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Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion
Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Clinical Study
Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion Xiaolong Shen, Hailong Zhang, Xin Gu, Guangfei Gu, Xu Zhou, Shisheng He ⇑ Department of Orthopedics, Shanghai Tenth People’s Hospital, Tongji University School of Medicine, 301 Yanchang Road, Shanghai 200072, China
a r t i c l e
i n f o
Article history: Received 14 August 2013 Accepted 16 November 2013 Available online xxxx Keywords: Minimally invasive Spinal fusion TLIF Unilateral pedicle screw fixation
a b s t r a c t Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) has become an increasingly popular method of lumbar arthrodesis. However, there are few published studies comparing the clinical outcomes between unilateral and bilateral instrumented MIS TLIF. Sixty-five patients with degenerative lumbar spine disease were enrolled in this study. Thirty-one patients were randomized to the unilateral group and 34 to the bilateral group. Recorded demographic data included sex, age, preoperative diagnosis, and degenerated segment. Operative time, blood loss, hospital stay length, complication rates, and fusion rates were also evaluated. The Oswestry Disability Index (ODI) score and Visual Analog Scale (VAS) pain score data were obtained. All patients were asked to follow-up at 3 and 6 months after surgery, and once every 6 months thereafter. The mean follow-up was 26.6 months (range 18–36 months). The two groups were similar in sex, age, preoperative diagnosis, and operated level. The unilateral group had significantly shorter operative time, lower blood loss, and shorter hospital time than the bilateral group. The average postoperative ODI and VAS scores improved significantly in each group. No significant differences were found between the two groups in relation to ODI and VAS. All patients showed evidence of fusion at 12 months postoperatively. The total fusion rate, screw failure, and general complication rate were not significantly different. Results showed that single-level MIS TLIF with unilateral pedicle screw fixation would be sufficient in the management of preoperatively stable patients with lumbar degenerative disease. It seems that MIS TLIF with unilateral pedicle screw instrumentation is a better choice for single-level degenerative lumbar spine disease. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction A large number of techniques have been developed for lumbar spinal fusion. Interbody fusion has become widely popular because it provides a large surface area for fusion with the graft under compression. Harms first described the transforaminal lumbar interbody fusion (TLIF) technique with cage fusion that, due to the lateral approach to the disc space, reduced the amount of thecal sac and nerve root retraction required [1]. Although TLIF is a unilateral procedure, it is usually combined with posterior bilateral pedicle screw fixation. The TLIF procedure allows a single point of access to be used for interbody fusion and posterior instrumentation. It preserves the anterior longitudinal ligament and a major portion of the posterior ligament complex with minimal compromise of spinal stability. However the need for paraspinal muscle dissection and retraction remains a drawback that can lead to muscle denervation, atrophy and consequently persistent low back ⇑ Corresponding author. Tel.: +86 138 1783 0920; fax: +86 021 6630 6549. E-mail address: [email protected] (S. He).
pain [2]. Advances in lumbar fusion techniques have concentrated on reducing soft-tissue damage and neural retraction while maintaining the ability to achieve neural decompression and interbody fusion. Minimally invasive (MIS) TLIF was introduced by Foley et al. in 2002 [3]. It has become an increasingly popular method of lumbar arthrodesis. Recent technological advances in spinal instrumentation have culminated in the development of MIS TLIF with unilateral pedicle screw fixation [4]. The potential shortfall is an insufficiently stable construct that may result in a higher incidence of instrumentation failure. A higher incidence of nonunion may also be a risk. Biomechanical studies have shown that unilateral fixation after TLIF provided less rotational stability and stiffness than bilateral pedicle screw fixation [5]. Slucky et al. reported that the unilateral pedicle screw construct provided only half of the improvement in stiffness compared with bilateral constructs and allowed for significant off-axis rotational motion after TLIF [6]. However, several studies have also reported that unilateral pedicle screw fixation is as effective as bilateral pedicle screw fixation in lumbar spinal fusion [7,8]. There are few published studies on clin-
http://dx.doi.org/10.1016/j.jocn.2013.11.055 0967-5868/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
2
X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
ical outcomes of MIS TLIF with unilateral pedicle screw fixation, even though perioperative and postoperative complications and surgical outcomes have been well described in the literature [9]. The purpose of this prospective study was to compare the clinical outcomes between unilateral and bilateral instrumented MIS TLIF. 2. Patients and methods 2.1. Patients Sixty-five patients with single-level degenerative lumbar spine disease at L4–L5 or L5–S1 were recruited from July 2009 to June 2011. All patients had suffered from low back pain, severe unilateral radicular pain or neurological symptoms. All patients underwent at least 6 months of conservative management before surgery, with no response or an inadequate response. All patients were confirmed to have single-level degenerative lumbar spine disease with plain radiographs, CT scans, and MRI. They were randomly divided into two groups using a computer-generated number list. Thirty-one patients were assigned to MIS TLIF with unilateral pedicle screw fixation (Group A, Fig. 1), and 34 were assigned to MIS TLIF with bilateral pedicle screw fixation (Group B, Fig. 2). Demographics and procedure data for the two groups are listed in Table 1. In this study, a stable level was defined as a degenerative disc without spondylolisthesis. Patients were included if they were aged between 40–70 years and only had one level of degenerative disease. Patients were excluded if they were elderly (>70 years old), had isthmic or degenerative spondylolisthesis, were significantly obese (body mass index P35 kg/m2), had undergone previous lumbar fusion or discectomy, or had multi-level disease. 2.2. Surgical approaches After induction of general endotracheal anesthesia, patients were placed in the prone position on a radiolucent operating table, with the abdomen hanging free and slight flexion of the lower limbs. C-arm fluoroscopy was used to position the diseased segments and to determine the incision site. A 2–2.5 cm incision was made overlying the affected level and continued down through the posterior lumbar fascia. Sequential dilators were introduced until a METRx tubular retractor (Medtronic Sofamor Danek,
Fig. 1. (Left) Anteroposterior and (right) lateral CT scan showing unilateral pedicle screw fixation in lumbar spinal fusion.
