Precision of foot alignment measures in Charcot arthropathy

Foot deformity associated with diabetes mellitus (DM) and peripheral neuropathy (PN) contributes to joint instability, ulceration and amputation. This study reports the intrarater and inter-rater measurement precision and least significant change (LSC) of radiological measures of foot deformity in subjects with DM, PN, and foot related complications.

Cuboid height, Meary's angle, calcaneal pitch and hindfoot-forefoot angle were measured from plain-film radiographs on 15 subjects with DM, PN, and foot-related complications. A foot and ankle fellowship-trained orthopedic surgeon with 23 years of experience (Rater 1) measured radiographs twice. A foot and ankle fellowship-trained orthopedic surgeon with 2 years of experience (Rater 2) and a radiologist in residency training (Rater 3) measured radiographs once. Root mean square standard deviation and LSC were calculated to determine measurement precision and the smallest change considered biologically real, not the result of chance.

Intrarater measurement precision was: 0.9 mm for cuboid height, 3 degrees for Meary's angle, and 2 degrees for calcaneal pitch and hindfoot-forefoot angle. Inter-rater measurement precision for rater 1 versus 2 and 1 versus 3 were: 1.7 and 1.6 mm for cuboid height, 4 degrees for Meary's angle, 2 degrees for calcaneal pitch, and 3 degrees for the hindfoot-forefoot angle. The LSC was less than or equal to: 4.7 mm for cuboid, 12 degrees for Meary's angle, 6 degrees for calcaneal pitch, and 8 degrees for hindfoot-forefoot angle.

Cuboid height, calcaneal pitch, and hindfoot-forefoot angle measures can be completed with relatively good measurement precision.