Updating the Assignment of Levels of Evidence

Orthopaedic surgeons, like all physicians, must make clinical decisions based on the best available evidence. This evidence comes from individual clinical experience and external sources1. Although clinical experience is left to the physician, the medical and surgical literature provides the best external evidence. To facilitate the process of determining the best evidence to answer a clinical question, The Journal of Bone these studies may be graded upward if there is a dramatic effect size. For example, a high-quality randomized controlled trial (RCT) should have ≥80% follow-up, blinding, and proper randomization. The Level of Evidence assigned to systematic reviews reflects the ranking of studies included in the review (i.e., a systematic review of Level-II studies is Level II). A complete assessment of the quality of individual studies requires critical appraisal of all aspects of study design.3.Investigators formulated the study question before the first patient was enrolled.4.In these studies, “cohort” refers to a nonrandomized comparative study. For therapeutic studies, patients treated one way (e.g., cemented hip prosthesis) are compared with those treated differently (e.g., cementless hip prosthesis).5.Investigators formulated the study question after the first patient was enrolled.6.Patients identified for the study on the basis of their outcome (e.g., failed total hip arthroplasty), called “cases,” are compared with those who did not have the outcome (e.g., successful total hip arthroplasty), called “controls.”7.Sufficient numbers are required to rule out a common harm (affects >20% of participants). For long-term harms, follow-up duration must be sufficient.