Force-generating capacity of thumb adductor muscles in the parallel and perpendicular plane of adduction.

The description of thumb movements, especially for adduction at the carpometacarpal joint, still gives rise to a confusion among clinicians and researchers. The purpose of this study was to elucidate this confusion by comparing twitch, tetanic, and voluntary isometric force measurements of thumb adductors with the thumb positioned perpendicular and parallel to the palm of the hand. Fourteen healthy adult subjects, aged between 22 and 40 years, volunteered their participation. Maximum twitch, tetanic, and voluntary contractions were recorded using a strain-gauge mounted on a wooden platform. Twitch and tetanic contractions were evoked by an electrical stimulator that passed current through surface electrodes to the skin overlying the ulnar nerve at the wrist. The results show no statistical difference for the tetanic and voluntary force measurements between the two planes of adduction (p > 0.5). The significant changes observed for the twitch responses between the two planes were attributed to a change in the compliance of the muscle-transducer unit. To conclude, the present findings provide clinicians and researchers with an objective and quantitative basis for assessing the force-generating capacity of thumb adductor muscles in either the parallel or the perpendicular plane of adduction.

[Macroscopic, histologic and ultrastructural study of 89 prostheses of anterior cruciate ligament excised because of prosthesis failure]. / Etude macroscopique, histologique et ultrastructurale de 89 prothèses du ligament croisé antérieur explantées pour échec.

PURPOSE OF THE STUDY: This study concerns the etiology of failed synthetic anterior cruciate ligament (ACL) prostheses, and attempts to identify the primary mechanisms that lead to their premature rupture. MATERIAL AND METHODS: A total of 89 failed and surgically excised ACL prostheses were retrieved from young and active patients (27 +/- 7 years) at various orthopaedic centres in France. Their average duration of implantation was 34 +/- 24 months. They were examined macroscopically, histologically and by scanning electron microscopy (SEM) to determine the model, the manufacturer, the surgical technique used at implantation, the extent of healing, the site of rupture, as well as the morphology of the damage fibers. RESULTS: Seventy two of these explants represented 6 different models. While all 6 were fabricated from polyester fibres, each had a different textile construction, and each were associated with a unique healing and mechanical response in vivo. SEM observations confirmed that abrasion of the textile fibres were a phenomenon common to all models, and were the primary cause of prosthesis failure. Such wear zones were particularly prevalent at the exit of the tibial tunnel and around the femoral condyle. Collagenic infiltration into the synthetic ACL was poorly organized and unpredictable. It did not increase with the duration of implantation. In fact in certain models, it appeared to have caused deterioration and fraying of the textile structure rather than serving as a reinforcing matrix around the prosthesis. DISCUSSION: A synthetic ACL prosthesis is to be preferred for patients who do not have tissue available for autologous ligamentoplasty. Yet none of the synthetic devices examined in the present study were capable of stabilizing the knee over the long term. Among the factors that influenced their failure we found that the three most common mechanisms were flat abrasion against an osseous surface, flexural and rotational fatigue of the fibres, and loss of integrity of the textile structure due to unpredictable tissue infiltration during healing. CONCLUSION: The results of the present study show that none of the current models succeed in replacing the natural ACL. Future improvements may be achieved by developing surgical procedures for implantation combined with a prosthesis made from fibres and textile structures which are more abrasion resistant and promote predictable and controlled tissue infiltration.

Effects of TENS and topical skin anesthesia on soleus H-reflex and the concomitant influence of skin/muscle temperature.

