Eur Spine J DOI 10.1007/s00586-014-3221-2
REVIEW ARTICLE
Comparison of unilateral versus bilateral pedicle screw fixation in degenerative lumbar diseases: a meta-analysis Ying-Chao Han • Zhu-Qing Liu • Shan-Jin Wang Li-Jun Li • Jun Tan
•
Received: 24 September 2013 / Revised: 26 January 2014 / Accepted: 27 January 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Traditionally, lumbar spinal surgery is performed with bilateral pedicle screw fixation to provide stability as the fusion heals. However, many studies have reported that unilateral pedicle screw fixation is as effective as bilateral constructs. To compare the clinical outcomes, complications, and surgical trauma between the two techniques for treatment of degenerative lumbar diseases, we conducted a meta-analysis. Methods We searched MEDLINE, EMBASE, PubMed, Google Scholar, and Cochrane databases for relevant controlled studies up to August 2013 that compared unilateral with bilateral fixation for the treatment of degenerative lumbar diseases. We independently performed title/ abstract screening and full-text screening. A random effects model was used for heterogeneous data; otherwise, a fixed effect model was used, pooling data using mean difference (MD) for continuous outcomes and odds ratio (OR) for dichotomous outcomes. Results A total of 12 articles (865 participants) were eligible. Overall, there were significant differences
between the two groups for blood loss (MD = -171.73, 95 % CI = -281.70 to -61.76; p = 0.002), operation time (MD = -66.02, 95 % CI = -115.52 to -16.51; p = 0.009), and fusion rate (OR = 0.50, 95 % CI = 0.26–0.96; p = 0.004). However, there were no significant differences in hospital stay (MD = -4.44, 95 % CI = -13.37 to 4.50), ODI (MD = -0.09, 95 % CI = -0.59 to 0.42; p = 0.74), JOA (MD = 0.18, 95 % CI = -0.77 to 1.14; p = 0.71), VAS (MD = -0.04, 95 % CI = -0.16 to 0.08; p = 0.49), SF-36 (PF: MD = -1.11, 95 % CI = -4.38 to 2.17, p = 0.51; GH: MD = 1.22, 95 % CI = -2.17 to 4.60, p = 0.48; MH: MD = -0.22, 95 % CI = -3.83 to 3.38, p = 0.90) and complications (OR = 1.15, 95 % CI = 0.72–1.85; p = 0.56). Conclusions This meta-analysis shows that there was significantly less blood loss in unilateral group and less operating time; however, the fusion rate was significantly higher in the bilateral group. The outcomes of hospital stay, ODI, JOA, VAS, SF-36 score, and complications are similar in the two groups. Keywords Unilateral Bilateral Pedicle screw fixation Degenerative lumbar diseases Meta-analysis
Y.-C. Han and Z.-Q. Liu contributed equally to this work. Y.-C. Han S.-J. Wang (&) L.-J. Li J. Tan (&) Department of Spinal Surgery, East Hospital, Tongji University School of Medicine, 150# Jimo RD, Pudong New Area, Shanghai 200120, China e-mail: [email protected] J. Tan e-mail: [email protected] Z.-Q. Liu Department of Medical Oncology, Shanghai Tenth People’s Hospital, Tongji University School of Medicine, Shanghai, China
Introduction An increasing number of adults experience chronic low back pain, especially that caused by degenerative lumbar diseases [1]. Lumbar spinal fusion is a common surgical procedure and is recognized as an effective treatment for degenerative lumbar diseases, such as spondylolisthesis, lumbar spinal canal stenosis associated with deformities, or discogenic pain identified by provocative discography [2–4]. Lumbar fusion can achieve solid arthrodesis, immobilizing the
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unstable segment and degenerated intervertebral disk area [5, 6]. Currently, pedicle screws and intervertebral cage devices are frequently used to provide spinal stability. It is generally accepted that rigid pedicle screw fixation is important for excellent fusion rates and lowers the chances of non-union at the graft site [7–9]. The additional instrumentation also has the advantages of no external immobilization, early ambulation, restoration of sagittal alignment, and segment height [3, 10, 11]. Bilateral pedicle screw fixation after interbody fusion is regarded as a standard instrumentation construct for the management of a variety of spinal conditions and has both biomechanical and clinical advantages [12–14]. However, rigid fixation also has inconveniences. In animal model, decrease of the mineral content of the fixed area has been appreciated [15, 16], but some biomechanical comparison of unilateral and bilateral pedicle screw fixation is also have debate [17, 18]. In addition, the technique is associated with increased complications, and there have been doubts as to its costs and benefits [19, 20]. Alternatively, the less rigid technique of unilateral pedicle fixation is considered to be as effective as bilateral constructs from a biomechanical and clinical perspective. Unilateral pedicle fixation also avoids soft tissue disruption on the contralateral side, has a significantly reduced operation time, and is associated with lower implant costs [21–23]. However, some studies have raised concerns that unilateral fixation may result in non-union and postoperative back pain due to the opposite facet’s dysfunction, metal failure, pseudarthrosis, or cage migration due to the decreased strength or inherent asymmetry of this system [21, 24]. Previous studies that have compared the clinical effects of bilateral and unilateral screw fixation for the treatment of degenerative lumbar diseases are conflicting, but it is still uncertain whether unilateral or bilateral screw fixation is more effective. Therefore, to clarify these ambiguous findings we performed a meta-analysis, comparing the two techniques for the treatment of degenerative lumbar diseases.
