Thumb strength affected by carpal tunnel syndrome.

UNLABELLED: We examined the effects of carpal tunnel syndrome on thumb strength in multiple directions to test the hypothesis that a force deficit would be most severe in directions associated with abduction. Twelve right-handed women with carpal tunnel syndrome in the right hand, and 12 age-matched, gender-matched, right-handed control subjects were included. Thumb strength was measured in all directions in the transverse plane perpendicular to the longitudinal axis of the thumb. Force envelopes, the boundary of maximal force magnitude, were constructed using the directional forces. The force envelope or envelope area did not differ between the control subjects and the patients with carpal tunnel syndrome. The percentage contributions of force quadrant to the envelope area did not differ between the patients and the control subjects. Our results support the concept that thumb strength is relatively preserved with carpal tunnel syndrome, and failed to support the traditional belief that carpal tunnel syndrome preferentially impairs thumb abduction strength. The data suggest the commonly used testing of thumb abduction strength may not be an effective means to evaluate the existence or severity of carpal tunnel syndrome. LEVEL OF EVIDENCE: Diagnostic study, Level III (study of nonconsecutive patients; without consistently applied "gold" standard). See the Guidelines for Authors for a complete description of levels of evidence.

Circumferential force production of the thumb.

We developed an apparatus to measure maximal continuous circumferential forces of a digit in the transverse plane that is perpendicular to the longitudinal axis. Subjects with asymptomatic hands were asked to produce maximal forces in all directions at the proximal phalanx of the thumb. The force components during circumferential trials were used to construct a force envelope for each subject. The force envelope enlarged as the number of trials increased, and converged to a stable pattern after several trials. The shape of the force envelope was asymmetric and oblique, skewed towards the flexion/adduction direction. Maximal force (112.1 +/- 14.8 N) was generated in the direction combining flexion and adduction. The lowest force produced was only 50.3% of the maximal force in a direction combining extension and abduction. The forces in the direction of adduction, extension, abduction, and flexion were 60.1%, 61.9%, 51.5%, and 92.9% of the maximal force, respectively. The forces generated by circumferential exertions were comparable to the forces by focused directional exertions except in the flexion direction. Our methods have the potential to identify deviations from the normative force output pattern and help detect underlying impairments resulting from neuromuscular disorders.

Motion enslaving among multiple fingers of the human hand.

The purpose of the current study was to examine motion enslaving characteristics of multiple fingers during isolated flexion of the distal interphalangeal joints. Because the distal interphalangeal joints are flexed by multiple tendons of the single flexor digitorum profundus, the current experimental design provided a unique advantage to understand inter-finger enslaving effects due to the flexor digitorum profundus. Eight subjects were instructed to flex the distal interphalangeal joint of each individual finger from the fully extended position to the fully flexed position as quickly as possible. Maximal angular displacements, velocities, or accelerations of individual fingers were used to calculate the enslaving effects. An independence index, defined as the ratio of the maximal displacement of a master finger to the sum of the maximal displacements of the master and slave fingers, was used to quantify relative independence of each finger. The angular displacements of the index, middle, ring, and little fingers were 68.6(degrees) (+/-7.7), 68.1(degrees) (+/-10.1), 68.1(degrees) (+/-9.7), and 74.7(degrees) (+/-13.3), respectively. The motion of a master finger was invariably accompanied by motion of 1 or 2 slave fingers. Angular displacements of master and slave fingers increased to maximum values with time monotonically. Velocity curves demonstrated bell-shaped profile, and the acceleration curves were sinusoidal. Enslaving effects were generated mainly on the neighboring fingers. The amount of enslaving on the middle and ring fingers exceeded more than 60% of their own maximum angular displacements when a single adjacent finger moved. The index finger had the highest level of independence as indicated by the lowest enslaving effects on other fingers or by other fingers. The independence indices of the index, middle, ring, and little fingers were 0.812 (+/-0.070), 0.530 (+/-0.051), 0.479 (+/-0.099), and 0.606 (+/-0.148), respectively. In all tasks, motion of slave fingers always lagged with respect to the master finger. Time delays, on average, ranged from 7.8 (+/-5.0) to 35.9 (+/-22.1) ms. Our results suggest that there exist relatively large enslaving effects among the compartments of the flexor digitorum profundus, and functional independence of fingers in daily activities is likely enhanced through synergistic activities of multiple muscles, including flexors and extensor.

Thumb force deficit after lower median nerve block.

PURPOSE: The purpose of this study was to characterize thumb motor dysfunction resulting from simulated lower median nerve lesions at the wrist. METHODS: Bupivacaine hydrochloride was injected into the carpal tunnel of six healthy subjects to locally anesthetize the median nerve. Motor function was subsequently evaluated by measuring maximal force production in all directions within the transverse plane perpendicular to the longitudinal axis of the thumb. Force envelopes were constructed using these measured multidirectional forces. RESULTS: Blockage of the median nerve resulted in decreased force magnitudes and thus smaller force envelopes. The average force decrease around the force envelope was 27.9%. A maximum decrease of 42.4% occurred in a direction combining abduction and slight flexion, while a minimum decrease of 10.5% occurred in a direction combining adduction and slight flexion. Relative decreases in adduction, extension, abduction, and flexion were 17.3%, 21.2%, 41.2% and 33.5%, respectively. Areas enclosed by pre- and post-block force envelopes were 20628 +/- 7747 N.N, and 10700 +/- 4474 N.N, respectively, representing an average decrease of 48.1%. Relative decreases in the adduction, extension, abduction, and flexion quadrant areas were 31.5%, 42.3%, 60.9%, and 52.3%, respectively. CONCLUSION: Lower median nerve lesion, simulated by a nerve block at the wrist, compromise normal motor function of the thumb. A median nerve block results in force deficits in all directions, with the most severe impairment in abduction and flexion. From our results, such a means of motor function assessment can potentially be applied to functionally evaluate peripheral neuropathies.