S. Coupaud

High-volume FES-cycling partially reverses bone loss in people with chronic spinal cord injury

Spinal cord injury (SCI) leads to severe bone loss in the paralysed limbs and to a resulting increased fracture risk thereof. Since long bone fractures can lead to comorbidities and a reduction in quality of life, it is important to improve bone strength in people with chronic SCI. In this prospective longitudinal cohort study, we investigated whether functional electrical stimulation (FES) induced high-volume cycle training can partially reverse the loss of bone substance in the legs after chronic complete SCI. Eleven participants with motor-sensory complete SCI (mean age 41.9+/-7.5 years; 11.0+/-7.1 years post injury) were recruited. After an initial phase of 14+/-7 weeks of FES muscle conditioning, participants performed on average 3.7+/-0.6 FES-cycling sessions per week, of 58+/-5 min each, over 12 months at each individuals highest power output. Bone and muscle parameters were investigated in the legs by means of peripheral quantitative computed tomography before the muscle conditioning (t1), and after six (t2) and 12 months (t3) of high-volume FES-cycle training. After 12 months of FES-cycling, trabecular and total bone mineral density (BMD) as well as total cross-sectional area in the distal femoral epiphysis increased significantly by 14.4+/-21.1%, 7.0+/-10.8% and 1.2+/-1.5%, respectively. Bone parameters in the femoral shaft showed small but significant decreases, with a reduction of 0.4+/-0.4% in cortical BMD, 1.8+/-3.0% in bone mineral content, and 1.5+/-2.1% in cortical thickness. These decreases mainly occurred between t1 and t2. No significant changes were found in any of the measured bone parameters in the tibia. Muscle CSA at the thigh increased significantly by 35.5+/-18.3%, while fat CSA at the shank decreased by 16.7+/-12.3%. Our results indicate that high-volume FES-cycle training leads to site-specific skeletal changes in the paralysed limbs, with an increase in bone parameters at the actively loaded distal femur but not the passively loaded tibia. Thus, we conclude that high-volume FES-induced cycle training has clinical relevance as it can partially reverse bone loss and thus may reduce fracture risk at this fracture prone site.

Effect of detraining on bone and muscle tissue in subjects with chronic spinal cord injury after a period of electrically-stimulated cycling: a small cohort study

OBJECTIVE To investigate adaptive changes in bone and muscle parameters in the paralysed limbs after detraining or reduced functional electrical stimulation (FES) induced cycling following high-volume FES-cycling in chronic spinal cord injury. SUBJECTS Five subjects with motor-sensory complete spinal cord injury (age 38.6 years, lesion duration 11.4 years) were included. Four subjects stopped FES-cycling completely after the training phase whereas one continued reduced FES-cycling (2-3 times/week, for 30 min). METHODS Bone and muscle parameters were assessed in the legs using peripheral quantitative computed tomography at 6 and 12 months after cessation of high-volume FES-cycling. RESULTS Gains achieved in the distal femur by high-volume FES-cycling were partly maintained at one year of detraining: 73.0% in trabecular bone mineral density, 63.8% in total bone mineral density, 59.4% in bone mineral content and 22.1% in muscle cross-sectional area in the thigh. The subject who continued reduced FES-cycling maintained 96.2% and 95.0% of the previous gain in total and trabecular bone mineral density, and 98.5% in muscle cross-sectional area. CONCLUSION Bone and muscle benefits achieved by one year of high-volume FES-cycling are partly preserved after 12 months of detraining, whereas reduced cycling maintains bone and muscle mass gained. This suggests that high-volume FES-cycling has clinical relevance for at least one year after detraining.