Methods Eligibility and exclusion criteria Studies published in English were considered to be eligible if they met the following criteria: (1) involved adult patients (aged 18–80 years) of both genders; (2) patients had degenerative lumbar diseases, such as degenerative spondylolisthesis, symptomatic degenerative disk disease, or symptomatic lumbar stenosis with segmental instability; (3) patients had persistent or recurrent low back or leg pain resulting in a significant reduction of quality of life, despite
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conservative therapy for at least 3 months; (4) used a randomized or non-randomized controlled clinical study design on unilateral and bilateral screw fixation for the treatment of degenerative lumbar disease; (5) one- or twolevel intended interbody fusion between L1 and S1; and (6) outcome assessment was based on the primary and secondary outcome. The primary outcomes included major surgical complications, radiographic outcomes, fusion rate, or patient-related outcome measures of pain, and quality of life using various validated questionnaires, such as the Japanese Orthopedic Association scores (JOA), the Visual Analogue Score (VAS), the Oswestry Disability Index (NDI), and the short-form health survey (SF-36). The secondary outcomes included surgical data, such as the operation time, blood loss, and the length of the hospital stay. Studies were excluded if they (1) involved patients without degenerative lumbar diseases, such as those with lumbar fractures; (2) involved patients with another disease, such as severe osteoporosis, active infection, metabolic disease or symptomatic vascular disease; (3) involved previous lumbar surgery; (4) only described unilateral or bilateral screw fixation; and (5) were case reports, biomechanical research, or systematic reviews. Search strategies We searched for published results of relevant trials in the Cochrane Library (Cochrane Library 2013), MEDLINE (1966–August 2013), EMBASE (1974–August 2013), PubMed (1966–August 2013) and Google Scholar (1966– August 2013). The following search terms were used: ‘‘degenerative lumbar diseases’’, ‘‘lumbar spinal fusion’’, ‘‘pedicle screw fixation’’, ‘‘unilateral’’, and ‘‘bilateral’’, with various combinations of the operators ‘‘AND’’, ‘‘NOT’’, and ‘‘OR’’. We restricted the language to English. References cited in the articles and relevant review articles were checked to identify additional studies. The full search strategy is available upon request from the corresponding author (Jun Tan). The quality of the studies was independently assessed by two authors (Han and Liu), and the level of agreement between reviewers was recorded. Inclusion of resultant titles was determined by manual screening of titles and abstracts, followed by full-text screening by the same reviewers. If additional data or clarifications were necessary, we contacted the study authors. Any disagreement between reviewers was resolved by discussion with another reviewer (Wang). Data extraction and management Data were independently extracted by two reviewers (Han and Liu), with further discussion with another independent
Study design
RCT
RCT
RCT
Retrospective
RCT
RCT
RCT
RCT
RCT
RCT
Prospective
Retrospective
References
Choi et al. [26]
Kai et al. [27]
Lin et al. [28]
Mao et al. [34]
Xue et al. [29]
Duncan et al. [31]
Xie et al. [30]
Aoki et al. [32]
Feng et al. [33]
FernandezFairen et al. [23]
Suk et al. [21]
Kabins et al. [22]
16
47
40
20
25
56
46
37
28
43
33
26
20
40
42
20
25
52
56
43
32
42
35
27
52
53.0 (32–68)
61.4 (51–70)
53.8 (37–72)
66.2 ± 8.3
56.2 (34–66)
53.5 (18–77)
57.1 ± 8.1
48.0 ± 8.1
67 (57–74)
59.4 ± 10.2
53.39 ± 14.31
48
54.7 (31–71)
60.8 (50–70)
53.2 (25–73)
65.6 ± 8.8
55.0 (34–68)
55.7 (26–82)
58.2 ± 7.6
52.0 ± 7.2
65.5 (58–76)
55.7 ± 11.6
56.22 ± 12.62
Bilateral
Unilateral
Unilateral
Bilateral
Mean age (years)
Sample size
Table 1 Characteristics of the included studies
8 M/8 F
13 M/34 F
16 M/24 F
12 M/7 F
8 M/17 F
24 M/32 F
20 M/26 F
17 M/20 F
16 M/12 F
19 M/24 F
14 M/19 F
12 M/14 F
Unilateral
9 M/11 F
9 M/31 F
15 M/27 F
10 M/10 F
12 M/13 F
24 M/28 F
20 M/36 F
18 M/25 F
18 M/14 F
20 M/22 F
10 M/25 F
9 M/18 F
Bilateral
Sex(male/female)
23.4 (14–40)
24
55.6 (39–77)
24
31.0 (24–37)
36–48
25.1
25.3
18
26 (18–32)
25.6 (18–36)
27.52 ± 3.30
Unilateral (m)
26.5 (12–36)
59.7 (38–78)
31.2 (24–42)
28.85 ± 4.37
Bilateral
Follow-up (months, years) Bilateral
VSP, autograft/ allograft
Moss Miami system or VSP
Cage, autograft
TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
TLIF, PEEK cage, autograft/allograft
TLIF, saber lumbar I/F cage, autograft
TLIF, PEEK cage, autograft
Mis-TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
Unilateral
Type of operation
Bilateral
1-segment
1-segment, 2-segments
1-segment, 2-segments
1-segment
1-segment
1-segment, 2-segments
1-segment
1-segment, 2-segments
1-segment
1-segment
2-segments
1-segment
Unilateral
Surgical segments
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Eur Spine J Table 2 Details and heterogeneity of clinical outcome measurement of the included studies References
Hospital stay
Operation time
Blood loss
JOA
VAS
ODI
SF-36
fusion rate
Complications
Cost
Choi et al. [8]
NR
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
NR
Kai et al. [27]
Yes
Yes
Yes
NR
Yes
Yes
Yes
Yes
Yes
Yes
Lin et al. [24]
NR
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
NR
Mao et al. [34]
Yes
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
NR
Xue et al. [29]
Yes
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
Yes
Duncan et al. [31]
NR
NR
NR
NR
NR
NR
NR
NR
Yes
NR NR
Xie et al. [30]
Yes
Yes
Yes
Yes
NR
NR
Yes
NR
Yes
Aoki et al. [32]
NR
Yes
Yes
Yes
Yes
NR
NR
Yes
Yes
NR
Feng et al. [33]
Yes
Yes
Yes
Yes
Yes
Yes
NR
NR
NR
YES
FernandezFairen et al. [23] Suk et al. [21]
Yes
Yes
Yes
NR
NR
NR
Yes
Yes
Yes
NR
NR
Yes
Yes
NR
NR
NR
NR
Yes
Yes
Yes
Kabins et al. [22]
NR
YES
YES
NR
NR
NR
NR
YES
NR
NR
Number of patients involved
438, 214 M/ 224 F
749, 371 M/ 378 F
749, 371 M/ 378 F
198, 101 M/ 97 F
436, 212 M/ 224 F
386, 187 M/ 199 F
258, 129 M/ 129 F
709, 351 M/ 358 F
789, 392 M/ 397 F
275, 137 M/ 138 F
expert (Wang). The following data were extracted: (1) the characteristics of the included papers, including the authors, study design, year of publication, sample size, age, gender, duration of follow-up, type of operation, and the surgical segments (Table 1); and (2) details of the clinical outcome measurement, including the length of hospital stay, blood loss, operation time, JOA, VAS, NDI, SF-36, fusion rate, and the type of complications (Table 2). All included studies met the inclusion and exclusion criteria. The extracted data were rechecked for accuracy by one of the authors (Wang). Risk of bias assessment The risk of bias in randomized controlled studies was assessed by the two reviewers (Han and Liu) according to the 12 criteria and instructions recommended by the Cochrane Back Review Group (CBRG) [25]. For each criterion, ‘yes’, ‘no’, or ‘not reported’ was recorded. Studies were rated as having a low risk of bias when at least 6 of the 12 CBRG criteria were met and the study had no serious flaws. Studies with serious flaws or those in which fewer than six of the criteria were met were rated as having a high risk of bias. The quality of non-randomized controlled trials was assessed using the Newcastle Ottawa Quality Assessment Scale (NOQAS). This scale allocates a maximum of nine points for quality of selection, comparability, exposure, and outcome of study participants.
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Statistical analysis All statistical tests were performed using Review Manager software (RevMan version 5.1; The Cochrane Collaboration, Copenhagen, Denmark). Statistical heterogeneity was assessed using the Chi squared and I2 tests. A value of I2 [ 50 % was considered to represent substantial heterogeneity. A probability of p \ 0.05 was considered to be statistically significant. The results were expressed in terms of mean difference (MD) and 95 % CI for continuous outcomes and as odds ratio (OR), and 95 % confidence interval (95 % CI) for dichotomous outcomes. A random effects model was used for heterogeneous data; otherwise, a fixed effect model was used. Collected data were checked and entered into the computer by the two reviewers (Han and Liu).