Fig. 2. (Left) Anteroposterior and (right) lateral CT scan showing bilateral pedicle screw fixation in lumbar spinal fusion. Table 1 Demographic data and distribution of fused levels in the two study groups with unilateral pedicle screw fixation (Group A) or bilateral pedicle screw fixation (Group B)
Patients Sex (female/male) Age, years Mean height, cm Mean weight, kg Diagnosis Unilateral lumbar disc herniation Foraminal stenosis Discogenic low back pain Level of fusion L4–L5 L5–S1
Group A
Group B
31 14/17 57.3 ± 11.7 169.5 ± 9.4 68.8 ± 8.4
34 18/16 58.9 ± 10.1 171.2 ± 10.6 69.6 ± 9.5
10 15 6
12 18 4
15 16
15 19
p value 0.462 0.153 0.317 0.462 0.579
0.730
Data are presented as mean ± standard deviation or number.
Memphis, TN, USA) was placed. The operating microscope was moved into the field and the laminar edge was identified. The isthmus, the unilateral posterior arch of the vertebrae and the inferior joint facet of the subjacent vertebra were removed. This bone was kept for use as an autograft during the interbody fusion. The thecal sac and traversing nerve root were identified. The operating table was tilted down contralaterally and the microscope was angled toward the medial side. The deep cortical surface of the contralateral lamina was removed and drilling was extended to the contralateral lateral recess and foramen. Finally, the ligamentum flavum and its bony attachment edge were removed. Then, a thorough discectomy and endplate preparation were performed. The disc space was packed with autograft bone. A polyetheretherketone (PEEK) interbody graft (Capstone, Medtronic Sofamor Danek) was then obliquely inserted and placed in the center of the disc space. The entire procedure was carried out using the surgical microscope with variable magnification and sufficient lighting of the operative field. Once the interbody discectomy and arthrodesis were completed, the working channel was removed. With the assistance of the Sextant system (Medtronic Sofamor Danek), percutaneous lumbar pedicle screws were inserted. The screws were compressed over the interbody cage to provide a degree of segmental lordosis and compression across the cage. In Group B, contralateral percutaneous pedicle screw fixation was also performed. All procedures
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
3
were carried out by the same surgeon (S. H.) using the method described in detail by Foley and Gupta [10]. 2.3. Outcome assessment The demographic data captured included sex, age, preoperative diagnosis, and degenerated segment. Operative time, blood loss, hospital stay length, complication rates, and fusion rates were also evaluated. The Oswestry Disability Index (ODI) score and Visual Analog Scale (VAS) pain score data were obtained for all patients 24 hours before the operation and at each follow-up visit. CT scans were used to evaluate fusion at 6 and 12 months after surgery. Fusion was defined as an absence of radiolucent lines covering >50% of either implant, translation of 63 mm and angulation <5° on flexion–extension radiographs, and continuous trabecular bone growth connecting the vertebral bodies on CT scan cut [11]. 2.4. Statistical analysis The Statistical Package for the Social Sciences version 16.0 (SPSS, Chicago, IL, USA) was used for the statistical calculations. Demographic data were compared by means of a chi-squared test. Patient age, operative time, blood loss and hospital time were analyzed by unpaired Student t-tests. Analysis of variance (repeated measures design) was used to compare VAS and ODI. In all analyses, p values <0.05 were considered statistically significant. 3. Results 3.1. Patient characteristics The mean follow-up was 26.6 months, ranging from 18 to 36 months. There were no statistically significant differences between the two groups in terms of demographic data (Table 1). 3.2. Operative parameters and clinical outcomes The unilateral group (Group A) had a significantly shorter operative time, less blood loss, and shorter hospital time compared with the bilateral group (Table 2). All patients showed evidence of fusion 12 months postoperatively (Fig. 3). The total fusion rate, screw failure, and general complication rate were not significantly different between the groups. At 6 month follow-up, radiological evidence showed that 96.8% (30 of 31) of patients in Group A and 100.0% of patients in Group B achieved successful fusion, with no significant difference (p > 0.05). One patient in Group A did not achieve successful fusion at 6 months, but he achieved solid fusion at his 12 month follow-up. During the follow-up period, screw loosening was not observed in any patient. Neither group showed any signs of screw breakages or infection. The average postoperative VAS and ODI scores improved significantly in each group. No significant differences were found between the two groups in relation to ODI and VAS at any time (Table 3). Table 2 Operative data from the two groups undergoing minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation (Group A) or bilateral pedicle screw fixation (Group B)
Operative time, minutes Blood loss, ml Hospital time, days Complications Fusion
Group A
Group B
p value
101.4 ± 27.2 52.5 ± 39.7 4.4 ± 1.5 4 30/31
143.1 ± 22.5 106.3 ± 53.8 6.6 ± 2.1 3 34/34
0.000 0.000 0.000 0.314 0.662
Data are presented as mean ± standard deviation or number.
