The concentric circles method to define and assess anterior subluxation in bony mallet finger.

We have described and validated the concentric circles method for assessing anterior subluxation in the bony mallet finger. We retrospectively analysed 114 radiographs from cases of bony mallet finger assessed by four hand surgeons and one radiologist using three approaches: subjective visual inspection, the concentric circles method and the malalignment method. The concentric circles method defines subluxation as a disruption of the normal concentric annulus between the middle phalangeal head and distal phalangeal articular surface on true lateral radiographs. It showed improved accuracy (94%), higher sensitivity (91%) and specificity (97%) compared with the other methods, with excellent inter- and intra-observer reliabilities.Level of evidence: III.