New research shows that university students who most frequently use a smartphone are more likely to have an enlarged median nerve and to have impaired hand function and pinch strength compared with those who use their smartphones less often.
However, the study, published online June 3 in Muscle & Nerve, was cross-sectional and doesn't yet clearly link heavy smartphone use to carpal tunnel syndrome (CTS).
"The exact clinical relevance of the study findings is not known," said lead author Esra Erkol Inal, MD, Faculty of Medicine, Department of Physical Medicine and Rehabilitation, Süleyman Demirel University, Isparta, Turkey. "Future studies are warranted to address the clinical relevance of median nerve enlargement in high smartphone users."
Still, she adds, "Youngsters should be aware of the dangers of these pocket devices," said Dr Inal.
A hand-held smartphone compels the user to engage in repetitive flexion/extension of the wrist and to use their thumb to text, movements that are involved in the etio-pathophysiology of CTS, the researchers note.
The issue is of increasing importance as more young people use smartphones and other hand-held devices. Research suggests that students now typically spend more than 3 hours a day texting, emailing, scheduling, and browsing the Internet on their mobile phone.
The current study included 102 university students, 66 of whom used a single-hand-held smartphone and 36 of whom didn't use a smartphone. Researchers divided participants into 3 groups according to their level of smartphone use: nonusers, low users, and high users.
They based this use according to the Smartphone Addiction Scale (SAS). The Turkish version of this scale consists of 33 questions rated on a 6-point scale, with higher scores indicating higher risk for smartphone addiction.
There are no official diagnostic criteria for smartphone addiction, but based on Internet addiction, it's defined as the overuse of smartphones to the extent that it disturbs the users' daily lives, said Dr Inal.
"It has been reported that smartphone addiction has many features of addiction, such as tolerance, withdrawal symptoms, preoccupation, mood dysregulation, craving, and loss of control," she noted.
Students in the study with an SAS score of 84 (the median score) or greater were considered high users and those with a score under 84 were considered low users.
Researchers carried out several functional evaluations. To assess hand function, they used the Duruöz Hand Index, an 18-item questionnaire that evaluates daily activities, including those requiring force and rotational motions, those requiring dexterity and precision, and those affecting the flexibility of the first 3 fingers. Participants rated the difficulty in performing these tasks.
To evaluate grip and pinch strength, researchers used a Jamar hand dynamometer and pinch meter while participants squeezed the handle as hard as possible and maintained maximal grip contraction.
The investigators also carried out bilateral ultrasonography. They observed the longitudinal and axial views of the flexor pollicis longus (FPL) tendon from the distal insertion point to the wrist, at rest and during passive flexion/extension. They imaged bilateral thumb joints axially and longitudinally.
Using a visual analogue scale (VAS), participants rated pain in the dominant hand during the previous week while the hand was at rest and while moving the hand.
The researchers found that the median nerve ratios were significantly higher in participants with high smartphone use compared with nonusers (P = .022). Ultrasonography also showed the enlargement of FPL tendon in all groups, but most markedly in high smartphone users.
This suggests overuse, noted Dr Inal. "Clinicians should be careful about the median nerve and the flexor pollicis longus tendon when examining the hand of someone who is a frequent smartphone user."
The study also showed that SAS scores correlated with pinch strength and that VAS pain in movement was significantly higher among high smartphone users and nonusers than in lower smartphone users (P = .016 and P > .05, respectively).
Pain in the thumb rose with an increase in SAS score, noted Dr Inal. Overuse of the thumb may explain the thumb pain, which could have affected pinch strength in overusers, she said.
It might be possible to prevent the repetitive flexion/extension of the wrist and lessen the enlargement of the medial nerve by using a smartphone with two hands instead of one. Putting the keys at the top of the smartphone may also lessen these risks.
"But we think that duration of daily smartphone use is the most important factor affecting the median nerve, pinch strength, and hand function," said Dr Inal.
Dr Inal has disclosed no relevant financial relationships.
Muscle Nerve. Published online June 3, 2015. Abstract
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Cite this: Smartphone Overuse May Affect Hand Function - Medscape - Jun 12, 2015.