Fig. 3. (A) Preoperative axial CT scan showing separation of the posterior ring apophysis of the L5 vertebrae, and the bone intruding into the spinal canal. (B) Preoperative axial T2-weighted MRI of the same patient showing discoligamentous disruption and retropulsion of disc material into the left side of spinal canal. (C) Sagittal CT image reconstruction 12 months after surgery showing that solid fusion was achieved. (D) Coronal CT scan demonstrating solid fusion. (E) Axial CT scan demonstrating placement of an interbody cage with unilateral pedicle screw instrumentation.
3.3. Complications One patient in Group A developed root irritation due to the violation of the pedicle cortex by a screw. A screw in Group B had been positioned in a parapedicular position, falling into the spinal canal, without any symptomatic consequence. This complication called for immediate rerouting of screws. One patient in Group A experienced incomplete relief of radicular symptoms. This patient was treated with traditional Chinese medicine and the radiculopathy improved with time. Two patients in Group A and one patient in group B suffered dural tear. These patients were managed with bed rest for 6–10 days with no long-term sequelae. There was one case of urinary tract infection in Group B. No wound infections occurred in either group (Table 2).
4. Discussion Kabins et al. reported that fusion results with unilateral variable screw placement instrumentation to single-level (L4–L5) fusion
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
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X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Table 3 Pain and functional evaluation outcomes of Visual Analogue Scale and Oswestry Disability Index scores in patients undergoing minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation (Group A) or bilateral pedicle screw fixation (Group B) Group A
VAS ODI (%)
Group B
Preop
3m
12 m
18 m
Preop
3m
12 m
18 m
6.8 ± 1.6 56.56 ± 19.12
2.4 ± 1.8 27.46 ± 15.82
2.1 ± 1.0 23.93 ± 16.47
2.0 ± 1.3 21.38 ± 14.33
7.2 ± 2.1 51.58 ± 16.38
2.3 ± 1.6 25.96 ± 16.51
2.2 ± 1.9 22.47 ± 16.22
2.2 ± 1.4 22.84 ± 15.65
Data are presented as mean ± standard deviation. m = months, ODI = Oswestry Disability Index, Preop = preoperatively, VAS = Visual Analogue Scale.
were nearly identical to those with bilateral instrumentation [7]. Furthermore, Suk et al. reported that unilateral pedicle screw fixation was as effective as bilateral pedicle screw fixation in lumbar spinal fusion, independent of the number of fusion segments (one or two segments) or pedicle screw systems used [8]. In spinal fusion surgery, the need for unilateral or bilateral instrumentation is a controversial issue. Biomechanical studies have demonstrated that unilateral fixation after TLIF provides less rotational stability and stiffness than bilateral pedicle screw fixation [5,6]. However, extensive destruction of tissue structures, which exacerbates the instability of the spine, was used in these in vitro biomechanical studies. In addition, the maintenance of lumbar stability simply relied on unilateral pedicle screw fixation without any support device. Despite data suggesting the inferiority of unilateral pedicle screw fixation after TLIF in biomechanical studies, many clinical trials have reported good results of unilateral pedicle screw fixation after TLIF [8,12]. In the MIS spine surgery literature, a few reports and studies have demonstrated good outcomes and fusion rates following unilateral pedicle screw fixation during MIS TLIF [9,13]. At the time of writing, the general consensus is that unilateral instrumentation should be confined to a single-level fusion and not be extended to multi-level fusion because of its inadequate fixation strength. Suk et al. found a lower fusion rate (91.5%) for unilateral pedicle screw fixation compared to bilateral pedicle screw fixation (97.5%) in lumbar spinal fusion, although this difference was not statistically significant [8]. In our study, we found that good outcomes and similar fusion rates were achieved with unilateral and bilateral instrumentation for MIS TLIF. Our fusion rate for unilateral pedicle screw fixation is higher than previous studies [8,14]. During the operation, autograft bone was tightly packed into the disc space. A PEEK interbody graft was then obliquely inserted and placed in the center of the disc space (Fig. 3C, D). Thus we speculate that adequate amounts of autograft bone may explain the differences between reported fusion rates. One of the drawbacks of open TLIF is that detachment and retraction of paraspinal muscle and excessive intraoperative dissection can result in denervation, atrophy and irreversible muscle injury. With the advent of MIS techniques to achieve spinal fusion, it has become essential to use minimal instrumentation without compromising the final stiffness of the spine. Reduced soft tissue dissection allows for early recovery and rehabilitation of the patient [15–17]. It has also been reported that unilateral MIS TLIF procedure using unilateral pedicle screw instrumentation instead of bilateral pedicle screws could further reduce tissue injury and blood loss [13]. We found that unilateral pedicle screw fixation after MIS TLIF led to shorter operative time, less blood loss, and shorter hospital time compared to bilateral pedicle screw fixation, which is consistent with previous studies. This procedure provided excellent clinical results during a middle-term follow-up period. Bilateral decompression via a unilateral approach for lumbar canal stenosis was initially described by Young et al. [18]. Studies on cadaver spine specimens proved the feasibility of this unilateral approach [19]. Postoperative clinical improvement and radiological findings demonstrated that bilateral ligamentectomy and
