Showing papers in "Journal of Rehabilitation Research and Development in 2000"

Treadmill training of paraplegic patients using a robotic orthosis

Abstract: Recent studies have confirmed that regular treadmill training can improve walking capabilities in incomplete spinal cord-injured subjects. At the beginning of this training the leg movements of the patients have to be assisted by physiotherapists during gait on the moving treadmill. The physical capabilities and the individual experience of the therapists usually limit this training. A driven gait orthosis (DGO) has been developed that can move the legs of a patient in a physiological way on the moving treadmill. The orthosis is adjustable in size so different patients can use it. Actuators at the knee and hip joints are controlled by a position controller. With the DGO the legs of patients with different degrees of paresis and spasticity could be trained for more than half an hour, and physiological gait patterns were obtained.

Development of robots for rehabilitation therapy: the Palo Alto VA/Stanford experience.

Abstract: For over 25 years, personal assistant robots for severely disabled individuals have been in development More recently, using robots to deliver rehabilitation therapy has been proposed This paper summarizes the development and clinical testing of three mechatronic systems for post-stroke therapy conducted at the VA Palo Alto in collaboration with Stanford University We describe the philosophy and experiences that guided their evolution Unique to the Palo Alto approach is provision for bimanual, mirror-image, patient-controlled therapeutic exercise Proof-of-concept was established with a 2-degree-of-freedom (DOF) elbow/forearm manipulator Tests of a second-generation therapy robot producing planar forearm movements in 19 hemiplegic and control subjects confirmed the validity and reliability of interaction forces during mechanically assisted upper-limb movements Clinical trials comparing 3-D robot-assisted therapy to traditional therapy in 21 chronic stroke subjects showed significant improvement in the Fugl-Meyer (FM) measure of motor recovery in the robot group, which exceeded improvements in the control group

Increasing Productivity and Quality of Care : Robot-aided Neuro Rehabilitation

Abstract: This paper presents an overview of our research in robot-aided stroke neuro-rehabilitation and recovery. At the onset of this research we had to confront squarely (and solve!) a critical question: If anatomy is destiny, can we influence it? Our efforts over the last five years have been focused on answering this question and we will present a few of our clinical results from over 2,000 hours of robot-aided therapy with 76 stroke patients. To determine if exercise therapy influences plasticity and recovery of the brain following a stroke, we needed the appropriate "microscope" that would allow us to concomitantly control the amount of therapy delivered to a patient, while objectively measuring patient's performance. Back-driveable robots are the key enabling technology. Our results to date using common clinical scales suggest that robot-aided sensorimotor training does have a genuinely positive effect on reduction of impairment and the reorganization of the adult brain. Yet while clinical scales can help us to examine the impact in the neuro-recovery process, their coarse nature requires extensive and time-consuming trials, and on top of that they fail to show us details important for optimizing therapy. Alternative, robot-based scales offer the potential benefit of new finer measurements-and deeper insight into the process of recovery from neurological injury. We also plan to use present technology to establish the practicality and economic feasibility of clinician-supervised, robot-administered therapy, including classroom therapy. We feel quite optimistic that the march of progress will accelerate substantially in the near future and allow us to transfer this technology from the research realm to the everyday treatment of stroke survivors.

A mechanized gait trainer for restoration of gait.

Abstract: The newly developed gait trainer allows wheel-chair-bound subjects the repetitive practice of a gait-like movement without overstressing therapists. The device simulates the phases of gait, supports the subjects according to their abilities, and controls the center of mass (CoM) in the vertical and horizontal directions. The patterns of sagittal lower limb joint kinematics and of muscle activation for a normal subject were similar when using the mechanized trainer and when walking on a treadmill. A non-ambulatory hemiparetic subject required little help from one therapist on the gait trainer, while two therapists were required to support treadmill walking. Gait movements on the trainer were highly symmetrical, impact free, and less spastic. The vertical displacement of the CoM was bi-phasic instead of mono-phasic during each gait cycle on the new device. Two cases of non-ambulatory patients, who regained their walking ability after 4 weeks of daily training on the gait trainer, are reported.

