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Reduction of epidural fibrosis and dural adhesions after lamina reconstruction by absorbable cement: an experimental study
The Spine Journal 14 (2014) 113–118
Basic Science
Reduction of epidural fibrosis and dural adhesions after lamina reconstruction by absorbable cement: an experimental study Mehdi Zeinalizadeh, MDa,b,*, Seyed Mojtaba Miri, MDa,b, Farid Azmoodeh Ardalan, MDc, Farid Maleki, MDb, Marjan Zakeri, MDb, Elham Aghajanzadeh, MDb, Zohreh Habibi, MDa,b a
Department of Neurosurgery, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran 1419733141, Iran b Brain and Spinal Cord Injuries Repair Research Center, Imam Khomeini Hospital, Tehran 1419733141, Iran c Department of Pathology, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran 1419733141, Iran Received 28 April 2013; accepted 24 June 2013
Abstract
BACKGROUND CONTEXT: Post-laminectomy epidural fibrosis complicates revision spine surgery and is implicated in cases of ‘‘failed back syndrome.’’ Several materials have been used to minimize epidural fibrosis with varying results. PURPOSE: The aim of this study was to examine the impact of reconstruction of laminectomy site with a type of absorbable cement (Jectos) to reduce epidural fibrosis. STUDY DESIGN: This investigation is an experimental controlled study, which is designed to evaluate the preventive effects of laminectomy site reconstruction in rat laminectomy model. METHODS: Twenty wistar rats were included in this study and divided randomly to two equal groups, namely, subject and control. In both groups, laminectomy was performed in L2 and L4 levels. Control group received no additional treatment. In the subject group, L4 levels were reconstructed by Jectos and L2 levels were non-reconstructed as internal controls. Six months after surgery the rats were sacrificed and the dural adhesion and epidural fibrosis were evaluated macroscopically and microscopically. The study was financially supported by Brain and Spinal Cord Injuries Repair Center. None of the authors have any conflict of interest. RESULTS: Non-reconstructed levels in both groups showed dense epidural fibrosis with marked dural adherence. L4 reconstructed levels in subject group showed reduced epidural fibrosis macroscopically (p5.024) and microscopically (p5.041). No foreign body reaction or ossification occurred at reconstructed sites. CONCLUSIONS: In the present study, lamina reconstruction with absorbable cement was a safe method that significantly reduced post-laminectomy epidural fibrosis and dural adhesions in rat laminectomy model. Ó 2014 Elsevier Inc. All rights reserved.
Keywords:
Epidural fibrosis; Dural adhesion; Laminectomy; Revision spine surgery; Lamina reconstruction
Introduction Postoperative epidural fibrosis, the development of a dense scar tissue adjacent to the dura matter after surgical laminectomy, is a natural process of healing [1–3]. Cells
FDA device/drug status: Not approved for this indication (Jectos: Dicalcium phosphate 55% and Tricalcium phosphate 45%, Kasios, Germany). Author disclosures: MZe: Nothing to disclose. SMM: Nothing to disclose. FAA: Nothing to disclose. FM: Nothing to disclose. MZa: Nothing to disclose. EA: Nothing to disclose. ZH: Nothing to disclose. * Corresponding author. Department of Neurosurgery, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran 1419733141, Iran. Tel.: (98) 216-119-2634-5; fax: (98) 216-659-1320. E-mail address: [email protected] (M. Zeinalizadeh) 1529-9430/$ - see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.06.065
that generate fibrosis are fibroblasts that come from the adjacent paraspinal musculature. This physiologic scar may become a hypertrophic enveloping film, creating the socalled post-laminectomy membrane described by LaRocca and Macnob [4] in 1974. This extradural fibrotic tissue may extend into the vertebral canal and adhere to the dura matter and nerve roots, causing recurrent symptoms including radicular pain [5–10]. Furthermore, epidural fibrosis makes the next exploration of the operative field technically challenging because of increase in the risk of nerve root damage, dural tears, and iatrogenic injuries [8,11–13]. The prevention of scar formation is one of the main concerns in spine surgery that has been the subject of research for many years. A variety of biological, pharmacological, and synthetic materials have been investigated
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to prevent scar formation after laminectomy. Silastic, ADCON-L, Gore-Tex membrane, Dacron, Vicril mesh, Zenoderm, methacrylate, polyethylene oxide, biodegradable polymers, bioelastic polymers, fat grafts, sodium hyaluronate, steroids, mitomycin C, pimecrolimus, recombinant plasminogen activator, and anti-inflammatory medications have been used with inconsistent results [1,2,4,8,14–25]. The use of a physical barrier to protect tissue surfaces as they heal has been shown to be one of the most effective methods of reducing adhesions in animal models of spine surgery [26]. Even if, the human trials are still a long way off. The present study was designed to evaluate the impact of laminectomy site reconstruction with absorbable cement in rat laminectomy model to observe whether it can reduce epidural fibrosis.
