One digit interruption: the altered force patterns during functionally cylindrical grasping tasks in patients with trigger digits

Abstract

Most trigger digit (TD) patients complain that they have problems using their hand in daily or occupational tasks due to single or multiple digits being affected. Unfortunately, clinicians do not know much about how this disease affects the subtle force coordination among digits during manipulation. Thus, this study examined the differences in force patterns during cylindrical grasp between TD and healthy subjects. Forty-two TD patients with single digit involvement were included and sorted into four groups based on the involved digits, including thumb, index, middle and ring fingers. Twelve healthy subjects volunteered as healthy controls. Two testing tasks, holding and drinking, were performed by natural grasping with minimal forces. The relations between the force of the thumb and each finger were examined by Pearson correlation coefficients. The force amount and contribution of each digit were compared between healthy controls and each TD group by the independent t test. The results showed all TD groups demonstrated altered correlation patterns of the thumb relative to each finger. Larger forces and higher contributions of the index finger were found during holding by patients with index finger involved, and also during drinking by patients with affected thumb and with affected middle finger. Although no triggering symptom occurred during grasping, the patients showed altered force patterns which may be related to the role of the affected digit in natural grasping function. In conclusion, even if only one digit was affected, the subtle force coordination of all the digits was altered during simple tasks among the TD patients. This study provides the information for the future studies to further comprehend the possible injuries secondary to the altered finger coordination and also to adopt suitable treatment strategies.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. The cylindrical simulator and functional tasks.

(A) Diagram of the cylindrical simulator, showing five force/torque transducers, the accelerometer and their local coordinate systems. Based on the obtained acceleration data, thus four movement events in the (B) holding and (C) drinking tasks were determined.

Figure 2. The determination of four movement events in each task.

The events were found by the specific turning points of acceleration (A) along Za axis during the holding task including He1 (the first turning point of the first positive peak of acceleration), He2 (the first point of the sustained plateau which follows a negative peak), He3 (the turning point at the end of plateau which is followed by a negative peak) and He4 (the final peak), and (B) along Ya axis by determining the four turning points (De1, De2, De3 and De4) of on trapezoid-shaped profile. Three phases were then defined in between sequential events in each task.

Figure 3. The significant difference of applied RF between TDI and HC during holding.

The RF of each digit at all events and the averaged RF during second phase of the holding task by HC (upper) and TDI (lower). Larger forces of the index finger were found at He2 and He3 and during second phase for TDI when compared to those for HC. Significant differences are indicated by * (p<0.05).

Figure 4. The significant difference of applied RF between TDI and HC during drinking.

The RF of each digit at all events and the averaged RF during second phase of the drinking task by HC (upper) and TDT (lower). Lower forces for the little finger were found at De2 and De3 and during second phase for TDT than those for HC. Significant differences are indicated by * (p<0.05).

Figure 5. The significant difference of CR between TDI and HC during holding.

The force contribution ratios of each digit during the holding task in HC and TDI. A higher CR of the index finger and lower CR of the ring and middle fingers were noticed in TDI. Significant differences (p<0.05) in CR with regard to specific digits between HC and TD groups are indicated by the following symbols: α means the index finger and γ means the ring finger.

Figure 6. The significant difference of CR between TDI and HC during drinking.

The force contribution ratios of each digit during the holding task in HC, TDT and TDM. A higher CR of the index finger and lower CR of the middle and little fingers were noticed in TDI and TDM. Significant differences (p<0.05) in CR with regard to specific digits between HC and TD groups are indicated by the following symbols: α means the index finger, β means the middle finger and δ means the little finger.