Testing silicone digit extensions as a way to suppress natural sensation to evaluate supplementary tactile feedback.

Dexterous use of the hands depends critically on sensory feedback, so it is generally agreed that functional supplementary feedback would greatly improve the use of hand prostheses. Much research still focuses on improving non-invasive feedback that could potentially become available to all prosthesis users. However, few studies on supplementary tactile feedback for hand prostheses demonstrated a functional benefit. We suggest that confounding factors impede accurate assessment of feedback, e.g., testing non-amputee participants that inevitably focus intently on learning EMG control, the EMG's susceptibility to noise and delays, and the limited dexterity of hand prostheses. In an attempt to assess the effect of feedback free from these constraints, we used silicone digit extensions to suppress natural tactile feedback from the fingertips and thus used the tactile feedback-deprived human hand as an approximation of an ideal feed-forward tool. Our non-amputee participants wore the extensions and performed a simple pick-and-lift task with known weight, followed by a more difficult pick-and-lift task with changing weight. They then repeated these tasks with one of three kinds of audio feedback. The tests were repeated over three days. We also conducted a similar experiment on a person with severe sensory neuropathy to test the feedback without the extensions. Furthermore, we used a questionnaire based on the NASA Task Load Index to gauge the subjective experience. Unexpectedly, we did not find any meaningful differences between the feedback groups, neither in the objective nor the subjective measurements. It is possible that the digit extensions did not fully suppress sensation, but since the participant with impaired sensation also did not improve with the supplementary feedback, we conclude that the feedback failed to provide relevant grasping information in our experiments. The study highlights the complex interaction between task, feedback variable, feedback delivery, and control, which seemingly rendered even rich, high-bandwidth acoustic feedback redundant, despite substantial sensory impairment.

Long-Term Non Anesthetic Preclinical Study Available Extra-Cranial Brain Activator (ECBA) System for the Future Minimally Invasive Human Neuro Modulation.

In recent years, electroceuticals have been spotlighted as an emerging treatment for various severe chronic brain diseases, owing to their intrinsic advantage of electrical interaction with the brain, which is the most electrically active organ. However, the majority of research has verified only the short-term efficacy through acute studies in laboratory tests owing to the lack of a reliable miniaturized platform for long-term animal studies. The construction of a sufficient integrated system for such a platform is extremely difficult because it requires multi-disciplinary work using state-of-the-art technologies in a wide range of fields. In this study, we propose a complete system of an implantable platform for long-term preclinical brain studies. Our proposed system, the extra-cranial brain activator (ECBA), consists of a titanium-packaged implantable module and a helmet-type base station that powers the module wirelessly. The ECBA can also be controlled by a remote handheld device. Using the ECBA, we performed a long-term non-anesthetic study with multiple canine subjects, and the resulting PET-CT scans demonstrated remarkable enhancement in brain activity relating to memory and sensory skills. Furthermore, the histological analysis and high-temperature aging test confirmed the reliability of the system for up to 31 months. Hence, the proposed ECBA system is expected to lead a new paradigm of human neuromodulation studies in the near future.

Intraneural sensory feedback restores grip force control and motor coordination while using a prosthetic hand.

OBJECTIVE: Tactile afferents in the human hand provide fundamental information about hand-environment interactions, which is used by the brain to adapt the motor output to the physical properties of the object being manipulated. A hand amputation disrupts both afferent and efferent pathways from/to the hand, completely invalidating the individual's motor repertoire. Although motor functions may be partially recovered by using a myoelectric prosthesis, providing functionally effective sensory feedback to users of prosthetics is a largely unsolved challenge. While past studies using invasive stimulation suggested that sensory feedback may help in handling fragile objects, none explored the underpinning, relearned, motor coordination during grasping. In this study, we aimed at showing for the first time that intraneural sensory feedback of the grip force (GF) improves the sensorimotor control of a transradial amputee controlling a myoelectric prosthesis. APPROACH: We performed a longitudinal study testing a single subject (clinical trial registration number NCT02848846). A stacking cups test (CUP) performed over two weeks aimed at measuring the subject's ability to finely regulate the GF applied with the prosthesis. A pick and lift test (PLT), performed at the end of the study, measured the level of motor coordination, and whether the subject transferred the motor skills learned in the CUP to an alien task. MAIN RESULTS: The results show that intraneural sensory feedback increases the subject's ability in regulating the GF and allows for improved performance over time. Additionally, the PLT demonstrated that the subject was able to generalize and transfer her manipulation skills to an unknown task and to improve her motor coordination. SIGNIFICANCE: Our findings suggest that intraneural sensory feedback holds the potential of restoring functionally effective tactile feedback. This opens up new possibilities to improve the quality of life of amputees using a neural prosthesis.