Role of peripheral quantitative computed tomography in identifying disuse osteoporosis in paraplegia

ObjectiveDisuse osteoporosis is a major long-term health consequence of spinal cord injury (SCI) that still needs to be addressed. Its management in SCI should begin with accurate diagnosis, followed by targeted treatments in the most vulnerable subgroups. We present data quantifying disuse osteoporosis in a cross-section of the Scottish paraplegic population to identify subgroups with lowest bone mineral density (BMD).Materials and methodsForty-seven people with chronic SCI at levels T2-L2 were scanned using peripheral quantitative computed tomography at four tibial sites and two femoral sites, at the Queen Elizabeth National Spinal Injuries Unit, Glasgow (UK). At the distal epiphyses, trabecular BMD (BMDtrab), total BMD, total bone cross-sectional area (CSA) and bone mineral content (BMC) were determined. In the diaphyses, cortical BMD, total bone CSA, cortical CSA and BMC were calculated. Bone, muscle and fat CSAs were estimated in the lower leg and thigh.ResultsBMDtrab decreased exponentially with time since injury at different rates in the tibia and femur. At most sites, female paraplegics had significantly lower BMC, total bone CSA and muscle CSA than male paraplegics. Subjects with lumbar SCI tended to have lower bone values and smaller muscle CSAs than in thoracic SCI.ConclusionAt the distal epiphyses of the tibia and femur, there is generally a rapid and extensive reduction in BMDtrab after SCI. Female subjects, and those with lumbar SCI, tend to have lower bone values than males or those with thoracic SCI, respectively.

Decreases in bone mineral density at cortical and trabecular sites in the tibia and femur during the first year of spinal cord injury.

BACKGROUND Disuse osteoporosis occurs in response to long-term immobilization. Spinal cord injury (SCI) leads to a form of disuse osteoporosis that only affects the paralyzed limbs. High rates of bone resorption after injury are evident from decreases in bone mineral content (BMC), which in the past have been attributed in the main to loss of trabecular bone in the epiphyses and cortical thinning in the shaft through endocortical resorption. METHODS Patients with motor-complete SCI recruited from the Queen Elizabeth National Spinal Injuries Unit (Glasgow, UK) were scanned within 5weeks of injury (baseline) using peripheral Quantitative Computed Tomography (pQCT). Unilateral scans of the tibia, femur and radius provided separate estimates of trabecular and cortical bone parameters in the epiphyses and diaphyses, respectively. Using repeat pQCT scans at 4, 8 and 12months post-injury, changes in BMC, bone mineral density (BMD) and cross-sectional area (CSA) of the bone were quantified. RESULTS Twenty-six subjects (5 female, 21 male) with SCI (12 paraplegic, 14 tetraplegic), ranging from 16 to 76years old, were enrolled onto the study. Repeated-measures analyses showed a significant effect of time since injury on key bone parameters at the epiphyses of the tibia and femur (BMC, total BMD, trabecular BMD) and their diaphyses (BMC, cortical BMD, cortical CSA). There was no significant effect of gender or age on key outcome measures, but there was a tendency for the female subjects to experience greater decreases in cortical BMD. The decreases in cortical BMD in the tibia and femur were found to be statistically significant in both men and women. CONCLUSIONS By carrying out repeat pQCT scans at four-monthly intervals, this study provides a uniquely detailed description of the cortical bone changes that occur alongside trabecular bone changes in the first year of complete SCI. Significant decreases in BMD were recorded in both the cortical and trabecular bone compartments of the tibia and femur throughout the first year of injury. This study provides evidence for the need for targeted early intervention to preserve bone mass within this patient group.

Feedback Control of Oxygen Uptake During Robot-Assisted Gait

Body-weight-supported robot-assisted devices can be used to promote gait rehabilitation and as exercise tools for neurologically impaired persons such as stroke and spinal-cord-injured patients. Here, we propose a novel feedback-control structure for real-time control of oxygen uptake during robot-assisted gait, in which we use the following methods. 1) A feedback-control structure is proposed, consisting of a dynamic controller operating on target and actual levels of oxygen uptake in order to set a target work rate. Target work rate is achieved by an inner volitional feedback loop which relies on the subjects exercise input. 2) The dynamic oxygen-uptake controller is based on an empirically derived model of the oxygen-uptake dynamics and is synthesized by pole placement. 3) The resulting control system is tested during the robot-assisted treadmill ambulation of five able-bodied subjects. A single linear controller was designed based on identification data from tests with one subject and used for closed-loop control tests with all five subjects. In all cases, the actual oxygen-uptake response closely followed the ideal response as specified by the feedback design parameters. The control of oxygen uptake during body-weight-supported robot-assisted ambulation is feasible in the able-bodied population; the robustness of the system is demonstrated within the class of subjects tested. Further testing is required to validate the approach with neurologically impaired subjects.

