- Email: [email protected]
Transarticular Fixation with a Bioabsorptive Screw for Cervical Spondylolisthesis
Peer-Review Short Reports
Transarticular Fixation with a Bioabsorptive Screw for Cervical Spondylolisthesis Kyongsong Kim1, Toyohiko Isu2, Tomoko Omura1, Daijiro Morimoto3, Shiro Kobayashi1, Akira Teramoto4
Key words Bioabsorptive screw - Cervical - Cervical compression myelopathy - Laminoplasty - Posterior fixation -
Abbreviations and Acronyms LMS: Lateral mass screw MRI: Magnetic resonance imaging PLLA: Poly-L-lactide TAS: Transarticular screw uHA: Uncalcined, unsintered hydroxyapatite VA: Vertebral artery From the 1Department of Neurosurgery, Chiba Hokuso Hospital, Nippon Medical School, Chiba; 2 Department of Neurosurgery, Kushiro Rosai Hospital, 3 Hokkaido; Department of Neurosurgery, Shin-Midori General Hospital, Kanagawa; and 4Department of Neurosurgery, Nippon Medical School, Tokyo, Japan To whom correspondence should be addressed: Kyongsong Kim, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2013). http://dx.doi.org/10.1016/j.wneu.2013.01.024 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2013 Elsevier Inc. All rights reserved.
- OBJECTIVE:
Patients with cervical instability and intramedullary signal intensity changes on preoperative magnetic resonance imaging scans may benefit from not only cervical decompression but also from fusion surgery. Transarticular screw (TAS) fixation is a useful technique for posterior fixation. We first report treating a patient with cervical spondylosis and instability by cervical laminoplasty with TAS fixation using a bioabsorptive screw.
- METHODS:
A 66-year-old woman who had undergone surgery for carcinoma of the tongue via the anterior approach experienced cervical myelopathy. Radiologic findings showed severe cervical canal stenosis with myelomalacia and spondylolisthesis at C4/C5 with instability.
- RESULTS:
We performed laminoplasty of C3 to C7 and TAS fixation of C4/C5 using a bioabsorptive poly-L-lactide screw that contained hydroxyapatite. Her postoperative course was uneventful, and at 1 year after treatment we confirmed C4/C5 fusion.
- CONCLUSIONS:
Our method has advantages over metal instrumentation. The treated area can be evaluated with the use of magnetic resonance imaging, and the space left after screw absorption is filled by newly formed bone. Because our screw contains hydroxyapatite, it is osteoconductive. This may increase the fusion rate and induce substitution with new bone. To our knowledge this is the first patient treated by cervical posterior TAS fixation via the use of a bioabsorptive screw. Our method is safe and economical and free of the complications elicited by the use of metal parts. TAS fixation with a bioabsorptive screw may be appropriate for one fixation in patients without severe instability.
INTRODUCTION Cervical posterior decompression is an accepted surgical treatment for cervical diseases. Segmental and kyphotic instability associated with vertebral slippage may affect surgical results (2, 20). Some patients present with cervical instability and intramedullary signal intensity changes on preoperative magnetic resonance imaging (MRI) resulting from the accumulation of minor spinal cord traumas secondary to an unstable cervical spine. To treat such patients with cervical compression myelopathy, Yagi et al. (22) recommend adding posterior fixation to cervical laminoplasty or performing anterior spinal fusion. Transarticular screw (TAS) fixation is a useful technique for posterior fixation, and the insertion of a TAS in the middle and lower cervical spine is simple and can be performed safely with the use of lateral fluoroscopic guidance (18). This method
has been used to strengthen posterior cervical spine fixation (5, 7, 11). To our knowledge, we are the first to report treating a patient with cervical spondylosis and instability by cervical laminoplasty with TAS fixation by the use of a bioabsorptive screw. CASE REPORT A 66-year-old woman who had undergone surgery for cervical anterior tongue carcinoma had a 1-year history of bilateral arm numbness, clumsiness with both hands, and gait disturbance. On admission to our hospital she manifested numbness of the limbs and clumsiness of both hands. She had difficulty walking as the result of bilateral lower-limb spasticity. Her deep tendon reflex of the limbs was increased, and she was positive for the bilateral
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Babinski reflex and lower-limb myoclonus. Standard lateral radiographs of the cervical spine revealed spondylolisthesis at C4/C5 and dynamic study showed increased slippage (Figure 1). Cervical MRI demonstrated canal stenosis at the level of C4/C5 to C6/C7, particularly at C4/C5, and intramedullary signal intensity changes on T2-weighted images at the C4/C5 level (Figure 2). On cervical magnetic resonance angiography, the bilateral vertebral artery (VA) was patent. Because the patient’s symptoms failed to improve under observation therapy we performed surgery. We planned posterior decompression from C3 to C7 and posterior fusion at the C4/C5 level because her previous history of surgery to address anterior tongue carcinoma complicated the anterior approach. She was placed in the prone position under systemic anesthesia.
