Arthroscopic discectomy and interbody fusion of the thoracic spine: A report of ipsilateral 2-portal approach

Background

The standard approach to the thoracic disc is through thoracotomy. The video-assisted thoracoscopic approach has been used as an alternative to the open approach for nearly 20 years, and more recently, extracavitary, posterolateral approaches have been introduced. Both the transthoracic procedures involve deflating the lung for access to the spine, and postoperative thoracic drainage is necessary; postoperative morbidity can be significant. The retropleural procedures are in their infancy, but the published results are promising. The purpose of this study is to introduce the posterolateral arthroscopic thoracic decompression and fusion procedure, which is extrapleural, less disruptive to normal anatomy, and cost-effective.

Methods

Fifteen consecutive patients who underwent arthroscopic decompression and interbody fusion of the thoracic spine were prospectively studied according to the hospital's institutional review board protocol. The Short Form 36 and visual analog scale questionnaires were completed preoperatively and postoperatively. Paired t tests were used for statistical analysis. The patient was placed in the prone position on a radiolucent table, and instrumentation was performed under fluoroscopic control. Two portals were developed ipsilaterally (one for the arthroscope and the other for instruments) on the side of disc herniation, and a single portal was used on the contralateral side. Various instruments were used for disc excision and exploration of the spinal canal. Fusion was accomplished with bilateral corticocancellous dowels obtained from the iliac crests. Infiltration of the access channel and facet injections of the contiguous joints were performed with bupivacaine, for immediate postoperative pain control.

Results

Fifteen patients with a mean age of 54 years were followed up for 28 months postoperatively. The overall back pain score decreased from 7.2 (SD, 1.5) to 3 (SD, 2) after the procedure (P < .005). Eleven patients were satisfied with their current lifestyle postoperatively as opposed to one preoperatively. Two patients had reoccurrences. Hospital stay averaged 18.5 hours. The operating room cost and the cost of hospital stay was 51.9% of the cost of anterior open discectomy.

Conclusions

The extrapleural, biportal, ipsilateral arthroscopic approach for the decompression and interbody fusion of the thoracic spine is feasible, cost-effective, less traumatic, and associated with minimal complications. The best results were obtained in patients with single-level thoracic disc herniation. The technique is applicable for most thoracic disc herniations.

Use of a postoperative lumbar corset after lumbar spinal arthrodesis for degenerative conditions of the spine. A prospective randomized trial

BACKGROUND

Lumbosacral corsets and braces have been used to treat a variety of spinal disorders. Although their use after lumbar arthrodesis for degenerative conditions has been reported, there is a lack of evidence on which to base guidelines on their use. The purpose of this study was to evaluate the effect of a postoperative corset on the outcome of lumbar arthrodesis.

METHODS

A prospective randomized trial was performed in which patients who wore a postoperative lumbar corset for eight weeks full-time after a posterior lumbar arthrodesis for a degenerative spinal condition were compared with those who did not use a corset after such an operation. Ninety patients were randomized to one of the two treatments. A history was recorded and patients were assessed with a physical examination, radiographs, and functional outcome questionnaires (the Dallas Pain Questionnaire [DPQ] and the Short Form-36 [SF-36]) preoperatively and at one year and two years following the surgery. The primary outcome measure of the study was the DPQ, a disease-specific patient-derived functional measure of the spine, and secondary end points included the SF-36 scores, complications, rates of fusion as determined radiographically, and reoperation rates.

RESULTS

Follow-up analysis was performed for seventy-two patients, thirty-seven randomized to the brace (experimental) group and thirty-five randomized to the control group. Regardless of the treatment method, the patients had substantial improvement in the disease-specific and general health measures by two years postoperatively. At two years, there was no difference in the DPQ category scores (the primary outcome parameter) of the two treatment groups. There was also no difference in the mean SF-36 component scores at two years. Postoperative complications occurred in 22% and 23% of patients in the experimental and control groups, respectively, and a subsequent lumbar spinal operation was performed in 19% and 14%, respectively. Seven patients (five in the experimental group and two in the control group) with radiographic evidence of nonunion underwent revision surgery.

CONCLUSIONS

This study does not indicate a significant advantage or disadvantage to the use of a postoperative lumbar corset following spinal arthrodesis for degenerative conditions of the lumbar spine.

