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Use of carbon fiber cages for treatment of cervical myeloradiculopathies
Spine
Use of Carbon Fiber Cages for Treatment of Cervical Myeloradiculopathies Angelo Tancredi, M.D.,* Antonino Agrillo, M.D.,† Roberto Delfini, M.D.,† Dario Fiume, M.D.,* Alessandro Frati, M.D.,† and Alessandro Rinaldi, M.D.* *Department of Neurosurgery, “San Filippo Neri” Hospital, Rome; and †Department of Neurosurgery, University of Rome “La Sapienza,” Rome, Italy
Tancredi A, Agrillo A, Delfini R, Fiume D, Frati A, Rinaldi A. Use of carbon fiber cages for treatment of cervical myeloradiculopathies. Surg Neurol 2004;61:221– 6. BACKGROUND
Different types of intersomatic fixation systems are available for use in the treatment of cervical disc pathologies. In this paper, we report our experience using carbon fiber cages (Brantigan I/F cage, De Puy Acromed, Raynham, MA; Mikai distrib.) for acute and chronic cervical disc pathologies. METHODS
Between 1997 and 2001, 97 patients underwent surgical treatment for cervical disc pathologies. Follow-up ranged from 1 to 60 months. In all cases a microdiscectomy according to Caspar was performed; anterior stabilization was performed in cases with evidence of instability and in post-traumatic disc herniations. RESULTS
A total number of 119 carbon fiber cages, ranging in height from 4 to 8 mm, were employed as well as 10 anterior plates with screws. The type of material used to fill the cages was homologous bone (50.5%), heterologous bone (22.3%), hydroxyapatite (21.1%), and autologous bone (6%). In all cases, follow-up radiograms performed after at least 6 months demonstrated bone fusion. None of the patients had either spontaneous displacement of the implant or symptoms from nerve compression. CONCLUSIONS
These preliminary results suggest that anterior cervical fusion with carbon fiber cages are valid to restore intervertebral disc height and to promote bone fusion with low complications rate. © 2004 Elsevier Inc. All rights reserved. KEY WORDS
Anterior cervical discectomy, surgery, carbon fiber cages, bone fusion.
Address reprint requests to: Antonino Agrillo, M.D., Via Salvatore Quasimodo 113, 00144 Roma, Italy Received April 17, 2003; accepted July 28, 2003. © 2004 Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010 –1710
urrently, different types of intersomatic fixation systems are available for use in the treatment of cervical disc pathologies. Their principal advantages are the restoration of the height of the intervertebral space, solid fusion with restoration of cervical lordosis, lower incidence of postoperative complications (implant mobilization) and pseudoarthrosis with respect to bone grafting: another advantage, in comparison to autografting, is that there is no need for bone harvesting from the iliac crest [5,6,12]. Carbon fiber systems were introduced at the beginning of the 1990s. As evidenced by Brantiham et al, carbon is preferable to titanium because it is radiolucent (thus, allowing an easier evaluation of bone fusion in the follow-up with X-ray films) and also does not induce any kind of bone corrosive or inflammatory reaction [4]. Carbon cages presented excellent resistance and strength properties when submitted to pullout and compression in mechanical tests as reported by the same authors [4]. However, very few clinical studies related to a limited number of cases have been published to date regarding their application for cervical pathologies [3–5]. In this paper, our experience using carbon fiber cages for acute and chronic cervical disc pathologies is reported.
