Cerebellar control of constrained and unconstrained movements. II. EMG and nuclear activity.
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The aim of this study was to see in monkeys if neurons in dentate and lateral interposed deep cerebellar nuclei are preferentially active in relation to certain movements relative to others. Simple and compound digit movements were trained with digits, hand, and elbow constrained in a cast. The constrained simple movement was flexion of Thumb or Index; the constrained compound movement, flexion of Thumb+Index. An unconstrained compound movement consisted of a reach to, pinch of, and retrieval of a small food reward (Reach+Pinch). Electromyographic (EMG) recording showed that many muscles in the upper extremity, shoulder girdle, and trunk were active in all movements. EMG/muscle stimulation during the constrained digit movements showed that the digit prime movers were active during, sufficient for, and necessary for performance of these digit tasks. By contrast, EMG/muscle stimulation showed that the proximal muscles (though co-active during the tasks) were neither sufficient nor necessary for performance of the digit tasks. A fraction of those neurons that were active during both the constrained and the unconstrained movements fired at a higher frequency during the unconstrained task. Some neurons were active during Reach+Pinch only; a few others were active during one or more of Thumb, Index, Thumb+Index only. There was no distinct preferential discharge relationship to the compound Thumb+Index as compared with the simple Thumb or Index. These correlational data are consistent with an interpretation that the cerebellar discharge influenced all of these movements-simple and compound, constrained, and unconstrained-no one type seemingly more than any other. (+info)
Fatigue of paralyzed and control thenar muscles induced by variable or constant frequency stimulation.
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Muscles paralyzed by chronic (>1 yr) spinal cord injury fatigue readily. Our aim was to evaluate whether the fatigability of paralyzed thenar muscles (n = 10) could be reduced by the repeated delivery of variable versus constant frequency pulse trains. Fatigue was induced in four ways. Intermittent supramaximal median nerve stimulation (300-ms-duration trains) was delivered at 1) constant high frequency (13 pulses at 40 Hz each second for 2 min); 2) variable high frequency (each second for 2 min). The first two intervals of each variable frequency train were 5 and 20 ms. The remaining pulses were evenly distributed in time across 275 ms. The number of pulses varied for each subject such that the force time integral in the unfatigued state matched that evoked by a constant 40-Hz train; 3) constant low frequency (7 pulses at 20 Hz each second for 4 min); and 4) variable low frequency (each second for 4 min). The pulse pattern was the same as that for variable high frequency except that the force-time integral was matched to that produced by the constant low-frequency stimulation. These same experiments were performed on the thenar muscles of five able-bodied control subjects. The variable high-frequency trains used to fatigue paralyzed and control muscles had an average (+/- SE) of 12 +/- 2 and 10 +/- 1 pulses, respectively. Variable low-frequency trains had 7 +/- 1 and 6 +/- 1 pulses, respectively. Significant mean force declines of comparable magnitude (to 20-25% initial fatigue force or to 13-21% initial 50 Hz force) were seen in paralyzed muscles with all four stimulation protocols. The force reductions in paralyzed muscles were always accompanied by significant increases in half-relaxation time and decreases in force-time integral, irrespective of the stimulation protocol. Significant force decreases also occurred in control muscles during each fatigue test. Again, these force declines were similar whether constant or variable pulse patterns were used at high or low frequencies (to 40-60% initial fatigue force or to 29-36% initial 50 Hz force). The force reductions in control muscles were significantly less than those seen in paralyzed muscles, except when constant high-frequency stimulation was used. The variations in stimulation frequency, pulse pattern, and pulse number used in this study therefore had little influence on thenar muscle fatigue in control subjects or in spinal cord-injured subjects with chronic paralysis. (+info)
Motor unit firing during and after voluntary contractions of human thenar muscles weakened by spinal cord injury.
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Spinal cord injury may change both the distribution and the strength of the synaptic input within a motoneuron pool and therefore alter force gradation. Here, we have studied the relative contributions of motor unit recruitment and rate modulation to force gradation during voluntary contractions of thenar muscles performed by five individuals with chronic (>1 yr) cervical spinal cord injury. Mean +/- SD thenar unit firing rates were low during both steady-level 25% (8.3 +/- 2.2 Hz, n = 27 units) and 100% maximal voluntary contractions (MVCs, 9.2 +/- 3.1 Hz, n = 23 units). Thus modest rate modulation, or a lack of it in some units, was seen despite an average fourfold increase in integrated surface electromyographic activity and force. During ramp contractions, units were recruited at 5.7 +/- 2.5 Hz, but still only reached maximal firing rates of 12.8 +/- 4.9 Hz. Motor units were recruited up to 85% of the maximal force achieved (14.6 +/- 5.6 N). In contrast, unit recruitment in control hand muscles is largely complete by 30% MVC. Thus, during voluntary contractions of thenar muscles weakened by cervical spinal cord injury, motor unit rate modulation was limited and recruitment occurred over a wider than usual force range. Those motor units that were stopped voluntarily had significantly lower derecruitment versus recruitment thresholds. However, 8 units (24%) continued to fire long after the signal to end the voluntary contraction at a mean frequency of 5.9 +/- 0.8 Hz. The forces generated by this prolonged unit activity ranged from 0.3 to 7.2% maximum. Subjects were unable to stop this involuntary unit activity even with the help of feedback. The mechanisms that underlie this prolonged motor unit firing need to be explored further. (+info)
Thumb metastasis from small cell lung cancer treated with radiation.
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A rare case of thumb metastasis from small cell lung cancer is presented. The patient underwent local radiotherapy with complete palliation of symptoms. She died 4 months later with disseminated disease. Considerations about incidence, treatment, and physiopathology of this kind of dissemination are made. Conservative treatment of finger metastasis with radiation may be considered due to the poor outcome of these patients. (+info)
Trapezial arthroplasty with silicone rubber implantation for advanced osteoarthritis of the trapeziometacarpal joint of the thumb.
