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Vertebroplasty Versus Kyphoplasty in the Cancer Setting: Rethinking the Relative Indications
Supportive Cancer Therapy
commentary Daryl R. Fourney, MD, FRCSC
Vertebroplasty Versus Kyphoplasty in the Cancer Setting: Rethinking the Relative Indications The review by Khanna et al in this issue of Supportive Cancer Therapy summarizes some of the major advances in percutaneous vertebral augmentation for patients with cancer-related spinal pain secondary to osteolysis and pathologic fracture. This complements well the review of vertebroplasty published by Wu and Forney in the January 2005 issue of this journal (Volume 2, Number 2).1
Vertebroplasty and Kyphoplasty in the Cancer Setting The minimally invasive nature of vertebroplasty and kyphoplasty is well suited to the cancer setting. Although both procedures have been shown to be safe and effective methods of achieving pain control and spinal stabilization, Khanna et al suggest there are some theoretical advantages of kyphoplasty over vertebroplasty. First, they argue that kyphoplasty can restore vertebral body height and reduce kyphosis, thereby reestablishing nearnormal biomechanical forces to the spine. It is a myth that vertebroplasty does not result in vertebral body height restoration or improvement in sagittal balance. The authors quote a clinical series I coauthored in 2003.2 Fourney et al reported that among 32 kyphoplasty procedures, the mean percentage of restored vertebral body height was 42% ± 21%. In a review of digital radiographs of 73 vertebral bodies in 53 patients before and after vertebroplasty, Teng et al reported a mean restoration percentage of 27%.3 Vertebroplasty also resulted in reduction of local kyphosis of 4.3° and wedge angle reduction of 7.4°. Similar findings have been reported by others.4-6
of dynamic fracture mobility than of the method of vertebral body augmentation used (vertebroplasty vs. kyphoplasty).7 To my knowledge, dynamic mobility of vertebral body fractures has only been reported for nonneoplastic (osteoporotic) compression fractures. In hindsight, it is regrettable that my previous work did not include an evaluation of fracture reduction after vertebroplasty but instead focused solely on height restoration and kyphosis correction after kyphoplasty.2 Whether vertebroplasty can improve spinal deformity in patients with cancer-related spinal fractures remains an interesting area for further research. Khanna et al go on to suggest that by restoring vertebral body height and reducing kyphosis, patients treated with kyphoplasty are less likely to suffer from adjacent-level vertebral body fractures because “the restoration to near-normal alignment decreases abnormal forces throughout the spine.” Adjacent-level fractures are a problem with both procedures, but they have been reported with twice the frequency after kyphoplasty (22.6% vs. 12.4% for vertebroplasty).8-10 Again, these findings were derived from experience in patients with osteoporosis rather than spinal tumors. The cause of these adjacent-level fractures is uncertain; however, it is hypothesized that the increased stiffness of the treated vertebral body may alter the distribution of forces to the nearby vertebrae, thus increasing the risk of fracture.10 The importance of adjacent-level collapse in patients with cancer-related vertebral body fractures is less clear than in patients with osteoporosis because nonosteoporotic adjacent vertebrae may be able to tolerate these altered biomechanics within the limited remaining life span of the patient.1
Restoration of Vertebral Body Height
Efficacy and Safety Profile
This phenomenon appears to be secondary to the intrinsic property of many vertebral fractures to change configuration in different body positions.6 Nussbaum et al have suggested that restoration of vertebral body height may be more a function
In their enthusiasm for this “compelling” biomechanical argument for kyphoplasty, Khanna et al go as far to say “protection of anatomic alignment and sagittal balance becomes a principal indication for kyphoplasty, and the alle-
26
Division of Neurosurgery, Royal University Hospital Saskatoon, Saskatchewan Canada
viation of pain becomes an added benefit rather than a primary indication driving intervention.” The primary indication for vertebral augmentation procedures in the setting of cancer is the alleviation of pain and thus improved quality of life. Vertebroplasty and kyphoplasty have both been shown to be efficacious in this regard.2 One has to question whether vertebral body height restoration has any relevant clinical effect. A multivariate analysis of 46 patients who underwent vertebroplasty showed no association between vertebral body height restoration and postoperative pain relief or quality of life.11 To my knowledge, no such analysis has been performed for kyphoplasty despite the suggestion of benefit by advocates of this technique. The second major advantage of