1 History and Introduction to Vertebral Augmentation
Summary
Vertebral augmentation is a category of minimally invasive procedures that have become central in the treatment of pathologic and painful vertebral compression fractures (VCFs) due to osteoporosis, trauma, and neoplasia. Osteoporotic VCFs are the most common indication for vertebral augmentation, which has also been used to treat fractures in patients with benign tumors such as hemangiomas or Langerhans cell vertebral histiocytosis (LCVH) and in genetic disorders that give rise to weak vertebrae such as osteogenesis imperfecta. In theory, near immediate anterior column stability and pain relief follows an intravertebral injection of bone cement that stabilizes the osseous fractures and eliminates osseous and periosteal movements, while thermal polymerization of the cement ablates pain receptors in the basivertebral plexus, trabecular bone, and subjacent to the vertebral end plates. Over three decades of innovation and advancements have produced treatment options with improved safety and efficacy. Results of numerous studies have demonstrated reduction of pain, and improved function and quality of life. Responses have been significant and durable across a wide range of etiologies.
1.1 Introduction
Acrylic cements have been used for augmentation of weakened or partially destroyed bones for decades. The first use of methyl methacrylate as an adjunct to internal fixation of malignant neoplastic fractures was reported in 1972. 1 Vertebral augmentation has since become central in the treatment of pathologic vertebral compression fractures (VCFs) due to osteoporosis, trauma, and neoplasia. The procedure has also been used to treat fractures in patients with benign tumors such as hemangiomas or LCVH and in genetic disorders that give rise to weak vertebrae such as osteogenesis imperfecta. 2 – 7
Osteoporotic VCFs (OVCFs) are the most common indication for vertebral augmentation. As with any fracture, principles of fixation for VCFs include vertebral body (VB) reduction to restore normal anatomical relationships, fixation to provide absolute or relative stability, preservation of blood supply to soft tissues and bone, and early safe mobilization of the injured part and the patient (▶Fig. 1.1).
Before the availability of vertebral augmentation, the principal surgical option for compression fractures was decompression and instrumented fusion. Outcomes were often dismal in elderly osteoporotic patients. 8 Nonoperative management options were equally disappointing. Initial management included bed rest and immobilization in an external orthotic if feasible and tolerable, depending on the degree of kyphosis and pain. Narcotics were prescribed for analgesia and nasal calcitonin for antiresorptive and analgesic effects. Bed rest and immobilization, however, led to accelerated osteoporotic bone loss and many elderly patients were at risk of polypharmacy and narcotic side effects including constipation, confusion, and respiratory depression as well as the many unappreciated consequences of social isolation. 9 , 10 Patients treated with nonsurgical management (NSM) were also at an increased risk of mortality primarily from pneumonia due to their deconditioned status. 11
1.2 Mechanisms of Pain Relief
Two general hypotheses prevail regarding the mechanism of pain relief offered by augmentation of VCFs: (1) an intravertebral injection of polymethyl methacrylate (PMMA) cement stabilizes micro-fractures and eliminates periosteal micro-movements and pain; (2) thermal polymerization of PMMA following injection ablates pain receptors in the trabecular bone, vertebral periosteum, and vascular structures. This combination leads to near immediate postoperative anterior column stability and pain relief. 12 Although ablation of the basivertebral nerve within the VB does produce significant pain relief in patients with diskogenic back pain, degenerative end plate changes, and an intact VB, 13 low exothermic or nonexothermic bone cements can produce equivalent pain relief in patients with VCFs to that of cements with thermal neuroablation capability. 14 The pain relief in patients with VCFs, therefore, is much more likely or completely due to the reestablishment of the mechanical stability of the VB rather than the ablative effects of the fill material on the VB innervation.
1.3 Procedures
1.3.1 Vertebroplasty
Vertebroplasty was first performed in 1984 but not reported until 1987. In the first known image-guided percutaneous vertebral augmentation, Galibert et al successfully injected PMMA into a C2 vertebra that had been partially destroyed by an aggressive hemangioma. 15
Vertebroplasty involves the percutaneous injection of cement such as PMMA directly into the cancellous bone of a fractured VB to alleviate pain and prevent further loss of VB height or progression of kyphotic deformity. Although the procedure does not improve spinal deformity, it stabilizes the vertebra and improves the function of individuals debilitated by painful VCFs (▶Fig. 1.2).
