The Spine Journal
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Clinical Study
Minimally invasive transforaminal lumbar interbody fusion: one surgeon’s learning curve Sreeharsha V. Nandyala, BA, Steve J. Fineberg, MD, Miguel Pelton, BS, Kern Singh, MD* Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite 400, Chicago, IL 60612, USA Received 9 May 2012; revised 26 June 2013; accepted 23 August 2013
Abstract
BACKGROUND CONTEXT: The published literature has not characterized the surgeon’s learning curve with the technically demanding technique of a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). PURPOSE: To characterize based on intra- and perioperative parameters, the learning curve for one spine surgeon during his initial phases of performing an MIS TLIF. STUDY DESIGN/SETTING: Retrospective analysis of a single institution and single surgeon experience with the unilateral MIS TLIF technique between July 2008 and April 2011. PATIENT SAMPLE: Sixty-five consecutive patients, with at least 1 year of follow-up, who underwent a unilateral, single-level, index MIS TLIF for the diagnosis of degenerative disk disease or lumbar spinal stenosis with grade I or II spondylolisthesis were analyzed based on data obtained from the medical records and postoperative imaging (computed tomography). OUTCOME MEASURES: Postoperative radiographic assessment of fusion at 1 year via computed tomography. Surgical parameters of surgical time (skin-skin, minutes), anesthesia time (induction-extubation, minutes), estimated blood loss (mL), intravenous fluids during surgery (mL), intraoperative complications (durotomy), and postoperative complications (pseudarthrosis, implant failure, malpositioned implants, graft-related complications) were also assessed. METHODS: The senior author’s first 100 consecutive MIS TLIFs were evaluated initially. Patients undergoing revision or multilevel surgery were excluded leaving a total of 65 consecutive primary MIS TLIFs. The first 33 patients were compared with the second 32 patients in terms of radiographic arthrodesis rates, surgical parameters, and intra-/postoperative complications. A two-tailed Student t test was used to assess for differences between the two cohorts where a p value of less than or equal to .05 denoting statistical significance. Pearson’s correlation coefficient was used to determine any association between the date of surgery and surgical time. RESULTS: Average surgical time, estimated blood loss, intraoperative fluids, and duration of anesthesia was significantly longer in the first cohort (p!.05). There were no significant differences in intraoperative complications (two durotomies in both groups) or length of stay. There was no significant difference in postoperative complications at final follow-up based on computed tomography analysis (11 vs. 9, p5.649). In the first cohort, these complications included two cases of radiographic pseudarthrosis: one case of graft migration and one case of medial pedicle wall violation necessitating two revision surgeries. There were two cases of pseudarthrosis and one case of an early surgical site infection identified in the second group requiring three revision surgeries. Last, four cases of neuroforaminal bone growth were demonstrated, two in each cohort. Pearson’s correlation coefficient demonstrated a negative correlation between the date of surgery and surgical time (r50.44; p!.001) estimated blood loss (r50.49; p!.001), duration of anesthesia (r50.41; p5.001), and intravenous fluids (r50.42; p5.001).
FDA device/drug status: Not Approved for this indication (rhBMP-2 use as a graft extender in the setting of MIS TLIF). Author disclosures: SVN: Nothing to disclose. SJF: Nothing to disclose. MP: Nothing to disclose. KS: Royalties: Stryker (D), Lippincott (C), Thieme (C), Consulting: Depuy (B), Stryker (B), Globus (B); Board of Directors: Vital 5, LLC (stock options, none). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. 1529-9430/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.08.045
Institutional review board approval was granted for this study (ORA number 10101108-IRB02). * Corresponding author. Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite 400, Chicago, IL 60612, USA. Tel.: (312) 432-2373; fax: (708) 492-5373. E-mail address: [email protected] (K. Singh)
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CONCLUSIONS: The MIS TLIF is a technically difficult procedure to the practicing spine surgeon with regard to intra- and perioperative parameters of surgical time, estimated blood loss, intravenous fluid, and duration of anesthesia. Operative time and proficiency improved with understanding the minimally invasive technique. Further studies are warranted to delineate the methods to minimize the complications associated with the learning curve. Ó 2013 Elsevier Inc. All rights reserved. Keywords:
MIS TLIF; Learning; Technique; Complications; Surgery
Introduction As minimally invasive surgical techniques become more popular, the need to understand factors that characterize proficiency in these procedures becomes paramount. Current literature supports that mastery of the open technique is necessary to successfully perform a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) [1]. Few studies have attempted to characterize the learning curve experience for an MIS TLIF. Proficiency measurements are characterized by plateaus in operative time, blood loss, accuracy of pedicle screw placement, and intraoperative and postoperative complications [2]. Most studies of the surgical learning curve are usually of a single surgeon’s experience and of relatively low numbers of patient cohorts [3]. Conclusions drawn from these analyses agree that larger number of patient samples and more publications of results are necessary to add to the growing literature of the surgical learning curve [4,5]. Minimally invasive transforaminal lumbar interbody fusion has been established as a viable alternative to the open procedure with less disruption of spinal anatomy [6–8]. Clear indications or contraindications for the minimally invasive approach may lie in the comfort and proficiency of the particular surgeon [9]. This study attempts to add to the growing literature of the surgical learning curve based on the experience of one board-certified/fellowship-trained spine surgeon.
