Diagnosis of Seronegative Rheumatoid Arthritis (SNRA) is based on clinical, radiological, and MRI findings with set criteria. High specificity is provided by plain X-rays in the differential diagnosis of rheumatic disorders.
In the study by C Rex et al of pelvis X-rays, they found that ischiopubic ramus enthesopathy was more common than sacroiliitis and they have coined that enthesopathy finding as “hanging drop sign” because of its characteristic appearance.
A total of 152 proven (92 Females, 60 Males) SNRA cases (based on ACR*/EULAR**criteria and ASAS***criteria) were studied for enthesopathy features in their plain X-ray of pelvis. In addition to sacroiliitis, calcification/ ossification of attachment of pelvic muscle and ligaments was documented. Hanging drop enthesopathy was noted in ischiopubic ramus in most of the cases. A cadaveric study was done on 10 specimens just to understand the corresponding anatomical origin of this enthesopathy.
The key findings of the study were:
• Of the 152 pelvic radiographs studied, 110 revealed radiological evidence of SNRA.
• Among them, 64 patients had hanging drop sign (58.18%), 25 patients had sacroiliitis (22.72%), and 21 patients had other features like hip arthritis, calcifications around greater trochanter, iliac crest, and acetabular region.
• This hanging drop sign can be single (n = 52) or multiple (n = 12) and can be unilateral (n = 14) or bilateral (n = 50).
• The cadaveric study revealed that the hanging drop sign corresponds to the adductor part of adductor magnus muscle and gracilis muscle origin in the ischiopubic ramus.
“We conclude that the incidence of ischiopubic ramus enthesopathy presenting as “hanging drop sign” is higher than the incidence of sacroiliitis. Hanging drop sign can be considered as a reliable complementing sign to identify SNRA using standard diagnostic criteria. However, large volume and larger follow-ups are required to confirm the prevalence in various subtypes of axial spondyloarthropathies” the author commented.
Further reading:
“Hanging Drop Sign” in pelvis X-ray
C. Rex et al
Indian Journal of Orthopaedics (2025) 59:644–649
https://doi.org/10.1007/s43465-025-01360-2
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