recess decompression can be adequately and successfully achieved via the unilateral approach [20]. CT scans showed significant enlargement of the cross-sectional area of the dural sac in patients after surgery [21]. In this technique, the thecal sac and bilateral nerve roots can be decompressed without injuring the supra or inter-spinous ligament complex and the contralateral paraspinal muscles [22,23]. The use of a unilateral laminotomy for bilateral decompression can result in less injury to the support structures of the spine. However, some authors have reported that this method can lead to lumbar instability which requires spinal fusion [21,24]. A total facetectomy was carried out in our study, so we considered fixation and fusion was necessary in these patients. In our study, MIS TLIF and bilateral decompression via a unilateral laminotomy were successfully performed in patients with degenerative stenosis. This procedure afforded a persistently satisfactory outcome for lumbar degenerative disease even over follow-up periods longer than 18 months. We carried out MIS bilateral decompression under a microscope using a unilateral approach in patients with acquired spinal stenosis, whose symptoms were unilateral or bilateral. All patients in both groups achieved solid fusion at 12 month follow-up. More importantly, no significant scoliosis was found in the unilateral group during the follow-up period. Compared to previous studies, this procedure has the advantages of both MIS surgery and unilateral pedicle screw instrumentation. It seems that MIS TLIF with unilateral pedicle screw instrumentation is the optimal treatment choice for single-level degenerative lumbar spine disease. 4.1. Study limitations In our middle-term follow-up study, we found that good outcomes and similar fusion rates were achieved with unilateral and bilateral instrumentation for MIS TLIF. Longer-term studies involving a larger sample are needed to validate the long-term efficacy of MIS TLIF with unilateral pedicle screw instrumentation.
5. Conclusions MIS TLIF with unilateral pedicle screw fixation had a significantly shorter operative time, less blood loss, and shorter hospital length of stay compared to MIS TLIF with bilateral pedicle screw fixation. No significant differences were found between the two groups in relation to ODI and VAS scores. The total fusion rate, screw failure, and general complication rate were not significantly different between the groups. It appears that MIS TLIF with unilateral pedicle screw instrumentation is the optimal treatment choice for single-level degenerative lumbar spine disease.
Conflicts of Interest/Disclosures The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
References [1] Harms JG, Jeszenszky D. Die posteriore, lumbale, interkorporalle fusion in unilateraler transforminaler technik. Orthop Traumatol 1998;10:90–102. [2] Tsahtsarlis A, Wood M. Minimally invasive transforaminal lumber interbody fusion and degenerative lumbar spine disease. Eur Spine J 2012. [3] Foley KT, Lefkowitz MA. Advances in minimally invasive spine surgery. Clin Neurosurg 2002;49:499–517. [4] Schizas C, Tzinieris N, Tsiridis E, et al. Minimally invasive versus open transforaminal lumbar interbody fusion: evaluating initial experience. Int Orthop 2009;33:1683–8. [5] Harris BM, Hilibrand AS, Savas PE, et al. Transforaminal lumbar interbody fusion: the effect of various instrumentation techniques on the flexibility of the lumbar spine. Spine (Phila Pa 1976) 2004;29:E65–70. [6] Slucky AV, Brodke DS, Bachus KN, et al. Less invasive posterior fixation method following transforaminal lumbar interbody fusion: a biomechanical analysis. Spine J 2006;6:78–85. [7] Kabins MB, Weinstein JN, Spratt KF, et al. Isolated l4–l5 fusions using the variable screw placement system: unilateral versus bilateral. J Spinal Disord 1992;5:39–49. [8] Suk KS, Lee HM, Kim NH, et al. Unilateral versus bilateral pedicle screw fixation in lumbar spinal fusion. Spine 2000;25:1843–7. [9] Deutsch H, Musacchio MJ Jr. Minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation. Neurosurg Focus 2006;20:E10. [10] Foley KT, Gupta SK, Justis JR, et al. Percutaneous pedicle screw fixation of the lumbar spine. Neurosurg Focus 2001;10:E10. [11] Burkus JK, Foley K, Haid RW, et al. Surgical interbody research group– radiographic assessment of interbody fusion devices: fusion criteria for anterior lumbar interbody surgery. Neurosurg Focus 2001;10:E11. [12] Chen HH, Cheung HH, Wang WK, et al. Biomechanical analysis of unilateral fixation with interbody cages. Spine (Phila Pa 1976) 2005;30:E92–6. [13] Beringer WF, Mobasser JP. Unilateral pedicle screw instrumentation for minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus 2006;20:E4.