Adequacy of power wheelchair control interfaces for persons with severe disabilities: a clinical survey.

Abstract: The extreme difficulty with which persons with severe disabilities have been taught to maneuver a power wheelchair has been described in case studies, and anecdotal evidence suggests the existence of a patient population for whom mobility is severely limited if not impossible given currently available power wheelchair control interfaces. Since our review of the literature provided little evidence either in support or refutation of the adequacy of existing power wheelchair control interfaces, we surveyed 200 practicing clinicians, asking them to provide information about their patients and to give their impressions of the potential usefulness of a new power wheelchair navigation technology. Significant survey results were: Clinicians indicated that 9 to 10 percent of patients who receive power wheelchair training find it extremely difficult or impossible to use the wheelchair for activities of daily living. When asked specifically about steering and maneuvering tasks, the percentage of patients reported to find these difficult or impossible jumped to 40. Eighty-five percent of responding clinicians reported seeing some number of patients each year who cannot use a power wheelchair because they lack the requisite motor skills, strength, or visual acuity. Of these clinicians, 32 percent (27 percent of all respondents) reported seeing at least as many patients who cannot use a power wheelchair as who can. Nearly half of patients unable to control a power wheelchair by conventional methods would benefit from an automated navigation system, according to the clinicians who treat them. We believe these results indicate a need, not for more innovation in steering interfaces, but for entirely new technologies for supervised autonomous navigation.

The Timed Get-up-and-Go test revisited: measurement of the component tasks

Abstract: The "Timed Get-up-and-Go" (TGUG) test measures the overall time to complete a series of functionally important tasks. In the "Expanded Timed Get-up-and-Go" (ETGUG) test, times for the component tasks are measured using a multimemory stopwatch. Results from the ETGUG test were compared to those from the TGUG test on three groups of subjects: nonimpaired young, nonimpaired elderly, and elderly subjects at risk of falling. Significant differences were found between the two control groups and the at-risk group for all components of the test. Walking speed was the only measurement found to be significantly different between the young and elderly controls. The ETGUG test is a sensitive and objective assessment of function that requires minimal equipment, training, or expense. It better isolates functional deficits, thereby aiding the clinician in devising prevention strategies and guiding both treatment and further testing.

Continuous passive motion (CPM): theory and principles of clinical application.

Abstract: Stiffness following surgery or injury to a joint develops as a progression of four stages: bleeding, edema, granulation tissue, and fibrosis. Continuous passive motion (CPM) properly applied during the first two stages of stiffness acts to pump blood and edema fluid away from the joint and periarticular tissues. This allows maintenance of normal periarticular soft tissue compliance. CPM is thus effective in preventing the development of stiffness if full motion is applied immediately following surgery and continued until swelling that limits the full motion of the joint no longer develops. This concept has been applied successfully to elbow rehabilitation, and explains the controversy surrounding CPM following knee arthroplasty. The application of this concept to clinical practice requires a paradigm shift, resulting in our attention being focused on preventing the initial or delayed accumulation of periarticular interstitial fluids.

A practical EMG-based human-computer interface for users with motor disabilities.

Abstract: In line with the mission of the Assistive Technology Act of 1998 (ATA), this study proposes an integrated assistive real-time system which "affirms that technology is a valuable tool that can be used to improve the lives of people with disabilities." An assistive technology device is defined by the ATA as "any item, piece of equipment, or product system, whether acquired commercially, modified, or customized, that is used to increase, maintain, or improve the functional capabilities of individuals with disabilities." The purpose of this study is to design and develop an alternate input device that can be used even by individuals with severe motor disabilities. This real-time system design utilizes electromyographic (EMG) biosignals from cranial muscles and electroencephalographic (EEG) biosignals from the cerebrum's occipital lobe, which are transformed into controls for two-dimensional (2-D) cursor movement, the left-click (Enter) command, and an ON/OFF switch for the cursor-control functions. This HCI system classifies biosignals into "mouse" functions by applying amplitude thresholds and performing power spectral density (PSD) estimations on discrete windows of data. Spectral power summations are aggregated over several frequency bands between 8 and 500 Hz and then compared to produce the correct classification. The result is an affordable DSP-based system that, when combined with an on-screen keyboard, enables the user to fully operate a computer without using any extremities.

