Prevalence and diagnostic accuracy of in-toeing and out-toeing of the foot for patients with abnormal femoral torsion and femoroacetabular impingement : implications for hip arthroscopy and femoral derotation osteotomy

Aims
Abnormal femoral torsion (FT) is increasingly recognized as an additional cause for
femoroacetabular impingement (FAI). It is unknown if in-toeing of the foot is a specific
diagnostic sign for increased FT in patients with symptomatic FAI. The aims of this study
were to determine: 1) the prevalence and diagnostic accuracy of in-toeing to detect
increased FT; 2) if foot progression angle (FPA) and tibial torsion (TT) are different among
patients with abnormal FT; and 3) if FPA correlates with FT.

Patients and Methods
A retrospective, institutional review board (IRB)-approved, controlled study of 85
symptomatic patients (148 hips) with FAI or hip dysplasia was performed in the gait
laboratory. All patients had a measurement of FT (pelvic CT scan), TT (CT scan), and FPA
(optical motion capture system). We allocated all patients to three groups with decreased
FT (< 10°, 37 hips), increased FT (> 25°, 61 hips), and normal FT (10° to 25°, 50 hips). Cluster analysis was performed.

Results
We found a specificity of 99%, positive predictive value (PPV) of 93%, and sensitivity of
23% for in-toeing (FPA < 0°) to detect increased FT > 25°. Most of the hips with normal or
decreased FT had no in-toeing (false-positive rate of 1%). Patients with increased FT had
significantly (p < 0.001) more in-toeing than patients with decreased FT. The majority of the patients (77%) with increased FT walk with a normal foot position. The correlation between FPA and FT was significant (r = 0.404, p < 0.001). Five cluster groups were identified.

Conclusion
In-toeing has a high specificity and high PPV to detect increased FT, but increased FT can
be missed because of the low sensitivity and high false-negative rate. These results can
be used for diagnosis of abnormal FT in patients with FAI or hip dysplasia undergoing hip
arthroscopy or femoral derotation osteotomy. However, most of the patients with increased FT walk with a normal foot position. This can lead to underestimation or misdiagnosis of abnormal FT. We recommend measuring FT with CT/MRI scans in all patients with FAI.

Cite this article: Bone Joint J 2019;101-B:1218–1229.