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[14] Choi UY, Park JY, Kim KH, et al. Unilateral versus bilateral percutaneous pedicle screw fixation in minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus 2013;35:E11. [15] Schwender JD, Holly LT, Rouben DP, et al. Minimally invasive transforaminal lumbar interbody fusion (tlif): technical feasibility and initial results. J Spinal Disord Tech 2005;18:S1–6. [16] Mobbs RJ, Sivabalan P, Li J. Minimally invasive surgery compared to open spinal fusion for the treatment of degenerative lumbar spine pathologies. J Clin Neurosci 2012;19:829–35. [17] Lawton CD, Smith ZA, Barnawi A, et al. The surgical technique of minimally invasive transforaminal lumbar interbody fusion. J Neurosurg Sci 2011;55:259–64. [18] Young S, Veerapen R, O’Laoire SA. Relief of lumbar canal stenosis using multilevel subarticular fenestrations as an alternative to wide laminectomy: preliminary report. Neurosurgery 1988;23:628–33. [19] Spetzger U, Bertalanffy H, Naujokat C, et al. Unilateral laminotomy for bilateral decompression of lumbar spinal stenosis. Part i: anatomical and surgical considerations. Acta Neurochir (Wein) 1997;139:392–6. [20] Spetzger U, Bertalanffy H, Reinges MH, et al. Unilateral laminotomy for bilateral decompression of lumbar spinal stenosis. Part ii: clinical experiences. Acta Neurochir (Wein) 1997;139:397–403. [21] Hong SW, Choi KY, Ahn Y, et al. A comparison of unilateral and bilateral laminotomies for decompression of l4–l5 spinal stenosis. Spine (Phila Pa 1976) 2011;36:E172–8. [22] Poletti CE. Central lumbar stenosis caused by ligamentum flavum: unilateral laminotomy for bilateral ligamentectomy: preliminary report of two cases. Neurosurgery 1995;37:343–7. [23] Weiner BK, Walker M, Brower RS, et al. Microdecompression for lumbar spinal canal stenosis. Spine (Phila Pa 1976) 1999;24:2268–72. [24] Costa F, Sassi M, Cardia A, et al. Degenerative lumbar spinal stenosis: analysis of results in a series of 374 patients treated with unilateral laminotomy for bilateral microdecompression. J Neurosurg Spine 2007;7:579–86.
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
Contents lists available at ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Clinical Study
Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion Xiaolong Shen, Hailong Zhang, Xin Gu, Guangfei Gu, Xu Zhou, Shisheng He ⇑ Department of Orthopedics, Shanghai Tenth People’s Hospital, Tongji University School of Medicine, 301 Yanchang Road, Shanghai 200072, China
a r t i c l e
i n f o
Article history: Received 14 August 2013 Accepted 16 November 2013 Available online xxxx Keywords: Minimally invasive Spinal fusion TLIF Unilateral pedicle screw fixation
a b s t r a c t Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) has become an increasingly popular method of lumbar arthrodesis. However, there are few published studies comparing the clinical outcomes between unilateral and bilateral instrumented MIS TLIF. Sixty-five patients with degenerative lumbar spine disease were enrolled in this study. Thirty-one patients were randomized to the unilateral group and 34 to the bilateral group. Recorded demographic data included sex, age, preoperative diagnosis, and degenerated segment. Operative time, blood loss, hospital stay length, complication rates, and fusion rates were also evaluated. The Oswestry Disability Index (ODI) score and Visual Analog Scale (VAS) pain score data were obtained. All patients were asked to follow-up at 3 and 6 months after surgery, and once every 6 months thereafter. The mean follow-up was 26.6 months (range 18–36 months). The two groups were similar in sex, age, preoperative diagnosis, and operated level. The unilateral group had significantly shorter operative time, lower blood loss, and shorter hospital time than the bilateral group. The average postoperative ODI and VAS scores improved significantly in each group. No significant differences were found between the two groups in relation to ODI and VAS. All patients showed evidence of fusion at 12 months postoperatively. The total fusion rate, screw failure, and general complication rate were not significantly different. Results showed that single-level MIS TLIF with unilateral pedicle screw fixation would be sufficient in the management of preoperatively stable patients with lumbar degenerative disease. It seems that MIS TLIF with unilateral pedicle screw instrumentation is a better choice for single-level degenerative lumbar spine disease. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction A large number of techniques have been developed for lumbar spinal fusion. Interbody fusion has become widely popular because it provides a large surface area for fusion with the graft under compression. Harms first described the transforaminal lumbar interbody fusion (TLIF) technique with cage fusion that, due to the lateral approach to the disc space, reduced the amount of thecal sac and nerve root retraction required [1]. Although TLIF is a unilateral procedure, it is usually combined with posterior bilateral pedicle screw fixation. The TLIF procedure allows a single point of access to be used for interbody fusion and posterior instrumentation. It preserves the anterior longitudinal ligament and a major portion of the posterior ligament complex with minimal compromise of spinal stability. However the need for paraspinal muscle dissection and retraction remains a drawback that can lead to muscle denervation, atrophy and consequently persistent low back ⇑ Corresponding author. Tel.: +86 138 1783 0920; fax: +86 021 6630 6549. E-mail address: [email protected] (S. He).
