Biomedical subjects

R Kobetic

Publications and source records attributed to R Kobetic.

At least 19 recordsLinked to original sources

PubMed2001

Percutaneous implantation of iliopsoas for functional neuromuscular stimulation.

Hip flexion is required for walking and stair climbing. Percutaneous electrical stimulation of the iliopsoas muscle is a potentially useful and reliable method of providing hip flexion in individuals who are paralyzed. In this study, groin, lateral abdominal, and paraspinal approaches of percutaneous electrode implantation for electrical stimulation of the iliopsoas muscle are described. The paraspinal approach using stimulation of the second and third lumbar roots gave the best hip flexion response; however, it often was accompanied by unwanted stimulation of the hip adductor and abdominal muscles. Wire breakage and electrode movement were the most common causes for failure of maintaining hip flexion. The paraspinal approach, using double helix electrodes, provided an average of 110 weeks of functional hip flexion sufficient for walking. It is feasible to implant electrodes in the iliopsoas muscle. An open technique for permanent implantation of intramuscular electrodes is being developed to selectively stimulate the iliopsoas, which will extend the range and duration of hip flexion that will allow stair climbing in individuals who are paraplegic.

Adult↗

PubMed2000

The Case Western Reserve University hybrid gait orthosis.

Six individuals with paraplegia and injury levels from C-1 through T-12 participated in a study to evaluate the functional capabilities of a hybrid gait orthotic system. Subjects learned to use a custom-built reciprocal gait orthosis without stimulation and with electrical stimulation activating between 4 and 16 muscles. Outcomes were scored with standard physical therapy measures including the Tinetti test, a timed get up and go, Borg rating of perceived exertion, and the Functional Index Measure (FIM). Subjects have successfully accomplished sit to stand, stand to sit, and walking maneuvers measured for time, speed, and distance. Metabolic consumption was measured for walking in the light work region of 5.1 to 6.5 metabolic equivalents (METs) 1 MET = 3.5 ml of O2/kg/min with hybrid gait orthosis. Perceived exertion as measured with the Borg scale indicated that use of the bracing system with functional electrical stimulation was "easier" than without stimulation. Subjects using a hybrid system were able to walk up to 350 m at average speeds of 0.25 m/s. Walking speeds for 30- and 50-meter distances reached 0.45 m/s. Additionally, walking distances with stimulation were 2 times greater than those of non-stimulated reciprocal gait. FIM scores indicated that system users would become slightly more independent in mobility. Results were used to determine the most useful brace modifications for the next generation of Case Western Reserve University hybrid gait orthoses to allow an expanded function that will include stair climbing and side stepping.

Adult↗

PubMed2000

The use of selective electrical stimulation of the quadriceps to improve standing function in paraplegia.

Persons with spinal cord injury (SCI) can benefit significantly from functional neuromuscular stimulation (FNS) systems for standing if manual tasks can be performed while upright. Using FNS to sufficiently activate the knee extensors to rise from a sitting position often results in inadvertent activation of the rectus femoris and/or sartorius, which flex the hip. In this study, intramuscular electrodes implanted in the vastus lateralis and medialis of four subjects with SCI were used to activate these muscles individually and simultaneously to measure knee extension moment. Support forces applied to the arms and feet were measured while upright to quantify the effects of recruiting rectus femoris and/or sartorius. In three of the four subjects, vastus lateralis, by itself, generated adequate knee extension moment for rising from a chair and to maintain static standing. Simultaneous activation of the vastus lateralis and medialis using a bifurcated electrode generated adequate knee extension moment in one subject, and was within 10% of the required moment in another. While upright, activation of the rectus femoris resulted in arm support force increases of 4-11% body weight, while deactivation resulted in arm support force decreases of 6-9% body weight. The results indicate that selective activation of the vastus lateralis, individually or in combination with vastus medialis, can improve current FNS standing systems by reducing the arm support forces required to remain upright.

Biomechanical Phenomena↗

PubMed1999

Walking with a hybrid orthosis system.