Bone morphology of the femur and tibia captured by statistical shape modelling predicts rapid bone loss in acute spinal cord injury patients

After spinal cord injury (SCI), bone loss in the paralysed limbs progresses at variable rates. Decreases in bone mineral density (BMD) in the first year range from 1% (slow) to 40% (rapid). In chronic SCI, fragility fractures commonly occur around the knee, with significant associated morbidity. Osteoporosis treatments await full evaluation in SCI, but should be initiated early and targeted towards patients exhibiting rapid bone loss. The potential to predict rapid bone loss from a single bone scan within weeks of a SCI was investigated using statistical shape modelling (SSM) of bone morphology, hypothesis: baseline bone shape predicts bone loss at 12-months post-injury at fracture-prone sites. In this retrospective cohort study 25 SCI patients (median age, 33 years) were scanned at the distal femur and proximal tibia using peripheral Quantitative Computed Tomography at <5 weeks (baseline), 4, 8 and 12 months post-injury. An SSM was made for each bone. Links between the baseline shape-modes and 12-month total and trabecular BMD loss were analysed using multiple linear regression. One mode from each SSM significantly predicted bone loss (age-adjusted P<0.05 R(2)=0.37-0.61) at baseline. An elongated intercondylar femoral notch (femur mode 4, +1 SD from the mean) was associated with 8.2% additional loss of femoral trabecular BMD at 12-months. A more concave posterior tibial fossa (tibia mode 3, +1 SD) was associated with 9.4% additional 12-month tibial trabecular BMD loss. Baseline bone shape determined from a single bone scan is a valid imaging biomarker for the prediction of 12-month bone loss in SCI patients.

Predicting patient-specific rates of bone loss at fracture-prone sites after spinal cord injury

Purpose: People with spinal cord injury (SCI) experience bone loss and have an elevated rate of fracture in the paralysed limbs. The literature suggests an exponential time course of bone loss after SCI, but true rates may vary between patients. We propose systematic evaluation of bone status in the early stages of SCI to identify fast bone losers. Method: A case series of six patients with complete SCI were scanned using peripheral quantitative computed tomography within 5 weeks and at 4, 8 and 12 months post-injury. Bone mineral density (BMD) and bone mineral content (BMC) were measured at fracture-prone sites in the tibia and femur. Patient-specific-predictions (PSP) of expected rates of bone loss were produced by individualising published model equations according to each patient’s measured values at baseline. Wilcoxon Signed-Rank tests were used to identify changes between time-points; chi-squared tests for differences between measured and PSP values. Results: In the lower limbs, mean values decreased significantly between baseline and 8 months post-injury, by 19–31% for trabecular BMD, 21–32% for total BMD, and 9–29% for BMC. Most subjects showed no significant differences between PSP and measured values, but individuals with significantly faster rates of bone loss than predicted should be investigated further. Conclusions: There was considerable intersubject variability in rates of bone loss after SCI. Patients showing the fastest bone loss could benefit from continued follow-up and possibly treatment. Implications for Rehabilitation Spinal cord injury (SCI) leads to extensive muscle paralysis, and is often accompanied by significant bone loss and increased fracture risk. Repeat bone scans within months of injury can be used to “red-flag” patients who are losing bone faster than predicted. A patient-specific approach to osteoporosis management will facilitate targeted treatment aimed at those who need it most, in SCI and other patient groups.

