Introduction

Smartphones have a vital role in our life with advantages like internet communication than other devices.¹ The rate of smartphone addiction has been very high in the last decades. However, this smartphone addiction can affect our health and cause musculoskeletal manifestations like hand and wrist pain.²

The posture of smartphone use requires fixing the device with hands, looking at the device and the thumb is used to touch the screen.² Increased duration and frequency of smart-phone use with frequent movement of the upper limbs have been found to be major risk factors for musculoskeletal manifestations incidence.³

Musculoskeletal symptoms of smartphone use not only involve the hands but also many areas all over the body including neck, wrists, thumb, and elbows especially with overuse.⁴ Also, the repeated flexion and extension movements during smartphone use can lead due to narrowing and increase pressure in the carpal tunnel and may lead to carpal tunnel syndrome (CTS). Median nerve is a mixed nerve having contributions from ventral roots of C5-C7 of lateral cord and C8 and T1 of medial cord. Sensory fibers are more prone to damage from nerve compression firstly before the motor fibers.⁵ In 20-10% of CTS patients, the incidence of pain and paresthesia proximal to the wrist level has been reported. Sensory impairment usually involves palmar surface of the lateral 3Vi fingers and spares thenar eminence as the palmar cutaneous sensory branch of the thenar eminence emerges proximal to the carpal tunnel.⁶ Also, median nerve is mainly involved in muscle movements during smartphone use as it innervates 1st and 2nd lumbrical muscles and thenar muscles by its motor and recurrent branches.^4,7

CTS is defined as the most common entrapment neuropathy caused by median nerve compression inside the carpal tunnel.⁵ The characteristic clinical symptoms of CTS from which we need at least two for diagnosis are nocturnal paresthesias; reproduction of paresthesias or pain by provocative tests (Tinel or Phalen's signs) or aggravation of paresthesias by activities like driving, holding a book or telephone; and relief of symptoms by shaking the hand.⁸ Electrodiagnostic studies are necessary to confirm CTS diagnosis with electrodiagnostic criteria including, prolongation of the median motor distal latency (MDL) longer than 4.0 ms and slowing of nerve conduction velocity (NCV) less than 49 m/s with sensory peak latency longer than 3.3 ms.^9,10

Musculoskeletal ultrasonography is used to assess the cross-sectional area (CSA) of median nerve, but still there is no definitive cutoff value of median nerve CSA to diagnose CTS as it is affected by several demographic factors like height, age, weight, sex, and ethnicity.¹¹ Some studies considered 6.8 mm² as a cutoff point of CSA,¹¹ while others consider 8.5 mm² as a cutoff point,¹² and others consider 9 mm² as a cutoff point for median nerve CSA.¹³

Smartphone overuse affects flexor pollicis longus tendon increasing its thickness, joints of the thumb, hands. Hand musculoskeletal disorders include joint affection such as osteoarthritis of the carpometacarpal joint.¹⁴ The aim of this study is to early detect musculoskeletal hand disorders using ultrasonography and detect nerve entrapment using clinical evaluation, ultrasonographic and electrophysiological studies in our university employees younger than 35 years using smartphones with assessment of functional Michigan Hand Outcomes Questionnaire (MHQ).

Materials and methods

Ultrasonographic evaluation

Ultrasonographic evaluation of median nerve was done bilaterally with PHILIPS-HD11XE linear transducer 7-12 MHz array probe placed over the median nerve (Fig. 1). The arms were semi flexed resting on a pillow on the subjects legs with fully supinated hands. CSA of median nerve in mm² was evaluated just before carpal tunnel entrance with axial imaging.²³

Fig. 1 Axial gray scale U/S image at the level of the proximal carpal raw showing transverse plane of the median nerve with cross sectional area = 0.85mm². 

The metacarpophalangeal and interphalangeal joints of the first finger, and the proximal and distal interphalangeal joints of the second, third, fourth and fifth fingers were examined (10 joints per hand examined) (Fig. 2). For each joint, ultrasonographic (U/S) evaluation score with six features (synovial effusion; synovial hypertrophy; tenosynovitis; hyper vascularization; bone erosions; and signs of Enthesopathy) was used assigning 1 point for every feature when present and 0 point when absent (each joint examined has score from 0 to 6; 10 joints examined per hand; so the maximum score for each hand is 60).²⁴ The ultrasound evaluations were performed by the same clinician, who was blinded to the SAS scores.

Fig. 2 Sagittal U/S image showing the proximal interphalangeal joint of the index finger with minimal joint effusion. 

