On the Levels

When I was invited to become the editor of The American Journal of Sports Medicine, I was acutely aware that I had assumed the stewardship of an enterprise that was flourishing for decades before I came on board and would continue to thrive long after I had sailed off into the sunset. I felt that my charge was to foster the growth and development of the Journal along the trajectory established by its founders until it was time to pass the responsibility on to the next steward. A paramount tenet of that stewardship has been to respect the wise precedents established in the first decades of the Journal and, when new issues were encountered, let my decisions be informed by the established traditions. My principal guides have been the journal archives and historical narratives of the first two editors. However, I have also had the privilege of calling on both of my predecessors for specific advice. When Bob Leach handed the helm of the AJSM over to me in late 2001, he shared several guidelines that had served him well in his years as editor. The most explicit of these was what Bob called The ACL Rule. The essence of The ACL Rule was simple: never include too many articles about the anterior cruciate ligament in any one issue of the Journal. For many years, clinical and laboratory research related to the ACL had been a vital part of orthopaedic sports medicine, and the AJSM had become the forum for important publications on the topic. However, Bob recognized that orthopaedic sports medicine extended far beyond the boundaries of the intercondylar notch, so it was essential not to allow the ACL to permeate our journal’s pages to the point that the AJSM, de facto, became The ACL Journal. I thought this was sage advice and, accordingly, codified it in the instructions that are distributed to all AJSM reviewers. These instructions call upon them to scrutinize with particularly critical judgment any paper that deals with the ACL. AJSM certainly doesn’t want to discourage authors from submitting papers about the ACL for consideration, but we do want to attract the best work on this topic. A systematic review article by Samuelsson and colleagues in this month’s journal provides evidence that our reviewers are doing their job well. Our associate editor, Tim Foster, makes the publication decisions on all review articles, so I was not aware that this paper had even been submitted until the page proofs appeared in my electronic inbox. Its title, ‘‘Level of Evidence in Anterior Cruciate Ligament Reconstruction Research: A Systematic Review,’’ immediately caught my attention. The specifics of this literature analysis were straightforward. The authors culled through 3 databases for studies that examined the results of primary ACL reconstruction in adults. They restricted their attention to Englishlanguage papers that focused on the therapeutic outcome of this surgery. Accordingly, many publications related to the ACL were excluded, including laboratory investigations, epidemiology, economic analysis, and clinical studies that primarily concerned rehabilitation, imaging, histology, or biomechanics. This left 1510 original studies and review papers published between 1995 and 2011 that were examined in detail. The authors classified these papers according to the original Levels of Evidence system developed by the Oxford Centre for Evidence-Based Medicine (CEBM). (The CEBM has subsequently introduced a modification of the Levels of Evidence matrix, although the original version has become institutionalized and is the one used by the AJSM.) Most orthopaedic surgeons are by now familiar with the concept of levels of evidence, although the details of the system may seem a bit arcane. The Oxford system restricts itself to the classification of clinical research. Papers are placed in an evidence matrix that contains 5 columns: therapeutic studies, which investigate the outcome of a treatment; prognostic studies, which investigate the effect of various patient characteristics on the course of a disease; diagnostic studies, which investigate the usefulness of a diagnostic test; differential diagnosis or symptom prevalence studies; and economic and decision analyses. The lion’s share of clinical research reported in the orthopaedic literature belongs in the therapeutic studies column, and this is the case for the papers reviewed by Samuelsson and colleagues. Within each column of the matrix, individual studies are sorted into 5 levels of evidence. Higher level studies, indicated by smaller cardinal numbers, are considered as supplying more robust evidence than lower level studies, which are indicated by larger numbers. The description of each level varies somewhat among the 5 columns. For a given paper, classification primarily hinges upon the general method used to gather the supporting evidence. For therapeutic studies, the key design elements for determining the evidence level include whether the investigation was prospective, whether there was a comparison of 2 different groups, and whether group assignment was allocated on a random basis. Randomized controlled trials (RCTs) are the only therapeutic study design whose level of evidence may be explicitly affected by the rigor with which the investigation was conducted. In general, ‘‘high quality’’ RCTs are considered Level 1 evidence, but a faulty randomization process, unblinded allocation, or excessive loss to follow-up can relegate an RCT to Level 2, where nonrandomized Editorial