pain [2]. Advances in lumbar fusion techniques have concentrated on reducing soft-tissue damage and neural retraction while maintaining the ability to achieve neural decompression and interbody fusion. Minimally invasive (MIS) TLIF was introduced by Foley et al. in 2002 [3]. It has become an increasingly popular method of lumbar arthrodesis. Recent technological advances in spinal instrumentation have culminated in the development of MIS TLIF with unilateral pedicle screw fixation [4]. The potential shortfall is an insufficiently stable construct that may result in a higher incidence of instrumentation failure. A higher incidence of nonunion may also be a risk. Biomechanical studies have shown that unilateral fixation after TLIF provided less rotational stability and stiffness than bilateral pedicle screw fixation [5]. Slucky et al. reported that the unilateral pedicle screw construct provided only half of the improvement in stiffness compared with bilateral constructs and allowed for significant off-axis rotational motion after TLIF [6]. However, several studies have also reported that unilateral pedicle screw fixation is as effective as bilateral pedicle screw fixation in lumbar spinal fusion [7,8]. There are few published studies on clin-
http://dx.doi.org/10.1016/j.jocn.2013.11.055 0967-5868/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
2
X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
ical outcomes of MIS TLIF with unilateral pedicle screw fixation, even though perioperative and postoperative complications and surgical outcomes have been well described in the literature [9]. The purpose of this prospective study was to compare the clinical outcomes between unilateral and bilateral instrumented MIS TLIF. 2. Patients and methods 2.1. Patients Sixty-five patients with single-level degenerative lumbar spine disease at L4–L5 or L5–S1 were recruited from July 2009 to June 2011. All patients had suffered from low back pain, severe unilateral radicular pain or neurological symptoms. All patients underwent at least 6 months of conservative management before surgery, with no response or an inadequate response. All patients were confirmed to have single-level degenerative lumbar spine disease with plain radiographs, CT scans, and MRI. They were randomly divided into two groups using a computer-generated number list. Thirty-one patients were assigned to MIS TLIF with unilateral pedicle screw fixation (Group A, Fig. 1), and 34 were assigned to MIS TLIF with bilateral pedicle screw fixation (Group B, Fig. 2). Demographics and procedure data for the two groups are listed in Table 1. In this study, a stable level was defined as a degenerative disc without spondylolisthesis. Patients were included if they were aged between 40–70 years and only had one level of degenerative disease. Patients were excluded if they were elderly (>70 years old), had isthmic or degenerative spondylolisthesis, were significantly obese (body mass index P35 kg/m2), had undergone previous lumbar fusion or discectomy, or had multi-level disease. 2.2. Surgical approaches After induction of general endotracheal anesthesia, patients were placed in the prone position on a radiolucent operating table, with the abdomen hanging free and slight flexion of the lower limbs. C-arm fluoroscopy was used to position the diseased segments and to determine the incision site. A 2–2.5 cm incision was made overlying the affected level and continued down through the posterior lumbar fascia. Sequential dilators were introduced until a METRx tubular retractor (Medtronic Sofamor Danek,
Fig. 1. (Left) Anteroposterior and (right) lateral CT scan showing unilateral pedicle screw fixation in lumbar spinal fusion.
Fig. 2. (Left) Anteroposterior and (right) lateral CT scan showing bilateral pedicle screw fixation in lumbar spinal fusion. Table 1 Demographic data and distribution of fused levels in the two study groups with unilateral pedicle screw fixation (Group A) or bilateral pedicle screw fixation (Group B)
Patients Sex (female/male) Age, years Mean height, cm Mean weight, kg Diagnosis Unilateral lumbar disc herniation Foraminal stenosis Discogenic low back pain Level of fusion L4–L5 L5–S1
Group A
Group B
31 14/17 57.3 ± 11.7 169.5 ± 9.4 68.8 ± 8.4
34 18/16 58.9 ± 10.1 171.2 ± 10.6 69.6 ± 9.5
10 15 6
12 18 4
15 16
15 19
p value 0.462 0.153 0.317 0.462 0.579
0.730
Data are presented as mean ± standard deviation or number.