LEVEL OF EVIDENCE

Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.

Functional electrical stimulation for walking in paraplegia: 17-year follow-up of 2 cases

OBJECTIVE

To assess the safety and effectiveness of long-term use of functional electrical stimulation (FES) for exercise, standing, and walking in individuals with paraplegia, using percutaneous intramuscular wire electrodes.

DESIGN

Case study with more than 17 years of follow-up.

SETTING

Institutional rehabilitation practice.

STUDY PARTICIPANTS

Two long-term (17 years) volunteer participants with paraplegia who were able to stand and walk using FES.

INTERVENTION

Chronically indwelling percutaneous intramuscular wire electrodes connected to a portable microprocessor-controlled stimulator were used to exercise muscles while controlling trunk, hips, knees, and ankles and develop activation patterns to produce standing and walking.

MAIN OUTCOME MEASURES

Clinical complications, electrode performance and survival probability, and functional performance.

RESULTS

The most noted clinical complications included localized inflammation at the electrode site and superficial infection that responded well to topical and oral antibiotic treatment. The change from coil-wire electrodes, with a survival of 35% after 1 year, to double-helix electrodes improved electrode survival to 80% at 1 year and 48% at 5 years. Maintenance of the multichannel percutaneous FES walking system required replacement of an average of 2 electrodes every 6 months. Participants were able to use their system for independent exercise and standing and for walking with standby assistance.

CONCLUSION

Although the FES system was devised as a temporary means of achieving functional activation until permanent means could be achieved, it was found to be effective and relatively safe for more than 17 years. Two long-time users of the system had no adverse effects to their skeletal system. The most common problems were daily care of electrodes at exit sites, frequent irritation of the skin around electrodes, and replacement of failed electrodes. The percutaneous system has the potential for short-term rehabilitation in individuals with incomplete paraplegia or stroke.

Performance of an intramuscular electrode during functional neuromuscular stimulation for gait training post stroke

The goal of rehabilitation for stroke patients in this research was to improve the volitional coordination of the swing phase and stance phases of gait. Functional neuromuscular stimulation (FNS) is a promising rehabilitation tool for restoring motor control. For our gait training protocols, FNS systems with surface electrodes were impractical. For the rehabilitation protocols that we defined, available implantable electrode designs did not meet desired criteria regarding fracture rate, invasiveness of placement procedures, and maintenance of position at the motor point. The criteria for the new intramuscular (IM) electrode design included minimally invasive electrode placement technique, accurate placement of electrodes, good muscle selectivity, consistency of muscle activation, good position maintenance of the electrode at the motor point, comfortable stimulus, and practical donning time for the system. A percutaneous electrode was designed for placement beneath the skin at the motor point of seven paralyzed or paretic muscles in the lower limb. A single-helical coil lead, a double-helical coil electrode, and fine wire barbs were design features that enhanced the anchoring capability of the electrode. A polypropylene core enhanced electrode durability. Implantation tools were custom-designed to enable accurate electrode placement without incision. We studied 17 subjects with a total of 124 electrodes. With the use of IM electrodes, FNS was provided for 1,413.8 electrode months. During this time, no instances of infection occurred. The measure of electrode integrity showed a 99% electrode survival rate. Throughout the treatment protocols, 93% of the electrodes delivered a good muscle response; 7% (nine electrodes) moved from the motor point and delivered a poor muscle response during the treatment protocol. Anchoring performance was higher for electrodes implanted in muscles that moved the hip (96.0%) and ankle joints (97.45%) compared with electrodes implanted in muscles that moved the knee joint (88.5%). Ninety-seven percent of the electrodes delivered a comfortable stimulus. Three percent delivered a stimulus that was uncomfortable at therapeutic levels and therefore were not used. We achieved gains in subject impairment and disability measures. The system proved to be practical for use in both clinical and home environments.

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.