Time-dependent effects of intermittent hydrostatic pressure on articular chondrocyte type II collagen and aggrecan mRNA expression.

Abstract: The normal loading of joints during daily activities causes the articular cartilage to be exposed to high levels of intermittent hydrostatic pressure. This study quantified effects of intermittent hydrostatic pressure on expression of mRNA for important extracellular matrix constituents. Normal adult bovine articular chondrocytes were isolated and tested in primary culture, either as high-density monolayers or formed aggregates. Loaded cells were exposed to 10 MPa of intermittent hydrostatic pressure at a frequency of 1 Hz for periods of 2, 4, 8, 12, and 24 hrs. Other cells were intermittently loaded for a period of 4 hrs per day for 4 days. Semiquantitative reverse transcription polymerase chain reaction assays were used to assess mRNA signal levels for collagen types II and I and aggrecan. The results showed that type II collagen mRNA signal levels exhibited a biphasic pattern, with an initial increase of approximately five-fold at 4 and 8 hrs that subsequently decreased by 24 hrs. In contrast, aggrecan mRNA signal increased progressively up to three-fold throughout the loading period. Changing the loading profile to 4 hrs per day for 4 days increased the mRNA signal levels for type II collagen nine-fold and for aggrecan twenty-fold when compared to unloaded cultures. These data suggest that specific mechanical loading protocols may be required to optimally promote repair and regeneration of diseased joints.

Effect of exercise on perceived quality of life of individuals with Parkinson's disease

Abstract: The purpose of this study was to determine if individuals with Parkinson's disease (PD) who completed an 8-week, supervised PoleStriding exercise program would undergo significant improvements in cognitive skills, activities of daily living, motor function, and quality of life. The Unified Parkinson's Disease Rating Scale (UPDRS) and the Parkinson's Disease Questionnaire (PDQ-39) were used to measure functional independence. Six male volunteers (72.7+/-3.7 years of age) performed PoleStriding exercise three times per week for 37+/-3 minutes. Differences in the participants' pre- and post-training scores on the UPDRS and PDQ-39 were analyzed using the Wilcoxin Signed Ranks Test. A statistically significant improvement occurred in the UPDRS (P<0.026) and PDQ-39 (P<0.028) scores following the moderate-intensity exercise intervention. The results of this nonrandomized clinical trial indicate that an 8-week individualized PoleStriding exercise program increases perceived functional independence and quality of life in individuals with PD.

Mechanobiology in the development, maintenance, and degeneration of articular cartilage.

Abstract: During skeletal development, the establishment of a layer of cartilage at the ends of long bones is intimately linked to the process of endochondral ossification. Previous in vivo studies and computer models suggest that mechanobiological factors can play a key role in modulating cartilage growth and ossification. Specifically, intermittent hydrostatic pressure is thought to maintain cartilage, and shear stresses encourage cartilage destruction and ossification. In the present investigation we examined the combined effects of hydrostatic pressure and shear stress--in the form of an osteogenic index--on the development of a layer of articular cartilage, using an idealized finite element computer model. The results of our analyses provide further support for the view that mechanobiological factors play a key role in regulating the distribution of cartilage thickness and in maintaining a stable cartilage layer at maturity. The model predicts that joints that experience higher contact pressures will have thicker cartilage layers. These predictions are consistent with observations of cartilage thickness in both humans and animals. Variations in articular mechanical load are predicted to modulate cartilage thickness. These results are consistent with the view that the mechanobiological factors responsible for the development of diarthrodial joints eventually lead to cartilage degeneration and osteoarthritis (OA) with aging.