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INTRODUCTION: Arthritis in the trapeziometacarpal joint of the thumb can cause swelling and loss of motion. Treatment options include arthrodesis, replacement arthroplasty and interposition arthroplasty. Our objective in this clinical study was to determine outcomes after trapezial arthroplasty with a silicone rubber implant and the relationship between self-reported and measured outcomes. METHODS: At the Hand and Upper Limb Centre, St. Joseph's Hospital, London, Ont., a tertiary care centre, we reviewed a series of 26 patients with advanced osteoarthritis who underwent silicone rubber trapezial arthroplasty. The follow-up averaged 6.5 years. We assessed the outcomes subjectively, and by clinical, functional and radiographic examination. RESULTS: Although 88% of patients reported some improvement in pain and satisfaction, when quantified the improvement was less impressive: only 5.7 (on a visual analogue scale of 1-10, poor-excellent) for pain and 5.6 for satisfaction. Superior subjective results were reported by patients older than 60 years. Osteoarthritic changes had caused pronounced functional impairment in the hands of patients who underwent surgery and those who did not, so that any long-term benefit of surgery was not measurable. Patients had difficulty manipulating both small and large objects on the Jebsen's hand function test. Peri-implant and carpal radiographic lytic changes were observed in 90% of patients. Six patients (20%) required revision surgery (3 early, 3 late), including 1 with a pathologic scaphoid fracture. CONCLUSIONS: Although clinical, functional and radiographic results were poor, they did not predict either satisfaction or pain improvement reported by patients, illustrating the need for a comprehensive standardized outcome evaluation to make informed decisions on the value of surgical intervention for osteoarthritis of the trapeziometacarpal joint. (+info)
Pollical oblique ligament in humans and non-human primates.
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A morphological study of the oblique ligament in the thumb is presented. The ligament was consistently described in human specimens and compared with dissections of non-human primates from different species. The oblique ligament was found in some, but not all, specimens in each of the following species examined: chimpanzee, orangutan, gibbon, anubis baboon, hamadryas baboon, squirrel monkey, lemur and marmoset. A revised identity of the oblique ligament is proposed as a reinforced distal border of a fibro-osseous annular pollical flexor sheath and whose function is not independent of the flexor sheath. The constant presence and tendinous trait of the pollical oblique ligament in humans, when compared with non-human primates, supports the notion that the oblique ligament strengthens the pollical flexor sheath in humans for restraint of the flexor pollicis longus tendon during forceful precision pinching. A derivation of the pollical oblique ligament is considered as representing a vestigial radial limb of a flexor pollicis superficialis tendon in the thumb. (+info)
Accelerometry of adductor pollicis muscle predicts recovery of respiratory function from neuromuscular blockade.
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BACKGROUND: Residual paralysis increases the risk of pulmonary complications but is difficult to detect. To test the hypothesis that accelerometry predicts effects of residual paralysis on pulmonary and upper airway function, the authors related tests of pulmonary and pharyngeal function to accelerometry of adductor pollicis muscle in 12 partially paralyzed volunteers. METHODS: Rocuronium (0.01 mg/kg + 2-10 microg x kg-1 x min-1) was administered to maintain train-of-four (TOF) ratios (assessed every 15 s) of approximately 0.5 and 0.8 over a period of more than 5 min. The authors evaluated pharyngeal and facial muscle functions during steady state relaxation and performed spirometric measurements every 5 min until recovery. Upper airway obstruction was defined as a mean ratio of expiratory and inspiratory flow at 50% of vital capacity of greater than 1. The TOF ratio associated with "acceptable" pulmonary recovery (forced vital capacity and forced inspiratory volume in 1 s of > or =90% of baseline) was calculated using a linear regression model. RESULTS: At peak blockade (TOF ratio 0.5 +/- 0.16), forced inspiratory flow was impaired (53 +/- 19%) to a greater degree than forced expiratory flow (75 +/- 20%) with a mean ratio of expiratory and inspiratory flow at 50% of vital capacity of 1.18 +/- 0.6. Upper airway obstruction, observed in 8 of 12 volunteers, paralleled an impaired ability to swallow reported by 10 of 12 volunteers. In contrast, all volunteers except one could sustain a head lift for more than 5 s. The authors calculated that a mean TOF ratio of 0.56 (95% confidence interval, 0.22-0.71) predicts "acceptable" recovery of forced vital capacity, whereas forced inspiratory volume in 1 s was impaired until a TOF ratio of 0.95 (0.82-1.18) was reached. A 100% recovery of TOF ratio predicts an acceptable recovery of forced vital capacity, forced inspiratory volume in 1 s, and mean ratio of expiratory and inspiratory flow at 50% of vital capacity in 93%, 73%, and 88% of measurements (calculated negative predictive values), respectively. CONCLUSION: Impaired inspiratory flow and upper airway obstruction frequently occur during minimal neuromuscular blockade (TOF ratio 0.8), and extubation may put the patient at risk. Although a TOF ratio of unity predicts a high probability of adequate recovery from neuromuscular blockade, respiratory function can still be impaired. (+info)
Lacrosse stick entrapment injury to the thumb.
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A case of injury to the left thumb following an errant stick check, and subsequent entrapment of the digit in the open sidewall of a lacrosse stick, is presented. A circumferential laceration, severe swelling, and bruising to the proximal phalanx resulted. This case report emphasises the need to limit the dimensions of openings in the sidewalls of lacrosse sticks to prevent the occurrence of this and other preventable injuries. (+info)