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Objective To assess structural changes at peripheral entheses and the association with spinal bone formation in patients with long-standing radiographic axial spondyloarthritis (r-axSpA) overall and stratified by sex.Methods Peripheral entheses were examined cross-sectionally using ultrasound (US) in patients fulfilling the modified New York criteria for ankylosing spondylitis (AS) and assessed for Outcome Measures in Rheumatology consensus-based structural lesions (enthesophytes, calcifications and erosions) summed to a damage US score (0–42). Spinal radiographs were graded with the modified Stoke AS Spinal Score (mSASSS). Associations between US damage score and mSASSS were assessed with negative binomial regression analyses overall, by sex and by age quartiles.Results US was performed in 173 patients, 54% males, with a mean (SD) age of 55 (13) years and symptom duration of 29 (13) years. The prevalence of any structural US lesion was 92%. The US damage score was higher in males than females (mean (SD) 4.7 (3.0) versus 3.3 (2.4), p<0.001) and increased significantly with age, as did mSASSS. Univariate associations between US damage score and mSASSS were found overall and in males, but diminished with older age. The association remained significant for males when the multivariable model was adjusted for symptom duration (rate ratio (95% CI) for log-transformed mSASSS+1: 1.32 (1.04 to 1.67)). Overall, mSASSS was not associated with the US damage score when the multivariable model was adjusted for age or symptom duration.Conclusion Structural lesions at the peripheral entheses are common in long-standing r-axSpA and accumulate with age, which may obscure the possible association with spinal bone formation.