Materials and methods After obtaining institutional review board approval, retrospective data were reviewed from the senior author’s (KS) first 100 patients undergoing a minimally invasive transforaminal lumbar interbody fusion. The experience began 3 years into the surgical practice. Patients were then excluded using the following criteria: revision cases and multilevel procedures, resulting in 65 patients. These first 65 patients were then divided into two equal groups: patients 1–33 and patients 34–65. Ages ranged from 26 to 79 years with a mean age of 59.2 years for the first half (patients 1–33, N533) and 54.2 years for the second half (patients 34–65, N532). All patients had at least 1 year of total follow-up with computed tomography (CT) scan analysis and complications were then analyzed. Every patient had a diagnosis of either degenerative disk disease
or grade I or II spondylolisthesis with stenosis. Demographic characteristics were similar in both groups based on the Charlson Comorbidity Index. Characteristics of both patient groups are presented in Table 1. Surgical technique A unilateral approach was undertaken through a paramedian (4.5 cm lateral to the midline) skin incision using the Wiltse technique under fluoroscopy. After incising the skin and fascia, a plane was developed between the multifidus and longissimus muscles, whereby the pathway to the spine was enlarged by sequential dilators. A high-speed burr was used to remove the facet and pars. After exiting and traversing nerve roots were identified and completely visualized, a high speed burr was also used to complete the laminectomy. Local bone graft that had been obtained from the laminectomy and facetectomy was collected in a bone trap. The interbody space was identified under fluoroscopic imaging. Sequential end plate cutters were used to prepare the end plates. An appropriately sized DePuy Concorde cage (DePuy Spine, Raynham, MA, USA) was filled with either 4.2 mg (small kit) or 12 mg (large kit) of rhBMP-2, along with 5 mL bone marrow aspirate from the cannulated pedicle and local bone graft. BMP was used as an ‘‘off-label’’ application. Local bone was also placed anterior to the cage in the intervertebral space. The cage was then gently impacted obliquely into the intervertebral space. Unilateral pedicle screws were placed percutaneously over a guide wire. A rod was placed percutaneously through a separate stab incision and brought into the gap between the screw heads and locking nuts. The course of the rod was confirmed using anteroposterior and lateral fluoroscopy. Once in place, the screws were compressed along the rod and the nuts were tightened using a torque wrench. Compression was placed across the graft and the wound was then closed in layers. The laminectomy, bilateral decompression of the spinal canal, and transforaminal lumbar interbody fusion were performed with a 21-mm nonexpandable tube. No posterolateral fusion was performed. Midline muscular and ligamentous structures were all preserved during the procedure. Primary analysis The first 33 consecutive patients were compared with the second 32 consecutive patients based on perioperative outcomes measures (operative times; minutes), estimated
S.V. Nandyala et al. / The Spine Journal Table 1 Patient demographics Variable Gender Male Female Smoker Yes No Age at admission (yr) Diagnosis Degenerative disc disease Spondylolisthesis/stenosis Comorbidities Yes No Charlson Comorbidity Index
Patients 1–33 (N533)
Patients 34–65 (N532)
13 20
17 15
.267
6 27 59.24610.73
11 21 54.22615.49
.224
3 30
6 26
.260
5 28 1.660.89
3 29 2.660.58
.433
p Value
.132
.119
blood loss (EBL; mL), intravenous fluids during surgery (mL), length of stay (days), and anesthesia time from intubation to extubation (minutes). In addition, intraoperative complications (durotomy) and postoperative complications (infection, pseudarthrosis, implant failure, malpositioned implants) were compared between the two study groups. Adverse events related to the rhBMP-2 bone graft (neuroforaminal bone growth and cage migration/osteolysis) were also recorded. Last, CT scans were used at 12-month follow-up to assess for arthrodesis. Resultant needs for reoperations were also assessed in both patient groups. To assess for fusion, CT scans with contiguous 2.0-mm axial cuts perpendicular to the disc space (along with sagittal and coronal reconstructions) were obtained at the operative level at 6 and 12 months after the index surgery. CT assessment of fusion included three criteria: contiguous bridging bone on at least two consecutive coronal and sagittal reconstructions within the intervertebral space, blurring of the bone graft-endplate junction, and absence of a radiological cleft within the fusion mass. Noncontiguous
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bone formation, the presence of cage subsidence with end plate cyst formation, haloing around the cage and screws, or graft migration was defined as pseudarthrosis. CT scans were also used to determine any adverse events specific to the rhBMP-2, such as ectopic muscle ossification, laminar bone regrowth, neuroforaminal bone growth, and intra-/extradural ossification. Statistical analysis Microsoft Excel 2007 (Redmond, WA, USA) was used for data management and SPSS Inc. v17.0 Graduate Package (Chicago, IL, USA) was used for statistical analysis. Descriptive and frequency statistics were evaluated. Student t test was used to test for significance between the means of patients 1–33 and patients 34–65. Fisher’s exact probability test was used to evaluate differences between nonparametric data. Pearson’s correlation coefficient was used to characterize the relationship between surgical date and perioperative outcomes measures. Differences between groups were deemed to be statistically significant when p#.05.
Results Average surgical time, estimated blood loss, intraoperative fluids, and duration of anesthesia were significantly longer in the first cohort (p!.05) (Table 2). There were no significant differences in the intraoperative complications (two durotomies in each group) or length of stay. Additionally, there was no significant difference in the postoperative complications at the final 1-year follow-up based on CT analysis (7 vs. 5, p5.561). In the first group, complications consisted of four cases of implant screw displacements (three lateral wall breaches and one medial wall breach), two cases of pseudarthrosis, and one case of graft migration. The patient that sustained a medical wall breach underwent an immediate revision surgery 2 days after the
Table 2 Surgical variables Variable
Patients 1–33 (N533)
Patients 34–65 (N532)
p Value
Surgical time (skin-skin) Duration of anesthesia (induction-extubation) Intravenous fluids during surgery (mL) Estimated blood loss (mL) Length of stay (days) Intraoperative complications (number of patients) Intraoperative complication (lateral screw placement) Postoperative complications (number of patients) Neuroforaminal bone growth (number of patients) Total complication rate (%) Reoperations (number of patients, %) Arthrodesis (number of patients, %)
124 182 2,089 176 2.39 2* 3 4y 2 11 (33) 2 (6.1) 31 (94)
98 154 1,703 85 2.25 2* 2 3z 2 9 (28) 3 (9.4) 30 (94)
!.001 !.001 .004 !.001 .643 1.000 .667 .721 1.000 .649 .616 1.000
* Two cases of durotomies. y Two cases of pseudarthrosis, one case of graft migration, and one case of screw violation of the medial pedicle wall. z Two cases of pseudarthrosis and one case of surgical site infection.
