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Uni- vs bilateral pedicle screw fixation in minimally invasive lumbar interbody fusion

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Uni- vs bilateral pedicle screw fixation in minimally invasive lumbar interbody fusion

Vol: 4| Issue: 2| Number:27| ISSN#: 2564-2537
Study Type:Therapy
OE Level Evidence:1
Journal Level of Evidence:N/A

A Meta-Analysis of Unilateral versus Bilateral Pedicle Screw Fixation in Minimally Invasive Lumbar Interbody Fusion

PLoS One. 2014 Nov 6;9(11):e111979.

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6 studies (5 randomized controlled trials, 1 clinical controlled trial) encompassing 298 patients were included in this meta-analysis with the purpose of comparing the efficacy and safety of unilateral versus bilateral pedicle screw fixation in minimally invasive lumbar interbody fusion for one-level degenerative lumbar spine disease. Unilateral pedicle screw fixation achieved significantly shorter operative time and reduced blood loss compared to bilateral screw fixation. However, VAS back pain, VAS leg pain, ODI scores, overall fusion rate, overall incidence of complications, and length of hospital stay were similar between uni- and bilateral pedicle screw fixation.

Publication Funding Details +
Non-Industry funded
Basic-Clinical Cooperation Project in Capital Medical University, Beijing Outstanding Talent Training Project
None disclosed

Risk of Bias


Reporting Criteria


Fragility Index


Were the search methods used to find evidence (original research) on the primary question or questions stated?

Was the search for evidence reasonably comprehensive?

Were the criteria used for deciding which studies to include in the overview reported?

Was the bias in the selection of studies avoided?

Were the criteria used for assessing the validity of the included studies reported?

Was the validity of all of the studies referred to in the text assessed with use of appropriate criteria (either in selecting the studies for inclusion or in analyzing the studies that were cited)?

Were the methods used to combine the findings of the relevant studies (to reach a conclusion) reported?

Were the findings of the relevant studies combined appropriately relative to the primary question that the overview addresses?

Were the conclusions made by the author or authors supported by the data and or analysis reported in the overview?

How would you rate the scientific quality of this evidence?

Yes = 1

Uncertain = 0.5

Not Relevant = 0

No = 0

The Reporting Criteria Assessment evaluates the transparency with which authors report the methodological and trial characteristics of the trial within the publication. The assessment is divided into five categories which are presented below.




Accessing Data


Analysing Data





Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbé KA. J Clin Epidemiol. 1992;45:255-65

The Fragility Index is a tool that aids in the interpretation of significant findings, providing a measure of strength for a result. The Fragility Index represents the number of consecutive events that need to be added to a dichotomous outcome to make the finding no longer significant. A small number represents a weaker finding and a large number represents a stronger finding.

Why was this study needed now?

Minimally invasive (MIS) lumbar interbody fusion is advantageous for a variety of lumbar degenerative disorders as it reduces morbidity and offers early ambulation when compared to traditional open surgery. Usually, bilateral pedicle screw (PS) fixation is the standard procedure in lumbar interbody fusion. However, recent studies suggest unilateral PS fixation is an equally effective technique that requires shorter operating time. The objective of this meta-analysis was to compare the efficacy of unilateral versus bilateral PS fixation in MIS lumber interbody fusion for one-level degenerative lumbar spine disease.

What was the principal research question?

How does the efficacy and safety compare between unilateral and bilateral pedicle screw fixation in minimally invasive lumbar interbody fusion for single-level degenerative lumbar spine disease?

Study Characteristics -
Data Source:
A search for relevant studies published in peer-reviewed journals was conducted using MEDLINE/PubMed, EMBASE, BIOSIS Previews, and Cochrane Library from inception to March 30, 2014. References of selected studies were manually searched to identify additional articles.
Index Terms:
Key terms included 'lumbar interbody fusion', 'pedicle screw fixation', 'minimally invasive', 'unilateral', and 'bilateral'.
Study Selection:
Full-text, English-language randomized controlled trials and clinical controlled trials published in peer reviewed journals that investigated bilateral versus unilateral pedicle screw fixation procedures in patients diagnosed with single-level lumbar degenerative disease were selected. Study retrieval was performed independently by two reviewers, and any disagreements were resolved by a third reviewer. Six studies (5 randomized controlled trials, 1 clinical controlled trial) with a total of 298 patients were selected.
Data Extraction:
Data on the primary outcome measures including visual analogue leg and back pain score (VAS), Oswestry disability index (ODI), fusion rate, and complications were extracted. Secondary outcome measures including intra-operative blood loss, operating time, and hospital stay were also retrieved. The methodological quality of included studies was assessed by two authors independently.
Data Synthesis:
Dichotomous outcomes were presented as odds ratio (OR) with 95% confidence intervals (CIs) while continuous outcomes were summarized using mean difference (MD) and 95% CI. In the absence of significant statistical heterogeneity a fixed-effect model was employed, otherwise a random-effects model was used. The summary statistic for each individual study was calculated using the meta-analysis program of the Cochrane Collaboration (Review Manager 5.2).

What were the important findings?

  • Pooled results were similar between unilateral and bilateral groups with respect to VAS back pain (5 studies: MD= -0.02 [95% CI -0.17 to 0.13]; p=0.77), VAS leg pain (3 studies: MD= -0.10 [95% CI -0.20 to 0.01]; p=0.06), and ODI scores (5 studies: MD= 0.31 [95% CI -0.66 to 1.27]; p=0.54).
  • The overall fusion rate was not significantly different between the unilateral (134/146) and bilateral (146/152) groups (OR=0.47 [95% CI 0.18 to 1.27]; p=0.14). Likewise, the overall incidence of complications was not significant different between the unilateral (8/146) and bilateral (7/152) groups (OR=1.25 [95% CI 0.44 to 3.59]; p=0.67).
  • Operative time was significantly shorter (4 studies; p=0.02) and blood loss was significantly reduced (4 studies; p=0.002) with unilateral pedicle screw fixation, but hospital stay was not significantly different between groups (3 studies; p=0.54).

What should I remember most?

Unilateral and bilateral pedicle screw fixation offered similar clinical outcome and fusion rate in patients undergoing minimally invasive lumbar interbody fusion surgery. Unilateral and bilateral pedicle screw fixation differed in blood loss and operative time, both of which were significantly reduced in unilateral cohorts.

How will this affect the care of my patients?

It appears that unilateral pedicle screw fixation has the ability to shorten operative time and reduce blood loss while achieving similar clinical outcomes and fusion success to bilateral pedicle screw fixation. The authors acknowledge that the presence of methodological limitations, existence of heterogeneity among studies, and lack of complete data recording weaken the results of this study. Additional high-quality randomized controlled trials with large sample sizes and long-term follow-up are necessary before the wider application of unilateral pedicle screw fixation can be recommended.

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