The purpose of this study was to determine, in ten healthy subjects, the extent of soleus motoneuronal excitability during conditions of increased (transcutaneous electrical nerve stimulation [TENS]), decreased (Xylocaine [lidocaine]a anaesthesia) and normal (placebo anaesthesia) cutaneous inputs. Increased cutaneous activity was evoked using a TENS unit, with the two pairs of electrodes placed respectively over the Achilles (S2 dermatome) and tibialis anterior (L5 dermatome) tendons. Experimental and placebo topical anaesthesia were obtained after rubbing Xylocaine (5%) and Vaselineb ointment, respectively, on the skin surface overlying the Achilles tendon. Sets of ten H-responses (Hmax/2) were evoked at a frequency of 1 shock/30s and averaged at regular time intervals before, during and after the testing conditions. The results showed a gradual increase (up to 40% after 20 minutes) of H-reflex amplitude during TENS regardless of whether it was applied on the L5 or S2 dermatome. Furthermore, placebo anesthesia (Vaseline) caused the same gradual facilitatory response (up to 100% after 50 minutes) as that obtained during Xylocaine anaesthesia. Power spectral analysis of the H-responses obtained over time showed that the increase in the peak-to-peak H-response value was accompanied by a shift of the spectral content toward low frequencies. This shift occurred concomitantly with a cooling of the skin overlying the soleus muscle.

Histopathological and immunological investigations of synthetic fibres and structures used in three prosthetic anterior cruciate ligaments: in vivo study in the rat.

Three types of prosthetic anterior cruciate ligaments were investigated by enzymatic and histological analysis of the tissue surrounding each implant and immunologically by a cytofluorometric analysis of T-cell populations in the peripheral blood of rats. Two of the prostheses had a braided construction, one made from polyester and the other from high performance polyethylene fibres. The third type also contained high performance polyethylene fibres, but had been manufactured in a knitted construction (Raschel high performance polyethylene). Five specimens from each prosthesis were implanted intraperitoneally in rats by a trocar for different periods of time up to 4 wk. A control group of rats underwent the surgery, but not the implant. No modification in peripheral T-cell populations was induced by the presence of any implant. Whilst the levels of acid phosphatase and esterase activity appeared to have increased slightly following implantation of any of the prostheses, such increases were not highly significant. Histologically, all three materials induced an intense acute inflammatory reaction at 3 d which gave way to a typical chronic response after 4 wk. The only major difference between the prostheses was that after 4 wk the polyester fibres exhibited less inflammation, and the surrounding tissue was more mature, more vascularized and more densely infiltrated with collagen than with the two high performance polyethylene implants. In conclusion, all three devices provided satisfactory biocompatibility in terms of cellular and healing response.

Cutaneous versus Muscular Perception of Electrically Evoked Tetanic Pain.

This work was supported in part by Laval University (sabbatical leave of Dr. A.Y. Bélanger), the School of Kinesiology at Simon Fraser University, and Medtronic of Canada Inc. There is much speculation in athletic, physical therapy, and sports medicine circles about the relative cutaneous (superficial) vs. muscular (deep) perception of pain felt during maximum electrically evoked tetanic muscle contraction. To date, very few studies have addressed the basic question of whether pain perception during electrical stimulation is more superficial (cutaneous) or deep in muscular tissue. The purpose of this study was to determine, in a group of 10 healthy male subjects, the effect of a complete sensory nerve block at the thigh on the qualities (intensity, sensory, affective) of pain (elicited by electrically induced tetanic muscle contraction) as measured by the Short-Form McGill Pain Questionnaire felt during high amplitude, 50-Hz electrical stimulation (ES) of the vastus lateralis muscle. The findings from this study provide clear evidence that a healthy individual's tolerance level to pain induced during electrically evoked maximum tetanic muscle contraction depends as much on deep muscle stimulation as it does on cutaneous or superficial stimulation. Indeed, the results show a statistically significant decrease of approximately 50% in all three qualities of pain (intensity, sensory, and affective) following the elimination of cutaneous pain pathways via the nerve blocking procedure (p < 0.05). Until it is demonstrated that the same results hold for patients who often experience pain prior to ES treatments, any clinical implications would seem to be premature. For now, clinicians must be aware that muscle, as much as skin, may limit one's ability to tolerate high amplitude ES treatments. Further research is needed on the cutaneous vs. muscular perception of electrically evoked pain in healthy and diseased populations as well as on the issue of subject and patient experience vs. nonexperience with ES. J Orthop Sports Phys Ther 1992;16(4):162-168.

A comparison of contractile properties in the preferred and nonpreferred leg in a mixed sample of dystrophic patients.