A preliminary investigation of pelvic obliquity patterns during gait in persons with transtibial and transfemoral amputation.

Abstract: Differences in pelvic obliquity between small groups of persons with unilateral lower limb amputation and subjects without amputation were analyzed. Kinematic walking data were collected as six males with transtibial amputation and three males with transfemoral amputation walked over a range of speeds. The pelvic obliquity patterns and amplitudes from the groups with amputation were compared to normal data. Results showed that smaller peak-to-peak amplitudes of pelvic obliquity were associated with higher amputation levels. Pelvic drop during early prosthetic-limb stance tended to be smaller than during early sound-limb stance. Most of the subjects with amputation exhibited an obliquity pattern in which the hip on the prosthetic side was raised above the stance-side hip during prosthetic swing phase, indicative of a compensatory action known as hip-hiking. The subjects with transfemoral amputation exhibited this hip-hiking pattern during sound-limb swing phase as well. Results from this study suggest that further investigation is required to determine those limitations of current prosthetic technology that adversely affect pelvic obliquity in the gait of persons with amputation, and to determine if significant benefit can be realized by restoring a normal pattern of pelvic obliquity to the gait of persons with amputation.

Differential effects of embryonic immobilization on the development of fibrocartilaginous skeletal elements.

Abstract: The importance of mechanical influences during skeletal development has been well established in both experimental studies and computer models. Under conditions of embryonic immobilization, it has been observed that the early stages of joint formation proceed normally (up to and including interzone formation), but the later stages of joint cavitation and maintenance are impaired, resulting in fusion of the cartilaginous elements across the presumptive joint line. Two structures in particular are noticeably absent from late-stage synovial joints in immobilized chick embryos: the menisci of the tibiofemoral joint and the plantar tarsal sesamoid of the tibiotarsal joint. Both of these fibrocartilaginous structures are known to serve mechanical functions in postnatal animals, helping to distribute loads within the joint and, in the case of sesamoid structures, to provide a mechanical advantage to muscles acting across the joint. We demonstrate in this study that embryonic immobilization differentially affects the developmental fate of these two distinct fibrocartilages. The absence of the plantar tarsal sesamoid in late-stage immobilized embryos is due to a failure in the initial formation of this structure. In contrast, the early stages of meniscus formation proceed normally. Without the normal mechanical stimuli of skeletal muscle contractions, however, the meniscus fails to mature and ultimately degenerates.

Bone mineral and geometric changes through the femur with immobilization due to spinal cord injury.

Abstract: This cross-sectional study describes bone mineral and geometric properties of the midshaft and distal femur in a control population and examines effects of immobilization due to spinal cord injury (SCI) at these skeletal sites. The subject populations were comprised of 118 ambulatory adults (59 men and 59 women) and 246 individuals with SCI (239 men and 7 women); 30 of these were considered to have acute injury (SCI duration <1 year). Bone mineral density (BMD) was assessed at the femoral neck, and midshaft and distal femur by dual energy absorptiometry. Geometric properties, specifically cortical area, polar moment of inertia, and polar section modulus, were estimated at the midshaft from cortical dimensions obtained by concurrent radiography. Reduction in BMD was noted in all femoral regions (27%, 25%, and 43% for femoral neck, midshaft, and distal femur, respectively) compared with controls. In contrast, although endosteal diameter was enlarged, geometric properties were not significantly reduced in the midshaft attributable to the age-related increase in periosteal diameter. These results suggest that simultaneous assessment of bone mineral and geometric properties may improve clinically relevant evaluation of skeletal status.

Methods for evaluating the progression of osteoarthritis.