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index operation. In the second group, two cases of implant screw displacements (lateral wall breaches), two cases of pseudarthrosis, and one early surgical site infection were identified (Table 2). The patient that developed the early surgical site infection returned to surgery on postoperative day 3 for a purulent wound infection. No persistent dural leaks were identified in either group. Pearson’s correlation coefficient demonstrated that the date of surgery and case number is related to decreased surgical time (r50.44; p!.001) (Fig. 1), decreased EBL (r50.50; p!.001) (Fig. 2), decreased duration of anesthesia (r50.41; p5.001) (Fig. 3), and decreased intravenous fluids (r50.42; p5.001) (Fig. 4). Graft related neuroforaminal bone growth was ascertained in both patient cohorts (2 vs. 2; p51.00). Overall, two patients in each cohort required reoperations to address the surgical complications. In addition to the these reoperation cases, one patient in each cohort required reoperation (ventral laminoforaminotomy) for pseudarthrosis causing pain and disability. Last, 12-month CT scan results demonstrated a 94% (n531) and 94% (n530) arthrodesis rates for the first and second patient cohorts, respectively.
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Fig. 2. Graph of the learning curve based on estimated blood loss plotted against case number.
Successful clinical outcomes of an MIS TLIF depend primarily on the surgeon’s experience and level of comfort with the procedure [1]. Attempts at an assessment of the learning curve are sparse in the surgical literature. Few studies acknowledge that the surgical learning curve is steep [10]. Others assert that trends toward better clinical outcomes are seen with an increased number of cases [11]. In an attempt to construct a learning curve model, our study created a multiple clinical parameter analysis of one surgeon’s experience with MIS TLIF procedures. Our results indicate that improvements in intraoperative clinical outcomes occur with increasing case numbers. Significant changes in surgical time and estimated blood loss
were identified between the first and second cohorts. Reasons for decreases in both parameters intuitively make sense. Efficiency is gained as the surgeon gains familiarity with surgical anatomy in the constrained workspace space of the tubular retractor system. Neal and Rosner recently examined the learning curve of a single resident’s experience with 28 patients undergoing a minimal access TLIF [3]. Although there was a trend toward decreases in operative times with an increase in case number, the results did not differ significantly between the two groups (p5.25). Various studies have reported on the surgical learning curve of other spinal surgeries. McLoughlin and Fourney assessed 52 patients undergoing a minimally invasive microdiscectomy using a tubular retractor system and found that by case 15, surgical time had reached a steady state of 60 minutes [12]. Hyde and Seits retrospectively reviewed 78 consecutive XLIF patients (Extreme Latera Interbody Fusion) in terms of perioperative and follow-up outcomes measures [13]. Over the course of the experience, both blood loss and operative time were reduced. However, in comparison of the first 10 patients with the last 10 patients,
Fig. 1. Graph of the learning curve based on surgical time plotted against case number.
Fig. 3. Graph of the learning curve based on duration of anesthesia plotted against case number.
Discussion
S.V. Nandyala et al. / The Spine Journal
Fig. 4. Graph of the learning curve based on intravenous fluids use plotted against case number.
the authors found no significant differences in blood loss (p5.554) and operative time (p5.355). It was concluded that although there was a slight learning curve associated with the procedure it was not significant. Because averages of operative times and blood losses were initially low at the onset of the study, there was not much deviation from these numbers. Additionally, this lack of significant differences between the first and last 10 patients suggested that the XLIF procedure (Extreme Latera Interbody Fusion) could be mastered relatively early. Importantly, the occurrence of intraoperative and postoperative complications did not differ between our two treatment groups. Two durotomies were noted in each cohort (n54, 5.3%, total). These intraoperative complications highlight the intrinsic difficulty of the MIS TLIF procedure, even as experience is gained and efficiency is improved. Postoperative complications in the first half included four cases of implant screw displacements (three lateral wall breaches and one medial wall breach), two cases of pseudarthrosis, and one case of graft migration. In the second half, two cases of implant screw displacements (lateral wall breaches), two cases of pseudarthrosis, and one early surgical site infection were identified. Although these differences are not significant (p5.561), clearly the potential exists in any case of MIS TLIF for implant screw displacement and pseudarthrosis. Additionally, our analysis suggests that this absence of significant differences in complications translated into no observable differences in the 12-month arthrodesis rates (94% vs. 94%) and reoperation rates (6.1% vs. 6.1%) between the two surgical cohorts (first and second group, respectively). Ways to minimize these inherent risks include proper end plate preparation, cage sizing, and the use of osteobiologic adjuvants [14]. Additionally, our study demonstrates that as the surgeon gains familiarity with the procedure these potential complications can be minimized. Several changes to the surgeon’s practice have been adopted to address the complications demonstrated in this study. At the time of this study, a large BMP kit was used.
