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Reliability and Agreement of Measures Used in Radiographic Evaluation of the Adult Hip



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.


We examined the reproducibility of 20 radiographic parameters of the hip used in clinical practice.


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.


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.


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.

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Fig. 1A–B


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We thank the AO Foundation for their continued support of international collaboration and study. We also thank Anne Mannion PhD, for valuable insight in editing and preparation of the manuscript.

Author information

Correspondence to Nicholas H. Mast MD.

Additional information

One or more of the authors (NHM) received financial support from AO North America (Paoli, PA, USA).

Each author certifies all investigations related to this study were conducted in conformity with ethical principles of research.

This work was performed at Schulthess Klinik, Zurich, Switzerland.

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Mast, N.H., Impellizzeri, F., Keller, S. et al. Reliability and Agreement of Measures Used in Radiographic Evaluation of the Adult Hip. Clin Orthop Relat Res 469, 188–199 (2011).

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  • Femoral Head
  • Intraclass Correlation Coefficient
  • Alpha Angle
  • Minimal Detectable Change
  • Intrarater Reliability