In orthopaedics, register studies have most commonly been used in joint replacement surgery for the surveillance of the quality of the large numbers of different prostheses and techniques in use, many of which are otherwise undocumented. Registers usually record patients with certain diagnoses or treatments in a defined population, and their outcome is assessed. Registers can be valuable tools both in research and in quality control. Too few randomized controlled trials (RCTs) are performed in orthopaedics. Since results from clinical trials with satisfactory follow-up do not exist for the majority of orthopaedic devices and treatments, one alternative is to use register studies, which are observational and not experimental.


Medical registers usually cover patients of one or a few diagnostic groups, or patients who receive certain treatments (e.g. operations). Registers may cover patients from a whole country, a region, a group of hospitals, or from a group of surgeons. The patients are followed until death or during a limited time period. The results of the different treatment modalities are assesed and compared on the basis of the collected data.


In arthroplasty registers, the aims most commonly are to survey joint replacement surgery, to compare the quality of different prostheses, cements, and operative techniques, and to detect inferior implants and procedures as early as possible. In general, the aims of medical registers might be to assess and compare results of the different devices or treatments that are in use, and the most appropriate outcome or response measure must be defined accordingly.


Revision surgery and prosthesis survival are usually chosen as athe outcome or response in arthroplasty registers. With baseline data on the primary operations and data from the revisions, the survival of different implant components can be assesed and the possible causes for revisions established. Further, if sufficient data are registered on age, gender, diagnosis, operative techniques, use of antibiotic prophylaxis, and other patient-, surgeon- or hospital-related risk factors on the revision rates can also be investigated.

Patient identification and follow up

In the Scandinavian arthroplasty registers, the surgeon reports the patient's national personal identification (ID) numbers for identification of the patient and the surgery. In some countries, as Norway, the surgeon needs patient's consent to be allowed to send data with this information to most central registries, and the registries must treat data with patients ID confidentially. By use of the ID numbers (CNP-Romania's case) the information on outcomes (revisions) can be linked to the baseline information (primary operation) even if the outcome is discovered or treated at another hospital then tha primary operation. With such a system, in which all hospitals and all surgeons are participating and where data on patients' death or emigration are available, the follow-up of patients will be near complete. .

In countries without national ID numbers or in regional registries, other systems for follow-up, such as questionnaires to the surgeons or patients, must be established.

Selection of a minimal set of necessary data

The recording of data should be based on individual reports for each patient. A register should comprise both baseline data (e.g. primary operations) and the outcome response (e.g. revision) at follow-up. The aims of the study must be decided upon early in the planning process, and based on these aims decisions can be made about the minimal necessary set of well-defined data to be collected.

Source: "Outcome Measures in Orthopaedics and Orthopaedic Trauma" by Paul Pynsent, Jeremy Fairbank & Andrew Carr