Results Search results Through initial electronic database searches, a total of 1,153 relevant titles were identified. Of these, 971 were excluded after review of the abstract and title for the following reasons: being on an unrelated topic; not working with humans; not comparative studies; or being biomechanical studies, case reports, review articles, or other forms of investigation. Subsequently, 155 studies were
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the comparison of hospital stay. However, four studies did not provide the standard deviation, and, therefore, only two studies could be included in the meta-analysis. The available data of hospital stay demonstrated high heterogeneity (I2 = 100 %), perhaps because there were only two studies which were performed in different countries (Fig. 2). Eleven studies reported intraoperative blood loss and operation time (371 patients for unilateral and 378 patients for bilateral). However, eight studies did not provide the standard deviation, so a meta-analysis could only be performed with three studies. Blood loss and operation time was significantly higher in the bilateral group than in the unilateral one (blood loss: MD = -171.73, 95 % CI = -281.70 to -61.76; p = 0.002; operation time: MD = -66.02, 95 % CI = -115.52 to -16.51; p = 0.009; Figs. 3, 4). There was significant heterogeneity in blood loss and operation time between the studies (heterogeneity: I2 = 86 and 98 %, respectively), which could not be explained using our predefined subgroup analysis. Therefore, the quality of evidence for this outcome is low (Figs. 3, 4). Fig. 1 Flow diagram detailing study inclusion
JOA, VAS, ODI and SF-36
excluded due to failure to fit the inclusion criteria after review of the full text. A further 15 studies were excluded due to insufficient follow-up, being duplicate reports, or other intervention. In the end, 12 studies were identified as meeting the eligibility criteria [21–23, 26–34], including 9 randomized studies, 1 prospective study, and 2 retrospective studies. Study inclusion is detailed in Fig. 1.
The demographic characteristics of the studies included are presented in Table 1. The 12 studies included a total of 865 patients; 428 patients underwent unilateral fixation and 437 underwent bilateral fixation with various grafts, including autografts, allografts, and cages. All participants in the 12 studies had undergone follow-up for at least 18 months. The studies’ risk of bias is summarized in Tables 3 and 4. One report of a RCT had a methodological quality score of 5 (high risk of bias), while other RCTs had a quality score of 6–9 (low risk of bias). All of the non-randomized studies scored 8 points on the Newcastle Ottawa Quality Assessment Scale (NOQAS). Hence, all of the studies were of a relatively high quality.
With a mean follow-up of at least 18 months, three studies used the JOA score to assess the clinical outcome (198 patients). There was no significant difference in the final follow-up JOA score between the unilateral and the bilateral group (MD = 0.18, 95 % CI = -0.77 to 1.14; p = 0.71) with moderate heterogeneity (I2 = 63 %; Fig. 5). Seven studies included reports of back VAS scores (212 in the unilateral group and 224 in the bilateral group) and one report was excluded from the meta-analysis as it did not report the standard deviation. There was no difference in VAS score between the two groups (MD = -0.04, 95 % CI = -0.16 to 0.08; p = 0.49) with moderate heterogeneity (I2 = 43 %; Fig. 6). Six studies reported final follow-up ODI scores and one report was excluded for lacking standard deviation. There was no significant difference in the ODI score between the two treatment groups (MD = -0.09, 95 % CI = -0.59 to 0.42; p = 0.74; Fig. 7). Three trials reported the SF-36 (129 unilateral cases and 129 bilateral) and three evaluation indices (physical function, PF; general health, GH; mental health, MH) were included. All three indices were similar (p = 0.51, 0.48, 0.90), and the available data showed low heterogeneity (Fig. 8).
Clinical outcome analysis
Fusion rate and complications
Hospital stay, blood loss and operation time
Nine studies reported the fusion rate assessed by radiographs (293 unilateral cases, 300 bilateral). There was significantly a higher fusion rate in the bilateral group than in the unilateral group (OR = 0.50, 95 % CI = 0.26–0.96;
Demographic characteristics and quality assessment
A total of 438 patients from 6 studies (214 patients for unilateral and 224 patients for bilateral) were included in
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Eur Spine J Table 3 Risk of bias assessment of the randomized studies
Choi et al. [26]
Kai et al. [27]
Lin et al. [28]
Xue et al. [29]
Duncan et al. [31]
Xie et al. [30]
Aoki et al. [32]
Feng et al. [33]
FernandezFairen et al. [23]
Adequate randomization
Yes
Yes
NR
Yes
Yes
Yes
No
Yes
Yes
Allocation concealment
NR
NR
NR
NR
NR
Yes
No
NR
NR
Blinding of patients
No
No
No
No
No
No
No
No
No
Blinding of care providers
No
No
No
No
No
No
No
No
No
Blinding of outcome assessors
NR
NR
NR
NR
NR
Yes
No
NR
NR
Baseline comparability
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Drop-out rate is described
No
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Free of selective outcome reporting
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Co-interventions were similar
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Acceptable compliance between groups
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Intention-totreatment analysis
No
No
No
No
No
No
No
No
No
Similar timing of outcome assessment
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Overall quality (max 12)
6
7
6
7
5
9
6
7
7
Table 4 Quality assessment according to the Newcastle–Ottawa scale of the non-randomized studies References
Selection
Comparability
Exposure
Total score
Mao et al. [34]
3
2
3
8
Suk et al. [21]
3
2
3
8
Kabins et al. [22]
2
2
3
7
p = 0.004) with no heterogeneity (I2 = 0 %; Fig. 9). Ten trials reported complications (392 unilateral cases, 397 bilateral); however, the records of postoperative complications were variable. Some studies described all complications, whereas some provided only major complications. The incidence of total complications was similar in the two groups (OR = 1.15, 95 % CI = 0.72–1.85; p = 0.56) and there was also no difference for the complication of
Fig. 2 The forest plot for hospital stay between unilateral group and bilateral group
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Fig. 3 The forest plot for blood loss between unilateral group and bilateral group
Fig. 4 The forest plot for operation time between unilateral group and bilateral group
Fig. 5 The forest plot for JOA score between unilateral group and bilateral group
Fig. 6 The forest plot for VAS score between unilateral group and bilateral group
Fig. 7 The forest plot for ODI score between unilateral group and bilateral group
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Fig. 8 The forest plot for SF-36 between unilateral group and bilateral group
Fig. 9 The forest plot for fusion rate between unilateral group and bilateral group
infection and cage migration, with no heterogeneity (I2 = 0 %; Fig. 10).
Discussion Currently, pedicle screws are frequently used to provide an initially stable environment to improve the rate of fusion and speed patient recovery after surgery [35, 36].
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It is widely accepted that bilateral pedicle screws are the standard instrumentation constructs used in lumbar fusion. However, many studies have reported that increased stiffness of bilateral pedicle screw fixation results in many complications. With the development of surgical technology, advances in lumbar fusion techniques have concentrated on reducing soft tissue injury, maintaining the ability to achieve neural decompression and fewer complications [37–39]. Therefore, many spinal
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Fig. 10 The forest plot for complications between unilateral group and bilateral group
surgeons have been attracted by unilateral pedicle screw fixation. However, some studies, especially biomechanical studies, are less positive about the ability of unilateral fixation to maintain adequate support of the spine for fusion. In an in vitro study, Goel and colleagues [17] demonstrated differences in rigidity between unilateral and bilateral screw fixation and diminish the stress rising in the upper and lower adjacent levels. Harris and colleagues [13] reported that unilateral fixation was slightly weaker than in bilateral fixation in all directions (flexion, extension, bending, and rotation). Slucky and colleagues [40] found that due to reduced stiffness, unilateral fixation provided less rotational stability and increased the rate of instrument
failure and pseudoarthrosis on long-term follow-up. However, some studies have reported satisfactory clinical results in both groups. In an in vitro biomechanics study, Chen and colleagues [41] found that unilateral fixation with cage implantation was sufficient to maintain the stability of the lumbar spine. In 1992, Kabins and colleagues [22] first reported that unilateral screw fixations had similar clinical outcomes to bilateral fixations for single-level (L4–L5) posterolateral fusion. Although many prospective, randomized studies comparing unilateral and bilateral fixations have been reported, the evidence regarding whether unilateral is superior to bilateral remains insufficient, owing to the ambiguous results. We, therefore, conducted the present meta-analysis.
