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

Abstract

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. CONCLU-SION: 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. AbstractObjective To investigate the ability of coronal non-weightbearing MR images to discriminate between normal and abnormal hindfoot alignment. Methods Three different measurement techniques (calcaneal axis, medial/lateral calcaneal contour) based on weightbearing 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°v algus); (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.

Three-dimensional hindfoot alignment measurements based on biplanar radiographs: comparison with standard radiographic measurements

“…However, so far no method is available that allows a precise measurement of hindfoot alignment in daily radiological practice [11,12].…”

“…Incorrect positioning of the foot can lead to substantial measurement errors when assessing the hindfoot alignment on radiographs, which is the current reference standard [12]. In patients with foot deformities, the exact positioning can be quite difficult for the radiology technician, and a measurement stability of ± 5° has been considered acceptable for these radiographs [12,17].…”

“…In patients with foot deformities, the exact positioning can be quite difficult for the radiology technician, and a measurement stability of ± 5° has been considered acceptable for these radiographs [12,17]. A hindfoot angle of about 5° valgus is considered as a normal hindfoot axis, and both valgus angles over 10° or any hindfoot varus angle are considered abnormal [12,17].…”

“…In patients with foot deformities, the exact positioning can be quite difficult for the radiology technician, and a measurement stability of ± 5° has been considered acceptable for these radiographs [12,17]. A hindfoot angle of about 5° valgus is considered as a normal hindfoot axis, and both valgus angles over 10° or any hindfoot varus angle are considered abnormal [12,17]. With a measurement stability of ± 5° for different rotational positions and a considerable interreader variability for standard radiographic measurements, there is however no clear boundary between normal and abnormal hindfoot angles [12].…”

“…Measurements on long axial view radiographs are characterized by a superior interreader agreement, compared to Cobey view radiographs [11]. However, all hindfoot alignment measurements based on standard radiographs have a considerable interobserver variability and even moderate malpositioning can lead to substantial measurement errors [12,11].…”