kyphoplasty according to Khanna et al is its safety profile. The argument is that, because the bone cement used during vertebroplasty is of low viscosity and is injected directly into the collapsed vertebral body, the risk of cement extravasation into the spinal canal (resulting in spinal cord compression) or into the perivertebral venous plexus (resulting in pulmonary embolism) is greater; thus, kyphoplasty may involve less risk than vertebroplasty. These authors again reported results of the clinical series I coauthored to make their point: 6 of 65 (9.2%) vertebroplasty procedures were associated with cement leakage, whereas no cement extravasation was seen at the 32 levels treated with kyphoplasty.2 What is repeatedly omitted by the proponents of kyphoplasty who quote this work is that the study was not designed to compare the 2 procedures. There was no randomization to vertebroplasty or kyphoplasty; in fact, selection criteria for the 2 procedures differed. All 6 cases of cement leakage in that series were entirely asymptomatic. Indeed, the vast majority of cases of cement extravasation reported throughout the literature are asymptomatic,7 and the rate by which they are reported depends largely on the vigilance of
Volume 3, Number 1 • October 2005
the person interpreting the postoperative radiographs and whether computed tomography is used to evaluate the presence of leakage.12 Early vertebroplasty series reported leakage rates as high as 73% for patients with osteolytic metastasis or myeloma evaluated by postoperative computed tomography. However, vertebroplasty has undergone several refinements during the past 10 years. Most current practitioners allow the cement to polymerize slightly (until it is roughly the consistency of toothpaste) before injection. In the past, large injection volumes (up to 10 mL) probably contributed to cement leakage. Biomechanical studies have shown that vertebral strength can be restored to regions where as little as 2 mL of cement is injected.13 By reducing the injection volume, one can not only lower the risk of cement extravasation but also the theoretical risk of adjacent vertebral body collapse.14 High-pressure injection during vertebroplasty is another issue. Baroud et al have shown that most of the pressure required for cement delivery is derived from the force needed to move the cement along the long, thin vertebroplasty cannula and not from within the highly porous cancellous bone.15 In a previous issue of Supportive Cancer Therapy, Baroud described a redesigned cannula for vertebroplasty injection that reduces injection pressure by approximately 44% in ex vivo cadaveric testing.16 Kyphoplasty has a number of disadvantages compared with vertebroplasty.1,2,7 Kyphoplasty is a more complex and invasive procedure. Whereas most vertebroplasty cases are performed under local anesthesia, kyphoplasty is almost always performed under general anesthesia. Patients with painful vertebral body collapse secondary to metastatic cancer or myeloma bone disease often have significant medical comorbidities and are at increased risk for general anesthesia.
Procedural times are longer for kyphoplasty, and prolonged prone positioning increases the chance of rib fractures.7 Whereas vertebroplasty can be accomplished with a unilateral transpedicular injection in approximately two thirds of cases,2 kyphoplasty is almost routinely performed bilaterally. Whereas most patients who undergo vertebroplasty are discharged the same day, kyphoplasty patients are often admitted for overnight observation.7 Vertebroplasty is usually performed with a relative thin diameter (11- or 13gauge) bone needle; however, the diameter of the kyphoplasty working cannula (4.2 mm) is not much smaller than the diameter of a typical thoracic spine pedicle screw (5-6 mm). Nussbaum et al suggested a possible association between the diameter of the working cannula and an increased risk of pedicle fractures and spinal cord compression with kyphoplasty. The specialized equipment necessary for kyphoplasty (inflatable bone tamp), additional hospital and physician costs for performing a longer procedure, anesthesia, and an overnight hospital stay all result in increased costs. Vertebroplasty is estimated to be roughly US $6000 less expensive than kyphoplasty per treated level.17
Conclusion There are still relatively few clinical series that report on kyphoplasty in the setting of cancer compared with vertebroplasty.1 Although I certainly agree with Khanna et al, that both treatments have been shown to be safe and effective, the precise indications for vertebroplasty versus kyphoplasty remain to be defined. Each technique has potential advantages and disadvantages. Discussion of these issues is fairly controversial. Given the additional cost and complexity of kyphoplasty, a methodologically sound randomized trial comparing this treatment with vertebroplasty is necessary to determine whether there is any relevant clinical advantage.