C
Materials and Methods We included in this study all patients who underwent surgical treatment with anterior cervical discectomy and fusion for acute or chronic cervical disc pathologies between 1997 and 2001, in 2 different institutions. In all cases a microdiscectomy according to Cas0090-3019/04/$–see front matter doi:10.1016/j.surneu.2003.07.014
222 Surg Neurol 2004;61:221– 6
par was performed, subsequently using a drill to prepare the intervertebral space. Anterior stabilization was performed in cases with marked evidence of cervical kyphosis (with fulcrum at the level of the discopathy) and/or radiologic signs of instability. All patients were submitted to preoperative X-rays (in neutral lateral and anterior-posterior projections) and cervical spine computed tomography (CT) scan. Postoperatively, an orthopedic collar was worn for 6 to 8 weeks. Follow-up consisted of standard radiographs in 2 projections performed 1 day and 1, 3, 6 months after surgery. A 1-year follow-up evaluation was done using CT in all cases and magnetic resonance imaging (MRI) only in those cases that presented significant signal alterations of spinal cord preoperatively. Preoperative evaluation of cervical spine curvature as well as postoperative recovery or maintenance of the physiologic lordosis has been evaluated on the basis of the lateral radiographs performed preoperatively and 6 months after surgery, respectively. Cervical spine alignment was classified as lordotic (normal), hyperlordotic, straight, kyphotic on the basis of overall shape and the following simple method: On neutral lateral cervical radiographs, we drew a line between the posterior edges on the inferior endplate of C2 and C7 vertebral bodies (VBs), respectively. Lordosis was considered when the others VBs were anterior to this line. Basically, if any of the others VBs intersected this line, the spine curvature was evaluated as kyphotic. Conversely, if the posterior border of VB just touched this line without crossing it, the curvature was considered straight. The cervical spine angle (CSA) (C2-C7) formed by tangent lines to posterior edges of C2 and C7 was also measured in patients affected preoperatively by kyphosis to assess modifications in the spine curvature [7]. Initially, fusion was evaluated on the 6-month lateral radiograph, and was considered effective when this evidenced enough trabecular bone tissue to eliminate the lucencies between the cage and the plates of the vertebral bodies (at the level where discectomy was performed) [1]. Later, 1-year postoperative CT scan was performed mostly with the purpose of evaluating the intersomatic bone fusion, and thus confirming the results of the above-mentioned 6-month postoperative X-ray films. Postoperative CT was also compared to preoperative CT to assess if there was a change in the size of the intervertebral foramina.
Tancredi et al
1
Distribution of the Levels Operated (97 cases)
LEVEL C2–C3 C3–C4 C4–C5 C5–C6 C6–C7 C7–D1
NO
CASES
1 7 9 47 53 2
% 0.8% 5.9% 7.6% 39.4% 44.5% 1.7%
Results Ninety-seven patients (52 males and 45 females; median age 46.5 years) underwent surgical treatment. Clinical symptoms consisted of mono or bilateral radiculopathy in 73 patients (75.3%) and radiculopathy plus myelopathy in 24 (24.7%). An alteration of cervical lordosis in the form of straightening or kyphosis of the spine was present in 30 cases (31%). Furthermore, 20 of them were affected by kyphosis, while 10 by straightening of the cervical spine. No cases of hyperlordosis were evidenced. Thirteen patients (13%) presented a significant increased signal within the spinal cord on the preoperative T2WI. The pathology requiring surgical treatment was simple disc herniation in 38 cases (39.1%), spondylodiscarthrosis in 52 (53.6%), posttraumatic herniation in 7 (7.2%). Surgery involved only 1 level in 75 cases (77.3%), 2 levels in 22 (22.7%). The overall distribution of the levels involved showed a prevalence of the lower cervical segments (Table 1). Anterior stabilization with plates and screws was only necessary in 10 cases (10.3%), 7 posttraumatic and 3 that displayed a certain amount of preoperative displacement; among these patients, the number operated at either 1 or 2 levels was equal. Follow-up ranged from 1 to 60 months. In 91 patients (94%) follow-up has been 1 year or more. All these patients underwent a CT scan at 1 year. One (1%) patient was lost to follow-up after 2 months, the other 5 (5%) after 6 months. In all cases follow-up radiograms performed after at least 6 months demonstrated bone fusion. This was confirmed by a 1-year postoperative CT scan in all cases but the cases lost in follow-up as noted above. None of the patients had either spontaneous displacement of the implant or symptoms from nerve compression. Postoperative radiograms also confirmed that the height of the interspace did not undergo modification over time, as well as a tendency to regain physiologic lordosis of the spine in 21 of the 30 patients affected preoperatively by straightening or kyphosis, probably favored by the
Cervical Carbon Fiber Cages
Surg Neurol 223 2004;61:221– 6
(A) Preoperative MRI. (B) Same case, MRI performed 1 year after surgery. Note the absence of artifacts at the site of implantation and good restoration of cervical lordosis. (C) Sagittal and (D) axial CT images 3 years after implantation surgery on which the endoprosthetic bone bridge is well visualized.
