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Int Orthop. 2016 Apr;40(4):687-95. doi: 10.1007/s00264-015-2834-3. Epub 2015 Jul 2.

Modified head-neck offset for diagnosing anterior femoro-acetabular impingement.

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Clinique Saint Jean du Languedoc, 20 route de Revel, 31400, Toulouse, France.
Service de Chirurgie Orthopédique, Secteur A, 5ème étage, Hôpital Pierre-Paul Riquet, CHU Toulouse Purpan, Place du Docteur Baylac, TSA 40 031, 31059, Toulouse CEDEX 9, France.



The head-neck offset described by Eijer et al. (eHNO), which is used to diagnose anterior femoro-acetabular impingement (FAI), can be difficult to measure. The aim of this study was to verify if a modified head-neck offset (mHNO) provides more accurate and reproducible values than those of the eHNO.


The eHNO, mHNO, cephalic radius and alpha angle were measured on frog-leg radiographs of a group of patients with FAI and a control group (T); three independent reviewers measured the 50 hips in each group twice. The comparison of the two HNOs focused on reproducibility (intraclass correlation coefficient), validity (correlation with alpha angle), practical utility (difference between means in the FAI and control groups) and accuracy of the diagnostic thresholds.


The mHNO had better reproducibility (p < 0.05) within and between observers in all study subjects than that of the eHNO (0.938 and 0.979 vs 0.881 and 0.904). The correlation with the alpha angle was also better (p < 0.05) for the mHNO than that for the eHNO. The diagnostic performances of the mHNO and mAOR thresholds were higher than those of the eHNO, eAOR and alpha angle.


The new HNO is easier to measure, more reproducible and more accurate. A modified HNO <5 mm and a modified AOR <0.100 on the frog-leg view argued in favour of a pathological cam-type head-neck junction.


Alpha angle; Cam effect; Femoro-acetabular impingement; Frog-leg view; Head-neck offset

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