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There was significantly less blood loss and shorter operation times in unilateral fixation in this meta-analysis, since unilateral fixation only involves the dissection of one side of the paravertebral muscles and it is not necessary to expose the contralateral bone structure. Less soft tissue dissection allows for reduced blood loss and operation time. The hospital stays were similar between the two groups, but there are only two studies, with high heterogeneity (I2 = 100 %). However, many studies have reported that the hospital stay for unilateral fixation is shorter than that for bilateral fixation [27, 29, 30, 34], due to early recovery and rehabilitation [9]. In the meta-analysis, the functional outcomes, including ODI, VAS, JOA, and SF-36 scores, were similar in the two groups; however, both groups demonstrated a significant improvement at the final follow-up compared to the preoperative assessment. These clinical outcomes demonstrate that either unilateral or bilateral fixation can maintain the initial stability of the lumbar spine after intervertebral decompression. In the current meta-analysis, patients who underwent unilateral fixation had a significantly different fusion rate from bilateral cases (p = 0.04), with a fusion rate of 90.4 % in unilateral and 95.0 % in bilateral cases. This result demonstrates that although unilateral instrumentation may achieve sufficient stability, the greater stiffness of the bilateral screw is superior in terms of improving fusion for the final follow-up. Therefore, we propose that unilateral instrumentation is more suitable for a single-level fusion. We selected total complications for the meta-analysis to evaluate complication-related outcomes and found a similar incidence of total complications and subgroups with the two techniques. There was no heterogeneity between the two groups for total complications. However, many studies have reported that unilateral fixation is not stable enough to prevent fusion cage migration [31]. The main reason would be that the unilateral screw fixation inherently results in asymmetry. Therefore, the cage should be inserted obliquely into the disk space, and the cage of the anterior part should cross the midline of the vertebral body to support the contralateral anterior column. In addition, implant costs in the bilateral fixation group were higher than those in the unilateral fixation group. There are several limitations to this meta-analysis. First, all of the RCTs occurred at a single center. Further multicenter studies with more patients should be performed. Second, clinical heterogeneity might be caused by the various indications for surgery and the surgical technologies used at different treatment centers. Third, there is a variable length of follow-up between the studies, which is particularly important for evaluating surgery results, and a longer follow-up is necessary to confirm the results. Finally, these studies lack a gold standard outcome to evaluate the postoperative clinical effect.
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Conclusion To our knowledge, this is the first meta-analysis to compare unilateral fixation with bilateral fixation for the treatment of degenerative lumbar diseases. Based on this analysis, the following conclusions may be drawn: the clinical outcomes of unilateral cases are superior to bilateral for blood loss and operation time, but inferior regarding fusion rate. However, the outcomes of ODI, JOA, VAS, and SF-36 scores and complications are equivalent between the two groups. Therefore, future studies with high methodological quality and long-term follow-up periods are needed for updated meta-analyses to better evaluate the two procedures. Conflict of interest No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. The authors declare no conflicts of interest.
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Eur Spine J 13. Harris BM, Hilibrand AS, Savas PE, Pellegrino A, Vaccaro AR, Siegler S, Albert TJ (2004) Transforaminal lumbar interbody fusion: the effect of various instrumentation techniques on the flexibility of the lumbar spine. Spine 29:E65–E70 14. Potter BK, Freedman BA, Verwiebe EG, Hall JM, Polly DW Jr, Kuklo TR (2005) Transforaminal lumbar interbody fusion: clinical and radiographic results and complications in 100 consecutive patients. J Spinal Disord Tech 18:337–346 15. McAfee PC, Farey ID, Sutterlin CE, Gurr KR, Warden KE, Cunningham BW (1989) 1989 Volvo Award in basic science. Device-related osteoporosis with spinal instrumentation. Spine 14:919–926 16. McAfee PC, Farey ID, Sutterlin CE, Gurr KR, Warden KE, Cunningham BW (1991) The effect of spinal implant rigidity on vertebral bone density. A canine model. Spine 16:S190–S197 17. Goel VK, Lim TH, Gwon J, Chen JY, Winterbottom JM, Park JB, Weinstein JN, Ahn JY (1991) Effects of rigidity of an internal fixation device. A comprehensive biomechanical investigation. Spine 16:S155–S161 18. Chen SH, Lin SC, Tsai WC, Wang CW, Chao SH (2012) Biomechanical comparison of unilateral and bilateral pedicle screws fixation for transforaminal lumbar interbody fusion after decompressive surgery—a finite element analysis. BMC Musculoskelet Disord 13:72. doi:10.1186/1471-2474-13-72 19. Kuntz KM, Snider RK, Weinstein JN, Pope MH, Katz JN (2000) Cost-effectiveness of fusion with and without instrumentation for patients with degenerative spondylolisthesis and spinal stenosis. Spine 25:1132–1139 20. Katz JN, Lipson SJ, Lew RA, Grobler LJ, Weinstein JN, Brick GW, Fossel AH, Liang MH (1997) Lumbar laminectomy alone or with instrumented or noninstrumented arthrodesis in degenerative lumbar spinal stenosis. Patient selection, costs, and surgical outcomes. Spine 22:1123–1131 21. Suk KS, Lee HM, Kim NH, Ha JW (2000) Unilateral versus bilateral pedicle screw fixation in lumbar spinal fusion. Spine 25:1843–1847 22. Kabins MB, Weinstein JN, Spratt KF, Found EM, Goel VK, Woody J, Sayre HA (1992) Isolated L4–L5 fusions using the variable screw placement system: unilateral versus bilateral. J Spinal Disord 5:39–49 23. Fernandez-Fairen M, Sala P, Ramirez H, Gil J (2007) A prospective randomized study of unilateral versus bilateral instrumented posterolateral lumbar fusion in degenerative spondylolisthesis. Spine 32:395–401. doi:10.1097/01.brs. 0000255023.56466.44 24. Zhao J, Zhang F, Chen X, Yao Y (2011) Posterior interbody fusion using a diagonal cage with unilateral transpedicular screw fixation for lumbar stenosis. J Clin Neurosci: Off J Neurosurg Soc Aust 18:324–328. doi:10.1016/j.jocn.2010.06.007 25. Furlan AD, Pennick V, Bombardier C, van Tulder M, Editorial Board CBRG (2009) 2009 updated method guidelines for systematic reviews in the Cochrane Back Review Group. Spine 34:1929–1941. doi:10.1097/BRS.0b013e3181b1c99f 26. Choi UY, Park JY, Kim KH, Kuh SU, Chin DK, Kim KS, Cho YE (2013) Unilateral versus bilateral percutaneous pedicle screw fixation in minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus 35:E11. doi:10.3171/2013.2. FOCUS12398 27. Kai Z, Wei S, Chang-Qing Z, Hua L, Wei D, You-Zhuan X, Xiao-Jiang S, Jie Z (2013) Unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in two-level degenerative lumbar disorders: a prospective randomised study. Int Orthop. doi:10.1007/s00264-013-2026-y
