Faculty Bibliography

To reduce and optimize the work load imposed on the musculoskeletal system in a given situation, three main areas of interest are work technique, workplace design, and the produced work itself. Ergonomically sound work techniques should be taught early and should be repeatedly evaluated and encouraged. Workplace and tool design must be adapted and modified according to the task performed at the workplace. The work produced has to be evaluated in terms of handling comfort and discomfort by the employee: the greater the comfort, the greater the productivity will be. Especially in the rehabilitation of patients with back injuries, these factors must always be considered to avoid recurrent episodes of pain and disability

1. A series of experiments were conducted to investigate the effect of endogenous opioids on blood pressure of laboratory rats during stress. 2. Rats subjected to 120 min immobilization showed a significant drop in systolic pressure which could be prevented by pretreatment injections of naloxone. 3. Adrenalectomized rats subjected to the same kind of stress showed a drop in systolic pressure equivalent to only 30% of the systolic pressure drop in the intact animals. This decrease in systolic pressure could also be prevented by pretreatment injections of naloxone. 4. It was concluded that the decrease in systolic pressure in intact rats during immobilization was mostly due to endogenous opioids released from the adrenal glands, whereas opioids of other origins such as the pituitary gland, were also important

The lack of trunk muscle strength and endurance has frequently been cited as a suspected factor in the etiology of low-back pain. Several investigators have suggested that asymptomatic patients have stronger trunk muscles than patients with low-back pain. People who are physically fit appear to have a decreased incidence of low-back pain. Increased trunk muscle endurance also have been observed to decrease the incidence of low-back pain. The objective evaluation of the strength and endurance of trunk musculature may, therefore, be significant. Part 1 of this study was designed to develop a reproducible strength-endurance screening procedure and to establish normal isometric-isokinetic trunk muscle strength and endurance parameters for women. This study showed that isometric trunk flexion varied from 19-109 Nm and trunk extension from 38-168 Nm. Peak values for isokinetic trunk flexion at two speeds (30 degrees per second and 60 degrees per second) varied from 17-191 Nm and isokinetic trunk extension from 14-208 Nm. The average endurance time for trunk extensors tested with the Sorensen test was 196 seconds

Several studies have shown positive correlations between muscle strength, flexibility, and the frequency of low-back pain. Weak trunk musculature and decreased endurance have thereby come to be identified as significant risk factors in the development of occupational back problems. Because it is widely accepted that exercise plays an important role in the conservative treatment and prevention of low-back pain, the goals of most rehabilitative programs involves improving the strength and endurance of the low-back pain patient. Whereas electrical stimulation has been shown to increase the muscle strength of the lower extremities, this effect has not been demonstrated for the trunk muscles. Part 2 is a prospective controlled study designed to document and to compare objectively the effects of electrical stimulation and exercise on trunk muscle strength. A total of 117 healthy women were divided randomly into four groups. Two groups received electrical stimulation with different electrical parameters, one group received exercises, and one group acted as a control group. The results showed that low-frequency electrical stimulation and exercises significantly (P less than .05) increased isokinetic back-muscle strength compared to the control and medium-high-frequency electrical stimulation groups. Both types of electrical stimulation, however, significantly increased (P less than .05) the endurance in the back muscles compared with the control and the exercise groups. This study showed that electrical stimulation may be a valuable treatment in the early care of low-back pain patients in maintaining and increasing strength and endurance of back muscles when a more active exercise program is too painful to perform

The effect of local skin cooling on the behavior of low- and high-threshold mechanoreceptive afferents innervating glabrous and non-glabrous skin was studied in microneurographic recordings on awake human subjects. Cooling with ice or ethyl chloride to a skin surface temperature below 10 degrees C caused a reduction of receptor sensitivity in 49 out of 52 studied low-threshold afferents. This effect was reversible upon warning but some reduction often persisted for a few minutes after normal skin temperature had been reached. The subjects' sensations of application and removal of von Frey hair stimuli were more resistant than had reappeared before the sensation of sustained pressure. This could be explained by shorter recovery times for fast than for slowly adapting units and by a relative preservation of the dynamic responses of the slowly adapting units. During the recovery phase some low-threshold mechanoreceptive afferents exhibited a transient 'spontaneous' discharge in the absence of external mechanical stimulation. The suppression of afferent C-fibre responses to needle strokes was more pronounced and long-lasting than the effect on A-fibre responses and largely paralleled the recovery of sensation of pain. It is concluded that the local anaesthetic effect of skin cooling is to a large extent explicable in terms of receptor desensitization although other mechanisms may contribute