Surgical technique for installing an eight-channel neuroprosthesis for standing

A standardized surgical procedure to implant an eight-channel functional neuromuscular stimulation system in the lower extremities for standing, exercise, and transfers for individuals with spinal cord injury has been developed. The implanted components include: (1) one eight-channel receiver-stimulator, (2) epimysial electrodes, (3) intramuscular electrodes, and (4) inline connectors. The development process included identifying the target muscle set for electrode placement and the corresponding surgical approaches, determining the stages of the surgical procedure, and assessing the effectiveness and stability of the implanted neuroprosthesis. The bilateral muscle set consists of the vastus lateralis, the gluteus maximus, the semimembranosus, and the erector spinae. Surgical approaches to the nerve entry points were developed through a series of cadaveric studies and intraoperative tests. Electrode placement is related to bony landmarks and based on standard orthopaedic approaches. The components of the neuroprosthesis are installed in one surgical session, with three stages. This procedure has been applied successfully in seven individuals, resulting in strong, isolated stimulated contractions adequate to raise and lower the body, maintain standing with a walker, and perform pivot transfers. The standardized surgical procedure is repeatable and teachable and will be used in upcoming multicenter clinical trials of the implanted neuroprosthesis.

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.

Feasibility of gait training for acute stroke patients using FNS with implanted electrodes

Following stroke, many patients do not regain a normal, safe gait pattern even after receiving conventional physical therapy. One promising technique is functional neuromuscular stimulation (FNS) with intramuscular (IM) electrodes (FNS-IM). Five subjects were admitted into the study at 3 weeks to 3 months following the stroke. For each subject, electrodes were placed intramuscularly at the motor point of up to seven lower extremity paretic muscles. Subjects were treated for 6 months, twice weekly with FNS-IM for exercise and gait training. The stimulator and software provided individualized stimulation patterns, with flexible stimulus parameters and activation timings of multiple muscles. Outcome measures were active joint movement, coordination (Fugl-Meyer scale), balance (Tinetti scale), gait (Tinetti scale), activities of daily living (functional independence measure), and therapist and subject satisfaction (survey instrument). Subjects tolerated well the placement of IM electrodes with no adverse effects, and subjects lost no conventional rehabilitation time. Therapists and subjects were satisfied with the FNS-IM system as a rehabilitation tool. Post treatment, subjects demonstrated improvements in impairment and disability in active joint movement, coordination, balance, gait and activities of daily living. Considered together with prior research for chronic stroke subjects, this research suggests that FNS-IM can be successfully and efficaciously utilized for gait training for those with acute stroke.

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.

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.

Implantation of a 16-channel functional electrical stimulation walking system

A 16-channel electrical stimulation system was implanted in a 39-year-old patient with T10 paraplegia to restore sit to stand, walking, and exercise functions. System implantation required two surgical sessions. In the first session, the posterior muscle set consisting of bilateral semimembranosus, adductor magnus, and gluteus maximus muscles were exposed and epimysial electrodes sutured at the point of greatest muscle contraction. Closed double helix intramuscular electrodes were implanted in the erector spinae. Two weeks later, epimysial electrodes were attached to the eight anterior muscles consisting of the tibialis anterior, sartorius, tensor fasciae latae, and vastus lateralis with all 16 electrode leads passed to the anterior abdominal wall. The electrodes were connected to two eight-channel stimulators placed in the iliac fossae, and the system was checked by activating the individual muscles. The implanted stimulators received stimulation instructions and power via a radio frequency link to an external control. Stimulation patterns for standing, walking, sitting, and exercise functions were chosen from a preprogrammed menu via a finger key pad. After 3 weeks of restricted patient activity, all electrodes stimulated either the target muscle or had an acceptable spillover pattern. The patient is undergoing a 16-week rehabilitation course of stimulated exercises gradually increasing in intensity. At the conclusion, the goal is to discharge the patient with the system for spontaneous use. Although long term followup is required to determine system reliability, preliminary clinical results indicate that targeted, repeatable, functional muscle contractions in the lower extremity can be achieved with a system consisting of epimysial electrodes.

