Abstract
Vertebral augmentation procedures, which generally refer to vertebroplasty and kyphoplasty, are interventional procedures used to treat vertebral compression fractures that may result from a variety of conditions, including osteoporosis, hemangiomas, multiple myeloma, and metastatic lesions. The primary goals of vertebral augmentation procedures are to reduce pain and improve function and either stabilize or correct the loss of height associated with the fracture. They utilize the injection of a cement polymer into the affected vertebral body in vertebroplasty; in kyphoplasty a cavity is created prior to injection of the cement polymer in order to restore vertebral body height.
The majority of prospective cohort studies and randomized controlled trials have shown that both vertebroplasty and kyphoplasty significantly reduce visual analog pain scores and improve function. Kyphoplasty has also been shown to have added benefits when compared to vertebroplaty, which include decreased rates of cement extravasation, improved vertebral body height restoration, and improved pulmonary function tests which correlate with the kyphotic angle correction. These procedures are generally well tolerated with low rates of clinically significant complications. Complications that occur may include adjacent segment fractures, infection, bleeding, and cement embolization, which is usually not clinically significant.
Keywords
kyphoplasty, osteoporosis, vertebral augmentation procedures, vertebral compression fractures, vertebroplasty
Introduction
Vertebroplasty (VP) and kyphoplasty (KP) are interventional techniques that utilize the placement of various polymers (e.g., acrylic-based cement) within a vertebral body for the correction of a vertebral compression fracture (VCF), and/or replacement of lost intramedullary bone secondary to neoplastic lesions. In KP, a cavity is also created within the vertebral body through the use of instrumentation consisting of a balloon, osteotome, or other method prior to instilling the acrylic-based cement, which is commonly a barium sulfate containing polymethylmethacrylate or other polymer. Barium sulfate is usually present within these cement mixtures because it is radiopaque.
Initially, correction of a VCF using an acrylic-based cement was described as an open surgical procedure and has been clinically used since at least the 1970s. In 1987, Galibert et al. published the first description of percutaneous VP for vertebral hemangioma in a painful C2 hemangioma. Since then, there have been significant refinements in the indications and technique of performing these procedures, as well as the development of several versions of acrylic-based cement polymers. Although various versions of barium sulfate containing polymethylmethacrylate are most frequently utilized, there are nonacrylic cement polymers commercially available and in various stages of development.
Indications
The clinical indications for the performance of VP and KP have become controversial. Nevertheless, both modalities have been reported as being useful in the treatment of symptomatic VCF due to a broad range of causes in the published literature.
Osteoporosis is the most common cause of VCF, with multiple myeloma, metastatic disease, painful vertebral body hemangiomas, and others (e.g., Kümmell disease) comprising “secondary” indications for vertebral augmentation procedures. Although osteoporosis has been a somewhat controversial indication since the publication of two negative articles in the New England Journal of Medicine in 2009, it remains the most common reason people undergo vertebral augmentation procedures.
Osteoporosis
Osteoporosis is a disease of bone, which itself is a connective tissue, responsible for hematopoiesis, mechanical and structural support, and mineral storage of inorganic salts and organic material. It is broken down and rebuilt constantly to optimally provide for skeletal support and other functions. Bone loss occurs once the balance of bone turnover favors bone resorption, and after peak bone mass is achieved by about 35 years of age, bone mass continues to decrease until death. Osteoporosis is a common and sometimes debilitating metabolic bone disease that occurs when an increase in bone resorption and a decrease in new bone formation lead to a chemically normal but reduced bone mass per unit volume. This, in turn, results in decreased skeletal function and elasticity, progressive spinal deformity, and vulnerability to fractures.
Epidemiological Characteristics
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Osteoporosis affects more women than men, as women possess 10% to 25% less total bone mass at maturity.
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Caucasian and Asian women are at highest risk of developing an osteoporotic fracture due to low bone mineral density (BMD).
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In the United States, 35% of women over the age of 65 years and 15% of Caucasian postmenopausal women are osteoporotic.
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In the United States, this debilitating disease causes fractures in 1 million individuals per year with $14 billion spent for treatment.
