The Spine Journal 15 (2015) 1118–1132

Review Article

Anterior lumbar spine surgery: a systematic review and meta-analysis of associated complications Dexter K. Bateman, BS*, Paul W. Millhouse, MD, Niti Shahi, BS, Abhijeet B. Kadam, MD, Mitchell G. Maltenfort, PhD, John D. Koerner, MD, Alexander R. Vaccaro, MD, PhD Department of Orthopaedic Surgery, Rothman Institute/Thomas Jefferson University, 925 Chestnut St, 5th Floor, Philadelphia, PA 19107, USA Received 26 May 2014; revised 22 December 2014; accepted 18 February 2015

Abstract

BACKGROUND CONTEXT: The anterior approach to the lumbar spine is increasingly used to accomplish various surgical procedures. However, the incidence and risk factors for complications associated with anterior lumbar spine surgery (ALS) have not been fully elucidated. PURPOSE: To identify and document types of complications and complication rates associated with ALS, determine risk factors for these events, and evaluate the effect of measures used to decrease complication rates. STUDY DESIGN: Systematic review and meta-analysis. METHODS: A systematic review of the English-language literature was conducted for articles published between January 1992 and December 2013. A MEDLINE search was conducted to identify articles reporting complications associated with ALS. For each complication, the data were combined using a generalized linear mixed model with a binomial probability distribution and a random effect based on the study. Predictors used were the type of procedure (open, minimally invasive, or laparoscopic), the approach used (transperitoneal vs. retroperitoneal), use of recombinant bone morphogenetic protein-2, use of preoperative computed tomography angiography (CTA), and the utilization of an access surgeon. Open surgery was used as a reference category. RESULTS: Seventy-six articles met final inclusion criteria and reported complication rates in 11,410 patients who underwent arthrodesis and/or arthroplasty via laparoscopic, mini-open, and open techniques. The overall complication rate was 14.1%, with intraoperative and postoperative complication rates of 9.1% and 5.2%, respectively. Only 3% of patients required reoperation or revision procedures. The most common complications reported were venous injury (3.2%), retrograde ejaculation (2.7%), neurologic injury (2%), prosthesis related (2%), postoperative ileus (1.4%), superficial infection (1%), and others (1.3%). Laparoscopic and transperitoneal procedures were associated with higher complication rates, whereas lower complication rates were observed in patients

FDA device/drug status: Not applicable. Author disclosures: DKB: Nothing to disclose. PWM: Stock Ownership: Globus Medical ($0). NS: Nothing to disclose. ABK: Nothing to disclose. MGM: Nothing to disclose. JDK: Nothing to disclose. ARV: Royalties: DePuy (C), Medtronic (H), Stryker Spine (G), Biomet Spine (C), Globus Medical (F), NuVasive (B), Aesculap (B); Stock Ownership: Replication Medica (15,000 shares, value B), Globus Medical (123,398 shares, value I), K-2 Medical, Paradigm Spine (975,000 shares, value F), Stout Medical (1% company, value E), Spine Medica (25,000 stock options, unknown value), Computational Biodynamics (50% ownership, unknown value), Progressive Spinal Technologies (30% ownership, unknown value), Spinology (8,125 shares, unknown value), Small Bone Innovations (15,000 shares, unknown value), Cross Current (62,500 shares, paid 50,000), Syndicom 2,750 shares, value 5,032), In Vivo (123,935 shares, unknown value), Flagship Surgical (Invested 50,000, value D), Advanced Spinal Intellectual Properties (30% ownership, unknown value), Cytonics (25,000 shares, unknown value), Bonovo Orthopedics (100,000 shares, paid 116,500), Electrocore (50,000 shares, unknown value), Gamma Spine (15% ownership, unknown value), Location Based Intelligence (20% http://dx.doi.org/10.1016/j.spinee.2015.02.040 1529-9430/Ó 2015 Elsevier Inc. All rights reserved.

ownership, unknown value), Flow Pharma (2,000,000 nonqualified stock options, unknown value), R.S.I (50% ownership, unknown value), Rothman Institute and Related Properties (practice, unknown value), Innovative Surgical (30% ownership, unknown value), Design (Unknown), Spinicity (53,000 shared, 3.4% ownership); Consulting: Gerson Lehrman Group (B), Guidepoint Global (B), Medacorp (B), Stout Medical (B), Innovative Surgical Design (B), Orthobullets (A); Board of Directors: AO Spine, Innovative Surgical Design, Association of Collaborative Spine Research, Spinicity; Grants: Stryker Spine, Cerapedics, NuVasive (C). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. Disclosures: This work had no outside funding, and the authors present no conflicts of interest in relation to this study. * Corresponding author. Department of Orthopaedic Surgery, Rothman Institute/Thomas Jefferson University, 925 Chestnut St, 5th Floor, Philadelphia, PA 19107, USA. Tel.: (404) 642-5137; fax: (215) 503-0568. E-mail address: [email protected] (D.K. Bateman)

D.K. Bateman et al. / The Spine Journal 15 (2015) 1118–1132

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receiving mini-open techniques. Our analysis indicated that the use of recombinant bone morphogenetic protein-2 was associated with increased rates of retrograde ejaculation; however, there may be limitations in interpreting these data. Data regarding the use of preoperative CTA and an access surgeon were limited and demonstrated mixed benefit. CONCLUSIONS: Overall complication rates with ALS are relatively low, with the most common complications occurring at a rate of 1% to 3%. Complication rates are related to surgical technique, approach, and implant characteristics. Further randomized controlled trials are needed to validate the use of preventative measures including CTA and the use of an access surgeon. Ó 2015 Elsevier Inc. All rights reserved. Keywords:

Anterior approach; Lumbar spine surgery; Complications; Systematic review; Bone morphogenetic protein; Retrograde ejaculation

Introduction The rate of lumbar arthrodesis has steadily increased over the past couple of decades and can be readily accomplished via anterior, posterior, or combined approaches [1]. Originally developed for the treatment of tuberculous lesions in the early 20th century, anterior approaches are now used for a wide array of degenerative, deformity, tumor, trauma, and infection-related spinal pathologies [2]. Proponents of the anterior approach cite direct access to the anterior vertebral column, allowing more extensive decompression of the interbody space and better end plate preparation for arthrodesis as a critical advantage [3]. Moreover, the ability for improved deformity correction without posterior approach–related morbidity, such as neurologic injury and paraspinal muscle trauma, is often reported as a major advantage [4]. Despite its appeal as a surgical option for access to the intervertebral space, however, anterior lumbar spine surgery (ALS) is associated with various intraoperative and postoperative complications. Considerable anatomic variations exist in the neurovascular structures anterior to the lumbar vertebral column. Reported complications are myriad, including intraoperative vascular, neurologic, and visceral injury, as well as postoperative complications, such as thromboembolism, infection, retrograde ejaculation (RE), and implant-related complications. In an effort to reduce these risks, access surgeons are often used to facilitate safe visualization of the vertebral space while protecting atrisk vascular and neurologic structures. Additionally, preoperative imaging, including computed tomography angiography (CTA), is used to fully define the vascular anatomy and identify anatomic aberrations. Currently, diverse literature exists regarding the incidence and impact of various complications associated with ALS. Additionally, given the variety of surgical approaches and procedures, guidelines for effective complication management are numerous and inconsistent. In this study, we intend to present a systematic literature review of the incidence and risk factors for complications after anterior lumbar procedures. Additionally, we aim to specifically answer the following questions: What is the incidence of intraoperative and postoperative complications associated with

ALS?; what risk factors contribute to an increased rate of complications?; and what measures decrease the incidence of intraoperative and postoperative complications?

