C sign: talocalcaneal coalition or flatfoot deformity?

Area of Science:

• Orthopedics
• Radiology
• Podiatry

Background:

• The C sign on radiographs is a potential indicator for talocalcaneal coalition (TCC).
• Understanding the prevalence and diagnostic value of the C sign is crucial for accurate diagnosis and management of foot deformities.

Purpose of the Study:

• To determine the prevalence of the C sign in patients with TCC.
• To investigate the association between the C sign and TCC or hindfoot alignment.

Main Methods:

• Retrospective review of radiographs from 88 feet with TCC and 260 flexible flatfeet.
• Classification of the C sign into complete and interrupted types (A, B, C).
• Analysis of interobserver variability and measurement of seven radiographic parameters.

Main Results:

• The C sign was present in 77% of TCC cases (14.5% complete, 62.5% interrupted).
• The C sign was present in 45% of flatfeet, exclusively interrupted types.
• Pathologic radiographic parameters were more common when the C sign was present; interobserver agreement (κ) was 0.663.

Conclusions:

• The true C sign (complete or type A interrupted) indicates TCC and is unrelated to flatfoot deformity, but only present in 41% of TCC cases.
• Interrupted C signs, particularly type C, are more indicative of flatfoot deformity than TCC.