Materials and methods This study was conducted in the animal Lab of Brain and Spinal cord Injuries Repair Center between 2011 and 2012. Twenty male wistar rats weighing 300 to 350 g were randomly assigned into two equal cohorts, namely, subject and control. Laminectomy was performed in L2 and L4 levels of both groups. Control animals received no additional treatment, whereas lamina reconstruction was done in L4 levels of subject rats. In the later group, L2 levels were non-reconstructed to act as internal controls. Accordingly, 10 levels received the treatment and 30 levels were in the control arm including L2 and L4 levels in control group and L2 levels in subject group. Absorbable cement The material used for lamina reconstruction was a type of absorbable cement (Jectos: Dicalcium phosphate 55% and Tricalcium phosphate 45%, Kasios, Germany). The cement is obtained by blending a liquid and a solid (powder) phase for 1 minute, followed by a few minutes leaving the mixture in room temperature for further thickening to have an easily shaped injectable paste.
the absorbable cement (Jectos) without compression on dura matter. The wound was closed in layers with interrupted 3-0 nylon sutures. Postoperative evaluation After the recovery period, the animals were evaluated for medical condition and neurologic status. All rats were then allowed cage activity for 6 months. On the 180th postoperative day, the animals were sacrificed by intracardiac perfusion of paraformaldehyde 4% under general anesthesia. All laminectomy sites were grossly evaluated using loupe magnification by a single neurosurgeon. For gross evaluation of epidural adhesions, the scoring system stated in Table 1 was used. This system ranks from 1 to 3 based on the surgeon’s observation to assess how paraspinal muscles were separated from dura matter during dissection; ‘‘the more difficult dissection, the higher grade of adhesion’’ (Table 1). After gross evaluation, blocks of tissue containing dura, epidural tissue, and surrounding soft tissues were obtained and kept in paraformaldehyde 4% solution for histologic assessment. The cement was removed from the dura and surrounding tissues during exposure and tissue handling to keep the pathologist completely blinded about the cohorts. Histologic examination Samples containing bone cement were decalcified in ethylenediaminetetraacetic acid solution to have the pathologist be blinded about the samples. All specimens were embedded in paraffin, sectioned by microtome apparatus, and stained with Masson trichrome and Hematoxylin and Eosin. These two staining methods were used for grading of fibrosis density and extension, respectively. Sections were examined using an Olympus microscope by a single pathologist in two different ways: 1. Evaluating the density of fibrosis using an observational scaling method (mild, moderate, and severe) based on the intensity of Masson trichrome staining (Fig. 1). The more prominent staining, the more density and compactness of fibrosis (Fig. 1). 2. Evaluating the extension of fibrosis to surrounding tissues, namely, epidural fat (Score 1), muscle (Score
Surgical procedure The procedure was performed under general anesthesia obtained by intraperitoneal injection of ketamine (35 mg/ kg) and Xylozine (5 mg/kg). Preoperative intraperitoneal cefazolin sodium (75 mg/kg) was administered for infection prophylaxis. Skin and fascia were incised in midline at lumbar region under loupe magnification. After separation of paraspinal muscles and resection of spinous process, rectangular 52 mm laminectomy defects were created at L2 and L4, leaving the dura clean and fully exposed. After hemostasis via gentle compression of cotton, L4 laminectomy defects in treatment group were reconstructed by
Table 1 Scoring system for detailed macroscopic evaluation of epidural adhesions Score
Description
1
Absence of adhesion between paraspinal muscles and dura matter, with near normal separation plane of tissues Mild-to-moderate adhesion, and separation of epidural fibrosis from dura matter was easy by a dissector Severe adhesion, and separation of epidural fibrosis from dura matter was hard or impossible by a dissector
2 3
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Fig. 1. Photomicrograph of laminectomy sites showing mild (Left), moderate (Middle), and severe (Right) epidural fibrosis. Masson trichrome, original magnification 40.
2), and neural tissue (Score 3) via Hematoxylin and Eosin staining (Fig. 2). Again, this scoring system was observational based on the pathologist’s surveillances. The involvement of epidural fat only was the mildest degree, whereas taking the epidural fat plus strait muscle was ranked as Score 2. Extension of fibrosis to neural elements was considered as maximal intensity. For each level, the sum of both microscopic scores was used for final statistical analysis. Statistical analysis The scores of fibrosis density and extension were compared between the control and treatment sites using chisquare, Mann-Whitney, Spearman, and Wilcoxon signed rank tests. All statistical analyses were performed using SPSS software version 18 (SPSS Inc., Chicago, IL, USA), and p value less than .05 was considered statistically significant. The study was financially supported by Brain and Spinal cord Injuries Repair Center. None of the authors have any conflict of interest. In this study, all interventions and gross evaluations were performed under loupe magnification by a single author (MZ), and all microscopic specimens were evaluated by a single pathologist (FAA) in blinded manner. The study was approved by the institutional medical research ethics committee.