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The surgeon now uses an extra-small BMP kit. For patients who develop a pseudarthrosis, those with a dynamic spondylolisthesis, a higher grade spondylolisthesis, or a large disc space will undergo a contralateral fixation. It should be noted that there is some variation in operative times in our analysis. Neal and Rosner speculate that this variation occurs after several cases of an MIS TLIF, because familiarity with the constrained work space is gained and the surgeon is more willing to attempt more challenging cases [3]. These difficult cases in turn translate to slight increases in operative time. Our analysis demonstrates this same effect with a small increase in surgical time. We attribute this increase to surgeon familiarity of the MIS anatomy resulting in a more thorough decompression and end plate preparation, two rate-limiting factors of the technique. Our intraoperative and postoperative results are similar to other reported studies on the MIS TLIF surgical technique. Scheufler et al. reported an average surgical time of 104 minutes and an average total blood loss of 55 mL over a span of 53 MIS TLIF–treated patients [5]. Additionally, the authors reported a single case of dural violation during spinal decompression and no cases of implant fracture or loosening, loss of correction, interbody cage dislodgement, or subsidence within the entire 16-month observation period [5]. Beringer and Mobasser reported on a series of eight patients undergoing a unilateral pedicle screw MIS TLIF with a mean operative time of 160 minutes and a mean estimated blood loss of 100 mL [4]. Postoperatively, there were no cases of radiculopathy or malpositioned screws. One patient required removal of pedicle screw instrumentation for muscle spasms and pain [4]. The generalizability of the ‘‘learning curve’’ involves many surgical factors including the number and frequency of cases, training, the use of navigation, mean patient size, disease severity, and other hospital factors. This study is a reflection of one surgeon’s progression in his experience with MIS TLIF, and therefore, may not apply to all surgeons adopting minimally invasive spine surgery. Limitations of our analysis should be noted. First, the surgical experience is only of a single surgeon at a single academic institution. Future studies should attempt to correlate a surgical learning curve for multiple surgeons at multiple institutions. Second, our use of unilateral pedicle screw instrumentation and lack of posterolateral fusion is only one of several strategies that can be used to perform the MIS TLIF technique. This variation in technique can lead to variability in reports of operative times, estimated blood losses, and may increase the rate of clinically symptomatic pseudarthrosis. Last, our analysis is retrospective in nature, which carries inherent bias. We attempted to reduce this bias by excluding revision surgeries and multiple level fusions. Strength in our analysis lies in the objective measurement of blood loss, via a suction canister that directly collects operative blood both directly and from the surgical sponges used in the surgical field. Also we used factors that were neutral of surgeon bias including recorded operative times
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(made by the nursing staff), anesthetic times (recorded by the anesthesiologist), and intraoperative fluid parameters (indirect measure of operative time and blood loss).
Conclusion The learning curve of the MIS TLIF procedure appears to be objectively reproducible based on our study. Surgical familiarity gained with increased operative experience with the MIS technique demonstrated significant decreases in operative time, estimated blood loss, intravenous fluid use, and duration of anesthesia. We also observed a slight increase in operative times during the surgical evolution that we attribute to surgical familiarity with the operative anatomy resulting in a more thorough decompression and end plate preparation. Last, our results indicate that the potential for intraoperative and postoperative complications, inherent to all surgeries, seems to be present regardless of a surgical learning curve. References [1] Ozgur B, Benzel EC, Garfin SR. Minimally invasive spine surgery: a practical guide to anatomy and techniques. London, UK: Springer London, Limited, 2009. [2] Wang B, Lu G, Patel AA, et al. An evaluation of the learning curve for a complex surgical technique: the full endoscopic interlaminar approach for lumbar disc herniations. Spine J 2011;11:122–30.
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[3] Neal CJ, Rosner MK. Resident learning curve for minimal-access transforaminal lumbar interbody fusion in a military training program. Neurosurg Focus 2010;28:E21. [4] Beringer WF, Mobasser JP. Unilateral pedicle screw instrumentation for minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus 2006;20:E4. [5] Scheufler KM, Dohmen H, Vougioukas VI. Percutaneous transforaminal lumbar interbody fusion for the treatment of degenerative lumbar instability. Neurosurgery 2007;60(4 Suppl 2):203–12; discussion 212–3. [6] Rouben D, Casnellie M, Ferguson M. Long-term durability of minimal invasive posterior transforaminal lumbar interbody fusion: a clinical and radiographic follow-up. J Spinal Disord Tech 2011;24:288–96. [7] Wu RH, Fraser JF, Hartl R. Minimal access versus open transforaminal lumbar interbody fusion: meta-analysis of fusion rates. Spine 2010;35:2273–81. [8] Peng CW, Yue WM, Poh SY, et al. Clinical and radiological outcomes of minimally invasive versus open transforaminal lumbar interbody fusion. Spine 2009;34:1385–9. [9] Mayer HM. Minimally invasive spine surgery: a surgical manual. London, UK: Springer, 2005. [10] Eck JC, Hodges S, Humphreys SC. Minimally invasive lumbar spinal fusion. J Am Acad Orthop Surg 2007;15:321–9. [11] Hoogland T, van den Brekel-Dijkstra K, Schubert M, Miklitz B. Endoscopic transforaminal discectomy for recurrent lumbar disc herniation: a prospective, cohort evaluation of 262 consecutive cases. Spine 2008;33:973–8. [12] McLoughlin GS, Fourney DR. The learning curve of minimallyinvasive lumbar microdiscectomy. Can J Neurol Sci 2008;35:75–8. [13] Hyde J, Seits M. Clinical experience, outcomes, and learning curve following XlIf for lumbar degenerative conditions. World Spinal Column J 2011;2:21–6. [14] Wang MY. Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). In: Baaj AA, ed. Handbook of spine surgery. New York, NY: Thieme, 2011.