27
References 1. Fourney DR, Wu AS. Supportive care aspects of vertebroplasty in patients with cancer. Support Cancer Ther 2005; 2:98-104. 2. Fourney DR, Schomer DF, Nader R, et al. Percutaneous vertebroplasty and kyphoplasty for painful vertebral body fractures in cancer patients. J Neurosurg (Spine 1) 2003; 98:21-30. 3. Teng MM, Wei CJ, Wei LC, et al. Kyphosis correction and height restoration effects of percutaneous vertebroplasty. AJNR Am J Neuroradiol 2003; 24:1893-1900. 4. Hiwatashi A, Moritani T, Numaguchi Y, et al. Increase in vertebral body height after vertebroplasty. AJNR Am J Neuroradiol 2003; 24:185-189. 5. Lee ST, Chen JF. Closed reduction vertebroplasty for the treatment of osteoporotic vertebral compression fractures. Technical note. J Neurosurg (Spine 4) 2004; 100:392-396. 6. McKiernan F, Jensen R, Faciszewski T. The dynamic mobility of vertebral compression fractures. J Bone Miner Res 2003; 18:24-29. 7. Nussbaum DA, Gailloud P, Murphy K. A review of complications associated with vertebroplasty and kyphoplasty as reported to the Food and Drug Administration medical device related Web site. J Vasc Interv Radiol 2004; 15:1185-1192. 8. Fribourg D, Tang C, Sra P, et al. Incidence of subsequent vertebral fracture after kyphoplasty. Spine 2004; 29:2270-2276. 9. Harrop JS, Prpa MK, Reinhardt MK, et al. Primary and secondary osteoporosis’ incidence of subsequent vertebral compression fractures after kyphoplasty. Spine 2004; 29:2120-2125. 10. Uppin AA, Hirsch JA, Centenera LV, et al. Occurrence of new vertebral body fracture after percutaneous vertebroplasty in patients with osteoporosis. Radiology 2003; 226:119-124. 11. McKiernan F, Faciszewski T, Jensen R. Does vertebral height restoration achieved at vertebroplasty matter? J Vasc Interv Radiol 2005; 16:973-979. 12. Cotton A, Dewatr F, Cortet B, et al. Percutaneous vertebroplasty for osteolytic metastases and myeloma: effects of percentage of lesion filling and the leakage of methyl methacrylate at clinical follow-up. Radiology 1996; 200: 525-530. 13. Belkoff SM, Mathis JM, Jasper LE, et al. The biomechanics of vertebroplasty. The effect of cement volume on mechanical behavior. Spine 2001; 26:1537-1541. 14. Baroud G, Heini P, Nemes J, et al. Biomechanical explanation of adjacent fractures following vertebroplasty. Radiology 2003; 229:606-607. 15. Baroud G, Bohner M, Heini P, et al. Injection biomechanics of bone cements used in vertebroplasty. Biomed Mater Eng 2004; 14:487-504. 16. Baroud G. A brief update on the biomechanisms underlying cement injection and leakage in vertebroplasty. Support Cancer Ther 2005; 2:105-108. 17. Health Research Institute. US markets for adjunctive and nonfusion spine technologies. Medtech Insights 2003; Report #103-1-US-0103.
