Vertebral Augmentation

Kyphoplasty and vertebroplasty currently are used to treat neurologically intact patients suffering from vertebral compression fractures resulting from osteoporosis and certain neoplasms. Percutaneous vertebroplasty (PV) is an imaging-guided procedure that reinforces a compromised vertebra with polymethylmethacrylate (PMMA), alleviating pain and improving the patient’s mobility. Initially described in 1987 as a treatment for painful hemangiomas,¹ the procedure now is used most widely to treat fractures and destructive lesions that cause vertebral collapse and pain. The goal of vertebral augmentation procedures is to reduce fracture pain by stabilizing the vertebral fracture, allowing patients to return to their daily living activities and exercise.

The primary indications for PV are persistently painful compression fractures, most commonly related to osteoporosis, that are unresponsive to correct medical treatment, and benign or malignant osteolytic neoplasms (e.g., hemangioma, metastasis, and myeloma). In the setting of osteoporotic fracture, PV is done primarily for pain management and secondarily to prevent further collapse.² For neoplasm, the indications are somewhat broader, and the procedure may be done for pain management and/or stabilization. PV is not an ablative procedure, but reinforcement may reduce pain while facilitating other therapies such as radiation therapy or surgical resection and fixation and minimizing the risk of further collapse or fracture.

The specific indications for PV are as follows:

The indications have been expanded to include nonunions of chronic traumatic fractures, which typically show a pseudarthrosis with a fluid-filled cleft or cystic findings on MRI evaluation.

As with any spine operation, precise patient selection is essential to the therapeutic success of PV. Patients with prior unsuccessful spinal surgery generally do not respond as well to PV.

The absolute contraindications to PV for either osteoporotic or neoplastic conditions are as follows:

Relative contraindications include the following:

Other, less common, relative contraindications are (1) retropulsion of fracture fragment(s) causing substantial spinal canal compromise (e.g., a burst-type fracture); (2) neoplasm extending into the epidural space with substantial spinal canal compromise; (3) severe vertebral collapse such that it would be technically challenging to place a needle; (4) chronic stable fracture without pain; and (5) treatment of more than three levels at any one time. Acute traumatic fracture of a nonosteoporotic vertebra also is considered a contraindication.

Patient Selection

Preoperative evaluation entails imaging to demonstrate the level of fracture (by plain radiography), to confirm an “active” fracture by MRI (demonstrating bone marrow edema) or nuclear medicine scintigram (“bone scan”), and excluding unsuspected malignancy or degenerative disease (e.g., herniated discs). This usually entails obtaining recent MRI examinations, within 7 to 10 days of consultation.

Plain radiography is useful for showing the vertebral level involved and to determine the degree of collapse. With complete or near complete vertebral collapse, PV usually is unlikely to be successful.

A specific protocol is employed with sagittal T1-weighted conventional spin echo (CSE), sagittal T2-weighted fast spin echo (FSE), or turbo spin echo (TSE) with fat saturation and axial T2-weighted FSE through areas of abnormality. If fat suppression is not available for the T2-weighted images, then a short tau inversion recovery (STIR) sequence should be substituted. The fluid-sensitive sequences (T2 with fat suppression or STIR images) are necessary to identify an “active” compression fracture. While the causes of bone marrow edema are legion, in the context of compression fractures and appropriate clinical symptoms, it often indicates a persistent pain generator. The age of the compression fracture is less important than the presence of bone marrow edema on MRI. This becomes relevant for people who have had symptoms for months or years due to unhealed fractures.

Concordant pain evaluation also is a critical aspect for determining whether patients with benign compression fractures will respond to PV. Under fluoroscopy, the back may be percussed and palpated over the spinous processes, marking the areas of tenderness relative to the recognized compression fracture. The patient also may assume any position that triggers the pain while the physician marks the painful site. If the pain corresponds to the fracture level (usually within one level above or below), then the symptoms are likely to be amenable to PV at that vertebral level. If pain is not concordant (for instance, lumbosacral pain associated with a thoracolumbar fracture), PV is much less likely to help.