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Figure 1. Preoperative radiographs of the cervical spine. Sagittal alignment is kyphosis and C4/C5 slippage is increased by flexion posture. (A) X-P,
We confirmed the cervical alignment by lateral fluoroscopy and adjusted her position to achieve maximum reduction of subluxation. After exposing the lamina of C3 to C7, we performed C4/C5 facet fixation by TAS fixation. We first curetted the articular cartilage, then drilled holes from the C4 lateral mass anterocaudally to the C4/C5 facet joint under lateral fluoroscopy, and cut a tap. We then inserted a bioabsorptive, 3.5-mm diameter uncalcined, unsintered hydroxyapatite (uHA)-poly-Llactide (PLLA) screw (SUPER-FIXSORB; Takiron Co. Ltd., Osaka, Japan; Figure 3) under lateral fluoroscopy (Figure 4). The appropriate screw length (13 mm) was determined with a depth gauge. We then performed laminectomy of C3 and laminoplasty of C4 to C7 using ceramic spacers. In and around the bilateral C4/C5 facet, we placed autologous bone chips obtained from the lamina of C3 and the spinous process of C3 to C7; we used no artificial bone material. We encountered no complications related to screw insertion such as injury to the VA or nerve root. Postoperatively, the patient’s symptoms improved but slight bilateral arm numbness persisted. She wore a cervical collar for
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lateral view, neutral posture; (B) X-P, lateral view, flexion posture; (C) X-P, lateral view, extension posture.
8 weeks. Computed tomography and MRI studies performed 24 months after surgery confirmed adequate spinal canal decompression and fusion at the C4/C5 level without the development of a screw birdcage (Figure 5). Dynamic cervical radiographic performed at that time confirmed fusion at the C4/C5 level (Figure 6). DISCUSSION Some patients with cervical compression myelopathy require posterior fixation to obtain a good treatment outcome (2, 20, 22). The use of pedicle screws provides strong fixation for posterior cervical fusion; however, their placement, especially at C3 to C6 where the pedicle diameter is small, may result in catastrophic complications such as injury to the VA, spinal cord, or nerve roots (10). Although lateral mass screw (LMS) fixation is useful for cervical posterior fusion and less demanding technically, it is expensive, screw placement is dictated by the configuration of holes in the plate, and it can result in damage to the VA, nerve root, and spinal cord (5). TAS fixation in the middle and lower cervical spine is a simple alternative method
that results in immediate cervical stabilization without rods and connectors (18). It is also economical (5), and the risk for nerve root invasion is lower with TAS than LMS (8). In comparative biomechanical studies in which authors compared TAS and LMS, TAS yielded greater (7) or similar (5, 11) stability and provided satisfactory biomechanical stability for posterior cervical spine fixation. Furthermore, facet fusion with TAS is easily combined with expansive laminoplasty, whereas the use of LMS in this setting may create problems related to the trajectory of the screws (18). Thus, TAS fixation is a useful alternative in patients with cervical compression myelopathy with focal instability. We used a bioabsorptive screw for TAS fixation. The utility of bioabsorptive products in patients undergoing cervical spine surgery and the use of bioabsorptive mesh and/or screws instead of metal instrumentation in patients treated by cervical anterior fusion has been reported (6, 13, 21). However, our search of the literature found no earlier documentation of the use of bioabsorptive screws for TAS fixation. We used uHA-PLLA screws that contain hydroxyapatite particles (30 wt%). The enduring strength of these screws during the
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.01.024
PEER-REVIEW SHORT REPORTS KYONGSONG KIM ET AL.
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Figure 2. Preoperative MRI of the cervical spine (T2-weighted images). The images show cervical canal stenosis at the C4/C5, C5/C6 and C6/C7 level and intramedullary signal intensity changes on T2WI at the C4/C5 level.
first stage facilitates fixation, and they are completely absorbed by resolution to water and carbon dioxide upon in vivo hydrolysis (15-17). The initial bend strength of our screws is 270 Mpa and greater than that of PLLA screws without hydroxyapatite or cortical bone (15). Their strength remains at
Figure 3. Photographs of uncalcined, unsintered hydroxyapatite poly-L-lactide screws.
