A method for detecting functional weakness

A simple electrophysiological method is described for detecting weaknes of psychiatric origin. The method involves the interpolation of a single indirect stimulus to a muscle during the course of a supposedly maximal voluntary contraction. Incomplete motor activation is revealed by the presence of a twitch superimposed on the recording of voluntary torque.

The effects of baclofen on gamma motoneurones supplying gastrocnemius muscle in the rabbit

The effect of baclofen on gamma motoneurones supplying gastrocnemius medialis muscle in the rabbit has been investigated. Baclofen was found to decrease the frequency of firing of tonic gamma motoneurones, and in some cells to inhibit the tonic discharge altogether. Baclofen also increased the regularity of tonic gamma motoneurone discharge. The drug was found to raise the threshold for firing of gamma motoneurones in response to electrical stimulation of the sural nerve, indicating a depression of reflex transmission between the sural nerve and the motoneurones. The results are discussed and brief consideration given to the possible consequences of these results for the action of the drug in human spasticity.

Peripheral nerve blocks at the knee and ankle in operations for common foot disorders

Two hundred eighty-four outpatients who had common foot disorders underwent operation after administration of regional anesthesia, peripheral nerve blocks at the knee and ankle and an ankle tourniquet. In a prospective series of 59 patients, the technique used in analgesic blocks of the foot is described, and the amount and latency of the local anesthetic agent were evaluated, as well as the duration of analgesia. The blocks were complete in 95% of the patients. Reblocking was never necessary. None of the 284 patients showed signs of postanesthetic neuralgia. The method is inexpensive, easy to perform and recommended for treatment of foot disorders.

Stretch reflexes of triceps surae in normal man

In order to learn more about stretch reflex behaviour of triceps surae, normal human subjects sat in a chair with one foot on a platform attached to a torque motor that produced phasic dorsiflexion displacements on the ankle. EMG activity was recorded from triceps surae and responses were obtained for various conditions. When the subjects's foot was relaxed, stretch of triceps surae produced a single EMG component at short-latency which increased in magnitude with increasing velocity of stretch. The response was not altered if the subject was asked to plantarflex or dorsiflex the ankle voluntarily when he felt the perturbation. It was reduced by vibration of the Achilles tendon. If the triceps surae was stretched while the subject plantarflexed his ankle, the short-latency response was followed by one and sometimes two long-latency responses. Like the short-latency reflex when the foot was relaxed, none of these responses was altered by the subject's planned movement after feeling the perturbation. All of the responses were suppressed to a similar degree by vibration. The long-latency reflexes depended on long-duration of stretching and relatively slow acceleration of stretch. The reflexes persisted after anaesthesia to the foot suggesting that muscle afferents were responsible. Interactions between H-reflexes and stretch-reflexes revealed that the afferent volley producing a stretch reflex acted like the afferent volley producing a small H-reflex. Responses at an interval of 30 ms to both an electrical stimulus for an H-reflex and a stretch stimulus were possible if the electrical stimulus produced only a small H-reflex and if the subject had been plantarflexing the ankle. The short-latency reflex when the foot was relaxed or exerting a background force appears to be the monosynaptic, Ia mediated stretch reflex. The physiological properties of the long latency reflexes are similar to those of the short-latency reflex, and they may represent, at least to a certain extent, response of the motor neuron pool to successive Ia bursts.

Timed repetitive ankle jerk responses in early diabetic neuropathy

A 14-year experience with timed repetitive ankle jerk (TRAJ) testing provides fundamental insights into diabetic neuropathy (DN), both its diagnosis and treatment. Advantages of TRAJ include ease of performance, relative economy of the equipment, reproducibility of results, and a parameter that encompasses the entire reflex arc. Euthyroid patients with features suggesting DN often have prolongation of ankle jerk responses on one or both sides only after repetitive stimulation. Prolongation of TRAJ responses were elicited from 41% of overt diabetics and from 27% and 30% of patients with decreased glucose tolerance demonstrated by morning or afternoon testing, respectively. This characteristic response appears to reflect altered neuromuscular function in DN and was not encountered in patients with myasthenia gravis or thyroid dysfunction in the absence of concomitant glucose metabolic aberrations.

Is the functional stretch response servo controlled or preprogrammed?