Results In treatment group, one rat died before completing follow-up period for unknown reason and one was excluded
because of developing infection at Operation Site 3 weeks after surgery. The results of macroscopic severity and microscopic density of epidural fibrosis of operated segments in case and control groups are tabularized in Table 2. Macroscopic and microscopic evaluation of L2 and L4 levels in control group compared with L2 levels in subject group (internal control ) revealed no statistically significant difference. Even so, both density and extension of microscopic epidural fibrosis in L4 levels of subject group (treated levels) were found to be significantly lower than control levels (p5.041). In macroscopic observations, the scar tissue in treated levels was less than controls too (p5.024). There was not any linear relation between microscopic and macroscopic differences in treatment group, however (p5.074). No case in treatment group developed foreign body ossification around the cement, although some granulomatous reactions were seen. Microscopic findings of chronic inflammation were remarkable in all sections taken from both groups.
Discussion Postoperative epidural fibrosis The formation of dense and thick epidural scar tissue after lumbar laminectomy and discectomy may contribute to unfavorable clinical outcomes and recurring symptoms such as radicular and/or low back pain [19,20,27–29]. Epidural fibrosis is often initiated by injury to the epidural space after surgical procedures [20]. A pain-free interval of shorter than 12 months after previous discectomy with slow onset of complaints is characteristic of epidural fibrosis, with the tethered nerve roots being the major underlying cause of symptoms [2,15,20,30,31]. The tethering
Fig. 2. Photomicrograph of laminectomy sites showing the extension of fibrosis to epidural fat tissue (arrow, Left), striated muscles (arrowheads, Middle), and nerve bundles (asterisk, Right). Hematoxylin and Eosin, original magnification 40.
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Table 2 The severity of macroscopic and microscopic post-laminectomy epidural fibrosis in case and control groups Group
Control
Case
L2
L4
L2
L4
Fibrosis severity/density
Mac severity
Mic density
Mac severity
Mic density
Mac severity
Mic density
Mac severity
Mic density
1/Mild 2/Moderate 3/Severe Total
0 3 7 10
0 3 7 10
0 3 7 10
1 5 4 10
0 3 5 8
0 3 5 8
6 0 2 8
3 3 2 8
Mac, macroscopic; Mic, microscopic.
may impede nerve mobility and increase tension on the nerve during motion, leading to nerve injury [2]. Although extensive epidural scar adhesions can be removed and the tethered nerve roots can be released through reexploration, adhesions tend to recur after the second surgery and the patient’s symptoms may become even worse than before [32–35]. Fibroblasts originating from the overlying muscles and the extension of postoperative hematoma into the vertebral canal can produce epidural fibrosis [8,17,23]. The migration of fibroblasts from the surface of erector spinae musculature was stated as the main source of postoperative scar tissue [8,17].
that the Jectos cement had been replaced by bone [42]. Consequently, recreating a scheme of near normal anatomical planes with this particular cement can work as an adhesion barrier following spine surgeries. Some accepted advantages of this composite include the following: the injectability of the cement gives perfect adaptation to the defect, Jectos shows resistance on compression that is equal to or better than that of cancellous bone, the paste thickness reduces the risk of leakage into soft tissue and neural elements [42].
Strategies to minimize scar formation Research to identify a technique or agent to prevent excessive scar formation and preserve the correct anatomical planes of different tissues—without interfering with the normal healing processes—has been an area of intense activities in recent years [20]. Even so, attempts to minimize scar formation via variable surgical techniques such as microdiscectomy and the use of local antiinflammatory medications and different biologic and synthetic materials including free fat graft, Gel foam and Avitene, Silastic, poly lactic acid, Gore-Tex membranes, and ADCON-L have generally had inconsistent results [1,2,16,18,19,23,26,36–39]. To preserve or restore an anatomical plane between dura matter and surrounding soft tissues, we investigated the hypothesis that the use of a new barrier with some similarities to normal bony lamina would reduce the extent of epidural fibrosis and prevent subsequent adhesion of these tissues to the dura matter.
Lamina reconstruction: safe and effective in animal model In this investigation, macroscopic (gross) and histopathological analyses were performed after 6 months, which is normally the needed period to complete the establishment of epidural fibrosis [34]. Our analysis showed that there was less epidural scarring in the reconstructed laminectomy sites compared with control sites. Indeed, intense fibrosis and strong tissue adhesion were observed in control spaces in gross and histologic evaluations. The result of the present study showed absorbable cement (Jectos) to be relatively safe and well tolerated in this animal model because there was no undesirable reaction or foreign body ossification. In all the implanted sites, the soft tissues appeared to be well healed, and the microscopic examination of the tissues showed some evidence of chronic inflammation similar to that of control sites. Shortcomings and needs for further studies
The rationale to use absorbable biodegradable cement The material used for lamina reconstruction in subject group was a calcium phosphate compound—Jectos—which acts as an absorbable biodegradable cement. The rationale to use this composite comes from previous tissue engineering studies, oral cavities investigations, and some clinical orthopedic experiences, which demonstrated its good biocompatibility, high degradability, and advanced bone formation [40–42]. In clinical setting, histologic examinations found
There were several limitations in the present study: No behavioral test was done to compare motor activities before animal sacrifice. No imaging study was obtained before animal sacrifice, and the assessment was based on gross and histologic assessments only. Both histologic scoring systems (for scar density and extension) were observational and based on the
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pathologist’s surveillance. A method for quantifying adhesion and scarring was lacking. The results of this study need to be replicated in larger sample, preferably using radiologic and behavioral data before gross anatomical and histologic observations.
