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.