28. Lin B, Xu Y, He Y, Zhang B, Lin Q, He M (2013) Minimally invasive unilateral pedicle screw fixation and lumbar interbody fusion for the treatment of lumbar degenerative disease. Orthopedics 36:e1071–e1076. doi:10.3928/01477447-20130724-26 29. Xue H, Tu Y, Cai M (2012) Comparison of unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in degenerative lumbar diseases. Spine J: Off J North Am Spine Soc 12:209–215. doi:10.1016/j.spinee.2012.01.010 30. Xie Y, Ma H, Li H, Ding W, Zhao C, Zhang P, Zhao J (2012) Comparative study of unilateral and bilateral pedicle screw fixation in posterior lumbar interbody fusion. Orthopedics 35:e1517–e1523. doi:10.3928/01477447-20120919-22 31. Duncan JW, Bailey RA (2013) An analysis of fusion cage migration in unilateral and bilateral fixation with transforaminal lumbar interbody fusion. Eur Spine J: Off Publ Eur Spine Soc Eur Spinal Deformity Soc Eur Sect Cervical Spine Res Soc 22:439–445. doi:10.1007/s00586-012-2458-x 32. Aoki Y, Yamagata M, Ikeda Y, Nakajima F, Ohtori S, Nakagawa K, Nakajima A, Toyone T, Orita S, Takahashi K (2012) A prospective randomized controlled study comparing transforaminal lumbar interbody fusion techniques for degenerative spondylolisthesis: unilateral pedicle screw and 1 cage versus bilateral pedicle screws and 2 cages. J Neurosurg Spine 17:153–159. doi:10.3171/2012.5.SPINE111044 33. Feng ZZ, Cao YW, Jiang C, Jiang XX (2011) Short-term outcome of bilateral decompression via a unilateral paramedian approach for transforaminal lumbar interbody fusion with unilateral pedicle screw fixation. Orthopedics 34:364. doi:10.3928/ 01477447-20110317-05 34. Mao L, Chen GD, Xu XM, Guo Z, Yang HL (2013) Comparison of lumbar interbody fusion performed with unilateral or bilateral pedicle screw. Orthopedics 36:e489–e493. doi:10.3928/ 01477447-20130327-28 35. Roy-Camille R, Saillant G, Mazel C (1986) Internal fixation of the lumbar spine with pedicle screw plating. Clin Orthop Relat Res :7–17. doi:10.1097/00003086-198602000-00003 36. Krag MH, Beynnon BD, Pope MH, Frymoyer JW, Haugh LD, Weaver DL (1986) An internal fixator for posterior application to short segments of the thoracic, lumbar, or lumbosacral spine. Design and testing. Clin Orthop Relat Res :75–98. doi:10.1097/ 00003086-198602000-00011 37. Dhall SS, Wang MY, Mummaneni PV (2008) Clinical and radiographic comparison of mini-open transforaminal lumbar interbody fusion with open transforaminal lumbar interbody fusion in 42 patients with long-term follow-up. J Neurosurg Spine 9:560–565. doi:10.3171/SPI.2008.9.08142 38. Armin SS, Holly LT, Khoo LT (2008) Minimally invasive decompression for lumbar stenosis and disc herniation. Neurosurg Focus 25:E11. doi:10.3171/FOC/2008/25/8/E11 39. Guiot BH, Khoo LT, Fessler RG (2002) A minimally invasive technique for decompression of the lumbar spine. Spine 27:432–438 40. Slucky AV, Brodke DS, Bachus KN, Droge JA, Braun JT (2006) Less invasive posterior fixation method following transforaminal lumbar interbody fusion: a biomechanical analysis. Spine J: Off J North Am Spine Soc 6:78–85. doi:10.1016/j.spinee.2005.08.003 41. Chen HH, Cheung HH, Wang WK, Li A, Li KC (2005) Biomechanical analysis of unilateral fixation with interbody cages. Spine 30:E92–E96
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REVIEW ARTICLE
Comparison of unilateral versus bilateral pedicle screw fixation in degenerative lumbar diseases: a meta-analysis Ying-Chao Han • Zhu-Qing Liu • Shan-Jin Wang Li-Jun Li • Jun Tan
•
Received: 24 September 2013 / Revised: 26 January 2014 / Accepted: 27 January 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Traditionally, lumbar spinal surgery is performed with bilateral pedicle screw fixation to provide stability as the fusion heals. However, many studies have reported that unilateral pedicle screw fixation is as effective as bilateral constructs. To compare the clinical outcomes, complications, and surgical trauma between the two techniques for treatment of degenerative lumbar diseases, we conducted a meta-analysis. Methods We searched MEDLINE, EMBASE, PubMed, Google Scholar, and Cochrane databases for relevant controlled studies up to August 2013 that compared unilateral with bilateral fixation for the treatment of degenerative lumbar diseases. We independently performed title/ abstract screening and full-text screening. A random effects model was used for heterogeneous data; otherwise, a fixed effect model was used, pooling data using mean difference (MD) for continuous outcomes and odds ratio (OR) for dichotomous outcomes. Results A total of 12 articles (865 participants) were eligible. Overall, there were significant differences
between the two groups for blood loss (MD = -171.73, 95 % CI = -281.70 to -61.76; p = 0.002), operation time (MD = -66.02, 95 % CI = -115.52 to -16.51; p = 0.009), and fusion rate (OR = 0.50, 95 % CI = 0.26–0.96; p = 0.004). However, there were no significant differences in hospital stay (MD = -4.44, 95 % CI = -13.37 to 4.50), ODI (MD = -0.09, 95 % CI = -0.59 to 0.42; p = 0.74), JOA (MD = 0.18, 95 % CI = -0.77 to 1.14; p = 0.71), VAS (MD = -0.04, 95 % CI = -0.16 to 0.08; p = 0.49), SF-36 (PF: MD = -1.11, 95 % CI = -4.38 to 2.17, p = 0.51; GH: MD = 1.22, 95 % CI = -2.17 to 4.60, p = 0.48; MH: MD = -0.22, 95 % CI = -3.83 to 3.38, p = 0.90) and complications (OR = 1.15, 95 % CI = 0.72–1.85; p = 0.56). Conclusions This meta-analysis shows that there was significantly less blood loss in unilateral group and less operating time; however, the fusion rate was significantly higher in the bilateral group. The outcomes of hospital stay, ODI, JOA, VAS, SF-36 score, and complications are similar in the two groups. Keywords Unilateral Bilateral Pedicle screw fixation Degenerative lumbar diseases Meta-analysis
Y.-C. Han and Z.-Q. Liu contributed equally to this work. Y.-C. Han S.-J. Wang (&) L.-J. Li J. Tan (&) Department of Spinal Surgery, East Hospital, Tongji University School of Medicine, 150# Jimo RD, Pudong New Area, Shanghai 200120, China e-mail: [email protected] J. Tan e-mail: [email protected] Z.-Q. Liu Department of Medical Oncology, Shanghai Tenth People’s Hospital, Tongji University School of Medicine, Shanghai, China
Introduction An increasing number of adults experience chronic low back pain, especially that caused by degenerative lumbar diseases [1]. Lumbar spinal fusion is a common surgical procedure and is recognized as an effective treatment for degenerative lumbar diseases, such as spondylolisthesis, lumbar spinal canal stenosis associated with deformities, or discogenic pain identified by provocative discography [2–4]. Lumbar fusion can achieve solid arthrodesis, immobilizing the
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unstable segment and degenerated intervertebral disk area [5, 6]. Currently, pedicle screws and intervertebral cage devices are frequently used to provide spinal stability. It is generally accepted that rigid pedicle screw fixation is important for excellent fusion rates and lowers the chances of non-union at the graft site [7–9]. The additional instrumentation also has the advantages of no external immobilization, early ambulation, restoration of sagittal alignment, and segment height [3, 10, 11]. Bilateral pedicle screw fixation after interbody fusion is regarded as a standard instrumentation construct for the management of a variety of spinal conditions and has both biomechanical and clinical advantages [12–14]. However, rigid fixation also has inconveniences. In animal model, decrease of the mineral content of the fixed area has been appreciated [15, 16], but some biomechanical comparison of unilateral and bilateral pedicle screw fixation is also have debate [17, 18]. In addition, the technique is associated with increased complications, and there have been doubts as to its costs and benefits [19, 20]. Alternatively, the less rigid technique of unilateral pedicle fixation is considered to be as effective as bilateral constructs from a biomechanical and clinical perspective. Unilateral pedicle fixation also avoids soft tissue disruption on the contralateral side, has a significantly reduced operation time, and is associated with lower implant costs [21–23]. However, some studies have raised concerns that unilateral fixation may result in non-union and postoperative back pain due to the opposite facet’s dysfunction, metal failure, pseudarthrosis, or cage migration due to the decreased strength or inherent asymmetry of this system [21, 24]. Previous studies that have compared the clinical effects of bilateral and unilateral screw fixation for the treatment of degenerative lumbar diseases are conflicting, but it is still uncertain whether unilateral or bilateral screw fixation is more effective. Therefore, to clarify these ambiguous findings we performed a meta-analysis, comparing the two techniques for the treatment of degenerative lumbar diseases.
