Fingers have dominant sensory sides and non-dominant sensory sides that should be considered during hand surgery, particularly when selecting a donor for heterodigital island flaps. One text proposes that the radial side of the index and middle finger and the ulnar side of the ring and little fingers are dominant sensory sides1. Other literature suggests that each finger has its own unique sensibility value. Specifically, the thumb, the radial sides of the index and middle fingers, and the ulnar side of the little finger are highly valuable due to their sensibility. Alternatively, the ulnar sides of the middle and ring finger are less valuable and constitute donor areas2. Traditionally, the radial sides of fingers, opposite the thumb, are considered dominant sensory sides345. This concept, however, is outdated and based on activities commonly performed prior to the advent of modern devices. These activities include writing, opening doors, and grasping things when working.

The modern day increase in the use of electronic devices has made our lives convenient, while, at the same time, changing our patterns of finger use. These conveniences, however, have had unexpected consequences. One such consequence was that specific areas of the fingers became more important for electronic device use. Areas previously thought to be non-dominant are now important for electronic device utilization. Therefore, the traditional concept of dominant sensory sides of the fingers, based on writing and use of other tools, may be outdated. To address this, we investigated finger areas that are more commonly used in office workers that utilize electronic devices.

We selected 26 office workers mainly in computer work (11 male, 15 female; aged 26–54 years old; average age: 33) for this study. The participants' hand dominance was surveyed prior to the experiment. We painted fluorescent ink (highlighter ink; Pelikan Co., Hanover, Germany) on the volar sides of the participants' fingers and palms. The fluorescent material was mixed with distilled water prior to application. This material is colorless and harmless to the human body and therefore did not interfere with daily life or work. To validate the staining technique, we used the same concentration and amount of fluorescent dye. A baseline photograph was taken under special lighting (SIGMAB20; Sunsea Industrial Co., Ltd., Incheon, Korea), and the participants underwent 6–8 hours of work and daily life as usual. All volunteers were told not to wash or wipe their hands until the end of the experiment to prevent the elimination of the fluorescent material. Photographs of the participants' hands were taken after the work period ended and analysed to determine the amount of fluorescent material remaining. To take photos under the same conditions, the camera (EOS 450D; Canon Co., Tokyo, Japan) was fixed in position with an ISO 400, the shutter speed was set at 1/30 second, and participants' hands were positioned in the same location and manner as the first photograph and fixed with special lighting.

We used ‘ImageJ’ software, developed and provided for free by the National Institute of Health (Bethesda, MD, USA; http://rsbweb.nih.gov/ij/), to analyse the photographs. Each finger was divided into an ulnar and radial side (Fig. 1), and the brightness of each side of the finger was compared with the baseline photograph (Fig. 2).

Data were analysed using the Kruskal-Wallis test and post-hoc according to Conover for comparing ten compartments simultaneously in each hand. Mann-Whitney test was used to compare the ulnar and radial side dominance in each finger. MedCalc software (ver. 19.03, Ostend, Belgium) was used. All statistical significance was determined based on a significance level of 0.05.

Participants were all office workers. All of them were in charge of dealing with computers, receiving calls or working with documents. Smartphones and tablet PCs have also been used frequently. But most of the work was dealing with computers. The participants worked 6 to 8 hours (average 6.5 hours). Only one person was left hand dominant. On average, 74% of the fluorescence material remained after the work period, 73% remained on the dominant hand and 75% remained on the non-dominant hand. In the dominant hand, the residual fluorescence material was 73% on the thumb radial side, 73% on the thumb ulnar side, 72% on the index finger radial side, 71% on the index finger ulnar side, 73% on the middle finger radial side, 71% on the middle finger ulnar side, 78% on the ring finger radial side, 71% on the ring finger ulnar side, 79% on the little finger radial side, and 70% on the little finger ulnar side. In the non-dominant hand, the residual fluorescence material was 74% on the thumb radial side, 76% on the thumb ulnar side, 72% on the index finger radial side, 76% on the index finger ulnar side, 74% on the middle finger radial side, 76% on the middle finger ulnar side, 76% on the ring finger radial side, 75% on the ring finger ulnar side, 77% on the little finger radial side, and 75% on the little finger ulnar side (Table 1).

In the dominant hand, the radial sides of ring and little finger retained significant more fluorescent material than other compartments (p<0.001). However, in the non-dominant hand, no compartments displayed a statistically significant difference (Table 1).

When ulnar and radial side of each finger were analysed, there was a significant difference between ulnar side and radial side of ring and little finger of dominant hand. The other fingers were statistically not significant (Table 1).