If the patient is a candidate for PV, a further workup is required. Patients taking warfarin must have it discontinued prior to the procedure and potentially be switched to heparin for the periprocedural period. Patients with a fever, leukocytosis, or an elevated erythrocyte sedimentation rate must wait until the cause is diagnosed and treated (presumably an infection). For patients taking steroids, it is necessary to work closely with the primary care provider to manage the dose during the periprocedural period.

The informed consent process usually is a comprehensive discussion of the risks, benefits, and alternatives to PV. Risks include bleeding, infection, allergic reaction to the PMMA, fracture (pedicle or rib), and PMMA extravasation. Pneumothorax also is a potential risk for thoracic levels. Informed consent should also explain the goal of treatment (e.g., pain management, prevention of further deformity, stabilization for radiation therapy), theoretical background (e.g., stabilization by internal “casting”), technical aspects (e.g., needle procedure versus open surgery), and clinical data regarding PV. This often includes answering questions regarding the nature of osteoporosis and the status of PV as “standard of care” versus an “experimental procedure,” including the off-label use of the cement (PMMA) and the modification of PMMA by additional sterile barium to increase opacification (thus allowing early detection of extravasation). The possible need for emergent spinal decompression should be addressed with the patient.

Anesthesia for PV may be accomplished with neuroleptic anesthesia (i.e., conscious sedation), with the advantage that the patient is able to report any symptoms of a complication immediately, allowing the operator to halt the injection and minimize further injury. It also facilitates PV as a same-day outpatient procedure with a quicker recovery period. For these reasons, intravenous CS (IVCS) is considered the preferred mode of sedation for PV. Intravenous antibiotic coverage is recommended using cefazolin, or vancomycin if the patient has penicillin allergy, as infection prophylaxis.

Technical Performance of Vertebroplasty

The traditional mode for PV has been to perform bilateral injections via a transpedicular or dorsolateral (parapedicular) approach using a two-needle technique (Figs. 220-1 to 220-5). Unipedicular injections also can provide substantial vertebral reinforcement when enough cement is injected to cross the midline of the vertebral body and provide a similar distribution to bipedicular injections.³

FIGURE 220-1 Parasagittal approach. Anteroposterior projection fluoroscopic images show the typical position for the parasagittal transpedicular puncture. A, Note that the initial puncture site is with the needle tip located in the superolateral corner of the ring shadow of the pedicle (arrowhead). B, The needle has been advanced to the ventral one third of the vertebral body, and the tip is somewhat centrally located but still ipsilateral. Note the intradiscal cement from injection of the level above (arrow).

FIGURE 220-2 “Scotty dog” approach. Oblique projection fluoroscopic image shows the typical position for transpedicular puncture when using the “Scotty dog” approach. Note that the target is the ring shadow of the pedicle in an approximately 45-degree obliquity (arrowhead points to the pedicle below the punctured level for reference). This trajectory places the needle tip centrally and facilitates filling of both sides from a unilateral injection.

FIGURE 220-3 Needle-tip position. Sagittal projection fluoroscopic image shows appropriate needle-tip position within the ventral one quarter to one third of the vertebral body. Note the small amount of cement injected that has begun to fill the fracture line (arrow).

FIGURE 220-4 Cement extravasation. Sagittal projection fluoroscopic image shows a small amount of cement that has extravasated ventrally (arrow) outside of the vertebral body into the retroperitoneum. Extravasation in this location usually is not clinically significant.

FIGURE 220-5 Cement distribution. The axial CT image shows hyperattenuating cement in the ventral and mid-portions of the vertebral body. Note that the dorsal vertebral margin is concave (arrowhead). This forms the dorsal vertebral line on lateral radiography or fluoroscopy and also is the location where the basivertebral venous plexus perforates the cortex (not shown). Therefore, cement should not be injected in an attempt to fill the entire dorsal aspect of the vertebral body under fluoroscopy.

The modalities used for imaging are either fluoroscopy or CT. PV can be accomplished with either single-plane or biplane fluoroscopy. Biplane fluoroscopy is considered ideal because one can view orthogonal projections without changing tube position, greatly reducing procedure time. CT requires repositioning the gantry between needle manipulations, imaging, and injection, consuming useful injection. CT fluoroscopy allows the user to generate real-time CT sections while performing procedures, but concerns with CT fluoroscopy revolve around the increased radiation dose delivered to personnel and the operator in the room during the procedure. For most purposes, C-arm fluoroscopy provides adequate imaging, is readily available, and is less time-consuming.