No study of how muscle contractile function is related to limb preference in human muscular dystrophy is presently available. The purpose of this study was to determine if the ankle plantarflexor (PF) and dorsiflexor (DF) muscle groups of the preferred leg are more or less affected than the nonpreferred one in a mixed sample of myotonic and limb-girdle patients. Measurements of lower limb preference were made as well as of PF and DF evoked and voluntary contractile responses. Isometric contractile properties and peak values for torque production during maximum isometric twitch and voluntary contractions were measured. No significant difference was found in terms of contractile properties between the preferred and nonpreferred leg for both DF and PF muscle groups, except for the large PF twitch torque observed in the nonpreferred side (P less than 0.05). These results, however, reveal a clear tendency for both muscle groups on the preferred side to be weaker than those on the nonpreferred side. This last finding, in conjunction with the equally if not presumably stronger PF/DF muscles on the preferred leg of healthy adult subjects, would suggest that the equivalent bilateral muscle force observed in the present study may be interpreted as giving support to the hypothesis that overwork or overuse of dystrophic muscles may be harmful in weakening the musculature.

Contractile properties of human skeletal muscle in childhood and adolescence.

Using a combination of single maximal stimuli and maximum voluntary contractions, a comparison has been made of muscle properties in pre- and post-pubertal male subjects. In the dorsiflexor and plantarflexor muscles of the ankle, the twitch and maximum voluntary torques were approximately twice as large in the older subjects; the mean height and mean weight increased by factors of 1.20 and 1.86 respectively. The only other muscle parameter that changed, as a function of age, was the contraction time of the ankle dorsiflexors; the mean value was significantly longer in the older subjects. In the younger subjects, there were already clear differences between the dorsiflexor and plantarflexor muscles, the former developing smaller torques and having shorter contraction and half-relaxation times, greater post-activation potentiation and more susceptibility to fatigue. Even in the youngest subject, motor unit activation was complete in the ankle dorsiflexors; although this was not always true of the plantarflexors, the difference between the two subject groups was not significant.

Study of human muscle contraction using electrically evoked twitch responses during passive shortening and lengthening movements.

Electrically evoked twitch properties of the human plantarflexor muscles were measured with the muscles at a constant length (static) and during passive shortening and lengthening. A Kin-Com dynamometer system was used to passively move the ankle joint at 0.52 rad s-1 (30 degrees s-1), as well as to record the twitch responses which were elicited by supramaximal electric shocks applied over the tibial nerve in the popliteal fossa. In the lengthening and shortening conditions, twitches were evoked by triggering the shocks so that the twitch response occurred at a similar angular position for all three conditions. The lengthening twitch peak torque was about twice as large as that recorded for the shortening condition. There was, however, no statistical difference in the twitch time course in these three testing conditions. This twofold increase in the peak twitch torque during lengthening, compared to shortening, is much greater than the torque increase reported during eccentric, as compared to concentric maximal voluntary contractions. These findings suggest that a deactivation process of the contractile system occurs during muscle shortening, while in contrast, during passive lengthening a potentiation mechanism is acting, and that both these mechanisms are independent of volitional muscle activation. The present study is the first to demonstrate the possibility of electrically evoked contractions of human muscles during passive lengthening and shortening. We believe that the use of such evoked contractions may be promising for the study of contractile behaviour of human skeletal muscles during eccentric and concentric conditions.

Neuromuscular function in limb girdle dystrophy.

The contractile properties of ankle dorsiflexor and plantarflexor muscles in 20 patients with limb girdle muscular dystrophy have been compared with those in matched controls. Twitch and voluntary torques were significantly smaller in the patient population and in nine patients it was impossible to record a twitch from tibialis anterior, a dorsiflexor muscle studied in detail. The disease process evidently ran a more rapid course in tibialis anterior than in plantarflexor muscles and this susceptibility was related to some aspect of the muscle other than its fibre type composition. Surviving fibres in dorsiflexor and plantarflexor muscles did not reveal evidence of excitation-contraction uncoupling; they exhibited normal post-activation potentiation and fatigue properties. Some patients were initially incapable of exciting their motor units maximally during voluntary contractions. A finding of possible pathogenetic significance was that one patient, with prominent calves, developed exceptionally large voluntary torque in his plantarflexor muscles.