Materials and methods Search strategy A systematic MEDLINE search via PubMed was performed using various combinations of the following search terms: ‘‘anterior lumbar,’’ ‘‘surgery,’’ ‘‘procedure,’’ ‘‘operation,’’ ‘‘lumbar fusion,’’ ‘‘lumbar arthroplasty,’’ and ‘‘complications.’’ Peer-reviewed articles published between 1992 and 2013 reporting the incidence of complications during ALS were included. Case reports, editorials, reviews without quantitative data, and articles not written in the English language were excluded. Studies including trauma, tumor, or infection as primary surgical indications for greater than 5% of the study population were excluded. If multiple articles from the same author(s) clearly reported the same cohort of patients, only the most recently published articles with the largest sample size were included. To expand the search results, reference lists of key articles were also examined for eligible articles. Data extraction Data were extracted by two authors (PWM, NS) and independently reviewed by a third author (DKB). All articles were reviewed and analyzed to extract the following data: study design, type of surgical procedure and approach, number of patients and demographic information, participation of an access surgeon, utilization of preoperative CTA, use of recombinant bone morphogenetic protein-2 (rhBMP-2), and reported complications. The type of surgical procedure was classified as described by the original study author (eg, ‘‘minimally invasive’’ or ‘‘mini-open’’ vs. open). An access surgeon was defined as ‘‘a vascular, urological, or general surgeon who conducts the surgical exposure instead of solely the orthopedic surgeon’’ [5]. Complications were stratified into two categories: intraoperative or approach related (hereinafter referred to as intraoperative) and postoperative. If a study

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presented multiple cohorts separated by surgical procedure or approach, data were combined as independent groups. Levels of evidence ratings were assigned to each article independently using the criteria described by Wright et al. [6]. Disagreements were resolved by a consensus among reviewers. Statistical analysis All extracted information was compiled using Microsoft Excel software (Microsoft Corp., Redmond, WA, USA), and analyses were performed using the lme4 package in the R statistical platform (R Foundation for Statistical Computing, Vienna, Austria). No attempt was made to adjust p values for multiple comparisons. The potential for inflated Type I error is considered in the Discussion section. For each complication, the data were combined using a generalized linear mixed model (GLMM) with a binomial probability distribution and a random effect based on the study. This GLMM was a logistic regression that controlled for variations among study populations, similar to performing a random-effects meta-analysis. If the study did not include the particular complication, it was excluded from the model. Predictors used were the type of procedure (open, minimally invasive, or laparoscopic), approach (transperitoneal [TP] vs. retroperitoneal [RP]), use of preoperative angiography, use of rhBMP-2, and the inclusion of an access surgeon. Open surgery was used as a control category for drawing comparisons.

Results Study characteristics A systematic literature search yielded 1,813 publications, and 1,712 articles were eliminated based on abstract and title screening. One hundred one full-text articles were assessed for eligibility, and 25 articles were excluded based on established exclusion criteria. Ultimately, data were extracted from 76 articles (Fig. 1). Characteristics of the 76 included studies, such as patient demographic information, follow-up duration, and surgical parameters, are summarized in Table 1. A total of 11,410 patients were included for analysis in 104 unique surgical cohorts. The mean age of the study population was 44 years. Seventeen studies reported complications in 22 subgroups from the time of index procedure until hospital discharge (N53,870) [5,7–22]. Fifty-nine studies reported extended postoperative complications in 82 surgical cohorts with a mean follow-up duration of 21.6 months (N57,540) [23–81]. Forty-seven of the studies provided Level IV evidence, 16 studies provided Level III evidence, four studies provided Level II evidence, and nine studies provided Level I evidence. A variety of approaches were reported for different anterior lumbar surgical procedures. Forty-nine studies included patients who underwent an open procedure, 20 studies included patients who underwent a mini-open procedure, and 20 studies included patients who underwent laparoscopic procedures. A RP approach was used in 48 open cohorts, 20 mini-open cohorts, and 8 laparoscopic cohorts. A TP

Fig. 1. Flowchart depicting study selection process.

D.K. Bateman et al. / The Spine Journal 15 (2015) 1118–1132 Table 1 Characteristics of included studies Characteristic

Number

Study information Included studies 76 Unique surgical cohorts 104 Average FW duration (mo) 21.6 Level of evidence (no. of studies) 1 9 2 4 3 16 4 47 Patient demographics Sex Male (%) 51.4 Female (%) 48.1 Not specified (%) 0.5 Average age (y) 44.1 Smokers (%) 32.3 Prior lumbar surgery (%) 31.7 WC claim (%) 35.9 Surgical parameters Open 63 RP 48 RP or TP 9 TP 6 Mini-open 21 RP 20 TP 1 Laparoscopic 20 RP 8 TP 12 ALIF 73 ADR 11 ALS 20 rhBMP-2 12 Access surgeon 28 CTA 3 Levels treated Single (%) 6,793 (69.7) Multi (%) 2,964 (30.4)

No. of patients included in analysis 11,410 11,410 7,540 1,751 756 1,500 7,403

5,870 5,484 56 9,177 3,418 4,667 1,894 7,092 5,760 1,120 212 3,421 3,370 51 897 378 519 6,318 1,242 3,850 1,254 4,422 580 9,747 9,747

FW, follow-up; WC, worker’s compensation; RP, retroperitoneal; TP, transperitoneal; ALIF, anterior lumbar interbody fusion; ADR, anterior disc replacement; ALS, anterior lumbar surgery; rhBMP-2, recombinant bone morphogenetic protein-2; CTA, computed tomography angiography.

approach was used in 6 open cohorts, 1 mini-open cohort, and 12 laparoscopic cohorts. A combination of RP or TP approach was used in nine open surgical cohorts. Seventy-three cohorts reported complications in patients undergoing anterior lumbar interbody fusion (ALIF), 11 cohorts reported complications in anterior disc replacement (ADR), and 20 cohorts reported complications in ALS, which included combinations of multiple procedures (ie, ALIF and ADR) and circumferential (anterior and posterior) fusion. Question 1: What is the incidence of intraoperative and postoperative complications associated with ALS? The overall incidence of complications associated with ALS reported by individual studies ranged widely from