Methods Eligibility and exclusion criteria Studies published in English were considered to be eligible if they met the following criteria: (1) involved adult patients (aged 18–80 years) of both genders; (2) patients had degenerative lumbar diseases, such as degenerative spondylolisthesis, symptomatic degenerative disk disease, or symptomatic lumbar stenosis with segmental instability; (3) patients had persistent or recurrent low back or leg pain resulting in a significant reduction of quality of life, despite
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conservative therapy for at least 3 months; (4) used a randomized or non-randomized controlled clinical study design on unilateral and bilateral screw fixation for the treatment of degenerative lumbar disease; (5) one- or twolevel intended interbody fusion between L1 and S1; and (6) outcome assessment was based on the primary and secondary outcome. The primary outcomes included major surgical complications, radiographic outcomes, fusion rate, or patient-related outcome measures of pain, and quality of life using various validated questionnaires, such as the Japanese Orthopedic Association scores (JOA), the Visual Analogue Score (VAS), the Oswestry Disability Index (NDI), and the short-form health survey (SF-36). The secondary outcomes included surgical data, such as the operation time, blood loss, and the length of the hospital stay. Studies were excluded if they (1) involved patients without degenerative lumbar diseases, such as those with lumbar fractures; (2) involved patients with another disease, such as severe osteoporosis, active infection, metabolic disease or symptomatic vascular disease; (3) involved previous lumbar surgery; (4) only described unilateral or bilateral screw fixation; and (5) were case reports, biomechanical research, or systematic reviews. Search strategies We searched for published results of relevant trials in the Cochrane Library (Cochrane Library 2013), MEDLINE (1966–August 2013), EMBASE (1974–August 2013), PubMed (1966–August 2013) and Google Scholar (1966– August 2013). The following search terms were used: ‘‘degenerative lumbar diseases’’, ‘‘lumbar spinal fusion’’, ‘‘pedicle screw fixation’’, ‘‘unilateral’’, and ‘‘bilateral’’, with various combinations of the operators ‘‘AND’’, ‘‘NOT’’, and ‘‘OR’’. We restricted the language to English. References cited in the articles and relevant review articles were checked to identify additional studies. The full search strategy is available upon request from the corresponding author (Jun Tan). The quality of the studies was independently assessed by two authors (Han and Liu), and the level of agreement between reviewers was recorded. Inclusion of resultant titles was determined by manual screening of titles and abstracts, followed by full-text screening by the same reviewers. If additional data or clarifications were necessary, we contacted the study authors. Any disagreement between reviewers was resolved by discussion with another reviewer (Wang). Data extraction and management Data were independently extracted by two reviewers (Han and Liu), with further discussion with another independent
Study design
RCT
RCT
RCT
Retrospective
RCT
RCT
RCT
RCT
RCT
RCT
Prospective
Retrospective
References
Choi et al. [26]
Kai et al. [27]
Lin et al. [28]
Mao et al. [34]
Xue et al. [29]
Duncan et al. [31]
Xie et al. [30]
Aoki et al. [32]
Feng et al. [33]
FernandezFairen et al. [23]
Suk et al. [21]
Kabins et al. [22]
16
47
40
20
25
56
46
37
28
43
33
26
20
40
42
20
25
52
56
43
32
42
35
27
52
53.0 (32–68)
61.4 (51–70)
53.8 (37–72)
66.2 ± 8.3
56.2 (34–66)
53.5 (18–77)
57.1 ± 8.1
48.0 ± 8.1
67 (57–74)
59.4 ± 10.2
53.39 ± 14.31
48
54.7 (31–71)
60.8 (50–70)
53.2 (25–73)
65.6 ± 8.8
55.0 (34–68)
55.7 (26–82)
58.2 ± 7.6
52.0 ± 7.2
65.5 (58–76)
55.7 ± 11.6
56.22 ± 12.62
Bilateral
Unilateral
Unilateral
Bilateral
Mean age (years)
Sample size
Table 1 Characteristics of the included studies
8 M/8 F
13 M/34 F
16 M/24 F
12 M/7 F
8 M/17 F
24 M/32 F
20 M/26 F
17 M/20 F
16 M/12 F
19 M/24 F
14 M/19 F
12 M/14 F
Unilateral
9 M/11 F
9 M/31 F
15 M/27 F
10 M/10 F
12 M/13 F
24 M/28 F
20 M/36 F
18 M/25 F
18 M/14 F
20 M/22 F
10 M/25 F
9 M/18 F
Bilateral
Sex(male/female)
23.4 (14–40)
24
55.6 (39–77)
24
31.0 (24–37)
36–48
25.1
25.3
18
26 (18–32)
25.6 (18–36)
27.52 ± 3.30
Unilateral (m)
26.5 (12–36)
59.7 (38–78)
31.2 (24–42)
28.85 ± 4.37
Bilateral
Follow-up (months, years) Bilateral
VSP, autograft/ allograft
Moss Miami system or VSP
Cage, autograft
TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
TLIF, PEEK cage, autograft/allograft
TLIF, saber lumbar I/F cage, autograft
TLIF, PEEK cage, autograft
Mis-TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
TLIF, capstone cage, autograft
Unilateral
Type of operation
Bilateral
1-segment
1-segment, 2-segments
1-segment, 2-segments
1-segment
1-segment
1-segment, 2-segments
1-segment
1-segment, 2-segments
1-segment
1-segment
2-segments
1-segment
Unilateral
Surgical segments
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Eur Spine J Table 2 Details and heterogeneity of clinical outcome measurement of the included studies References
Hospital stay
Operation time
Blood loss
JOA
VAS
ODI
SF-36
fusion rate
Complications
Cost
Choi et al. [8]
NR
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
NR
Kai et al. [27]
Yes
Yes
Yes
NR
Yes
Yes
Yes
Yes
Yes
Yes
Lin et al. [24]
NR
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
NR
Mao et al. [34]
Yes
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
NR
Xue et al. [29]
Yes
Yes
Yes
NR
Yes
Yes
NR
Yes
Yes
Yes
Duncan et al. [31]
NR
NR
NR
NR
NR
NR
NR
NR
Yes
NR NR
Xie et al. [30]
Yes
Yes
Yes
Yes
NR
NR
Yes
NR
Yes
Aoki et al. [32]
NR
Yes
Yes
Yes
Yes
NR
NR
Yes
Yes
NR
Feng et al. [33]
Yes
Yes
Yes
Yes
Yes
Yes
NR
NR
NR
YES
FernandezFairen et al. [23] Suk et al. [21]
Yes
Yes
Yes
NR
NR
NR
Yes
Yes
Yes
NR
NR
Yes
Yes
NR
NR
NR
NR
Yes
Yes
Yes
Kabins et al. [22]
NR
YES
YES
NR
NR
NR
NR
YES
NR
NR
Number of patients involved
438, 214 M/ 224 F
749, 371 M/ 378 F
749, 371 M/ 378 F
198, 101 M/ 97 F
436, 212 M/ 224 F
386, 187 M/ 199 F
258, 129 M/ 129 F
709, 351 M/ 358 F
789, 392 M/ 397 F
275, 137 M/ 138 F