The needles used are standard bone marrow biopsy-type needles that have a Luer-lock connection. Either beveled or pointed tips can be used effectively, and which to use is based largely on operator preference and experience. The goal is to fill the focus of the fracture, which typically is ventral and rostral, and to avoid injection into the larger vascular sinusoids of the basivertebral plexus, which could allow extravasation into the epidural space. Initial cortical puncture and purchase should be obtained by hand, and then needle advancement may be by hand or with the assistance of a mallet. For lumbar levels, 10- to 11-gauge needles are used, but for the thoracic levels, some authors advocate using 13- to 14-gauge needles. The needle tips should be advanced to the ventral one fourth to one third of the vertebral body, approaching the midline.

The cement flow must be monitored carefully, and the injection should cease if there is resistance or if cement approaches the dorsal vertebral margin. If any extraosseous cement is identified, the injection should be terminated immediately. Up to three levels can be done in a single operation. The risk of doing more numerous levels simultaneously is the possibility that PMMA could cause fat emboli syndrome and respiratory compromise through marrow displacement.

Postprocedure, the patient remains flat in bed for at least 1 hour, followed by bedrest for an additional 1 to 3 hours with the head of bed elevated less than 45 degrees. If any new, severe pain or new neurologic symptoms develop, a CT scan should be done immediately to evaluate the distribution of cement.

Treating Tumors

Vertebroplasty may play an important role in palliation for the patient with vertebral metastases and in improving independence and function during more definitive systemic therapy. Tumors that are particularly radiosensitive are most appropriate to PV, because local control can be obtained as easily after stabilization as before. Tumors that require resection with a surgical margin, such as primary malignancies or locally aggressive benign tumors, are not appropriate for PV. Although there is some theoretical margin of tumor-kill associated with the thermal effect of the PMMA mass,⁸ the application of PV in the setting of neoplasm is not intended as an ablative procedure, and the goal is to provide structural support primarily, with the secondary goal of pain relief. The amount of PMMA used may be greater in an osteolytic spinal lesion than in a compression fracture, because the trend to minimize injectant volume in osteoporosis (i.e., filling the fracture line) does not apply in an erosive or destructive lesion.

Metastases are the lesions most commonly treated by PV, but large, symptomatic hemangiomas also may require ablation and stabilization with PMMA injection. Hemangiomas have a benign histology, but may grow aggressively and cause pain through either tissue distortion or pathologic fracture. PV stabilizes the vertebral body and obliterates the vascular sinusoids that make up the mass of the hemangioma. Subsequent surgery may then be focused on decompression, if needed.⁹ In this fashion, PV is another adjuvant treatment akin to intralesional sclerosis or embolotherapy preoperatively. PV also is effective in treating vertebral metastases that result in pain or instability, providing immediate and long-term pain relief.¹⁰ MRI is crucial for preoperative planning to evaluate the soft tissue extent of the tumor (e.g., spinal canal involvement, neuroforaminal encroachment, and status of the posterior longitudinal ligament).

The goal in PMMA application during tumor treatment is to obtain craniocaudal filling (attempting to get superior-to-inferior end-plate filling) that crosses the midline transversely, providing a vertical strut. The cement may fill part of the tumor, but this is not the goal. Metastatic lesions and plasma cell tumors are not cystic structures—any space filled with cement likely represents tumor tissue that has been displaced somewhere. There is a small risk that the neoplastic tissue may be displaced into the canal or neural foramen, causing root or cord compression. Adjuvant therapy (surgery, chemotherapy, or radiation therapy) will be required to control the tumor locally. For cases involving malignant neoplasm, there often is concern regarding vascular seeding of the displaced tumor as the PMMA infiltrates the tumor bed, displacing tumor into the vascular system. Although there is no literature to support or refute this concern, it is believed to be a nontrivial risk.