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2% [20] to 69% [48] (Table 2). Intraoperative and approach-related complications ranged from 0% [32,45] to 50% [48], whereas postoperative complications ranged from 0% [7,12,25,34–36,45,46,50,55,56,59,68] to 38% [29]. In studies with follow-up beyond the index procedure, reoperation and revision rates ranged from 0% [7,14,15,24,30,32– 35,37,38,41,44,46,49,50,52,55,56,59,62,72,75] to 32% [48]. Data for specific intraoperative and postoperative complications pooled from all patients are shown in Table 3. The overall total complication rate was 14.1%, with an intraoperative complication rate of 9.1% and a postoperative complication rate of 5.2%. Only 3% of patients required reoperation or revision procedures. The most common complications reported were venous injury (3.2%), RE (2.73%), neurologic injury (2%), prosthesis or fusion construct related (1.97%), postoperative ileus (1.4%), superficial infection (1%), and others (1.3%). Veins most commonly reported to be lacerated were the left common iliac, inferior vena cava, and iliolumbar vein, which mostly occurred during the retraction of the great vessels. Neurologic adverse events included intraoperative neurologic damage, postoperative sympathetic dysfunction, and other neurologic deficits, such as leg and groin dysthesias, which were typically transient and most commonly in the region of the lateral cutaneous nerve. These pooled results should be interpreted cautiously as the overall rates favor the studies with larger populations. Question 2: What risk factors contribute to an increased rate of complications? The combined incidences of specific complications pooled by surgical parameters are shown in Table 3. Overall complication rates ranged from 7% to 33% and depended on surgical technique and approach. The incidence of intraoperative complications ranged from 5% to 30%, whereas postoperative complications ranged from 2% to 8%. Reoperation rates ranged from 0% to 4%. The highest overall complication rate occurred in patients undergoing laparoscopic procedures, whereas the lowest total complication rate occurred in patients receiving a miniopen technique (Fig. 2). Open versus laparoscopic versus mini-open. Certain surgical techniques and approaches were associated with an increased risk of specific intraoperative and postoperative complications. The forest plots presented in Fig. 3 depict the estimated odds ratios that were significant or of borderline significance (p value slightly above .05) in the GLMM analyses. Borderline odds ratios may reflect situations where the available studies did not provide sufficient statistical power, and new studies would be beneficial. One such case is laparoscopic surgery compared with open surgery, which was associated with increased total intraoperative complications (p5.08) and decreased postoperative urologic complications (p5.09), both of which were just

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Table 2 Studies reporting complications after anterior surgery Reported complications

Study information

Intraoperative & approach-related Approach Open RP Newman et al., 1992 [23] Kuslich et al., 1998 [27] Katkhouda et al., 1999 [30] Zeegers et al., 1999 [29] Cohen et al., 2000 [31] Cowles et al., 2000 [8] Christensen et al., 2002 [39] Bianchi et al., 2003 [44] Escobar et al., 2003 [45] Madan et al., 2003 [42] McAfee et al., 2003 [41] Scaduto et al., 2003 [43] Duggal et al., 2004 [47] el-Masry et al., 2004 [50] Farooq and Grevitt, 2004 [12] Niemeyer et al., 2004 [51] Saraph et al., 2004 [52] Bertagnoli et al., 2005 [53] Blumenthal et al., 2005 [54] Blumenthal et al., 2005 [54] Gumbs et al., 2005 [13] Lemaire et al., 2005 [57] Aryan et al., 2007 [62] Aryan et al., 2007 [62] Shim et al., 2007 [61] Brewster et al., 2008 [16] Hamdan et al., 2008 [17] Jarrett et al., 2009 [5] Jarrett et al., 2009 [5] Peng et al., 2009 [18] Thalgott et al., 2009 [63] Aunoble et al., 2010 [68] Garg et al., 2010 [19] Li et al., 2010 [67] Delamarter et al., 2011 [71] Schroeder et al., 2011 [20] Smith et al., 2011 [21] Edgard-Rosa et al., 2012 [73] Quraishi et al., 2013 [22] Snyder et al., 2013 [81] Open RP or TP Kozak et al., 1994 [24] Burkus et al., 2002 [40] Sasso et al., 2004 [48] Sasso et al., 2004 [48] Sasso et al., 2005 [14] Sasso et al., 2005 [14] Tropiano et al., 2005 [55] Acosta et al., 2009 [66] Gornet et al., 2011 [70] Gornet et al., 2011 [70] Open TP Tiusanen et al., 1996 [26] Asha et al., 2012 [75] Asha et al., 2012 [75] Asha et al., 2012 [75]

Postoperative

Overall

Reoperation

Surgery

% (n/N)

ALIF ALIF ALIF ADR ALIF ALIF ALS ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALS ALIF ADR ADR ALIF ALIF ADR ALS ALIF ADR ALIF ALIF ALS ALS ALS ALIF ALIF ALIF ALIF ALS ALIF ALS ALIF ALIF ALIF

2.8 9.1 8.3 34 9.4 17.1 10 5.6 0 3.9 6.7 11.4 3 6.7 18.8 31.5 36.4 1 7.8 8.1 4.7 5 16.7 12 5.3 9.4 11.3 4.8 12.4 9.5 25 9.5 10.8 1.8 9.7 1 2.6 1.1 15.1 4.3

(1/36) (54/591) (1/12) (17/50) (5/53) (7/41) (7/70) (4/72) (0/20) (2/51) (4/60) (10/88) (1/33) (2/30) (3/16) (17/54) (12/33) (1/104) (16/205) (8/99) (3/64) (5/100) (4/24) (3/25) (3/57) (12/128) (54/480) (3/63) (25/202) (7/74) (10/40) (4/42) (23/212) (2/112) (7/72) (1/102) (1/39) (5/469) (46/304) (10/231)

8.3 12.7 8.3 70 7.5 7.3 14.3 6.9 5 11.8 10 5.7 9.1 0 0 11.1 12.1 3.8 17.1 31.3 15.6 6 12.5 8 5.3 6.3 0 6.3 4 5.4 10 0 0.5 10.7 6.9 1 25.6 1.1 4.9 9.5

(3/36) (75/591) (1/12) (35/50) (4/53) (3/41) (10/70) (5/72) (1/20) (6/51) (6/60) (5/88) (3/33) (0/30) (0/16) (6/54) (4/33) (4/104) (35/205) (31/99) (10/64) (6/100) (3/24) (2/25) (3/57) (8/128) (/480) (4/63) (8/202) (4/74) (4/40) (0/42) (1/212) (12/112) (5/72) (1/102) (10/39) (5/469) (15/304) (22/231)

11.1 21.8 16.7 104 17 24.4 24.3 12.5 5 15.7 16.7 17 12.1 6.7 18.8 42.6 48.5 4.8 24.9 39.4 20.3 11 29.2 20 10.5 15.6 11.3 11.1 16.3 14.9 35 9.5 11.3 12.5 16.7 2 28.2 2.1 20.1 13.9

(4/36) (129/591) (2/12) (52/50) (9/53) (10/41) (17/70) (9/72) (1/20) (8/51) (10/60) (15/88) (4/33) (2/30) (3/16) (23/54) (16/33) (5/104) (51/205) (39/99) (13/64) (11/100) (7/24) (5/25) (6/57) (20/128) (54/480) (7/63) (33/202) (11/74) (14/40) (4/42) (24/212) (14/112) (12/72) (2/102) (11/39) (10/469) (61/304) (32/231)

* 10.7 8.3 * * 1.1 * 0.9

(2/231)

ALIF ALIF ALIF ALIF ALIF ALIF ADR ALIF ADR ALIF

4.4 7.9 50 38.7 1.6 10.1 18.2 1.5 9.9 8.7

(2/45) (22/279) (39/78) (24/62) (4/243) (23/228) (10/55) (2/130) (40/405) (15/172)