OBJECTIVE: The purpose of this case study was to determine the functional effectiveness of the hybrid orthosis system (HOS) for sit-to-stand and walking compared with the reciprocal gait orthosis (RGO) alone in a subject with significant orthopedic abnormalities. DESIGN: A subject with complete T7 paraplegia and a 13 cm leg length discrepancy was implanted with 14 intramuscular electrodes and fitted with a custom isocentric RGO. The subject was instructed in the use of the HOS and a two wheeled walker in the home and community settings. MAIN OUTCOME MEASURES: Using the Functional Independence Measure (FIM), and the Borg exertion scale the subject's level of independence and his perceived exertion was determined as well as the safety and efficacy of system use in the community. RESULTS: Results show that the HOS provided safe, independent ambulation with a two wheeled walker and met established criteria for limited community use. Walking in the RGO alone was feasible, however, the addition of functional electrical stimulation (FES) allowed this subject to walk farther and with less perceived exertion. CONCLUSION: This case study suggests that a hybrid orthosis system can be an effective clinical option for individuals with significant orthopedic complications that might otherwise contra-indicate the prescription of either conventional braces or FES alone.

Adult↗

PubMed1999

Implanted functional electrical stimulation system for mobility in paraplegia: a follow-up case report.

A 16-channel functional electrical stimulation (FES) system has been implanted in a person with T10 paraplegia for over a year. The system consists of two eight-channel radio frequency controlled receiver-stimulators delivering stimuli through a network of 14 epimysial and two intramuscular electrodes. Using this system and a walker for support, the subject was able to stand up for 8 min and walk regularly for 20 m. The standing duration was limited by arm fatigue since upper extremities supported an average of 25% of body weight. This was due to suboptimal hip extension and some undesired recruitment of rectus femoris and sartorius with stimulation of quadriceps electrodes. The left quadriceps exhibited rapid fatigue that limited walking distance and duration. The metabolic energy requirements were well within the aerobic limits of the sedentary paraplegic population. At one-year follow-up evaluation all electrodes are functional except one intramuscular electrode. The implant caused no adverse physiological effects and the individual reported health benefits such as increased energy and overall fitness as a result of the FES system use. With further improvements in muscle response through innovative surgical techniques, the 16-channel implanted FES system can be a viable addition to exercise and mobility function in persons with paraplegia.

Adult↗

PubMed1997

Muscle selection and walking performance of multichannel FES systems for ambulation in paraplegia.

A minimal set of muscles (8 to 16) were identified as candidates for implantation in a clinical system to provide walking function to individuals with complete paraplegia using functional electrical stimulation (FES). Three subjects with complete motor and sensory paraplegia had percutaneous intramuscular electrodes implanted in all major muscles controlling the trunk, hips, knees, and ankles. Stimulation patterns for walking with FES were generated for different sets of eight and 16 muscles. The quality and repeatability of the resulting gait produced by walking patterns consisting of various combinations of muscles were determined. Most eight-channel stimulation patterns resulted in scissoring or insufficient hip flexion, preventing forward progression. One eight-channel system allowed a maximum speed of 0.1 m/s with a cadence of 22 steps/min and a stride length less than 0.3 m. Improved walking performance was observed with 16 channels of stimulation. This ranged from slow step- to gait at 0.1 m/s to smooth reciprocal gait at 0.5 m/s. In all three subjects, the favored combination of 16 channels included erector spinae for trunk extension; gluteus maximus, posterior portion of adductor magnus and hamstrings for hip extension; tensor fasciae latae and either sartorius or iliopsoas for hip flexion; vastus lateralis/intermedius for knee extension; and tibialis anterior/peroneous longus for ankle dorsiflexion. In one subject the 16-channel FES system provided repeatable day-to-day gait averaging 0.4 m/s, 58 steps/min and a stride length at 0.8 m. A maximum repeatable walking distance with 16 channels was 34 m. Multiple 34-m trials were possible with minimal rests between walks. Fatigue of both the hip extensors and upper body was a limiting factor. The selection of target muscles for implantation is critical to the performance of FES systems. This study provides guidelines to muscle selection for walking with FES based on objective measures of gait performance. The findings indicate that a 16-channel FES system for total implantation is feasible for repeatable short distance, independent, walker-support walking in paraplegia.

Adult↗

PubMed1997

Rail supporting transducer posts for three-dimensional force measurement.

Parallel bars supported on transducer posts were designed, instrumented and calibrated to measure three-dimensional (3-D) forces applied to the rails. These instrumented rails were designed for measuring forces applied by paraplegic patients during development and evaluation of functional electrical stimulation (FES) patterns for standing, side stepping, and ascending and descending stairs. The focus of this study was on the adaptation of the system for measuring support forces during stair climbing and descent. The specific problems with crosstalk among the three axes, nonlinearity, and hysteresis were investigated. In this design, the crosstalk between axes was less than 5%, nonlinearity was less than 2% of full scale, and force accuracy was better than 5%.