1
224 Surg Neurol 2004;61:221– 6
2
Tancredi et al
(A) Preoperative image of the right foramen. (B) Postoperative CT image showing an increase in the height of the foramen.
wedge-shaped contour of the implant (Figure 1). Moreover, among the 20 patients affected by kyphosis, 9 did not improve their cervical spinal cord curvature significantly, while eleven presented either recovery of normal lordosis (3 cases) or significant improvement of kyphosis (8 cases). All patients (10 cases) affected preoperatively by straightening spine curvature recovered the normal lordosis. Furthermore, all patients (66 cases) with no sagittal X-ray evidence of preoperative alteration of physiologic cervical spine curvature, maintained lordosis at the 6-month postoperative
X-ray follow-up. The postoperative CT scan evidenced a bilateral increase in the height of the foramina at the levels involved by surgery in 85 patients (93.4%), while no changes were detected in 6 cases (6.6%) (Figure 2). Of the 13 patients with relevant alterations of spinal cord signal on preoperative MRI, 12 underwent a 1 year postoperative MRI that evidenced no significant changes compared to the preoperative exams (no worsening, and a mild improvement of the increased signal within the spinal cord on the preoperative T2WI).
Cervical Carbon Fiber Cages
2
Surg Neurol 225 2004;61:221– 6
Postoperative Complications
● Surgical revision Postoperative hematoma Symptomatic osteophyte ● Horner’s syndrome Total: 99 operations in 97 patients
2 1 1 1
In Table 2 the postoperative complications encountered are summarized. Only 1 case required further surgery, 1 year later, for another cervical discopathy involving an adjacent level. Lastly, 1 patient presented slight displacement of the implant because of a cervical trauma that occurred 2 months after operation; surgical revision was not necessary.
ilar measurements made on the postoperative CT images of the patients of our series and compared with preoperative data, confirmed a bilateral increase in the height of the foramina at the levels involved by surgery (Figure 2). Future radiographic control data will make it possible to check whether this postoperative correction remains unchanged in the middle- to long-term range. In fact, the enormous advantages offered by the radiotransparency of carbon fiber implants are mainly appreciable in postoperative radiologic imaging: easy assessment of the degree of fusion and the absence of artifacts on MRI, which are always visible to some degree even when MRI compatible materials such as titanium have been used (Figure 1).
Conclusions Discussion In our experience, carbon fiber implants proved to have excellent properties of stability and resistance, guaranteeing stability of the cervical spine and favoring fusion in all the cases with sufficient follow-up. The principal biomechanical properties of carbon fiber cages have been addressed in previous studies [10,11]. Considering the heterogenous nature of the endoprosthetic material employed, we believe that the results obtained in our study were largely because of the structural characteristics of the implants used. Generally speaking, “horseshoeshaped” cages allow better preservation of the height of the intervertebral space than cylindrical ones, thanks to a lower amount of subsidence, greater segmental elasticity and better long-term restoration of cervical lordosis [8,9]. The considerable initial stability of carbon fiber implants together with a certain amount of elasticity, favor complete fusion with a low rate of implant-related complications [1]. Furthermore, carbon fiber implants seem to present better osteo-integration in comparison to metallic materials. Finally, the elasticity of carbon fiber implants, almost equal to that of cortical bone, reduces the so-called phenomenon of “stress protection.” In other words, it allows distribution of the physiologic load to the bone graft inside the implant, thus stimulating bone formation and improving the quality of fusion [5,8,11,12] with less involvement of (stress) the adjacent vertebral segments. In a recent article, the effect of implantation on the size of the intervertebral foramina was measured for the first time, even in long-term [2]. Sim-
