19 Vertebral Augmentation for Insufficiency Fractures
Vertebral compression fractures (VCF) are a common pathology in the aging osteoporotic spine. Percutaneous vertebral augmentation (PVA) after a reasonable trial of conservative treatment has been demonstrated to be an effective treatment option for vertebral body insufficiency fractures that frequently occur in older adults. The two types of PVA, vertebroplasty and kyphoplasty, both utilize cannulation devices to access the vertebral body and inject cement. Research published in 2009 suggested that the procedure was no more effective than sham, but these studies have been found to have serious methodological flaws. Numerous studies have been subsequently published that support the use of PVA in appropriately selected patients to reduce overall pain, narcotic use, and increase activity level. The procedure is well accepted and recommended by the guidelines of numerous specialty societies.
Vertebral compression fractures (VCF) are a common pathology in the aging osteoporotic spine.
Percutaneous vertebral augmentation (PVA) after a reasonable trial of conservative treatment has been demonstrated to be an effective treatment option for vertebral body insufficiency fractures that frequently occur in older adults.
Research published in 2009 suggesting that the procedure was no more effective than sham but have been found to have numerous flaws. Numerous studies have been subsequently published that support the use of PVA in the appropriately selected patient and the procedure is well accepted and recommended by the guidelines of numerous specialty societies.
19.1 Indications and Contraindications
Common indications for percutaneous vertebral augmentation (PVA) are acute to subacute vertebral compression fractures (VCFs) that are resistant to conservative pain management strategies, without concomitant infection, anticoagulation, or other barriers to surgery. Typically, patients present with severe back pain that worsens with movements such as transferring from a bed or chair. The patients are often greater than 55 years old and have a history of osteopenia. They often have no history of trauma and rarely exhibit any neurological deficits. In some cases, the pain can be reproduced by pressure over the spinous process of the affected level.
PVA is not indicated for fractures causing minimal pain, even if they are proven to be acute. The role of this intervention in stabilizing an asymptomatic fracture or in the prophylactic treatment of patients with osteoporotic vertebrae thought to be at high risk for fracture remains unproven. Similarly, younger patients with normal bone mineral density and traumatic VCFs are generally not considered candidates for PVA, as it is expected they will heal well without intervention. In patients less than 55 years of age with no history of trauma, or those with a known history of malignancy, PVA is not contraindicated, but further evaluation of the etiology of the fracture is warranted. A biopsy during the PVA can evaluate for a malignant etiology.
Imaging can help determine fracture acuity, allowing for proper patient selection. A good candidate for PVA has an acute or subacute fracture. In these patients, significant pain relief can be expected in 80–90% postprocedurally. 1 , 2 , 3 Plain radiographs or computed tomography (CT) imaging are excellent at identifying compression fractures through the loss of height of the vertebral body, but often do not provide information on the age of the fracture. Additionally, in many cases these studies demonstrate multiple compression deformities, making the localization of the symptomatic level difficult. Magnetic resonance imaging (MRI) is the best indicator of the age of the fracture along with the patient’s pain history. Hypointensity on T1-weighted imaging and hyperintensity on T2-weighted imaging and short tau inversion recovery (STIR) is consistent with an acute or subacute fracture. This population tends to have a substantial improvement in pain with PVA. 4 If, however, the fracture is more chronic with minimal edema, the likelihood of substantial pain relief with treatment is much lower. 4 , 5 Bone scintigraphy, while less commonly used, is also very good at establishing the age of the fracture and in some cases may be more sensitive than MRI (Fig. 19‑1). It should be considered for patients unable to undergo MRI. Increased tracer activity at the level of a VCF is highly predictive of a positive clinical response to PVA treatment.
There is no clear guideline as to how long conservative treatments should be pursued before offering PVA. In general, most patients undergo conventional medical therapies for at least one month before undergoing the procedure. In patients who have uncontrollable pain causing them to be bedridden or remaining hospitalized, many advocate treatment as early as weeks or days following the injury.
