Ossur Scientific E-letter
30 March 2009
Ossur Academy's scientific E-letter Issue #1 2009
Dear readers
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Hope the year of 2009 has started in harmony and welcome to the first issue of our Scientific E-letter of 2009. We are happy to share pertinent and interesting scientific news with you!
This E-letter includes nine different scientific papers. The articles cover the subjects of amputation/rehabilitation, prosthetics/biomechanics, orthotics/biomechanics and bionics.
Five of the selected papers have been published in 2009, three in 2008 and one in 2006.
Enjoy the reading!
Amputation/Rehabilitation
Johannesson A. Larsson G-U. Ramstrand N. Turkiewicz A. Wiréhn A-B. Atroshi I. Incidence of Lower Limb Amputation in the diabetic and nondiabetic general population: A 10-year Population-based Cohort Study of Initial, Contralateral and Re-amputations
Diabetes Care 32:275-280, 2009
Severe peripheral arterial disease causing critical ischemia is a common reason for performing lower limb amputations. By estimating the incidence of vascular lower limb amputation (LLA) in diabetic and nondiabetic persons, important information regarding changes in the incidence over time can be provided. This can assist in the planning of preventative care and rehabilitation and facilitate assessment of the effects of interventions, such as arterial reconstruction and amputation at specific levels. It can also have an effect on the success of prosthetic rehabilitation.
Johannesson and his study group have compared the incidence of lower limb amputation (LLA) in the at-risk diabetic and nondiabetic general population by performing a population-based cohort study. In an area of Sweden all vascular LLA performed from 1997 through 2006 were consecutively registered and classified into initial amputation, reamputation or contra lateral amputation. Upon these facts estimations were calculated as incidences in the diabetic and non-diabetic general population aged 45 years or older.
The results of the calculations showed that the incidence per 100,000 person-years in the at-risk general population was for diabetic women 192 and for diabetic men 197 and for non-diabetic women 22 and for non-diabetic men 24. The incidence increased from the age of 75 years. 74% of all amputations were at transtibial level.
The incidence of reamputation and of contra lateral amputation per 100 amputee-years in diabetic women amputees was 16 and 15 and among diabetic men 21 and 18, respectively. The corresponding rates in non-diabetic women amputees were 18 and 14 and among men 24 and 13, respectively.
The authors could conclude from the result of their study that the incidence of vascular LLA, at or above transmetatarsal level, in the general population aged 45 years or older is 8 times higher in persons with diabetes than in those without diabetes. Further they concluded that one in four amputees may require reamputation and/or contralateral amputation.
Mulvey M.R. Fawkner H.J. Radford H. Johnson M.I.The use of transcutaneous electrical nerve stimulation (TENS) to aid perceptual embodiment of prosthetic limbs
Medical Hypotheses Volume 72, Issue 2, February 2009, Pages 140-142
Mulvey and colleagues reports in this article about a hypothesis how to facilitate the process of perceptual embodiment of a prosthesis into the body schema of amputees by using non-invasive transcutaneous electrical nerve stimulation (TENS). Electrical stimulation of afferent nerves using implanted electrodes can generate sensations of touch, joint movement, and position, in the missing, phantom limbs of amputees. This hypothesis was based on the fact that integration of prosthetic limb awareness into body schema was likely to aid manual control of the prosthesis. Clinicians have earlier used techniques to generate mechanical, visual and/or auditory feedback related to stimulation of the stump and proximal residual limb to improve prosthetic limb awareness.
The study group used a modified version of the rubber hand illusion (RHI), and found that TENS paraesthesiae could be made to feel like it was coming from a prosthetic hand in healthy participants with intact limbs. In addition the authors reported that participants described perceptual embodiment of the prosthetic hand into their own body schema, i.e. it felt as if it is part of their body.
Mulvey et al predicted that projecting TENS paraesthesiae into the prosthetic limb(s) of amputees will offer sufficient sensory input to facilitate perceptual embodiment. They meant it could prove to be a simple and inexpensive training aid to improve ambulation and prosthesis success.