Complications

Fortunately, major complications are uncommon. The most common complication is radicular pain caused by migration of cement into the epidural venous plexus. In most patients, intradiscal and paravertebral leaks of cement have no clinical importance.¹¹ However, there have been case reports of severe neurologic complications, underscoring the need for appropriate safeguards as outlined previously.¹² Permanent paralysis has been reported, but is exceptionally uncommon if the procedure is performed in a controlled, image-guided fashion (by using a biplane real-time fluoroscopy suite). Rib, pedicle, or transverse process fractures also have been noted. One case has been reported of a pulmonary embolism caused by acrylic cement. This rare complication was believed to have occurred because perivertebral venous migration was not recognized.¹³ The anticipated complication rate is higher when treating neoplasms (10%) than for osteoporotic compression fractures (1% to 3%).

Outcomes

Taylor et al. performed a systematic review and meta-regression to compare the efficacy and safety of balloon kyphoplasty and vertebroplasty for the treatment of vertebral compression fractures, and to examine the prognostic factors that predict outcome. They found level III evidence to support balloon kyphoplasty and vertebroplasty as effective therapies in the management of patients with symptomatic osteoporotic vertebral compression fractures refractory to conventional medical therapy. Although there was a good ratio of benefit to harm for both procedures, balloon kyphoplasty appeared to offer the better adverse event profile.¹⁴

In a follow-up study, the same authors concluded that in direct comparison to conventional medical management, patients undergoing kyphoplasty experienced superior improvements in pain, functionality, vertebral height, and kyphotic angle, at least up to 3 years postprocedure. Reductions in pain with kyphoplasty appeared to be greatest in patients with newer fractures. The authors concluded that there are prospective studies of low bias, with follow-up of 12 months or more, that demonstrate balloon kyphoplasty to be more effective than medical management of osteoporotic vertebral compression fractures and at least as effective as vertebroplasty.¹⁵

Kallmes et al. randomly assigned 131 patients who had one to three painful osteoporotic vertebral compression fractures to undergo either vertebroplasty or a simulated procedure without cement injection (served as control group).¹⁶ The primary outcomes were scores on the modified Roland-Morris Disability Questionnaire (RDQ) and patients’ ratings of average pain intensity during the preceding 24 hours at 1 month. Patients were allowed to cross over to the other study group after 1 month. Interestingly, both groups had immediate improvement in disability and pain scores after the intervention. At 1 month, there was no significant difference between the vertebroplasty group and the control group in either the RDQ score or the pain rating. The authors found a trend toward a higher rate of clinically meaningful improvement in pain (a 30% decrease from baseline) in the vertebroplasty group at 1 month. At 3 months, there was a higher crossover rate in the control group than in the vertebroplasty group. There was one serious adverse event in each group. The authors concluded that improvements in pain and pain-related disability associated with osteoporotic compression fractures in patients treated with vertebroplasty were similar to the improvements in a control group.

In a prospective study of 30 consecutive patients, Muijs et al. analyzed clinical and radiologic outcome 36 months after percutaneous vertebroplasty for osteoporotic vertebral compression fractures unresponsive to conservative treatment for at least 8 weeks. The authors also examined the quality of life (QOL). The authors reported good pain relief and significant increase in QOL scores, despite finding asymptomatic leakage of cement in 47 of 58 (81%) of treated vertebrae. The authors concluded that percutaneous vertebroplasty in the treatment of chronic vertebral compression fractures results in an immediate, significant, and lasting reduction in back pain, as well as overall improvement in physical and mental health.¹⁷

A meta-analysis to study the amount of pain reduction using the visual analog scale (VAS) with kyphoplasty and vertebroplasty in the treatment of osteoporotic vertebral compression fractures revealed that both procedures reduce pain in symptomatic osteoporotic vertebral compression fractures that have failed conservative treatment.¹⁸

Pain relief and risk of complications associated with vertebroplasty versus kyphoplasty were evaluated by Eck et al.¹⁹ The authors identified a total of 1036 abstracts for potential inclusion. Of these, 168 studies met the inclusion criteria. Mean preoperative and postoperative VAS scores for vertebroplasty were 8.36 and 2.68, respectively, with a mean change of 5.68 (P < .001). The mean preoperative and postoperative VAS scores for kyphoplasty were 8.06 and 3.46, respectively, with a mean change of 4.60 (P < .001). Statistically greater improvement was found with vertebroplasty versus kyphoplasty (P < .001). The risk of new fracture was 17.9% with vertebroplasty versus 14.1% with kyphoplasty (P < .01). The risk of cement leak was 19.7% with vertebroplasty versus 7.0% with kyphoplasty (P < .001). The authors concluded that vertebroplasty had a significantly greater improvement in pain scores but also had statistically greater risk of cement leakage and new fracture.

