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Commentary: Is bilateral pedicle screw fixation necessary when performing a transforaminal lumbar interbody fusion? An analysis of clinical outcomes, radiographic outcomes, and cost
The Spine Journal 12 (2012) 216–217
Commentary
Commentary: Is bilateral pedicle screw fixation necessary when performing a transforaminal lumbar interbody fusion? An analysis of clinical outcomes, radiographic outcomes, and cost Jeffrey A. Rihn, MD* Department of Orthopaedic Surgery, Thomas Jefferson University Hospital, The Rothman Institute, Philadelphia, PA 19107, USA Received 17 February 2012; accepted 3 March 2012
COMMENTARY ON: Xue H, Tu Y, Cai M. Comparison of unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in degenerative lumbar diseases. Spine J 2012;12:209–15 (in this issue).
The transforaminal lumbar interbody fusion (TLIF) procedure allows for an anterior and posterolateral fusion through a single posterior approach. Furthermore, the approach to the intervertebral space is more lateral than the traditional posterior lumbar interbody fusion approach and theoretically minimizes retraction of the traversing nerve when preparing the interbody space and placing the interbody cage and/or bone graft. Traditionally, TLIF procedure is performed through an open approach, with the use of bilateral pedicle screw/rod fixation to provide stability as the fusion heals. More recently, a ‘‘minimally invasive’’ approach to the TLIF procedure has been proposed as a safe and effective alternative. Both bilateral and unilateral pedicle screw fixation techniques have been described when using a minimally invasive surgery (MIS) approach [1,2]. The unilateral construct is attractive because, other things being equal, it avoids soft-tissue disruption of the contralateral side, may take less time, and can be associated with lower implant costs. The potential downside 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. Two separate cadaveric biomechanical studies DOI of original article: 10.1016/j.spinee.2012.01.010. FDA device/drug status: Approved (lumbar pedicle screws). Author disclosures: JAR: Other Office: Federation of Spine Associations (Nonfinancial, President); Grants: Depuy Spine Inc (D, Paid directly to institution/employer). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. * Corresponding author. Thomas Jefferson University Hospital, The Rothman Institute, Philadelphia, PA 19107, USA. Tel.: (267) 339-3500. E-mail address: [email protected] (J.A. Rihn) 1529-9430/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2012.03.001
have shown that unilateral fixation after a TLIF procedure provides less rotational stability and stiffness than bilateral pedicle screw fixation, but whether the more rigid construct is needed was not addressed [3,4]. Two randomized controlled clinical trials showed no clinical benefit from bilateral over unilateral instrumentation in posterolateral fusion alone [5,6]. The question however, for the TLIF operation, remains whether there is a difference in long-term clinical and/or radiographic outcome when comparing unilateral with bilateral fixation. If in fact, as shown by Suk et al. and Fernandez-Fairen et al. in posterolateral fusion, no difference exists in long-term radiographic or clinical outcome between the two constructs, the unilateral construct would be preferable to those performing open or MIS TLIF procedures and would provide more value (ie, less cost but no difference in outcome). The present study entitled ‘‘Comparison of unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in degenerative lumbar diseases’’ attempts to answer the question posed above, that is, are there small differences in clinical and radiographic outcomes between unilateral and bilateral pedicle screw fixation [5]. The comparison really is between minimally invasive TLIF with unilateral fixation and open TLIF with bilateral fixation. There was a difference in the approach to surgery between groups in addition to the difference in fixation. One potential limitation of this study is the patient group size. The authors did not present a power analysis and therefore it is difficult to determine whether the study was adequately powered to detect small- or medium-sized differences between the two groups. The end points to be considered when comparing these two groups are instrumentation
J.A. Rihn / The Spine Journal 12 (2012) 216–217
failure and nonunion, two outcomes that could theoretically be more likely to occur with unilateral fixation. The problem with these end points is that their occurrence is relatively rare, thus requiring relatively large patient numbers in each group to have adequate power to detect differences in the rate of such outcomes. In the present study, the fusion rate was 95.4% (95% confidence interval [CI], 83.7, 99.6) in the bilateral group compared with 91.9% (95% CI, 78.0, 97.94) with wide CIs. Similarly, the rate of screw failure while low in both groups was lower in patients who underwent bilateral fixation. No corroborative superiority in clinical outcomes was detected. The radiological fusion differences were not found to be ‘‘significant’’ (Fisher exact test, two-tailed test, p5.658), but, again, without a power analysis it is difficult to know whether the study was adequately powered to detect very small differences. It should be noted that, although the authors do include implant cost in their analysis, this is not a cost-effectiveness study (nor do the authors imply that it is). It is not entirely clear how the cost data that are provided in the study benefit the reader. It is intuitive that implant cost associated with unilateral fixation will be less than that associated with bilateral fixation. When discussing cost, it is important to consider the question: cost to whom? In China, where the study was performed, implants are often directly purchased by the patient’s family. In the current payment system in the United States, the hospital, institution, or less commonly the insurer but rarely the patient would realize the reported difference in implant cost. To adequately study the costeffectiveness of one technique compared with the other, it is preferable that direct costs, including those related to differences in operating room time, implant costs, and reoperation rates (for nonunion and/or malpositioned instrumentation), as well as indirect costs (eg, return to work and loss of productivity) be considered. Patients with a minimally invasive approach with unilateral approach may go back to work earlier and have less implant expenses. But even a very small increase in rates of reoperation could overwhelm earlier system saving. These aspects of cost analysis are important to consider when planning a costeffectiveness study. The authors of the present study present interesting findings that set the stage for potentially larger multicenter