Several contraindications to the procedure exist. One absolute contraindication is an active infection such as osteomyelitis, discitis, or epidural abscess. These are far more common in a patient with a history of intravenous drug abuse, diabetes, or alcohol abuse. Emergent performance of PVA is rarely, if ever, required, and treatment of patients with fever or sepsis should be postponed until they are afebrile and leukocytosis has resolved.
Another absolute contraindication for PVA is an uncorrectable coagulopathy, since it would significantly increase the risk of hematoma when placing the working channel in close approximation to the central canal and spinal cord. Likewise, patients must be able to be taken off of anticoagulant medications and have normal coagulation studies prior to the procedure.
A neurological deficit or severe spinal cord compression at the vertebral body level requiring treatment is an absolute contraindication to PVA. This stenosis can be due to degenerative changes or retropulsion of bone into the spinal canal. The latter most commonly involves the superior endplate. In a severely stenotic area, even a small amount of cement extravasation into the canal could create enough compression to cause permanent spinal cord injury. In this population, the procedure may be performed following decompression of the stenotic canal. Radiculopathy, although rare, can also occur with a VCF. While this is not a contraindication to the procedure, the patient should be counseled that their radicular pain is unlikely to improve. Fractures can involve the posterior cortical wall or the pedicle without resultant stenosis. While this is not an absolute contraindication to PVA, there is certainly an increased risk of cement extravasation into the central canal.
Fractures with greater than 70% loss of vertebral height can be technically difficult to treat. This is most commonly the result of difficulty in correctly being able to position the working channels in the remaining vertebral body. Similarly, fractures above the T5-T6 levels are more difficult to treat due to smaller pedicles as well as less favorable pedicle orientation. Compression fractures due to insufficiency tend to cluster at T12-L1 and to a lesser degree around T7-T8. These pedicles are usually large enough to accept the working needle safely for PVA. It is also much more common to find a single symptomatic fracture versus multiple fractures at any one time.
Compression fractures that are the result of malignancy have a far greater risk of complications in general. These are more likely to have involvement of the pedicle and posterior vertebral body and the resultant increased risk of extravasation of cement or tumor displacement into the central canal and neural foramina.
19.2 Technique Description
The first percutaneous vertebroplasty was performed in 1984 at the University Hospital of Amiens for a painful C2 hemangioma with excellent results. This case, as well as six others, were described in a 1987 publication. 6 The procedure was introduced in the United States in 1994 at the University of Virginia, and the results were subsequently published in 1997. 7 The first kyphoplasty occurred one year later, in 1998, with excellent results. 8 , 9 With the exception of some minor technical differences, both procedures are minimally invasive procedures in which a working cannula is placed percutaneously into the vertebral body using fluoroscopic X-ray guidance(Fig. 19‑2).
The procedure can be performed under general anesthesia, light sedation, or local anesthesia depending on the patient’s needs. Patients are placed in a prone position with a bolster placed under the sternum and pelvis. Care must be taken in patient positioning in the severely osteoporotic patient to avoid additional iatrogenic fractures. One or two fluoroscopic C-arms are placed so that anteroposterior and lateral imaging can be easily performed.
Needle placement is most commonly accomplished via a transpedicular route. This trajectory is in most cases the safest route of entry, since there are no structures within the pedicle that can be damaged during accurate transpedicular needle insertion. The pedicles also provide a discreet, easily identifiable target on imaging. This needle insertion pathway can be taken in the majority of cases. 2
A second trajectory into the vertebral body is the transcostovertebral (or parapedicular) route. The entry site for this is the lateral vertebral margin and the needle enters above the transverse process and pedicle. Entry should not be performed below the transverse process and pedicle, as this could result in damage to the exiting nerve root and induce a postprocedural radicular pain syndrome. This placement technique can be used when the pedicle is very small or cannot be seen on imaging due to severe osteoporosis. It can also be used in patients in whom one or more pedicle(s) are destroyed by tumor involvement. This trajectory, while safe, does pose additional risks to nearby structures. In some patients, the lung may bulge beyond the lateral rib margin into the needle trajectory, and patients can get a periprocedural pneumothorax. This area also contains many arteries and veins that can be damaged, resulting in bleeding and hematoma. This problem can be compounded by the fact that there is no effective way to apply direct pressure to the underlying tissue. If bleeding does occur, it is much easier to control in the transpedicular approach, since direct pressure can be applied to the underlying tissue.