Conclusions The present study suggests that lamina reconstruction with absorbable cement is a safe and effective method that merits further evaluation as a potential way to inhibit the formation of epidural scar after laminectomy. Further studies are required to prove the excellent efficacy of lamina reconstruction with Jectos and also to reveal the drawbacks of this material.
Acknowledgments The authors thank Dr Farideh Nejat for reviewing the manuscript and statistics. References [1] Alkalay RN, Kim DH, Urry DW, et al. Prevention of postlaminectomy epidural fibrosis using bioelastic materials. Spine 2007;28: 1659–65. [2] Temel SG, Ozturk C, Temiz A, et al. A new material for prevention of epidural fibrosis after laminectomy. J Spinal Disord Tech 2006;19: 270–5. [3] Watts CC, Bremer A, Nguyen T. Autogenic fat transplants in the epidural space in routine spine surgery. Neurosurgery 1980;13:37. [4] LaRocca H, Macnab I. The laminectomy membrane: studies in its evolution, characteristics, effects and prophylaxis in dogs. J Bone Joint Surg Br 1974;56:545–50. [5] Bartynski W, Petropoulou K. The MR imaging features and clinical correlates in low back pain—related syndromes. Magn Reson Imaging Clin N Am 2007;15:137–54. [6] Burton CV. Causes of failure of surgery in the lumbar spine: 10 year follow-up. Mt Sinai J Med 1991;58:183–7. [7] Gill GG, Scheck M, Kelley ET. Pedicle fat graft for prevention of scar in low back surgery: a preliminary report on the first 92 cases. Spine 1985;10:662–7. [8] Liu J, Ni B, Zhu L, et al. Mitomycin C-polyethylene glycol controlled-release film inhibits collagen secretion and induces apoptosis of fibroblasts in the early wound of a postlaminectomy rat model. Spine J 2010;10:441–7. [9] Robertson JT. Role of prediural fibrosis in the field back: a review. Eur Spine J 1996;5(1 Suppl):S2–6. [10] Sizer PS Jr, Phelps V, Dedrick G, Matthijs O. Differential diagnosis and management of spinal nerve root-related pain. Pain Pract 2002;2: 98–121. [11] Chandler K, Cappello R. Laminectomy membrane formation in dogs: is the answer still elusive? Vet J 2006;172:1–2. [12] Jou IM, Tai TW, Tsai CL, et al. Spinal somatosensory evoked potential to evaluate neurophysiologic changes associated with postlaminotomy fibrosis: an experimental study. Spine 2007;19:2111–8. [13] Kato T, Haro H, Komori H, Shinomiya K. Evaluation of hyaluronic acid sheet for the prevention of postlaminectomy adhesions. Spine J 2005;5:479–88.
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[14] Akeson WH, Massie JB, Huang B, et al. Topical high-molecularweight hyaluronan and a roofing barrier sheet equally inhibit postlaminectomy fibrosis. Spine J 2005;5:180–90. [15] Cemil B, Tun K, Kaptanoglu E, et al. Use of pimecrolimus to prevent epidural fibrosis in a postlaminectomy rat model. J Neurosurg Spine 2009;11:758–63. [16] Foulkes GD, Robinson JS Jr. Intraoperative dexamethasone irrigation in lumbar microdiskectomy. Clin Orthop 1990;261:224–8. [17] Kemaloglu S, Ozkan U, Yilmaz F, et al. Prevention of spinal epidural fibrosis by recombinant tissue plasminogen activator in rats. Spinal Cord 2003;141:427–31. [18] Kemaloglu S, G€ur A, Yılmaz F, et al. Comparative preventive efficacy of recombinant tissue plasminogen activator (rt-pA), urokinase, hyaluronic acid and enoxaparin in post laminectomy epidural fibrosis in rats. Eur J Gen Med 2011;8:170–5. [19] Lee JY, Stenzel W, Ebel H, et al. Mitomycin C in preventing spinal epidural fibrosis in a laminectomy model in rats. J Neurosurg Spine 2004;100(Suppl 1):52–5. [20] Lee JY, Stenzel W, L€ohr M, et al. The role of mitomycin C in reducing recurrence of epidural fibrosis after repeated operation in a laminectomy