Diagnostic performance of MRI measurements to assess hindfoot malalignment. An assessment of four measurement techniques.

OBJECTIVE: To investigate the ability of coronal non-weight-bearing MR images to discriminate between normal and abnormal hindfoot alignment.
METHODS: Three different measurement techniques (calcaneal axis, medial/lateral calcaneal contour) based on weight-bearing hindfoot alignment radiographs were applied in 49 patients (mean, 48 years; range 21-76 years). Three groups of subjects were enrolled: (1) normal hindfoot alignment (0°-10° valgus); (2) abnormal valgus (>10°); (3) any degree of varus hindfoot alignment. Hindfoot alignment was then measured on coronal MR images using four different measurement techniques (calcaneal axis, medial/lateral calcaneal contour, sustentaculum tangent). ROC analysis was performed to find the MR measurement with the greatest sensitivity and specificity for discrimination between normal and abnormal hindfoot alignment.
RESULTS: The most accurate measurement on MR images to detect abnormal hindfoot valgus was the one using the medial calcaneal contour, reaching a sensitivity/specificity of 86 %/75 % using a cutoff value of >11° valgus. The most accurate measurement on MR images to detect abnormal hindfoot varus was the sustentaculum tangent, reaching a sensitivity/specificity of 91 %/71 % using a cutoff value of <12° valgus.
CONCLUSION: It is possible to suspect abnormal hindfoot alignment on coronal non-weight-bearing MR images. KEY POINTS: • Abnormal hindfoot alignment can be identified on coronal non-weight-bearing MR images. • The sustentaculum tangent was the best predictor of an abnormally varus hindfoot. • The medial calcaneal contour was the best predictor of a valgus hindfoot.