Biomechanical Phenomena↗

PubMed1996

Implanted Functional Neuromuscular Stimulation systems for individuals with cervical spinal cord injuries: clinical case reports.

OBJECTIVE: To determine the feasibility of providing the ability to stand and to facilitate the performance of standing transfers to individuals with cervical-level spinal cord injuries via functional neuromuscular stimulation (FNS). The applicability of implantable technology to this population was investigated, and the characteristics of the potential system users were explored. The effects of FNS on the effort and assistance required to stand and complete standing transfers were examined. SETTING: Institutional rehabilitation practice. DESIGN: Nonrandomized controlled trial. PATIENTS: Twenty-four individuals with low cervical spinal cord injuries were evaluated for inclusion in a program of lower extremity FNS, four of whom received the intervention. INTERVENTION: Chronically indwelling percutaneous intramuscular electrodes were used to exercise the hip, knee, and trunk extensors and develop activation patterns to produce standing function. These temporary systems were then replaced with silicone-enclosed helical wire electrodes suitable for eventual use with an eight-channel implantable receiver/stimulator. MAIN OUTCOME MEASURES: Full sensory and motor evaluations were performed and physical contraindications to stimulation were catalogued. For active subjects, American Spinal Injury Association Total Motor Scores with and without FNS were recorded, along with quadriceps strength and ability to complete exercise, standing, controlled sitting, and standing transfer maneuvers. Performances of implanted electrodes were determined by the stability of recruitment properties, impedances or surface potentials, and serial radiographs. RESULTS: Motor scores increased an average of nine points with stimulation over baseline volitional values. With FNS, all four volunteers were able to exercise, stand, and sit independently or with minimal assistance. Although they required varying degrees of assistance with the pivot phase of the transfer maneuver, all were able to raise and lower their body weight independently with stimulation and to use the system to facilitate standing transfers. One participant received the implantable receiver/stimulator, which remains operational at follow-up more than 3 years later. CONCLUSION: FNS can provide the ability to exercise, stand, and transfer to individuals with tetraplegia, even in the presence of medical complications and upper extremity impairment. FNS facilitates standing transfers by eliminating the heavy lifting usually required by a caregiver, thus decreasing the effort and assistance necessary to gain access to places impossible to approach with conventional sliding transfers.

Adult↗

PubMed1994

Augmentation of transfers for a quadriplegic patient using an implanted FNS system. Case report.

A 22 year old man with incomplete quadriplegia (C6-7) was unable to perform either a sliding or a pivot transfer. He was instrumented with an implanted functional neuromuscular stimulation (FNS) system, radio frequency-linked to a belt-worn controller. The system activated eight muscles selected from among quadriceps, hamstrings, posterior portion of the adductor magnus, gluteus maximus, and erector spinae, bilaterally. The two-stage implantation procedure included electrode implantation with percutaneous leads followed by stimulator implantation and removal of the percutaneous leads. All implants were well tolerated with no adverse effects. The subject was able independently to put on the external controller portion of the system and to perform a standing pivot transfer with only standby assistance. An unexpected outcome of the FNS system use was increased voluntary upper body strength that resulted in improvement of the sliding transfer from 'inability' to 'independent'.

Adult↗

PubMed1992

Effect of functional neuromuscular stimulation on anterior tibial compartment pressure.

Intramuscular pressures in the anterior tibial compartment were measured in five paraplegic subjects who used functional neuromuscular stimulation (FNS) by percutaneous intramuscular electrodes for exercise and walking. Effects of two types of stimulation pattern were tested: continuous stimulation for 15 minutes and cyclic stimulation for 60 minutes, with duty cycle and stimulation levels similar to that used in walking. Resting compartment pressure levels before stimulation were less than 7 mm Hg in all subjects. Continuous stimulation at maximum parameters produced compartment pressure levels up to 116 mm Hg, but these were not sustained. They decreased to below 40 mm Hg within one minute in all except one subject, who was having repeated spasms. Cyclical stimulation raised mean muscle pressure to between 70 and 80 mm Hg in two patients. Muscle contraction pressure increased to 153 mm Hg in one patient, but was below 100 mm Hg in all patients after two minutes, except during spasms. Muscle relaxation pressure stayed below 30 mm Hg in four subjects. After stimulation, the pressure returned to prestimulation levels within 15 minutes. These results suggest that FNS subjects are not in danger of developing compartment syndrome. Nevertheless, occasional testing of compartment pressures is recommended, especially when activity levels rise significantly.

