PROSPECTIVE ASSOCIATION BETWEEN OBJECTIVELY MEASURED SMARTPHONE SCREEN TIME AND THUMB JOINT POSITION SENSE ERROR IN FIRST-YEAR MBBS STUDENTS

The widespread integration of smartphones into medical education has substantially altered the ergonomic and neuromuscular demands placed on undergraduate students. Smartphone ownership among young adults has reached near saturation, with medical students representing a particularly high-intensity user group.1,2 Medical students increasingly rely on smartphones for academic resources, communication, and recreational activities, resulting in prolonged periods of repetitive thumb-dominant interaction with touchscreen interfaces.

 

Although smartphones enhance accessibility to educational and clinical information, sustained use imposes repetitive low-load mechanical stress on the thumb, a structure evolutionarily optimized for opposition and grasping rather than high-frequency precision movements.3 This biomechanical mismatch has been implicated in a spectrum of musculoskeletal conditions commonly described as “text thumb” or smartphone-related thumb disorders, including tendinopathies, reduced pinch strength, and wrist pain.3,4,6 Systematic reviews have reported a high prevalence of musculoskeletal complaints associated with smartphone use, with hand and wrist involvement affecting up to one-third of users.4

 

Beyond overt pain and structural pathology, the potential subclinical neurological consequences of excessive smartphone use remain insufficiently explored. Proprioception, derived from afferent input from muscle spindles, joint mechanoreceptors, and cutaneous receptors, is fundamental for fine motor control and joint stability.7 Alterations in joint position sense (JPS) may precede pain and functional impairment, serving as an early indicator of sensorimotor maladaptation. Continuous static loading and repetitive thumb movements during prolonged screen interaction may induce changes in mechanoreceptor sensitivity and afferent signaling, resulting in subtle proprioceptive deficits.7,8

 

Existing studies examining the relationship between smartphone use and thumb proprioception are limited predominantly to cross-sectional designs and rely heavily on self-reported screen-time estimates, which are prone to recall bias and systematic underestimation.9,10 Furthermore, objective quantification of screen exposure and standardized proprioceptive testing protocols remain inconsistently applied. The present study addresses these limitations by employing a prospective design with objectively logged smartphone screen-time data and validated digital inclinometry to evaluate the association between smartphone use and thumb joint position sense accuracy in first-year MBBS students.

 

A total of 120 first-year MBBS students were enrolled at baseline, of whom 114 (95.0%) completed the study and were included in the final analysis. Six participants were excluded due to incomplete follow-up data.

 

The mean age of participants was 20.4 ± 1.6 years. The cohort consisted of 58 males (50.9%) and 56 females (49.1%), with all participants being right-hand dominant. The mean objectively measured daily smartphone screen time was 6.8 ± 1.4 hours.

 

 

Table 1: Baseline Characteristics and Smartphone Usage Profile:

Based on established SAS-SV cut-off scores, 58.3% of participants were classified as being at high risk for smartphone addiction. (Fig 1) Participants classified as high-risk demonstrated significantly higher average daily screen time compared with those in the low-risk group (p < 0.001).

 

Fig 1: Pie diagram showing prevalence of Smart phone addiction

At Week 8, a statistically significant positive correlation was observed between average daily smartphone screen time and mean absolute thumb JPS error (r = 0.42, p < 0.001). Higher screen exposure was associated with progressively greater proprioceptive error across all tested angles.

 

Participants were stratified into tertiles based on average daily screen time:

·       Low usage: <4.5 hours/day

·       Moderate usage: 4.5–7.0 hours/day

·       High usage: >7.0 hours/day

 

 

Table 2: Thumb joint position sense error (degrees) by screen-time tertile

Participants in the high-usage group demonstrated nearly double the mean proprioceptive error compared with the low-usage group, with the largest differences observed at 60° of thumb flexion/abduction. (Table 2)

 

Mean SAS-SV scores showed a strong positive correlation with objective screen time (r = 0.68, p < 0.001) and a moderate correlation with thumb JPS error (r = 0.28, p = 0.003).

 

VAS pain scores demonstrated a modest positive correlation with mean JPS error (r = 0.35, p = 0.001), indicating that greater proprioceptive impairment was associated with higher subjective discomfort, although pain levels remained low overall.