Our results suggest that this new cervical device may represent a valid option to restore intervertebral disc space and promote arthrodesis in cervical disc surgery, with a minimal complication rate. Furthermore, because of the carbon fiber radiolucency, the bone fusion can be easily visualized with standard radiograms. REFERENCES 1. Agrillo U, Mastronardi L, Puzzilli F. Anterior cervical fusion with carbon fiber cage containing coralline hydroxyapatite: preliminary observations in 45 consecutive cases of soft-disc herniation. J Neurosurg 2002;96(3 Suppl):273–6. 2. Bartels R, Donk R, Van Dijk Azn R. Height of cervical foramina after anterior discectomy and implantation of a fiber cage. J Neurosurg (Spine 1) 2001;95:40 –2. 3. Brantigan J, Cunningham B, Shono Y, Warden K, McAfee P, Steffee A. The use of carbon fiber implant in reconstructing anterior spinal column defects. Orthop Trans 1992;16:139 –40. 4. Brantigan J, Steffee A, Geiger J. A carbon fiber implant to aid interbody fusion. Mechanical testing. Spine 1991;16(S6):277–82. 5. Brooke NS, Rorke AW, King AT, Gullan RW. Preliminary experience of carbon fiber cage prostheses for treatment of cervical spine disorders. Br J Neurosurg 1997;11(3):221–7. 6. Fernyhough J, White J, La Rocca H. Fusion rates in multi-level cervical spondylosis comparing allograft fibula with autograft fibula in 126 patients. Spine 1991; 16(S):561–4. 7. Gore DR, Sepic SB, Gardner GM. Roentgenographic findings of the cervical spine in asymptomatic people. Spine 1986;6:521–4. 8. Kettler A, Wilke HJ, Claes L. Effects of neck movements on stability and subsidence in cervical interbody fusion: an in vitro study. J Neurosurg (Spine 1) 2001;94:97–107. 9. Maciejczak H, Ciach M, Radek M, Radek A, Awrej-
226 Surg Neurol 2004;61:221– 6
10. 11.
12.
13.
cewicz J. Immediate stiffness of the C5-C6 segment after discectomy with the Cloward technique: an in vitro biomechanical study on a human cadaveric model. Neurosurg 2001;49(6):1399 –408. Oleson H, Levander B, Kofoed H. Strength of implanted carbon fibers. Studies of the lumbar spine in goats. Acta Orthop Scand 1988;59:53–5. Shono Y, McAfee P, Cunningham B, Brantigan J. A biomechanical analysis of decompression and reconstruction methods in the cervical spine. Emphasis on a carbon-fiber-composite cage. J Bone Joint Surg 1993;11:1674 –84. Wilke HJ, Kettler A, Goetz C, Claes L. Subsidence resulting from simulated postoperative neck movements: an in vitro investigation with a new cervical fusion cage. Spine 2000;25:2762–70. Yamamoto I, Ikeda A, Shibuya N, Tsugane R, Sato O. Clinical long-term results of anterior discectomy without interbody fusion for cervical disc disease. Spine 1991;16(3):272–9.
COMMENTARY
Tancredi et al present the use of carbon fiber cages as an interbody support structure in the anterior cervical spine. This intriguing concept is gaining credibility with the use of either carbon cages or aryl-aromatic polymers (such as PEEK) as interbody spacers in the spine. The advantages are ob-
Tancredi et al
vious: radiolucency to assess fusion, a more compatible modulus of elasticity compared to titanium, and the ability for precision design and mass production. We are currently using PEEK polymers with either autologous bone or rh-BMP2 with an anterior plate in the cervical spine. Our early results are promising. Potential drawbacks include fracture as a standalone device (without anterior plating) or a reactive inflammatory response to carbon. Carbon debris does not seem to be problematic with the interbody space, as it is not exposed to a synovial joint. Carbon can fracture with loading, so it remains unclear as to the requirement of an additional anterior osteosynthetic support stucture, such as a plate or staple. It is clear that nonresorbable polymers such as carbon or PEEK are becoming part of our armamentarium for spinal stabilization. What remains to be determined are the exact parameters of their usage. Regis William Haid, Jr., M.D. Department of Neurosurgery Emory Clinic Atlanta, Georgia
orld War II veterans joining IBM were instructed to consult with wives because “once you came aboard you were a member of the corporate family for life.” Alternatively, in the early to mid-1990s nearly half of all big firms laid off workers. Putnam explains that these were large cuts, averaging 10 percent of each company’s workforce. GenXers watched their parents or their friends’ parents lose jobs after long commitments to organizations. Many suggest this common experience helped mold the cynicism GenXers harbor toward organizations.
