Spine
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A retrospective review of prospectively collected data. ⋯ 3.
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Retrospective review of data from a prospective patient outcomes registry. ⋯ 3.
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A nonrandomized controlled trial. ⋯ 2.
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A retrospective study. ⋯ 3.
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A kinematic study of cervical spine. ⋯ N/A.