A comparison of contractile properties in human arm and leg muscles.

Isometric twitch properties have been compared in two pairs of opposing human limb muscles; these were the brachial biceps and triceps, and the anterior tibial and plantarflexor muscles. All four muscles were examined in each of 24 healthy subjects (16 men and 8 women). The brachial triceps had the shortest contraction and half-relaxation times and the greatest twitch potentiation, while the plantarflexors had the most prolonged twitches and least potentiation; the anterior tibial and brachial biceps muscles had similar characteristics. Susceptibility to fatigue was less in the plantarflexors than in the other three muscles. When muscles were assessed without reference to their anatomical sites, a significant relationship was noted between contraction time and potentiation, but not between either of these features and fatiguability. There was no evidence that muscles were uniformly 'faster' or 'slower' in some subjects than in others.

Contractile properties of muscles in myotonic dystrophy.

A study has been made of the contractile properties of plantarflexor and dorsiflexor muscles in 25 patients with myotonic dystrophy and in the same number of closely-matched control subjects. As anticipated, the mean torques developed during maximal voluntary contraction and during the isometric twitch were significantly reduced in the patient population, as were the mean amplitudes of the respective maximum muscle compound action potentials (M-waves). There was considerable variation in weakness between patients, however, and in some there was a striking discrepancy between the results for the plantarflexor and dorsiflexor muscles. It was also found that, in both muscle groups, the mean twitch contraction times were significantly shorter in patients than in controls, but no differences could be demonstrated in relation to fatiguability and post-activation of the twitch. Some patients had great difficulty in obtaining full activation of plantarflexor motor units but there was improvement with repeated effort.

Physiological properties of two antagonist human muscle groups.

The physiological features of two antagonistic muscle groups, the dorsiflexors (DF) and plantarflexors (PF) of the ankle, have been compared in 46 healthy subjects (31 men and 15 women) aged 19-65 years. The DF muscles, of which tibialis anterior (TA) was studied most thoroughly, had relatively small twitches, with moderately fast contraction and relaxation phases, and had marked post-activation potentiation; they were susceptible to fatigue during isometric exercise. The PF muscles had comparatively large twitches, with slow contraction and relaxation phases, and poor post-activation potentiation; they were more resistant to fatigue. Women differed from men in having smaller TA twitches and slower PF twitches; PF twitches were also slower in older subjects. The marked differences in physiological properties between DF and PF muscles contrasted with relatively modest histochemical differences found by ourselves and others.

Control of soleus motoneuron excitability during muscle stretch in man.

The relative contributions of intramuscular and extramuscular receptors to changes in the reflex excitability of soleus motoneurons, following muscle stretch, have been studied in man. It was found that reflex excitability was decreased by muscle stretch. The extent of the decrease was related to the amount of stretch, irrespective of whether the latter was produced by dorsiflexion of the ankle or by depression of the Achilles tendon with the ankle joint fixed. The results were unaffected by anaesthesia of the skin. It would appear that neither joint receptors nor cutaneous mechanoreceptors contribute significantly to the decrease in reflex excitability during ankle dorsiflexion and that the intramuscular receptors are mainly responsible for the effects observed.

Influence of joint position on ankle plantarflexion in humans.

The contractile properties of the triceps surae (medial and lateral gastrocnemii and soleus) have been studied in humans. In comparison with most other human muscles, the triceps complex had a slow twitch (mean contraction and half-relaxation times 112.4 +/- 11.1 and 99.6 +/- 14.4 ms, respectively) and a low tetanus fusion frequency (60 Hz). Stretching the muscle caused both the contraction and half-relaxation times to become longer. With the knee bent, the optimum length for torque development corresponded to almost full dorsiflexion of the ankle. Similar results were obtained with the knee extended. The optimum position of the ankle differed considerably from the position of the joint when the leg was at rest. Although the position of the ankle joint affected electromyographic (EMG) activity recorded during maximal voluntary contraction, there was little change in the EMG-to-M wave ratio.