Abstract: This article discusses methods for evaluating the progression of osteoarthritis through dynamic functional imaging as opposed to current static techniques. Comparison is made between static and dynamic methods of evaluating knee alignment. The correlation between dynamic knee moments during gait and bone mineral content is discussed. Knee loading is considered in terms of high tibial osteotomy, knee braces, pain, and non-steroidal anti-inflammatory drugs. New image-processing techniques for quantitating cartilage loss are described, and computational methods for generating true three-dimensional (3-D) maps of cartilage thickness are developed. Finally, new approaches to cross-correlate magnetic resonance images with kinematic measurements are described. These new techniques promise to become powerful diagnostic tools to detect and characterize pathological load distributions across articular cartilage.

A body-powered functional upper limb orthosis.

Abstract: This paper describes the development and preliminary testing of a functional upper-limb orthosis for people that have limited strength in their arms. This is symptomatic of conditions such as muscular dystrophy (MD), spinal muscular atrophy (SMA), and partial spinal cord injury. The exoskeletal orthosis is wheelchair mounted, has two links and four degrees of freedom. It uses linear elastic elements to balance out the effects of gravity in three dimensions. Preliminary results on testing with ten subjects will be presented.

Voltage-gated sodium channels and the molecular pathogenesis of pain: a review.

Abstract: Pain pathways begin with spinal sensory (dorsal root ganglion, DRG) neurons that produce nociceptive signals and convey them centrally. Following injury to the nervous system, DRG neurons can become hyperexcitable, generating spontaneous action potentials or abnormal high-frequency activity that contributes to chronic pain. Because the generation of action potentials in DRG neurons depends on voltage-gated sodium channels, an understanding of the expression and function of these channels in DRG neurons is important for an understanding of pain. Molecular studies have indicated that at least eight distinct voltage-gated sodium channels, sharing a common overall motif but encoded by different genes that endow them with different amino acid sequences, are present within the nervous system. The DRG neurons express six different sodium channels, including several sensory-neuron-specific sodium channels that are not present at significant levels within other parts of the nervous system. Following injury to their axons within peripheral nerve, DRG neurons down-regulate some sodium channel genes, and up-regulate others. As a result, a different repertoire of sodium channels is inserted into the DRG neuron cell membrane following injury, which is a molecular change that is accompanied by changes in physiological properties that contribute to hyperexcitability in these cells. Sodium channel expression is also altered in experimental models of inflammatory pain. The multiplicity of sodium channels, and the dynamic nature of their expression, makes them important targets for pharmacologic manipulation in the search for new therapies for pain.

Compelled weightbearing in persons with hemiparesis following stroke: the effect of a lift insert and goal-directed balance exercise.

Abstract: The hypotheses have been tested that 1) symmetry of weightbearing in persons who have sustained a stroke could be improved by the addition of a lift to the shoe on the non-paretic lower limb and 2) compelled weightbearing resulting from the addition of a lift in conjunction with targeted exercise helps to overcome the learned disuse of the paretic limb. Weightbearing on the paretic side was measured in eight persons with hemiparesis during quiet standing and in conditions of compelled weight shift. Compelled weight shifts were applied with special lifts to the shoe on the non-paretic limb of the subjects. An increase in symmetrical weightbearing was recorded in conditions of compelled weight shifts: 10-mm lift provided the best symmetry of bipedal standing. We suggest that improved symmetry of bipedal standing obtained with the lift of the non-paretic limb would help in overcoming the learned disuse of the affected limb. Pre- and post-test results of a person with hemiparesis who was wearing a shoe lift on the non-paretic limb during a 6-week physical therapy program showed statistically significant improvement of walking speed, stride length, and weightbearing. Such findings support the idea of using compelled weightbearing via lifting and targeted exercise during treatment.

