Comparative studies are often quite similar to cohort studies in what they measure and how. Key differences are: the sizes of groups with particular designs may be smaller, designs may or may not be new, and their focus is not on state-of-the-art but on how well certain devices work compared to a selected other. In the case of a new design, or a design with a feature or concept that is not well known or mainstream, it is usual to compare it against a device that is well-established and generally accepted to provide good outcomes.
Comparative studies can include functional assessments like stability, range of motion, how normally patients can walk (gait study). They may compare patient reported outcomes (PROMs) focussing on standard ‘activities of daily living’ or on higher level activities like sport. They may also compare levels of patient satisfaction between groups. Some recent studies also ask patients whether or not they can essentially forget about their knee during a range of activities.
Studies like this are usually undertaken by surgeons or hospitals that are assessing whether or not to use a new design or a design that is not previously used in that hospital. Sometimes these studies are undertaken by surgeons who were involved in developing the knee design with the manufacturer. If this is the case, the end of the article will state any association the authors have with the manufacturer of the design included in the study. Because the study article will have been reviewed by independent assessors before publication, you should be able to consider the results to be reliable. However it may be worth searching or waiting for other articles published by independent authors to further substantiate the qualities of a new design.
The more reliable comparative studies are known as a ‘prospective randomised controlled trial’ (pRCT). These studies are performed according to particular rules to avoid potential for any bias in the results. Steps include randomly selecting patients to receive one of the designs being compared and preventing anyone who is taking measurements or assessing outcomes to know which design each patient has. Studies like this are subject to strict codes of practice and must be approved by ethics committee. As a result, their outcomes can be very informative to professionals seeking to advance quality of care. They can also provide a useful to patients.