W
—The Physician Executive November 䡠 December 2003
Use of Carbon Fiber Cages for Treatment of Cervical Myeloradiculopathies Angelo Tancredi, M.D.,* Antonino Agrillo, M.D.,† Roberto Delfini, M.D.,† Dario Fiume, M.D.,* Alessandro Frati, M.D.,† and Alessandro Rinaldi, M.D.* *Department of Neurosurgery, “San Filippo Neri” Hospital, Rome; and †Department of Neurosurgery, University of Rome “La Sapienza,” Rome, Italy
Tancredi A, Agrillo A, Delfini R, Fiume D, Frati A, Rinaldi A. Use of carbon fiber cages for treatment of cervical myeloradiculopathies. Surg Neurol 2004;61:221– 6. BACKGROUND
Different types of intersomatic fixation systems are available for use in the treatment of cervical disc pathologies. In this paper, we report our experience using carbon fiber cages (Brantigan I/F cage, De Puy Acromed, Raynham, MA; Mikai distrib.) for acute and chronic cervical disc pathologies. METHODS
Between 1997 and 2001, 97 patients underwent surgical treatment for cervical disc pathologies. Follow-up ranged from 1 to 60 months. In all cases a microdiscectomy according to Caspar was performed; anterior stabilization was performed in cases with evidence of instability and in post-traumatic disc herniations. RESULTS
A total number of 119 carbon fiber cages, ranging in height from 4 to 8 mm, were employed as well as 10 anterior plates with screws. The type of material used to fill the cages was homologous bone (50.5%), heterologous bone (22.3%), hydroxyapatite (21.1%), and autologous bone (6%). In all cases, follow-up radiograms performed after at least 6 months demonstrated bone fusion. None of the patients had either spontaneous displacement of the implant or symptoms from nerve compression. CONCLUSIONS
These preliminary results suggest that anterior cervical fusion with carbon fiber cages are valid to restore intervertebral disc height and to promote bone fusion with low complications rate. © 2004 Elsevier Inc. All rights reserved. KEY WORDS
Anterior cervical discectomy, surgery, carbon fiber cages, bone fusion.
Address reprint requests to: Antonino Agrillo, M.D., Via Salvatore Quasimodo 113, 00144 Roma, Italy Received April 17, 2003; accepted July 28, 2003. © 2004 Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010 –1710
urrently, different types of intersomatic fixation systems are available for use in the treatment of cervical disc pathologies. Their principal advantages are the restoration of the height of the intervertebral space, solid fusion with restoration of cervical lordosis, lower incidence of postoperative complications (implant mobilization) and pseudoarthrosis with respect to bone grafting: another advantage, in comparison to autografting, is that there is no need for bone harvesting from the iliac crest [5,6,12]. Carbon fiber systems were introduced at the beginning of the 1990s. As evidenced by Brantiham et al, carbon is preferable to titanium because it is radiolucent (thus, allowing an easier evaluation of bone fusion in the follow-up with X-ray films) and also does not induce any kind of bone corrosive or inflammatory reaction [4]. Carbon cages presented excellent resistance and strength properties when submitted to pullout and compression in mechanical tests as reported by the same authors [4]. However, very few clinical studies related to a limited number of cases have been published to date regarding their application for cervical pathologies [3–5]. In this paper, our experience using carbon fiber cages for acute and chronic cervical disc pathologies is reported.
