Control of wrist movement in deafferented man: evidence for a mixed strategy of position and amplitude control.

There is a continuing debate about control of voluntary movement, with conflicted evidence about the balance between control of movement vectors (amplitude control) that implies knowledge of the starting position for accuracy, and equilibrium point or final position control, that is independent of the starting conditions. We tested wrist flexion and extension movements in a man with a chronic peripheral neuronopathy that deprived him of proprioceptive knowledge of his wrist angles. In a series of experiments, we demonstrate that he could scale the amplitude of his wrist movements in flexion/extension, even without visual feedback, and appeared to adopt a strategy of moving via a central wrist position when asked to reach target angles from unknown start locations. When examining the relationship between positional error at the start and end of each movement in long sequences of movements, we report that he appears to have three canonical positions that he can reach relatively successfully, in flexion, in extension and in the centre. These are consistent with end-point or position control. Other positions were reached with errors that suggest amplitude control. Recording wrist flexor and extensor EMG confirmed that the flexion and extension canonical positions were reached by strong flexor and extensor activity, without antagonist activity, and other positions were reached with graded muscle activation levels. The central canonical position does not appear to be reached by either maximal co-contraction or by complete relaxation, but may have been reached by matched low-level co-contraction.

Preserved and impaired aspects of feed-forward grip force control after chronic somatosensory deafferentation.

BACKGROUND: Although feed-forward mechanisms of grip force control are a prerequisite for skilled object manipulation, somatosensory feedback is essential to acquire, maintain, and adapt these mechanisms. OBJECTIVE: Individuals with complete peripheral deafferentation provide the unique opportunity to study the function of the motor system deprived of somatosensory feedback. METHODS: Two individuals (GL and IW) with complete chronic deafferentation of the trunk and limbs were tested during cyclic vertical movements of a hand-held object. Such movements induce oscillating loads that are typically anticipated by parallel modulations of the grip force. Load magnitude was altered by varying either the movement frequency or object weight. RESULTS: GL and IW employed excessive grip forces probably reflecting a compensatory mechanism. Despite this overall force increase, both deafferented participants adjusted their grip force level according to the load magnitude, indicating preserved scaling of the background grip force to physical demands. The dynamic modulation of the grip force with the load force was largely absent in GL, whereas in IW only slower movements were clearly affected. CONCLUSIONS: The authors hypothesize that the deafferented patients may have utilized visual and vestibular cues and/or an efferent copy of the motor command of the arm movement to scale the grip force level. Severely impaired grip force-load coupling in GL suggests that sensory information is important for maintaining a precise internal model of dynamic grip force control. However, comparably better performance in IW argues for the possibility that alternative cues can be used to trigger a residual internal model.

Gait of a deafferented subject without large myelinated sensory fibers below the neck.

We evaluated the gait pattern of a deafferented subject who suffered a permanent loss of large sensory myelinated fibers below the neck following an acute episode of purely sensory neuropathy 21 years ago. The subject has developed several strategies to achieve a secure gait, namely: (1) a reduction of the degrees of freedom by freezing the knee articulations during the stance phase, (2) a preservation of body balance by enlarging his base of support, and (3) visual monitoring of his step by stabilizing the head-trunk linkage together with a characteristic forward tilt. As a result, the gait of the deafferented subject lacks the fluidity of normal gait. Compared with normal subjects, the gait pattern of the deafferented subjects is characterized by a shorter cycle length, a longer cycle duration, a slower speed, and a lower cadence. Using a dual-task paradigm, the attentional demands for walking were particularly important (as indexed by longer probe reaction times) during the double-support phase, suggesting that the deafferented subject uses the double-support phase as a transitory stable phase to update cognitively the postural features necessary for generating his next step.

On the late failure of spinal cord stimulation for deafferentation pain.

Two cases are described in which spinal cord stimulation was effective in abolishing previously intractable deafferentation pain for a number of years, but in which late failure occurred for non-technical reasons. A possible explanation for this is advanced; namely that the dorsal column fibres have altered electrical properties due to a form of transganglionic degeneration.

Osteogenic protein-1 (bone morphogenetic protein-7) in the treatment of tibial nonunions.