Future Considerations

In a randomized study, Yang et al. compared the outcomes in patients with metastatic spinal tumors treated with either vertebroplasty alone or vertebroplasty combined with interstitial implantation of iodine-125 seeds.³⁴ A total of 80 patients with metastatic spinal tumors were randomized to receive vertebroplasty alone (40 cases) or vertebroplasty combined with iodine-125 seed implantation (40 cases). Visual analogue scores and Karnofsky performance scores were superior in the iodine-125 group. The authors concluded that clinical outcomes can be enhanced by the addition of interstitial implantation of iodine-125 seeds to the treatment protocol.

Summary

As the population ages and osteoporosis becomes more prevalent, and as oncologic therapies increase the life span of patients afflicted by vertebral metastases, the incidence of symptomatic vertebral compression fractures is almost certain to increase. For those patients with severe pain or progressive collapse due to osteoporotic or osteolytic vertebral compression fractures, early vertebral augmentation with percutaneous vertebroplasty affords excellent early pain relief and early return to function, and restores and maintains sagittal alignment. Recent 2-year follow-up data suggest that the benefits of the procedure persist with time.

Surgical Indications

Kyphoplasty currently is indicated for progressive, painful osteoporotic vertebral compression fractures (VCFs) in the absence of neurologic signs. Even though the natural history of vertebral compression fractures is for two thirds of patients to eventually become pain free, one must appreciate that (1) not one of those vertebral bodies ever regains its normal height, (2) the presence of a vertebral collapse predicts increased mortality, and (3) there is a five-fold increase in further fractures at adjacent or remote levels within 1 year.^1–3 Therefore, the indications are pain relief and protection of sagittal spinal alignment.

The contraindications to kyphoplasty include local active osteomyelitis, systemic pathology, coagulopathy, and cardiopulmonary pathology. Other relative contraindications include vertebral bodies with deficient dorsal cortices, burst fracture configurations, and patients presenting with neurologic signs or symptoms.

Technique

With the patient under general or local anesthesia in the prone position on a radiolucent spinal frame, two C-arms are positioned for anteroposterior and lateral fluoroscopic images. Once positioned, the C-arms or patient is not moved, to ensure repeatable images throughout the case. Two 5-mm incisions are made at the vertebral level, parallel to the pedicles in both planes. Then a guidewire or biopsy needle is advanced into the vertebral body via a transpedicular or extrapedicular approach, depending on fracture configuration and the patient’s anatomy. The guidewire is exchanged for the working cannula, using a series of obturators. Once the working cannula is positioned, the surgeon reams out a corridor to accommodate the inflatable bone tamp (IBT) and positions the IBT under the collapsed end plate. To deploy the IBT, inflation proceeds slowly under fluoroscopy until maximum fracture reduction is achieved or the balloon reaches a cortical wall. At this point, the surgeon deflates and removes the IBT, mixes the cement, prefills the cement cannulae, and allows the cement to partially cure in the cement cannulae. Once partially cured, PMMA is slowly extruded into the vertebral body through each pedicle under continuous lateral fluoroscopic guidance. This technique permits a controlled fill. In most instances, the volume of cement can slightly exceed that of the bone cavity, to interdigitate filler from the central bolus with the surrounding bone. Once filling is complete and the cement has hardened, the surgeon removes the cannula and closes the 5-mm incisions.

