Association Between Smartphone Usage Duration and Cervico-Scapulothoracic Postural Alterations and Musculoskeletal Symptoms Among Young Adults: A Cross Sectional Correlational Study

Abstract Background: The unprecedented rise in smartphone usage among young adults has created a public health concern regarding cervico-scapulothoracic postural alterations and associated musculoskeletal symptoms. Despite growing evidence linking prolonged smartphone use to forward head posture (FHP) and scapular dyskinesis, integrated assessment of cervical, thoracic, and scapular regions remains underexplored in the Indian population. Objective: This study aimed to establish the association between smartphone usage duration and cervico-scapulothoracic postural alterations (measured through occipital protuberance–C7 spinous process distance, phonoion–sternal angle distance, and Scapulothoracic Index) and musculoskeletal symptoms among young adults aged 18–25 years. Methods: A cross-sectional correlational study was conducted with 180 healthy young adults (90 males, 90 females) recruited from educational institutions. Smartphone usage was assessed through self-reported daily usage hours and validated Smartphone Addiction Scale–Short Version (SAS SV). Postural assessments included: (1) Forward head posture using occipital protuberance–C7 distance measurement; (2) Head–thorax alignment using phonoion–sternal angle; (3) Scapular positioning using Scapulothoracic Index (STI) via photograph analysis. Musculoskeletal symptoms were evaluated using Visual Analogue Scale (VAS) for neck and shoulder pain and Neck Disability Index (NDI) for functional disability. Pearson correlation analysis and multivariate linear regression were performed to determine associations. Results: Mean smartphone usage duration was 5.2±1.8 hours per day (range: 2–9 hours). Occipital protuberance–C7 distance was significantly reduced in high-usage group (mean: 4.2±0.8 cm) compared to low-usage group (6.1±0.9 cm; p<0.001), indicating forward head posture. Phonoion sternal angle demonstrated significant reduction with increased smartphone usage (r=−0.68, p<0.001), indicating decreased head–thorax alignment. Scapulothoracic Index showed significant asymmetry in 73% of high-usage participants (p<0.001). Neck pain severity (VAS) positively correlated with smartphone duration (r=0.64, p<0.001), and NDI scores were significantly elevated in high-usage group (mean: 18.2±7.4 vs. 6.8±3.2; p<0.001). Multiple regression analysis revealed that smartphone usage duration independently predicted 52% of variance in neck pain severity (β=0.68, p<0.001) and 48% of variance in NDI scores (β=0.62, p<0.001). Gender showed significant interaction effect, with females demonstrating greater postural alterations (p=0.024). Smartphone addiction scores (SAS-SV) were strongly associated with cervical flexion angle (r=0.71, p<0.001) and scapular dyskinesis (r=0.65, p<0.001). Conclusion: Smartphone usage duration is significantly associated with forward head posture, reduced head–thorax alignment, and scapular asymmetry among young adults. These postural alterations are strong independent predictors of neck and shoulder pain and functional disability. The integrated cervico-scapulothoracic assessment model effectively captures smartphone-related postural pathomechanics and demonstrates superior predictive validity compared to isolated cervical measures. Early intervention addressing postural awareness and ergonomic smartphone usage is warranted to prevent progressive musculoskeletal disorders in this vulnerable population.