Carpal tunnel syndrome impairs index finger responses to unpredictable perturbations

Abstract

The fine-tuning of digit forces to object properties can be disrupted by carpal tunnel syndrome (CTS). CTS' effects on hand function have mainly been investigated using predictable manipulation tasks; however, unpredictable perturbations are commonly encountered during manual tasks, presenting situations which may be more challenging to CTS patients given their hand impairments. The purpose of this study was to investigate muscle and force responses of the index finger to unpredictable perturbations in patients with CTS. Nine CTS patients and nine asymptomatic controls were instructed to stop the movement of a sliding plate by increasing index finger force following an unexpected perturbation. The electrical activity of the first dorsal interosseous muscle and forces exerted by the index finger were recorded. CTS patients demonstrated 20.9% greater muscle response latency and 12.0% greater force response latency compared to controls (p<0.05). The duration of plate sliding was significantly different between groups (p<0.05); the CTS group's duration was 142.2±5.8ms compared to the control group's duration of 133.1±8.4ms. Although CTS patients had increased muscle and force response durations comparatively, these differences were not statistically significant. Findings from this study suggest CTS-induced sensorimotor deficits interfere with accurate detection, processing and response to unpredictable perturbations. These deficits could be accounted for at multiple levels of the peripheral and central nervous systems. Delayed and decreased responses may indicate inefficient object manipulation by CTS patients and may help to explain why CTS patients tend to drop objects.

Understanding the constraints of finger motor control

“…A similar chain of events and vicious cycle, but then leading to scar tissue formation between muscle heads of extrinsic finger muscles, has been proposed earlier as a mechanism for the development of muscle disorders in the forearm associated with repetitive work (Maas and Huijing, 2005). The effects of CTS on finger motor control is the topic of a third paper on CTS in this special issue (Grandy et al, 2017). For a task in which subjects had to stop a suddenly sliding plate with their index finger, longer latencies of muscle activity and finger force responses were found in the CTS patients.…”

Smartphone and Musculoskeletal Risk Factors: A Systematic Review

“…Repetitiveness and prolonged gripping while texting cause hand pain-a phenomenon so prevalent among BlackBerry users that that condition was accorded its own term, that is, "BlackBerry thumb" (or hand) [29,30]. Finger and wrist positions influence deformity in the median nerve, which causes numbness and clumsiness in hand movements involved in daily routines [12,[31][32][33]. The SP-related neck pain known as text neck syndrome is a result of maintained and awkward posture while texting, especially when a user is holding a heavy SP for a long period as his/her neck is flexed [2,34].…”