The results of TKA: what the registries don't tell us

National registries have provided valuable feedback to surgeons and improved patient care by decreasing revision rates and identifying defective or poorly performing devices. Although there have been thousands of peer review publications in the literature, significant gaps exist in relevant knowledge relating to performance of hip and knee devices due to shortcomings in many published studies. Most studies come from specialty centers and may not reflect the results that can be expected from devices in widespread use. Sample sizes are frequently small, and studies are underpowered to draw major conclusions or to stratify data based on clinically important variables. National registries effectively address many of these problems, but also have shortcomings. Registry data are now being used to promote specific devices, which opens the door to potential abuse of this information. While device design can impact implant survival, other factors, such as surgical technique, surgeon, hospital, patient factors, and even country, may have far more impact on revision rate than implant design. Revision rates often differ among different designs by as little as 5% to 10% while these previously mentioned factors can result in differences in revision rate and order of magnitude higher. Failure to control these numerous other potentially confounding variables can lead to false or misleading conclusions. In general, registries are far more effective in identifying poorly performing devices that manifest in clusters of failures than in identifying small differences in performance among relatively well-designed devices. It is important for surgeons interpreting data generated from registries to be aware of potential pitfalls of these data as well as their value.