Outcome instruments: rationale for their use.

The number of outcome instruments available for use in orthopaedic observational studies has increased dramatically in recent years. Properly developed and tested outcome instruments provide a very useful tool for orthopaedic research. Criteria have been proposed to assess the measurement properties and quality of health-status instruments. Unfortunately, not all instruments are developed with use of strict quality criteria. In this article, we discuss these quality criteria and provide the reader with a tool to help select the most appropriate instrument for use in an observational study. We also review the steps for future use of outcome instruments, including the standardization of their use in orthopaedic research.