A thin-film multichannel electrode for muscle recording and stimulation in neuroprosthetics applications.

OBJECTIVE: We propose, design and test a novel thin-film multichannel electrode that can be used for both recording from and stimulating a muscle in acute implants. APPROACH: The system is built on a substrate of polyimide and contains 12 recording and three stimulation sites made of platinum. The structure is 420 µm wide, 20 µm thick and embeds the recording and stimulation contacts on the two sides of the polyimide over an approximate length of 2 cm. We show representative applications in healthy individuals as well as tremor patients. The designed system was tested by a psychometric characterization of the stimulation contacts in six tremor patients and three healthy individuals determining the perception threshold and current limit as well as the success rate in discriminating elicited sensations (electrotactile feedback). Also, we investigated the possibility of using the intramuscular electrode for reducing tremor in one patient by electrical stimulation delivered with timing based on the electromyographic activity recorded with the same electrode. MAIN RESULTS: In the tremor patients, the current corresponding to the perception threshold and the current limit were 0.7 ± 0.2 and 1.4 ± 0.7 mA for the wrist flexor muscles and 0.4 ± 0.2 and 1.5 ± 0.7 mA for the extensors. In one patient, closed-loop stimulation resulted in a decrease of the tremor power >50%. In healthy individuals the perception threshold and current limits were 0.9 ± 0.6 and 2.1 ± 0.6 mA for the extensor carpi radialis muscle. The subjects could distinguish four or six stimulation patterns (two or three stimulation sites × two stimulation current amplitudes) with true positive rate >80% (two subjects) and >60% (one subject), respectively. SIGNIFICANCE: The proposed electrode provides a compact multichannel interface for recording electromyogram and delivering electrical stimulation in applications such as neuroprostheses for tremor suppression and closed-loop myoelectric prostheses.

An Alumina Ceramic Total Talar Prosthesis for Avascular Necrosis of the Talus.

Avascular necrosis tends to occur in the talus because of poor blood supply caused by the extended coverage to the articular cartilage on its surface. Treatment is conservative in the earlier stage of this disease; however, surgical treatment is usually indicated in the advanced stage. Nonunion, leg length discrepancy, or hindfoot instability may occur in patients treated with ankle or tibio-talo-calcaneal fusion. Arthroplasty using a customized total talar prosthesis designed using the computed tomography image of contralateral talus has the potential advantages of weightbearing in the earlier postoperative phase, prevention of lower extremity discrepancy, and maintenance of joint function.

Design and Characterization of a Soft Robotic Therapeutic Glove for Rheumatoid Arthritis.

The modeling and experimentation of a pneumatic actuation system for the development of a soft robotic therapeutic glove is proposed in this article for the prevention of finger deformities in rheumatoid arthritis (RA) patients. The Rehabilitative Arthritis Glove (RA-Glove) is a soft robotic glove fitted with two internal inflatable actuators for lateral compression and massage of the fingers and their joints. Two mechanical models to predict the indentation and bending characteristics of the inflatable actuators based on their geometrical parameters will be presented and validated with experimental results. Experimental validation shows that the model was within a standard deviation of the experimental mean for input pressure range of 0 to 2 bars. Evaluation of the RA-Glove was also performed on six healthy human subjects. The stress distribution along the fingers of the subjects using the RA-Glove was also shown to be even and specific to the finger sizes. This article demonstrates the modeling of soft pneumatic actuators and highlights the potential of the RA-Glove as a therapeutic device for the prevention of arthritic deformities of the fingers.

Feasibility of Round Window Stimulation by a Novel Electromagnetic Microactuator.