Clinical Results

Our published data from the Cleveland Clinic show that kyphoplasty provides a safe and effective treatment for pain and disability in patients with vertebral compression fractures secondary to osteoporosis and multiple myeloma.^4–8 Outcome data were obtained by administering the Short Form-36 health survey (SF-36) and visual analogue scale (VAS) for pain rating. In addition, the patients underwent detailed neurologic and radiographic examinations preoperatively and postoperatively. In our experience there were no clinically significant cement leaks and no perioperative complications attributable to the inflatable bone tamp or tools. Preoperative and postoperative SF-36 data are available on over 210 patients with average follow-up periods of 10.8 months. SF-36 scores improved in every category, statistically significant in all but the General Health modality. Physical function improved from 15.0 to 30.0 (P < .001). Role-physical improved from 9.3 to 27.3 (P = 0.004). Bodily pain improved from 22.0 to 32.0 (P ≤ .001). Vitality improved from 30.0 to 40.0 (P ≤ .001). Social function improved from 37.5 to 50.0 (P ≤.001). Role-emotional improved from 33.3 to 66.7 (P = .39). Mental health improved from 64.0 to 72.0 (P < .001). General health was unchanged from 52.0 to 55.0 (P = .051). The VAS scores improved from a preoperative level of 7.0 to an initial postoperative level of 3.2 (P < .0001). At last follow-up examination, the value remained unchanged at 3.4 (P < .0001).

Ledlie et al. reported functional and radiographic outcomes in the first 117 consecutive patients with 151 fractures.⁹ Their report focused on the results for the subset of 77 patients completing follow-up. With regard to pain as rated by the patient using a 10-point VAS, the mean pain score was decreased from 8.9 ± 1.5 before surgery to 2.8 ± 2.9 at 1 week postoperatively, and stayed low at 1.5 ± 1.8 at 2 years postoperatively. The proportion of patients who were fully ambulatory increased from 45% before surgery to 85% at 1 week postoperatively, and 88% at the 2-year follow-up.

Garfin et al. reported clinical results from a total of 155 subjects with 214 VCFs who underwent balloon kyphoplasty at 19 study centers from August 2000 to June 2001.¹⁰ Mean pain ratings decreased from 15.0 (full mark: 20) before surgery to 6.0 within 7 days after kyphoplasty (P < .001), a 60% reduction, and remained decreased throughout follow-up to 24 months. The mean number of days of the previous 28 days spent in bed decreased from 8.8 at baseline to 1.9, 2.2, 0.7, and 1.4 at 1, 3, 12, and 24 months after kyphoplasty.

Wardlaw et al. reported the results of their randomized controlled trial at 21 sites in 8 countries¹¹ in which 300 patients were randomly assigned by a computer-generated sequence to review kyphoplasty treatment (n = 149) or nonsurgical care (n = 151). Among them, 138 participants in the kyphoplasty group and 128 controls completed follow-up at 1 month. By use of repeated measures mixed effects modeling, all 300 randomized participants were included in the analysis. The mean SF-36 physical component summary (PCS) score improved by 7.2 points (95% CI, 5.7–8.8), from 26.0 at baseline to 33.4 at 1 month, in the kyphoplasty group, and by 2.0 points (95% CI, 0.4–3.6), from 25.5 to 27.4, in the nonsurgical group (difference between groups 5.2 points, 2.9–7.4, P < .0001). The frequency of adverse events did not differ between groups. These results suggest that balloon kyphoplasty is an effective and safe procedure for patients with acute vertebral fractures and can be considered as an early treatment option.

In addition to good clinical results, height restoration by kyphoplasty has been reported in several studies. Our initial results showed height restoration in 70% of 70 fractured vertebrae treated with kyphoplasty.⁴ In patients in whom the vertebral fractures were reduced by kyphoplasty, vertebral height was increased by a mean of 46.8%.