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Clinical Study
Minimally invasive transforaminal lumbar interbody fusion: one surgeon’s learning curve Sreeharsha V. Nandyala, BA, Steve J. Fineberg, MD, Miguel Pelton, BS, Kern Singh, MD* Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite 400, Chicago, IL 60612, USA Received 9 May 2012; revised 26 June 2013; accepted 23 August 2013
Abstract
BACKGROUND CONTEXT: The published literature has not characterized the surgeon’s learning curve with the technically demanding technique of a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). PURPOSE: To characterize based on intra- and perioperative parameters, the learning curve for one spine surgeon during his initial phases of performing an MIS TLIF. STUDY DESIGN/SETTING: Retrospective analysis of a single institution and single surgeon experience with the unilateral MIS TLIF technique between July 2008 and April 2011. PATIENT SAMPLE: Sixty-five consecutive patients, with at least 1 year of follow-up, who underwent a unilateral, single-level, index MIS TLIF for the diagnosis of degenerative disk disease or lumbar spinal stenosis with grade I or II spondylolisthesis were analyzed based on data obtained from the medical records and postoperative imaging (computed tomography). OUTCOME MEASURES: Postoperative radiographic assessment of fusion at 1 year via computed tomography. Surgical parameters of surgical time (skin-skin, minutes), anesthesia time (induction-extubation, minutes), estimated blood loss (mL), intravenous fluids during surgery (mL), intraoperative complications (durotomy), and postoperative complications (pseudarthrosis, implant failure, malpositioned implants, graft-related complications) were also assessed. METHODS: The senior author’s first 100 consecutive MIS TLIFs were evaluated initially. Patients undergoing revision or multilevel surgery were excluded leaving a total of 65 consecutive primary MIS TLIFs. The first 33 patients were compared with the second 32 patients in terms of radiographic arthrodesis rates, surgical parameters, and intra-/postoperative complications. A two-tailed Student t test was used to assess for differences between the two cohorts where a p value of less than or equal to .05 denoting statistical significance. Pearson’s correlation coefficient was used to determine any association between the date of surgery and surgical time. RESULTS: Average surgical time, estimated blood loss, intraoperative fluids, and duration of anesthesia was significantly longer in the first cohort (p!.05). There were no significant differences in intraoperative complications (two durotomies in both groups) or length of stay. There was no significant difference in postoperative complications at final follow-up based on computed tomography analysis (11 vs. 9, p5.649). In the first cohort, these complications included two cases of radiographic pseudarthrosis: one case of graft migration and one case of medial pedicle wall violation necessitating two revision surgeries. There were two cases of pseudarthrosis and one case of an early surgical site infection identified in the second group requiring three revision surgeries. Last, four cases of neuroforaminal bone growth were demonstrated, two in each cohort. Pearson’s correlation coefficient demonstrated a negative correlation between the date of surgery and surgical time (r50.44; p!.001) estimated blood loss (r50.49; p!.001), duration of anesthesia (r50.41; p5.001), and intravenous fluids (r50.42; p5.001).
FDA device/drug status: Not Approved for this indication (rhBMP-2 use as a graft extender in the setting of MIS TLIF). Author disclosures: SVN: Nothing to disclose. SJF: Nothing to disclose. MP: Nothing to disclose. KS: Royalties: Stryker (D), Lippincott (C), Thieme (C), Consulting: Depuy (B), Stryker (B), Globus (B); Board of Directors: Vital 5, LLC (stock options, none). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. 1529-9430/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.08.045
Institutional review board approval was granted for this study (ORA number 10101108-IRB02). * Corresponding author. Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite 400, Chicago, IL 60612, USA. Tel.: (312) 432-2373; fax: (708) 492-5373. E-mail address: [email protected] (K. Singh)
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CONCLUSIONS: The MIS TLIF is a technically difficult procedure to the practicing spine surgeon with regard to intra- and perioperative parameters of surgical time, estimated blood loss, intravenous fluid, and duration of anesthesia. Operative time and proficiency improved with understanding the minimally invasive technique. Further studies are warranted to delineate the methods to minimize the complications associated with the learning curve. Ó 2013 Elsevier Inc. All rights reserved. Keywords:
MIS TLIF; Learning; Technique; Complications; Surgery
Introduction As minimally invasive surgical techniques become more popular, the need to understand factors that characterize proficiency in these procedures becomes paramount. Current literature supports that mastery of the open technique is necessary to successfully perform a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) [1]. Few studies have attempted to characterize the learning curve experience for an MIS TLIF. Proficiency measurements are characterized by plateaus in operative time, blood loss, accuracy of pedicle screw placement, and intraoperative and postoperative complications [2]. Most studies of the surgical learning curve are usually of a single surgeon’s experience and of relatively low numbers of patient cohorts [3]. Conclusions drawn from these analyses agree that larger number of patient samples and more publications of results are necessary to add to the growing literature of the surgical learning curve [4,5]. Minimally invasive transforaminal lumbar interbody fusion has been established as a viable alternative to the open procedure with less disruption of spinal anatomy [6–8]. Clear indications or contraindications for the minimally invasive approach may lie in the comfort and proficiency of the particular surgeon [9]. This study attempts to add to the growing literature of the surgical learning curve based on the experience of one board-certified/fellowship-trained spine surgeon.
