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Bone and Mineral Metabolism

SAT-732 - Ultrasound Assessment of Knee and Ankle Enthesopathies in Adults with X‑Linked Hypophosphatemia: A Multicenter Observational Study.

Saturday, June 13, 2026
9:30 AM - 4:30 PM CT
Location: ENDOExpo; Poster Floor
Background
X-linked hypophosphatemia (XLH) is a rare genetic disorder caused by PHEX mutations leading to
excess FGF23 activity and chronic hypophosphatemia. In adults, XLH is associated with substantial
musculoskeletal morbidity, including enthesopathies that contribute to pain, stiffness, and
functional limitation, yet remain under-recognized.
Objective
To describe ultrasound findings of enthesopathies in adults with XLH, focusing on weight-bearing
entheses of the knee and Achilles tendon.
Methods
This multicenter cross-sectional observational study included 28 adults with confirmed XLH. Bilateral
ultrasound evaluation of the patellar tendon (origin and insertion) and Achilles tendon insertion was
performed using standardized protocols. Enthesopathy was defined according to OMERACT criteria,
including hypoechogenicity, tendon thickening, cortical erosions, calcifications, enthesophytes, and
power Doppler signal. Findings were reported descriptively per enthesis and side.
Results
Twenty-eight adults with XLH were included (75% women; median age 36.5 years, IQR 27.5–44.3).
At the patellar enthesis, right knee ultrasound showed thickening in 14.3%, hypoechogenicity in
14.3%, erosions in 21.4%, enthesophytes in 25.0%, and calcifications in 17.9%; corresponding values
in the left knee were 10.7%, 7.1%, 25.0%, 35.7%, and 21.4%, respectively.
At the Achilles enthesis, the right side demonstrated thickening in 21.4%, hypoechogenicity in 21.4%,
erosions in 35.7%, enthesophytes in 50.0%, and calcifications in 32.1%, while the left side showed
thickening in 17.9%, hypoechogenicity in 21.4%, erosions in 35.7%, enthesophytes in 53.6%, and
calcifications in 35.7%.
Power Doppler signal was negative in all evaluated entheses.
Conclusion
Ultrasound revealed a high prevalence of structural entheseal abnormalities in adults with XLH,
predominantly affecting weight-bearing patellar and Achilles entheses, in the absence of Doppler
detected active inflammation. These findings support the role of ultrasound in the comprehensive
musculoskeletal characterization of adult XLH.

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