Memphis, TN, USA) was placed. The operating microscope was moved into the field and the laminar edge was identified. The isthmus, the unilateral posterior arch of the vertebrae and the inferior joint facet of the subjacent vertebra were removed. This bone was kept for use as an autograft during the interbody fusion. The thecal sac and traversing nerve root were identified. The operating table was tilted down contralaterally and the microscope was angled toward the medial side. The deep cortical surface of the contralateral lamina was removed and drilling was extended to the contralateral lateral recess and foramen. Finally, the ligamentum flavum and its bony attachment edge were removed. Then, a thorough discectomy and endplate preparation were performed. The disc space was packed with autograft bone. A polyetheretherketone (PEEK) interbody graft (Capstone, Medtronic Sofamor Danek) was then obliquely inserted and placed in the center of the disc space. The entire procedure was carried out using the surgical microscope with variable magnification and sufficient lighting of the operative field. Once the interbody discectomy and arthrodesis were completed, the working channel was removed. With the assistance of the Sextant system (Medtronic Sofamor Danek), percutaneous lumbar pedicle screws were inserted. The screws were compressed over the interbody cage to provide a degree of segmental lordosis and compression across the cage. In Group B, contralateral percutaneous pedicle screw fixation was also performed. All procedures
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
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were carried out by the same surgeon (S. H.) using the method described in detail by Foley and Gupta [10]. 2.3. Outcome assessment The demographic data captured included sex, age, preoperative diagnosis, and degenerated segment. Operative time, blood loss, hospital stay length, complication rates, and fusion rates were also evaluated. The Oswestry Disability Index (ODI) score and Visual Analog Scale (VAS) pain score data were obtained for all patients 24 hours before the operation and at each follow-up visit. CT scans were used to evaluate fusion at 6 and 12 months after surgery. Fusion was defined as an absence of radiolucent lines covering >50% of either implant, translation of 63 mm and angulation <5° on flexion–extension radiographs, and continuous trabecular bone growth connecting the vertebral bodies on CT scan cut [11]. 2.4. Statistical analysis The Statistical Package for the Social Sciences version 16.0 (SPSS, Chicago, IL, USA) was used for the statistical calculations. Demographic data were compared by means of a chi-squared test. Patient age, operative time, blood loss and hospital time were analyzed by unpaired Student t-tests. Analysis of variance (repeated measures design) was used to compare VAS and ODI. In all analyses, p values <0.05 were considered statistically significant. 3. Results 3.1. Patient characteristics The mean follow-up was 26.6 months, ranging from 18 to 36 months. There were no statistically significant differences between the two groups in terms of demographic data (Table 1). 3.2. Operative parameters and clinical outcomes The unilateral group (Group A) had a significantly shorter operative time, less blood loss, and shorter hospital time compared with the bilateral group (Table 2). All patients showed evidence of fusion 12 months postoperatively (Fig. 3). The total fusion rate, screw failure, and general complication rate were not significantly different between the groups. At 6 month follow-up, radiological evidence showed that 96.8% (30 of 31) of patients in Group A and 100.0% of patients in Group B achieved successful fusion, with no significant difference (p > 0.05). One patient in Group A did not achieve successful fusion at 6 months, but he achieved solid fusion at his 12 month follow-up. During the follow-up period, screw loosening was not observed in any patient. Neither group showed any signs of screw breakages or infection. The average postoperative VAS and ODI scores improved significantly in each group. No significant differences were found between the two groups in relation to ODI and VAS at any time (Table 3). Table 2 Operative data from the two groups undergoing minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation (Group A) or bilateral pedicle screw fixation (Group B)
Operative time, minutes Blood loss, ml Hospital time, days Complications Fusion
Group A
Group B
p value
101.4 ± 27.2 52.5 ± 39.7 4.4 ± 1.5 4 30/31
143.1 ± 22.5 106.3 ± 53.8 6.6 ± 2.1 3 34/34
0.000 0.000 0.000 0.314 0.662
Data are presented as mean ± standard deviation or number.
Fig. 3. (A) Preoperative axial CT scan showing separation of the posterior ring apophysis of the L5 vertebrae, and the bone intruding into the spinal canal. (B) Preoperative axial T2-weighted MRI of the same patient showing discoligamentous disruption and retropulsion of disc material into the left side of spinal canal. (C) Sagittal CT image reconstruction 12 months after surgery showing that solid fusion was achieved. (D) Coronal CT scan demonstrating solid fusion. (E) Axial CT scan demonstrating placement of an interbody cage with unilateral pedicle screw instrumentation.
3.3. Complications One patient in Group A developed root irritation due to the violation of the pedicle cortex by a screw. A screw in Group B had been positioned in a parapedicular position, falling into the spinal canal, without any symptomatic consequence. This complication called for immediate rerouting of screws. One patient in Group A experienced incomplete relief of radicular symptoms. This patient was treated with traditional Chinese medicine and the radiculopathy improved with time. Two patients in Group A and one patient in group B suffered dural tear. These patients were managed with bed rest for 6–10 days with no long-term sequelae. There was one case of urinary tract infection in Group B. No wound infections occurred in either group (Table 2).
4. Discussion Kabins et al. reported that fusion results with unilateral variable screw placement instrumentation to single-level (L4–L5) fusion
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
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X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
Table 3 Pain and functional evaluation outcomes of Visual Analogue Scale and Oswestry Disability Index scores in patients undergoing minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation (Group A) or bilateral pedicle screw fixation (Group B) Group A
VAS ODI (%)
Group B
Preop
3m
12 m
18 m
Preop
3m
12 m
18 m
6.8 ± 1.6 56.56 ± 19.12
2.4 ± 1.8 27.46 ± 15.82
2.1 ± 1.0 23.93 ± 16.47
2.0 ± 1.3 21.38 ± 14.33
7.2 ± 2.1 51.58 ± 16.38
2.3 ± 1.6 25.96 ± 16.51
2.2 ± 1.9 22.47 ± 16.22
2.2 ± 1.4 22.84 ± 15.65
Data are presented as mean ± standard deviation. m = months, ODI = Oswestry Disability Index, Preop = preoperatively, VAS = Visual Analogue Scale.