Materials and methods After obtaining institutional review board approval, retrospective data were reviewed from the senior author’s (KS) first 100 patients undergoing a minimally invasive transforaminal lumbar interbody fusion. The experience began 3 years into the surgical practice. Patients were then excluded using the following criteria: revision cases and multilevel procedures, resulting in 65 patients. These first 65 patients were then divided into two equal groups: patients 1–33 and patients 34–65. Ages ranged from 26 to 79 years with a mean age of 59.2 years for the first half (patients 1–33, N533) and 54.2 years for the second half (patients 34–65, N532). All patients had at least 1 year of total follow-up with computed tomography (CT) scan analysis and complications were then analyzed. Every patient had a diagnosis of either degenerative disk disease
or grade I or II spondylolisthesis with stenosis. Demographic characteristics were similar in both groups based on the Charlson Comorbidity Index. Characteristics of both patient groups are presented in Table 1. Surgical technique A unilateral approach was undertaken through a paramedian (4.5 cm lateral to the midline) skin incision using the Wiltse technique under fluoroscopy. After incising the skin and fascia, a plane was developed between the multifidus and longissimus muscles, whereby the pathway to the spine was enlarged by sequential dilators. A high-speed burr was used to remove the facet and pars. After exiting and traversing nerve roots were identified and completely visualized, a high speed burr was also used to complete the laminectomy. Local bone graft that had been obtained from the laminectomy and facetectomy was collected in a bone trap. The interbody space was identified under fluoroscopic imaging. Sequential end plate cutters were used to prepare the end plates. An appropriately sized DePuy Concorde cage (DePuy Spine, Raynham, MA, USA) was filled with either 4.2 mg (small kit) or 12 mg (large kit) of rhBMP-2, along with 5 mL bone marrow aspirate from the cannulated pedicle and local bone graft. BMP was used as an ‘‘off-label’’ application. Local bone was also placed anterior to the cage in the intervertebral space. The cage was then gently impacted obliquely into the intervertebral space. Unilateral pedicle screws were placed percutaneously over a guide wire. A rod was placed percutaneously through a separate stab incision and brought into the gap between the screw heads and locking nuts. The course of the rod was confirmed using anteroposterior and lateral fluoroscopy. Once in place, the screws were compressed along the rod and the nuts were tightened using a torque wrench. Compression was placed across the graft and the wound was then closed in layers. The laminectomy, bilateral decompression of the spinal canal, and transforaminal lumbar interbody fusion were performed with a 21-mm nonexpandable tube. No posterolateral fusion was performed. Midline muscular and ligamentous structures were all preserved during the procedure. Primary analysis The first 33 consecutive patients were compared with the second 32 consecutive patients based on perioperative outcomes measures (operative times; minutes), estimated
S.V. Nandyala et al. / The Spine Journal Table 1 Patient demographics Variable Gender Male Female Smoker Yes No Age at admission (yr) Diagnosis Degenerative disc disease Spondylolisthesis/stenosis Comorbidities Yes No Charlson Comorbidity Index
Patients 1–33 (N533)
Patients 34–65 (N532)
13 20
17 15
.267
6 27 59.24610.73
11 21 54.22615.49
.224
3 30
6 26
.260
5 28 1.660.89
3 29 2.660.58
.433
p Value
.132
.119
blood loss (EBL; mL), intravenous fluids during surgery (mL), length of stay (days), and anesthesia time from intubation to extubation (minutes). In addition, intraoperative complications (durotomy) and postoperative complications (infection, pseudarthrosis, implant failure, malpositioned implants) were compared between the two study groups. Adverse events related to the rhBMP-2 bone graft (neuroforaminal bone growth and cage migration/osteolysis) were also recorded. Last, CT scans were used at 12-month follow-up to assess for arthrodesis. Resultant needs for reoperations were also assessed in both patient groups. To assess for fusion, CT scans with contiguous 2.0-mm axial cuts perpendicular to the disc space (along with sagittal and coronal reconstructions) were obtained at the operative level at 6 and 12 months after the index surgery. CT assessment of fusion included three criteria: contiguous bridging bone on at least two consecutive coronal and sagittal reconstructions within the intervertebral space, blurring of the bone graft-endplate junction, and absence of a radiological cleft within the fusion mass. Noncontiguous
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bone formation, the presence of cage subsidence with end plate cyst formation, haloing around the cage and screws, or graft migration was defined as pseudarthrosis. CT scans were also used to determine any adverse events specific to the rhBMP-2, such as ectopic muscle ossification, laminar bone regrowth, neuroforaminal bone growth, and intra-/extradural ossification. Statistical analysis Microsoft Excel 2007 (Redmond, WA, USA) was used for data management and SPSS Inc. v17.0 Graduate Package (Chicago, IL, USA) was used for statistical analysis. Descriptive and frequency statistics were evaluated. Student t test was used to test for significance between the means of patients 1–33 and patients 34–65. Fisher’s exact probability test was used to evaluate differences between nonparametric data. Pearson’s correlation coefficient was used to characterize the relationship between surgical date and perioperative outcomes measures. Differences between groups were deemed to be statistically significant when p#.05.
Results Average surgical time, estimated blood loss, intraoperative fluids, and duration of anesthesia were significantly longer in the first cohort (p!.05) (Table 2). There were no significant differences in the intraoperative complications (two durotomies in each group) or length of stay. Additionally, there was no significant difference in the postoperative complications at the final 1-year follow-up based on CT analysis (7 vs. 5, p5.561). In the first group, complications consisted of four cases of implant screw displacements (three lateral wall breaches and one medial wall breach), two cases of pseudarthrosis, and one case of graft migration. The patient that sustained a medical wall breach underwent an immediate revision surgery 2 days after the
Table 2 Surgical variables Variable
Patients 1–33 (N533)
Patients 34–65 (N532)
p Value
Surgical time (skin-skin) Duration of anesthesia (induction-extubation) Intravenous fluids during surgery (mL) Estimated blood loss (mL) Length of stay (days) Intraoperative complications (number of patients) Intraoperative complication (lateral screw placement) Postoperative complications (number of patients) Neuroforaminal bone growth (number of patients) Total complication rate (%) Reoperations (number of patients, %) Arthrodesis (number of patients, %)
124 182 2,089 176 2.39 2* 3 4y 2 11 (33) 2 (6.1) 31 (94)
98 154 1,703 85 2.25 2* 2 3z 2 9 (28) 3 (9.4) 30 (94)
!.001 !.001 .004 !.001 .643 1.000 .667 .721 1.000 .649 .616 1.000
* Two cases of durotomies. y Two cases of pseudarthrosis, one case of graft migration, and one case of screw violation of the medial pedicle wall. z Two cases of pseudarthrosis and one case of surgical site infection.