commentary Daryl R. Fourney, MD, FRCSC
Vertebroplasty Versus Kyphoplasty in the Cancer Setting: Rethinking the Relative Indications The review by Khanna et al in this issue of Supportive Cancer Therapy summarizes some of the major advances in percutaneous vertebral augmentation for patients with cancer-related spinal pain secondary to osteolysis and pathologic fracture. This complements well the review of vertebroplasty published by Wu and Forney in the January 2005 issue of this journal (Volume 2, Number 2).1
Vertebroplasty and Kyphoplasty in the Cancer Setting The minimally invasive nature of vertebroplasty and kyphoplasty is well suited to the cancer setting. Although both procedures have been shown to be safe and effective methods of achieving pain control and spinal stabilization, Khanna et al suggest there are some theoretical advantages of kyphoplasty over vertebroplasty. First, they argue that kyphoplasty can restore vertebral body height and reduce kyphosis, thereby reestablishing nearnormal biomechanical forces to the spine. It is a myth that vertebroplasty does not result in vertebral body height restoration or improvement in sagittal balance. The authors quote a clinical series I coauthored in 2003.2 Fourney et al reported that among 32 kyphoplasty procedures, the mean percentage of restored vertebral body height was 42% ± 21%. In a review of digital radiographs of 73 vertebral bodies in 53 patients before and after vertebroplasty, Teng et al reported a mean restoration percentage of 27%.3 Vertebroplasty also resulted in reduction of local kyphosis of 4.3° and wedge angle reduction of 7.4°. Similar findings have been reported by others.4-6
of dynamic fracture mobility than of the method of vertebral body augmentation used (vertebroplasty vs. kyphoplasty).7 To my knowledge, dynamic mobility of vertebral body fractures has only been reported for nonneoplastic (osteoporotic) compression fractures. In hindsight, it is regrettable that my previous work did not include an evaluation of fracture reduction after vertebroplasty but instead focused solely on height restoration and kyphosis correction after kyphoplasty.2 Whether vertebroplasty can improve spinal deformity in patients with cancer-related spinal fractures remains an interesting area for further research. Khanna et al go on to suggest that by restoring vertebral body height and reducing kyphosis, patients treated with kyphoplasty are less likely to suffer from adjacent-level vertebral body fractures because “the restoration to near-normal alignment decreases abnormal forces throughout the spine.” Adjacent-level fractures are a problem with both procedures, but they have been reported with twice the frequency after kyphoplasty (22.6% vs. 12.4% for vertebroplasty).8-10 Again, these findings were derived from experience in patients with osteoporosis rather than spinal tumors. The cause of these adjacent-level fractures is uncertain; however, it is hypothesized that the increased stiffness of the treated vertebral body may alter the distribution of forces to the nearby vertebrae, thus increasing the risk of fracture.10 The importance of adjacent-level collapse in patients with cancer-related vertebral body fractures is less clear than in patients with osteoporosis because nonosteoporotic adjacent vertebrae may be able to tolerate these altered biomechanics within the limited remaining life span of the patient.1
Restoration of Vertebral Body Height
Efficacy and Safety Profile
This phenomenon appears to be secondary to the intrinsic property of many vertebral fractures to change configuration in different body positions.6 Nussbaum et al have suggested that restoration of vertebral body height may be more a function
In their enthusiasm for this “compelling” biomechanical argument for kyphoplasty, Khanna et al go as far to say “protection of anatomic alignment and sagittal balance becomes a principal indication for kyphoplasty, and the alle-
26
Division of Neurosurgery, Royal University Hospital Saskatoon, Saskatchewan Canada
viation of pain becomes an added benefit rather than a primary indication driving intervention.” The primary indication for vertebral augmentation procedures in the setting of cancer is the alleviation of pain and thus improved quality of life. Vertebroplasty and kyphoplasty have both been shown to be efficacious in this regard.2 One has to question whether vertebral body height restoration has any relevant clinical effect. A multivariate analysis of 46 patients who underwent vertebroplasty showed no association between vertebral body height restoration and postoperative pain relief or quality of life.11 To my knowledge, no such analysis has been performed for kyphoplasty despite the suggestion of benefit by advocates of this technique. The second major advantage of kyphoplasty according to Khanna et al is its safety profile. The argument is that, because