Reliability and agreement of measures used in radiographic evaluation of the adult hip.

BACKGROUND Several mechanical derangements reportedly contribute to the development of noninflammatory arthritis of the hip. Diagnosis of these derangements involves the use of specific radiographic measures (eg, alpha angle, lateral center edge angle, cross-over sign). The reliability of some of these measures is not known, whereas others have not been confirmed. QUESTIONS/PURPOSES We examined the reproducibility of 20 radiographic parameters of the hip used in clinical practice. METHODS Twenty radiographic parameters on standardized digital AP and cross-table lateral radiographs were evaluated by two observers on two different occasions. The parameters were evaluated from the standpoint of reproducibility (reliability and agreement). The intraclass correlation coefficient (ICC), kappa coefficient, and standard error of measurement were calculated. The minimal detectable change was calculated where possible. RESULTS Interrater reliability ranged from 0.45 to 0.90 for ICC depending on the measure. Intrarater reliability ranged from 0.55 to 0.99. Measurements that could be measured directly (femoral head diameter) were more reliable than measurements requiring estimation on the part of the observer (Tönnis angle, neck-shaft angle). Categorical parameters had interrater and intrarater reliability kappa values greater than 0.90 for all parameters measured. Agreement between repeated measurements, as given by the minimal detectable change, showed many parameters with low absolute reliability have clinical use in the context of the large changes seen in clinical practice. CONCLUSION Radiographic hip measures show clinical utility when evaluated from the perspective of agreement and reliability. CLINICAL RELEVANCE All measures investigated show clinical utility when evaluated from the perspective of reliability and agreement. LEVEL OF EVIDENCE Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.