Trends in lower limb amputation in the Veterans Health Administration, 1989-1998

Abstract: Objective; To assess trends in lower limb amputation performed in Veterans Health Administration (VHA) facilities. Methods: All lower limb amputations recorded in the Patient Treatment File for 1989-1998 were analyzed using the hospital discharge as the unit of analysis. Age-specific rates were calculated using the VHA user-population as the denominator. Frequency tables and linear, logistic, and Poisson regression were used respectively to assess trends in amputation numbers, reoperation rates, and age-specific amputation rates. Results: Between 1989-1998, there were 60,324 discharges with amputation in VHA facilities. Over 99.9% of these were in men and constitute 10 percent of all US male amputations. The major indications were diabetes (62.9%) and peripheral vascular disease alone (23.6%). The age-specific rates of major amputation in the VHA are higher than US rates of major amputation. VHA rates of major and minor amputation declined an average of 5% each year, while the number of diabetes-associated amputations remained the same. Conclusion: The number and age-specific rates of amputations decreased over 10 years despite an increase in the number of veterans using VHA care.

A model of mechanobiologic and metabolic influences on bone adaptation.

Abstract: Bone adaptation, the process through which bone mass is modified in the body, plays a key role in the development of osteoporosis. Bone adaptation is known to be influenced by both mechanical and metabolic stimuli. Previous studies have concentrated on changes in bone adaptation caused by mechanical stimuli (mechanobiologic influences), yet current treatments for osteoporosis depend significantly on metabolic influences. We develop a theoretical model of bone adaptation that accounts for both mechanobiologic and metabolic influences. We demonstrate the utility of this model using a simulation of the cellular processes of bone adaptation on a representative volume of cancellous bone. Our long-term objective is the development of a more comprehensive computational model that will aid in the study of osteoporosis and other bone diseases.

Osteoporosis and bone functional adaptation: mechanobiological regulation of bone architecture in growing and adult bone, a review.

Abstract: During life, bone is continually optimized for its load-bearing role by a process of functionally adaptive (re)modelling. This process, which is more active in growing bone, is dominated by high-magnitude, high-rate strains, presented in an unusual distribution. Adaptation occurs at an organ level, involving changes in whole bone architecture and bone mass. The repetitive coordinated bone loading associated with habitual activity may have little role in the preservation of bone mass, and may even reduce the osteogenic potential of an otherwise highly osteogenic stimulus. Cells of the osteocyte/osteoblast network are best placed to appreciate mechanical strain. Among the strain-related responses they show, is a reduced rate of apoptosis. This may serve to regulate and target osteoclast activity. A more complete understanding of the stimuli and pathways involved in both the physiology and pathology of this structural homeostatic mechanism will allow the design of more appropriate exercise regimens and targeted pharmacological interventions to limit morbidity and mortality by reducing bone fragility.

Force-directed design of a voluntary closing hand prosthesis.

Abstract: This paper presents the design of a body-powered voluntary closing prosthetic hand. It is argued that the movement of the fingers before establishing a grip is much less relevant for good control of the object held than the distribution of forces once the object has been contacted. Based on this notion, the configurations of forces on the fingers and the force transmission through the whole mechanism were taken as a point of departure for the design, rather than movement characteristics. For a good distribution of pinching forces on the object and a natural behavior, the prosthesis is made adaptive and flexible. To achieve good force feedback, the disturbing influences of the cosmetic glove are strongly reduced by a compensation mechanism. To further improve the transmission of forces, friction is reduced by furnishing the whole mechanism with rolling links. This force-directed design approach has led to a simple mechanism with low operating force and good feedback of the pinching force.

Influence of trunk flexion on biomechanics of wheelchair propulsion.