the bone cement used during vertebroplasty is of low viscosity and is injected directly into the collapsed vertebral body, the risk of cement extravasation into the spinal canal (resulting in spinal cord compression) or into the perivertebral venous plexus (resulting in pulmonary embolism) is greater; thus, kyphoplasty may involve less risk than vertebroplasty. These authors again reported results of the clinical series I coauthored to make their point: 6 of 65 (9.2%) vertebroplasty procedures were associated with cement leakage, whereas no cement extravasation was seen at the 32 levels treated with kyphoplasty.2 What is repeatedly omitted by the proponents of kyphoplasty who quote this work is that the study was not designed to compare the 2 procedures. There was no randomization to vertebroplasty or kyphoplasty; in fact, selection criteria for the 2 procedures differed. All 6 cases of cement leakage in that series were entirely asymptomatic. Indeed, the vast majority of cases of cement extravasation reported throughout the literature are asymptomatic,7 and the rate by which they are reported depends largely on the vigilance of
Volume 3, Number 1 • October 2005
the person interpreting the postoperative radiographs and whether computed tomography is used to evaluate the presence of leakage.12 Early vertebroplasty series reported leakage rates as high as 73% for patients with osteolytic metastasis or myeloma evaluated by postoperative computed tomography. However, vertebroplasty has undergone several refinements during the past 10 years. Most current practitioners allow the cement to polymerize slightly (until it is roughly the consistency of toothpaste) before injection. In the past, large injection volumes (up to 10 mL) probably contributed to cement leakage. Biomechanical studies have shown that vertebral strength can be restored to regions where as little as 2 mL of cement is injected.13 By reducing the injection volume, one can not only lower the risk of cement extravasation but also the theoretical risk of adjacent vertebral body collapse.14 High-pressure injection during vertebroplasty is another issue. Baroud et al have shown that most of the pressure required for cement delivery is derived from the force needed to move the cement along the long, thin vertebroplasty cannula and not from within the highly porous cancellous bone.15 In a previous issue of Supportive Cancer Therapy, Baroud described a redesigned cannula for vertebroplasty injection that reduces injection pressure by approximately 44% in ex vivo cadaveric testing.16 Kyphoplasty has a number of disadvantages compared with vertebroplasty.1,2,7 Kyphoplasty is a more complex and invasive procedure. Whereas most vertebroplasty cases are performed under local anesthesia, kyphoplasty is almost always performed under general anesthesia. Patients with painful vertebral body collapse secondary to metastatic cancer or myeloma bone disease often have significant medical comorbidities and are at increased risk for general anesthesia.
Procedural times are longer for kyphoplasty, and prolonged prone positioning increases the chance of rib fractures.7 Whereas vertebroplasty can be accomplished with a unilateral transpedicular injection in approximately two thirds of cases,2 kyphoplasty is almost routinely performed bilaterally. Whereas most patients who undergo vertebroplasty are discharged the same day, kyphoplasty patients are often admitted for overnight observation.7 Vertebroplasty is usually performed with a relative thin diameter (11- or 13gauge) bone needle; however, the diameter of the kyphoplasty working cannula (4.2 mm) is not much smaller than the diameter of a typical thoracic spine pedicle screw (5-6 mm). Nussbaum et al suggested a possible association between the diameter of the working cannula and an increased risk of pedicle fractures and spinal cord compression with kyphoplasty. The specialized equipment necessary for kyphoplasty (inflatable bone tamp), additional hospital and physician costs for performing a longer procedure, anesthesia, and an overnight hospital stay all result in increased costs. Vertebroplasty is estimated to be roughly US $6000 less expensive than kyphoplasty per treated level.17
Conclusion There are still relatively few clinical series that report on kyphoplasty in the setting of cancer compared with vertebroplasty.1 Although I certainly agree with Khanna et al, that both treatments have been shown to be safe and effective, the precise indications for vertebroplasty versus kyphoplasty remain to be defined. Each technique has potential advantages and disadvantages. Discussion of these issues is fairly controversial. Given the additional cost and complexity of kyphoplasty, a methodologically sound randomized trial comparing this treatment with vertebroplasty is necessary to determine whether there is any relevant clinical advantage.