C
Materials and Methods We included in this study all patients who underwent surgical treatment with anterior cervical discectomy and fusion for acute or chronic cervical disc pathologies between 1997 and 2001, in 2 different institutions. In all cases a microdiscectomy according to Cas0090-3019/04/$–see front matter doi:10.1016/j.surneu.2003.07.014
222 Surg Neurol 2004;61:221– 6
par was performed, subsequently using a drill to prepare the intervertebral space. Anterior stabilization was performed in cases with marked evidence of cervical kyphosis (with fulcrum at the level of the discopathy) and/or radiologic signs of instability. All patients were submitted to preoperative X-rays (in neutral lateral and anterior-posterior projections) and cervical spine computed tomography (CT) scan. Postoperatively, an orthopedic collar was worn for 6 to 8 weeks. Follow-up consisted of standard radiographs in 2 projections performed 1 day and 1, 3, 6 months after surgery. A 1-year follow-up evaluation was done using CT in all cases and magnetic resonance imaging (MRI) only in those cases that presented significant signal alterations of spinal cord preoperatively. Preoperative evaluation of cervical spine curvature as well as postoperative recovery or maintenance of the physiologic lordosis has been evaluated on the basis of the lateral radiographs performed preoperatively and 6 months after surgery, respectively. Cervical spine alignment was classified as lordotic (normal), hyperlordotic, straight, kyphotic on the basis of overall shape and the following simple method: On neutral lateral cervical radiographs, we drew a line between the posterior edges on the inferior endplate of C2 and C7 vertebral bodies (VBs), respectively. Lordosis was considered when the others VBs were anterior to this line. Basically, if any of the others VBs intersected this line, the spine curvature was evaluated as kyphotic. Conversely, if the posterior border of VB just touched this line without crossing it, the curvature was considered straight. The cervical spine angle (CSA) (C2-C7) formed by tangent lines to posterior edges of C2 and C7 was also measured in patients affected preoperatively by kyphosis to assess modifications in the spine curvature [7]. Initially, fusion was evaluated on the 6-month lateral radiograph, and was considered effective when this evidenced enough trabecular bone tissue to eliminate the lucencies between the cage and the plates of the vertebral bodies (at the level where discectomy was performed) [1]. Later, 1-year postoperative CT scan was performed mostly with the purpose of evaluating the intersomatic bone fusion, and thus confirming the results of the above-mentioned 6-month postoperative X-ray films. Postoperative CT was also compared to preoperative CT to assess if there was a change in the size of the intervertebral foramina.
Tancredi et al
1
Distribution of the Levels Operated (97 cases)
LEVEL C2–C3 C3–C4 C4–C5 C5–C6 C6–C7 C7–D1
NO
CASES
1 7 9 47 53 2
% 0.8% 5.9% 7.6% 39.4% 44.5% 1.7%
Results Ninety-seven patients (52 males and 45 females; median age 46.5 years) underwent surgical treatment. Clinical symptoms consisted of mono or bilateral radiculopathy in 73 patients (75.3%) and radiculopathy plus myelopathy in 24 (24.7%). An alteration of cervical lordosis in the form of straightening or kyphosis of the spine was present in 30 cases (31%). Furthermore, 20 of them were affected by kyphosis, while 10 by straightening of the cervical spine. No cases of hyperlordosis were evidenced. Thirteen patients (13%) presented a significant increased signal within the spinal cord on the preoperative T2WI. The pathology requiring surgical treatment was simple disc herniation in 38 cases (39.1%), spondylodiscarthrosis in 52 (53.6%), posttraumatic herniation in 7 (7.2%). Surgery involved only 1 level in 75 cases (77.3%), 2 levels in 22 (22.7%). The overall distribution of the levels involved showed a prevalence of the lower cervical segments (Table 1). Anterior stabilization with plates and screws was only necessary in 10 cases (10.3%), 7 posttraumatic and 3 that displayed a certain amount of preoperative displacement; among these patients, the number operated at either 1 or 2 levels was equal. Follow-up ranged from 1 to 60 months. In 91 patients (94%) follow-up has been 1 year or more. All these patients underwent a CT scan at 1 year. One (1%) patient was lost to follow-up after 2 months, the other 5 (5%) after 6 months. In all cases follow-up radiograms performed after at least 6 months demonstrated bone fusion. This was confirmed by a 1-year postoperative CT scan in all cases but the cases lost in follow-up as noted above. None of the patients had either spontaneous displacement of the implant or symptoms from nerve compression. Postoperative radiograms also confirmed that the height of the interspace did not undergo modification over time, as well as a tendency to regain physiologic lordosis of the spine in 21 of the 30 patients affected preoperatively by straightening or kyphosis, probably favored by the
Cervical Carbon Fiber Cages
Surg Neurol 223 2004;61:221– 6
(A) Preoperative MRI. (B) Same case, MRI performed 1 year after surgery. Note the absence of artifacts at the site of implantation and good restoration of cervical lordosis. (C) Sagittal and (D) axial CT images 3 years after implantation surgery on which the endoprosthetic bone bridge is well visualized.