217
studies to look at the questions of unilateral versus bilateral pedicle screw/rod fixation and fusion not only in TLIF but also in posterolateral fusion as well. This adds to the ongoing debate of instrumentation versus no instrumentation for lumbar fusion, with instrumentation adding considerable cost and risk, likely improving fusion rates but having an unclear effect on clinical outcome [7,8]. A recent study by Kotil et al. [9] compared TLIF with and without posterior instrumentation in patients without evidence of spinal instability and found that the addition of a posterior pedicle screw/rod construct provided similar outcomes to TLIF performed without any posterior instrumentation. As the quest to define the value of instrumentation in lumbar fusion continues, adequately powered studies that include direct and indirect cost measures and outcome measures with longterm follow-up are needed. References [1] Deutsch H, Musacchio MJ Jr. Minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation. Neurosurg Focus 2006;20:E10. [2] Villavicencio AT, Burneikiene S, Nelson EL, et al. Safety of transforaminal lumbar interbody fusion and intervertebral recombinant human bone morphogenetic protein-2. J Neurosurg Spine 2005;3:436–43. [3] 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 2004;29:E65–70. [4] 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. [5] Suk KS, Lee HM, Kim NH, Ha JW. Unilateral versus bilateral pedicle screw fixation in lumbar spinal fusion. Spine 2000;25:1843–7. [6] Fernandez-Fairen M, Sala P, Ramirez H, Gil J. A prospective randomized study of unilateral versus bilateral instrumented posterolateral lumbar fusion in degenerative spondylolisthesis. Spine 2007;32: 395–401. [7] Fischgrund JS, Mackay M, Herkowitz HN, et al. 1997 Volvo Award winner in clinical studies. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation. Spine 1997;22:2807–12. [8] Abdu WA, Lurie JD, Spratt KF, et al. Degenerative spondylolisthesis: does fusion method influence outcome? Four-year results of the spine patient outcomes research trial. Spine 2009;34:2351–60. [9] Kotil K, Ali Akcetin M, Savas Y. Clinical and radiologic outcomes of TLIF applications with or without pedicle screw: a double center prospective pilot comparative study. J Spinal Disord Tech 2012 Feb 8 [Epub ahead of print].
Commentary
Commentary: Is bilateral pedicle screw fixation necessary when performing a transforaminal lumbar interbody fusion? An analysis of clinical outcomes, radiographic outcomes, and cost Jeffrey A. Rihn, MD* Department of Orthopaedic Surgery, Thomas Jefferson University Hospital, The Rothman Institute, Philadelphia, PA 19107, USA Received 17 February 2012; accepted 3 March 2012
COMMENTARY ON: Xue H, Tu Y, Cai M. Comparison of unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in degenerative lumbar diseases. Spine J 2012;12:209–15 (in this issue).
The transforaminal lumbar interbody fusion (TLIF) procedure allows for an anterior and posterolateral fusion through a single posterior approach. Furthermore, the approach to the intervertebral space is more lateral than the traditional posterior lumbar interbody fusion approach and theoretically minimizes retraction of the traversing nerve when preparing the interbody space and placing the interbody cage and/or bone graft. Traditionally, TLIF procedure is performed through an open approach, with the use of bilateral pedicle screw/rod fixation to provide stability as the fusion heals. More recently, a ‘‘minimally invasive’’ approach to the TLIF procedure has been proposed as a safe and effective alternative. Both bilateral and unilateral pedicle screw fixation techniques have been described when using a minimally invasive surgery (MIS) approach [1,2]. The unilateral construct is attractive because, other things being equal, it avoids soft-tissue disruption of the contralateral side, may take less time, and can be associated with lower implant costs. The potential downside 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. Two separate cadaveric biomechanical studies DOI of original article: 10.1016/j.spinee.2012.01.010. FDA device/drug status: Approved (lumbar pedicle screws). Author disclosures: JAR: Other Office: Federation of Spine Associations (Nonfinancial, President); Grants: Depuy Spine Inc (D, Paid directly to institution/employer). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. * Corresponding author. Thomas Jefferson University Hospital, The Rothman Institute, Philadelphia, PA 19107, USA. Tel.: (267) 339-3500. E-mail address: [email protected] (J.A. Rihn) 1529-9430/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2012.03.001