2.2 9.7 25.6 37.1 0.8 1.8 0 2.3 4.2 9.3

(1/45) (27/279) (20/78) (23/62) (2/243) (4/228) (0/55) (3/130) (17/405) (16/172)

6.7 17.6 75.6 75.8 2.5 11.8 18.2 3.8 14.1 18

(3/45) (49/279) (59/78) (47/62) (6/243) (27/228) (10/55) (5/130) (57/405) (31/172)

0 9 11.5 32.3 0.8 0 0 0 4.2 8.1

(0/45) (25/279) (9/78) (20/62) (2/243) (0/228) (0/55) (0/130) (17/405) (14/172)

ALIF ALIF ALIF & ADR ADR

47.1 18.8 17.6 12.5

(41/87) (15/80) (3/17) (3/24)

4.6 1.3 5.9 0

(4/87) (1/80) (1/17) (0/24)

51.7 20 23.5 12.5

(45/87) (16/80) (4/17) (3/24)

10.3 0 0 0

(9/87) (0/80) (0/17) (0/24)

& ADR

& ADR

& ADR

& ADR & ADR

8.3 0.8 0 24 1.9

(3/36) (5/591) (0/12) (12/50) (1/53)

* 7.1 (5/70) 0 (0/72) * 2 0 1.1 3 0

(1/51) (0/60) (1/88) (1/33) (0/30)

9.3 0 1 5.4 9.1

(5/54) (0/33) (1/104) (11/205) (9/99)

5 0 8 3.5

(5/100) (0/24) (2/25) (2/57)

*

*

* * * * * 5 (2/40) 2.4 (1/42) (12/112) (6/72)

(5/469)

(Continued)

D.K. Bateman et al. / The Spine Journal 15 (2015) 1118–1132

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Table 2 (Continued ) Reported complications

Study information

Intraoperative & approach-related Approach Mini-open RP Zdeblick and David, 2000 [32] Brau, 2002 [38] Rodr
ıguez et al., 2002 [36] Chung et al., 2003 [46] Escobar et al., 2003 [45] Brau et al., 2004 [11] Lee et al., 2004 [49] Saraph et al., 2004 [52] Choi et al., 2005 [56] Chung et al., 2006 [59] Datta et al., 2007 [15] Kang et al., 2009 [64] Kim et al., 2009 [65] Bohinski et al., 2010 [69] Delamarter et al., 2011 [71] Hrabalek et al., 2014 [72] Silvestre et al., 2012 [74] Shin et al., 2013 [80] Mini-open TP Kaiser et al., 2002 [37] Laparoscopic RP Henry et al., 1997 [7] Cowles et al., 2000 [8] Thalgott et al., 2000 [33] Boos et al., 2001 [35] Escobar et al., 2003 [45] Farooq and Grevitt, 2004 [12] Aunoble et al., 2006 [58] Frantzides et al., 2006 [60] Laparoscopic TP Mahvi and Zdeblick, 1996 [25] Henry et al., 1997 [7] Katkhouda et al., 1999 [30] Regan et al., 1999 [28] Lieberman et al., 2000 [9] Zdeblick and David, 2000 [32] Kleeman et al., 2001 [34] Kaiser et al., 2002 [37] Kleeman et al., 2002 [10] Rodr
ıguez et al., 2002 [36] Chung et al., 2003 [46] Escobar et al., 2003 [45]

Surgery

% (n/N)

ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF ADR ALIF ALIF ALIF ALIF ADR ALIF ALIF ALIF

0 3.8 35.7 9.1 9.8 1.9 5.5 30.4 4.5 13.9 7.5 10.4 2.1 4 3.6 19.2 6.1 2.5

& ADR

& ADR

& ADR & ADR

(0/25) (26/686) (5/14) (2/22) (5/51) (25/1,310) (4/73) (7/23) (1/22) (5/36) (4/53) (43/412) (1/48) (2/50) (6/165) (23/120) (11/179) (1/40)

Postoperative

4 0.6 0 0 0 0 9.6 4.3 0 0 9.4 2.2 8.3 2 0.6 9.2 5 0

(1/25) (4/686) (0/14) (0/22) (0/51) (0/1,310) (7/73) (1/23) (0/22) (0/36) (5/53) (9/412) (4/48) (1/50) (1/165) (11/120) (9/179) (0/40)

5.9 (3/51)

Overall

4 4.4 35.7 9.1 9.8 1.9 15.1 34.8 4.5 13.9 17 12.6 10.4 6 4.2 28.3 11.2 2.5

(1/25) (30/686) (5/14) (2/22) (5/51) (25/1,310) (11/73) (8/23) (1/22) (5/36) (9/53) (52/412) (5/48) (3/50) (7/165) (34/120) (20/179) (1/40)

ALIF

19.6 (10/51)

ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF

32 26.5 12.9 25 20 10.5 10 25

(8/25) (9/34) (26/202) (5/20) (6/30) (2/19) (2/20) (7/28)

0 2.9 1 0 0 5.3 15 14.3

(0/25) (1/34) (2/202) (0/20) (0/30) (1/19) (3/20) (4/28)

32 29.4 13.9 25 20 15.8 25 39.3

(8/25) (10/34) (28/202) (5/20) (6/30) (3/19) (5/20) (11/28)

ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF ALIF & ADR ALIF ALIF

20 3.9 29.2 10.3 14.9 16 13.6 27.7 16.5 22.6 9.1 17.6

(4/20) (2/51) (7/24) (6/58) (7/47) (4/25) (3/22) (13/47) (23/139) (7/31) (2/22) (6/34)

0 7.8 8.3 5.2 4.3 4 0 2.1 1.4 3.2 4.5 0

(0/20) (4/51) (2/24) (3/58) (2/47) (1/25) (0/22) (1/47) (2/139) (1/31) (1/22) (0/34)

20 11.8 37.5 15.5 19.1 20 13.6 29.8 18 25.8 13.6 17.6

(4/20) (6/51) (9/24) (9/58) (9/47) (5/25) (3/22) (14/47) (25/139) (8/31) (3/22) (6/34)

Reoperation

0 (0/25) 0 (0/686) * 0 (0/22) * * 0 0 0 0 0 0.5 2.1 4 2.4 0 0.6 2/5

25.5 (13/51)

(0/73) (0/23) (0/22) (0/36) (0/53) (2/412) (1/48) (2/50) (4/165) (0/120) (1/179) (1/40)

0 (0/51) 0 (0/25) * 0 (0/202) 0 (0/20) * * 5 (1/20) 14.3 (4/28) 5 5.9 0 8.6 6.4 0 0 0 * * 0 *

(1/20) (3/51) (0/24) (5/58) (3/47) (0/25) (0/22) (0/47)

(0/22)

RP, retroperitoneal; ALIF, anterior lumbar interbody fusion; ADR, anterior disc replacement; ALS, anterior lumbar surgery; TP, transperitoneal. * Not reported.