(A) Axial view, C3/4 level; (B) axial view, C4/5 level; (C) axial view, C5/6 level; (D) axial view, C6/7 level; (E) sagittal view.
85% until the twelfth postoperative week, decreases to 75% by week 24, and to 50% by week 50 (15). The speed of this decrease is slow for our screws compared with other absorptive materials (1, 12, 13, 21), which provides for adequate strength during the
Figure 4. Illustration of the entry point and trajectory of the screw. The entry point was cranial and medial from the mid-point of the lateral mass and the trajectory was slightly lateral with a gentle slope to the spinal canal. (A) Sagittal view; (B) coronal view.
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period required for fixation. Also, different from other materials, the uHA-PLLA screws can be visualized on radiological studies and they do not elicit a strong tissue reaction due to their complete resolution (1, 9, 13, 15-17, 19, 21). In Japan, our absorptive screws can be used for the maintenance of alignment and fixation of fractures, osteotomies, arthrodeses, or bone grafts. Our method has other advantages. The surgical area can be evaluated postoperatively by MRI and after fusion, the screw is absorbed and desirable bone remodeling occurs. Facet fusion in which the screw disappears after fusion is theoretically desirable (1). Absorption of the screw creates space for new bone formation across the facet, eliminating the need for stress shielding (1). In addition, the osteoconductivity of the uHA-PLLA material may contribute to an increase in the fusion rate and to substitution by newly-formed bone (15-17).
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Figure 5. Computed tomography (CT) and magnetic resonance imaging scans of the cervical spine obtained 24 months after surgery. The cervical CT shows fusion at the C4/C5 level. Note the uHA-PLLA screw used for
On the other hand, our method has some limitations. When absorbable screws are used, complete substitution of
bone may be obstructed by connective organized tissue surrounding the resorbed screw and splinters of immature bone and
Figure 6. Radiographs of the cervical spine obtained 24 months after surgery. Dynamic cervical radiography shows C4/C5 level fusion. (A) X-P,
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posterior fusion (arrow). (A-D) CT, axial view, C4/5 level; (E) CT, sagittal view, right side; (F) CT, sagittal view, left side; (G) CT, sagittal view, midline; (H) Magnetic resonance imaging, sagittal view, midline.
resolved material may coexist during the resorption process (3, 4, 14). The osteoconductivity of uHA-PLLA can overcome
lateral view, neutral posture; (B) X-P, lateral view, flexion posture; and (C) X-P, lateral view, extension posture.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.01.024
PEER-REVIEW SHORT REPORTS KYONGSONG KIM ET AL.
these potential problems and induces bone development (15). In addition, uHA-PLLA screws do not elicit a strong tissue reaction because they are small and resolve uniformly and completely (9, 17, 19). Sevastjanova et al. (14) reported that the biomechanical conditions created by implanted material in adjacent tissues depend on its particle size and geometric shape and that changes in biomechanical properties and morphology attributable to degradation of the PLLA material are factors that may intensify foreign body reactions. Human cervical cadaveric studies revealed no significant difference in the strength or stiffness between metal screws and the stiffer 1-mm absorptive screws used to address odontoid fractures (1, 12). We used a 3.5-mm diameter screw to avoid lateral mass breakage, although with thicker screws, a strength close to that of metal screws may be obtainable. Unlike the stronger metal screws, ours may not be resistant to traumatic dislocation (15) and uHA-PLLA screws require the cutting of a tap to allow twisting off because their shearing strength is weaker. However, the inserted screws remain strong although their pull-out strength is somewhat lower than of titanium (16). We recommend the use of our screws in patients with cervical spondylosis without severe instability for example, in patients who had suffered trauma. The placement of TASs can be challenging because the occipital bone protuberance makes it difficult to achieve the proper screw trajectory (18). Facet fracture may also occur during TAS placement (23). As our absorptive screws do not provide the rod and connection system, we recommend that other fusion methods be used in cases with failed TAS insertion. Zhao et al. (23), who compared 3 previously-reported methods of TAS placement (5, 7, 18), reported that complications such as facet fracture and injury of the cervical nerve roots and VA may depend on the entry point and trajectory of the screw. To avoid these complications, they recommended the technique of Klekamp et al. (7). In this technique, the screw is inserted 1 mm medial and 1 mm inferior to the midpoint of the lateral mass at a 40 caudal and 20 lateral angle. To minimize the elicitation of complications, we recommend that the entry point of the TAS be
