Introduction

Kyphoplasty, along with vertebroplasty and newer, related procedures, are forms of vertebral body augmentation (VBA). The procedures employ percutaneous injection of polymethylmethacrylate (PMMA) acrylic cement into a fractured vertebral body to restore strength and stiffness. Other indications, such as pathologic fractures from metastasis, are becoming more common. High energy, bursting, and extension fracture patterns should be avoided because of the increased PMMA extravasation risk.

In appropriately indicated patients, kyphoplasty yields excellent early pain relief and return to activity. Potential disadvantages of kyphoplasty include procedural risks, such as cement leakage and possible fracture of adjacent segment.

Brief Description

Spinal osteoporosis alone is asymptomatic. If allowed to progress, however, it confers increasing risk of fragility fracture. The principal manifestation of osteoporotic vertebral compression fractures (VCFs) is back pain. Some minimally symptomatic patients do not present for medical evaluation.¹ Others require hospital admission for unrelenting pain. Typically, over 3 months, the fracture heals and the back pain subsides.² Although the nonunion rate is low, not all VCFs heal.

Back pain can persist after fracture healing. From 33% to 75% of fractures precipitate chronic back pain.³ The chronic pain has been attributed to hyperkyphosis, leading to excessive muscular strain. Excessive anterior vertebral body loading engendered by this malalignment may propagate stress fractures in the surrounding endplates.⁴ Late kyphosis is occasionally associated with myelopathy.⁵

Indications and Contraindications

The goal of kyphoplasty is to interrupt the cycle of pain and functional decline associated with VCFs. Given the limited data comparing long-term impacts of kyphoplasty relative to nonoperative management, injecting all fractures cannot be justified. Because many patients improve quickly, most patients should try nonoperative management before considering kyphoplasty.

The duration of this nonoperative trial is inversely related to the patient’s pain level and functional limitations. Consider early intervention in patients unable to return to ambulation after a few days. Protracted bed rest may be riskier than procedural risks. At least 150,000 VCFs per year are refractory to nonoperative measures and require hospitalization, with bed rest and IV narcotics. Ambulatory patients should undergo 4 to 8 weeks of nonoperative care. In this group, treatment often includes limited contact thoracolumbar bracing, activity limitations, and sparing use of pain medications. For fractures of L2 and above, a CASH or Jewett brace is recommended. Low lumbar fractures may respond to a chairback brace. Fractures above T6 are more frequently related to metastasis than osteoporosis. Fractures less likely to improve with standard medical management include those with the following:

Over time, kyphoplasty indications have gradually been expanded to include conditions such as multiple myeloma and osteolytic metastases. Moreover, kyphoplasty has been added to open decompression and internal fixation procedures. Hybrid procedures may be indicated for more complex fracture patterns, significant compression of the neural elements, and neoplastic lesions with cortical destruction.⁷ Another hybrid option combines radiosurgery and kyphoplasty. Conventional radiotherapy remains the index treatment in many patients with vertebral body metastasis.⁷ Used alone, radiation is associated with delayed pain relief and further vertebral collapse due to both the previous bone erosion and the radiation itself. Newer radiation therapy techniques allow more focused radiation to be applied via intense treatments over a shorter time course.

Absolute contraindications to kyphoplasty include the following:

In this setting, “young” suggests patients younger than 65 years. The stronger the host bone, the less effectively polymethylmethacrylate restores stiffness. Patients with good bone stock fracture only after high energy loading. In this setting, PMMA leakage is more common. Calcium phosphate kyphoplasty (and other resorbable materials) is under study for this indication. Though isolated reports suggest pain improvement with kyphoplasty for sacral fractures, this indication is not widely accepted.

While less common than VCF, osteoporotic burst fractures (senile burst fractures) are not rare. Any fracture precipitating more than 50% height loss will have associated posterior cortical compromise. In many cases, this compromise takes the form of cortical buckling. When the canal occlusion is less than 33%, kyphoplasty can be considered. On the other hand, in the face of cortical comminution, avoid percutaneous kyphoplasty because of the increased risk of cement extravasation. In patients with neurologic injury, open surgery may be required.

Open surgery is indicated in patients with osteoporotic bones who also have progressive neurologic deficit. Unfortunately, in this frail population, operative intervention confers high risk. Similarly, spinal instrumentation systems often fail in osteoporotic bone. PMMA augmentation increases screw pull-out strength. Combination of kyphoplasty with open decompression restores anterior column load bearing and limits the scope of the reconstruction necessary.

