Archives of Physical Medicine and Rehabilitation journal homepage: www.archives-pmr.org Archives of Physical Medicine and Rehabilitation 2015;96:620-6

ORIGINAL RESEARCH

Pressure Changes Under the Ischial Tuberosities During Gluteal Neuromuscular Stimulation in Spinal Cord Injury: A Comparison of Sacral Nerve Root Stimulation With Surface Functional Electrical Stimulation Liang Qin Liu, PhD,a Martin Ferguson-Pell, PhDb From the aDepartment of Adult, Child and Midwifery, School of Health and Education, Middlesex University, London, United Kingdom; and b Faculty of Rehabilitation, University of Alberta, Edmonton, Alberta, Canada.

Abstract Objective: To compare the magnitude of interface pressure changes during gluteal maximus contraction by stimulating sacral nerve roots with surface electrical stimulations in patients with spinal cord injuries (SCIs). Design: Pilot interventional study. Setting: Spinal injury research laboratory. Participants: Adults (NZ18) with suprasacral complete SCI. Interventions: Sacral nerve root stimulation (SNRS) via a functional magnetic stimulator (FMS) or a sacral anterior root stimulator (SARS) implant; and surface functional electrical stimulation (FES). Main Outcome Measures: Interface pressure under the ischial tuberosity (IT) defined as peak pressure, gradient at peak pressure, and average pressure. Results: With optimal FMS, a 29% average reduction of IT peak pressure was achieved during FMS (mean  SD: 160.124.3mmHg at rest vs 114.718.0mmHg during FMS, t5Z6.3, PZ.002). A 30% average reduction of peak pressure during stimulation via an SARS implant (143.231.7mmHg at rest vs 98.521.5mmHg during SARS, t5Z4.4, PZ.007) and a 22% average decrease of IT peak pressure during FES stimulation (153.734.8mmHg at rest vs 120.526.1mmHg during FES, t5Z5.3, PZ.003) were obtained. In 4 participants who completed both the FMS and FES studies, the percentage of peak pressure reduction with FMS was slightly greater than with FES (mean difference, 7.8%; 95% confidence interval, 1.6%e14.0; PZ.04). Conclusions: SNRS or surface FES can induce sufficient gluteus maximus contraction and significantly reduce ischial pressure. SNRS via an SARS implant may be more convenient and efficient for frequently activating the gluteus maximus. Archives of Physical Medicine and Rehabilitation 2015;96:620-6 ª 2015 by the American Congress of Rehabilitation Medicine

Pressure ulcer (PrU) is one of the most common complications in spinal cord injury (SCI). According to the National Pressure Ulcer Advisory Panel/European Pressure Ulcer Advisory Panel, a PrU is

Supported by the Royal National Orthopaedic Hospital, Stanmore, United Kingdom (grant no. 03/010); and by the ASPIRE Stanmore, United Kingdom, for providing equipment enabling us to run this project. Disclosures: none.

described as an area of localized damage to the skin as a result of prolonged pressure alone or pressure in combination with shearing forces.1 After SCI, patients generally mobilize in a wheelchair, leading to prolonged external pressure being applied to the atrophied gluteus muscles; consequently, the ischial tuberosity (IT) is one of the most vulnerable sites for PrU formation. Up to 85% of adults with SCI will develop a PrU at some point during their lifetime,2-4 with an estimated 36% to 50% of PrUs resulting from sitting in a wheelchair.5

0003-9993/14/$36 - see front matter ª 2015 by the American Congress of Rehabilitation Medicine http://dx.doi.org/10.1016/j.apmr.2014.10.008