In most cases, vertebroplasty can be performed via a unipedicular or bipedicular technique. Kyphoplasty is most often performed with the bipedicular approach. When using a unipedicular approach, the needle is advanced more to the midline of the vertebral body on the anteroposterior view.
Once in place, in cases where the etiology of a compression fracture is in question, the working channel needle can be used to perform a vertebral body and pedicle biopsy. Then cement, most commonly polymethylmethacrylate (PMMA), is injected via the cannula into the trabecular bone under continuous fluoroscopic control. Early vertebroplasties utilized a cranioplastic acrylic cement that contained no radio-opaque agent, making tracing cement insertion challenging. Poly(methyl methacrylate) (PMMA), and other agents used for contemporary PVA, universally contain radio-opaque agents. Injection is halted when the PMMA reaches the posterior two-thirds of the vertebral body or there are any signs that it breached into an extraosseous space.
Some technical differences exist between vertebroplasty and kyphoplasty. For vertebroplasty, cement is injected directly into the bone without first creating any kind of a cavity. Since the cement must be forced into this cancellous bone surrounding the needle tip, it must be injected under a higher pressure. Thus, this is considered a high-pressure technique. Kyphoplasty, on the other hand, is a variation of a vertebroplasty that involves the creation of a cavity in the vertebral body for cement placement. Once working needles are in place, an inflatable balloon is used to create a void within the cancellous bone. The balloons are then deflated, removed and the cement injected into the newly created space. Since the cement is going into a void, it can be injected under a lower pressure at a higher viscosity. This is therefore considered a low-pressure technique. The balloon had several theoretical advantages. Its inflation could be used to restore some of the height of the collapsed vertebral body. While some studies have demonstrated a modest height restoration, its clinical significance seems to be negligible. Additionally, since a cavity is created by the balloon, and higher viscosity cement can be injected, there is a theoretically decreased risk of extravasation.
With either approach, the operator needs to remain cognizant that the vertebral body is not simply a box, as it appears on intraoperative imaging. Since it has a concave posterior margin, if cement extends to what appears to be the posterior margin on fluoroscopy, then it has likely already leaked beyond the true concave portion of the posterior wall into the central canal. This potentially serious complication can be minimized by halting placement of cement when it reaches the posterior quarter of the vertebral body.
Fracture morphology affects surgical technique and patient selection. The most common type is compression of the anterior superior endplate. These fractures are very amenable to PVA, and needle placement is fairly straightforward. Some compression fractures contain clefts or cavities. In general, these will fill preferentially with cement and provide substantial improvements in pain. Some fractures appear to be mobile on imaging, with changes in height during respiration or patient movement. This is a potential opportunity for height restoration when it is observed, and perhaps kyphoplasty would be preferable to vertebroplasty in this population. Regardless of the ability to restore height, these patients seem to have significant pain relief with PVA treatment. Importantly, the amount of vertebral body height loss from the fracture does not correlate to the amount of pain the patient experiences or how long pain will last with conservative treatment.
19.3 Benefits and Risks
The primary benefit of PVA is pain relief and stabilization of fracture that can lead to increased activity level and decreased dependence on opioids. The average patient who undergoes a PVA achieves an average of a 40-point reduction in a visual analog score for pain, with similar gains for other pain scales. 10 , 11 Upwards of 95% of patients achieve pain relief in the immediate postoperative period. 12 Similarly, opioid usage decreases by over 50%, and activity levels increase in 80% of patients. 13
The mechanisms of PVA pain relief in osteoporotic fractures are not completely understood. Stabilization of the fracture likely plays a major role in the procedures success. As in fractures in other areas of the body, fixating the broken bone decreases motion and painful nerve stimulation. When PMMA polymerizes, it generates heat in an exothermic polymerization reaction. It has been hypothesized that the heat of polymerization causes thermal necrosis of neural tissue and pain relief. Whether enough heat is produced to cause such an effect is arguable. The PMMA monomer is also known to be cytotoxic. Whether the concentration present following a PVA procedure is high enough to cause significant damage to the surrounding tissue is also unknown. Histologic studies performed of the bone bordering the cement have demonstrated a zone of necrosis thought to be secondary to the toxic-thermic effect of PMMA used in the majority of cases. Another possibly etiology of this zone of necrosis is ischemia due to the cement destroying blood supply to tis area of bone.