This prospective observational study demonstrates a significant association between objectively measured smartphone screen time and impaired thumb joint position sense (JPS) accuracy among first-year MBBS students. Participants with higher daily screen exposure exhibited greater proprioceptive error, suggesting that excessive smartphone use may induce early sensorimotor alterations even before the development of overt musculoskeletal symptoms.

 

Most previous research on smartphone-related morbidity has focused on clinically apparent outcomes such as pain syndromes, grip strength reduction, tendon pathology, and peripheral nerve involvement. In contrast, the present findings suggest that proprioceptive dysfunction may represent an earlier, subclinical manifestation of excessive smartphone use. Given that proprioception is essential for fine motor coordination and joint stability, even subtle deterioration in JPS may have functional implications for precision-dependent tasks.

 

The observed association is biologically plausible and may be explained by sustained low-load static contractions and repetitive thumb movements during prolonged smartphone interaction. Continuous activation of intrinsic and extrinsic thumb muscles may result in mechanoreceptor desensitization, altered muscle spindle firing, and impaired afferent feedback to the central nervous system. Similar mechanisms have been described in repetitive-use occupational activities, supporting the plausibility of early proprioceptive compromise.

 

The present findings are consistent with the broader literature reporting adverse health effects associated with prolonged smartphone use. Deglomine G et al.11 systematically reviewed 41 studies involving over 17,000 participants and reported a strong overall association between smartphone use and negative health outcomes, particularly musculoskeletal complaints and functional impairments, though most studies were cross-sectional. Peripheral nerve involvement has also been documented. Patel J et al.12 demonstrated significant reductions in median nerve conduction velocity and grip strength with increasing smartphone use, while Samuel PS et al.13 reported structural changes in the median nerve and flexor pollicis longus tendon among high-addiction users.

 

Muscle performance impairments have likewise been described. Osailan A et al.14 found an inverse relationship between smartphone usage duration and hand-grip and pinch-grip strength, while Hundekari JC et al.15 reported progressively reduced median motor nerve conduction velocity with longer duration of smartphone use among medical students. Additionally, Alshahrani A et al.16 observed reduced neck flexor endurance in smartphone-addicted individuals, highlighting the broader neuromusculoskeletal impact of prolonged device use.

 

Notably, JPS error in the present study was most pronounced at larger thumb angles, particularly at 60° of flexion/abduction. This is clinically relevant, as wide thumb excursions are commonly required during one-handed smartphone operation, especially for scrolling and corner-screen interactions. Increased mechanical and neuromuscular demand at these positions may further exacerbate proprioceptive inaccuracies.

 

The strengths of this study include its prospective design, use of objectively logged screen-time data, and standardized assessment of thumb JPS using a validated digital inclinometer, addressing key limitations of earlier studies that relied predominantly on cross-sectional designs and self-reported exposure measures. However, the single-center setting and relatively short follow-up period may limit generalizability and preclude assessment of long-term adaptations or recovery. Minor measurement variability related to device placement cannot be entirely excluded.

 

The findings of the current study suggest that excessive smartphone use may adversely affect thumb proprioception at an early stage, underscoring the need for preventive strategies and ergonomic awareness, particularly among young adults and medical students with high digital exposure.

This prospective study demonstrates that higher objectively measured smartphone screen time is associated with a measurable decline in thumb joint position sense accuracy in first-year MBBS students. These findings suggest that excessive smartphone use may contribute to early proprioceptive alterations preceding clinically apparent musculoskeletal disorders. Early identification of such changes may inform preventive ergonomic strategies and targeted educational interventions aimed at preserving hand function in medical trainees.

 

Acknowledgments

The authors acknowledge the cooperation of the participating students and the support provided by the Department of Physiology during data collection and testing.

 

Conflicts of Interest

The authors declare that there are no conflicts of interest related to this study.

 

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

 

Author Contributions

Conceptualization, study design, data collection, statistical analysis, and manuscript preparation were performed by the authors. All authors reviewed and approved the final manuscript.

 

Informed Consent

Written informed consent was obtained from all participants prior to enrolment in the study

Abbreviations

JPS – Joint Position Sense

SAS-SV – Smartphone Addiction Scale–Short Version

VAS – Visual Analog Scale

ICC – Intraclass Correlation Coefficient

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