Smartphone addiction, thumb-wrist symptoms, and first extensor compartment ultrasonographic findings in young adults: a multicentre prospective study with six-month follow-up.

PURPOSE: To evaluate the relationship between smartphone addiction and thumb-wrist symptoms and first dorsal compartment ultrasonographic abnormalities in young adults, and to investigate whether addiction severity and usage patterns are associated with these findings.

METHODS: This multcentre prospective observational study included 477 university students aged 18-30 years. Smartphone addiction was assessed using the Smartphone Addiction Scale-Short Version (SAS-SV). Clinical evaluation included bilateral Finkelstein testing and pain assessment using the Visual Analog Scale (VAS). Standardized ultrasonographic examinations of the first dorsal extensor compartment were performed according to OMERACT recommendations. Tendon sheath thickening, fluid accumulation, retinacular thickening, and Doppler activity were recorded as positive findings. Participants classified as addicted at baseline were reassessed at six months and re-stratified according to their follow-up addiction status.

RESULTS: Smartphone addiction was significantly associated with female sex, symptom presence, higher pain scores, longer daily smartphone use, and increased ultrasonographic abnormalities on both dominant and non-dominant sides (all p < 0.001). Addicted participants demonstrated higher VAS scores and greater prevalence of bilateral ultrasonographic findings compared with non-addicted individuals. Dominant-side ultrasonographic abnormalities were associated with addiction status, symptom presence, and daily usage duration, whereas non-dominant-side findings were additionally associated with grip pattern. Among baseline-addicted participants reassessed at six months, those who no longer met the addiction threshold showed significant reductions in pain scores and regression of ultrasonographic findings, whereas those who remained addicted demonstrated persistence or progression of symptoms and structural findings despite partial reductions in screen time.

CONCLUSION: Smartphone addiction is associated with increased thumb-wrist symptoms and first dorsal compartment ultrasonographic abnormalities in young adults. These findings suggest that excessive smartphone use may represent a relevant biomechanical exposure contributing to early tendon changes. Behavioral modification may facilitate partial recovery, whereas persistent abnormalities in addicted individuals highlight the importance of addressing usage behavior in prevention and management strategies. Further longitudinal studies with objective exposure measurements are warranted.