1
224 Surg Neurol 2004;61:221– 6
2
Tancredi et al
(A) Preoperative image of the right foramen. (B) Postoperative CT image showing an increase in the height of the foramen.
wedge-shaped contour of the implant (Figure 1). Moreover, among the 20 patients affected by kyphosis, 9 did not improve their cervical spinal cord curvature significantly, while eleven presented either recovery of normal lordosis (3 cases) or significant improvement of kyphosis (8 cases). All patients (10 cases) affected preoperatively by straightening spine curvature recovered the normal lordosis. Furthermore, all patients (66 cases) with no sagittal X-ray evidence of preoperative alteration of physiologic cervical spine curvature, maintained lordosis at the 6-month postoperative
X-ray follow-up. The postoperative CT scan evidenced a bilateral increase in the height of the foramina at the levels involved by surgery in 85 patients (93.4%), while no changes were detected in 6 cases (6.6%) (Figure 2). Of the 13 patients with relevant alterations of spinal cord signal on preoperative MRI, 12 underwent a 1 year postoperative MRI that evidenced no significant changes compared to the preoperative exams (no worsening, and a mild improvement of the increased signal within the spinal cord on the preoperative T2WI).
Cervical Carbon Fiber Cages
2
Surg Neurol 225 2004;61:221– 6
Postoperative Complications
● Surgical revision Postoperative hematoma Symptomatic osteophyte ● Horner’s syndrome Total: 99 operations in 97 patients
2 1 1 1
In Table 2 the postoperative complications encountered are summarized. Only 1 case required further surgery, 1 year later, for another cervical discopathy involving an adjacent level. Lastly, 1 patient presented slight displacement of the implant because of a cervical trauma that occurred 2 months after operation; surgical revision was not necessary.
ilar measurements made on the postoperative CT images of the patients of our series and compared with preoperative data, confirmed a bilateral increase in the height of the foramina at the levels involved by surgery (Figure 2). Future radiographic control data will make it possible to check whether this postoperative correction remains unchanged in the middle- to long-term range. In fact, the enormous advantages offered by the radiotransparency of carbon fiber implants are mainly appreciable in postoperative radiologic imaging: easy assessment of the degree of fusion and the absence of artifacts on MRI, which are always visible to some degree even when MRI compatible materials such as titanium have been used (Figure 1).
Conclusions Discussion In our experience, carbon fiber implants proved to have excellent properties of stability and resistance, guaranteeing stability of the cervical spine and favoring fusion in all the cases with sufficient follow-up. The principal biomechanical properties of carbon fiber cages have been addressed in previous studies [10,11]. Considering the heterogenous nature of the endoprosthetic material employed, we believe that the results obtained in our study were largely because of the structural characteristics of the implants used. Generally speaking, “horseshoeshaped” cages allow better preservation of the height of the intervertebral space than cylindrical ones, thanks to a lower amount of subsidence, greater segmental elasticity and better long-term restoration of cervical lordosis [8,9]. The considerable initial stability of carbon fiber implants together with a certain amount of elasticity, favor complete fusion with a low rate of implant-related complications [1]. Furthermore, carbon fiber implants seem to present better osteo-integration in comparison to metallic materials. Finally, the elasticity of carbon fiber implants, almost equal to that of cortical bone, reduces the so-called phenomenon of “stress protection.” In other words, it allows distribution of the physiologic load to the bone graft inside the implant, thus stimulating bone formation and improving the quality of fusion [5,8,11,12] with less involvement of (stress) the adjacent vertebral segments. In a recent article, the effect of implantation on the size of the intervertebral foramina was measured for the first time, even in long-term [2]. Sim-