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Hip and vertebral fractures occur in women at a rate of 250,000 and 500,000 cases per year, respectively, and an additional 250,000 fractures are experienced by men every year.
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Vertebral fractures in women increase as menopause approaches, and in old age, with a ratio of 2:1 compared to men.
Due to various endocrine-related factors (e.g., decline in estrogen production), women lose 3% to 7% of BMD around the onset of menopause, followed by a 1% to 2% annual decline in the postmenopausal period. Although men also lose trabecular bone as they age at rates similar to postmenopausal women, they continue to increase cortical bone through periosteal deposition until the age of 75 years.
There are three main types of osteoporosis, which can be categorized as primary, secondary, and iatrogenic. The two types of primary osteoporosis, as noted by Riggs and Melton, are postmenopausal and senile ( Table 70.1 ). Before making a diagnosis of primary osteoporosis, secondary and iatrogenic causes must be excluded ( Table 70.2 ). Common causes of iatrogenic osteoporosis include prolonged corticosteroid administration, furosemide, thyroid supplements which suppress thyroid-stimulating hormone (TSH) production, anticonvulsants, heparin, lithium (by causing hyperparathyroidism), and cytotoxic agents.
| Type I | Type II |
|---|---|
| Postmenopausal | Senile |
| Primarily trabecular bone | Primarily cortical bone |
| 6:1 female-to-male ages 51–65 years | 2:1 female-to-male of age ≥75 years |
| No calcium deficiency | Calcium deficiency, decreased vitamin D, and increased parathyroid hormone activity |
| Estrogen deficiency | No estrogen deficiency |
| Vertebral and Colles’ fractures prevalent | Pelvic, hip, proximal tibia, and proximal humerus fractures prevalent |
| Risk factors: low calcium intake, low weight-bearing regimen, cigarette smoking, and excessive alcohol consumption | Related to low calcium intake |
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Diagnosis and Initial Evaluation
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Medical evaluation to determine whether or not someone suffers from osteoporosis requires performing a thorough history and physical examination, including family and past medical history.
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Secondary causes or coexisting diseases may be the catalyst for, or exacerbate, bone loss.
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A complete blood cell count, serum chemistry, and a urinalysis including a pH count should be performed.
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Consider obtaining thyrotropin, a 24-hour urinary calcium excretion, erythrocyte sedimentation rate, parathyroid hormone and 25-hydroxyvitamin D concentrations, dexamethasone suppression test, acid-base studies, serum or urine protein electrophoresis, bone biopsy and/or bone marrow examination, and an iliac bone biopsy as appropriate.
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The American Association of Clinical Endocrinologists recommend routing dual-energy X-ray absorptiometry (DXA) screening of the lumbar spine and proximal femur for:
All women 65 years and older;
Any adult with a history of fracture not caused by severe trauma;
Younger postmenopausal women with clinical risk factors for fracture.
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Plain radiographs are an option, but changes are usually not detectable until there is more than 30% loss of bone mass, suggesting this is not a sensitive screening tool.
In 1994, the World Health Organization (WHO) established diagnostic criteria to designate the presence of osteoporosis based on DXA measurements. Normal individuals possess a BMD of one standard deviation of the mean for young adults. Osteopenia is indicated if the standard deviation of BMD is between 1.0 and 2.5 below the mean of a young adult population. If BMD measures 2.5 or more standard deviations below the mean of a young adult population, then osteoporosis is present.
Severe osteoporosis is noted when one or more accompanying fragility fractures are present. Low body mass index has been associated with an increased likelihood of developing a fracture. Based on these criteria, it is estimated that 38% of white females in their mid-seventies will have osteoporosis, and low bone mass will characterize 94% of that population. These criteria were established by the WHO for the purposes of establishing prevalence, and are not intended as guidelines for therapy.