have shown that unilateral fixation after a TLIF procedure provides less rotational stability and stiffness than bilateral pedicle screw fixation, but whether the more rigid construct is needed was not addressed [3,4]. Two randomized controlled clinical trials showed no clinical benefit from bilateral over unilateral instrumentation in posterolateral fusion alone [5,6]. The question however, for the TLIF operation, remains whether there is a difference in long-term clinical and/or radiographic outcome when comparing unilateral with bilateral fixation. If in fact, as shown by Suk et al. and Fernandez-Fairen et al. in posterolateral fusion, no difference exists in long-term radiographic or clinical outcome between the two constructs, the unilateral construct would be preferable to those performing open or MIS TLIF procedures and would provide more value (ie, less cost but no difference in outcome). The present study entitled ‘‘Comparison of unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in degenerative lumbar diseases’’ attempts to answer the question posed above, that is, are there small differences in clinical and radiographic outcomes between unilateral and bilateral pedicle screw fixation [5]. The comparison really is between minimally invasive TLIF with unilateral fixation and open TLIF with bilateral fixation. There was a difference in the approach to surgery between groups in addition to the difference in fixation. One potential limitation of this study is the patient group size. The authors did not present a power analysis and therefore it is difficult to determine whether the study was adequately powered to detect small- or medium-sized differences between the two groups. The end points to be considered when comparing these two groups are instrumentation
J.A. Rihn / The Spine Journal 12 (2012) 216–217
failure and nonunion, two outcomes that could theoretically be more likely to occur with unilateral fixation. The problem with these end points is that their occurrence is relatively rare, thus requiring relatively large patient numbers in each group to have adequate power to detect differences in the rate of such outcomes. In the present study, the fusion rate was 95.4% (95% confidence interval [CI], 83.7, 99.6) in the bilateral group compared with 91.9% (95% CI, 78.0, 97.94) with wide CIs. Similarly, the rate of screw failure while low in both groups was lower in patients who underwent bilateral fixation. No corroborative superiority in clinical outcomes was detected. The radiological fusion differences were not found to be ‘‘significant’’ (Fisher exact test, two-tailed test, p5.658), but, again, without a power analysis it is difficult to know whether the study was adequately powered to detect very small differences. It should be noted that, although the authors do include implant cost in their analysis, this is not a cost-effectiveness study (nor do the authors imply that it is). It is not entirely clear how the cost data that are provided in the study benefit the reader. It is intuitive that implant cost associated with unilateral fixation will be less than that associated with bilateral fixation. When discussing cost, it is important to consider the question: cost to whom? In China, where the study was performed, implants are often directly purchased by the patient’s family. In the current payment system in the United States, the hospital, institution, or less commonly the insurer but rarely the patient would realize the reported difference in implant cost. To adequately study the costeffectiveness of one technique compared with the other, it is preferable that direct costs, including those related to differences in operating room time, implant costs, and reoperation rates (for nonunion and/or malpositioned instrumentation), as well as indirect costs (eg, return to work and loss of productivity) be considered. Patients with a minimally invasive approach with unilateral approach may go back to work earlier and have less implant expenses. But even a very small increase in rates of reoperation could overwhelm earlier system saving. These aspects of cost analysis are important to consider when planning a costeffectiveness study. The authors of the present study present interesting findings that set the stage for potentially larger multicenter
217
studies to look at the questions of unilateral versus bilateral pedicle screw/rod fixation and fusion not only in TLIF but also in posterolateral fusion as well. This adds to the ongoing debate of instrumentation versus no instrumentation for lumbar fusion, with instrumentation adding considerable cost and risk, likely improving fusion rates but having an unclear effect on clinical outcome [7,8]. A recent study by Kotil et al. [9] compared TLIF with and without posterior instrumentation in patients without evidence of spinal instability and found that the addition of a posterior pedicle screw/rod construct provided similar outcomes to TLIF performed without any posterior instrumentation. As the quest to define the value of instrumentation in lumbar fusion continues, adequately powered studies that include direct and indirect cost measures and outcome measures with longterm follow-up are needed. References [1] Deutsch H, Musacchio MJ Jr. Minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation. Neurosurg Focus 2006;20:E10. [2] Villavicencio AT, Burneikiene S, Nelson EL, et al. Safety of transforaminal lumbar interbody fusion and intervertebral recombinant human bone morphogenetic protein-2. J Neurosurg Spine 2005;3:436–43. [3] 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 2004;29:E65–70. [4] 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. [5] Suk KS, Lee HM, Kim NH, Ha JW. Unilateral versus bilateral pedicle screw fixation in lumbar spinal fusion. Spine 2000;25:1843–7. [6] Fernandez-Fairen M, Sala P, Ramirez H, Gil J. A prospective randomized study of unilateral versus bilateral instrumented posterolateral lumbar fusion in degenerative spondylolisthesis. Spine 2007;32: 395–401. [7] Fischgrund JS, Mackay M, Herkowitz HN, et al. 1997 Volvo Award winner in clinical studies. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation. Spine 1997;22:2807–12. [8] Abdu WA, Lurie JD, Spratt KF, et al. Degenerative spondylolisthesis: does fusion method influence outcome? Four-year results of the spine patient outcomes research trial. Spine 2009;34:2351–60. [9] Kotil K, Ali Akcetin M, Savas Y. Clinical and radiologic outcomes of TLIF applications with or without pedicle screw: a double center prospective pilot comparative study. J Spinal Disord Tech 2012 Feb 8 [Epub ahead of print].