Prosthetics/Biomechanics
Hansen, Andrew (2008)'Effects of alignment on the roll-over shapes of prosthetic feet',
Prosthetics and Orthotics International, 32:4,390 — 402
Hansen has in this study investigated two hypothesises. Firstly that prosthesis foot roll-over shapes are translated and rotated in prosthesis coordinates with corresponding alignment changes. Secondly that change in alignment does not significantly affect the radius or arc length of the prosthetic foot’s roll over shape.
The author examined the effects of nine alignment settings on the roll-over shapes of two prosthetic feet with dissimilar mechanical properties. The feet were loaded in different extreme alignments. To measure the roll over shape the feet were rolled, from heel to toe loading, over a force plate.
The result of the study supported the first hypothesis; the idea that alignment changes move and rotate roll-over shapes of prosthetic feet in prosthesis coordinates. The second hypothesis, which the radius of curvature and arc length do not change for different alignments, was not strongly supported by the data.
The author means that a greater understanding of the best alignment for prosthesis components will enhance the quality of fitting and may also lead to alignment schemes that would allow prosthetists to build the right alignment into the prosthesis thus avoiding time consuming, costly and heavy alignment processes.
Portnoy S. Yizhar Z. Shabshin N. Itzchak Y.Kristal A. Dotan-Marom Y. Siev-Ner I. Gefen A.Internal mechanical conditions in the soft tissues of a residual limb of a trans-tibial amputee
Journal of Biomechanics 41 (2008) 1897–1909
Soft tissue complications are common problem among transtibial amputees using prosthesis. The interaction between the residual limb and the prosthetic socket causes elevated internal strains and stresses in the muscle and fat tissues in the residual limb, which may lead to deep tissue injury (DTI) and other complications.
Portnoy and colleagues aimed to characterize the mechanical conditions in the muscle flap of the residual limb of a transtibial amputated (TTA) patient after donning the prosthetic socket and during load-bearing. They meant that the knowledge of internal mechanical conditions in the muscle flap can be used to identify the risk for DTI and improve the fitting of the prosthesis.
To quantify the internal soft tissue strains and stresses a patient-specific modelling approach was used which involved an MRI scan, interface pressure measurements between the residual limb and the socket of the prosthesis and three-dimensional non-linear large-deformation finite-element (FE) modelling. Movement of the truncated tibia and fibula during load-bearing was measured by means of MRI and used as displacement boundary conditions for the FE model. Subsequently, the study group calculated the internal strains, strain energy density and stresses in the muscle flap under the truncated bones.
The result showed that internal strains under the tibia peaked at 85%, 129% and 106% for compression, tension and shear strains, respectively. Internal strains under the fibula peaked at substantially lower values; 19%, 22% and 19% for compression, tension and shear strains, respectively. Strain energy density peaked at the tibial end (104kJ/m3). The von Mises stresses peaked at 215kPa around the distal end of the tibia. Further it was found that stresses under the fibula were at least one order of magnitude lower than the stresses under the tibia.
The authors concluded that the used patient-specific modelling method was an important tool in understanding the etiology of DTI in the residual limbs of TTA patients.
Helgason B. Pálsson H. Rúnarsson T P. Frossard l. Viceconti M.Risk of failure during gait for direct skeletal attachment of a femoral prosthesis: A finite element study
Medical Engineering & Physics 2009 Jan 14
Osseointegrated attachments of prosthesis for transfemoral amputees have been the subject of clinical trials since the early nineties. This method of direct skeletal attachment gives many benefits to the amputee, such as an unrestricted range of motion around the hip joint, better sitting comfort, improved sensory feedback, improved limb control and reduced soft tissue problems. However, the length of the rehabilitation period is perceived as a weakness by the amputees and the clinicians.
Helgason and his study group wanted to estimate the risk of failure during gait for a patient with direct skeletal attachment of a femoral prosthesis, by using finite element analysis (FEA).
Material properties and loads were derived from subject-specific data and implant stability assumed secured by bone ingrowth into a porous implant surface. A simplified FEA was used to optimize the implant geometry with respect to load bearing capacity. The resulting geometry was then implemented in a subject-specific FE study.
The study group reported that the results of their study showed that the risk of failure for the implant system was approximately three times greater than what can be expected for an intact femur.
