Comparison of functional electrical stimulation to long leg braces for upright mobility for children with complete thoracic level spinal injuries.

OBJECTIVE: To prospectively compare functional electrical stimulation (FES) to long leg braces (LLB) as a means of upright mobility for children with motor-complete thoracic level spinal cord injuries (SCIs). DESIGN: Intrasubject group comparison of two interventions. SETTING: Nonprofit pediatric orthopedic rehabilitation facility specializing in SCI. PATIENTS OR OTHER PARTICIPANTS: Convenience sample of five children between 9 and 18 years old with motor-complete thoracic level SCI. The hip and knee extensors were excitable by electrical stimulation. INTERVENTIONS: The FES system consisted of percutaneous intramuscular electrodes implanted to the hip and knee extensors and a push-button activated stimulator worn about the waist. Standing was accomplished by simultaneous stimulation of all implanted muscles. For foot and ankle stability, either ankle-foot orthoses (AFO) or supramalleolar orthoses were used. The LLB system consisted of a custom knee-ankle foot orthosis (KAFO) for four subjects and a custom reciprocating gait orthosis (RGO) for one subject who required bracing at the hip. For both interventions, either a front-wheeled walker or Lofstrand crutches were used as assistive devices. Each subject was trained in the use of both FES and LLB in seven standardized upright mobility activities: stand and reach, high transfer, toilet transfer, floor to stand, 6-meter walk, stair ascent, and stair descent. MAIN OUTCOME MEASURES: For each mobility activity, five repeated measures of level of independence, using the 7-point Functional Independence Measure (FIM) scale, and time to completion were recorded for each intervention. Subjects were also asked which intervention they preferred. RESULTS: For 94% of comparisons, subjects required equal (70%) or less (24%) assistance using FES as compared with LLB. Six of the seven mobility activities required less time to complete using FES, two activities at significant levels. The FES system was preferred in 62% of the cases, LLB were desired 27% of the time, and there was no preference in 11% of the cases. CONCLUSIONS: The FES system generally provided equal or greater independence in seven mobility activities as compared with LLB, provided faster sit-to-stand times, and was preferred over LLB in a majority of cases. Follow-up evaluations of both modes of upright mobility are needed to compare long-term performance and satisfaction.

Implantable electrode lead in a growing limb.

An implantable electrode leadwire system used to provide limb function for individuals with spinal cord injuries (SCI's) was evaluated in a series of growing dogs to determine whether it could maintain its performance in the presence of growth. Thirty implantable electrodes (15 epimysial and 15 intramuscular) were implanted in the forelimb muscles of six young dogs. The electrodes' leads were tunneled subcutaneously and anchored proximally in the shoulder with excess lead incorporated into the subcutaneous space to accommodate growth. Six of the leads had some of this excess placed in pouches made from surgical membrane while the other 24 leads had excess placed freely within the subcutaneous space. Motor responses to the electrodes were tested before and after growth with tendon force transducers and were compared to the performance of new electrodes implanted to the same muscles of the mature dog during the explant procedure. Measured were the pulse duration at which a measurable force is first produced (threshold) and the percentage of the maximum force that could be attained from the target muscle before activation of adjacent muscles (usable force range). An analysis of variance indicated that there was no difference in the usable force range (p = 0.62) of the original electrodes before and after growth and that of the new electrodes placed at maturity. There was a difference in the threshold (p = 0.001) which can be attributed to an increase in the values measured from the original electrodes after growth. However, the increase in threshold with growth averaged 6 micros which is not clinically significant and can be accommodated through stimulation programming. Growth of the limb and unwinding of excess lead were quantified by radiograph. Extension of the freely placed excess lead was comparable to growth so that the pouch enclosures were found to be unnecessary for facilitating lead expansion. By radiograph and surgical observations, only two of 30 electrodes (both intramuscular) appeared to have been subjected to lead tension, although they continued to provide adequate motor responses. Insufficient excess lead was judged to be the cause of dislodgment for one of these electrodes. Results of this study suggest that for this implantable leadwire system, excess lead placed in the subcutaneous space can unwind on demand with limb growth such that an electrode will remain in position and provide a stable motor response.

Tissue response to chronically stimulated implanted epimysial and intramuscular electrodes.

Twenty-four epimysial and 16 intramuscular electrodes were implanted in five adult dogs for periods ranging from 11 to 50 months. Chronic stimulation was applied to half of the electrodes for eight weeks near the end of the implantation period. The tissue response was rated by the amount and appearance of the fibrous tissue and inflammatory cells seen in the capsule lining the region of the electrode. The encapsulation tissues were composed primarily of collagen and fibroblasts and some macrophages and few other inflammatory cells. The epimysial electrodes exhibited more variation between and within electrodes, but had more of the better scores than the intramuscular electrodes. No difference in the distribution of scores was measured between the control and stimulated groups for the epimysial electrodes. While the scores for the intra-muscular electrodes varied very little, variance was sufficient to indicate a trend for poorer ratings with the application of chronic stimulation. Fibrous capsules were generally thinner under the epimysial electrodes than around the intramuscular electrodes. For both electrode types, the thickness was not correlated with the application or level of chronic stimulation. Thickness was shown to be positively correlated to the degree of loss of the sutures used to anchor the epimysial electrodes.

Motor responses to FES electrodes in a growing limb.

A canine model was used to investigate the chronic performance of surgically implanted electrodes in a growing limb. Seven skeletally immature dogs were implanted with epimysial and intramuscular electrodes. Recruitment characteristics for each electrode, including the activation threshold, spillover muscle threshold, peak force, and force at spillover were recorded with tendon force transducers placed on the tendon of the target muscle and the first spillover muscle. Recruitment properties for the electrodes were measured at the time of implant and after growth was complete. Appropriate electrode positions were also remapped after maturity was reached. Data for 23 electrodes are reported. Average longitudinal growth of the ulna was 5.6 cm (39% increase). The measurements of threshold for target and spillover muscle activation show that appropriate muscle recruitment order was retained in 22 of 23 (96%) of the electrodes. The target muscle thresholds remained stable between implant and explant with variation on the order of that reported for these electrodes placed in mature animals. Overall, a multivariate analysis of variance for repeated measures indicates electrodes performed equally well at explant as they did at implant as measured by threshold and usable range of target muscle before spillover. New electrodes placed in the adult animal did not perform better than the chronically placed electrodes. The recruitment properties of 22 or 23 electrodes did not vary significantly with growth. This is encouraging evidence that a stable motor response can be retained with implantable intramuscular and epimysial electrodes in the presence of growth.