TA FIXATION WITH A BIOABSORPTIVE SCREW
more cranial and medial and that the trajectory be slightly lateral with a gentle slope to the spinal canal. CONCLUSIONS To our knowledge, this is the first report of a patient who underwent successful cervical posterior TAS fixation with a bioabsorptive screw. Our method is safe and economical and free of the complications elicited by metal instrumentation. TAS fixation with bioabsorptive screws may be appropriate to perform single fixations in patients without severe instability. REFERENCES 1. Ames CP, Crawford NR, Chamberlain RH, Deshmukh V, Sadikovic B, Sonntag VK: Biomechanical evaluation of a bioresorbable odontoid screw. J Neurosurg Spine 2:182-187, 2005. 2. Baba H, Furusawa N, Imura S, Kawahara N, Tsuchiya H, Tomita K: Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine 18:2167-2173, 1993. 3. Bergsma EJ, Rozema FR, Bos RR, de Bruijn WC: Foreign body reactions to resorbable poly(L-lactide) bone plates and screws used for the fixation of unstable zygomatic fractures. J Oral Maxillofac Surg 51:666-670, 1993. 4. Bostman OM: Osteoarthritis of the ankle after foreign-body reaction of absorbable pins and screws. J Bone Joint Surg Br 80:333-338, 1998. 5. DalCanto RA, Lieberman I, Inceoglu S, Kayanja M, Ferrara L: Biomechanical comparison of transarticular facet screws to lateral mass plates in two-level instrumentations of the cervical spine. Spine 30:892-897, 2005. 6. Kim K, Isu T, Sugawara A, Matsumoto R, Isobe M: Utility of new bioabsorptive screws in cervical anterior fusion. Surg Neurol 68:264-268, 2007. 7. Klekamp JW, Ugbo JL, Heller JG, Hutton WC: Cervical transfacet versus lateral mass screws: a biomechanical comparison. J Spinal Disord 13: 515-518, 2000. 8. Liu GY, Huang articular cervical 2007.
Xu RM, Ma WH, Ruan YP, Sun SH, L: Anatomic comparison of transscrews with lateral mass screws in vertebrae. Chin J Traumatol 10:67-71,
long fusion surgery. J Neurosurg Spine 11:555-561, 2009. 11. Miyanji F, Mahar A, Oka R, Newton P: Biomechanical differences between transfacet and lateral mass screw-rod constructs for multilevel posterior cervical spine stabilization. Spine 33:E865-E869, 2008. 12. Nourbakhsh A, Patil S, Vannemreddy P, Ogden A, Mukherjee D, Nanda A: The use of bioabsorbable screws to fix Type II odontoid fractures: a biomechanical study. J Neurosurg Spine 15:361-366, 2011. 13. Park MS, Aryan HE, Ozgur BM, Jandial R, Taylor WR: Stabilization of anterior cervical spine with bioabsorbable polymer in one- and two-level fusions. Neurosurgery 54:631-635, 2004. 14. Sevastjanova NA, Mansurova LA, Dombrovska LE, Slutskii LI: Biochemical characterization of connective tissue reaction to synthetic polymer implants. Biomaterials 8:242-247, 1987. 15. Shikinami Y, Okuno M: Bioresorbable devices made of forged composites of hydroxyapatite (HA) particles and poly-L-lactide (PLLA): part I. Basic characteristics. Biomaterials 20:859-877, 1999. 16. Shikinami Y, Okuno M: Bioresorbable devices made of forged composites of hydroxyapatite (HA) particles and poly L-lactide (PLLA). Part II: Practical properties of miniscrews and miniplates. Biomaterials 22:3197-3211, 2001. 17. Shikinami Y, Matsusue Y, Nakamura T: The complete process of bioresorption and bone replacement using devices made of forged composites of raw hydroxyapatite particles/poly l-lactide (F-u-HA/PLLA). Biomaterials 26:5542-5551, 2005. 18. Takayasu M, Hara M, Yamauchi K, Yoshida M, Yoshida J: Transarticular screw fixation in the middle and lower cervical spine. Technical note. J Neurosurg 99:S132-S136, 2003. 19. Tschakaloff A, Losken HW, Lalikos J: Experimental studies of DL-polylactic acid biodegradable plates and screws in rabbits: computed tomography and molecular weight loss. J Craniofac Surg 4:223-227, 1993. 20. Uchida K, Nakajima H, Sato R, Yayama T, Mwaka ES, Kobayashi S, Baba H: Cervical spondylotic myelopathy associated with kyphosis or sagittal sigmoid alignment: outcome after anterior or posterior decompression. J Neurosurg Spine 11:521-528, 2009. 21. Vaccaro AR, Carrino JA, Venger BH, Albert T, Kelleher PM, Hilibrand A, Singh K: Use of a bioabsorbable anterior cervical plate in the treatment of cervical degenerative and traumatic disc disruption. J Neurosurg 97:S473-S480, 2002.
