellent pain control and rapid mobilization for this “at risk” group of patients.⁵ However, risks pertaining to cement toxicity, exothermic reactions and tissue damage, embolism, and the potential neurologically devastating complication of cement extravasation outside the vertebral body (spinal canal, neuroforamen) remain.^2,6 Furthermore, concerns have been raised and debated about whether vertebral bodies augmented with PMMA (with or without intradiscal extravasation) are associated with a higher adjacent-level vertebral fracture (ALF) rate than would be expected because of the natural risk of additional fractures. Investigators have challenged the direct causal relationship between PMMA-augmented vertebral bodies and ALF, arguing that ALFs may simply be the result of the natural history of the underlying disease (osteoporosis). However, it is generally agreed that when fractures occur following PMMA augmentation, it is more common to see them occur within the first 3 months after the procedure, and they are more likely to occur at an adjacent level than elsewhere in the spinal column.⁷ In contrast, people with osteoporotic bones with compression fractures who have not had PMMA vertebral augmentation have subsequent vertebral fractures that are distributed more randomly throughout the spine and will occur sporadically throughout the following year. Data such as these do suggest that PMMA augmentation of vertebral bodies at least predisposes adjacent vertebral levels to fracture.^8–12

It has been proposed that the ideal bone cement for vertebral augmentation should be biodegradable and nontoxic, have a low setting temperature, and have a biomechanical profile close to that of human bone.¹³ To avoid some of the drawbacks of PMMA noted previously, and to provide an “ideal” biological cement for vertebral augmentation, a new option was developed that involves the minimally invasive injection of morselized allograft bone into a polyester expandable mesh container (OptiMesh, Spineology Inc., Minneapolis, Minn.). The bone injection procedure generates lifting force for potential fracture reduction, and the resultant bone graft strut is immediately load sharing and has a modulus of elasticity closely approximating that of native bone.

Indications and Contraindications

The primary indications for use of this mesh–bone construct include painful osteoporotic, traumatic, or steroid-induced Vertebral compression fractures (VCFs) from T4 to L5, with or without secondary kyphosis, that has not responded to a reasonable trial of conservative therapy. An additional indication is for benign but symptomatic vertebral hemangiomas. Pain and tenderness should be localized to the fracture level identified on x-ray, CT, MRI, or technetium Tc 99m bone scan. Patients should be medically stable to at least tolerate a percutaneous procedure and be able to assume a prone position for the procedure.

The main contraindication, as with all vertebral augmentation procedures, is the presence of an unstable vertebral fracture with retropulsed fragments causing more than 20% canal compromise (i.e., true burst fracture pattern) or any fracture pattern with neurologic deficit. The author has successfully and safely used this technique to treat compression fractures with “bowing” of the posterior cortex (posterior longitudinal ligament intact) along with fractures demonstrating minimal retropulsion of the superior or inferior endplate into the canal causing less than 20% canal compromise. Of interest, the use of this device as a minimally invasive option to treat true burst fractures with the AO classification of A1 has even been shown effective when combined with short-segment pedicle screw fixation.¹⁴

Because of issues of healing in the presence of adjuvant therapy as well as the inherent biologic aggressiveness of metastatic tumor leading to compression fractures, this device should not be used, when used with allograft bone as a filler material. Other absolute contraindications include comorbid conditions such as uncorrected coagulation or bleeding disorders, osteomyelitis, epidural abscess, and vertebra plana. Finally, the efficacy of prophylactic treatment in patients at high risk for VCFs has not been proved.

Description of the Device

The basic concept behind this technology is that a cavity within a fractured vertebra is created percutaneously through a relatively small access portal via a fluoroscopically guided unilateral, extrapedicular approach. A deflated porous polyester mesh bag (OptiMesh) is inserted and subsequently filled with allograft morsels, allowing a large load-sharing graft and strut to be built within the vertebral body. OptiMesh is designed to contain and reinforce morselized bone graft. The pore size of the mesh is nominally 1500 μm, allowing the mesh to effectively constrain the morselized allograft while also allowing ingrowth of vessels and native bone elements for ultimate graft incorporation and remodeling.

Using the principles of granular mechanics, impaction of bone granules into the mesh bag generates a distractive force, producing the capability for reduction (i.e., height restoration) of the fractured vertebra. Because the bone granules are tightly packed, force chains develop between the bone chips, thus creating a strut capable of supporting the axial loads of the spine.