The quality of studies was assessed with criteria for study design, use of clearly defined methods, rational and objective outcomes, appropriate follow-up, controlled variables, controlled study population and absence of mixed modalities. Studies that were graded level 1, 2, 3 and 4 according to the American College of Foot and Ankle Surgeons levels of clinical evidence guidelines were included; the lower number indicated higher quality of study design.
The authors did not state how many reviewers assessed study quality.