9. Matsusue Y, Yamamuro T, Yoshii S, Oka M, Ikeda Y, Hyon S, Shikinami Y: Biodegradable screw fixation of rabbit tibia proximal osteotomies. J Appl Biomater 2:1-12, 1991.
22. Yagi M, Ninomiya K, Kihara M: Horiuchi: Longterm surgical outcome and risk factors in patients with cervical myelopathy and a change in signal intensity of intramedullary spinal cord on magnetic resonance imaging. J Neurosurg Spine 12:59-65, 2010.
10. Miyamoto H, Sumi M, Uno K: Utility of modified transarticular screw in the middle and lower cervical spine as intermediate fixation in posterior
23. Zhao L, Xu R, Liu J, Sochacki KR, Ma W, Jiang W, Liu G, Cao J, Hua Q: The study on comparison of 3 techniques for transarticular
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screw placement in the lower cervical spine. Spine 37:E468-E472, 2012.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial
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TA FIXATION WITH A BIOABSORPTIVE SCREW
or financial relationships that could be construed as a potential conflict of interest.
Journal homepage: www.WORLDNEUROSURGERY.org
Received 12 April 2012; accepted 5 January 2013
1878-8750/$ - see front matter ª 2013 Elsevier Inc. All rights reserved.
Citation: World Neurosurg. (2013). http://dx.doi.org/10.1016/j.wneu.2013.01.024
Available online: www.sciencedirect.com
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.01.024
Transarticular Fixation with a Bioabsorptive Screw for Cervical Spondylolisthesis Kyongsong Kim1, Toyohiko Isu2, Tomoko Omura1, Daijiro Morimoto3, Shiro Kobayashi1, Akira Teramoto4
Key words Bioabsorptive screw - Cervical - Cervical compression myelopathy - Laminoplasty - Posterior fixation -
Abbreviations and Acronyms LMS: Lateral mass screw MRI: Magnetic resonance imaging PLLA: Poly-L-lactide TAS: Transarticular screw uHA: Uncalcined, unsintered hydroxyapatite VA: Vertebral artery From the 1Department of Neurosurgery, Chiba Hokuso Hospital, Nippon Medical School, Chiba; 2 Department of Neurosurgery, Kushiro Rosai Hospital, 3 Hokkaido; Department of Neurosurgery, Shin-Midori General Hospital, Kanagawa; and 4Department of Neurosurgery, Nippon Medical School, Tokyo, Japan To whom correspondence should be addressed: Kyongsong Kim, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2013). http://dx.doi.org/10.1016/j.wneu.2013.01.024 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2013 Elsevier Inc. All rights reserved.
- OBJECTIVE:
Patients with cervical instability and intramedullary signal intensity changes on preoperative magnetic resonance imaging scans may benefit from not only cervical decompression but also from fusion surgery. Transarticular screw (TAS) fixation is a useful technique for posterior fixation. We first report treating a patient with cervical spondylosis and instability by cervical laminoplasty with TAS fixation using a bioabsorptive screw.
- METHODS:
A 66-year-old woman who had undergone surgery for carcinoma of the tongue via the anterior approach experienced cervical myelopathy. Radiologic findings showed severe cervical canal stenosis with myelomalacia and spondylolisthesis at C4/C5 with instability.
- RESULTS:
We performed laminoplasty of C3 to C7 and TAS fixation of C4/C5 using a bioabsorptive poly-L-lactide screw that contained hydroxyapatite. Her postoperative course was uneventful, and at 1 year after treatment we confirmed C4/C5 fusion.
- CONCLUSIONS:
Our method has advantages over metal instrumentation. The treated area can be evaluated with the use of magnetic resonance imaging, and the space left after screw absorption is filled by newly formed bone. Because our screw contains hydroxyapatite, it is osteoconductive. This may increase the fusion rate and induce substitution with new bone. To our knowledge this is the first patient treated by cervical posterior TAS fixation via the use of a bioabsorptive screw. Our method is safe and economical and free of the complications elicited by the use of metal parts. TAS fixation with a bioabsorptive screw may be appropriate for one fixation in patients without severe instability.