model in rats. J Neurosurg Spine 2006;4:329–33. [21] Nakano M, Matsui H, Miaki K, Tsuji H. Postlaminectomy adhesion of the cauda equina. Inhibitory effects of anti-inflammatory drugs on cauda equina adhesion in rats. Spine 1998;23:298–304. [22] Nussbaum CE, Charles E, McDonald JV, Baggs RB. Use of vicryl (polyglactin 910) mesh to limit epidural scar formation after laminectomy. Neurosurgery 1990;26:649–54. [23] Quist JJ, Dhert WJ, Meij BP, et al. The prevention of peridural adhesions. A comparative long-term histomorphometric study using a biodegradable barrier and a fat graft. J Bone Joint Surg Br 1998;3:520–6. [24] Rodgers KE, Robertson JT, Espinoza T, et al. Reduction of epidural fibrosis in lumbar surgery with Oxiplex adhesion barriers of carboxymethylcellulose and polyethylene oxide. Spine J 2003;3: 277–84. [25] Boot DA, Hughes SP. The prevention of adhesions after laminectomy. Adverse results of Zenoderm implantations into laminectomy sites in rabbits. Clin Orthop Relat Res 1987;215:296–302. [26] Mikawa Y, Hamagami H, Shikata J, et al. An experimental study on prevention of postlaminectomy scar formation by the use of new materials. Spine 1986;11:843–6. [27] Devulder J, Bogaert L, Castille F, et al. Relevance of epidurography and epidural adhesiolysis in chronic failed back surgery patients. Clin J Pain 1995;11:147–50. [28] Merrild U, Søgaard I. Sciatica caused by perifibrosis of the sciatic nerve. J Bone Joint Surg Br 1986;68:706. [29] Siqueira EB, Kranzler LI, Dharkar DD. Fibrosis of the dura mater: a cause of ‘‘failed back’’ syndrome. Surg Neural 1993;19:168–70. [30] Benoist M, Ficat C, Baraf P, Cauchoix J. Postoperative lumbar epiduroarachnoiditis. Spine 1980;5:432–6. [31] Finnegan WJ, Fenlin JM, Marvel JP, et al. Results of surgical intervention in the symptomatic multiply-operated back patient. Analysis of sixty-seven cases followed for three to seven years. J Bone Joint Surg Am 1979;61:1077–82. [32] Burton CV, Kirkaldy-Willis WH, Yong-Hing K, Heithoff KB. Causes of failure of surgery on the lumbar spine. Clin Orthop 1981;157: 191–9. [33] de Tribolet N, Porchet F, Lutz TW, et al. Clinical assessment of a novel antiadhesion barrier gel: prospective, randomized, multicenter, clinical trial of ADCON-L to inhibit postoperative peridural fibrosis and related symptoms after lumbar discectomy. Am J Orthop 1998;27:111–20. [34] Long DM. Failed back surgery syndrome. Neurosurg Clin N Am 1991;2:899–919. [35] North RB, Bwend MG, Lawton MT. Failed back surgery syndrome: 5 year follow-up in 102 patients undergoing repeated operation. Neurosurgery 1991;28:685–91.
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[36] Jacobs RR, McClain O, Neff J. Control of postlaminectomy scar formation: an experimental and clinical study. Spine 1980;5:223–9. [37] Langenskiold A, Kiviluoto O. Prevention of epidural scar formation after operations on the lumbar spine by means of free fat transplants. Clin Orthop 1976;115:92–5. [38] Lawson KJ, Malycky JL, Berry BL, Steffee AD. Lamina. Repair and replacement to control laminectomy membrane formation in Canines. Spine 1991;16:222–6. [39] Neel HB. Impacts of Gore-Tex. Arch Otolaryngol 1983;190:427–33.
[40] Wang L, Shi H, Chen Y, et al. Healing of acute alveolar bone dehiscence following treatment with porous biphasic calcium phosphate in beagle dogs. Clin Oral Investig 2011;15:983–91. [41] Felix Lanao RP, Hoekstra JW, Wolke JG, et al. Porous calcium phosphate cement for alveolar bone regeneration. J Tissue Eng Regen Med 2012. [Epub ahead of print]. [42] Oberta L, Lepagea D, Gassea N, et al. Extra-articular distal radius malunion: the phosphate cement alternative. Orthop Traumatol Surg Res 2010;96:574–8.
