Spine
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Case-control. ⋯ 3.
-
Retrospective case-control study. ⋯ 4.
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Retrospective review of an administrative database. ⋯ 3.
Case-control. ⋯ 3.
Retrospective case-control study. ⋯ 4.
Retrospective review of an administrative database. ⋯ 3.