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index operation. In the second group, two cases of implant screw displacements (lateral wall breaches), two cases of pseudarthrosis, and one early surgical site infection were identified (Table 2). The patient that developed the early surgical site infection returned to surgery on postoperative day 3 for a purulent wound infection. No persistent dural leaks were identified in either group. Pearson’s correlation coefficient demonstrated that the date of surgery and case number is related to decreased surgical time (r50.44; p!.001) (Fig. 1), decreased EBL (r50.50; p!.001) (Fig. 2), decreased duration of anesthesia (r50.41; p5.001) (Fig. 3), and decreased intravenous fluids (r50.42; p5.001) (Fig. 4). Graft related neuroforaminal bone growth was ascertained in both patient cohorts (2 vs. 2; p51.00). Overall, two patients in each cohort required reoperations to address the surgical complications. In addition to the these reoperation cases, one patient in each cohort required reoperation (ventral laminoforaminotomy) for pseudarthrosis causing pain and disability. Last, 12-month CT scan results demonstrated a 94% (n531) and 94% (n530) arthrodesis rates for the first and second patient cohorts, respectively.
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Fig. 2. Graph of the learning curve based on estimated blood loss plotted against case number.
Successful clinical outcomes of an MIS TLIF depend primarily on the surgeon’s experience and level of comfort with the procedure [1]. Attempts at an assessment of the learning curve are sparse in the surgical literature. Few studies acknowledge that the surgical learning curve is steep [10]. Others assert that trends toward better clinical outcomes are seen with an increased number of cases [11]. In an attempt to construct a learning curve model, our study created a multiple clinical parameter analysis of one surgeon’s experience with MIS TLIF procedures. Our results indicate that improvements in intraoperative clinical outcomes occur with increasing case numbers. Significant changes in surgical time and estimated blood loss
were identified between the first and second cohorts. Reasons for decreases in both parameters intuitively make sense. Efficiency is gained as the surgeon gains familiarity with surgical anatomy in the constrained workspace space of the tubular retractor system. Neal and Rosner recently examined the learning curve of a single resident’s experience with 28 patients undergoing a minimal access TLIF [3]. Although there was a trend toward decreases in operative times with an increase in case number, the results did not differ significantly between the two groups (p5.25). Various studies have reported on the surgical learning curve of other spinal surgeries. McLoughlin and Fourney assessed 52 patients undergoing a minimally invasive microdiscectomy using a tubular retractor system and found that by case 15, surgical time had reached a steady state of 60 minutes [12]. Hyde and Seits retrospectively reviewed 78 consecutive XLIF patients (Extreme Latera Interbody Fusion) in terms of perioperative and follow-up outcomes measures [13]. Over the course of the experience, both blood loss and operative time were reduced. However, in comparison of the first 10 patients with the last 10 patients,
Fig. 1. Graph of the learning curve based on surgical time plotted against case number.
Fig. 3. Graph of the learning curve based on duration of anesthesia plotted against case number.
Discussion
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Fig. 4. Graph of the learning curve based on intravenous fluids use plotted against case number.
the authors found no significant differences in blood loss (p5.554) and operative time (p5.355). It was concluded that although there was a slight learning curve associated with the procedure it was not significant. Because averages of operative times and blood losses were initially low at the onset of the study, there was not much deviation from these numbers. Additionally, this lack of significant differences between the first and last 10 patients suggested that the XLIF procedure (Extreme Latera Interbody Fusion) could be mastered relatively early. Importantly, the occurrence of intraoperative and postoperative complications did not differ between our two treatment groups. Two durotomies were noted in each cohort (n54, 5.3%, total). These intraoperative complications highlight the intrinsic difficulty of the MIS TLIF procedure, even as experience is gained and efficiency is improved. Postoperative complications in the first half included four cases of implant screw displacements (three lateral wall breaches and one medial wall breach), two cases of pseudarthrosis, and one case of graft migration. In the second half, two cases of implant screw displacements (lateral wall breaches), two cases of pseudarthrosis, and one early surgical site infection were identified. Although these differences are not significant (p5.561), clearly the potential exists in any case of MIS TLIF for implant screw displacement and pseudarthrosis. Additionally, our analysis suggests that this absence of significant differences in complications translated into no observable differences in the 12-month arthrodesis rates (94% vs. 94%) and reoperation rates (6.1% vs. 6.1%) between the two surgical cohorts (first and second group, respectively). Ways to minimize these inherent risks include proper end plate preparation, cage sizing, and the use of osteobiologic adjuvants [14]. Additionally, our study demonstrates that as the surgeon gains familiarity with the procedure these potential complications can be minimized. Several changes to the surgeon’s practice have been adopted to address the complications demonstrated in this study. At the time of this study, a large BMP kit was used.