outside the range of statistical significance. Other data for laparoscopic compared with open surgery were also mixed, with significant reductions in total postoperative complications and ileus, along with significant increases in intraoperative bladder and peritoneal injury (Fig. 3A). There was no difference in overall complication rates between laparoscopic and open surgery (p5.99). Although individual reports found laparoscopic techniques to be safe and efficacious [7,9,25,28,33–35,58,60], direct comparisons with open or mini-open procedures revealed increased rates of

overall complications, operative time, and cost associated with laparoscopy [8,12,30,32,36,37,45,46]. In contrast, reports of mini-open techniques were all favorable, with investigators noting reduced complications and improved clinical outcomes [11,15,32,36–38,45,46,49, 52,56,59,64,65,69,71,72,74]. Pooled data for mini-open exposure were associated with reduced rates of overall, postoperative, urologic, and prosthesis-related complications, as well as lower rates of reoperation, superficial infection, and RE compared with open techniques (Fig. 3B). Two

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Table 3 Incidence of specific complications associated with anterior lumbar surgery Surgical parameter (patients, N)

Open

Mini-open

Laparoscopic

CTA

Complication, n (%)

RP & TP RP (5,760) TP (212) (1,120)

RP (3,370) TP (51)

RP (378) TP (519)

No (10,830) Yes (580) No (9,617) Yes (1,254) No (6,832) Yes (4,422) (11,410)

(0.06) (1.65) (0) (0.1) (0.25) (0.08) (0.1) (2.72) (0.39)

0 2 0 0 0 1 0 1 0

Access surgeon

Overall

(0) 0 (0) (3.92) 29 (7.67) (0) 0 (0) (0) 4 (1.06) (0) 14 (3.7) (1.96) 0 (0) (0) 2 (0.53) (1.96) 6 (1.59) (0) 2 (0.53)

2 11 0 6 0 0 5 8 5

(0.39) (2.12) (0) (1.16) (0) (0) (0.96) (1.54) (0.96)

16 330 18 15 39 10 21 179 62

(0.16) (3.39) (0.19) (0.16) (0.41) (0.11) (0.22) (1.87) (0.65)

0 8 0 0 1 0 1 1 0

(0) (1.38) (0) (0) (0.17) (0) (0.17) (0.17) (0)

16 315 18 13 38 9 15 170 56

(0.17) 0 (0) (3.39) 19 (2.12) (0.24) 0 (0) (0.17) 0 (0) (0.51) 2 (0.22) (0.14) 1 (0.11) (0.2) 5 (0.56) (2.26) 5 (0.56) (0.61) 6 (0.67)

9 183 18 6 35 5 12 160 23

(0.14) 7 (0.16) (2.84) 155 (3.62) (0.35) 0 (0) (0.12) 9 (0.24) (0.68) 5 (0.13) (0.1) 5 (0.2) (0.23) 10 (0.26) (3.11) 20 (0.53) (0.36) 39 (0.91)

16 338 18 15 40 10 22 180 62

(0.15) (3.15) (0.2) (0.17) (0.45) (0.13) (0.25) (2.01) (0.58)

(0.36) 0 (0.87) 1 (0.89) 5 (0.15) 0 (5.14) 10

(0) 0 (4.55) 2 (9.8) 5 (0) 1 (19.61) 65

(0) (1.25) (1.32) (0.26) (17.2)

3 35 9 0 84

(0.58) (15.22) (1.73) (0) (16.18)

16 132 122 32 963

(0.16) 0 (2.93) 2 (1.48) 2 (0.39) 0 (9.48) 15

(0) (0.50) (0.34) (0) (2.59)

15 104 114 31 906

(0.16) 1 (0.11) (2.73) 30 (4.12) (1.52) 7 (0.88) (0.41) 1 (0.13) (9.74) 56 (6.24)

7 70 71 24 606

(0.11) 9 (2.44) 64 (1.41) 53 (0.48) 8 (9.4) 372

(0.21) (3.14) (1.39) (0.21) (8.68)

16 134 124 32 978

(0.15) (2.73) (1.4) (0.36) (9.11)

(0) (0) (0.3) (0) (0.15) (0.08) (0.15) (1.88) (0.4)

(0) (1.96) (1.96) (0) (0) (0) (1.96) (0) (0)

(0) (0) (0.53) (0) (0.26) (0.57) (0) (0) (1.85)

1 1 0 1 0 0 5 3 6

(0.19) (0.19) (0) (0.19) (0) (0) (1) (0.6) (1.16)

9 43 90 7 9 36 64 98 175

(0.1) (0.49) (1.09) (0.08) (0.11) (0.51) (0.85) (1.36) (2.09)

(0) (1.03) (0.17) (0) (0.17) (0) (0.34) (0.34) (0.17)

9 42 82 7 10 31 53 95 145

(0.11) 0 (0) (0.53) 2 (0.25) (1.09) 9 (1.13) (0.09) 0 (0) (0.13) 0 (0) (0.5) 5 (0.63) (0.81) 13 (1.26) (1.5) 5 (0.56) (1.93) 27 (3.01)

7 39 58 7 7 25 42 74 126

(0.14) (0.77) (1.15) (0.14) (0.14) (0.51) (0.79) (1.49) (2.45)

(0.05) (0.23) (0.87) (0) (0.08) (0.4) (0.86) (0.93) (1.31)

9 49 91 7 10 36 66 100 176

(0.1) (0.53) (1.03) (0.08) (0.11) (0.47) (0.81) (1.29) (1.97)

0 1 1 0 0 0 1 0 0

0 0 2 0 1 1 0 0 7

0 6 1 0 1 0 2 2 1

2 10 33 0 3 11 24 26 50

(0.56) 0 (0) 5 (1.69) 12 (3.81) 206 (3.05) 10 (1.72) 175 (2.92) 31 (3.89) 174 (4.19) 42 (1.32) 216 (2.95) (1.59) 3 (5.89) 11 (2.91) 17 (3.28) 522 (5.39) 13 (2.24) 470 (5.33) 56 (6.24) 376 (5.83) 159 (4.18) 535 (5.22) (6.73) 13 (25.49) 76 (20.11) 101 (19.46) 1,485 (14.62) 28 (4.83) 1,376 (14.8) 112 (12.47) 982 (15.22) 531 (12.39) 1,513 (14.09)

CTA, computed tomography angiography; rhBMP-2, recombinant bone morphogenetic protein-2; RP, retroperitoneal; TP, transperitoneal.