1.3.2 Kyphoplasty
Kyphoplasty was first performed in 1998 as a modification of vertebroplasty with the intent of restoring vertebral height and reducing kyphotic angulation for improved outcomes and reduced procedural risks. VCFs cause debilitating pain and may also be associated with significant kyphosis. Kyphosis reduces compartment sizes of the chest, abdomen, and pelvis, which results in pulmonary restriction, decreased appetite, and urinary incontinence. These processes can lead to life-altering deconditioning, weight loss, social isolation, and depression.
During kyphoplasty, a balloon tamp is inflated within the VB to compress and displace cancellous bone prior to the injection of cement. This creates a cavity that can reduce the vertebral fracture and after removal of the balloon allows the injection of cement directly into the cavity that is the path of least resistance. This injection of cement into the cavity allows for greater control of the cement and reduces the risk of cement leakage (▶Fig. 1.3).
Inflation of the tamp restores VB height and reduces kyphotic angulation to improve sagittal alignment, attenuating the risk of progressive deformity by reducing the bending moment (M). 16 , 17 Illustrating the importance of the moment arm, Archimedes said, “Give me a lever long enough and a place to stand and I will move the earth.” VB failure is believed to result from an excessive bending moment, which is the product of the moment arm (the distance between the mid VB and the plumb line representing the center of gravity, D) and the force (gravity, F) applied to the moment arm 18 (▶Fig. 1.4). The moment arm, and therefore the bending moment and risk of VB failure, increases as kyphosis progresses.
1.3.3 Radiofrequency Kyphoplasty
A novel technique approved for use in the United States in 2008 (StabiliT Vertebral Augmentation System, Merit Medical, Jordan, UT, United States) is radiofrequency kyphoplasty (RFK). RFK uses radiofrequency heat to control the viscosity of the PMMA that is injected into the VB. Rather than using inflatable bone tamps, a small navigational cannula is inserted unilaterally into the vertebra. The cannula creates pathways for the cement and preserves more of the existing cancellous bone. The pathways are filled with ultra–high viscosity bone cement, which permeates into the surrounding bone, stabilizes the fracture, and restores vertebral height (▶Fig. 1.5). The infusion of ultra–high viscosity cement in a slower and more controlled fashion is designed to reduce the risk of cement leakage. 19 – 23
1.3.4 Percutaneous Radiofrequency Ablation
Radiofrequency ablation (RFA) is a modified electrocautery technique for use in select patients with painful spinal metastases. 24 RFA and vertebral augmentation is a combination therapy for painful osseous metastases that cannot be or are incompletely palliated with radiation therapy. Combined treatment with RFA and vertebral augmentation has been successful in reducing pain and in improving function and quality of life. 24 – 28 Using image guidance, a partially insulated electrode attached to a radiofrequency generator is passed into the vertebra. 29 , 30 The heat generated by radiofrequency energy (50–90°C) causes destruction of the malignant tissue and creates a small cavity in the VB 31 , 32 (▶Fig. 1.6). Additionally, percutaneous radiofrequency ablation destroys sensory nerve fibers, and tumor cells that release nerve-stimulating factors. There is also evidence to show that RFA carried out before percutaneous vertebral augmentation reduces the risk of cement leakage. 33
Examples of devices for RFA include STAR Tumor Ablation System (Merit Medical, Jordan, UT, United States), CAVITY SpineWand (ArthroCare, Austin, TX, United States), and OsteoCool RF Ablation system (Medtronic, Dublin, Ireland). The OsteoCool ablation probe is internally cooled with circulating water. The RF energy heats the tissue, while circulating water moderates the temperature. The system automatically moderates power to keep RF heating within the desired treatment range. This combination creates large-volume lesions without excessive heating, thereby reducing risks of potential thermal damage to adjacent tissue.