Basic Science
Reduction of epidural fibrosis and dural adhesions after lamina reconstruction by absorbable cement: an experimental study Mehdi Zeinalizadeh, MDa,b,*, Seyed Mojtaba Miri, MDa,b, Farid Azmoodeh Ardalan, MDc, Farid Maleki, MDb, Marjan Zakeri, MDb, Elham Aghajanzadeh, MDb, Zohreh Habibi, MDa,b a
Department of Neurosurgery, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran 1419733141, Iran b Brain and Spinal Cord Injuries Repair Research Center, Imam Khomeini Hospital, Tehran 1419733141, Iran c Department of Pathology, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran 1419733141, Iran Received 28 April 2013; accepted 24 June 2013
Abstract
BACKGROUND CONTEXT: Post-laminectomy epidural fibrosis complicates revision spine surgery and is implicated in cases of ‘‘failed back syndrome.’’ Several materials have been used to minimize epidural fibrosis with varying results. PURPOSE: The aim of this study was to examine the impact of reconstruction of laminectomy site with a type of absorbable cement (Jectos) to reduce epidural fibrosis. STUDY DESIGN: This investigation is an experimental controlled study, which is designed to evaluate the preventive effects of laminectomy site reconstruction in rat laminectomy model. METHODS: Twenty wistar rats were included in this study and divided randomly to two equal groups, namely, subject and control. In both groups, laminectomy was performed in L2 and L4 levels. Control group received no additional treatment. In the subject group, L4 levels were reconstructed by Jectos and L2 levels were non-reconstructed as internal controls. Six months after surgery the rats were sacrificed and the dural adhesion and epidural fibrosis were evaluated macroscopically and microscopically. The study was financially supported by Brain and Spinal Cord Injuries Repair Center. None of the authors have any conflict of interest. RESULTS: Non-reconstructed levels in both groups showed dense epidural fibrosis with marked dural adherence. L4 reconstructed levels in subject group showed reduced epidural fibrosis macroscopically (p5.024) and microscopically (p5.041). No foreign body reaction or ossification occurred at reconstructed sites. CONCLUSIONS: In the present study, lamina reconstruction with absorbable cement was a safe method that significantly reduced post-laminectomy epidural fibrosis and dural adhesions in rat laminectomy model. Ó 2014 Elsevier Inc. All rights reserved.
Keywords:
Epidural fibrosis; Dural adhesion; Laminectomy; Revision spine surgery; Lamina reconstruction
Introduction Postoperative epidural fibrosis, the development of a dense scar tissue adjacent to the dura matter after surgical laminectomy, is a natural process of healing [1–3]. Cells
FDA device/drug status: Not approved for this indication (Jectos: Dicalcium phosphate 55% and Tricalcium phosphate 45%, Kasios, Germany). Author disclosures: MZe: Nothing to disclose. SMM: Nothing to disclose. FAA: Nothing to disclose. FM: Nothing to disclose. MZa: Nothing to disclose. EA: Nothing to disclose. ZH: Nothing to disclose. * Corresponding author. Department of Neurosurgery, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran 1419733141, Iran. Tel.: (98) 216-119-2634-5; fax: (98) 216-659-1320. E-mail address: [email protected] (M. Zeinalizadeh) 1529-9430/$ - see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.06.065
that generate fibrosis are fibroblasts that come from the adjacent paraspinal musculature. This physiologic scar may become a hypertrophic enveloping film, creating the socalled post-laminectomy membrane described by LaRocca and Macnob [4] in 1974. This extradural fibrotic tissue may extend into the vertebral canal and adhere to the dura matter and nerve roots, causing recurrent symptoms including radicular pain [5–10]. Furthermore, epidural fibrosis makes the next exploration of the operative field technically challenging because of increase in the risk of nerve root damage, dural tears, and iatrogenic injuries [8,11–13]. The prevention of scar formation is one of the main concerns in spine surgery that has been the subject of research for many years. A variety of biological, pharmacological, and synthetic materials have been investigated
114
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to prevent scar formation after laminectomy. Silastic, ADCON-L, Gore-Tex membrane, Dacron, Vicril mesh, Zenoderm, methacrylate, polyethylene oxide, biodegradable polymers, bioelastic polymers, fat grafts, sodium hyaluronate, steroids, mitomycin C, pimecrolimus, recombinant plasminogen activator, and anti-inflammatory medications have been used with inconsistent results [1,2,4,8,14–25]. The use of a physical barrier to protect tissue surfaces as they heal has been shown to be one of the most effective methods of reducing adhesions in animal models of spine surgery [26]. Even if, the human trials are still a long way off. The present study was designed to evaluate the impact of laminectomy site reconstruction with absorbable cement in rat laminectomy model to observe whether it can reduce epidural fibrosis.
Materials and methods This study was conducted in the animal Lab of Brain and Spinal cord Injuries Repair Center between 2011 and 2012. Twenty male wistar rats weighing 300 to 350 g were randomly assigned into two equal cohorts, namely, subject and control. Laminectomy was performed in L2 and L4 levels of both groups. Control animals received no additional treatment, whereas lamina reconstruction was done in L4 levels of subject rats. In the later group, L2 levels were non-reconstructed to act as internal controls. Accordingly, 10 levels received the treatment and 30 levels were in the control arm including L2 and L4 levels in control group and L2 levels in subject group. Absorbable cement The material used for lamina reconstruction was a type of absorbable cement (Jectos: Dicalcium phosphate 55% and Tricalcium phosphate 45%, Kasios, Germany). The cement is obtained by blending a liquid and a solid (powder) phase for 1 minute, followed by a few minutes leaving the mixture in room temperature for further thickening to have an easily shaped injectable paste.
