On the origin of the soleus H-reflex modulation pattern during human walking and its task-dependent differences.
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Recently, Brooke and colleagues have suggested "that the strong inhibition arising from passive movement about the knee and hip joints, lays down the base for the soleus H-reflex gain modulation seen during human gait." In particular stretch-evoked afferent activity from the quadriceps muscle was emphasized as the most important source of movement-induced inhibition of the H-reflex. To test this hypothesis we examined the kinematics and electromyographic (EMG) activity of the leg during human walking and correlated these with the modulation pattern of the soleus H-reflex. To further test the possible contribution of stretch-evoked quadriceps afferent activity to the soleus H-reflex modulation pattern during walking different walking gaits were studied. In one condition subjects were asked to walk with their knee locked in full extension by a rigid knee brace. In a second condition subjects were asked to walk backwards. During normal walking, the soleus H-reflex modulation pattern is strongly correlated with the EMG events of the soleus and tibialis anterior (TA), but not with hip, knee, or ankle angular displacement or velocity. When subjects walked with the knee locked in full extension, the amplitude of the H-reflex, its modulation pattern, and the task-dependent changes of its amplitude were the same as during normal walking. During backward walking, the H-reflex increases in late swing before activity of the soleus has begun and while the knee is flexing, an observation that highlights central control of the H-reflex amplitude. The effects of imposed flexion of the knee in passive subjects were also reexamined. The knee flexion imposed by the experimenter followed the same trajectory as that which occurred during the swing phase of the subject's step cycle. It was found that imposed knee flexions elicited a burst of TA EMG activity with an average latency of 81.6 ms (SD = 21 ms) in six out of eight subjects. Inhibition of the H-reflex, when it occurred, was associated with the occurrence of this burst. When subjects voluntarily flexed their right knee from an initial quiet standing posture, the inhibition of the soleus H-reflex began before flexion of the knee or that of any other leg segment. Once again the onset of inhibition was closely associated with the onset of activity in the TA. In the discussion section the present observations are examined in light of the predictions made by the movement-induced inhibition hypothesis of Brooke et al. It will be concluded that none of the predictions of this hypothesis were corroborated by present tests done during human walking. In consequence, we suggest that the modulation pattern of the H-reflex observed during normal human walking is centrally determined, as are the task-dependent differences of its amplitude (e.g., standing versus the stance phase of human walking). (+info)
The Baumann procedure for fixed contracture of the gastrosoleus in cerebral palsy. Evaluation of function of the ankle after multilevel surgery.
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We treated 22 children (28 limbs) with diplegic cerebral palsy who were able to walk by the Baumann procedure for correction of fixed contracture of the gastrosoleus as part of multilevel single-stage surgery to improve gait. The function of the ankle was assessed by clinical examination and gait analysis before and at two years (2.1 to 4.0) after operation. At follow-up the ankle showed an increase in dorsiflexion at initial contact, in single stance and in the swing phase. There was an increase in dorsiflexion at initial push-off without a decrease in the range of movement of the ankle, and a significant improvement in the maximum flexor moment in the ankle in the second half of single stance. There was also a change from abnormal generation of energy in mid-stance to the normal pattern of energy absorption. Positive work during push-off was significantly increased. Lengthening of the gastrocnemius fascia by the Baumann procedure improved the function of the ankle significantly, and did not result in weakening of the triceps surae. We discuss the anatomical and mechanical merits of the procedure. (+info)
Toe-walking in children younger than six years with cerebral palsy. The contribution of serial corrective casts.
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Our aim in this retrospective study was to analyse the value of serial corrective casts in the management of toe-walking in children aged less than six years with cerebral palsy. A total of 20 children (10 hemiplegic and 10 diplegic) had elongation of the triceps surae by serial casting at a mean age of four years and one month. The mean passive dorsiflexion of the foot with the knee in extension was 3 degrees (-10 to +5) and 12 degrees (0 to +15) with the knee in flexion. After removal of the cast passive dorsiflexion was 20 degrees (+10 to +30) with the knee in extension, and 28 (+10 to +35) with the knee in flexion. At a mean follow-up of 3.08 years (2.08 to 4.92), passive dorsiflexion was 9 degrees (-10 to +20) with the knee in extension and 18 degrees (0 to +30) with the knee in flexion. Serial corrective casts are useful for the treatment of equinus in young children as the procedure is simple and the results are at least equal to those of other non-operative techniques. It is a safe alternative to surgical procedures especially in young children. If the equinus recurs operation can be undertaken on a tendon which is not scarred. (+info)
Talocalcaneal coalition. Diagnosis with the C-sign on lateral radiographs of the ankle.