Our results suggest that this new cervical device may represent a valid option to restore intervertebral disc space and promote arthrodesis in cervical disc surgery, with a minimal complication rate. Furthermore, because of the carbon fiber radiolucency, the bone fusion can be easily visualized with standard radiograms. REFERENCES 1. Agrillo U, Mastronardi L, Puzzilli F. Anterior cervical fusion with carbon fiber cage containing coralline hydroxyapatite: preliminary observations in 45 consecutive cases of soft-disc herniation. J Neurosurg 2002;96(3 Suppl):273–6. 2. Bartels R, Donk R, Van Dijk Azn R. Height of cervical foramina after anterior discectomy and implantation of a fiber cage. J Neurosurg (Spine 1) 2001;95:40 –2. 3. Brantigan J, Cunningham B, Shono Y, Warden K, McAfee P, Steffee A. The use of carbon fiber implant in reconstructing anterior spinal column defects. Orthop Trans 1992;16:139 –40. 4. Brantigan J, Steffee A, Geiger J. A carbon fiber implant to aid interbody fusion. Mechanical testing. Spine 1991;16(S6):277–82. 5. Brooke NS, Rorke AW, King AT, Gullan RW. Preliminary experience of carbon fiber cage prostheses for treatment of cervical spine disorders. Br J Neurosurg 1997;11(3):221–7. 6. Fernyhough J, White J, La Rocca H. Fusion rates in multi-level cervical spondylosis comparing allograft fibula with autograft fibula in 126 patients. Spine 1991; 16(S):561–4. 7. Gore DR, Sepic SB, Gardner GM. Roentgenographic findings of the cervical spine in asymptomatic people. Spine 1986;6:521–4. 8. Kettler A, Wilke HJ, Claes L. Effects of neck movements on stability and subsidence in cervical interbody fusion: an in vitro study. J Neurosurg (Spine 1) 2001;94:97–107. 9. Maciejczak H, Ciach M, Radek M, Radek A, Awrej-
226 Surg Neurol 2004;61:221– 6
10. 11.
12.
13.
cewicz J. Immediate stiffness of the C5-C6 segment after discectomy with the Cloward technique: an in vitro biomechanical study on a human cadaveric model. Neurosurg 2001;49(6):1399 –408. Oleson H, Levander B, Kofoed H. Strength of implanted carbon fibers. Studies of the lumbar spine in goats. Acta Orthop Scand 1988;59:53–5. Shono Y, McAfee P, Cunningham B, Brantigan J. A biomechanical analysis of decompression and reconstruction methods in the cervical spine. Emphasis on a carbon-fiber-composite cage. J Bone Joint Surg 1993;11:1674 –84. Wilke HJ, Kettler A, Goetz C, Claes L. Subsidence resulting from simulated postoperative neck movements: an in vitro investigation with a new cervical fusion cage. Spine 2000;25:2762–70. Yamamoto I, Ikeda A, Shibuya N, Tsugane R, Sato O. Clinical long-term results of anterior discectomy without interbody fusion for cervical disc disease. Spine 1991;16(3):272–9.
COMMENTARY
Tancredi et al present the use of carbon fiber cages as an interbody support structure in the anterior cervical spine. This intriguing concept is gaining credibility with the use of either carbon cages or aryl-aromatic polymers (such as PEEK) as interbody spacers in the spine. The advantages are ob-
Tancredi et al
vious: radiolucency to assess fusion, a more compatible modulus of elasticity compared to titanium, and the ability for precision design and mass production. We are currently using PEEK polymers with either autologous bone or rh-BMP2 with an anterior plate in the cervical spine. Our early results are promising. Potential drawbacks include fracture as a standalone device (without anterior plating) or a reactive inflammatory response to carbon. Carbon debris does not seem to be problematic with the interbody space, as it is not exposed to a synovial joint. Carbon can fracture with loading, so it remains unclear as to the requirement of an additional anterior osteosynthetic support stucture, such as a plate or staple. It is clear that nonresorbable polymers such as carbon or PEEK are becoming part of our armamentarium for spinal stabilization. What remains to be determined are the exact parameters of their usage. Regis William Haid, Jr., M.D. Department of Neurosurgery Emory Clinic Atlanta, Georgia
orld War II veterans joining IBM were instructed to consult with wives because “once you came aboard you were a member of the corporate family for life.” Alternatively, in the early to mid-1990s nearly half of all big firms laid off workers. Putnam explains that these were large cuts, averaging 10 percent of each company’s workforce. GenXers watched their parents or their friends’ parents lose jobs after long commitments to organizations. Many suggest this common experience helped mold the cynicism GenXers harbor toward organizations.
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—The Physician Executive November 䡠 December 2003