Description of the Device

Kyphoplasty requires one or two high quality fluoroscopes and a kyphoplasty kit. The traditional set begins with a modified Jamshidi needle and a guide wire. Other systems remove the guide wire step (“express” and “one step”). Ultimately, each system is used to safely place two working cannulae through which KyphX balloon tamps can be inserted into the vertebral body. Smaller cannulae are available for upper thoracic vertebrae. The balloon tamps are modified angioplasty balloons. Currently, three sizes are available and are selected based on the size of the fractured vertebral body: 10, 15, and 20 mm. The balloons attach to a syringe with an integral pressure gauge. In the operating room, the balloons are prepped at the back table by instilling 10 ml of radiopaque contrast media. As volume is added to the balloon, the balloon pressure (measured in psi) increases. As the tamp displaces bone, the pressure gradually decays.

Kyphon (Sunnyvale, CA) manufactures several specific balloon products thought to assist in challenging clinical scenarios. For example, a bidirectional balloon (KyphX Elevate) emphasizes craniocaudal expansion and limits mediolateral enlargement. Another single-direction balloon (KyphX Exact) is deployed through a metal housing, which is thought to control balloon direction. These tamps confer additional cost to the procedure. There are no data demonstrating improved outcomes or decreased risk with these devices.

The system also includes bone void fillers, each of which holds 1.5 ml of PMMA. The bone void fillers are cannulae with plungers that allow gradual backfilling of the void created by the tamp. A modified bone void filler, the biopsy device, has sharper tips and can be deployed through the working cannula. PMMA with added barium to enhance fluoroscopic visibility and a mixing system are also available in a separate kit.

Background of Scientific Testing and Clinical Outcomes

The source of pain relief after kyphoplasty remains unclear. Currently, most authors suggest that restoration of strength and stiffness to the fractured vertebral body relieves pain. Both cement volume and percentage of the vertebral body filled can predict postaugmentation bone strength and stiffness. Overall, the more PMMA inserted, the higher the postinsertion vertebral strength and stiffness.

Outcomes data include a number of retrospective studies. Very recently prospective data have been reported from the FREE trial.¹⁰ This trial included 21 sites in 8 countries that enrolled 300 patients with acute VCF and randomized them to either kyphoplasty (149) or nonoperative care (151). As of this writing, the complete paper has not been published, but early pain relief seems to be a clear advantage of kyphoplasty. Whether that advantage persists is more difficult. The primary outcome was the difference in the Short Form (SF-36) physical component summary at 1 month. Quality of life measurements and spine radiographs were assessed through 12 months. Kyphoplasty subjects reported greater improvement than controls in their SF-36 physical component (5.2 point difference; p < 0001) at one month). By 12 months, the difference declined to 1.5 points and was no longer significant (p = .2). Kyphoplasty improved quality of life by the 1-point EuroQol questionnaire at 1 (0.18 points; 95% CI, 0.08–0.28; p < .001) and 12 (0.12; 95% CI, 0.01–0.22; p = .025) months. Back function, as measured by the 24-point Roland-Morris scale, was improved by 4.0 points by kyphoplasty at 1 month (p < .001) and 2.6 points at 12 months (p = .001). Kyphoplasty patients reported fewer days with limited activity, less back pain, and less use of analgesics and walking aids.

Of note, the FREE study was funded by the manufacturer and many of its authors are Kyphon consultants. On the other hand, three other small studies comparing kyphoplasty with conventional medical treatment also found that kyphoplasty consistently improved pain and physical function, with results sustained at 6 months.^11–13

In 2005, Hadjipavlou et al¹⁴ combined the available vertebroplasty and kyphoplasty outcome reports in an effort to compare the procedures. Using meta-regression techniques, the authors found that individual study design had a considerable impact on subsequent analysis. For prospective studies, the rates of success with vertebroplasty and kyphoplasty were not significantly different at 92% and 93% respectively. However, in retrospective studies, kyphoplasty was more successful (95% vs. 86%; p = .019)

Aside from pain relief, a major benefit of VBA lies in the restoration of mobility. In one series of 11 wheelchair-bound cancer patients, 73% were able to walk shortly after vertebroplasty.¹⁵ Other studies reported restoration of mobility after kyphoplasty in 84% to 100%.^8,16 In terms of other types of physical functioning, a number of different outcome measures have been used. In a retrospective analysis of patients with painful osteoporotic VCF, 49 patients who were available for follow-up at a mean 9-month interval had an improvement in visual analogue pain scale score of seven points (p < .05), and an improvement in Roland-Morris Disability Survey of 11 points (p < .05).¹⁷

In a retrospective analysis of 52 patients with 82 painful osteoporotic VCFs, kyphoplasty restored 4.6 mm and 3.9 mm to the heights of the anterior and medial columns, respectively.¹⁷ The mean Cobb angle increased by 14%. In a meta-analysis, Hadjipavlou et al concluded that, although postural reduction can improve vertebral height following a compression fracture, better reductions are obtained with kyphoplasty than with vertebroplasty.¹⁴ Better reductions may be achieved with earlier treatment.

Clinical Presentation and Evaluation