Abstract: Propulsion styles that are characterized by high stresses may influence the susceptibility of manual wheelchair users (MWCU) to upper limb injury. An experimental, cross-sectional study was designed to compare physiological and biomechanical characteristics of wheelchair propulsion in two groups of MWCU-a trunk flexion propulsion style group (FG) and a non-trunk flexion propulsion style group (NFG)-across fresh and fatigued states. Data on joint kinetics and kinematics, handrim kinetics, propulsion temporal characteristics, and electromyography were collected at the fresh and fatigued states, and oxygen uptake was collected continuously, to characterize wheelchair propulsion performance of 19 MWCU during a sub-maximal exercise test to exhaustion. The FG was characterized by a more flexed trunk position accompanied by greater shoulder flexion and elbow extension (p<0.05), which was accentuated with fatigue when compared to the NFG. When fatigued, marked decreases (p<0.05) in key propulsion muscle activity were observed in the FG, but not in the NFG. Temporally, the FG decreased contact time on the handrim by 1 percent of the propulsion cycle when fatigued, in contrast to the NFG who increased contact time by 7 percent (p<0.05). Results suggest that a trunk flexion style of wheelchair propulsion may lead to potentially debilitating upper limb injury, since these individuals appear to be compensating for peripheral muscle fatigue.

Comparative biomechanical evaluation of different wheelchair seat cushions.

Abstract: The aim of the present study was to perform a comparative biomechanical analysis of four antidecubitus wheelchair cushions. Thirty wheelchair users were considered divided into three groups: paraplegic subjects (with no cutaneous sensation), neurologic subjects (with intact cutaneous sensation), and elderly subjects. The biomechanical evaluation was performed using a piezoresistive sensor matrix system to quantify parameters referred to pressure distribution, seating surface and posture. Dedicated software was developed for the automatic elaboration of the raw data and the computation of the parameters of interest. Differences among cushion types and subject groups were analyzed. An analysis of time-transient behaviors was also performed. Results showed that no significant differences in pressure peak reduction were found among the four cushions. Moreover, no time-transient behavior was shown by any cushions. However, both the location of pressure peaks and posture were dependent on cushion types. Comparison of the three subject groups showed that elderly subjects had the highest mean pressure and the lowest contact surface, while paraplegics presented the highest pressure peaks. This procedure appears indicated for individualizing the prescription of a wheelchair cushion and even for customizing a cushion to induce a specific posture.

The mechanobiology of cancellous bone structural adaptation.

Abstract: The distinguishing morphological feature of cancellous bone is its high level of porosity relative to cortical bone. This porosity leads to more free surfaces and thus to more of the cellular constituents that inhabit those surfaces. As a result, cancellous bone is often more metabolically active and responsive to stimuli than cortical bone. This extends to the relationship between cancellous bone's internal structure and external mechanical loading. Observational investigations established this relationship as early as the late 19th century. These findings point to the interplay between biology and the cellular mechanical environment, forming the underpinnings of the modern term mechanobiology. Interestingly, it has proven to be more straightforward to assay the biological response than to quantify the precise mechanical environment of cancellous bone and the influence of cancellous bone structure. Despite this concern, significant insights into the nature of cancellous bone mechanobiology can be obtained from computational simulations that allow investigators to determine the morphological consequences of quantitative assumptions about cancellous bone mechanobiology. As the power of computers and the sophistication of these modeling techniques continue to grow, we can expect an increased impact in terms of clinical diagnosis and treatment. The next decade will bring improvements in exercise interventions to prevent and reverse bone loss; improved replacement-joint designs, particularly for those joints currently having poor expected outcomes; and an integration of computer simulation technology with clinical scanners.

Musculoskeletal health and the older adult.

Abstract: A decline in muscle mass and function, and in the mass and integrity of the skeletal system, are well-known consequences of aging. These changes impinge on the functional performance required for independent living and contribute to frailty and fracture risk. Resistance exercise has been shown to be an effective mode to circumvent age-related changes in the muscular system, although the benefit of exercise on bone mass in the aging skeleton is comparatively modest at best. This brief review highlights results from several studies that we have undertaken in older adults, examining aspects of the resistance training prescription as well as the potential beneficial role of hormones. What is common to all of these studies is the high degree of residual plasticity that remains in aging skeletal muscle. Risk factors for falls and fracture include reduced bone mass, muscle weakness, impaired balance, and lessened visual acuity. Among these, only muscle strength is reliably enhanced with resistance exercise, which may aid in reducing hip fracture risk as well as improving the ability to undertake daily activities and maintain independence.