INTRODUCTION Cervical posterior decompression is an accepted surgical treatment for cervical diseases. Segmental and kyphotic instability associated with vertebral slippage may affect surgical results (2, 20). Some patients present with cervical instability and intramedullary signal intensity changes on preoperative magnetic resonance imaging (MRI) resulting from the accumulation of minor spinal cord traumas secondary to an unstable cervical spine. To treat such patients with cervical compression myelopathy, Yagi et al. (22) recommend adding posterior fixation to cervical laminoplasty or performing anterior spinal fusion. Transarticular screw (TAS) fixation is a useful technique for posterior fixation, and the insertion of a TAS in the middle and lower cervical spine is simple and can be performed safely with the use of lateral fluoroscopic guidance (18). This method
has been used to strengthen posterior cervical spine fixation (5, 7, 11). To our knowledge, we are the first to report treating a patient with cervical spondylosis and instability by cervical laminoplasty with TAS fixation by the use of a bioabsorptive screw. CASE REPORT A 66-year-old woman who had undergone surgery for cervical anterior tongue carcinoma had a 1-year history of bilateral arm numbness, clumsiness with both hands, and gait disturbance. On admission to our hospital she manifested numbness of the limbs and clumsiness of both hands. She had difficulty walking as the result of bilateral lower-limb spasticity. Her deep tendon reflex of the limbs was increased, and she was positive for the bilateral
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Babinski reflex and lower-limb myoclonus. Standard lateral radiographs of the cervical spine revealed spondylolisthesis at C4/C5 and dynamic study showed increased slippage (Figure 1). Cervical MRI demonstrated canal stenosis at the level of C4/C5 to C6/C7, particularly at C4/C5, and intramedullary signal intensity changes on T2-weighted images at the C4/C5 level (Figure 2). On cervical magnetic resonance angiography, the bilateral vertebral artery (VA) was patent. Because the patient’s symptoms failed to improve under observation therapy we performed surgery. We planned posterior decompression from C3 to C7 and posterior fusion at the C4/C5 level because her previous history of surgery to address anterior tongue carcinoma complicated the anterior approach. She was placed in the prone position under systemic anesthesia.
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Figure 1. Preoperative radiographs of the cervical spine. Sagittal alignment is kyphosis and C4/C5 slippage is increased by flexion posture. (A) X-P,
We confirmed the cervical alignment by lateral fluoroscopy and adjusted her position to achieve maximum reduction of subluxation. After exposing the lamina of C3 to C7, we performed C4/C5 facet fixation by TAS fixation. We first curetted the articular cartilage, then drilled holes from the C4 lateral mass anterocaudally to the C4/C5 facet joint under lateral fluoroscopy, and cut a tap. We then inserted a bioabsorptive, 3.5-mm diameter uncalcined, unsintered hydroxyapatite (uHA)-poly-Llactide (PLLA) screw (SUPER-FIXSORB; Takiron Co. Ltd., Osaka, Japan; Figure 3) under lateral fluoroscopy (Figure 4). The appropriate screw length (13 mm) was determined with a depth gauge. We then performed laminectomy of C3 and laminoplasty of C4 to C7 using ceramic spacers. In and around the bilateral C4/C5 facet, we placed autologous bone chips obtained from the lamina of C3 and the spinous process of C3 to C7; we used no artificial bone material. We encountered no complications related to screw insertion such as injury to the VA or nerve root. Postoperatively, the patient’s symptoms improved but slight bilateral arm numbness persisted. She wore a cervical collar for
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lateral view, neutral posture; (B) X-P, lateral view, flexion posture; (C) X-P, lateral view, extension posture.
