Search Results (4)

Background/Objectives: The Wartenberg sign is a diagnostic feature of ulnar nerve neuropathy. It results from unbalanced activity of the abductor digiti minimi (ADM) and extensor digiti minimi (EDM) muscles secondary to weakness of the third palmar interosseous muscle. Rarely, this sign may occur in the absence of an underlying ulnar neuropathy, which we refer to as the “pseudo Wartenberg sign” (PWS). Methods: This is a retrospective review of 10 patients manifesting an inability to adduct the little finger towards the ring finger with no evidence of an ulnar neuropathy. We describe the clinical and electrodiagnostic (EDX) findings in these patients and discuss the pathophysiologic basis of PWS. Results: The most common cause was an injury in five (50.0%) patients: avulsion of the third volar interosseous muscle in two (20.0%), contracture of the ADM muscle in one (10.0%), and trauma-related dystonia in two (20.0%). The most frequent mechanism of PWS was focal dystonia of specific hand muscles in seven (70.0%) patients. Needle electromyography (EMG) demonstrated no denervation changes in ulnar nerve-innervated hand muscles; the motor and sensory conduction was normal in the ulnar nerve in all patients. Four (40.0%) patients underwent ultrasound studies, with a hyperechoic, avulsed third volar interosseous muscle in one, a hyperechoic and atrophic ADM muscle in one, normal hypothenar and extensor muscles in one, and a normal hypothenar muscle in one. Conclusions: Neurologists, neurosurgeons, and hand and orthopedic surgeons should be aware of the rare cases in which the inability to adduct the little finger may occur in the absence of ulnar neuropathy and look for other causes like avulsion of the third palmar interosseus muscle or focal hand dystonia. Full article

Background/Objectives: When manipulating an object placed on the palm, the eyes and fingers move together. To perform this task precisely, coordination of the eyes and fingers is needed. Based on this view, the present study examined the three-way interaction among the central motor drives to the eyes, index finger, and little finger. Methods: Healthy male participants abducted the right index and/or little finger with or without concomitant saccadic eye movement to the right in response to a visual cue, while the forearm was in the pronated or supinated position. We measured the reaction time (RT), velocity, and amplitude of the eye movements, as well as the RT and amplitude of the electromyographic (EMG) responses in the prime movers for the independent and dependent finger movements. Results: The velocity, amplitude, and RT of the eye movement were not changed by the additional involvement of the finger movement, indicating that the central motor drive to the finger does not influence the eye motor excitability and central motor drive to the eyes. On the one hand, the RT of the finger was not changed by the eye movement, indicating that the central motor drive to the eyes does not influence the central motor drive to the finger muscle. On the other hand, the EMG amplitude in the first dorsal interosseous muscle at the movement onset decreased during the concomitant eye movement, indicating that the central motor drive to the eyes suppresses the motor excitability of the independent finger muscle. The RT increased and EMG amplitude decreased in one finger muscle when the other finger concurrently moved, indicating that the central motor drive to one finger muscle suppresses the motor excitability of and central motor drive to the other finger muscle. The change in the RT and EMG amplitude in one finger muscle caused by the concomitant execution of the other finger movement and/or eye movement varied with forearm position, indicating that forearm proprioception influences the interaction of the motor execution processes among the fingers and eyes. Conclusions: The central motor drive to the eyes or finger muscles suppresses the motor excitability of the other finger muscles and the central motor drive to that muscle, but the central motor drive to the finger muscles does not influence those for the eyes. Forearm proprioception influences the motor excitability of the finger muscle and central motor drive to that muscle. Full article

This study investigated whether the motor execution process of one finger movement in response to a start cue is influenced by the participation of another finger movement and whether the process of the finger movement is dependent on the movement direction. The participants performed a simple reaction time (RT) task, the abduction or flexion of one (index or little finger) or two fingers (index and little fingers). The RT of the prime mover for the finger abduction was significantly longer than that for the flexion, indicating that the time taken for the motor execution of the finger response is dependent on the movement direction. The RT of the prime mover was prolonged when the abduction of another finger, whose RT was longer than the flexion, was added. This caused closer RTs between the prime movers for a two-finger response compared with the RTs for a one finger response. The absolute difference in the RT between the index and little finger responses became smaller when two fingers responded together compared with one finger response. Those results are well explained by a view that the common motor drive triggers the prime movers when two fingers move together in response to a start cue. Full article

Fiber-reinforced fluid-driven elastomer actuators have enabled the production of simple, low-cost and safe hand rehabilitation devices. However, so far, the actuators support only finger flexion-extension, and little has been reported on abduction-adduction, which is essential for manipulation tasks and grasping larger objects. The technical design difficulty of realizing abduction-adduction lies in the suppression of interference effects between the metacarpophalangeal (MCP) joint’s two orthogonal motion axes, caused by the necessary multi-chamber actuator structure and its reinforcements, under strong spatial constraints. This problem has not been solved yet, regardless of research efforts on designing various actuator structures. In this study, our goal was to enable flexion of all three finger joints and abduction-adduction of the MCP joint, while minimizing the interference and realizing required ranges of motion. For this, we propose two new types of fiber reinforcements (separate single loops and two-directional hitching) and their combination to direct a multi-chamber structure’s expansion and strengthen its force output into the wanted directions. The reinforcements’ effects on actuator response were evaluated by attaching prototypes to a dummy finger and measuring its range of motion and related joint torques and forces. Results showed that the single loops provided length extension, while the hitching constrained it from the bottom at the centerline and strengthened flexion. When combined, they could be used to adjust the amount of length extension and flexion along the actuator, without detrimentally affecting the flexion or abduction-adduction functions. In conclusion, the two new reinforcement types have the potential of being a major design factor for fitting the actuators’ response for different users’ finger kinematics. Full article