Ledlie et al. reported their radiographic measurement results for ventral and midline points of the fractured vertebrae using the two nearest normal vertebrae as reference points.¹² Pairs of preoperative and 2-year follow-up radiographs for 85 treated fractures were evaluated for vertebral height measurement. Mean preoperative ventral height (Ha), mid-height (Hm), and posterior height (Hp) were 61.3% ± 23.8%, 61.0% ± 20.1%, and 86.5% ± 18.4%, respectively. Compared to preoperative heights, mean Ha, Hm, and Hp were significantly higher (P < .001) at all postoperative intervals. Following kyphoplasty (1–6 weeks), mean Ha, Hm, and Hp were 81.2% ± 20.9%, 86.9% ± 17.9%, and 95.1% ± 10.1%, respectively. At 2-year follow-up, mean Ha, Hm, and Hp were 80.9% ± 19.8%, 88.1% ± 16.6%, and 91.4% ± 12.8%, respectively. There was no correlation between height increase and patient age, gender, fracture level, or fracture age.⁹

Garfin et al. reported the results of midline height restoration rates. The mean preoperative mid-vertebral height was 65% of the predicted height. Eighty-two percent had at least 10% lost height restored between pretreatment and posttreatment. The mean percent of mid-vertebral lost height restored was 32% overall and 44% among those with measurable height restoration.¹⁰

Complications

Many kyphoplasty studies have provided details on the number of cases that involved cement leakage. Tayler’s meta-analysis showed that a total of 189 (9%) cement leakages were reported in 2239 vertebrae that underwent kyphoplasty.¹³ This corresponds to 81 cement leaks per 1000 fractures undergoing kyphoplasty per year. One leak (0.001%) was reported by Majd et al.¹⁴ to be symptomatic L1 radiculopathy. A few cases also were reported as inappropriate cement injection and needle placement in the early phase.¹⁵ In our series of patients,^4,6 cement extravasation was seen in less than 10% of cases. No problems were identified clinically as a result of these extravasations, either immediately after surgery or at final follow-up. In one patient, a myocardial infarction occurred as a result of fluid overload during the procedure.

Ledlie et al. reported three complications in their series.⁹ Two weeks after kyphoplasty, a pulmonary embolism was diagnosed in a patient with a history of deep vein thrombosis (no evidence of PMMA leakage to the lungs by CT). One patient with preexisting metastatic, cardiac, vascular, severe chronic obstructive pulmonary disease required mechanical ventilation and subsequently died 5 days postoperatively. A third patient had perioperative confusion and generalized weakness that gradually resolved (negative brain CT and neurologic workup). No complications were related to the kyphoplasty technique. Minor cement extravasations were observed in 17 of 151 (11.3%) treated fractures, but none of the leaks were associated with any clinical consequence.

Garfin et al. also reported that extravasation of PMMA outside the vertebral body occurred in 21 of 214 (10%) treated levels.¹⁰ All PMMA exravasations were asymptomatic: the cement remained in the immediate area of the treated vertebrae, and no medical or surgical intervention was required to remove the extravasated PMMA.

To date, no reports of primary or secondary infection of the cement mantle have been published. In our series of over 300 patients we had no primary infections. We did, however, encounter one hematogenous infection 2 years after the kyphoplasty in a patient receiving multiple blood and platelet transfusions for Waldenstrom macroglobulinemia.

Kyphoplasty versus Vertebroplasty

Although both vertebroplasty and kyphoplasty provide excellent pain relief, kyphoplasty has the potential to improve spine biomechanics and decrease the risk of cement extravasation. PV usually will not expand the vertebral body or regain normal spine alignment. Hiwatashi et al. reported the increase in vertebral body height after vertebroplasty in preoperative MRI and postoperative CT scans to measure the vertebral heights.¹⁶ They measured the heights of 85 vertebral bodies in 37 patients before and after vertebroplasty. The results showed that the average increase in vertebral body height was 2.5 mm ventrally, 2.7 mm centrally, and 1.4 mm dorsally. However, they did not distinguish height corrections from positioning, and it is still unclear how much was corrected by the procedure itself. The significance of this methodology to measure the height between MRI and CT also is uncertain. Preliminary data indicate that kyphoplasty may restore near-normal height, preventing kyphosis that leads to respiratory and digestive problems. Restoration of height and sagittal alignment also may work to protect vulnerable vertebral levels above or below the site(s) treated by minimizing force transfer.