The conclusion that it is likely that a porous-coated implant could be beneficial for osseointegrated fixation was based on the calculated risk of failure factors. Further Helgason et al suggested that the proposed methodology can be used in future studies to explore mechanical stability of osseointegrated fixation in the view of improving direct skeletal attachments for lower limb amputees.
Orthotics /biomechanics
Zifchock R A. Davis I.A comparison of semi-custom and custom foot orthotic devices in high- and low-arched individuals during walking
Clin. Biomech. (2008), doi:10.1016/j.clinbiomech.2008.07.008
Foot orthotic devices are an often applied and can be a successful treatment for lower extremity injuries. However, the high cost of custom devices prevents some patients from purchasing them. Therefore less expensive, semi-custom alternative have been available.
Zifchock and Davis wanted to examine whether the semi-custom devices can provide similar rearfoot control and comfort as custom devices in individuals with excessively high- and low-arches. They collected rearfoot kinematics and comfort in three conditions: no-orthotic, custom orthotics, and semi-custom orthotics by letting thirty-seven subjects walk through a motion analysis lab.
The results indicated that both devices were effective at reducing eversion velocity and excursion. The custom device significantly decreased eversion velocity and the semi-custom device showed a trend toward decreased eversion when compared to no-orthotic condition.
In terms of comfort, high-arched individuals tended to be more comfortable in the semi-custom device in the heel and arch regions. However, the differences in comfort between the devices were generally small.
The authors interpreted the result, with respect to comfort and ability to control rearfoot motion, that the semi-custom orthotic device was a possible alternative to the custom orthotic device for high- and low-arched individuals.
Pittaccio A. Nespoli M. Pini E. Villa S. Besseghini F.
Mechanics of dropfoot rehabilitation with a shape memory alloy active splint
Journal of Biomechanics, Volume 39, Supplement 1, 2006, Pages S539-S540
Pittaccio and colleagues presented a new active splint for rehabilitation of dropfoot. They meant it may counterbalance the negative effects of prolonged AFO-supported walking through joint passive mobilisation and muscle strengthening.
The design of this orthosis was based on the biomechanical study of the ankle flexion movement through standard gait analysis techniques. A myoelectric assessment of suitable dropfoot cases was performed in order to evaluate residual tibialis anterior strength and the required range of motion.
The orthosis consisted of a plastic support, strapped onto the frontal aspect of shin and foot, and two active elements containing shape memory NiTiCu wires. The natural joint biomechanics imposed constraints on both the force and the deformation required from the actuators. In addition the investigators performed a careful choice of the alloy characteristics and thermo-mechanical treatments, as well as a validated design of the actuators.
The rehabilitation purpose of this orthosis was the training and functional recovery of the ankle flexors. As a consequence of this, the orthosis mainly activated degrees of freedom in the sagittal plane of the joint mechanical system. However the coronal and transverse plane movements were also monitored during clinical tests. In order to have a full understanding of the orthosis rehabilitative action further tests have to be performed.
The authors concluded that if recovery outcomes are satisfactory, this innovative and simple active orthosis could support, even at home, the work of physiotherapists for a better treatment of dropfoot patients.
Barrios J A. Crenshaw J R. Royer T D. Davis I S. Walking shoes and laterally wedged orthoses in the clinical management of medial tibiofemoral osteoarthritis: A one-year prospective controlled trial
The Knee Volume 16, Issue 2, March 2009, Pages 136-142
Knee osteoarthritis (OA) is a degenerative disease that affects
many. It has been estimated that the prevalence of diagnosed knee OA in the general population aged 45 years or older is at 12.5%. The high prevalence of medial tibiofemoral compartment involvement can be partially explained by that approximately 60–80% of the weight-bearing load is borne on the medial aspect of a normal knee during gait. There is no known cure for knee OA, nor are the accompanying structural changes reversible.
Barrios and colleagues wanted to examine the clinical efficacy of individually prescribed laterally wedged orthoses and walking shoes in the treatment of medial knee osteoarthritis. They performed the study by using a prospective, single-blind, block-randomized controlled design which included sixty-six subjects (29 males, 37 females, mean age 62.4 years, mean BMI 33.0kg/m2). The subjects were block-randomized to a lateral wedge (treatment) or neutral (control) orthotic group. Both groups were issued a standard walking shoe for use with the orthoses. Pain, stiffness, and functional limitations subscales of the Western Ontario and McMaster Universities index were primary outcome measures. Secondary outcome measures included the 6-minute walk distance and pain change, and stair negotiation time and pain change.