INTRODUCTION: Most implantable hearing aids currently available were developed to compensate the sensorineural hearing loss by driving middle ear structures (e.g., the ossicles). These devices are successfully used in round window (RW) stimulation clinically, although this was initially not the intended use. Here, a novel microactuator, specifically designed for RW stimulation, was tested in human temporal bones to determine actuator performance and applicability. METHODS: Stapes footplate response to RW stimulation was determined experimentally in human temporal bones and the obtained sound pressure output level was estimated. RESULTS: The actuator had a flat displacement response between 0.125 and 4 kHz, a resonance between 4 and 7 kHz, and a roll-off above. At increasing contact force, the stapes footplate displacement decreased by 5-10 dB re µm for forces ≥ 2 mN. The equivalent sound pressure level between 0.125 and 4 kHz amounted to 87-97 eq dB SPL and increased to 117 eq dB SPL for frequencies of 4-7 kHz. The total harmonic distortion (THD) of the actuator ranged within 15-40% for static forces of 5 mN. CONCLUSION: The feasibility of an electromagnetic actuator that may be placed into the RW niche was demonstrated but requires further optimization in terms of THD and static force sensitivity.

The Effect of Prosthesis Use on Hand Mental Rotation After Unilateral Upper-Limb Amputation.

Amputation of a limb induces changes in the so-called body schema, which might be influenced by the use of prosthetic devices. Changes in the body representation associated with prosthesis use could be investigated using a hand mental rotation task. However, direct neurophysiologic evidence for the effect of prosthesis use on hand mental rotation is still lacking. In this paper, we recruited two groups of unilateral upper-limb amputees, i.e., amputees using a prosthesis or with a history of prosthesis use (Pro group) and amputees without a prosthesis (non-Pro group), as well as a sample of matched healthy controls. Using concurrent behavioral and electrophysiological assessments, we found that Pro amputees were comparable to healthy controls in either behavior or event-related potentials (ERPs), while non-Pro amputees showed prolonged response time as well as divergent ERP patterns. The P200 amplitude of non-Pro amputees was significantly larger for the non-dominant hand pictures than that for the dominant hand pictures, while such a hand difference in P200 was not found in either healthy controls or Pro amputees. Furthermore, the typical angular modulation of the N200 amplitude in healthy controls and Pro amputees was not presented in non-Pro amputees. Our results suggest that prosthesis use could preserve mental rotation ability by maintaining the performance of motor imagery and visual perception of hands, which represents a preservation of the body schema.

A randomised, controlled clinical study on total hip arthroplasty using 4 different bearings: results after 10 years.

PURPOSE: To compare 4 different bearings in total hip arthroplasty (THA) in a randomised controlled clinical study on clinical performance. METHODS: 393 patients with osteoarthritis of the hip or avascular necrosis were included and allocated to 1 of the head-and-cup couples zirconia-on-polyethylene (group A), metal-on-metal (group B), zirconia-on-polyethylene with the liner moulded into the shell (group C), or alumina-on-alumina (group D). In the individual case the surgeon could choose other implants if indicated. RESULTS: 299 patients were operated with the allocated prosthesis. The estimated cumulated prosthesis survival percentages and 95% confidence interval after 10 years were: group A 84.6 (75.8-93.4); group B 95.0 (89.5-100); group C 93.2 (86.7-99.7); group D 66.1 (54.5-77.7). The patients' physical function was significantly improved and remained equally good in all 4 groups, however slightly declining with ageing. The luxation rate was initially high, and equal between the groups, but was reduced by improving the surgical procedure introducing capsule repair by reinsertion of the short external hip rotators. CONCLUSIONS: The metal-on-metal or zirconia-on-polyethylene prostheses had high 10-year survival percentages. The longevity of these bearing couples by themselves was not related to the combination of materials. The zirconia-on-polyethylene prosthesis with the liner mounted peroperatively possibly exhibited cases of backside wear which the corresponding bearing couple with moulded polyethylene (Asian) did not. The alumina-on-alumina bearing performed poorly - it was redesigned after our study initiation and later withdrawn from the market.

Alumina-alumina total hip arthroplasty for the sequelae of Legg-Calve-Perthes disease: A comparative study with adult-onset osteonecrosis.