BACKGROUND: The role of bone morphogenetic proteins (BMPs) in osseous repair has been demonstrated in numerous animal models. Recombinant human osteogenic protein-1 (rhOP-1 or BMP-7) has now been produced and was evaluated in a clinical trial conducted under a Food and Drug Administration approved Investigational Device Exemption to establish both the safety and efficacy of this BMP in the treatment of tibial nonunions. The study also compared the clinical and radiographic results with this osteogenic molecule and those achieved with fresh autogenous bone. MATERIALS AND METHODS: One hundred and twenty-two patients (with 124 tibial nonunions) were enrolled in a controlled, prospective, randomized, partially blinded, multi-center clinical trial between February, 1992, and August, 1996, and were followed at frequent intervals over 24 months. Each patient was treated by insertion of an intramedullary rod, accompanied by rhOP-1 in a type I collagen carrier or by fresh bone autograft. Assessment criteria included the severity of pain at the fracture site, the ability to walk with full weight-bearing, the need for surgical re-treatment of the nonunion during the course of this study, plain radiographic evaluation of healing, and physician satisfaction with the clinical course. In addition, adverse events were recorded, and sera were screened for antibodies to OP-1 and type-I collagen at each outpatient visit. RESULTS: At 9 months following the operative procedures (the primary end-point of this study), 81% of the OP-1-treated nonunions (n = 63) and 85% of those receiving autogenous bone (n = 61) were judged by clinical criteria to have been treated successfully (p = 0.524). By radiographic criteria, at this same time point, 75% of those in the OP-1-treated group and 84% of the autograft-treated patients had healed fractures (p = 0.218). These clinical results continued at similar levels of success throughout 2 years of observation, and there was no statistically significant difference in outcome between the two groups of patients at this point (p = 0.939). All patients experienced adverse events. Forty-four percent of patients in each treatment group had serious events, none of which were related to their bone grafts. More than 20% of patients treated with autografts had chronic donor site pain following the procedure. CONCLUSIONS: rhOP-1 (BMP-7), implanted with a type I collagen carrier, was a safe and effective treatment for tibial nonunions. This molecule provided clinical and radiographic results comparable with those achieved with bone autograft, without donor site morbidity.

Two-staged delayed open reduction and internal fixation of severe pilon fractures.

OBJECTIVE: To evaluate the use of a two-staged technique for the treatment of C3 pilon fractures. DESIGN: Retrospective. SETTING: Level I trauma center. PATIENTS/PARTICIPANTS: Twenty-one consecutive patients with twenty-two C3 pilon fractures. Patients with C1 or C2 fractures and patients with open growth plates were excluded. INTERVENTION: All patients underwent immediate fibular fixation and placement of a medial spanning external fixator. After, on average, twenty-four days, patients underwent removal of the external fixator and formal open reduction and internal fixation of the pilon fractures. MAIN OUTCOME MEASUREMENTS: At average follow-up of twenty-two months, all patients were evaluated by using subjective, objective, and radiographic measurements as described by Burwell and Chamley (J Bone Joint Surg 1965;47B:634-659). Range of motion and postoperative complications were also recorded. RESULTS: Twenty-one of the twenty-two fractures healed within an average of 4.2 months. Average range of motion was 7 degrees of dorsiflexion, 33 degrees of plantar flexion, 17 degrees of eversion, and 11 degrees of inversion. Subjective and objective measurements showed 77 percent good results, 14 percent fair results, and 9 percent poor results. Radiographic reduction showed 73 percent anatomic and 27 percent fair reductions. There were no infections or soft tissue complications. The arthrodesis rate was 9 percent. CONCLUSIONS: A two-staged approach offers acceptable results for the treatment of severe pilon fractures. These results compare favorably with those of primary open reduction and of internal fixation and external fixation techniques. The major advantages include limited soft tissue complications and improved articular reconstruction.

Psychotherapy with the chronic pain patient using coping skills development: outcome study.

This study provided outcome data measuring variables of a psychoeducational group approach to self-management of 88 chronic pain patients and 25 controls. Most of the injuries were back injuries and work related. At the completion of the 16 group sessions, patients reported decreased depression, pain severity, interference, and affective distress and increased life control and general activity. At 1-year follow-up, there was continued increased return to work, lowered workers' compensation, fewer health care visits, and less prescribed pain medication than demographically similar controls. Results suggest that a group psychoeducational program involving learning of general coping skills primarily and pain coping skills secondarily produces an effective approach for the management of chronic pain.

Use of laser Doppler flowmetry and transcutaneous oxygen tension electrodes to assess local autonomic dysfunction in patients with frozen shoulder.

The laser Doppler flowmeter (LDF), which measures changes in cutaneous blood flow, and the transcutaneous oxygen electrode which measures cutaneous perfusion, were used to study reflex changes in the microcirculation of the shoulder in 38 patients with frozen shoulder and 10 normal controls. In all controls and 22 patients with frozen shoulder, a normal LDF response to inspiration/expiration was observed. In 16 patients with frozen shoulder, LDF responses were either unilaterally or bilaterally absent. Comparison between the two patient groups showed a significant association (chi 2 = 6.43, P less than 0.02) between abnormality of response and the persistence of pain. TcPO2 was in the normal range in all patients and controls. These findings suggest that the LDF together with the TcPO2 may be a useful method of studying the skin microcirculation over the shoulder.