Adult↗

PubMed1989

Tetanic responses of electrically stimulated paralyzed muscle at varying interpulse intervals.

The influence of stimulus interpulse interval (IPI) on torque output during electrically-evoked contractions was investigated for the knee extensor muscles of paralyzed subjects. The parameters measured were the rise time, magnitude, and relaxation time of the contraction at stimulus IPI's ranging from 62 to 7 ms. Torque output increased as IPI's were decreased from 62 to 15 ms. Peak torques were recorded at IPI's of 12-15 ms; IPI's less than these resulted in an insignificant loss of torque. Rise times decreased as IPI's were decreased. Relaxation time generally increased as IPI's were decreased with the longest relaxation times occurring with stimulation at an IPI of 12 ms. To demonstrate the influence of IPI on muscle fatigue, the effect of prolonged stimulation at short (12 ms) and long (50 ms) IPI's was also compared. After 30 s of stimulation with an IPI of 12 ms, mean torque had declined to 5 +/- 3 percent and after 30 s of stimulation with an IPI of 50 ms, mean torque had declined to 82 +/- 4 percent of the initial value. Knowledge of how stimulus IPI influences the response of paralyzed muscle to electrical stimulation may assist in the development of rehabilitation devices which utilize these technologies.

Electric Stimulation Therapy↗

PubMed1989

Development and operation of portable and laboratory electrical stimulation systems for walking in paraplegic subjects.

Two new stimulation systems have been designed for use in functional neuromuscular stimulation of paralyzed people; one is portable and one is a nonportable laboratory system. Compared to previous systems, these have greatly enhanced capabilities, especially in terms of memory capacity, expandability, and user interface. They are extensively operator programmable. The laboratory stimulation system was designed to provide quick turnaround time for stimulation pattern or program changes while maintaining complete compatibility with the portable system. The lab system will also accomodate external closed-loop control.

Electric Stimulation Therapy↗

PubMed1988

Development of a practical electrical stimulation system for restoring gait in the paralyzed patient.

A percutaneous functional neuromuscular stimulation (FNS) system is being developed for restoring function in the lower extremities of spinal cord injured people with lesions between T4 and T11. Limitations of the current system are electrode failure, muscle fatigue, cumbersome electrical hardware, and an inefficient user-machine interface. Transforming this experimental system into a practical FNS system requires achieving acceptable levels of safety, reliability, function, metabolic energy requirement, ease of use, cosmesis, and cost. This eventually can be accomplished with development of implantable stimulators and totally implantable electrodes, intimate command devices with tactile feedback, and closed-loop control of muscle stimulation.

Adolescent↗

PubMed1987

Functional electrical stimulation for walking in paraplegia.

In paraplegic subjects who had functional transection of the spinal cord at a level between the fourth and the eleventh thoracic vertebra, independent reciprocal walking was achieved with the use of a portable microprocessor-controlled stimulator that electrically activated the muscles through percutaneous intramuscular wire electrodes. The electrodes were implanted, by means of hypodermic needles, in the flexors, extensors, abductors, and adductors of the hip; the extensors of the knee; and the plantar flexors and dorsiflexors of the ankle. The subjects had strong, selective, and reproducible muscular contractions that increased in strength during the twenty-two to forty-four months (average, thirty-two months) of training with the regimen. A basic pattern of stimulation was adapted for each individual; each step was initiated by the subject using a hand-operated switch. The subjects progressed to the use of a walker for support, and two of them were able to walk using axillary crutches. Three subjects were able to climb stairs.

Adult↗

PubMed1986

Implantation techniques and experience with percutaneous intramuscular electrodes in the lower extremities.

Innervated paralyzed muscles have been implanted with temporary percutaneous intramuscular electrodes in order to allow selective stimulation of as many muscles as necessary to achieve a cosmetically acceptable and energy-efficient gait in paraplegic subjects. Fine wire electrodes were implanted under sterile conditions at the motor points (MP) of hip extensors, flexors, abductors and adductors; knee extensors; and ankle plantar- and dorsi-flexors. Electrodes were routed to the MP's from one of four skin sites on the legs where the wires emerged. Employed were both a direct approach from the skin site to the MP and an indirect approach which involved one or more subcutaneous passages of the electrode wire from the MP to the skin site. Muscles were stimulated approximately 12 hours per week in daily electrical exercise and gait training. Electrodes were removed when they exhibited one of two types of failure: breakage, as determined by high impedance, or loss of adequate function as a result of electrode movement. Of 1025 electrodes implanted in 6 subjects over a period of 38 months, 35 percent failed within the first 4 months; more than 75 percent of those early failures resulted from electrode movement. Complete withdrawal of those electrodes was usually possible. The probability of electrode failure decreased exponentially during the first 4 months and reached less than 4 percent per month for electrodes implanted for longer than 6 months. These procedures have allowed multiple revisions toward a more functional neuro-orthotic system.