Reliability of closed double helix electrode for functional electrical stimulation

The reliability of a closed double helix electrode in the lower limbs was studied. This electrode is an implanted intramuscular electrode and is used for a totally implantable functional electrical stimulation system. Eighty electrodes were evaluated retrospectively with a mean period of 15 months. The total implant time was 1222 electrode months. The cumulative proportion surviving was 0.934 at 6 months, 0.855 at 1 year, 0.765 at 2 years, and 0.730 after 30 months. Fifteen of 80 electrodes failed, seven showed increasing electrode impedance, and eight had undesirable changes in recruitment. Of the failed electrodes, 2/3 failed during the first 10 months. The reliability was 0.91 at 6 months and 0.80 at 1 year after implantation in all muscle groups. The closed double helix electrode displayed an increased reliability when compared with the open double helix electrode at 6 months, and an equivalent reliability as compared with the electrodes developed by Handa and colleagues at 6 months and 1 year, using the chi squared test for independence. This study suggests that the closed double helix electrode has an acceptable reliability and can be used as a part of a totally implantable functional electrical stimulation system.

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.

Transforaminal and posterior decompressions of the lumbar spine. A comparative study of stability and intervertebral foramen area

STUDY DESIGN

Ten fresh, cadaveric, two-vertebrae, functional spinal units were used to study the pathoanatomy, intervertebral foraminal area, and flexibility changes after posterior and transforaminal decompression.

OBJECTIVES

To determine the feasibility of an endoscopic transforaminal approach as an alternative to conventional approaches, to establish the adequacy of transforaminal decompression without destabilizing the spine, and to study the structural changes in the spine after decompressions.

SUMMARY OF THE BACKGROUND DATA

Posterior decompression entails major dissection and excision of bone and ligaments to access the spinal canal. Posterior decompression may be complicated by acute or chronic spinal instability, and the adequacy of lateral decompression is highly subjective.

METHODS

The functional spinal units were mounted in quick-setting epoxy blocks. Pre- and postoperative computed tomography scans were taken to study changes in the foraminal area. Pre- and postoperative flexibility and anatomic studies were performed to compare the results.

RESULTS

A 45.5% increase in the intervertebral foraminal area was possible, there was no flexibility change, and minimal anatomic damage to the spine was noted after transforaminal decompression. A 34.2% increase in the intervertebral foraminal area and a significant increase in extension and axial rotation flexibility were noted after the posterior decompression.

CONCLUSION

Transforaminal decompression produced a significantly larger increase in the intervertebral foraminal area than posterior decompression, without increasing the range of motion or neutral zone in any direction. Because there was no violation of the anatomic integrity of the spine in the transforaminal approach, the risk of surgically induced instability was minimized. Endoscopic transforaminal decompression is a feasible alternative to current approaches.

Endoscopic transiliac approach to L5-S1 disc and foramen. A cadaver study

STUDY DESIGN

The toros of fresh cadavers were used to create endoscopic channels through the iliac wings to gain access to the L5-S1 disc and foramen. The spine and pelvis then were dissected out en bloc, and the anatomic relationships were studied.

OBJECTIVES

To determine the feasibility of a transiliac approach to the L5-S1 disc and foramen and to assess the safety of this approach by studying the anatomic relationships of the transiliac track.

SUMMARY OF BACKGROUND DATA

Because of its location deep in the pelvis, the L5-S1 disc and foramen are not easily accessible via a supra-iliac portal. A laparoscopic approach violates the abdominal cavity, and makes major vessels and viscera at risk for injury.

METHODS

A core drill was inserted over a guide wire into the iliac wing under fluoroscopy to obtain a core of bone, which then was removed to create a transiliac channel. An arthroscope was inserted through the channel to perform discoscopy or foraminoscopy. The spine was dissected out en bloc to study the relationships of the track.

RESULTS

It was possible to use a transiliac approach to L5-S1 in all the experiments. There was no damage of neural structures in any of the experiments.

CONCLUSIONS

The results of this study suggest that it is possible to access the L5-S1 disc and foramen through the ilium without injuring important structures. It would be necessary to conduct a study based on an animal model and to evaluate the results before using this procedure in a clinical situation.

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.