the absorbable cement (Jectos) without compression on dura matter. The wound was closed in layers with interrupted 3-0 nylon sutures. Postoperative evaluation After the recovery period, the animals were evaluated for medical condition and neurologic status. All rats were then allowed cage activity for 6 months. On the 180th postoperative day, the animals were sacrificed by intracardiac perfusion of paraformaldehyde 4% under general anesthesia. All laminectomy sites were grossly evaluated using loupe magnification by a single neurosurgeon. For gross evaluation of epidural adhesions, the scoring system stated in Table 1 was used. This system ranks from 1 to 3 based on the surgeon’s observation to assess how paraspinal muscles were separated from dura matter during dissection; ‘‘the more difficult dissection, the higher grade of adhesion’’ (Table 1). After gross evaluation, blocks of tissue containing dura, epidural tissue, and surrounding soft tissues were obtained and kept in paraformaldehyde 4% solution for histologic assessment. The cement was removed from the dura and surrounding tissues during exposure and tissue handling to keep the pathologist completely blinded about the cohorts. Histologic examination Samples containing bone cement were decalcified in ethylenediaminetetraacetic acid solution to have the pathologist be blinded about the samples. All specimens were embedded in paraffin, sectioned by microtome apparatus, and stained with Masson trichrome and Hematoxylin and Eosin. These two staining methods were used for grading of fibrosis density and extension, respectively. Sections were examined using an Olympus microscope by a single pathologist in two different ways: 1. Evaluating the density of fibrosis using an observational scaling method (mild, moderate, and severe) based on the intensity of Masson trichrome staining (Fig. 1). The more prominent staining, the more density and compactness of fibrosis (Fig. 1). 2. Evaluating the extension of fibrosis to surrounding tissues, namely, epidural fat (Score 1), muscle (Score
Surgical procedure The procedure was performed under general anesthesia obtained by intraperitoneal injection of ketamine (35 mg/ kg) and Xylozine (5 mg/kg). Preoperative intraperitoneal cefazolin sodium (75 mg/kg) was administered for infection prophylaxis. Skin and fascia were incised in midline at lumbar region under loupe magnification. After separation of paraspinal muscles and resection of spinous process, rectangular 52 mm laminectomy defects were created at L2 and L4, leaving the dura clean and fully exposed. After hemostasis via gentle compression of cotton, L4 laminectomy defects in treatment group were reconstructed by
Table 1 Scoring system for detailed macroscopic evaluation of epidural adhesions Score
Description
1
Absence of adhesion between paraspinal muscles and dura matter, with near normal separation plane of tissues Mild-to-moderate adhesion, and separation of epidural fibrosis from dura matter was easy by a dissector Severe adhesion, and separation of epidural fibrosis from dura matter was hard or impossible by a dissector
2 3
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Fig. 1. Photomicrograph of laminectomy sites showing mild (Left), moderate (Middle), and severe (Right) epidural fibrosis. Masson trichrome, original magnification 40.
2), and neural tissue (Score 3) via Hematoxylin and Eosin staining (Fig. 2). Again, this scoring system was observational based on the pathologist’s surveillances. The involvement of epidural fat only was the mildest degree, whereas taking the epidural fat plus strait muscle was ranked as Score 2. Extension of fibrosis to neural elements was considered as maximal intensity. For each level, the sum of both microscopic scores was used for final statistical analysis. Statistical analysis The scores of fibrosis density and extension were compared between the control and treatment sites using chisquare, Mann-Whitney, Spearman, and Wilcoxon signed rank tests. All statistical analyses were performed using SPSS software version 18 (SPSS Inc., Chicago, IL, USA), and p value less than .05 was considered statistically significant. The study was financially supported by Brain and Spinal cord Injuries Repair Center. None of the authors have any conflict of interest. In this study, all interventions and gross evaluations were performed under loupe magnification by a single author (MZ), and all microscopic specimens were evaluated by a single pathologist (FAA) in blinded manner. The study was approved by the institutional medical research ethics committee.
Results In treatment group, one rat died before completing follow-up period for unknown reason and one was excluded
because of developing infection at Operation Site 3 weeks after surgery. The results of macroscopic severity and microscopic density of epidural fibrosis of operated segments in case and control groups are tabularized in Table 2. Macroscopic and microscopic evaluation of L2 and L4 levels in control group compared with L2 levels in subject group (internal control ) revealed no statistically significant difference. Even so, both density and extension of microscopic epidural fibrosis in L4 levels of subject group (treated levels) were found to be significantly lower than control levels (p5.041). In macroscopic observations, the scar tissue in treated levels was less than controls too (p5.024). There was not any linear relation between microscopic and macroscopic differences in treatment group, however (p5.074). No case in treatment group developed foreign body ossification around the cement, although some granulomatous reactions were seen. Microscopic findings of chronic inflammation were remarkable in all sections taken from both groups.
