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Carpal Tunnel Syndrome Impairs Pinch Force Accuracy and Stability
Ke Li, PhD; Peter J. Evans, MD, PhD; William H. Seitz, MD; Zong-Ming Li, PhD
Cleveland Clinic, Cleveland, OH

Introduction: Carpal Tunnel syndrome (CTS) is caused by chronic compression of the median nerve in the carpal tunnel and it is the most common hand disorder in the general population. It is known that patients with CTS experience hand clumsiness and have difficulty in dexterously manipulate objects. The purpose of this study was to investigate the effects of CTS on the force accuracy and stability during a sustained precision pinch. We hypothesized that patients with CTS would have decreased force accuracy and increased force variation during the precision pinch.
Methods: Seven CTS patients (1 males, 6 females, Age: 45.7 8.0 y) and seven healthy volunteers (7 females, Age: 41.9 6.4 y) participated in this study. The subjects were instructed to pinch an instrumented apparatus with the pulps of the thumb and index finger for 60 s with a stable force output around a target line at 5 N. Visual feedback of both the real-time pinch force and the target line was provided for the first 30 s but removed for the remaining 30 s. The force accuracy was quantified as the difference between the real-time force and the target line. The force stability was quantified using standard deviation (SD) and coefficient of variation (CV).
Results: Results demonstrated that with visual feedback, there was no significant difference between the CTS and control groups for force accuracy or stability (p > 0.05, Figure 1). By contrast, CTS patients had greater force errors, SDs and CVs than the healthy controls when the visual feedback was not available (p < 0.001, Figure 1). Furthermore, we found that the thumb had lower force accuracy and stability than the index finger for both visual and non-visual conditions (p < 0.05).

Conclusions: CTS-induced sensorimotor deficits lead to reduced accuracy and lowered stability of the pinch force when there is no visually guided information of the force production. Patients with CTS may heavily rely on visual feedback to compensate for the loss of tactile sensation for force accuracy and stability. During precision pinch, the thumb had less force accuracy and stability than the index finger for both the CTS subjects and controls. This study provides insight into the sensoriomotor deficit caused by CTS and inter-digit force control mechanisms during precision pinch.

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