Spine
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A retrospective review of a prospectively collected database, the Nationwide Inpatient Sample (NIS), years 2003 to 2012. ⋯ 3.
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Prospective study. ⋯ 3.
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A retrospective clinical and radiographic study. ⋯ 4.
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A retrospective, multicenter, case-controlled study. ⋯ 4.
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A retrospective observational study. ⋯ 4.