Investigation of Robotic-Assisted Tilt-Table Therapy for Early-Stage Spinal Cord Injury Rehabilitation

Damage to the spinal cord compromises motor function and sensation below the level of injury, resulting in paralysis and progressive secondary health complications. Inactivity and reduced energy requirements result in reduced cardiopulmonary fitness and an increased risk of coronary heart disease and cardiovascular complications. These risks may be minimized through regular physical activity. It is proposed that such activity should begin at the earliest possible time point after injury, before extensive neuromuscular degeneration has occurred. Robotic-assisted tilt-table therapy may be used during early-stage spinal cord injury (SCI) to facilitate stepping training, before orthostatic stability has been achieved. This study investigates whether such a stimulus may be used to maintain pulmonary and coronary health by describing the acute responses of patients with early-stage (<1 yr) motor-complete SCI (cSCI) and motor-incomplete SCI (iSCI) to passive, active, and electrically stimulated robotic-assisted stepping. Active participation was found to elicit an increased response from iSCI patients. The addition of electrical stimulation did not consistently elicit further increases. Extensive muscle atrophy was found to have occurred in those patients with cSCI, thereby limiting the potential effectiveness of electrical stimulation. Active participation in robotic-assisted tilt-table therapy may be used to improve cardiopulmonary fitness in iSCI patients if implemented as part of a regular training program.

Prediction of risk of fracture in the tibia due to altered bone mineral density distribution resulting from disuse: A finite element study

The disuse-related bone loss that results from immobilisation following injury shares characteristics with osteoporosis in post-menopausal women and the aged, with decreases in bone mineral density leading to weakening of the bone and increased risk of fracture. The aim of this study was to use the finite element method to: (i) calculate the mechanical response of the tibia under mechanical load and (ii) estimate of the risk of fracture; comparing between two groups, an able-bodied group and spinal cord injury patients group suffering from varying degrees of bone loss. The tibiae of eight male subjects with chronic spinal cord injury and those of four able-bodied age-matched controls were scanned using multi-slice peripheral quantitative computed tomography. Images were used to develop full three-dimensional models of the tibiae in Mimics (Materialise) and exported into Abaqus (Simulia) for calculation of stress distribution and fracture risk in response to specified loading conditions – compression, bending and torsion. The percentage of elements that exceeded a calculated value of the ultimate stress provided an estimate of the risk of fracture for each subject, which differed between spinal cord injury subjects and their controls. The differences in bone mineral density distribution along the tibia in different subjects resulted in different regions of the bone being at high risk of fracture under set loading conditions, illustrating the benefit of creating individual material distribution models. A predictive tool can be developed based on these models, to enable clinicians to estimate the amount of loading that can be safely allowed onto the skeletal frame of individual patients who suffer from extensive musculoskeletal degeneration (including spinal cord injury, multiple sclerosis and the ageing population). The ultimate aim is to reduce fracture occurrence in these vulnerable groups.

A model for incorporating a clinically-feasible exercise test in paraplegic annual reviews: a tool for stratified cardiopulmonary stress performance classification and monitoring

Objectives: (i) To identify and characterize an exercise test for use in routine spinal cord injury clinical review, and (ii) to describe levels of, and factors affecting, cardiopulmonary stress performance during exercise in the chronic paraplegic population in Scotland, UK. Design: Cross-sectional study. Setting: Queen Elizabeth National Spinal Injuries Unit (Glasgow, Scotland). Patients: 48 subjects with chronic paraplegia resulting from spinal cord injury at neurological levels T2-L2. Methods: Peak oxygen uptake, peak power output, gas exchange threshold and peak heart rate were determined from an incremental arm-cranking exercise test. Using a general linear model, the effects of gender, high (injury level above T6) versus low paraplegia, time since injury, body mass and age on peak oxygen uptake and peak power output were investigated. Results: All 48 subjects completed the arm-cranking exercise test, which was shown to be practical for fitness screening in paraplegia. Men (n=38) had a peak oxygen uptake of 1.302 ± 0.326 l.min-1 (mean ± SD) and peak power output of 81.6 ± 23.2W, which was significantly higher than for women (n=10), at 0.832 ± 0.277 l.min-1 and 50.1 ± 27.8 W, respectively. There was large intersubject variability in cardiopulmonary performance during arm-cranking exercise testing, but the overall mean for the Scottish population was lower than reference values from other countries. Conclusions: Arm-cranking exercise tests are feasible in the clinical environment. The motivation for their implementation is threefold: (i) to determine cardiopulmonary stress performance of individual paraplegic patients, (ii)