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The surgeon now uses an extra-small BMP kit. For patients who develop a pseudarthrosis, those with a dynamic spondylolisthesis, a higher grade spondylolisthesis, or a large disc space will undergo a contralateral fixation. It should be noted that there is some variation in operative times in our analysis. Neal and Rosner speculate that this variation occurs after several cases of an MIS TLIF, because familiarity with the constrained work space is gained and the surgeon is more willing to attempt more challenging cases [3]. These difficult cases in turn translate to slight increases in operative time. Our analysis demonstrates this same effect with a small increase in surgical time. We attribute this increase to surgeon familiarity of the MIS anatomy resulting in a more thorough decompression and end plate preparation, two rate-limiting factors of the technique. Our intraoperative and postoperative results are similar to other reported studies on the MIS TLIF surgical technique. Scheufler et al. reported an average surgical time of 104 minutes and an average total blood loss of 55 mL over a span of 53 MIS TLIF–treated patients [5]. Additionally, the authors reported a single case of dural violation during spinal decompression and no cases of implant fracture or loosening, loss of correction, interbody cage dislodgement, or subsidence within the entire 16-month observation period [5]. Beringer and Mobasser reported on a series of eight patients undergoing a unilateral pedicle screw MIS TLIF with a mean operative time of 160 minutes and a mean estimated blood loss of 100 mL [4]. Postoperatively, there were no cases of radiculopathy or malpositioned screws. One patient required removal of pedicle screw instrumentation for muscle spasms and pain [4]. The generalizability of the ‘‘learning curve’’ involves many surgical factors including the number and frequency of cases, training, the use of navigation, mean patient size, disease severity, and other hospital factors. This study is a reflection of one surgeon’s progression in his experience with MIS TLIF, and therefore, may not apply to all surgeons adopting minimally invasive spine surgery. Limitations of our analysis should be noted. First, the surgical experience is only of a single surgeon at a single academic institution. Future studies should attempt to correlate a surgical learning curve for multiple surgeons at multiple institutions. Second, our use of unilateral pedicle screw instrumentation and lack of posterolateral fusion is only one of several strategies that can be used to perform the MIS TLIF technique. This variation in technique can lead to variability in reports of operative times, estimated blood losses, and may increase the rate of clinically symptomatic pseudarthrosis. Last, our analysis is retrospective in nature, which carries inherent bias. We attempted to reduce this bias by excluding revision surgeries and multiple level fusions. Strength in our analysis lies in the objective measurement of blood loss, via a suction canister that directly collects operative blood both directly and from the surgical sponges used in the surgical field. Also we used factors that were neutral of surgeon bias including recorded operative times
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(made by the nursing staff), anesthetic times (recorded by the anesthesiologist), and intraoperative fluid parameters (indirect measure of operative time and blood loss).
Conclusion The learning curve of the MIS TLIF procedure appears to be objectively reproducible based on our study. Surgical familiarity gained with increased operative experience with the MIS technique demonstrated significant decreases in operative time, estimated blood loss, intravenous fluid use, and duration of anesthesia. We also observed a slight increase in operative times during the surgical evolution that we attribute to surgical familiarity with the operative anatomy resulting in a more thorough decompression and end plate preparation. Last, our results indicate that the potential for intraoperative and postoperative complications, inherent to all surgeries, seems to be present regardless of a surgical learning curve. References [1] Ozgur B, Benzel EC, Garfin SR. Minimally invasive spine surgery: a practical guide to anatomy and techniques. London, UK: Springer London, Limited, 2009. [2] Wang B, Lu G, Patel AA, et al. An evaluation of the learning curve for a complex surgical technique: the full endoscopic interlaminar approach for lumbar disc herniations. Spine J 2011;11:122–30.
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[3] Neal CJ, Rosner MK. Resident learning curve for minimal-access transforaminal lumbar interbody fusion in a military training program. Neurosurg Focus 2010;28:E21. [4] Beringer WF, Mobasser JP. Unilateral pedicle screw instrumentation for minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus 2006;20:E4. [5] Scheufler KM, Dohmen H, Vougioukas VI. Percutaneous transforaminal lumbar interbody fusion for the treatment of degenerative lumbar instability. Neurosurgery 2007;60(4 Suppl 2):203–12; discussion 212–3. [6] Rouben D, Casnellie M, Ferguson M. Long-term durability of minimal invasive posterior transforaminal lumbar interbody fusion: a clinical and radiographic follow-up. J Spinal Disord Tech 2011;24:288–96. [7] Wu RH, Fraser JF, Hartl R. Minimal access versus open transforaminal lumbar interbody fusion: meta-analysis of fusion rates. Spine 2010;35:2273–81. [8] Peng CW, Yue WM, Poh SY, et al. Clinical and radiological outcomes of minimally invasive versus open transforaminal lumbar interbody fusion. Spine 2009;34:1385–9. [9] Mayer HM. Minimally invasive spine surgery: a surgical manual. London, UK: Springer, 2005. [10] Eck JC, Hodges S, Humphreys SC. Minimally invasive lumbar spinal fusion. J Am Acad Orthop Surg 2007;15:321–9. [11] Hoogland T, van den Brekel-Dijkstra K, Schubert M, Miklitz B. Endoscopic transforaminal discectomy for recurrent lumbar disc herniation: a prospective, cohort evaluation of 262 consecutive cases. Spine 2008;33:973–8. [12] McLoughlin GS, Fourney DR. The learning curve of minimallyinvasive lumbar microdiscectomy. Can J Neurol Sci 2008;35:75–8. [13] Hyde J, Seits M. Clinical experience, outcomes, and learning curve following XlIf for lumbar degenerative conditions. World Spinal Column J 2011;2:21–6. [14] Wang MY. Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). In: Baaj AA, ed. Handbook of spine surgery. New York, NY: Thieme, 2011.
