Bone Erosion on Ultrasound: OMERACT Definition and Diagnostic Pitfalls
Role of OMERACT in Standardization of Semiotics
OMERACT (Outcome Measures in Rheumatology) is an international initiative for standardization of outcome measures in rheumatology. The OMERACT group has developed consensus definitions of elementary ultrasound findings of joint pathology, including synovitis, tendon damage, and structural bone changes. Within OMERACT-OARSI, ultrasound semiotics of osteoarthritis has been developed, including semiquantitative description of osteophytes.
Bone Erosion Among Bone Changes
When assessing bone contours on ultrasound, the following findings are described: osteophytes, erosions, and irregularity of the cortical layer—within the resolution limits of ultrasound. Erosion is interpreted as a disruption of the continuity of the cortical bone surface. According to the literature, the specificity of ultrasound-detected erosions specifically for rheumatoid arthritis is a subject of separate analysis (Zayat AS et al. Ann Rheum Dis. 2015;74(5):897-903).
Diagnostic Pitfalls: Anatomical Variants
The main pitfall is the misinterpretation of normal anatomical features as erosive disease. It has been demonstrated that anatomical variants of the metatarsal heads can simulate erosive disease; this has been confirmed using cadaveric specimens with CT, radiography, and anatomical dissection (Torshizy H et al. AJR Am J Roentgenol. 2008;190(3):W175-W181). Therefore, before concluding that an erosion is present, one must consider the typical anatomy of the region being examined.
Differentiation from Vascular Channels
Vascular channels in the cortical layer can mimic a focal cortical defect. [note: specific differentiation criteria between vascular channels and erosions are not provided in the source fragments]. For correct interpretation, assessment in two planes and comparison with typical vascular anatomy is advisable.
Bone Erosion in Infection
Bone erosion is described in non-rheumatologic contexts as well. In acute osteomyelitis, longitudinal ultrasound scans demonstrate focal bone erosion filled with hypoechoic inflammatory soft tissue, with associated periosteal thickening and small subperiosteal exudate. Ultrasound signs of acute bone infection are nonspecific. In severe infection, the following may be present: cortical layer irregularity, reactive joint effusion, subperiosteal exudate or abscess, cortical destruction with extraosseous inflammatory mass.
Principle of Correct Description
When assessing a joint, it is recommended to systematically evaluate for the presence of bone erosion, subluxation, crystals, capsular hyperemia, and perivascular inflammation. The report should be descriptive: location, size, and morphology of the finding, rather than vague statements such as "diffuse changes," which are meaningless in an ultrasound protocol.
Frequently asked questions
Who develops standard definitions of bone erosion on ultrasound?
The OMERACT (Outcome Measures in Rheumatology) group—an international initiative for standardization of consensus definitions of elementary ultrasound findings of joint pathology.
Which anatomical area most commonly mimics erosion?
The metatarsal heads: their anatomical features can simulate erosive disease, as confirmed by cadaveric studies using CT, radiography, and dissection (Torshizy et al., 2008).
How specific is ultrasound-detected erosion for rheumatoid arthritis?
The specificity of ultrasound-detected bone erosions for rheumatoid arthritis is a subject of separate investigation (Zayat et al. Ann Rheum Dis. 2015).
What does erosion look like in osteomyelitis?
Focal bone erosion filled with hypoechoic inflammatory soft tissue, with periosteal thickening and subperiosteal exudate. Ultrasound signs of acute bone infection are nonspecific.
What should be evaluated when erosion is suspected in a joint?
Systematically assess for bone erosion, subluxation, crystals, capsular hyperemia, and perivascular inflammation; describe location, size, and morphology of findings.