Muscle & nerve
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The purpose of this review was to examine three issues that limit our understanding of motor unit physiology: (1) the range and distribution of the innervation ratios in a muscle; (2) the association between discharge rate and force; and (3) the variation in motor unit activity across contractions that differ in speed and type. We suggest that if more data were available on these issues, the understanding of neuromuscular function would be enhanced substantially, especially with regard to plasticity in the motor neuron pool, adequacy of the neural drive to muscle, and flexibility of activation patterns across various types of contractions. Current data are limited and these limitations influence our ability to interpret adaptations in muscle function in health and disease.
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Pudendal neuropathy is an unusual but important complication of orthopedic surgical procedures involving traction on the fracture table. We describe the clinical and electrophysiological features in six patients presenting with perineal sensory disorders and sexual dysfunction following surgical repair of femoral fracture, hip dislocation, or intra-articular foreign body, in which the traction table was used. ⋯ The outcome at 2-year follow-up was good, except in one patient with initially unrecordable PNTML. Perineal electrophysiological examination can thus confirm the pudendal neuropathy and give prognostic information.
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Unilateral intramuscular injections of acidic saline produce a bilateral, long-lasting hyperalgesia.
This study characterizes an animal model of persistent mechanical hyperalgesia induced by repeated intramuscular injections of low pH saline. Saline at pH 4, 5, 6, or 7.2 was injected twice, 2 to 10 days apart, into the gastrocnemius muscle of rats. To quantify hyperalgesia, paw withdrawal latency to radiant heat (heat hyperalgesia) and withdrawal threshold to mechanical stimuli (mechanical hyperalgesia) were measured. ⋯ Lidocaine injection into the gastrocnemius muscle or unilateral dorsal rhizotomy, 24 h after the second injection (pH 4), had no effect on the contralateral mechanical hyperalgesia. Minimal histopathology was observed in the injected muscle, and changes were similar between groups injected with pH 4 and pH 7.2. Thus, this new model of widespread, chronic muscle-induced pain is unrelated to tissue damage and is not maintained by continued primary afferent input from the site of injury.