The study group found a significant interaction favouring the treatment group where pain change during the 6-minute walk was observed. The treatment group demonstrated significant improvements at both 1month and 1 year compared to baseline. The control group only demonstrated significant improvements at 1 year. No other interactions were observed. Both groups were improved at each follow-up in the WOMAC subscales for pain, stiffness, and physical function. Both groups also improved in 6-minute walk test distance, stair negotiation test time, and stair negotiation test pain change.
The authors concluded that the results indicated that both neutral and laterally wedged orthoses may be beneficial in the management of medial knee osteoarthritis when used with walking shoes. However, the addition of lateral wedging was associated with early improvements in 6-minute walk test pain change not seen in the control group.
Bionics
Kato R. Yokoi H. Arieta A H. Yu W. Arai T.
Mutual adaptation among man and machine by using f-MRI analysis
Robotics and Autonomous Systems Volume 57, Issue 2, 28 February 2009, Pages 161-166
Robot based prosthetic equipment is a developing technology that aims to support disabled in their daily lives. Today advanced robotics technology provides the device with an adaptable prosthetic controller.
Using learning paradigms, this controller can discriminate the electromyographic (EMG) signal adapting to the different characteristics of human behavior. Every person has different EMG signal patterns; in order to overcome these individual differences, the adaptable controller can make rules that describe the relationship between the EMG signal and the human intention by incremental learning. Further, a human adapts to the behaviour of the prosthetic equipment too. In the case of limb amputation, a phantom limb image remains in the brain for sometime. This image is the representation of the limb in the cerebrum cortex's motion area. This phantom image is a part of the human body image in the brain.
The human adaptation can be observed by the changes in the f-MRI images, as an effect of the interaction with the prosthetic hand application. Such an adaptation system produces mutual adaptation, and gives important insight to the concern of embodiment.
Mutual adaptation is the result of the collaboration of two or more adaptive systems that communicate with each other for the purpose of goal-directed behaviours, in this case, the human body and the adaptive prosthetic system.
Kato et al studied and described in this paper the interesting reaction of the human brain to an adaptable prosthetic system.
The adaptable prosthetic system was composed of an EMG signal controlled robot hand with an EMG pattern recognition learning function for transradial prostheses. The mutual adaptation between the system and the human body was analyzed by using functional magnetic resonance imaging (f-MRI) in order to clarify the plasticity of the motor and sensory cortex area according to the changes in the prosthetic system.
The developed prosthetic hand had 13 degrees of freedom: three motors on the thumb, two motors for each finger, and two motors for the wrist. The tactile feedback was applied by using surface electrical stimulus.
After analysis of the f-MRI data of the brain the authors observed a process of replacement from a phantom limb image to a prosthetic hand image.
Two sets of results are obtained according to the presence or absence of tactile feedback, which can be resumed in adaptation and illusion generation.
- Adaptation: Without tactile feedback from the prosthesis, the primary motor area and primary sensory area are highly activated; the study group also found activation of the Parietal lobe. They reported that this result showed that the sensory motor coordination coupled tight between visual recognition and muscle control for grasping an object. With tactile feedback, activation of the Parietal lobe decreases. This showed how the information processing load was distributed, allowing for an effective sensory motor coordination, which might produce subconscious object manipulation.
- Illusion: Without tactile feedback from the prosthesis, normal sensory motor coordination between visual servo and hand motion was obtained without generating any illusion of possession of the artificial limb. Although, the tactile feedback made a strange reaction in the sensory area. The stimulus acted on the left hand side, but the reaction of the sensory area occured on the right hand side. This reaction was a misunderstanding of tactile feedback, so it was similar to the illusion. The authors reported that this result means that the active motion control determined priority of the cortex area, and the motor area and parietal area became the supervisor for the sensor. Therefore the illusions appeared as a result of human adaptation for control of the prosthetic hand.
Össur Academy is looking forward to providing you with more interesting scientific news in June!
Thank you for reading,
Össur Academy
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