8 weeks. Computed tomography and MRI studies performed 24 months after surgery confirmed adequate spinal canal decompression and fusion at the C4/C5 level without the development of a screw birdcage (Figure 5). Dynamic cervical radiographic performed at that time confirmed fusion at the C4/C5 level (Figure 6). DISCUSSION Some patients with cervical compression myelopathy require posterior fixation to obtain a good treatment outcome (2, 20, 22). The use of pedicle screws provides strong fixation for posterior cervical fusion; however, their placement, especially at C3 to C6 where the pedicle diameter is small, may result in catastrophic complications such as injury to the VA, spinal cord, or nerve roots (10). Although lateral mass screw (LMS) fixation is useful for cervical posterior fusion and less demanding technically, it is expensive, screw placement is dictated by the configuration of holes in the plate, and it can result in damage to the VA, nerve root, and spinal cord (5). TAS fixation in the middle and lower cervical spine is a simple alternative method
that results in immediate cervical stabilization without rods and connectors (18). It is also economical (5), and the risk for nerve root invasion is lower with TAS than LMS (8). In comparative biomechanical studies in which authors compared TAS and LMS, TAS yielded greater (7) or similar (5, 11) stability and provided satisfactory biomechanical stability for posterior cervical spine fixation. Furthermore, facet fusion with TAS is easily combined with expansive laminoplasty, whereas the use of LMS in this setting may create problems related to the trajectory of the screws (18). Thus, TAS fixation is a useful alternative in patients with cervical compression myelopathy with focal instability. We used a bioabsorptive screw for TAS fixation. The utility of bioabsorptive products in patients undergoing cervical spine surgery and the use of bioabsorptive mesh and/or screws instead of metal instrumentation in patients treated by cervical anterior fusion has been reported (6, 13, 21). However, our search of the literature found no earlier documentation of the use of bioabsorptive screws for TAS fixation. We used uHA-PLLA screws that contain hydroxyapatite particles (30 wt%). The enduring strength of these screws during the
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.01.024
PEER-REVIEW SHORT REPORTS KYONGSONG KIM ET AL.
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Figure 2. Preoperative MRI of the cervical spine (T2-weighted images). The images show cervical canal stenosis at the C4/C5, C5/C6 and C6/C7 level and intramedullary signal intensity changes on T2WI at the C4/C5 level.
first stage facilitates fixation, and they are completely absorbed by resolution to water and carbon dioxide upon in vivo hydrolysis (15-17). The initial bend strength of our screws is 270 Mpa and greater than that of PLLA screws without hydroxyapatite or cortical bone (15). Their strength remains at
Figure 3. Photographs of uncalcined, unsintered hydroxyapatite poly-L-lactide screws.
(A) Axial view, C3/4 level; (B) axial view, C4/5 level; (C) axial view, C5/6 level; (D) axial view, C6/7 level; (E) sagittal view.
85% until the twelfth postoperative week, decreases to 75% by week 24, and to 50% by week 50 (15). The speed of this decrease is slow for our screws compared with other absorptive materials (1, 12, 13, 21), which provides for adequate strength during the
Figure 4. Illustration of the entry point and trajectory of the screw. The entry point was cranial and medial from the mid-point of the lateral mass and the trajectory was slightly lateral with a gentle slope to the spinal canal. (A) Sagittal view; (B) coronal view.
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period required for fixation. Also, different from other materials, the uHA-PLLA screws can be visualized on radiological studies and they do not elicit a strong tissue reaction due to their complete resolution (1, 9, 13, 15-17, 19, 21). In Japan, our absorptive screws can be used for the maintenance of alignment and fixation of fractures, osteotomies, arthrodeses, or bone grafts. Our method has other advantages. The surgical area can be evaluated postoperatively by MRI and after fusion, the screw is absorbed and desirable bone remodeling occurs. Facet fusion in which the screw disappears after fusion is theoretically desirable (1). Absorption of the screw creates space for new bone formation across the facet, eliminating the need for stress shielding (1). In addition, the osteoconductivity of the uHA-PLLA material may contribute to an increase in the fusion rate and to substitution by newly-formed bone (15-17).
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Figure 5. Computed tomography (CT) and magnetic resonance imaging scans of the cervical spine obtained 24 months after surgery. The cervical CT shows fusion at the C4/C5 level. Note the uHA-PLLA screw used for
On the other hand, our method has some limitations. When absorbable screws are used, complete substitution of
bone may be obstructed by connective organized tissue surrounding the resorbed screw and splinters of immature bone and
Figure 6. Radiographs of the cervical spine obtained 24 months after surgery. Dynamic cervical radiography shows C4/C5 level fusion. (A) X-P,
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posterior fusion (arrow). (A-D) CT, axial view, C4/5 level; (E) CT, sagittal view, right side; (F) CT, sagittal view, left side; (G) CT, sagittal view, midline; (H) Magnetic resonance imaging, sagittal view, midline.
resolved material may coexist during the resorption process (3, 4, 14). The osteoconductivity of uHA-PLLA can overcome
lateral view, neutral posture; (B) X-P, lateral view, flexion posture; and (C) X-P, lateral view, extension posture.
