Subjects consisted of 30 healthy adults (23 males, 7 females) aged 23-33 years. They had an average age of 27.8 years (male: 28.1, female: 27.7), average height of 173.5 cm (male: 176.4±5.7, female: 168.8±7.4) and average weight of 68.6 kg (male: 74.3±7.3, female: 61.2±13.7). 23 of the subjects were right-handed (76.7%) and 7 were left-handed (23.3%).

All subjects had no lesion or history of lesion of the nervous, muscular and skeletal system which might affect their hand functionality. Those who had injury or pain at the time of the test were excluded (Table 1).

The Digitalized Pinch Dynamometer is a measuring instrument designed and developed by our Control and Measurement Engineering Department. It consists of a high-speed gauge and a two-fingered power measurement device. The two-fingered power measurement device uses the 3-axis power sensor method that allows precise measurement at 10-gram intervals. It measures the pressing power of two fingers and sends the measured values to a high-speed gauge to calculate the force, which Fig. 1. Digitalized Pinch Dynamometer. is displayed on the LCD and transmitted to the computer simultaneously. The measured values are transmitted to the computer every 0.8 second and these measurements are converted into a force graph which is displayed on the computer screen (Fig. 2).13

We used the Preston Pinch Gauge (Fig. 3) and Digitalized Pinch Dynamometer to measure pinch strength. Measurement was achieved by pressing the front part of the thumb together with the side part of the index finger (Fig. 4) in the standard position proposed by the American Society of Hand Therapists.14,15 In this position, subjects were seated in a chair, with their shoulders adducted and neutrally rotated, their elbows flexed 90 degrees, their forearms positioned neutrally, and their wrists flexed in 0-30 degrees and 0-15 degrees of ulnar deviation (Fig. 5). At first, rater 1 informed the subjects about the measurement procedure and gave them a verbal command to exert their maximum strength for 3 to 5 seconds. Mean values were recorded after measuring three consecutive tests with both their hands. According to those procedures, pinch strengths of the subjects' left and right hand were measured with the Preston Pinch Gauge, and then with the Digitalized Pinch Dynamometer after a 10-minute break. After this, pinch strength was measured again with the Digitalized Pinch Dynamometer after 10 minutes in order to evaluate the inter-instrumental reliability of the dynamometer. Rater 2 conducted the measurement in the same way one hour after the testing by rater 1 was concluded. The results of measurement of the two raters were kept hidden from the other rater.

We used statistical analysis tool SPSS version 17.0, and performed a paired T-test to check the difference of the measured values between the Preston Pinch Gauge and Digitalized Pinch Dynamometer. Intraclass correlation coefficient (ICC) was used to evaluate inter-instrumental and intra-rater reliability of the measurement. In this study, it was considered statistically significant when the p-value was 0.05 or less.

The mean values of measurement with the Preston Pinch Gauge were: 9.65±1.21 kg (right), 8.87±1.51 kg (left) for males, and 6.22±1.03 kg (right), 5.98±1.62 kg (left) for females (Table 2). The mean values of measurement with Digitalized Pinch Dynamometer conducted by rater 1 were: on the first test, 9.58±1.12 kg (right), 8.91±1.53 kg (left) for males, and 6.17±0.94 kg (right), 6.17±1.64 kg (left) for females; and on the second test, 9.50±1.26 kg (right), 8.69±1.56 kg (left) for males, and 6.48±1.05 kg (right), 5.92±1.41 kg (left) for females. The mean values of measurement conducted by rater 2 were: on the first test, 9.22±1.68 kg (right), 8.31±1.67 kg (left) for males, and 6.18±1.11 kg (right), 5.80±1.26 kg (left) for females; and on the second test; 9.07±1.62 kg (right), 8.48±1.79 kg (left) for males, and 5.90±1.33 kg (right), 5.44±1.15 kg (left) for females (Table 3).

The difference between the mean values of pinch strength measured with the Preston Pinch Gauge and Digitalized Pinch Dynamometer was not statistically significant when measured by rater 1, but was significant when measured by rater 2 (Table 4).

Correlation coefficients between the pinch strength values measured with the Preston Pinch Gauge and the values measured by each rater with the Digitalized Pinch Dynamometer were 0.82 for rater 1, and 0.78 for rater 2. All the correlation coefficients were statistically significant (Table 5) (p<0.001).

Correlation coefficients between the pinch strength values measured from the first test and the second test were 0.87 when done by rater 1, and 0.88 by rater 2. All the correlation coefficients were statistically significant (Table 6) (p<0.001).

The correlation coefficient between the pinch strength values measured by rater 1 and rater 2 was 0.75. This value was statistically significant (Table 7) (p<0.001).