Therapeutic neural effects of electrical stimulation

The use of a functional neuromuscular stimulation (FNS) device can have therapeutic effects that persist when the device is not in use. Clinicians have reported changes in both voluntary and electrically assisted neuromuscular function and improvements in the condition of soft tissue. Motor recovery has been observed in people with incomplete spinal cord injury, stroke, or traumatic brain injury after the use of motor prostheses. Improvement in voluntary dorsiflexion and overall gait pattern has been reported both in the short term (several hours) and permanently. Electrical stimulation of skin over flexor muscles in the upper limb produced substantial reductions for up to 1 h in the severity of spasticity in brain-injured subjects, as measured by the change in torque generation during ramp-and-hold muscle stretch. There was typically an aggravation of the severity of spasticity when surface stimulation reached intensities sufficient to also excite muscle. Animals were trained to alter the size of the H-reflex to obtain a reward. The plasticity that underlies this operantly conditioned H-reflex change includes changes in the spinal cord itself. Comparable changes appear to occur with acquisition of certain motor skills. Current studies are exploring such changes in humans and animals with spinal cord injuries with the goal of using conditioning methods to assess function after injury and to promote and guide recovery of function. A better understanding of the mechanisms of neural plasticity, achieved through human and animal studies, may help us to design and implement FNS systems that have the potential to produce beneficial changes in the subject's central nervous systems.

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.

Endoscopic electrode implantation. A new technique in an animal model

The purpose of this study was 2-fold: (1) to describe a technique of creating an endoscopic interstitial working space; and (2) to describe the technique of implanting the modified double helix and the Huntington cuff electrode in the space created. Two cannulated balloons were inserted on either side of a standard arthroscope, which had been inserted to identify the target branch of the sciatic nerve. Traction was applied on each cannula after inflating the balloons with 3 to 5 cc of saline, to create a cylindrical operating space between them. After mobilizing a segment of the nerve, either of the 2 electrodes was implanted with the aid of special instruments. The results indicate that (a) it is possible to create interstitial operating spaces reliably and consistently; (b) satisfactory hemostasis can be achieved through the tamponade effect of the balloons and endoscopic cautery units; (c) excellent visualization is achievable; and (d) it is possible to implant electrodes in a reproducible manner. The interstitial spaces are portable and can be used for various procedures in most anatomic locations. Modification of the cuff electrode will be necessary to make it easier for endoscopic implantation.

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'.

Posterolateral arthroscopic discectomies of the thoracic and lumbar spine

Posterolateral arthroscopic discoscopies were performed on the lumbar and thoracic spine of the cadaver of a 6-foot-tall man. The purpose of this study was to determine the anatomic relationships of the discotomies and to examine the feasibility of the procedure for thoracic discectomies. At most levels in the thoracic spine, the rib neck acted as a guide to the posterolateral disc and as a safeguard against penetration of the pleural cavity. The average distance from the dura to the discotomy was 0.79 cm, with this distance increasing caudally. The thoracic nerve roots were found, in general, to be at less risk of damage because of their initial posterolateral course as they entered the subcostal groove. In the lumbar spine, the average distance from discostomy to the dura was 11.5 mm. Access to the triangular working zone could be gained with angles of insertion ranging from 38 degrees to 65 degrees. At angles less than 35 degrees, there was a significant risk of nerve injury. It is concluded that some thoracic discs can be safely removed through this approach and that the lumbar ventral ramii are very vulnerable to injury because of their proximity to the annulotomy.

Endoscopic electrode implantation for enhanced stimulation of the hamstring branches of the sciatic nerve in paralyzed subjects

Seven hamstring branches of the sciatic nerves in eight posterior thighs of four paraplegics were implanted with electrodes endoscopically. Strong initial responses were obtained in each case on continuous electrical stimulation. Three of the implants were removed immediately due to rapid decay in the response to stimulation; two had muscle power reduced to grade IV and two to grade III over 2-week period postoperatively. We believe the reduction in strength was partly due to hematoma surrounding the electrode and partly due to migration of the electrode away from the target nerves. Further work needs to be done to improve the technique and implant designs to improve results. Due to the excellent visual control it offers, this technique has the potential for accurate implantation of electrodes without massive exposures and its attendant morbidity.