Results

Demographic and clinical parameters among the studied groups

Seventy four smartphone users were included divided into two groups: high smartphone users 18 male (47.4%), 20 female (52.6%), with a mean age 27.05 ±4.19 years, low smartphone users 19 male (52.8%), 17 female (47.2%) with a mean age 26.77 ± 3.95 years and non-smartphone users as a control group 16 male (45.7%), 19 female (54.3%) with a mean age 25.37 ± 4.15 years. No significant differences regarding age and gender between the three groups (p = 0.18, p = 0.82) respectively (Table 1).

Table 1 Demographic and clinical parameters among the studied groups. 

The VAS was significantly higher in the high than the low and non-smartphone user groups (5.60 ±1.46, 4.19 ±0.78 and 3.65 ±0.48) respectively (Table 1).

Ultrasonographic scores of both hands, were significantly higher in high compared to low and non-smartphone users (15.08 ±4.17, 6.46 ±1.38, 1.49 ±0.81, p< 0.001) respectively (Table 1).

Nerve conduction studies among the studied groups

Nerve sensory and motor conduction velocities and sensory and motor latencies of median nerve were compared, there were significant differences between the high, low, and non-smartphone users with non-significant differences of the ulnar nerve between the studied groups regarding motor conduction velocity and sensory latency (p = 0.55, p = 0.54) (Table 2).

Table 2 Nerve conduction studies among the studied groups. 

Correlation between CSA and SAS, VAS, MHQ and duration of smart phone use in high smart phone user group

There was significant positive correlation between CSA and SAS, duration of smartphone use and VAS with negative correlation with MHQin high smartphone users (r= 0.45, p = 0.004; r=0.80, p = <0.001; r=0.61, p<0.001; r=-0.63, p = <0.001), respectively (Table 3).

Table 3 Correlation between CSA and SAS, VAS, MHQ and duration of smart phone use in high smart phone user group. 

Comparison of CSAs of the dominant and non-dominant hands of the studied groups

CSAs of median nerves were significantly higher in the dominant hands of the studied groups (9.36 ±0.59, 8.18 ±0.69, 5.89 ± 0.23) compared to the non-dominant hands (9.23 ± 0.61, 7.97 ±0.72, 5.74 ±0.82), respectively with the highest CSAs in the dominant hand of high smartphone users (9.36 ±0.59, p< 0.001) (Table 4).

Table 4 Comparison of CSAs of the dominant and non- dominant hands of the studied groups. 

Discussion

Smartphone use has been significantly increased nowadays with both negative and positive advantages. it enables its users to easily communicate with others and send e-mails²⁶ and has been used in medicine especially for drug-addicted or psychiatric patients.^26,27

However musculoskeletal symptoms like De-Quervain tenosynovitis may develop in smartphone users. Frequent uses of smartphones and the repeated movements of the hands are the main contributing factors for these muscu-loskeletal symptoms. Also enlargement of the median nerve, Xie et al., 2016 and Lippi et al., 2016 reported high U/S hand scores in high smartphone users.^28,29 In the other line Koldas et al., 2011 found non-significant differences in ultra-sonographic hand scores between high, low and non-smart phone users. This may be contributed to the small number of studied subjects with short duration of smartphone use not affecting their hand joints.³⁰

In this study there was median nerve entrapment in the form of prolonged distal motor latencies and slow conduction velocities in high smart phone users (15 out 38), those patients have the characteristic clinical symptoms suggestive of nerve entrapment with CSA more than 9.11 (cut off point) and fulfilled the electrodiagnostic criteria of nerve entrapment. Ahamed et al., 2015 reported a prevalence of 35.3%.³¹ You et al., 2014 reported a very high prevalence of nerve entrapment (50%) in high smart phone users.³² This high prevalence is because they included patients who are manual workers and the occupational factors are known to cause nerve entrapment, but in our study we assess young population excluding any risk factors for nerve entrapment.

Significant affection of median nerve is contributed to repeated wrist flexion and extension with prolonged smart-phone use which increases the carpal tunnel pressure and decreases the space available for the median nerve inside the carpal tunnel.¹³ In this study; decreased motor and sensory conduction velocities (40.95 ± 6.09, 51.58 ± 6.79) and prolonged motor and sensory distal latencies (3.98 ±0.56, 3.36 ±0.74) in high smart phone users were found. (Table 2)

Several studies have proven the effect of smartphone use on the median nerve as studies by Inal et al., 2015 and Chammas et al., 2014.³³ Chammas et al., 2014 reported decreased conduction velocities among the studied groups (51.93 ±6.32, 54.38 ±6.42, 58.24 ±3.53) respectively and prolonged distal motor latencies in high (3.55 ± 0.55) compared to low (3.31 ±0.41) and non-smartphone users (2.90±0.34).¹⁰

