Femoroacetabular impingement: normal values of the quantitative morphometric parameters in asymptomatic hips.

OBJECTIVE

To determine the means and the reference intervals of the quantitative morphometric parameters of femoroacetabular impingement (FAI) in normal hips with high-resolution computed tomography (CT).

METHODS

We prospectively included 94 adult individuals who underwent CT for thoracic, abdominal or urologic pathologies. Patients with a clinical history of hip pathology and/or with osteoarthritis on CT were excluded. We calculated means and 95% reference intervals for imaging signs of cam-type (alpha angle at 90° and 45° and femoral head-neck offset) and pincer-type impingement (acetabular version angle, lateral centre-edge angle and acetabular index).

RESULTS

The 95 % reference interval limits were all far beyond the abnormal thresholds found in the literature for cam-type and to a lesser extent for pincer-type FAI. The upper limits of the reference intervals for the alpha angles (at 90°/45°) were 68°/83° (men) and 69°/84° (women), compared to thresholds from the literature (50°, 55° or 60°). Reference intervals were similar between genders for cam-type parameters, and slightly differed for pincer-type.

CONCLUSION

The 95% reference intervals of morphometric measurements of FAI in asymptomatic hips were beyond the abnormal thresholds, which was especially true for cam-type FAI. Our results suggest the need for redefining the current morphometric parameters used in the diagnosis of FAI.

KEY POINTS

• 95% reference intervals limits of FAI morphotype were beyond currently defined thresholds. • Reference intervals of pincer-type morphotype measurements were close to current definitions. • Reference intervals of cam-type morphotype measurements were far beyond the current definitions. • Current morphometric definitions of cam-type morphotype should be used with care.