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these potential problems and induces bone development (15). In addition, uHA-PLLA screws do not elicit a strong tissue reaction because they are small and resolve uniformly and completely (9, 17, 19). Sevastjanova et al. (14) reported that the biomechanical conditions created by implanted material in adjacent tissues depend on its particle size and geometric shape and that changes in biomechanical properties and morphology attributable to degradation of the PLLA material are factors that may intensify foreign body reactions. Human cervical cadaveric studies revealed no significant difference in the strength or stiffness between metal screws and the stiffer 1-mm absorptive screws used to address odontoid fractures (1, 12). We used a 3.5-mm diameter screw to avoid lateral mass breakage, although with thicker screws, a strength close to that of metal screws may be obtainable. Unlike the stronger metal screws, ours may not be resistant to traumatic dislocation (15) and uHA-PLLA screws require the cutting of a tap to allow twisting off because their shearing strength is weaker. However, the inserted screws remain strong although their pull-out strength is somewhat lower than of titanium (16). We recommend the use of our screws in patients with cervical spondylosis without severe instability for example, in patients who had suffered trauma. The placement of TASs can be challenging because the occipital bone protuberance makes it difficult to achieve the proper screw trajectory (18). Facet fracture may also occur during TAS placement (23). As our absorptive screws do not provide the rod and connection system, we recommend that other fusion methods be used in cases with failed TAS insertion. Zhao et al. (23), who compared 3 previously-reported methods of TAS placement (5, 7, 18), reported that complications such as facet fracture and injury of the cervical nerve roots and VA may depend on the entry point and trajectory of the screw. To avoid these complications, they recommended the technique of Klekamp et al. (7). In this technique, the screw is inserted 1 mm medial and 1 mm inferior to the midpoint of the lateral mass at a 40 caudal and 20 lateral angle. To minimize the elicitation of complications, we recommend that the entry point of the TAS be
TA FIXATION WITH A BIOABSORPTIVE SCREW
more cranial and medial and that the trajectory be slightly lateral with a gentle slope to the spinal canal. CONCLUSIONS To our knowledge, this is the first report of a patient who underwent successful cervical posterior TAS fixation with a bioabsorptive screw. Our method is safe and economical and free of the complications elicited by metal instrumentation. TAS fixation with bioabsorptive screws may be appropriate to perform single fixations in patients without severe instability. REFERENCES 1. Ames CP, Crawford NR, Chamberlain RH, Deshmukh V, Sadikovic B, Sonntag VK: Biomechanical evaluation of a bioresorbable odontoid screw. J Neurosurg Spine 2:182-187, 2005. 2. Baba H, Furusawa N, Imura S, Kawahara N, Tsuchiya H, Tomita K: Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine 18:2167-2173, 1993. 3. Bergsma EJ, Rozema FR, Bos RR, de Bruijn WC: Foreign body reactions to resorbable poly(L-lactide) bone plates and screws used for the fixation of unstable zygomatic fractures. J Oral Maxillofac Surg 51:666-670, 1993. 4. Bostman OM: Osteoarthritis of the ankle after foreign-body reaction of absorbable pins and screws. J Bone Joint Surg Br 80:333-338, 1998. 5. DalCanto RA, Lieberman I, Inceoglu S, Kayanja M, Ferrara L: Biomechanical comparison of transarticular facet screws to lateral mass plates in two-level instrumentations of the cervical spine. Spine 30:892-897, 2005. 6. Kim K, Isu T, Sugawara A, Matsumoto R, Isobe M: Utility of new bioabsorptive screws in cervical anterior fusion. Surg Neurol 68:264-268, 2007. 7. Klekamp JW, Ugbo JL, Heller JG, Hutton WC: Cervical transfacet versus lateral mass screws: a biomechanical comparison. J Spinal Disord 13: 515-518, 2000. 8. Liu GY, Huang articular cervical 2007.
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screw placement in the lower cervical spine. Spine 37:E468-E472, 2012.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial
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TA FIXATION WITH A BIOABSORPTIVE SCREW
or financial relationships that could be construed as a potential conflict of interest.
Journal homepage: www.WORLDNEUROSURGERY.org
Received 12 April 2012; accepted 5 January 2013
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Citation: World Neurosurg. (2013). http://dx.doi.org/10.1016/j.wneu.2013.01.024
Available online: www.sciencedirect.com
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.01.024