Altered motor control and spasticity after spinal cord injury: subjective and objective assessment.

Abstract: This study of measures of spasticity, or altered motor control, compares the clinically used Ashworth scale with a method based on surface electromyographic (sEMG) recordings called brain motor control assessment (BMCA) in a group of 97 subjects with spinal cord injury (SCI) and varying levels of motor dysfunction. In this paper, we describe how sEMG-derived scores relate to the severity of spasticity as judged clinically. When sEMG data from passive movements from the BMCA were analyzed by Ashworth category, we found that when the sEMG data were averaged for a limb, there was a significant difference between scores for those with Ashworth 0 vs. 2 and 3, and 1 vs. 2 and 3 (p<0.001), but not between 0 and 1. Analysis of the individual muscle scores improved the discrimination between Ashworth categories. Superiority of sEMG data over Ashworth category as an objective quantification of altered motor control ("spasticity") is argued.

Mechanobiology of tendon adaptation to compressive loading through fibrocartilaginous metaplasia.

Abstract: Tendons that wrap around bones often undergo fibrocartilaginous metaplasia. In this paper, we examine the biomechanical causes and consequences of this metaplasia. We propose an adaptation rule in which tissue permeability changes in response to local cyclic hydrostatic pressures associated with physical activity. The proposed rule predicts the development of a low-permeability region corresponding to the fibrocartilaginous region in a representative wrap-around tendon. A poroelastic finite element model is used to examine the time-dependent fluid pressures and compressive stresses and strains in the solid constituents of the tendon's extrafibrillar matrix. The low permeability in the adapted fibrocartilaginous region maintains fluid pressures, protecting the solid constituents of the tendon's extracellular matrix from high compressive stresses and strains that could disrupt the matrix organization. Adaptation through fibrocartilaginous metaplasia therefore allows wrap-around tendons to function effectively over a lifetime without sustaining excessive mechanical damage due to cyclic compressive loading.

The effectiveness of neurological rehabilitation in multiple sclerosis.

Abstract: The difficulties inherent in demonstrating the effectiveness of an intervention that is as all-inclusive and poorly defined as neurorehabilitation, especially in a condition as unpredictable and variable as Multiple Sclerosis (MS), are not to be underestimated. They require strict adherence to rigorous methodology and, in particular, the consistent use of a range of clinically appropriate and scientifically sound measures of outcome. Incorporating this approach, it is possible to evaluate rehabilitation at four different levels, including (1) the broadest concept of service delivery; (2) packages of comprehensive care; (3) individual components of the package; and finally, (4) the intrinsic elements of the rehabilitation process. Most recent studies have focused on in-patient rehabilitation and have demonstrated benefits across disability, handicap, and quality of life in patients with mild to severe disability. Such benefits persist following discharge into the community. Studies evaluating service delivery and components of the rehabilitation package are in progress, but few investigators have taken on the intrinsic elements or 'black box' of rehabilitation. These recent studies underline the fact that the evaluation of rehabilitation is feasible. Such studies are important, not simply to justify funding but to ensure continuing improvement of the way in which MS is managed.

Tendon and ligament adaptation to exercise, immobilization, and remobilization.

Abstract: This study provides a theoretical and computational basis for understanding and predicting how tendons and ligaments adapt to exercise, immobilization, and remobilization. In a previous study, we introduced a model that described the growth and development of tendons and ligaments. In this study, we use the same model to predict changes in the cross-sectional area, modulus, and strength of tendons and ligaments due to increased or decreased loading. The model predictions are consistent with the results of experimental exercise and immobilization studies performed by other investigators. These results suggest that the same fundamental principles guide both development and adaptation. A basic understanding of these principles can contribute both to prevention of tendon and ligament injuries and to more effective rehabilitation when injury does occur.