1.3.5 Vertebral Augmentation with Implants
Significant and lasting pain relief has been achieved with both vertebroplasty and kyphoplasty. Restoration of height does not appear requisite for pain relief, but height restoration and reduction of kyphotic angulation are important components in the reestablishment of normal sagittal balance and protection from future fractures. 17 , 34 Recovery of VB height during kyphoplasty may be partially lost over time. Newer next-generation vertebral augmentation systems have been introduced to improve fracture reduction, indefinitely restore the height of the VB, and further reduce risks of cement leakage. 35 , 36
SpineJack (Stryker, Kalamazoo, MI, United States) is a titanium implant inserted using a bilateral transpedicular approach to treat fractures between and including T5 and L5. A direct lift mechanism expands vertically like a car jack and allows for progressive controlled reduction of the fracture prior to cement injection (▶Fig. 1.7). 32
The OsseoFix Spinal Fracture Reduction System (Alphatec Spine, 2009) is a titanium mesh device that expands into the VB and acts as a scaffold to facilitate reduction and stabilization of fractures between and including T6 and L5. There is no direct lift mechanism, but the foreshortening of the titanium tube reduces the end plate by direct superior and inferior pressure from the center of the tube as it expands during the implant’s deployment. The mesh expands to compact the trabecular bone and increase the VB height, allowing cement interdigitation. 37 The device was introduced as an alternative to vertebroplasty and kyphoplasty to reduce cement leakage (▶Fig. 1.8).
The Vertebral Body Stenting System (VBS) consists of an expandable cobalt–chromium alloy stent mounted on a balloon catheter. The device is typically inserted via a bilateral transpedicular approach and inflated to maximum of 30 atm to symmetrically expand both stents. The stent is optimally expanded to a maximum diameter of 17 mm and balloons are deflated and removed, leaving both stents to maintain the restored height prior to injection of the cement (▶Fig. 1.9). 32
The Kiva VCF Treatment System, indicated for use in the treatment of spinal fractures in the thoracic and/or lumbar spine from T6 to L5, received clearance from the U.S. Food and Drug Administration on January 24, 2014. The Kiva implant is a percutaneous uniportal vertebral augmentation device that is designed to restore VB height and reduce cement leakage. The polyether ether ketone flexible implant (PEEK-OPTIMA) is inserted over a removable, fully coiled nitinol guidewire. 38 The coil is inserted into the VB and acts as a scaffold for the implant. The Kiva implant is then inserted around the coil, the coil is removed, and cement is injected through the perforated implant for controlled delivery (▶Fig. 1.10).
1.4 Indications and Contraindications
Primary indications for vertebral augmentation include osteoporotic compression fractures, vertebral metastasis, multiple myeloma, vertebral hemangioma, vertebral osteonecrosis, traumatic VCFs, and reinforcement of a pathologically weak VB before and during surgical stabilization procedures. In clinical practice, the most common indication is a painful osteoporotic vertebral fracture that has not responded to NSM including rest, immobilization in an orthotic brace, narcotic analgesic medications, and nasal calcitonin for antiresorptive and analgesic effects.
In 2018, a multidisciplinary expert panel of orthopaedic and neurosurgeons, interventional radiologists, and pain specialists, using the RAND/UCLA Appropriateness Method (RUAM), developed the Clinical Care Pathway (CCP), defining patient-specific recommendations for vertebral fragility fractures (VFF). The panel assessed the relative importance of signs and symptoms for the suspicion of VFF, the relevance of diagnostic procedures, and the appropriateness of vertebral augmentation versus NSM for a variety of clinical scenarios. Their report included the following guidelines for relative and absolute contraindications. 39
Absolute contraindications include active infection at the surgical site and untreated blood-borne infections, and a nonpainful osteoporotic vertebral fracture that is completely healed or is clearly responding to conservative management. Strong contraindications include osteomyelitis, pregnancy, allergy to fill material, coagulopathy, spinal instability, myelopathy from the fracture, the presence of a neurologic deficit, and neural impingement.
Relative contraindications include cardiorespiratory compromise such that safe sedation or anesthesia cannot be achieved, breach of the posterior vertebral cortex by a tumor, and/or tumor extension into the spinal canal. It was determined that fracture repulsion and canal compromise per se is not generally a contraindication, provided the fracture fragment is not causing neural impingement or clinical symptoms related to this compromise. Significant fracture retropulsion with canal compromise is a relative contraindication. A CT scan may be used to determine integrity of posterior wall in patients with mild retropulsion of fracture fragment(s). Vertebra plana has been previously mentioned as a relative contraindication as it renders the procedure technically difficult but the RUAM group determined that vertebra plana was not a relative contraindication to performing vertebral augmentation.
