Orthopedic registry research — limitations and future perspectives

Open Access-This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the source is credited. In 2015, there is nothing spectacular about registers. To collect information on the outcome of treatments is as old as medicine itself. Registries merely took the concept several steps further with (often) nationwide, prospective collection of outcome data combined with rigorous follow-up. This process requires some sort of reliable patient identification system, and due to their use of personal identification numbers, the Nordic countries became the first to implement registries. Orthopedic surgeons were pioneers in getting nationwide registries up and running: the Swedish Knee Arthroplasty Register (SKAR, www.knee.se), started in 1975, became a prototype that inspired orthopedic surgeons around the world, and the Swedish Hip Arthroplasty Register (SHAR, www.shpr. se) followed in 1979. The findings generated by these and other registries improved results after arthroplasty surgery in an evolutionary process that eliminated " bad " implants and inferior techniques. Over the years, orthopedic registry-based research has therefore become an integral part of the scientific literature. This being said, recent examples illustrate that the orthopedic community has not always been quick enough at picking up inferior concepts; take, for instance, the history of the articular surface replacement (ASR) device, which was withdrawn much too late. Limitations to registry-based research Observational studies must fulfill a number of critical meth-odological prerequisites. External validity of registry studies depends on a high degree of completeness and coverage. These numbers have to be supplied in each registry-derived publication, and the quality of the registration process must be continuously validated. But, even if such basic requirements are fulfilled, registry-based research can be criticized and questioned due to several methodological limitations: • By mathematical necessity, stunningly large numbers of patients and procedures can give rise to correspondingly small p-values and narrow confidence intervals related to a given set of hypotheses. But statistically significant findings may not always be clinically relevant. One can be tempted to genuflect at Fisher's 0.05-altar, but does, for instance, a minimal change in patient-reported outcome (with a p-value of < 0.001) always make a clinically relevant difference? We must always interpret registry-based results within a framework of clinical relevance, irrespective of whether we analyze implant survival, the incidence of a specific complication , or subjective outcome measures. • An ongoing debate about the …