Application of musculoskeletal ultrasound in endemic skeletal fluorosis: a comparative study of water-borne and brick-tea-borne subtypes.

BACKGROUND: Endemic skeletal fluorosis is a chronic disorder caused by prolonged excessive fluoride intake and is characterized by skeletal hyperostosis, periarticular soft-tissue degeneration, and joint dysfunction. Digital radiography (DR) is the conventional diagnostic modality, but it has limited sensitivity for early soft-tissue changes and provides little dynamic information. Musculoskeletal ultrasound (MSKUS) may address these limitations, yet comparative evidence across major fluorosis subtypes remains limited. OBJECTIVE: To characterize MSKUS findings in endemic skeletal fluorosis and compare the complementary value of MSKUS and DR in water-borne and brick-tea-borne disease cohorts. METHODS: This retrospective regional comparative study included 246 patients from Jishan County, a predominantly water-borne fluorosis area (n = 132), and Ruoergai County, a predominantly brick-tea-borne fluorosis area (n = 114). DR was performed at baseline and 3 months after fluoride-exposure reduction. MSKUS was performed only at the three-month follow-up and assessed elbow and knee abnormalities and forearm interosseous membrane (IOM) thickness. Because baseline MSKUS was unavailable, ultrasound findings were analyzed cross-sectionally. RESULTS: Patients from Jishan County were older (64.73 ± 7.73 vs. 59.35 ± 9.52 years) and more often female (58.33% vs. 44.83%) than those from Ruoergai County (both p < 0.05). Ruoergai patients had higher MSKUS detection rates of humeroulnar joint calcification (78.07% vs. 15.15%), humeroradial joint calcification (48.25% vs. 3.03%), elbow effusion (32.46% vs. 0.76%), and suprapatellar bursa effusion (39.47% vs. 12.12%; all p < 0.05). Forearm IOM thickness in pronation was also greater in Ruoergai patients (2.02 ± 0.54 vs. 1.83 ± 0.49 mm; p < 0.05). DR showed a higher observed detection rate for radial crest enlargement than MSKUS (94.3% vs. 50.0%), whereas MSKUS showed a higher observed detection rate for radius-ulna IOM calcification (73.6% vs. 15.9%). Fluorosis severity grades differed between baseline and follow-up (p < 0.05), but this short interval precludes inference of structural reversal. CONCLUSION: MSKUS and DR provide complementary information in endemic skeletal fluorosis. MSKUS may improve detection of superficial soft-tissue calcification and effusion, whereas DR remains important for osseous abnormalities. Prospective multicenter studies with standardized ultrasound protocols and paired baseline and follow-up MSKUS are warranted.