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Intraoperative & approach-related complications: incidence, n (%) Arterial injury 9 (0.18) 0 (0) 3 (0.27) 2 Venous injury 193 (3.76) 18 (8.65) 30 (2.68) 55 Spinal event 3 (0.06) 0 (0) 15 (1.34) 0 Ureteral/bladder injury 2 (0.04) 0 (0) 1 (0.09) 2 Peritoneal injury 18 (0.39) 0 (0) 3 (0.27) 5 Dural tear 7 (0.17) 0 (0) 1 (0.09) 1 Bowel injury 13 (0.28) 0 (0) 0 (0) 2 Neurologic injury 62 (1.33) 8 (3.85) 40 (3.57) 55 Deep venous 22 (0.43) 4 (1.92) 16 (1.43) 13 thrombosis Arterial thrombosis 1 (0.02) 0 (0) 0 (0) 12 Retrograde ejaculation 71 (2.34) 9 (9.28) 9 (1.62) 7 Ileus 64 (1.41) 18 (8.65) 5 (0.45) 18 Incisional hernia 20 (0.44) 5 (2.4) 3 (0.27) 3 Total intraoperative 460 (8.97) 62 (29.81) 126 (11.25) 171 Postoperative complications: incidence, n (%) Pulmonary embolism 8 (0.16) 0 (0) 0 (0) 0 Hematoma/seroma 37 (0.74) 0 (0) 2 (0.18) 8 Infection (superficial) 77 (1.69) 2 (0.96) 3 (0.27) 6 Infection (deep) 4 (0.09) 2 (0.96) 0 (0) 0 Wound dehiscence 6 (0.13) 0 (0) 0 (0) 3 Pneumonia/atelectasis 24 (0.53) 0 (0) 10 (0.93) 1 Urologic 51 (1.02) 0 (0) 7 (0.65) 2 Other 57 (1.24) 1 (5.88) 14 (1.3) 25 Prosthesis, graft, and 119 (2.56) 1 (0.48) 35 (3.13) 8 cage related Requiring reoperation 123 (3.63) 9 (4.33) 56 (5) 11 Total postoperative 374 (8.04) 6 (2.88) 71 (6.34) 53 Overall total 834 (16.25) 68 (32.69) 197 (17.59) 224

rhBMP-2

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revision procedures were observed with the MAVERICK lumbar disc prosthesis (Medtronic, Memphis, TN, USA) compared with the ALIF [70].

Fig. 2. Overall complication rates for different surgical groups and approaches.

retrospective reviews of patients undergoing ALIF reported RE rates of 2% to 6% for mini-open techniques compared with 25% to 45% for laparoscopic approaches [37,45]. However, there was an increased incidence of arterial thrombosis in the mini-open group, with 12 events occurring in 3,380 patients (0.35%) compared with 1 of 6,459 (0.02%) in open surgery (p!.01). All 12 thrombotic events were reported in two retrospective reviews of ALS [11,38] and occurred in the left iliac artery. Transperitoneal versus retroperitoneal. Anterior lumbar surgeries using a TP approach were associated with significantly higher rates of RE and borderline higher rates of postoperative ileus (p5.07) compared with RP approaches (Fig. 3C). There were 45 cases of RE in 353 males who underwent a TP approach, compared with 80 cases in 3,998 males in RP cohort (p!.01). Although two studies directly compared clinical outcomes in patients receiving an RP versus TP exposure, both of these were underpowered to detect significant differences in complication rates [7,45]. We observed a trend toward higher overall complication rates with TP exposures in all surgical groups, with the exception of laparoscopy, wherein the rates were similar (Fig. 2). Arthrodesis versus arthroplasty. The type of surgical procedure performed (ie, arthrodesis vs. arthroplasty) did not appear to impact the incidence of reported complications (Fig. 4). Overall and implant-related complication rates were similar in patients who underwent ADR compared with ALIF (p5.74 and .23, respectively). Similar to the pooled data, three investigational device exemption trials found no significant difference in overall complication rates, when directly comparing ADR with ALIF [54,70,71]. Higher rates of superficial infection were seen with the Charit
e Artificial Disc (DePuy Spine, Raynham, MA, USA), which was attributed to earlier mobilization in these patients [54]. Significantly lower revision rates were reported with ProDisc-L (Synthes USA, West Chester, PA, USA) compared with ALIF [71], whereas more

Threaded versus nonthreaded fusion devices. In patients who underwent ALIF, the use of a threaded fusion cage was associated with significantly higher overall and implant-related complication rates compared with nonthreaded devices (p!.01 and !.01, respectively; Fig. 4). Two studies directly compared complication rates in patients receiving threaded versus nonthreaded fusion devices and found significantly higher overall and intraoperative complication rates with threaded devices, mainly because of increased rates of intraoperative venous injury [14,48]. Use of rhBMP-2. Twelve studies reported complications in patients receiving rhBMP-2 as an alternative to autogenous bone graft [20,34,40,62,66,69,70,76–79,81]. The pooled data demonstrated no difference in total overall, intraoperative, and postoperative complications in patients who were treated with rhBMP-2 (pO.05). However, significantly higher rates of bowel injury and RE were observed in patients receiving rhBMP-2 (p5.02 and p!.01) (Fig. 3D). Additionally, borderline increases in prosthesis-related complications and reoperation rates were found with rhBMP-2 use (p5.06 and p5.06). Only two trials directly compared overall complication rates between patients receiving rhBMP-2 and a control group. One multicenter randomized controlled trial reported similar outcomes and postoperative complication rates with the use of rhBMP-2 versus iliac crest bone graft for ALIF, with reduced operative time and blood loss in the investigational group [40]. Although these authors reported higher rates of RE with rhBMP-2 use (6.4%) compared with iliac crest bone graft (1.5%), this difference was not significant (p5.216). Similarly, Gornet et al. [70] reported no difference in adverse event rates between ALIF with rhBMP-2 and lumbar disc arthroplasty. Individual reports specifically examining the association of rhBMP-2 and RE were contradictory: Comer et al. [76] found significantly higher rates of RE with rhBMP-2 exposure, whereas several other studies failed to demonstrate an increased risk [40,70,77–79]. Question 3: What preventative measures decrease the incidence of intraoperative and postoperative complications? Pooled complication rates in patients undergoing preventative measures, including CTA and the use of an access surgeon, are listed in Table 3. Access surgeons. Twenty-eight studies included the assistance of an access surgeon in 37 unique subgroups to facilitate intraoperative exposure [5,8–10,14,15,17,19,25,28,32–35,37, 38,41,43,44,46,54,63,65,73,75,77,79,81]. The participation of an access surgeon was associated with lower rates of reoperation, prosthesis-related complications, neurologic injury, and postoperative hematoma and seroma formation

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Fig. 3. Forest plots demonstrating the impact of surgical parameters on the incidence of reported complications. Parameters and control groups tested in generalized linear mixed model analysis include (A) laparoscopic and (B) mini-open compared with open techniques; (C) transperitoneal versus retroperitoneal approach; (D) utilization of rhBMP-2; (E) inclusion of an access surgeon; (F) and preoperative CTA. Data are presented as odds ratio (95% confidence interval). *Indicates significance (p!.05). rhBMP-2, recombinant bone morphogenetic protein-2; CTA, computed tomography angiography.

(Fig. 3E). However, this practice was also associated with significantly higher rates of venous thrombosis (p5.03). A borderline reduction in total postoperative complication rates (p5.07) was also observed. The only study to directly compare exposure-related morbidity with and without the use of an access surgeon reported no significant differences in complication rates between the two groups [5]. Preoperative CTA. Three studies used preoperative CTA in a total of 580 patients [15,28,73]. Computed tomography angiography use was associated with a borderline increase in postoperative complication rates (p5.07) with no significant impact on total intraoperative and overall complication

rates (pO.5) (Fig. 3F). None of the individual reports compared complication rates between patients receiving CTA and a control group.