In contrast to this study the studies by Chen et al., 2016 and Dillingham et al., 2016. Chen et al., 2016 reported significant differences in all parameters of the ulnar nerves between high and low smart phone users (p = 0.001, p = 0.003) respectively with non-significant affection of the median nerves (p = 0.854, p = 0.108), respectively.^34,35 This is explained by the origin of both nerves as the ulnar nerve origin is C8, T1 nerve roots which are completely compressed by neck flexion while median nerve origin is C5, C6, C8, and T1 which are partially compressed by the neck flexion.³⁶

This can be explained by the double crush theory which is defined as compressive neuropathy of nerve axon affecting its function because of impaired axoplasmic flow, at 2 distinct sites: proximal in the C-spine, and distal in the cubital tunnel, carpal tunnel, or elsewhere causing disabling pain, numbness, and weakness in the ambulatory and functioning patients. The double crush concept has gained some popularity because it seems to provide a rationale for evaluating the condition of the cervical spine and roots when treating CTS.³⁶

Regarding ulnar nerve dysfunction, the association of a peripheral ulnar neuropathy and cervical radiculopathy (CR) has also been reported. In patients diagnosed with DCS with both cubital tunnel syndrome and CR, have a poorer outcome due to several factors including that ulnar nerve symptoms present for more than a year, multiple electrophysi-ological studies diagnosed neuropathies and radiculopathies, and anterior cervical discectomy and arthrodesis performed before ulnar nerve release.³⁷

Investigations for DCS are important, as it is a clinically significant consideration which makes the treatment results of patients complaining of upper limbs symptoms less predictable.

Several aspects of smartphone use such as duration, tasks for use and positions during smartphone use cause chronic neck and hand pain and so affecting functional status of the hands causing disability. Our study reported the significant positive correlation between mean CSAs of median nerves and SAS, VAS and duration of smartphone use with negative correlation with MHQ. Pain was more severe with poor hand function and disability in high smartphone users (Table 3).

Ali, Asim et al., 2014 and Inal et al., 2015 reported that the pain was more severe with functional hand impairment in high smartphone users.^33,38 Also Inal et al., 2015 found significant positive correlation between SAS and VAS (p<0.05, r=0.345).³³ Kim et al., 2016 reported the significant association between the CSAs of median nerves and duration of smart phone use (p<0.05).³⁹

Repeated and sustained wrist flexion with smartphone over use increases the load on the median nerve inside the carpal tunnel and causing increase in its CSAs. This study showed significantly higher CSAs of median nerves in the dominant hands of the three studied groups (9.36 ±0.59, 8.18 ±0.69, 5.89 ±0.23) more than the non-dominant hands (9.23 ± 0.61, 7.97 ± 0.72, 5.74 ± 0.82), respectively with the highest CSAs in the dominant hand of high smartphone users (9.36 ± 0.59, p < 0.001) (Table 4).

Inal et al., 2015 and Akkaya et al., 2015 reported enlargement of median nerves in the dominant hands of high smartphone users.^33,40 Inal et al., 2015 reported the high CSAs of median nerve in high smart phone users (6.9 ±1.7, p = 0.058) compared to low (6.7 ±1.2) and non-smartphone users (6.3 ± 1.0).³³

Ultrasonographic measurement of median nerve CSA had a considerable variability in diagnostic accuracy of sonographic imaging for carpal tunnel syndrome.¹³ Median nerve CSA has a wide range (4-12 mm²),¹ study by Hersh et al used a 6.8 mm² as a cutoff point of median nerve CSA² while studies by Mohammadi et al and Boehm et al used 8.5 mm² as a cutoff point of median nerve CSA reporting that it is the best cutoff value of CSA at the tunnel inlet and outlet.^12,41 Another study by Klauser et al reported a cutoff value of 8.3 mm².⁴² In this study, the cut off point for the CSA of median nerve was 9.11 (Table 5).

Table 5 Clinical performance of CSA in high smart phone users. 

So, in this study we found that high smartphone users at high risk for developing hand musculoskeletal disorders especially median nerve entrapment, they have high SAS, VAS, prolonged distal motor latency and peak sensory latency with slow conduction velocity and poor hand function represented by low MHQ.

Conclusion

Increased median nerve CSAs among high smartphone users associated with prolongation of both sensory and motor latencies and slow conduction velocities. Caution should be taken upon using smartphones to minimize the risk of development of hand musculoskeletal disorders.