were nearly identical to those with bilateral instrumentation [7]. Furthermore, Suk et al. reported that unilateral pedicle screw fixation was as effective as bilateral pedicle screw fixation in lumbar spinal fusion, independent of the number of fusion segments (one or two segments) or pedicle screw systems used [8]. In spinal fusion surgery, the need for unilateral or bilateral instrumentation is a controversial issue. Biomechanical studies have demonstrated that unilateral fixation after TLIF provides less rotational stability and stiffness than bilateral pedicle screw fixation [5,6]. However, extensive destruction of tissue structures, which exacerbates the instability of the spine, was used in these in vitro biomechanical studies. In addition, the maintenance of lumbar stability simply relied on unilateral pedicle screw fixation without any support device. Despite data suggesting the inferiority of unilateral pedicle screw fixation after TLIF in biomechanical studies, many clinical trials have reported good results of unilateral pedicle screw fixation after TLIF [8,12]. In the MIS spine surgery literature, a few reports and studies have demonstrated good outcomes and fusion rates following unilateral pedicle screw fixation during MIS TLIF [9,13]. At the time of writing, the general consensus is that unilateral instrumentation should be confined to a single-level fusion and not be extended to multi-level fusion because of its inadequate fixation strength. Suk et al. found a lower fusion rate (91.5%) for unilateral pedicle screw fixation compared to bilateral pedicle screw fixation (97.5%) in lumbar spinal fusion, although this difference was not statistically significant [8]. In our study, we found that good outcomes and similar fusion rates were achieved with unilateral and bilateral instrumentation for MIS TLIF. Our fusion rate for unilateral pedicle screw fixation is higher than previous studies [8,14]. During the operation, autograft bone was tightly packed into the disc space. A PEEK interbody graft was then obliquely inserted and placed in the center of the disc space (Fig. 3C, D). Thus we speculate that adequate amounts of autograft bone may explain the differences between reported fusion rates. One of the drawbacks of open TLIF is that detachment and retraction of paraspinal muscle and excessive intraoperative dissection can result in denervation, atrophy and irreversible muscle injury. With the advent of MIS techniques to achieve spinal fusion, it has become essential to use minimal instrumentation without compromising the final stiffness of the spine. Reduced soft tissue dissection allows for early recovery and rehabilitation of the patient [15–17]. It has also been reported that unilateral MIS TLIF procedure using unilateral pedicle screw instrumentation instead of bilateral pedicle screws could further reduce tissue injury and blood loss [13]. We found that unilateral pedicle screw fixation after MIS TLIF led to shorter operative time, less blood loss, and shorter hospital time compared to bilateral pedicle screw fixation, which is consistent with previous studies. This procedure provided excellent clinical results during a middle-term follow-up period. Bilateral decompression via a unilateral approach for lumbar canal stenosis was initially described by Young et al. [18]. Studies on cadaver spine specimens proved the feasibility of this unilateral approach [19]. Postoperative clinical improvement and radiological findings demonstrated that bilateral ligamentectomy and
recess decompression can be adequately and successfully achieved via the unilateral approach [20]. CT scans showed significant enlargement of the cross-sectional area of the dural sac in patients after surgery [21]. In this technique, the thecal sac and bilateral nerve roots can be decompressed without injuring the supra or inter-spinous ligament complex and the contralateral paraspinal muscles [22,23]. The use of a unilateral laminotomy for bilateral decompression can result in less injury to the support structures of the spine. However, some authors have reported that this method can lead to lumbar instability which requires spinal fusion [21,24]. A total facetectomy was carried out in our study, so we considered fixation and fusion was necessary in these patients. In our study, MIS TLIF and bilateral decompression via a unilateral laminotomy were successfully performed in patients with degenerative stenosis. This procedure afforded a persistently satisfactory outcome for lumbar degenerative disease even over follow-up periods longer than 18 months. We carried out MIS bilateral decompression under a microscope using a unilateral approach in patients with acquired spinal stenosis, whose symptoms were unilateral or bilateral. All patients in both groups achieved solid fusion at 12 month follow-up. More importantly, no significant scoliosis was found in the unilateral group during the follow-up period. Compared to previous studies, this procedure has the advantages of both MIS surgery and unilateral pedicle screw instrumentation. It seems that MIS TLIF with unilateral pedicle screw instrumentation is the optimal treatment choice for single-level degenerative lumbar spine disease. 4.1. Study limitations In our middle-term follow-up study, we found that good outcomes and similar fusion rates were achieved with unilateral and bilateral instrumentation for MIS TLIF. Longer-term studies involving a larger sample are needed to validate the long-term efficacy of MIS TLIF with unilateral pedicle screw instrumentation.
5. Conclusions MIS TLIF with unilateral pedicle screw fixation had a significantly shorter operative time, less blood loss, and shorter hospital length of stay compared to MIS TLIF with bilateral pedicle screw fixation. No significant differences were found between the two groups in relation to ODI and VAS scores. The total fusion rate, screw failure, and general complication rate were not significantly different between the groups. It appears that MIS TLIF with unilateral pedicle screw instrumentation is the optimal treatment choice for single-level degenerative lumbar spine disease.
Conflicts of Interest/Disclosures The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055
X. Shen et al. / Journal of Clinical Neuroscience xxx (2014) xxx–xxx
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Please cite this article in press as: Shen X et al. Unilateral versus bilateral pedicle screw instrumentation for single-level minimally invasive transforaminal lumbar interbody fusion. J Clin Neurosci (2014), http://dx.doi.org/10.1016/j.jocn.2013.11.055