Recent findings in humans and primates suggest that the long latency electromyographic (EMG) responses, evoked by opposing sudden limb displacements, might be mediated via a transcortical pathway. However, it is not clear whether these "late" responses are servo controlled or preprogrammed. We have addressed these questions in two interrelated experimental series. Firstly, the late EMG responses (termed the FSR) evoked in the ankle muscles of 8-12 normal human subjects were mapped as a function of displacement amplitude and velocity. Secondly, the FSR evoked by sustained ramp displacements (lasting 500 msec) were compared with those elicited by transient pulse displacements (lasting 60 msec) having entirely different amplitude and velocity profiles. The findings demonstrated a general lack of a systematic relationship between the characteristics of the initial component of the FSR and displacement parameters, although exceptions were noted in individual subjects. Furthermore, no marked difference was found in either the latency or the rise time of the FSRs evoked by ramp and pulse displacements. The similarity of the FSRs in spite of widely different input patterns is not consistent with the behaviour of a servo response. However, such a finding is in agreement with the concept of a preprogrammed pattern of activity which, once triggered, has to run its full course without the possibility of modification. It is therefore concluded that, at least the initial part of the FSR is generated by the triggered release of a preformulated pattern of intended movement relatively independent of the specific pattern of limb displacement, rather than acting in the manner of a servo mechanism.

Surgical principles based on anatomy of the foot: preoperative planning

The time for planning an operative incision and approach begins in the office when the patient is first examined and his problem is reviewed. The area anatomy should be carefully studied in the interim prior to the surgical date. At surgery, a sterile marking pencil is employed and its outline carefully studied before the actual incision is made. A thorough knowledge of biomechanics dictates the procedures which may be considered feasible. Only by following such a carefully outlined course, can the surgeon feel reasonably secure that the surgery he proposes to his patient in his office, has a logical chance for a successful outcome.

Facilitation of transmission in Ib pathways by cutaneous afferents from the contralateral foot sole in man

Changes in the quadriceps H-reflex were used to study the effect of a weak contralateral cutaneous stimulation upon transmission in Ib pathways from ankle muscles to quadriceps in man. Provided it was applied to the contralateral foot sole, such a stimulation facilitated transmission in Ib pathways to quadriceps (inhibitory from extensors as well as excitatory from flexors). The central latency of this contralateral cutaneous facilitation was 1 msec longer than that of the ipsilateral cutaneous depression of Ib pathways. These findings are discussed with regard to the requirements of bipedal gait.

Sensory conduction studies of the branches of the superficial peroneal nerve

A method for obtaining antidromic conduction velocities in the sensory branches of the superficial peroneal nerve at the level of the ankle was evaluated. An essential prerequisite for the study of this nerve is knowledge of its exact topography. The method included the placing of surface recording electrodes directly over the branches of the nerve and stimulating the superficial peroneal nerve at the anterolateral aspect of the leg. The right lower extremity of 80 normal subjects was evaluated. The mean values obtained from the medial dorsal cutaneous branch at a distance of 14cm were 2.8 +/- 0.3 msec, 51.2 +/- 5.7 msec, 18.3 microV for the latency to onset of negative deflection, conduction velocity and amplitude, respectively. Similar values were obtained from studies of the intermediate dorsal cutaneous branch. In ease of performance and in reliability, sensory conduction studies in the branches of the superficial peroneal nerve were found to be equal to those of the sural nerve and superior to those of the saphenous nerve. The described technique should be helpful in the electrodiagnostic evaluation of peripheral neuropathy as well as of local neuropathic conditions and entrapment syndromes involving the peroneal nerve or its sensory branches.

Soleus motoneurone excitability in man: an indirect approach for obtaining quantitative data

Using combinations of H and T reflexes, spatial summation has been studied in the human soleus motoneurone pool. With certain assumptions, mathematical treatment of the results yielded estimates of the thresholds of motoneurones to monosynaptic activation by Ia nerve fibres. It was found that, on average, about 62 EPSPs were required to discharge a motoneurone and that a single Ia fibre supplied about 139 neurones.

Ski boot compression syndrome

The extensor tendons and peroneal nerve can be compressed at the ankle by the tongue of the ski boot. The resulting neuritis and synovitis may be severe enough to mimick an anterior compartment syndrome. Treatment consists of conservative methods but the paresthesiae may remain for long periods of time.