Survival test of submersible life support systems.

An experiment to validate predictions concerning submersible survivability was performed in December, 1975, by members of the Canadian Forces in the CF Submersible Lockout Vehicle SDL-1 in Halifax Harbour in water of 4 degrees C temperature at a depth of 40 ft. Data was collected relevant to the life support equipment to determine if it would operate for a simulated 6-h mission followed by a 24-h immobility period, at the end of which rescue was presumed to have occurred. Physiological data was collected from the submersible occupants in order to assess the degree of thermal stress experienced in this exercise. The experiment was terminated after a duration of approximately 25 h at 1 atm internal pressure due to exhaustion of two of the three on-board power supplies, causing the CO2 scrubbers to be inoperative and the CO2 content in the breathing gas to increase to toxic levels. Only two of the three submersible occupants experienced cold stress, one in the forward sphere and one in the aft sphere. At the end of 24 h, the core temperatures of both individuals had decreased by 0.5 degrees C and, during this time, skin temperatures, particularly of the extremities, had steadily and slowly decreased. Neither individual was hypothermic, but it was considered likely that after a 3-d exposure, at least two of the crew members would have had core temperatures of 35 degrees C or lower, assuming that CO2 poisoning had not occurred earlier.

Cochlear mechanics: analysis for a pure tone.

A three-dimensional hydroelastic model of the cochlea is analyzed, in which the fluid is viscous and the basilar membrane is an inhomogeneous orthotropic elastic plate. After the solution is obtained using a multiple-scale approximation, comparison is made with experiment for the human cochlea.

Evoked potentials in a man with a complete large myelinated fibre sensory neuropathy below the neck.

Cortical somatosensory evoked potentials (SEPs) were recorded from a man with a severe neuropathy without touch and proprioception below the neck. Peripheral neurophysiological tests showed a complete large myelinated fibre sensory neuropathy. Sensory threshold to electrical stimulation of the median nerve was 15 mA (normal 2-4 mA). With a stimulus of 39 mA, duration 400 microsecons, applied at the wrist a cortical SEP was recorded with a latency of 84 msec, giving a propagation velocity of 11.9 m/sec. At stimulation rates of above 3.3 Hz the SEP was absent. It is concluded that the SEPs recorded were conducted along A delta peripheral fibres.

The Level of Expressed Emotion Scale: a new measure of expressed emotion.

The Level of Expressed Emotion (LEE) scale was developed to provide an index of the perceived emotional climate in a person's influential relationships. Unlike existing measures, the scale was constructed on the basis of a conceptual framework described by expressed emotion theorists. In addition to providing an overall score, the 60-item scale assesses the following four characteristic attitudes or response styles of significant others: Intrusiveness, emotional response, attitude toward illness, and tolerance/expectations. The scale underwent extensive psychometric development procedures: (1) theoretically based item generation; (2) pilot testing with normal and psychiatric populations to select the final items; and (3) construct validation within a schizophrenic population. The results were quite favorable and indicate that the LEE scale has sound psychometric properties of internal consistency; reliability; independence from sex, age, and amount of contacts; and construct validity.

Acetabular fracture fixation via a modified Stoppa limited intrapelvic approach. Description of operative technique and preliminary treatment results.

Between March 1991 and December 1992 the authors surgically treated 55 acetabular fractures using a modified Stoppa anterior intrapelvic extensile approach. Indications for utilization of this approach included displaced anterior column or wall fractures, transverse fractures, T shaped fractures, both column fractures and anterior column or wall fractures associated with a posterior hemitransverse component. The approach involves a transverse skin incision 2 cm above the pubic symphysis followed by a midline split of the rectus abdominis. Access to the intrapelvic aspect of the pelvis and acetabulum is gained by retraction of the muscular, neurovascular and urological structures. This modified Stoppa approach affords excellent visualization of the pelvic ring, facilitating the development and utilization of improved reduction and plating options. Patients were followed for an average of 17.7 months. All fractures united 6-12 weeks postoperatively. Radiographic grades were excellent (64%), good (25%), fair (7%) and poor (4%). Fixation and subsequent reduction were lost in 1 patient. Two transient obturator nerve palsies were diagnosed. There was 1 infection and 1 inguinal hernia. Posttraumatic arthritic changes were noted in 6 patients within the first postoperative year. There was no significant heterotopic ossification, major vascular injury iatrogenic palsy or intraarticular hardware placement. Clinical results were excellent (47%), good (42%), fair (9%) and poor (2%). The modified Stoppa incision offers the experienced trauma surgeon a new approach for fixation of displaced acetabular fractures. The approach offers improved reduction and fixation possibilities and may decrease the rate of complications associated with extrapelvic or extensile approaches.

Limb lengthening by callotasis for children and adolescents. Early experience.

