How definition of "loosening" affects the incidence of loose total hip reconstructions.

Loosening is the most common long-term problem following total hip reconstruction. For many reasons, it is important to identify the loosened total hip reconstruction. For some purposes, radiographic interpretation is the sole or principal determinant in loosening. However, there are inherent problems with such interpretations, and these problems have neither been explored in any detail in the literature nor emphasized. This article is a review of the literature and one of the problems of defining loosening. Interpretations of radiographic criteria of loosening are matters of judgment, but this judgment is not reflected in the descriptions of precisely how radiographs were interpreted. Definitions in the literature, based on lucencies and position changes, influenced the loosening rate by a factor of at least two, and influenced the apparent importance of risk factors affecting the long-term results by as much as two to three times. Thus by merely altering a definition one can alter which factors seem more or less important. The selection of a definition of loosening must be designed to a specific purpose, but data and a rationale should be provided as a basis for its interpretation. In general, descriptions of radiograph interpretation need to be precise and less subjective.