Prevention
Antiresorptive therapy and preventive measures are indicated to manage and prevent osteoporosis, respectively. Numerous factors must be considered before administering an appropriate regimen of preventive and therapeutic measures to combat osteoporosis. Potential options are:
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Calcium and vitamin D supplementation
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Bisphosphonates
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Calcitonin
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Selective estrogen receptor modulators
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Parathyroid hormone or analogs (e.g., teriparatide)
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Sodium fluoride
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Exercise
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Modifiable risk factors, such as cigarette smoking, excessive alcohol consumption, and treatment of potential secondary causes (see Table 70.2 )
Other Fractures
Multiple myeloma is the most common primary malignant tumor of the bony spine, and it rarely affects the posterior elements. These tumors have an incidence rate of 2 to 3 per 100,000 people, and tend to be radiosensitive, and in some cases chemo-sensitive. The disease is usually multifocal in nature, and surgical consolidation with vertebrectomy and strut grafting is not usually necessary; nevertheless, a single-level lesion can be treated with some success by vertebrectomy. Initially, symptomatic patients with VCFs may report severe pain that is poorly responsive to analgesic therapy.
Vertebral augmentation offers a viable route for immediate pain relief, bone strengthening, and mobility. Although vertebral augmentation may restore the mechanical integrity of a vertebral body and provide pain relief, tumor growth is not prevented. Therefore, radiotherapy and/or chemotherapy accompanying augmentation are appropriate because they do not affect the properties of the bone cement, they may inhibit tumor growth, and they can complement pain relief and promote spine strengthening. A recent systematic review evaluating VP and KP for VCFs caused by multiple myeloma found equally significant improvement in pain scores and analgesic use at less than 1 week, 1 week to 1 year, and greater than 1 year for both interventions. Oswestry Disability Inventory scores also showed a trend towards improvement at all time periods in both groups. Although cement leakage occurred in 11% to 29% of patients, it did not have any effect on postprocedural pain scores.
Hemangiomas are benign bony spine lesions whose detection is usually incidental because of their asymptomatic disposition. They are often detected during the evaluation of back pain and subsequent routine imaging. Soft tissue extension of the lesion may compress the spinal cord and nerve roots, producing neurologic symptoms and even epidural hemorrhage. If extensive growth of the hemangioma occurs, vertebral integrity may be compromised, resulting in a fracture with associated pain at the level of the lesion. Hemangioma aggressiveness can be determined by both clinical symptoms and radiological evaluation. Vertebral collapse, neural arch invasion, and soft tissue mass extensions are signs of aggressive lesions, and may signify appropriateness for vertebral augmentation. Patients with lymphomas and eosinophilic granulomas also may be candidates for vertebral augmentation.
Approximately 10% of patients with metastatic tumors develop malignant lesions in the spine in the United States. Per year, 10% to 15% of 120,000 new patients with metastatic lesions to the spine develop VCFs. The most common location is the thoracic spine, but all levels can be affected, and usually more than one level is involved. Every kind of malignancy has been described to spread to the spine, with the most common culprits being breast, lung, and prostate cancers.
Contraindications ( Table 70.3 )
| Absolute | Relative |
|---|---|
| Uncorrectable coagulation disorders Allergy to polymethylmethacrylate or contrast Spinal instability Pregnancy Active site infection or sepsis Pain unrelated to fracture Solid tissue or osteoblastic tumor | Young age Loss of vertebral height ≥80% (vertebroplasty) Posterior wall destruction ≥20% retropulsion with spinal stenosis Previous spinal stenosis Vertebra plana, fractured pedicles, and burst fractures Multiple previous surgeries Poor pulmonary status Greater than three compression fractures |
Vertebroplasty and Kyphoplasty Technique
Only experienced physicians with appropriate training should perform vertebral augmentation procedures. Requirements for these procedures include: intravenous (IV) access, sedation or general anesthesia, image guidance, IV antibiotic prophylaxis (e.g., cefazolin 1 g or clindamycin 600 mg within 60 min prior to incision), and sterile precautions.
Both VP and KP are similar in the early stages of the procedure with regard to local anesthetic and imaging approach. There are two principal techniques for placing the introducer trocar: transpedicular and parapedicular. For the transpedicular approach, two methods can be utilized: an anteroposterior (AP) approach maintaining visualization of the medial and lateral cortices of the pedicle versus a coaxial approach. Regardless of approach, cranial tilt and lateral fluoroscopic views should be utilized to determine the accurate angle of entry toward the vertebral body.
