Femoral Version Abnormalities Significantly Outweigh Effect of Cam Impingement on Hip Internal Rotation.

BACKGROUND

The purpose of this study was to investigate the effects of femoral version, cam-type femoroacetabular impingement (FAI), and the combination of the 2 on the passive hip range of motion (ROM).

METHODS

We prospectively analyzed a consecutive cohort of 220 patients (440 hips) who presented with unilateral or bilateral hip pain. The passive hip ROM was measured bilaterally with the patient in prone, supine, and lateral positions. Femoral version was measured and the presence of cam-type deformity was determined on preoperative computed tomography (CT) scans. Diagnostic findings of cam-type FAI included an alpha angle of >50° on CT radial sequences of the head-neck junction and a femoral head-neck offset ratio of <0.18 on both radiographs and CT.

RESULTS

Multivariate linear regression analysis confirmed that femoral version, as compared with the presence of a cam lesion, was a stronger independent predictor of internal rotation ROM. Conversely, the presence of a cam lesion resulted in a significant decrease in the passive hip flexion ROM (p < 0.001) with no additional effects due to the degree of femoral version. The passive hip internal rotation ROM in neutral flexion/extension and with the hip in 90° of flexion were maximized in patients with femoral anteversion and decreased significantly with each incremental decrease in femoral version (p < 0.001).

CONCLUSIONS

Abnormalities in femoral version significantly outweigh the effect of cam-type impingement on the passive hip internal rotation ROM. In contrast, the presence of a cam lesion significantly decreases the hip flexion ROM, irrespective of the degree of femoral version. These findings help to inform surgical decision-making for patients with cam-type FAI or femoral version abnormalities.

CLINICAL RELEVANCE

It is common clinical practice to ascribe loss of hip internal rotation to the presence of a cam lesion and to assume that arthroscopic femoral osteoplasty will substantially improve internal rotation postoperatively. Our study shows that the cam lesion is more intimately tied to hip flexion than to hip internal rotation. This result directly impacts the clinical assessment of a patient presenting with radiographic findings of FAI.