Design and clinical application of a double helix electrode for functional electrical stimulation

An electrode, designed to be implanted without a surgical incision, was developed for skeletal muscle stimulation. Stainless steel, Teflon-insulated wire was wound into a helical lead around a polypropylene core and then rewound into a double helix configuration for stress relief during muscle contractions. The electrode tip was augmented with stainless steel barbs to increase anchoring strength. Electrodes were implanted with the help of specially modified hypodermic needles, sheaths, and passing tubes. 775 electrodes were implanted in a five year period in 22 subjects; accumulated implant time was 1,080 electrode years. 453 electrodes (65%) continue to produce strong, stable, muscle contractions. Electrode longevity varied with the location of implant. Electrodes were removed because of (1) inability to locate and properly place the electrode in a suitable site for stimulation during surgery (28.4%), (2) unwanted changes in muscle response to stimulation (91, 12%; one-third occurring during the first six weeks post implant), (3) increase in electrode impedance (74, 10%; assumed breakage, mostly occurring during the first year after implant), (4) intolerable pain during stimulation (8, 1%), and (5) infection (4, 0.5%). 67 (8%) electrodes were removed by accident or when the subjects left the program. This double helix electrode design has proven practical for achieving chronic stimulation of selected muscles in hemiplegic, paraplegic, stroke and brain-injured subjects with minimally invasive surgery.

Report on a conference on motor prostheses for workplace mobility of paraplegic patients in North America

On May 18, 1992 a symposium at Case Western Reserve University in Cleveland, Ohio, USA had the goal of defining the tasks needed to reach clinical utility of investigational neural prosthetic ambulation devices. The characteristics and stage of development of four systems were detailed: the Louiiana State University reciprocating gait orthosis (LSU-RGO) with muscle stimulation; the modular hybrid functional neuromuscular stimulation (FNS) orthosis; the Cleveland VA-Case Western Reserve University (VA-CWRU) implant system; and the Parastep system. Multicenter clinical trials are underway for the Parastep system and are planned to start within the next 2 years for the LSU-RGO with muscle stimulation, the VA-CWRU 8-channel system, and the floor reaction orthosis component of the modular hybrid FNS system. Current investigational systems provide little advantage over the standing wheelchair in some occupations but they do expand social, recreational, and exercise capabilities. Disabled people and some leading rehabilitation physicians are willing to test basic ambulation devices but the regulatory approvals must first be obtained for multicenter clinical trials. Corporate partners are central to the development of devices, their clinical testing, and their subsequent marketing. A key requirement for developing and disseminating motor prostheses is the education of clinicians so that they will participate in trials and be prepared to prescribe the prostheses when they reach the market.

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.

Augmentation of the accuracy of percutaneous electrode implantation by using a modified arthroscope to guide insertion

Using a clear polyvinyl fluoride sheath over an arthroscope, inserted through a 1-cm stab incision, we have demonstrated the feasibility of visualizing the sciatic nerve and its branches in the feline model. The purpose of this technique is to allow visual control, without a large surgical incision, of the exact site of implantation of electrodes used for functional neuromuscular stimulation. Currently, we determine the optimum site for percutaneous electrode implantation by stimulating the target nerve or muscle with a 26-gauge probe needle until maximal response is obtained. This method lacks accuracy because there is no direct visualization of the location of the tip of the probe or the electrode. With the new technique, we identified nerves by their distinctive vascular markings and we followed the nerves with minimal disruption of the soft tissues. In this way, individual branches were identified and targeted for instrumentation, allowing selective stimulation of specific muscle groups.

Metabolic responses to arm ergometry and functional neuromuscular stimulation

The hips and lower extremities of four complete paraplegic male subjects (T-6, T-7, T-8, and T-11) were stimulated with functional neuromuscular stimulation (FNS) via transcutaneous intramuscular electrodes (20 mA, 0-150 pulse width, and 20 Hz). Cardiopulmonary (CP) and/or cardiovascular (CV) responses were measured during maximal (seated) arm ergometry (AE), FNS, and FNS + AE. Subjects' lower extremities were stimulated with a 2 s walking cycle via a microprocessor computer. Data were collected with a SensorMedic MMC Horizon (VO2 and VCO2 at STPD and VE at BPTS). The mean MET level (1 MET = 3.5 ml O2/kg/min) during FNS was 4.8. Mean METS during FNS + AE was 10.3 and mean METS for AE was 7.2. Mean lactic acid (LA) after FNS, AE, and FNS + AE was 73 mg percent, 77 mg percent and 115 mg percent respectively. Respiratory exchange ratio (RER) (VCO2/VO2) was greater than 1.2 during the first 2 to 5 min of FNS but decreased to less than 1.0 during the second 5 min of FNS. Steady state VO2 and RER less than 1.0 indicated a FNS transition from anaerobic to aerobic metabolism. Subject T-11 had CV limitations during FNS and FNS + AE due to excessive LA from FNS (115 mg percent). Ventilatory (VE) responses during AE, FNS, and FNS + AE were consistent with VO2; and mean maximal VE and VO2 for subjects T-6, T-7, and T-8 during FNS + AE was greater than 90 percent of that observed in sedentary normals. The aerobic and anaerobic capacities of paraplegic subjects is primarily limited by available muscle mass rather than impaired CV or CP function.

