Peripheral mechanisms of fatigue in muscles of normal and dystrophic mice.

We evaluated the contribution of different processes to fatigue of normal and dystrophic mouse muscles using an in vitro electromyography chamber. Fatigue was induced by repetitive nerve stimulation at 30 Hz for 0.5 s, every 2.5 s until tension decreased by about 50%. We monitored the compound nerve action potential (AP), compound muscle AP, and isometric tension responses to nerve stimulation, and compound muscle AP and tension responses to direct muscle stimulation. In normal mice, about 50% reduction in nerve-evoked tension occurred by 2.4 min in extensor digitorum longus (EDL), 4.8 min in diaphragm, and 9 min in soleus. Analysis of the responses revealed that the fatigue was caused by failure of more than one process in all muscles, and failure of nerve conduction did not contribute to fatigue in any muscle. Failure of neuromuscular transmission, muscle membrane excitation, and excitation-contraction (E-C) coupling and contractility accounted for 55, 45, and 0%, respectively, of the fatigue in EDL, for 21, 74, and 5% of the fatigue in diaphragm, and for 2, 54, and 44% of the fatigue in soleus. In dystrophic mice, while about 50% reduction in nerve-evoked tension occurred by 8.1 min in EDL and 5.6 min in diaphragm, only 29% reduction in tension occurred by 80 min in soleus. Failure of neuromuscular transmission, muscle membrane excitation, E-C coupling and contractility accounted for 22, 63 and 15% of the fatigue in EDL, for 21, 79, and 0% of the fatigue in diaphragm, and for 15, 59, and 26% of the fatigue in soleus. The proportion of slow-twitch oxidative fibers was more than normal in dystrophic EDL, but the same as normal in dystrophic diaphragm and soleus. The slower onset of fatigue was attributable to lesser failure of neuromuscular transmission in dystrophic EDL, and to lesser failure of E-C coupling and contractility in dystrophic soleus.     

Paediatric dacryocystorhinostomy

Of 258 cases of dacryocystorhinostomy performed on children in the period September 1981 to September 1991, 130 were for simple, unresolved congenital nasolacrimal duct obstruction. Other indications for surgery included punctal agenesis, lacrimal fistula, post-traumatic and post-inflammatory canalicular obstruction. Of 177 children without canalicular pathology, 171 (96%) were relieved of symptoms with one operation, without canalicular intubation. Of 81 cases with canalicular disease, 55 of 70 (79%) who underwent DCR plus canalicular intubation, and 10 of 11 who underwent DCR plus Lester-Jones tube, were substantially improved with one operation. No child required peroperative or postoperative blood transfusion. Dacryocystorhinostomy in childhood, in experienced surgical hands, is a safe procedure, achieving relief of symptoms in most cases, particularly in the absence of canalicular disease.     

Functional evaluation of the spinal cord by magnetic resonance imaging in patients with rheumatoid arthritis and instability of upper cervical spine

Thirty-four patients with atlanto-axial instability due to rheumatoid arthritis were examined with plain x-ray views and functional magnetic resonance imaging (MR), and were neurologically evaluated. Transcranial brain stimulation was performed in 25 patients. In 22 cases, the authors observed inflammatory tissue thicker than 3 mm behind the odontoid peg. The spinal canal diameter was significantly decreased in the flexed position. Nine patients showed signs of cranial migration of the axis. The diameter of the spinal cord was measured to be 7.4 mm in the neutral position, and 6.5 mm in flexion. The difference between the diameter of the neutral and flexed positions was highly significant. Twelve of the 34 patients displayed clinical signs of cervical myelopathy, and 13 showed a significant delay of central motor latency, as calculated from the motor evoked potentials. Surgical intervention, either by a posterior approach only or combined with a transoral dens and inflammatory tissue resection, is recommended in patients with progressive atlanto-axial instability, pathologic clinical and neurophysiologic findings, and a spinal cord diameter of less than 6 mm in flexion. Severe pain and cranial migration of the axis, as measured by the MRI, also justify a surgical intervention.     

Reinterventions in postoperative instability of the lumbar spine

Among the many reasons for reinterventions in the lumbar spine, postoperative instability was chosen as the subject for investigation. Abnormal mobility can be described more precisely in terms of pathological, segmental movement than in terms of instability, as such movement not only represents a greater range of motion of one vertebra towards the adjacent one, but also movement with a restricted (or normal) amplitude of a pathological pattern. Three conditions create pathological postoperative movement: (1) nonunion after attempted fusion; (2) pathologically increased movement because of removal of important weight-bearing structures; (3) compensatory movement of the segment next to a fusion. At the Wilhelm Schulthess Clinic in Zürich, 26 patients underwent one or more operations on the lumbar spine because of persisting pain as a result of postoperative pathological movement. In accordance with the results reported in the literature, good results were rare in reoperations on the lumbar spine (only 8 patients were completely free of pain); 14 patients had intermittent or continuous lumbar pain and 4 patients became worse. The indications for several interventions are carefully analyzed. Better results could probably have been obtained by more stable fixation techniques (transpedicular fixation, combined ventral and dorsal fusions), but the best means of avoiding reoperation is to observe the following guidelines: first, in disectomy cases, the osseous, weight-bearing structures (lamina, facet joint) should remain untouched. If even partial removal seems to be inevitable, fusion should be added done as well.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fibre type characteristics of the lumbar paraspinal muscles in normal healthy subjects and in patients with low back pain

A knowledge of the alteration in the fibre type profile of paraspinal muscle associated with low back pain is essential for the design of successful rehabilitation programmes. In attempting to compare the muscles of patients with low back pain with those of controls, few previous studies have considered factors such as gender, age, and size of the subjects, each of which can potentially confound interpretation of the results. We obtained samples of lumbar paraspinal muscle during spinal surgery from 21 patients with low back pain and, using the percutaneous biopsy technique, from 21 control volunteers matched for gender, age, and body mass. The samples were subject to routine histochemicsl typcal analysis to determine characteristics of muscle fibre type. Compared with controls, the muscle of the patients had a significantly higher proportion of type-IIB (fast-twitch glycolytic) fibres than type- I (slow oxidatve) fibres. The mean size of a given fibre type did not differ between the patients and the controls. Consequently, the relative area of the muscle iccupied by type-IIB fibres was higher and that by type-I fibres Was lower in the patients. The patients had a greater number of muscle samples with more than 1% type-IIC fibres, and abnormalities that could be described as pathological were more marked in the patients than in the controls. In conclusion, the paraspinal muscles of patients who have low back pain display a more glycolytic (faster) profile; this can be expected to render them less resistant to fatigue.