Electrical stimulation for ischial pressure changes in SCI Once a PrU has developed, it can cause long hospital stays, delayed rehabilitation, and loss of independence. If a PrU is severe, it can lead to further disabilities, the need for surgical interventions, and even fatal infections.6 It is estimated that 7% to 8% of those who develop PrUs will die of related complications.7 Apart from significant personal consequences, PrUs also represent a significant cost burden for health and social care systems. The cost of treating a PrU varies from £1214 to £14,108 in the United Kingdom, with a total annual cost of £1.4 to £2.1 billion for PrU management.8,9 Given the significant personal consequences and serious health care burden, effective prevention of PrUs is vitally important for SCI. To date, most efforts to prevent PrUs tend to focus on methods to reduce external pressure. These include providing specialized cushions and educating patients to perform “pressure-relief” regimens.10,11 However, at best the efforts are only partially effective in SCI. There are still a significant number of people with SCI who continue to develop PrUs. These people either are unable to maintain a regular pressure-relief regimen or do not get sufficient benefit from pressure-relief cushions. A primary factor is that muscles below the lesion gradually atrophy after SCI. The gluteal bulk reduction leads to poor pressure distributions over the ITs. The idea of activating paralyzed gluteal muscles by using surface functional electrical stimulation (FES) was explored over 30 years ago in SCI.12,13 Yet surface FES requires repeated application of large electrodes to the buttocks to stimulate the muscles, which can result in local dermatitis and excoriation. Moreover, muscles will eventually reatrophy if stimulation is not continued. Therefore, surface FES has significant limitations for sustained benefit. We previously reported that sacral nerve roots via functional magnetic stimulation (FMS) can activate gluteal muscles noninvasively.14 FMS has advantages over surface FES because it is noninvasive and produces deep penetration. However, FMS may not be suitable for long-term use, in particular for patients to use at home, because of the heating effect of the magnetic coil together with the cumbersome equipment. Nevertheless, FMS can be a useful assessment tool for a sacral anterior root stimulator (SARS) implant. The SARS implant is a well-established device in SCI in the United Kingdom, in which the electrodes are usually implanted intra- or extradurally on bilateral S2, S3, or S4 sacral nerve roots for bladder management, bowel management, or both. In this study, we sought to evaluate whether sacral nerve root stimulation (SNRS) via FMS or an SARS implant reduces IT pressure more than surface FES in seated patients with SCI. Our objective was to compare the magnitude of IT pressure changes during gluteal maximus contraction during stimulation of sacral nerve roots via FMS or an SARS implant with pressure changes achieved using surface FES in patients with SCI.

List of abbreviations: FES FMS IT PrU SARS SCI SNRS

functional electrical stimulation functional magnetic stimulation ischial tuberosity pressure ulcer sacral anterior root stimulator spinal cord injury sacral nerve root stimulation

www.archives-pmr.org

621

Methods The project was approved by the National Health Service research ethics committee, Royal National Orthopaedic Hospital. All participants gave their informed consent.

Participants For the FMS study, subjects aged between 18 and 65 years who had suprasacral complete SCI were included; individuals who were pregnant or using a cardiac pacemaker were excluded. For the SARS implant study, subjects aged between 18 and 65 years who had suprasacral complete SCI and had an electrode implanted on the S2 nerve root in their SARS implant for bladder management, bowel management, or both were included. For the surface FES study, subjects aged between 18 and 65 years who had suprasacral complete SCI were included. Patients with a current PrU over the gluteal region or a history of severe autonomic dysreflexia were excluded from these studies.

Study design Three individual studies were conducted separately during a 12-month period. Each participant was invited to attend the research laboratory for 1.5 to 2 hours. Before the experiment, all participants were asked to empty their bladder and bowel.

Ischial pressure measurement Equipment used Ischial pressures were measured using an interface pressure mapping systema (3636 cells at 10-mm pitch). Each subject sat in a standard wheelchair with a fitted armrest and footrest. The pressure mat was placed between the participant and the standard foam cushion (high resilience foam, density 45kg/m3). Before the study, the interface pressure mat was calibrated according to the manufacturer’s instructions. An initial data set was recorded once the subjects had stabilized in a standard sitting position, defined as (1) backrest-to-seat angle of at least 80 and (2) footrest adjusted to keep the thighs parallel to the seat. Sample rate of pressure mapping was 7 frames per second. Real-time 2-dimensional images of pressure distribution at the seating interface were produced with the graphical display software provided with the pressure mapping system and saved to the personal computer. All data were then converted to ASCII format. Pressure parameters The pressure parameters included peak pressure, gradient at peak pressure, and average pressure under the IT. Peak pressure was defined as the highest value of an individual sensor under ITs. Gradient at peak pressure was defined as the average difference between the values of the highest sensors and surrounding 8 sensors. The average pressure was calculated as the total pressure divided by the number of loaded cells (sensors). We determined peak pressure and gradient at peak pressure under the ITs for each of the 6 frames within a data set and averaged the 6 frames. Initial data analysis showed no significant differences between the left and right ischial pressure; therefore, bilateral values were averaged for each subject. All pressure parameters were compared before and during stimulations in each study.