Electric Stimulation Therapy↗

PubMed1983

Functional walking in paralyzed patients by means of electrical stimulation.

Three partially paralyzed patients were unable to walk even after maximal rehabilitation attempts at a major rehabilitation center. One 36-year-old man had transverse myelitis, a 57-year-old man had had a stroke, and the third patient, a 35-year-old man, had incurred a traumatic brain injury. The three patients were unable to flex the hips, had adductor spasm and weak hip and knee extension, and lacked ankle dorsiflexion. Intramuscular stainless steel wire electrodes activated by timers were placed in the quadriceps, hip flexors, extensors, and abductors, as needed. Muscle force and foot contact evaluations were done using the Cybex and the Cleveland Veterans Administration Gait Laboratory. After implantation of intramuscular electrodes, all three patients had improved function but still desired some supervision in walking. A ten-fold increase in knee torque was noted in one patient, thereby providing him with nearly normal strength. No implant complications were noted. The study demonstrated the feasibility of functional neuromuscular stimulation (FNS) gait augmentation in a previously nonwalking patient outside the laboratory. Further improvements will require the development of an implantable, multichannel, programmable microprocessor-controlled stimulator.

Adult↗

PubMedDate not supplied

Ankle, knee, and hip moments during standing with and without joint contractures: simulation study for functional electrical stimulation.

Joint contractures have been one of the contraindications for use of functional electrical stimulation for standing in paraplegic patients. A simulation study using a three-segment link mechanical model of the human body was performed to calculate the muscle moments at the ankles, knees, and hips during standing with and without having joint contractures. The knee and hip angles were varied in 5 degrees increments, whereas the ankle angles were varied in 1 degree increments. It was assumed that energy efficient posture was obtained with the least sum of the squared moments of the ankles, knees, and hips joints by the muscles. Ankles at 5 degrees of dorsiflexion, knees at 0 degrees, and hips at 15 degrees of extension resulted in the most energy efficient posture without joint contractures. The muscle moments increased with the increase in angle of contractures. The joint contractures at ankle angles > or = 6 degrees of plantar flexion, knee angles > or = 20 degrees of flexion, and/or hip angles > or = 20 degrees of flexion produce a potentially unstable posture. These findings suggest that some degree of joint contractures can be tolerated in paraplegic patients using functional electrical stimulation for standing.

Algorithms↗

PubMedDate not supplied

Selectivity of intramuscular stimulating electrodes in the lower limbs.

Intramuscular (IM) electrodes have been used safely and effectively for decades to activate paralyzed muscles in neuroprosthetic systems employing functional electrical stimulation (FES). However, the response to stimulation delivered by these and any type of electrode can be limited by a phenomenon known as spillover, in which the stimulus intended to produce a contraction in a particular muscle inadvertently activates another muscle, causes adverse sensation, or triggers undesired reflexes. The purpose of this retrospective study was to determine the selectivity of monopolar intramuscular stimulating electrodes implanted in the lower limbs of individuals with motor and sensory complete paraplegia secondary to spinal cord injury (SCI) and to catalog the most common electrode spillover patterns. The performance records of 602 electrodes from 10 subjects who participated in a program of standing and walking with FES in our laboratory over the past decade were examined. Sixty percent (358) of these electrodes were "stable" (i.e., stimulated responses were consistent during the first 6 months postimplant), and 32% of all stable electrodes (113) exhibited spillover as noted in clinical and laboratory records. Common spillover patterns for eight muscle groups were tabulated and analyzed in terms of their functional implications. The beneficial (activation of synergistic muscles) or deleterious (activation of compromising reflexes, antagonists, or adverse sensation) effects of spillover were highly context dependent, with several potentially useful spillover patterns in certain phases of gait becoming undesirable and limiting in others. Knowledge of the selectivity of intramuscular electrodes and the patterns of spillover they exhibit should guide surgeons and rehabilitationists installing lower-limb neuroprostheses during the implantation process and allow them to better predict the ultimate functional usefulness of the electrodes they choose.

Electric Stimulation Therapy↗