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We analysed 42 weight-bearing lateral radiographs of the ankle, 20 of which were from patients with a clinical and plain radiological diagnosis of talocalcaneal coalition (TCC) who subsequently had CT. The remainder were from 22 healthy volunteers with no clinical findings suggestive of hindfoot pathology. Four observers, blinded to the CT findings, independently evaluated the radiographs on two separate occasions. With the 95% confidence interval and using the CT findings as the comparison we calculated the sensitivity, specificity, accuracy, and positive and negative predictive values for the C-sign, and for other signs known to be associated with TCC. Similarly, we also calculated the interobserver and intraobserver reliability for these signs using the kappa statistic. Our results suggest that the C-sign is highly sensitive and specific for TCC. It is an accurate indicator and significantly more reliable than other previously recognised radiological signs of TCC. Features of the C-sign, however, cannot be relied upon to indicate whether the TCC is fibrous or bony. (+info)
Reconstruction of the lateral ligaments of the ankle using solvent-dried and gamma-irradiated allogeneic fascia lata.
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We have described a method of anatomical reconstruction of the lateral ligaments of the ankles with instability using allogeneic fascia lata dried with solvents and sterilised with gamma irradiation. Twenty ankles of 20 patients were assessed objectively and subjectively after a mean follow-up of 4.2 years (3.1 to 10). The result was excellent in 12 (60%), good in seven (35%) and fair in one (5%); none had a poor result. Stress radiography showed that the angle of talar tilt improved from 12.3+/-4.2 degrees (mean +/- SD) to 5.9+/-3.0 degrees and that the anterior drawer distance decreased from 9.2+/-3.9 mm to 4.4+/-2.5 mm. Neither infection nor limitation of movement occurred after operation. Fascia lata allografts provide a good alternative to autogenous grafts such as the peroneus brevis tendon. (+info)
Stretch reflex distinguished from pre-programmed muscle activations following landing impacts in man.
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1. Electromyographic activity and joint rotation were measured whilst human subjects jumped down to land on a solid surface 0.45 m below them and then to a false collapsible surface at the same level. The collapsible surface did not produce ankle joint rotation. Objective evidence from post-take-off EMG onset latencies showed that the subjects were surprised by the false surface. 2. Following landing on the solid surface, the gastrocnemius and soleus muscles showed peak responses at latencies of 53 and 56 ms, respectively, and the antagonist m. tibialis anterior showed an early peak response with a latency of 26 ms. These responses occurred following landing on the solid surface but not following passage through the false surface. 3. The rectus femoris and biceps femoris muscles showed no clear reflex activity with this fall distance but pre-programmed activity was clearly present following impact. 4. It is concluded that the post-landing activity in m. soleus and m. gastrocnemius is a short-latency spinal reflex triggered by ankle joint rotation. (+info)
Modulation of the startle response during human gait.
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While many studies have shown that there is a phase-dependent modulation of proprioceptive and exteroceptive reflexes during gait, little is known about such modulation for auditory reflexes. To examine how startle reactions are incorporated in an ongoing gait pattern, unexpected auditory stimuli were presented to eight healthy subjects in six phases of the step cycle during walking on a treadmill at 4 km/h. For both legs, electromyographic activity (EMG) was recorded in the biceps femoris (BF), the rectus femoris (RF), the tibialis anterior (TA), and the soleus (SO). In addition, stance and swing phases of both legs, along with knee angles of both legs and the left ankle angle, were measured. All subjects showed various response peaks. Responses with latencies of approximately 60 ms (F1), approximately 85 ms (F2), and approximately 145 ms (F3) were found. The amplitude of the reflex responses was dependent on the timing of the startle stimulus in the step cycle. Although the startle response habituated rapidly, the phase-dependent modulation pattern generally remained the same. The phase-dependent amplitude modulations were not strictly correlated with the modulation of the background activity. The TA even showed a transition from facilitatory F2 responses during stance to suppressive responses during midswing. Responses were observed in both flexors and extensors, often in coactivation, especially during stance. Furthermore the gait characteristics showed a shortening of the subsequent step cycle and a small decrease in the range of motion of ankle and knees. These results suggest that the responses are adapted to achieve extra stability dependent on the phase of the step cycle. However, even in the first trials, the changes in kinematics were small allowing a smooth progression of gait. (+info)
Differences in men's and women's mean ankle ligamentous laxity.
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The incidence of ligamentous ankle injuries is known to be one of the most common athletic injuries that exists. Recently, there has been a great deal of interest regarding the increased risk of female ligamentous injury, such as the anterior cruciate ligament, lateral ankle sprains and others. The purpose of this study is to evaluate whether or not normal lateral ankle ligamentous laxity is similar in male and female athletes. This study selects 22 male and 27 female college athletes who have had no significant ligamentous ankle injuries requiring medical treatment. They were placed on a Telos ligamentous stress device and stressed to a level of 15 daN. Radiographs were then obtained to determine talar tilt at this level of ankle stress. Results were compared between men and women showing that there was a statistically significant difference. Women had a much greater ligamentous laxity of the lateral ankle than men. (+info)