Discussion Postoperative epidural fibrosis The formation of dense and thick epidural scar tissue after lumbar laminectomy and discectomy may contribute to unfavorable clinical outcomes and recurring symptoms such as radicular and/or low back pain [19,20,27–29]. Epidural fibrosis is often initiated by injury to the epidural space after surgical procedures [20]. A pain-free interval of shorter than 12 months after previous discectomy with slow onset of complaints is characteristic of epidural fibrosis, with the tethered nerve roots being the major underlying cause of symptoms [2,15,20,30,31]. The tethering
Fig. 2. Photomicrograph of laminectomy sites showing the extension of fibrosis to epidural fat tissue (arrow, Left), striated muscles (arrowheads, Middle), and nerve bundles (asterisk, Right). Hematoxylin and Eosin, original magnification 40.
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Table 2 The severity of macroscopic and microscopic post-laminectomy epidural fibrosis in case and control groups Group
Control
Case
L2
L4
L2
L4
Fibrosis severity/density
Mac severity
Mic density
Mac severity
Mic density
Mac severity
Mic density
Mac severity
Mic density
1/Mild 2/Moderate 3/Severe Total
0 3 7 10
0 3 7 10
0 3 7 10
1 5 4 10
0 3 5 8
0 3 5 8
6 0 2 8
3 3 2 8
Mac, macroscopic; Mic, microscopic.
may impede nerve mobility and increase tension on the nerve during motion, leading to nerve injury [2]. Although extensive epidural scar adhesions can be removed and the tethered nerve roots can be released through reexploration, adhesions tend to recur after the second surgery and the patient’s symptoms may become even worse than before [32–35]. Fibroblasts originating from the overlying muscles and the extension of postoperative hematoma into the vertebral canal can produce epidural fibrosis [8,17,23]. The migration of fibroblasts from the surface of erector spinae musculature was stated as the main source of postoperative scar tissue [8,17].
that the Jectos cement had been replaced by bone [42]. Consequently, recreating a scheme of near normal anatomical planes with this particular cement can work as an adhesion barrier following spine surgeries. Some accepted advantages of this composite include the following: the injectability of the cement gives perfect adaptation to the defect, Jectos shows resistance on compression that is equal to or better than that of cancellous bone, the paste thickness reduces the risk of leakage into soft tissue and neural elements [42].
Strategies to minimize scar formation Research to identify a technique or agent to prevent excessive scar formation and preserve the correct anatomical planes of different tissues—without interfering with the normal healing processes—has been an area of intense activities in recent years [20]. Even so, attempts to minimize scar formation via variable surgical techniques such as microdiscectomy and the use of local antiinflammatory medications and different biologic and synthetic materials including free fat graft, Gel foam and Avitene, Silastic, poly lactic acid, Gore-Tex membranes, and ADCON-L have generally had inconsistent results [1,2,16,18,19,23,26,36–39]. To preserve or restore an anatomical plane between dura matter and surrounding soft tissues, we investigated the hypothesis that the use of a new barrier with some similarities to normal bony lamina would reduce the extent of epidural fibrosis and prevent subsequent adhesion of these tissues to the dura matter.
Lamina reconstruction: safe and effective in animal model In this investigation, macroscopic (gross) and histopathological analyses were performed after 6 months, which is normally the needed period to complete the establishment of epidural fibrosis [34]. Our analysis showed that there was less epidural scarring in the reconstructed laminectomy sites compared with control sites. Indeed, intense fibrosis and strong tissue adhesion were observed in control spaces in gross and histologic evaluations. The result of the present study showed absorbable cement (Jectos) to be relatively safe and well tolerated in this animal model because there was no undesirable reaction or foreign body ossification. In all the implanted sites, the soft tissues appeared to be well healed, and the microscopic examination of the tissues showed some evidence of chronic inflammation similar to that of control sites. Shortcomings and needs for further studies
The rationale to use absorbable biodegradable cement The material used for lamina reconstruction in subject group was a calcium phosphate compound—Jectos—which acts as an absorbable biodegradable cement. The rationale to use this composite comes from previous tissue engineering studies, oral cavities investigations, and some clinical orthopedic experiences, which demonstrated its good biocompatibility, high degradability, and advanced bone formation [40–42]. In clinical setting, histologic examinations found
There were several limitations in the present study: No behavioral test was done to compare motor activities before animal sacrifice. No imaging study was obtained before animal sacrifice, and the assessment was based on gross and histologic assessments only. Both histologic scoring systems (for scar density and extension) were observational and based on the
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pathologist’s surveillance. A method for quantifying adhesion and scarring was lacking. The results of this study need to be replicated in larger sample, preferably using radiologic and behavioral data before gross anatomical and histologic observations.
Conclusions The present study suggests that lamina reconstruction with absorbable cement is a safe and effective method that merits further evaluation as a potential way to inhibit the formation of epidural scar after laminectomy. Further studies are required to prove the excellent efficacy of lamina reconstruction with Jectos and also to reveal the drawbacks of this material.
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