The callotasis technique of De Bastiani was used to perform 11 lower extremity lengthenings in ten pediatric and adolescent patients (aged 8.1-18 years). Average gain in length was 5.0 cm per segment (15% of original bone length). All lengthened segments healed without bone grafting or internal fixation. Healing index was 32 days per centimeter gained. The device was well tolerated and easily removed in the clinic setting. There were 13 minor complications, managed without hospitalization. Three angular deformities required manipulation under anesthesia. One angular deformity remains uncorrected, and one patient lacked 1.1 cm of achieving the desired length. All other patients gained the desired length. There were no refractures, deep infections, or other complications. Limb lengthening by the De Bastiani method is a satisfactory procedure for the pediatric and adolescent patient with moderate limb-length discrepancy.

The perceptions of force and of movement in a man without large myelinated sensory afferents below the neck.

1. Motor memory and the sense of effort have been investigated in a man with a complete large fibre sensory neuropathy for over 16 years. The perceptions of pain, heat, cold and muscular fatigue remained but he was without perceptions of light touch and proprioception below the neck. 2. The subject was able to discriminate weights held in the hand with an accuracy only slightly worse than control subjects (20 g in 200 g) when forearm movement and visual inspection were allowed. With eyes shut however he could only distinguish a weight of 200 g from 400 g. It is concluded that a crude sense of effort remains which may have a peripheral origin. 3. A limited motor memory was also present, which allowed him to maintain a posture or continue a simple repetitive movement. No novel movement was possible without visual feedback. 4. Differences in movement ability between this subject and others with similar if less pure sensory neuropathies are ascribed to rehabilitation.

Corticofugal actions on lemniscal neurons of the cuneate, gracile and lateral cervical nuclei of the cat.

Extracellular records were made from single identified lemniscal neurons of the cell-cluster regions of the cuneate and gracile nuclei, and of the lateral cervical nucleus, in pentobarbitone-anaesthetized cats. Forepaw, hind paw or face regions of the contralateral Sm I cortex were identified by recording through an inserted microelectrode which was then used for stimulation. The effect of a double cortical shock or train of shocks was usually inhibition: occasionally facilitation was observed, or mixed effects with facilitation preceding inhibition. Effects were seen in about half the cells studied in all three nuclei. Some cells of the lateral cervical nucleus were strongly excited, an effect not seen in the other nuclei. No component of these responses depended on suprathreshold stimulus intensities. Some lateral cervical cells were studied after deafferentiation by section of the dorsolateral spinal white matter; the same pattern of effects was seen. With an upper stimulus limit of 200 microA, cuneate but not gracile cells were affected from the cortical forepaw region, and gracile but not cuneate cells from the hind paw region. With threshold stimuli in an identified part of the forepaw cortical representation it was clear that cuneate cells with cutaneous receptive fields in corresponding parts of the forepaw had the lowest thresholds (minimum 6 microA). Threshold rose steeply with distance across the paw, suggesting quite sharp focusing of corticofugal effects in this system. When using similar procedures with the lateral cervical nucleus, with an upper limit of 200 microA, stimulation of forelimb cortex, or of facial cortex, affected both neurons with forelimb and those with hind limb fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Timing of corticofugal actions on the gracile and cuneate nuclei of the cat.

A comparison is presented of the latencies of corticofugal effects from the contralateral somatosensory cortex (SI) onto the cat's dorsal column nuclei (d.c.n.) under pentobarbitone anaesthesia. The latencies for transmission in the ascending pathway from d.c.n. to SI after stimulation within the gracile and cuneate nuclei were found to be 3.3 ms for the former and 2.8 ms for the latter. The time courses of inhibition of a medial lemniscal mass response following cortical conditioning and evoked by stimulation of peripheral nerves were measured. All latencies were corrected to exclude the different times taken for stimuli to reach the nuclei from the two limbs. The optimal condition-test interval was 12 ms with a duration of 14.3 ms for the superficial radial nerve (s.r.n.) and 45 ms and 30 ms respectively for the medial plantar nerve (m.p.n.). In each case cortical conditioning inhibited the wave by about 50%. The effect of cortical conditioning upon spontaneously firing d.c.n. single units was investigated. For cuneate cells the mean latency was 6.8 ms and the mean duration 36.8 ms. For gracile cells the latency of onset of inhibition was 17.2 ms and its duration 129 ms. In 75% of cells mixed effects were seen with facilitation preceding inhibition. The latencies of 'corticofugal reflex' action on the gracile and cuneate nuclei after stimulation of the s.r.n. and m.p.n. were determined. The gracile response had a latency approximately 4 times that for the cuneate response. The temporal asymmetry of these corticofugal effects suggests that the pathway is not purely a simple feed-back loop, but may be concerned in other physiological contexts, some of which are discussed.