"Absent middle facet": a sign on unenhanced radiography of subtalar joint coalition.
OBJECTIVE
We compared the accuracy of the previously unevaluated "absent middle facet" sign with the more commonly used "talar beak" sign and C sign for the detection of coalition of the subtalar joint middle facets on lateral foot radiographs obtained with the patient standing.


METHODS
Three musculoskeletal radiologists graded the visibility of these three signs on standing lateral radiographs of 32 feet that had been proven to have coalitions of the middle facets of the subtalar joint and 62 feet that had normal subtalar joints. The reviewers were unaware of the presence or absence of subtalar coalitions in these feet.


RESULTS
The absent middle facet sign had a sensitivity, specificity, and accuracy of 75%, 98%, and 90%, respectively, for the diagnosis of subtalar joint coalition in this patient population, whereas these values were 56%, 100%, and 85% for the C sign and 53%, 90%, and 78% for the talar beak sign, respectively. A finding of either a positive absent middle facet sign or a positive C sign resulted in a sensitivity, specificity, and accuracy of 84%, 98%, and 94%, respectively.


CONCLUSIONS
In this study population, the absent middle facet sign was more sensitive than and nearly as specific as the talar beak sign and C sign for diagnosing subtalar coalition on standing lateral foot radiographs. The highest accuracy was obtained when a finding of either a completely absent middle facet or a complete C sign was considered as a positive indicator of a subtalar coalition.
Liu
Patrick T
PT
Department of Diagnostic Radiology, Mayo Clinic Scottsdale, 13400 E Shea Blvd., Scottsdale, AZ 85259, USA. liu.patrick@mayo.edu
Roberts
Catherine C
CC
Chivers
F Spencer
FS
Kile
Todd A
TA
Claridge
Richard J
RJ
DeMartini
Joseph R
JR
Kenrich
Robert E
RE
Freed
Lewis H
LH
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013380:Subtalar Joint / Q000002:abnormalities* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013580:Synostosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing / Q000502:physiology*