For the AP approach, the target trocar site is the superior and lateral portion of the pedicle, sometimes described as the 10 o’clock or 2 o’clock for the left and right pedicle on AP view, respectively. If utilizing the coaxial view, the trocar should ideally be placed in the center of the pedicle ( Fig. 70.1 ), but lateral paracentral placement is acceptable for narrower pedicles. Local anesthetic is infiltrated to the periosteum of the pedicle. Then, a small incision is made with an 11-blade scalpel. The trocar is advanced to the pedicle using either a screwdriver technique or gentle tapping with an orthopedic hammer ( Fig. 70.2 ). Once properly engaged, AP and lateral views are obtained to confirm that the medial, superior, and inferior walls of the pedicle remain intact ( Fig. 70.3 ). For VP, the trocar is advanced into the anterior third of the vertebral body, and for KP into the posterior third ( Fig. 70.4 ).
The parapedicular approach involves placing the trocar lateral to the edge of the pedicle and advancing along the surface of the pedicle directly into the vertebral body. The vertebral body to pedicle junction will appear more anterior on lateral imaging. This method is useful when there is poor visualization or a fracture of the pedicle. More central placement of the trocar in the vertebral body, obviating the need for a second trocar, is more frequent with this approach ( Fig. 70.5 ).
Trocar placement for KP is similar to the VP approach except that the trocar is not advanced past the posterior one-third of the vertebral body, and trocar size may be slightly larger. After entering the posterior aspect of the vertebral body, the introducer is removed leaving the cannula in place. A hand-operated drill is advanced to the anterior quarter of the vertebral body in lateral imaging, taking care not to violate the anterior margin. Ideal placement on AP imaging is in the midline. The drill is removed and a negatively pressurized and deflated balloon is advanced through the cannula into the vertebral body. If a bilateral approach is used, a second introducer and balloon should be placed on the opposite side in a similar fashion. Each balloon is slowly inflated with iodinated contrast via a locking syringe with a manometer to measure pressure, or until the balloon tamp reaches a cortical margin. The balloon is then deflated and removed ( Fig 70.6 ).
Polymethyl methacrylate (PMMA) is prepared by adding normal saline to a powdered phase containing barium. After all ingredients are mixed, there is usually a short working time that varies with the room temperature and formulation. There is also a somewhat more dense bioactive glass ceramic polymer (e.g., Combeite) commercially available as an alternative to PMMA with similar reported efficacy.
With use of either formulation, a cannula is connected to the trocar and the cement is slowly injected under live fluoroscopy beginning in the lateral position, but with frequent AP views to avoid lateral leakage through fracture lines. The injection is stopped when the posterior one-third to one-fourth, or a cortical margin, is reached. If undesirable spread is observed, waiting a few minutes to allow the cement to harden or adjusting the cannula before resuming injection may prevent further spread into unwanted areas. The stylet is replaced into the cannula before extraction to avoid cement leakage back toward the pedicle or toward neuraxial structures ( Fig. 70.7 ).
Although some experts have anecdotally reported that the volume of cement instilled does not correlate with success, a recent study evaluating the SWISSspine national registry found that instillation of greater than 4.5 mL total cement fill during KP was a strong predictor of pain relief.
Complications ( Table 70.4 )
Among others, complications include infection, bleeding, and cement emboli into perivertebral segment vessels, and the aorta, heart, and lungs. Although pulmonary emboli may occur in up to 25% of patients undergoing VP, they usually lack clinical significance.
| Complications |
|---|
| Osteomyelitis |
| Hematoma (paraspinal or epidural) |
| Rib fracture |
| Adjacent vertebral fracture |
| Pedicle fracture |
| Pulmonary embolus of PMMA |
| Hypotension |
| Spinal cord compression |
| Epidural abscess |
| Neurologic complications |
| Allergic reaction to contrast or PMMA |
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