622

L.Q. Liu, M. Ferguson-Pell

Sacral nerve root stimulation Functional magnetic stimulation FMS was delivered using a magnetic stimulator (MagProb) with a large circular coil (120-mm diameter, producing maximum field strength of 2 tesla) placed over the sacral area. In order to obtain a smooth, tetanic fused contraction of the gluteal muscles, stimulation frequencies in the available range of 15 to 25 pulses per second were used. Stimulation intensities were adjusted individually by starting from the lowest level of 30% in steps of 5% (stimulation strength is indicated as percentage of the maximum output) to the highest level of patients’ tolerance. The maximum level of intensity used was 80%. To activate bilateral gluteus muscles, the coil position was at the midline. Fig 1

Finetech-Brindley SARS implant Electrical stimulation was applied bilaterally through a FinetechBrindley SARS implant.c A stimulation program was manually set up from an external control box. To avoid bladder/bowel activation, S3 and S4 stimulators were switched off. Only the S2 nerve root was stimulated. To obtain a smooth tetanic contraction, a stimulation frequency of 20 pulses per second was used. All patients were given the lowest amplitude of “1” to avoid activating deeper muscles or organs such as the bladder and bowel. However, to evaluate the magnitude of pressure reduction with an increase in strength of stimulation, the stimulation pulse width was adjusted individually by starting from the lowest pulse width of 8 microseconds to the highest level of patients’ tolerance. The maximum pulse width used was 700 microseconds. Surface FES FES was provided through large surface electrodes (PALS/Platinum, model 895240d) using Stock Microstim2,e a dual-channel neuromuscular stimulator. The specifications of the Microstim2 (v2) are as follows: (1) stimulation frequencies are 20Hz and 40Hz; (2) the maximum pulse width is 330 microseconds; (3) the maximum output amplitude is 100mA; and (4) the stimulation waveform is square with passive charge balancing. In order to be comparable with FMS and SARS, the stimulation frequency and duration of stimulation were set at 20Hz and 8 seconds, respectively. As per the stimulation amplitude, all participants started from the lowest level of “1” to the highest level of patients’ tolerance. The maximum level of amplitude was “9.” Before the experiment, participants were asked to rest 5 to 10 minutes, followed by being helped to lie down on a standard hospital bed in a prone position. Two large rectangle electrodes (59cm) were placed onto each side of the gluteus maximus. The stimulating anodes were then placed bilaterally just below the posterior superior iliac crest (fig 1). Then the participants were transferred to the study wheelchair.

Statistical analysis Descriptive statistics were calculated using Excel 2007f and SPSS (version 19g). All data were examined for normality using a Kolmogorov-Smirnov test. For comparison between before and during stimulation within the same subjects, we used a paired sample t test. Because of the small sample size of each study, nonparametric tests were also used to confirm the results from parametric tests where appropriate. We used the Wilcoxon signed-rank test for comparison between before and during stimulation within the same subjects. P values were 2-tailed, and

Electrode placement for gluteus maximus activation.

differences were considered to be statistically significant for a P value

Pressure changes under the ischial tuberosities during gluteal neuromuscular stimulation in spinal cord injury: a comparison of sacral nerve root stimulation with surface functional electrical stimulation.

To compare the magnitude of interface pressure changes during gluteal maximus contraction by stimulating sacral nerve roots with surface electrical st...
396KB Sizes 0 Downloads 11 Views