27
References 1. Fourney DR, Wu AS. Supportive care aspects of vertebroplasty in patients with cancer. Support Cancer Ther 2005; 2:98-104. 2. Fourney DR, Schomer DF, Nader R, et al. Percutaneous vertebroplasty and kyphoplasty for painful vertebral body fractures in cancer patients. J Neurosurg (Spine 1) 2003; 98:21-30. 3. Teng MM, Wei CJ, Wei LC, et al. Kyphosis correction and height restoration effects of percutaneous vertebroplasty. AJNR Am J Neuroradiol 2003; 24:1893-1900. 4. Hiwatashi A, Moritani T, Numaguchi Y, et al. Increase in vertebral body height after vertebroplasty. AJNR Am J Neuroradiol 2003; 24:185-189. 5. Lee ST, Chen JF. Closed reduction vertebroplasty for the treatment of osteoporotic vertebral compression fractures. Technical note. J Neurosurg (Spine 4) 2004; 100:392-396. 6. McKiernan F, Jensen R, Faciszewski T. The dynamic mobility of vertebral compression fractures. J Bone Miner Res 2003; 18:24-29. 7. Nussbaum DA, Gailloud P, Murphy K. A review of complications associated with vertebroplasty and kyphoplasty as reported to the Food and Drug Administration medical device related Web site. J Vasc Interv Radiol 2004; 15:1185-1192. 8. Fribourg D, Tang C, Sra P, et al. Incidence of subsequent vertebral fracture after kyphoplasty. Spine 2004; 29:2270-2276. 9. Harrop JS, Prpa MK, Reinhardt MK, et al. Primary and secondary osteoporosis’ incidence of subsequent vertebral compression fractures after kyphoplasty. Spine 2004; 29:2120-2125. 10. Uppin AA, Hirsch JA, Centenera LV, et al. Occurrence of new vertebral body fracture after percutaneous vertebroplasty in patients with osteoporosis. Radiology 2003; 226:119-124. 11. McKiernan F, Faciszewski T, Jensen R. Does vertebral height restoration achieved at vertebroplasty matter? J Vasc Interv Radiol 2005; 16:973-979. 12. Cotton A, Dewatr F, Cortet B, et al. Percutaneous vertebroplasty for osteolytic metastases and myeloma: effects of percentage of lesion filling and the leakage of methyl methacrylate at clinical follow-up. Radiology 1996; 200: 525-530. 13. Belkoff SM, Mathis JM, Jasper LE, et al. The biomechanics of vertebroplasty. The effect of cement volume on mechanical behavior. Spine 2001; 26:1537-1541. 14. Baroud G, Heini P, Nemes J, et al. Biomechanical explanation of adjacent fractures following vertebroplasty. Radiology 2003; 229:606-607. 15. Baroud G, Bohner M, Heini P, et al. Injection biomechanics of bone cements used in vertebroplasty. Biomed Mater Eng 2004; 14:487-504. 16. Baroud G. A brief update on the biomechanisms underlying cement injection and leakage in vertebroplasty. Support Cancer Ther 2005; 2:105-108. 17. Health Research Institute. US markets for adjunctive and nonfusion spine technologies. Medtech Insights 2003; Report #103-1-US-0103.