expert (Wang). The following data were extracted: (1) the characteristics of the included papers, including the authors, study design, year of publication, sample size, age, gender, duration of follow-up, type of operation, and the surgical segments (Table 1); and (2) details of the clinical outcome measurement, including the length of hospital stay, blood loss, operation time, JOA, VAS, NDI, SF-36, fusion rate, and the type of complications (Table 2). All included studies met the inclusion and exclusion criteria. The extracted data were rechecked for accuracy by one of the authors (Wang). Risk of bias assessment The risk of bias in randomized controlled studies was assessed by the two reviewers (Han and Liu) according to the 12 criteria and instructions recommended by the Cochrane Back Review Group (CBRG) [25]. For each criterion, ‘yes’, ‘no’, or ‘not reported’ was recorded. Studies were rated as having a low risk of bias when at least 6 of the 12 CBRG criteria were met and the study had no serious flaws. Studies with serious flaws or those in which fewer than six of the criteria were met were rated as having a high risk of bias. The quality of non-randomized controlled trials was assessed using the Newcastle Ottawa Quality Assessment Scale (NOQAS). This scale allocates a maximum of nine points for quality of selection, comparability, exposure, and outcome of study participants.
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Statistical analysis All statistical tests were performed using Review Manager software (RevMan version 5.1; The Cochrane Collaboration, Copenhagen, Denmark). Statistical heterogeneity was assessed using the Chi squared and I2 tests. A value of I2 [ 50 % was considered to represent substantial heterogeneity. A probability of p \ 0.05 was considered to be statistically significant. The results were expressed in terms of mean difference (MD) and 95 % CI for continuous outcomes and as odds ratio (OR), and 95 % confidence interval (95 % CI) for dichotomous outcomes. A random effects model was used for heterogeneous data; otherwise, a fixed effect model was used. Collected data were checked and entered into the computer by the two reviewers (Han and Liu).
Results Search results Through initial electronic database searches, a total of 1,153 relevant titles were identified. Of these, 971 were excluded after review of the abstract and title for the following reasons: being on an unrelated topic; not working with humans; not comparative studies; or being biomechanical studies, case reports, review articles, or other forms of investigation. Subsequently, 155 studies were
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the comparison of hospital stay. However, four studies did not provide the standard deviation, and, therefore, only two studies could be included in the meta-analysis. The available data of hospital stay demonstrated high heterogeneity (I2 = 100 %), perhaps because there were only two studies which were performed in different countries (Fig. 2). Eleven studies reported intraoperative blood loss and operation time (371 patients for unilateral and 378 patients for bilateral). However, eight studies did not provide the standard deviation, so a meta-analysis could only be performed with three studies. Blood loss and operation time was significantly higher in the bilateral group than in the unilateral one (blood loss: MD = -171.73, 95 % CI = -281.70 to -61.76; p = 0.002; operation time: MD = -66.02, 95 % CI = -115.52 to -16.51; p = 0.009; Figs. 3, 4). There was significant heterogeneity in blood loss and operation time between the studies (heterogeneity: I2 = 86 and 98 %, respectively), which could not be explained using our predefined subgroup analysis. Therefore, the quality of evidence for this outcome is low (Figs. 3, 4). Fig. 1 Flow diagram detailing study inclusion
JOA, VAS, ODI and SF-36
excluded due to failure to fit the inclusion criteria after review of the full text. A further 15 studies were excluded due to insufficient follow-up, being duplicate reports, or other intervention. In the end, 12 studies were identified as meeting the eligibility criteria [21–23, 26–34], including 9 randomized studies, 1 prospective study, and 2 retrospective studies. Study inclusion is detailed in Fig. 1.
The demographic characteristics of the studies included are presented in Table 1. The 12 studies included a total of 865 patients; 428 patients underwent unilateral fixation and 437 underwent bilateral fixation with various grafts, including autografts, allografts, and cages. All participants in the 12 studies had undergone follow-up for at least 18 months. The studies’ risk of bias is summarized in Tables 3 and 4. One report of a RCT had a methodological quality score of 5 (high risk of bias), while other RCTs had a quality score of 6–9 (low risk of bias). All of the non-randomized studies scored 8 points on the Newcastle Ottawa Quality Assessment Scale (NOQAS). Hence, all of the studies were of a relatively high quality.
With a mean follow-up of at least 18 months, three studies used the JOA score to assess the clinical outcome (198 patients). There was no significant difference in the final follow-up JOA score between the unilateral and the bilateral group (MD = 0.18, 95 % CI = -0.77 to 1.14; p = 0.71) with moderate heterogeneity (I2 = 63 %; Fig. 5). Seven studies included reports of back VAS scores (212 in the unilateral group and 224 in the bilateral group) and one report was excluded from the meta-analysis as it did not report the standard deviation. There was no difference in VAS score between the two groups (MD = -0.04, 95 % CI = -0.16 to 0.08; p = 0.49) with moderate heterogeneity (I2 = 43 %; Fig. 6). Six studies reported final follow-up ODI scores and one report was excluded for lacking standard deviation. There was no significant difference in the ODI score between the two treatment groups (MD = -0.09, 95 % CI = -0.59 to 0.42; p = 0.74; Fig. 7). Three trials reported the SF-36 (129 unilateral cases and 129 bilateral) and three evaluation indices (physical function, PF; general health, GH; mental health, MH) were included. All three indices were similar (p = 0.51, 0.48, 0.90), and the available data showed low heterogeneity (Fig. 8).