The First International Conference on Injuries in the Workplace was held in New York City, 1984. That conference was sponsored, as is the present conference, by the Occupational and Industrial Orthopaedic Center of the Hospital for Joint Diseases Orthopaedic Institute and The World Rehabilitation Fund; and co-sponsored by the World Health Organization and the International Labour Organization. The first conference established that there is a need in each industry for a multidiscipli-nary approach to the prevention of musculoskeletal workplace injuries and rehabilitation of the injured worker. To date, of those industries that have a prevention programme at all, only a few use a multidisciplinary approach. Prevention, if approached, and rehabilitation of the worker are often pursued in a fragmented and inefficient way. The workplace offers an exceptional opportunity to study, prevent and manage musculoskeletal workplace injuries. It is also the site where we are ableto promote and educate a healthy and economically productive life, and therefore form the basis of a healthy and economically productive industry. A substantial discrepancyexists today between the knowledge of workplace injury mechanisms and practical ways of implementation. The 1984 conference established that there is an urgent need for theexchange of prevention data and techniques between industry and scientists and betwee developed and developing nations, on a verypractical level. To prevent musculoskeletalinjuries in the workplace, industry must take an active part as must labour unions and, on a larger scale, nations. An international network of workplace injury data banks must be established for the worldwidetransnational exchange of musculoskeletal occupational injury data and used for prevention and rehabilitation programmes. Practical and realistic goals in terms of decreasing injuries must be set up in the same way that industries determine goals to increaseproductivity

Microneurographic recordings have for the first time been obtained from the human facial nerve trunk, close to its exit from the stylomastoid foramen. The aim was to search for evidence of an afferent or sympathetic component of the facial nerve at this level and to study the fascicular organization of motor fibres. Single unit discharges of motor axons were occasionally discerned, and all recordings showed multiunit motor impulses preceding the EMG activity of the appropriate facial muscles by about 5 ms during both blink reflexes and voluntary contractions. No evidence of low-threshold mechanoreceptive afferents was found. Electron microscopic studies at the level of recording showed unmyelinated axons but attempts to record nociceptive and sympathetic activity failed. However, deep facial pain evoked by intraneural stimulation suggested the presence of nociceptive afferents of non-cutaneous origin. Intrafascicular recording and stimulation showed that most fascicles were composed of motor axons innervating muscles within the whole ipsilateral half of the face

A local anaesthetic drug was injected around the peroneal nerve in healthy subjects in order to investigate whether the resulting loss in foot dorsiflexion power in part depended on a gamma-fibre block preventing 'internal' activation of spindle end-organs and thereby depriving the alpha-motoneurones of an excitatory spindle inflow during contraction. The motor outcome of maximal dorsiflexion efforts was assessed by measuring firing rates of individual motor units in the anterior tibial (t.a.) muscle, mean voltage e.m.g. from the pretibial muscles, dorsiflexion force and range of voluntary foot dorsiflexion movements. The tests were performed with and without peripheral conditioning stimuli, such as agonist or antagonist muscle vibration or imposed stretch of the contracting muscles. As compared to control values of t.a. motor unit firing rates in maximal isometric voluntary contractions, the firing rates were lower and more irregular during maximal dorsiflexion efforts performed during subtotal peroneal nerve blocks. During the development of paresis a gradual reduction of motor unit firing rates was observed before the units ceased responding to the voluntary commands. This change in motor unit behaviour was accompanied by a reduction of the mean voltage e.m.g. activity in the pretibial muscles. At a given stage of anaesthesia the e.m.g. responses to maximal voluntary efforts were more affected than the responses evoked by electric nerve stimuli delivered proximal to the block, indicating that impaired impulse transmission in alpha motor fibres was not the sole cause of the paresis. The inability to generate high and regular motor unit firing rates during peroneal nerve blocks was accentuated by vibration applied over the antagonistic calf muscles. By contrast, in eight out of ten experiments agonist stretch or vibration caused an enhancement of motor unit firing during the maximal force tasks. The reverse effects of agonist and antagonist vibration on the ability to activate the paretic muscles were evidenced also by alterations induced in mean voltage e.m.g. activity, dorsiflexion force and range of dorsiflexion movements. The autogenetic excitatory and the reciprocal inhibitory effects of muscle vibration rose in strength as the vibration frequency was raised from 90 to 165 Hz. Reflex effects on maximal voluntary contraction strength similar to those observed during partial nerve blocks were not seen under normal conditions when the nerve supply was intact.(ABSTRACT TRUNCATED AT 400 WORDS)