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.

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.

Energy costs of walking and standing with functional neuromuscular stimulation and long leg braces

Two complete paraplegic subjects (T4 and T8), implanted with intramuscular electrodes, walked via functional neuromuscular stimulation (FNS) using a rolling walker and a reciprocal gait. The subjects also ambulated with long leg braces (LLB), using a rolling walker, and a drag/swing-to gait; and they stood using LLB and FNS separately. Oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (VCO2/VO2), kcal/kg/meter, kcal/kg/minute, heart rate, blood pressure, and O2 debt with recovery time were recorded. During FNS walking, energy costs (kcal/kg/min) were 59% to 75% of maximal aerobic power (MAP), as determined during the combined activities of maximal arm ergometry and FNS leg stimulation. As the speed of FNS walking increased, there was no increase in energy costs; energy efficiency (kcal/kg/meter) equaled that of LLB ambulation. One subject showed decreased O2 debt with increased speed of FNS walking. At speeds approaching .4m/sec, FNS walking energy costs were similar to those of LLB ambulation. FNS energy costs relative to working muscle mass were less than those of LLB. When maximal stimulus parameters were used for FNS standing (20mA amplitude, 25 pps frequency, and 150 microseconds pulse width), energy costs were 100% more than those of normal or LLB standing. However, when the minimal stimulus necessary to maintain a standing position was used, FNS energy costs decreased by 35% to 47%. At speeds between .4 and .6m/sec, FNS walking is a viable alternative to LLB ambulation. Major energy cost reduction should be possible in the future.

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.

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.

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.

Upper and lower motor neuron lesions in the upper extremity muscles of tetraplegics

Paralysed upper extremity muscles of 24 tetraplegic patients were examined to determine whether their lower motor neuron was intact. Primary emphasis was placed on the forearm finger flexor muscles (Flexor Digitorum Superficialis and Flexor Digitorum Profundus) and finger extensor muscles (Extensor Digitorum Communis and Extensor Indicis). It was found that the vast majority of these muscles in C4, C5 and C6 subjects retained some or all of their lower motor neurons intact. In C5 subjects, examination was performed on additional muscles that were potentially most useful in an orthosis utilising functional stimulation. Similar to the results of the finger flexor and extensor muscles, the muscles of the wrist and thumb generally had the lower motor neuron at least partially intact. A muscle that often was an exception was M. Flexor Carpi Radialis. These studies indicate that most of the forearm muscles of the upper extremity in high level spinal cord injury patients which are paralysed have the lower motor neuron totally or partially intact. With electrically induced exercise, such muscles are strengthened to functional levels of contraction. Subsequent electrical activation enables the quadriplegic patients to use the muscle functionally.

Alteration in the force and fatigability of skeletal muscle in quadriplegic humans following exercise induced by chronic electrical stimulation

The paralyzed forearm finger flexor muscles of 10 quadriplegic subjects were exercised via electrical stimulation to determine changes in the contractile force and fatigability of the muscle that could be externally induced. The force of contraction initially produced by most muscles was less than that required for functional activity. Following exercise, the strength of all muscles was increased above the level for functional use. In general, no correlation was noted between the amount of exercise and the force change. Two subjects had high contraction forces after prolonged periods before stimulation began, and 4 subjects who were followed after the stimulation program maintained near the contractile force achieved at the end of the program in the absence of stimulation. Fatigue of the muscle during the course of the exercise program was increased to above that recorded initially, although this was more variable and sometimes dropped to less than that recorded initially. Generally, no correlation was demonstrated between usage and fatigue. It is concluded that exercise induced by electrical stimulation alters the cantractile properties of the muscle toward a state usable for functional, tonic activation.