Response to sudden torques about ankle in man: myotatic reflex

1. Sudden dorsiflexions and plantarflexions of the foot were imposed on normal human subjects under various states of voluntary activity. 2. Under conditions of constant muscle contraction, the myotatic reflex in soleus and lateral gastrocnemius muscles is linearly and highly correlated with the rate of muscle stretch. The slope of this curve characterizes part of the reflex arc "gain." 3. The gain is linearly proportional to the level of tonic voluntary activation. 4. The gain is reduced by tonic contraction of antagonists. 5. The above statements can be summarized by the following equation (formula: see text), where d theta/dt is the rate of joint rotation. Ts and Tat are measures of voluntary contraction (tension) of all the extensor and flexor muscles acting at the ankle. The term S represents the level of preexisting spinal excitability that can be altered by prior instruction to the subject. 6. A phasic voluntary contraction of the soleus muscle, which leads to muscle shortening, will alter the reflex gain. The gain initially increases with increasing rates of shortening, but at higher rates the gain is reduced. This is in contradiction to the observation for tonic activation as stated above and may be due to an inability of the coactivated fusimotor system to produce sufficiently rapid cocontraction of the spindle fibers. 7. During lengthening of a muscle caused by voluntary contraction of its antagonists, the myotatic reflex gain is reduced. 8. The above facts are interpreted to imply that a functional role for the myotatic reflex in the leg extensors is limited to conditions of postural maintenance or slow, precise movement. During rapid movement, the myotatic reflex is ineffective and load-compensating reactions are mediated by longer latency loops. 9. The duration of the myotatic reflex EMG is from 10 to 40 ms, too brief to be a simple response to a velocity-sensing receptor organ. Either the response is in large measure due to the initial burst of spindle activity that occurs at the start of a ramp stretch, or motoneuron pool dynamics act as a high-pass filter on afferent inputs. 10. In the anterior tibial muscle, the relationships between stretch velocity and reflex amplitude and tonic voluntary contraction and reflex gain are qualitatively similar to those found in the ankle extensors.

Incidence, severity, and time-course of motoneurone dysfunction in myotonic dystrophy: their significance for an understanding of anticipation

The numbers of functioning motor units and the amplitudes of the maximum evoked muscle responses have been measured in 198 muscles of 102 patients with myotonic dystrophy. Losses of units could be demonstrated in most of the extensor digitorum brevis and thenar muscles but less commonly in the hypothenar groups. A more proximal limb muscle, the soleus, was also shown to be involved frequently. Investigation of two premature infants withmyotonic dystrophy also revealed reductions of functiong units; in one infant clinical improvement was associated with increased muscle innervation. Repeated examinations of 10 adult patients disclosed an abnormal decline in neuromuscular function below the age of 60 years. The reduction in functioning units amounted to approximately 3% of the mean control value per annum. Analysis of 19 families showed that the severity of neuromuscular involvement was nearly always greater in members of later generations. If the predicted deterioration was also taken into account, the results strongly suggested that anticipation was a true genetic phenomenon rather than an artefact of selection. The combined results are considered to strengthen the concept of motoneurone dysfunction as the major pathogenetic factor in this form of dystrophy.

Sensory conduction in medial plantar nerve: normal values, clinical applications, and a comparison with the sural and upper limb sensory nerve action potentials in peripheral neuropathy

A method for recording the medial plantar sensory nerve action potential at the ankle with surface electrodes is described. Normal values in 69 control subjects are given and compared with the sural sensory nerve action potential in the same limb in the same subjects. Clinical applications were studied in 33 patients. The procedure may be applied in the diagnosis of L4-5 nerve plexus or root lesions, lesions of the sciatic, posterior tibial, and medial plantar nerves, and is a more sensitive test than other sensory nerve action potentials in the diagnosis of peripheral neuropathy.

Further motor unit studies in Duchenne muscular dystrophy

Numbers of functioning motor units have been estimated in 124 muscles of boys with Duchenne dystrophy; some of the patients were studied on several occasions. In the distal muscles examined (extensor digitorum brevis, thenar, and hypothenar muscles) the losses of units were probably present at birth and did not decrease with age. In contrast, the numbers of units and of excitable muscle fibres in the soleus muscles declined significantly, especially between the ages of 9 and 12 years.

Indirect estimation of spinal cord conduction velocity in man

A method is described for deriving an indirect estimate of the velocity of impulse propagation in the spinal cord of intact man. The estimate is computed from measurements of motor and sensory nerve conduction velocity in the limbs, F-wave latencies, and the latencies of somatosensory evoked potentials. The mean estimated spinal cord conduction velocicy in normal subjects was found to be 55.1 m/sec, with a standard deviation of 9.9. This method appears to have potential application in the electrophysiological evaluation of patients with myelopathic disorders.

Nerve blocks of the foot

Emergency treatment of foot injuries can be made less painful by regional block anesthesia. There is limited medical literature on these techniques and many physicians, while familiar with regional anesthesia of the upper extremity, are not experienced with nerve blocks in the lower extremity. Infiltration anesthesia of the plantar structures of the foot and toes can be very painful and may inhibit healing. Regional anesthesia avoids both of these problems and can prove effective and useful. This paper discusses the techniques and possible complications of nerve block anesthesia of the foot.