Clinical outcome analysis
Fusion rate and complications
Hospital stay, blood loss and operation time
Nine studies reported the fusion rate assessed by radiographs (293 unilateral cases, 300 bilateral). There was significantly a higher fusion rate in the bilateral group than in the unilateral group (OR = 0.50, 95 % CI = 0.26–0.96;
Demographic characteristics and quality assessment
A total of 438 patients from 6 studies (214 patients for unilateral and 224 patients for bilateral) were included in
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Eur Spine J Table 3 Risk of bias assessment of the randomized studies
Choi et al. [26]
Kai et al. [27]
Lin et al. [28]
Xue et al. [29]
Duncan et al. [31]
Xie et al. [30]
Aoki et al. [32]
Feng et al. [33]
FernandezFairen et al. [23]
Adequate randomization
Yes
Yes
NR
Yes
Yes
Yes
No
Yes
Yes
Allocation concealment
NR
NR
NR
NR
NR
Yes
No
NR
NR
Blinding of patients
No
No
No
No
No
No
No
No
No
Blinding of care providers
No
No
No
No
No
No
No
No
No
Blinding of outcome assessors
NR
NR
NR
NR
NR
Yes
No
NR
NR
Baseline comparability
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Drop-out rate is described
No
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Free of selective outcome reporting
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Co-interventions were similar
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Acceptable compliance between groups
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Intention-totreatment analysis
No
No
No
No
No
No
No
No
No
Similar timing of outcome assessment
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Overall quality (max 12)
6
7
6
7
5
9
6
7
7
Table 4 Quality assessment according to the Newcastle–Ottawa scale of the non-randomized studies References
Selection
Comparability
Exposure
Total score
Mao et al. [34]
3
2
3
8
Suk et al. [21]
3
2
3
8
Kabins et al. [22]
2
2
3
7
p = 0.004) with no heterogeneity (I2 = 0 %; Fig. 9). Ten trials reported complications (392 unilateral cases, 397 bilateral); however, the records of postoperative complications were variable. Some studies described all complications, whereas some provided only major complications. The incidence of total complications was similar in the two groups (OR = 1.15, 95 % CI = 0.72–1.85; p = 0.56) and there was also no difference for the complication of
Fig. 2 The forest plot for hospital stay between unilateral group and bilateral group
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Fig. 3 The forest plot for blood loss between unilateral group and bilateral group
Fig. 4 The forest plot for operation time between unilateral group and bilateral group
Fig. 5 The forest plot for JOA score between unilateral group and bilateral group
Fig. 6 The forest plot for VAS score between unilateral group and bilateral group
Fig. 7 The forest plot for ODI score between unilateral group and bilateral group
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Fig. 8 The forest plot for SF-36 between unilateral group and bilateral group
Fig. 9 The forest plot for fusion rate between unilateral group and bilateral group
infection and cage migration, with no heterogeneity (I2 = 0 %; Fig. 10).
Discussion Currently, pedicle screws are frequently used to provide an initially stable environment to improve the rate of fusion and speed patient recovery after surgery [35, 36].
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It is widely accepted that bilateral pedicle screws are the standard instrumentation constructs used in lumbar fusion. However, many studies have reported that increased stiffness of bilateral pedicle screw fixation results in many complications. With the development of surgical technology, advances in lumbar fusion techniques have concentrated on reducing soft tissue injury, maintaining the ability to achieve neural decompression and fewer complications [37–39]. Therefore, many spinal
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Fig. 10 The forest plot for complications between unilateral group and bilateral group
surgeons have been attracted by unilateral pedicle screw fixation. However, some studies, especially biomechanical studies, are less positive about the ability of unilateral fixation to maintain adequate support of the spine for fusion. In an in vitro study, Goel and colleagues [17] demonstrated differences in rigidity between unilateral and bilateral screw fixation and diminish the stress rising in the upper and lower adjacent levels. Harris and colleagues [13] reported that unilateral fixation was slightly weaker than in bilateral fixation in all directions (flexion, extension, bending, and rotation). Slucky and colleagues [40] found that due to reduced stiffness, unilateral fixation provided less rotational stability and increased the rate of instrument
failure and pseudoarthrosis on long-term follow-up. However, some studies have reported satisfactory clinical results in both groups. In an in vitro biomechanics study, Chen and colleagues [41] found that unilateral fixation with cage implantation was sufficient to maintain the stability of the lumbar spine. In 1992, Kabins and colleagues [22] first reported that unilateral screw fixations had similar clinical outcomes to bilateral fixations for single-level (L4–L5) posterolateral fusion. Although many prospective, randomized studies comparing unilateral and bilateral fixations have been reported, the evidence regarding whether unilateral is superior to bilateral remains insufficient, owing to the ambiguous results. We, therefore, conducted the present meta-analysis.
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There was significantly less blood loss and shorter operation times in unilateral fixation in this meta-analysis, since unilateral fixation only involves the dissection of one side of the paravertebral muscles and it is not necessary to expose the contralateral bone structure. Less soft tissue dissection allows for reduced blood loss and operation time. The hospital stays were similar between the two groups, but there are only two studies, with high heterogeneity (I2 = 100 %). However, many studies have reported that the hospital stay for unilateral fixation is shorter than that for bilateral fixation [27, 29, 30, 34], due to early recovery and rehabilitation [9]. In the meta-analysis, the functional outcomes, including ODI, VAS, JOA, and SF-36 scores, were similar in the two groups; however, both groups demonstrated a significant improvement at the final follow-up compared to the preoperative assessment. These clinical outcomes demonstrate that either unilateral or bilateral fixation can maintain the initial stability of the lumbar spine after intervertebral decompression. In the current meta-analysis, patients who underwent unilateral fixation had a significantly different fusion rate from bilateral cases (p = 0.04), with a fusion rate of 90.4 % in unilateral and 95.0 % in bilateral cases. This result demonstrates that although unilateral instrumentation may achieve sufficient stability, the greater stiffness of the bilateral screw is superior in terms of improving fusion for the final follow-up. Therefore, we propose that unilateral instrumentation is more suitable for a single-level fusion. We selected total complications for the meta-analysis to evaluate complication-related outcomes and found a similar incidence of total complications and subgroups with the two techniques. There was no heterogeneity between the two groups for total complications. However, many studies have reported that unilateral fixation is not stable enough to prevent fusion cage migration [31]. The main reason would be that the unilateral screw fixation inherently results in asymmetry. Therefore, the cage should be inserted obliquely into the disk space, and the cage of the anterior part should cross the midline of the vertebral body to support the contralateral anterior column. In addition, implant costs in the bilateral fixation group were higher than those in the unilateral fixation group. There are several limitations to this meta-analysis. First, all of the RCTs occurred at a single center. Further multicenter studies with more patients should be performed. Second, clinical heterogeneity might be caused by the various indications for surgery and the surgical technologies used at different treatment centers. Third, there is a variable length of follow-up between the studies, which is particularly important for evaluating surgery results, and a longer follow-up is necessary to confirm the results. Finally, these studies lack a gold standard outcome to evaluate the postoperative clinical effect.
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Conclusion To our knowledge, this is the first meta-analysis to compare unilateral fixation with bilateral fixation for the treatment of degenerative lumbar diseases. Based on this analysis, the following conclusions may be drawn: the clinical outcomes of unilateral cases are superior to bilateral for blood loss and operation time, but inferior regarding fusion rate. However, the outcomes of ODI, JOA, VAS, and SF-36 scores and complications are equivalent between the two groups. Therefore, future studies with high methodological quality and long-term follow-up periods are needed for updated meta-analyses to better evaluate the two procedures. Conflict of interest No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. The authors declare no conflicts of interest.
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