1.5 Risks and Complications
Complications are few but, as with any surgical procedure, may include infection, bleeding, cardiac or respiratory complications of anesthesia, injury, and failure to achieve intended goals. Potential complications specific to percutaneous augmentation include cement leakage, pulmonary embolism, radiculopathies, rib fractures, subsequent vertebral fractures, and spinal cord or neural compression. 40 – 42
1.6 Clinical Applications and Evidence
A comprehensive literature review is presented in Chapter 15. Numerous randomized controlled trials, systematic reviews, and meta-analyses have been employed to study and compare vertebral augmentation treatment options. 43 – 45 Although we consider results from randomized controlled trials, it is important to remember that these were developed to evaluate drug therapies, not devices and surgical procedures. 46 Given their relatively recent introduction, there are limited data available with sufficient power for decision-making with respect to newer vertebral augmentation implants and devices. Future trials with additional observations and longer follow-ups are anticipated.
1.6.1 Osteoporosis
VCFs are the most common type of fracture related to osteoporosis and are associated with significant rates of morbidity and mortality. Annual direct medical expenditures exceed $1 billion in the United States. 47 Contemporary natural history data suggest that more than 70% of patients with moderate or severe pain may fail to achieve significant pain relief within 12 months of symptom onset. 48 Physicians in the Neuroradiology Department at the University Hospital in Lyon, France, began to treat osteoporotic vertebral fractures with vertebroplasty in 1989. They used an 18-gauge needle to inject bone cement into seven patients, four of whom had OVCFs and the other three VCFs attributed to spinal metastases. 49 They reported that seven of the eight patients had an excellent pain reduction response to the vertebroplasty and that the eighth patient had a good response.
Vertebroplasty
Vertebroplasty was introduced to the United States when, in the early 1990s, clinicians from the University of Virginia performed the procedure using the technique introduced by the French clinicians. 50 The use of vertebroplasty then dramatically increased, primarily for the treatment of OVCFs, until the advent of balloon kyphoplasty (BKP) in the late 1990s.
In 2009, a great deal of controversy followed the publication of two randomized trials comparing vertebroplasty and sham procedures to treat osteoporotic vertebral fractures. The studies were intended to account for placebo effect in the setting of vertebroplasty. The authors reported that, although there were substantial reductions in overall pain in both study groups, there was no statistically significant benefit offered by vertebroplasty. Critics pointed out many flaws in design, patient selection, power, and generalization of inferences of both trials.
The first study randomized 75 participants with one or two painful osteoporotic vertebral fractures confirmed by MRI and less than 1 year’s duration to vertebroplasty or a sham procedure. Participants were stratified according to treatment center, sex, and duration of symptoms. The primary outcome was “overall pain” at 3 months. There were substantial reductions in overall pain in both study groups, but vertebroplasty was not better in any measured outcome compared to controls, regardless of duration of symptoms. This trial by Buchbinder et al was to include 200 patients, but only 78 were enrolled over 4 years. Two of the four study hospitals withdrew after including only five patients each. As a result, 68% of the procedures were performed in one hospital by one radiologist. Only 32% of patients received treatment within 6 weeks of onset of pain, suggesting that many fractures being treated were already healed with expected persistent edema on MR imaging.
The second trial randomly assigned 131 patients with one to three painful OVCFs to undergo either vertebroplasty or a simulated procedure without cement. The primary outcomes were disability and the patients’ ratings of average pain intensity during the preceding 24 hours at 1 month. This study involved only outpatients; inpatients hospitalized with acute fracture pain were excluded. The protocol required 4 weeks of medical therapy before enrollment was possible and fractures were present for up to 1 year. Only 44% of patients had pain of less than 6 weeks’ duration; 56% of patients had pain for over 3 months. The minimum pain score for enrollment was 3/10 and the average pain score was 6.9. As patients with maximal back pain tend to have the greatest improvement on pain score, bias was presumably introduced, as those patients with the greatest pain likely did not agree to participate in a trial that might randomize them to a nontreatment arm. Finally, a significantly greater crossover from the control group versus the vertebroplasty group could indicate dissatisfaction with the sham procedure that was not captured by pain scales. 51
Related posts:
2 Vertebral Compression Fractures
10 Cervical and Posterior Arch Augmentation
14 Appropriateness Criteria for Vertebral Augmentation
18 Predisposing Factors to Vertebral Fractures
23 Number of Levels Appropriately Treated with Vertebral Augmentation
30 Vertebral Augmentation in Instrumented Spinal Fusions
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