Discussion Anterior lumbar spine surgery is commonly used to treat a variety of conditions, including degenerative disc disease, trauma, infection, deformity, and malignancy. Because of increasing popularity among spine surgeons, examining the complications associated with ALS is essential. Diverse literature cites vascular, neurologic, and visceral injury,

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Fig. 4. Overall and implant-related complication rates for different anterior lumbar surgical procedures and fusion constructs. ALIF, anterior lumbar interbody fusion; ADR, anterior disc replacement.

infection, RE, and implant-related complications as examples of adverse events associated with ALS. Some of these complications, such as a vascular injury resulting in major blood loss, can prove to be life threatening if not promptly addressed. The overall incidence of complications associated with ALS is relatively low, and the findings in this report are consistent with previous reviews [2–4]. The most commonly reported complication was vascular injury, the predominance of which was because of venous laceration. Recent reviews reported the incidence of venous injury in ALS ranging from 0% to 18% [3] and !4% [2] and the rate of arterial injury ranging from 0% to 5% [3] and 0% to 0.9% [2]. Arterial injuries are less common than venous injuries, owing to greater vessel elasticity and superior mobility [2]. Moreover, injuries to arterial structures more commonly present as thrombosis, possibly related to prolonged stretch and compression of the left iliac artery during retraction [2,82]. The rates of thromboembolism in this review are comparable to previous reports with an incidence of 0% to 5% and 0% to 1.3% for venous and arterial events, respectively [2,3]. Higher rates have been associated with multilevel instrumentation, male sex, laparoscopic and TP techniques, and exposure of the L4–L5 intervertebral space [3,19]. In an effort to reduce these complications, some authors have advocated the use of intraoperative lower extremity pulse oximetry [11,38], handheld rather than self-retaining retractors [2], and cyclical release of retractor pressure [83] to prevent arterial vasospasm. Clearly, delicate handling of vascular structures throughout the procedure is fundamental to reducing vessel injuries and thrombotic events. Neurologic complications comprised the third most commonly reported complication after ALS. Nerve roots may be damaged during graft or implant insertion, and careful attention must be paid to the lumbosacral plexus during exposure and retractor placement. Only one study reported the use of neurophysiological monitoring as a preventative measure during ALS. Blumenthal et al. [54]

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routinely used somatosensory-evoked potential (SSEP) monitoring to help reduce the risk of neurologic injury. In many instances, loss of SSEP signals may be related to vascular ischemia after retractor placement during exposure [84]. Changes in SSEP signals may indicate early neural injury and allow the surgeon to take measures to prevent permanent damage (eg, retractor removal or repositioning) [85]. A recent retrospective review of intraoperative neuromonitoring in 189 patients undergoing ALIF reported alerts in 7.9% of cases with higher rates in multilevel procedures. No patients in this series had new postoperative neurologic deficits [85]. Data regarding the overall clinical utility of nerve monitoring during ALS remain limited. Minimally invasive techniques for ALS have been developed in an attempt to decrease complications related to open muscle-splitting incisions. Early proponents of laparoscopic procedures cited reduced blood loss and lower postoperative morbidity, shorter hospital stays, and an earlier return to work as potential advantages over open techniques [25,28,30]. However, higher complication rates, a significant learning curve because of limited visualization and unfamiliar instrumentation, and longer operating times have been seen as barriers to their widespread implementation [32,45,60,74]. Our data confirm these reservations, with significantly higher intraoperative risk to visceral structures observed with laparoscopy. As such, surgeons have increasingly adopted a mini-open approach that provides more direct visualization and sufficiently wide exposure of the intervertebral discs with reduced abdominal trauma and avoidance of posterior neural structures. One group specifically stated that they have abandoned the use of laparoscopy in favor of mini-open techniques, citing technical feasibility, lower rates of RE, decreased operating time, and reduced cost [45]. Long-term reports of mini-open fusion and arthroplasty have been favorable, with reduced complication rates consistent with our results [38,45,46,56,59,71,74]. The anterior RP approach, first described in 1963 by Harmon [86], maintains the integrity of the peritoneum, minimizing bowel retraction and other complications associated with direct TP exposure, while allowing access to multiple spinal levels [87]. Wood et al. [3] reported that patients receiving a TP approach were significantly more likely to have a vascular injury (3.6%) compared with those who underwent RP exposure (1.9%). We observed a similar trend with intraoperative vascular injury occurring in 4.2% (TP) versus 3.3% (RP), although this difference was not significant (p5.15). Retrograde ejaculation is a notorious complication specifically associated with anterior lumbar procedures. The superior hypogastric plexus, which coordinates bladder sphincter control during ejaculation, is intimately related to the anterior aorta and left common iliac vein, lying just beneath the peritoneum. Injury may occur when dividing the peritoneum, with traction on the plexus and surrounding vessels, and with accidental ligation [2]. Similar to our

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findings, a prospective multicenter study with 146 male patients found a 10-fold higher incidence of permanent RE in patients who underwent a single-level open TP fusion compared with RP exposure [88]. Since Food and Drug Administration approval for single-level ALIF was granted in 2002, the safety profile of rhBMP-2 has been thoroughly scrutinized, after reports of serious complications associated with increasing use [89]. An extensive systematic review of complications associated with rhBMP-2 utilization revealed possible methodological flaws and under-reporting of complication data, as well as financial conflicts of interest, in the original industry-sponsored trials investigating rhBMP-2 [89]. Two meta-analyses from the Yale University Open Data Access Project reported nonsignificant increases in RE rates with rhBMP-2 use in ALIF [90,91]. However, these authors noted that low event rates precluded strong statistical conclusions and cautioned about the presence of significant industry bias in all available studies [90,91]. We observed a 2.6-times significantly increased risk of RE with exposure to rhBMP-2 in the pooled data, whereas the Yale University Open Data Access analyses synthesized data from original internal manufacturer reports, which may have differed from the published data included in our model. Alternatively, significant increases in the risk profile of rhBMP-2 determined by our model may actually reflect differences between investigational sites rather than inherent properties of the biologic agent. Controversy remains in the reported literature, with contradictory reports regarding the risks of rhBMP-2 and association with RE [40,70,76–79]. Comer et al. [76] reported a significantly higher rate of RE in patients exposed to rhBMP-2 compared with control patients (6.9% vs. 0.9%; p5.0012). Of note, urologic consultation and laboratory evaluations (urine and ejaculate analyses for sperm) were used to confirm suspected RE cases identified by clinical questionnaires. In a multicenter and randomized investigational device exemption trial, Burkus et al. [40] found a similar fourfold increase in RE events with rhBMP-2 use but noted this difference did not reach statistical significance (6.5% vs. 1.5%; p5.216). Another prospective quantitative assessment of RE using semen analysis failed to demonstrate an association with rhBMP-2 and suggested that standard questionnaires may overestimate the rates of reported RE [79]. Most recently, a systematic review found a significantly increased risk of RE with rhBMP-2 utilization in ALIF (7.3% vs. 2.3%; p5.03) [92]. Certainly, the potential risk of RE must be thoroughly discussed with male patients before using rhBMP-2. Implant characteristics may also affect the rates of anterior surgical complications. Anterior lumbar interbody fusion may be accomplished using threaded fusion devices (eg, machined bone dowels and cylindrical titanium implants) or nonthreaded cages (eg, iliac crest autografts and femoral ring allografts). Our analysis revealed increased overall and implant-related complications with