The effectiveness of either the vertebroplasty or kyphoplasty technique has been demonstrated to be similar in most circumstances. Kyphoplasty does take longer to perform and is more expensive. In some circumstances, it does have a better ability to restore height. 14 This is especially true in fractures that appear to be mobile on imaging, with changes in height during respiration or patient movement. Whether this improves clinical outcome has not been proven. Vertebroplasty utilizes a smaller working channel that can be an advantage in cases of extreme vertebral body collapse.
In contrast to the benefits of pain relief, the risks of performing PVA are the following: failure for pain to improve, infection, hematoma, injury of surrounding structures by needle, extravasation of PMMA causing neural compression, embolization of PMMA, and adjacent VCF. Failure of the procedure to provide pain relief or additional pain relief compared to conservative measures is a common preoperative concern. Several studies have suggested high initial pain relief, with at least partial pain relief reported in up to 95 to 97% of patients in the immediate postoperative period, a result that diminishes with time. 1 , 10 While early randomized trials suggested that PVA did not provide significant pain relief compared to conservative management, these trials were plagued by methodological issues addressed below. 15 , 16 Additionally, the development of adjacent-level compression fractures, which may require additional PVA, is a concern. Recent studies indicate that the development of adjacent-level compression fractures may be as high as 8%. 2
While infection from the procedure is uncommon, patients can experience localized perioperative pain and low-grade fever in the first 72 hours. This is usually due to local bruising and tissue irritation and resolves with mild analgesics. Hematoma and local irritation can be minimized by 5 minutes of manual compression over the incision following trocar removal as well as the postoperative injection of local anesthetic. This almost universally resolves within 24 to 72 hours. If fever persists, an infection workup should be initiated.
Although clinically significant symptoms induced through cement extravasation are rare, it is a common finding on postoperative imaging, occurring in up to 30% of postoperative images. 11 , 12 This can occur through defects in the surface of the vertebral body or flow into nearby vasculature. To minimize the risk of extravasation, cement should be viscous enough that flow ceases immediately when the injection ends. Leakage into the disk space is more common when treating vertebral bodies that are significantly collapsed. While it has been speculated that this increases the risk of adjacent level fractures, this has never been substantiated.
Other rare complications occurring in percutaneous augmentation are intercostal neuralgia or radiculopathy. This can occur secondary to irritation or damage to an adjacent nerve root or the extravasation of cement into a foraminal vein or the foramen itself. It often resolves without specific treatment. Patients with significant postoperative radicular pain may require a brief course of nonsteroidal anti-inflammatory drugs, oral steroids, or local steroid injections at the affected area. Significant extravasation into epidural veins or the spinal canal can result in spinal cord compression and paraplegia requiting emergent decompression.
Arterial hypotension has been reported with PVA. This is likely due to pulmonary emboli. These may occur from cement extravasation into the vasculature or the displacement of blood products and fat from the vertebral body during balloon inflation and cement injection. While usually asymptomatic or transiently symptomatic, they can cause significant problems, even cardiopulmonary failure, in patients with a limited pulmonary reserve such as those with chronic obstructive pulmonary disease or preexisting pulmonary hypertension. In these populations, minimizing the number of levels treated at one time to no more than two or three can decrease the risk. Another concern in treating multiple levels in a single session is the theoretical cardiotoxic effect of free methylmethacrylate monomer.