The Vulcan salute sign: a non-sensitive but specific sign for Morton’s neuroma on radiographs

Abstract

Objectives: To assess the value of the divergence of toes on conventional radiographs of the foot for diagnosing Morton’s neuroma. Methods: This retrospective case–control study was approved by the local ethics committee. In 100 patients with MRI-proven Morton’s neuroma 2/3 or 3/4 (study group) and 100 patients without (control group), conventional weight-bearing dorso-plantar view radiographs were evaluated for the subjective presence of interphalangeal divergence, called the Vulcan salute sign or V-sign, by two blinded, independent musculoskeletal radiologists. Interphalangeal angles (2/3 and 3/4) and intermetatarsal angle I/V were measured. The t test and chi-squared test were used to compare the groups. Diagnostic performance was calculated. Interobserver reliability was assessed using κ statistics and intraclass correlation coefficient (ICC). Results: The difference between the groups was significant (P < 0.05) regarding the presence of the V-sign, which was found in 30 of 100 patients with Morton neuroma and in 3 of 100 control patients, with a sensitivity of 30% and a specificity of 97%. The differences between interphalangeal angles were significant (P < 0.05) between the groups. The interphalangeal angle 2/3 mean values were 7.9° (± 4.8) for the study group vs 5.4° (± 2.6) for the controls; the 3/4 angle values were 6.5° (± 3.8) and 3.4° (± 2.5), respectively. There was no significant difference between the groups in the intermetatarsal angle I/V. Interobserver agreement was substantial for the V-sign, with a κ value of 0.78. The ICC was excellent concerning angle measurements, with all values ≥ 0.94. Conclusion: The Vulcan salute sign on conventional radiographs is specific for Morton’s neuroma.