the use of threaded devices, which was consistent with two trials directly evaluating these techniques [14,48]. The authors of those reports attributed the increased complication rates to the additional instrumentation required to insert threaded devices and did not feel that the exposure itself had a significant impact. Care must be taken during implantation of interbody cages, and implant type should be considered with preoperative planning. Two preventative measures were evaluated to determine their impact on complication rates. Traditionally, preoperative CTA has been used to define complex vascular anatomy and identify any vascular anomalies or atherosclerotic disease. If significant anatomic variations are observed, some surgeons may choose an alternative procedure or approach or consult an access surgeon to facilitate exposure of the intervertebral space [15,93]. Datta et al. [15] described their use of preoperative CTA to accurately define the prevertebral vascular anatomy. The authors observed significant vascular anomalies or atherosclerotic disease in 12% and 17% of patients, respectively, and this information directly affected surgical decision making in 21% of cases [15]. However, a recent study found preoperative CTA to have low clinical utility for anterior spine surgery and cautioned against routine use because of considerable radiation exposure [93]. Our analysis found no significant benefits to preoperative CTA, with a borderline increase in postoperative complications. The higher incidence of postoperative complications seems to be counterintuitive and may potentially be attributed to an inflated Type 1 error. Alternatively, it is possible that CTA was used more often to plan for more complicated cases, such as deformity correction or for patients with vascular disease or thrombophilia, which inherently have an increased incidence of postoperative complications. However, we are unable to confirm this without adequate demographic information. Moreover, CTA use was evaluated by only three studies, and significant differences may exist between this group and the remaining cohort in terms of surgical indications and patient characteristics. Potential benefits of CTA must be carefully weighed, given a lack of reported clinical outcomes, increased cost, and risk of additional radiation exposure. Many authors have incorporated access surgeons into the surgical team because of their familiarity with visceral and RP structures [8–10,14,15,17,19,25,28,32–35,37,38,41,43, 44,46,54,63,65,73,75,81]. Although generally good results have been reported with this multidisciplinary approach, others argue it is unnecessary for adequately trained spine surgeons [5,21]. Our analysis found mixed benefits, as the assistance of an access surgeon was associated with lower rates of reoperation, prosthesis-related complications, neurologic injury, and postoperative hematoma or seroma, and higher rates of venous thrombosis. The increased risk of thrombotic events may be a reflection of access surgeons being consulted on more complex cases with increased risk

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because of anatomic variations, prior surgery, or multilevel instrumentation. Indeed, one group noted selective recruitment of access surgeons for cases considered to be more challenging [5]. The inclusion of an access surgeon remains contentious but may be advisable for less experienced surgeons and cases deemed at higher risk. Limitations All results should be viewed in light of the inherent limitations of our study design. Meta-analytic pooling of potentially dissimilar study data requires cautious interpretation under the best circumstances. Furthermore, comparing multiple endpoints runs a known risk of inflated Type I error. As such, it may happen that those complications, where a generally protective effect appeared harmful or the reverse, are because of random chance. This may explain seemingly counterintuitive results, such as marginally higher rates of postoperative complications with preoperative CTA or the higher rates of thrombotic events in mini-open procedures and with access surgeon involvement. Heterogeneity of study reporting standards and patient populations is a significant source of confounding. Studies differed in surgical indications and procedures, patient selection and follow-up, as well as in the assessment and reporting of complications. Most notably, there were inherent differences in evaluating and reporting both the severity and number of complications in each report. All individual complications listed in our analysis were assumed to be reportable events by the original study authors, unless explicitly stated otherwise. However, it is possible that a complication listed as not occurring in our aggregate model may not have been considered a reportable complication for a particular study. In this case, our pooled complication rates may be artificially low. This may explain the low overall infection rate as compared with some previous reports [94,95]. Our model did not control for surgical indication (ie, primary or revision), patient factors (eg, age, smoking status, obesity, intra-abdominal scarring from previous surgery, medical comorbidities), operative spinal level, or number of levels requiring surgery as independent risk factors. Revision ALS has been associated with a three to five times higher rate of complications [2], and it is has been suggested that elderly patients are at an increased risk of certain complications, such as vascular injury [96]. Unfortunately, many studies reported inadequate demographic information, and there may have been wide variations in these factors. Again, caution should be taken when extending the results presented here to a specific patient population. Another potential source of confounding lies in our selection of data groupings, which allowed broad comparisons to be made between surgical parameters. Intraoperative and approach-related complications were combined for

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reporting purposes. This group included complications, such as thrombotic events, RE, and incisional hernia that occurred postoperatively, but were felt to be intimately related to the operative technique or device in question. Ultimately, however, these distinctions were somewhat arbitrary. Finally, incomplete and/or inaccurate retrieval and pooling of identified research is another potential source of error. Although every effort was made to find and include all relevant articles within the study criteria, we cannot be certain that one or more key items were not overlooked. Furthermore, as with any meta-analysis, the reported results are likely to be biased toward the sample with the largest cohort. Brau et al. [11] reported on the largest patient sample, and it is possible that these results are influenced by their reporting standards. Last, although articles from the same author that obviously reported data from overlapping cohorts were excluded, this was not evident in every case, and some complications may have been reported in duplicate [11,38]. Given these significant limitations, the analyses presented here should be viewed not as inherently definitive but rather as a guide to designing confirmatory studies.

Conclusion Overall morbidity associated with ALS is relatively low, with the most common complications occurring at a rate of 1% to 3%. Complication rates, both overall and within specific complication types, can be affected by surgical technique and approach and implant characteristics. Further randomized controlled trials are needed to validate the use of preventative measures including CTA and the utilization of an access surgeon. Despite the relatively infrequent incidence of complications, the spine surgeon must be prepared to fully address any adverse events. References [1] Pannell WC, Savin DD, Scott TP, Wang JC, Daubs MD. Trends in the surgical treatment of lumbar spine disease in the United States. Spine J 2013 Oct 31. [Epub ahead of print]. [2] Czerwein JK, Thakur N, Migliori SJ, Lucas P, Palumbo M. Complications of anterior lumbar surgery. J Am Acad Orthop Surg 2011;19: 251–8. [3] Wood KB, Devine J, Fischer D, Dettori JR, Janssen M. Vascular injury in elective anterior lumbosacral surgery. Spine 2010;35(9 Suppl):S66–75. [4] Than KD, Wang AC, Rahman SU, Wilson TJ, Valdivia JM, Park P, et al. Complication avoidance and management in anterior lumbar interbody fusion. Neurosurg Focus 2011;31:E6. [5] Jarrett CD, Heller JG, Tsai L. Anterior exposure of the lumbar spine with and without an ‘‘access surgeon’’: morbidity analysis of 265 consecutive cases. J Spinal Disord Tech 2009;22:559–64. [6] Wright JG, Swiontkowski MF, Heckman JD. Introducing levels of evidence to the journal. J Bone Joint Surg Am 2003;85-A:1–3. [7] Henry LG, Cattey RP, Stoll JE, Robbins S. Laparoscopically assisted spinal surgery. JSLS 1997;1:341–4.

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