The vertebroplasty technique is much more prone to cement leaks, because the PMMA is injected in a liquid state and will take the path of least resistance through any cracks in surrounding bone. In administering vertebroplasty, the operator injects the liquid cement, typically pausing or stopping once a leak becomes evident. On the other hand, in kyphoplasty, the expanded balloon creates a cavity and pushes bone to the edges of the cavity, thus sealing off potential fissures and cracks. Greater placement control is possible in a kyphoplasty, in which the operator can fill the cavity with a more viscous cement to the point at which the cement bolus reaches and interdigitates with the bony margins. The initial kyphoplasty findings show lower rates of cement extravasation compared with published vertebroplasty series, supporting the hypothesis that filling with high-viscosity cement into a previously formed cavity may be an improvement over the injection of low-viscosity liquid cement into the unreduced vertebral body.

Recent Articles in the New England Journal of Medicine

In the August 9, 2009, issue of the New England Journal of Medicine, two new studies were reported.^17,18 Both were multicenter, randomized controlled trials that used a sham procedure rather than conventional conservative treatment as a control. In the study by Buchbinder et al.,¹⁷ a total of 78 patients were enrolled. Of those, 35 of 38 underwent PV, and 36 of 40 underwent a sham procedure in four Australian centers and completed the 6-month follow-up (91%). At 3 months, the mean reductions in the score for pain in the vertebroplasty and control groups were 2.6 ± 2.9 and 1.9 ± 3.3, respectively. Similar improvements were seen in both groups with respect to pain at night and at rest, physical functioning, quality of life, and perceived improvement. They concluded that there was no beneficial effect of vertebroplasty as compared with a sham procedure. In another randomized, controlled trial, the Investigational Vertebroplasty Safety and Efficacy Trial (INVEST), performed by Kallmes et al.,¹⁸ 68 patients underwent PV and 63 underwent a sham procedure. Both groups had immediate improvement in disability and pain scores after the intervention. Although there was a trend toward a higher rate of clinically meaningful improvement in pain (a 30% decrease from baseline) in the vertebroplasty group (64% vs. 48%, P = .06), the two groups did not differ significantly on any secondary outcome measure at 1 month. They also concluded that improvements in pain and pain-related disability associated with osteoporotic compression fractures in patients treated with vertebroplasty were similar to the improvements in a control group.

Although these two separate randomized controlled studies were well designed, several criticisms have arisen. Both studies initially were planned to include more patients, which would, therefore, have provided greater statistical power. Buchbinder et al.’s study originally was powered to detect a 2.5-point difference in pain between groups. They found that both groups showed small improvements and could not achieve a 2.5-point change. The study by Kallmes et al. might have shown greater improvement if the trial had been as large as planned. The question remains whether the study protocol was adequately or correctly powered to make the stated conclusions.

Moreover, the quoted “sham” procedure of analgesic injection of the periosteum is a distinct treatment that to date has not been validated. It should not be considered a “sham.” Another questionable issue is that both studies were performed by an interventional radiologist, which introduces selection and technique bias into the studies. Based on reviews of other published randomized controlled trials comparing vertebral augmentation with conservative therapy,^11,19 these surgical procedures contribute significantly to pain relief. Regardless of the shortcomings of the two New England Journal of Medicine articles, the question of the efficacy of vertebral augmentation needs further study. Ongoing randomized controlled trials will provide further information in the future.

Summary

Kyphoplasty is a modification of PV that may add a margin of safety by virtue of a lower observed incidence of cement leakage. Kyphoplasty has been shown to be worthwhile in acute vertebral fractures to predictably restore vertebral height and to facilitate a controlled fill of the vertebral body. Favorable outcomes appear to imply that kyphoplasty permits early mobilization, which has the potential to decrease mortality. Considering the greater mortality that is associated with osteoporotic compression fractures, early mobilization in these patients is of prime importance.

The next logical step beyond treatment of evident vertebral fractures is prophylactic augmentation. Prevention of osteoporotic vertebral fractures with a combination of pharmacologic approaches and timely reinforcement of at-risk osteoporotic vertebrae is the ultimate goal aside from prevention of osteoporosis itself. It is here that new osteoconductive synthetic composites will figure more prominently as an emerging alternative to cement. Advances in minimally invasive surgical techniques, imaging, and synthetic engineering are rapidly changing the treatment protocols available for osteoporotic compression fracture.