The sensation is equally important to hand function. Many neurovascular surgeries have been developed to restore finger sensation. To perform these surgeries, hand surgeons must be aware of dominant and non-dominant sensory sides of fingers. The dominant sensory sides of fingers in our concept are thought to be more used for touching, rubbing, pressing, holding and feeling. These sides should be used as a reference for selecting the portion to be reconstructed and the portion to be sacrificed through surgery. However, views differ regarding dominant versus non-dominant sensory areas of the fingers. In 1961, Tubiana and Duparc2 suggest that the value of sensibility is high on the entire thumb, the radial sides of the index and middle fingers, and the ulnar side of the little finger. However, the values of the ulnar sides of the middle and ring fingers are lower than others2. It has also been suggested that the radial sides of the index and middle fingers, and the ulnar sides of the ring and little fingers are dominant sides, particularly to provide protective sensation from trauma16. In 1996, Puckett et al.4 introduced a quartering technique to reduce donor morbidity of the neurovascular island flap and they used the ulnar side of the ring finger as the donor site. In 2006, Hashem3 introduced the idea that the opposite part of the thumb is dominant and that the ulnar sides of fingers are non-dominant. Finally, in 2013, Silva et al.5 suggested that the ulnar pulp of the thumb and the radial pulp of all other fingers are dominant while introducing the pulp switch flap. As shown, opinions regarding dominant sensory sides of fingers vary, likely due to a lack of accurate research into finger side sensory dominance. So, the author designed a new experiment that can identify finger use area in modern life.

Daily activities related to finger use are numerous and include writing, turning a key, and opening a heavy door7. However, the development of machinery and electronic devices has altered and added to this list of the most common activities. In the past, we commonly created documents with pens. Now we use a keyboard and a mouse. Turning a key is replaced by a button type lock. Starting an engine can be done by pressing a single button. Instead of push open a heavy door, we open doors with a button. Development of electronic devices and machines such as the automated teller machine or elevator changed our lifestyle. We also use many haptic devices and smartphones. All of these new activities require the use of the ulnar sides of fingers (Fig. 3).

This pattern of use is different from the traditional pattern for the dominant sensory zone. The results of this study show that the radial sides of the ring and little finger on dominant hand are used significantly less. But, the other compartments of the thumb and fingers showed similar use. According to these results, there are some differences from traditional sensory dominant sides of fingers. The ulnar sides of index and middle finger were not considered important in the past, but they are used with no significant difference from other compartments. On the other hand, the radial sides of ring and little finger which were considered important in some of past studies were not much used in this study. Further studies are needed but these findings may be used as basic data for re-establishing the sensory dominant sides of fingers. Furthermore, these findings may be helpful in better donor site selection for the neurovascular island flap and also be helpful to select the nerves to be reconstructed preferentially when reattaching the fingers.

But, in non-dominant hand, there was no statistically different compartment. We think it is because the tasks in office work are mostly single hand needed, except the keyboard job.

The standard deviation is large in our results because the data is non-parametric. The reason why our data is non-parametric is first, the business characteristics and the frequency of hand use of each person is different. Second, it was not easy to do one's work without washing hands for a long time, and it made experimental time variation which is responsible for the large standard deviation. However, our results were statistically analysed using the nonparametric Kruskal-Wallis tests and Mann-Whitney test. And highly significant results were obtained on dominant hand.

There are several limitations of this study. One is that it was only performed in office workers. Different results may be observed in manual workers or in other groups of individuals. To address this issue, further study is needed. However, many manual workers, due to injury, cannot perform their tasks and are apt to relocate to a simple office job. The results presented for office workers are important, particularly because office jobs are common and often a second career choice for manual workers. Second is that the experiment was not performed in the way that giving a task and then measure the elimination of fluorescent materials. It may have been lost by a simple touch, strong grasp or simply putting a hand on a desk. However, the author tried to estimate the approximate use of finger compartments through the daily life of modern office workers and it seems to have achieved those goals. In further clinical studies, task-based measurement research will be needed. Another limitation of this study is the lack of evidence in the experimental method. Many articles on finger sensory dominance have been reviewed, but there were no studies based on experiment for finger sensory dominance. Therefore, this study is the first study to evaluate the finger sensory dominance and nondominance by experiment.

As a result of this experiment, many fluorescent materials remained on the radial side of ring and little finger of dominant hand. This was statistically significant in the Kruskal-Wallis test, in which 10 compartments of the finger were simultaneously analyzed, and in the Mann-Whitney test, which compared the radial side and ulnar side of each finger. Therefore, this experiment shows that the two compartments tend to be less used in contemporary office workers, and the author believes that these compartments are less sensibly important. Alternatively, other compartments are found to be used with similar significance. Further evaluation and clinical trials are needed for the re-evaluation of sensory dominance of fingers. However, these results can be used as basic data for further study.