BACKGROUND: Total hip arthroplasty (THA) for sequelae of Legg-Calve-Perthes disease (LCPD) involves specific concerns for deformity, leg length discrepancy (LLD), and relatively young age. Excellent long-term outcome has been proven after Alumina-Alumina (Al-Al) THA for relatively young patients, however, there was no study for Al-Al THA for LCPD sequelae. The aim of this study is to evaluate the results of Al-Al THA for LCPD sequelae and to compare the results with those for adult-onset ONFH, in which THA is necessitated in relatively young age and excellent long term outcome has been proven after Al-Al THA. METHODS: Between 1997 and 2007, 41 Al-Al THA were performed in 37 patients with LCPD sequelae and followed-up for mean 10.4 years. Mean age at THA was 43.6 years. Using the propensity score matching, 41 THAs in 37 patients were identified from 339 hips in 256 patients with ONFH. The medical record and radiographic data was retrospectively reviewed. RESULTS: During follow-up, no revision was performed in both group. Harris Hip Score increased from 66.7 ± 17.4 points to 96.8 ± 6.8 points in LCPD group and from 47.9 ± 18.4 to 96.6 ± 4.6 in ONFH group. LLD decreased significantly from 2.0 ± 1.2 cm to 0.2 ± 0.9 cm in LCPD group and from 0.5 cm to 0.1 cm in ONFH group. Postoperative LLD showed no difference in both groups. As for complication, rate of intraoperative femoral fracture was significantly higher in LCPD group than in ONFH group. Other postoperative complication showed no difference. CONCLUSIONS: Despite the higher rate of intraoperative femoral crack, outcomes of Al-Al THA for LCPD were comparable to those for ONFH. Similar to ONFH, Al-Al THA may be a reliable treatment option for LCPD.

[Correction of congenital malformations by custom-made silicone implants: Contribution of computer-aided design. Experience of 611 cases]. / Chirurgie des malformations congénitales par implants sur mesure en silicone. Apport de la conception assistée par ordinateur (CAO). À propos d'une expérience de 611 cas opérés.

INTRODUCTION: Modern techniques of computer-aided design and tridimensional prototyping for manufacturing silicone elastomer custom implants are growing. They have widely modified the surgical indications in our unit. MATERIALS AND METHODS: By presenting their experience of 611 cases managed between 1993 and 2016, the authors describe the method of conception from CT-scans, the virtual image of the body and the manufacture of the custom-made implant perfectly adapted to the anatomy of each one. The operative techniques are described for the three main indications: the funnel chest or pectus excavatum (474 cases) according to a modified CHIN classification is corrected simply and very satisfactorily. This approach may render thoracic surgery techniques obsolete. Indeed, these operations remain risky and of doubtful functional utility; Poland syndrome (116 cases), where the use of a custom-made implant for compensation of muscle volume is frequently used, but can be improved by a transfer of adipose tissue or a classic breast implant; the leg atrophies (21 cases) receive custom elastomer implants introduced in a sub-fascial plane. RESULTS: The results are excellent for pectus excavatum but more difficult to optimize for the other two indications, requiring sometimes complementary techniques. Complications are rare and often benign, implants endure for life. Quality of life, psychological comfort and self-esteem have been improved with low morbidity and without having undergone a painful surgical experience. CONCLUSION: Reconstructive procedures of congenital malformations by custom-made silicone implants open a new field of activity for our surgical specialty with vast opportunities.

Somatotopical feedback versus non-somatotopical feedback for phantom digit sensation on amputees using electrotactile stimulation.

BACKGROUND: Transcutaneous electrical stimulation can provide amputees with tactile feedback for better manipulating an advanced prosthesis. In general, there are two ways to transfer the stimulus to the skin: somatotopical feedback (SF) that stimulates the phantom digit somatotopy on the stump and non-somatotopical feedback (NF) that stimulates other positions on the human body. METHODS: To investigate the difference between SF and NF, electrotactile experiments were conducted on seven amputees. Electrical stimulation was applied via a complete phantom map to the residual limb (SF) and to the upper arm (NF) separately. The behavior results of discrimination accuracy and response time were used to examine: 1) performance differences between SF and NF for discriminating position, type and strength of tactile feedback; 2) performance differences between SF and NF for one channel (1C), three channels (3C), and five channels (5C). NASA-TLX standardized testing was used to determine differences in mental workload between SF and NF. RESULTS: The grand-averaged discrimination accuracy for SF was 6% higher than NF, and the average response time for SF was 600 ms faster than NF. SF is better than NF for position, type, strength, and the overall modality regarding both accuracy and response time except for 1C modality (p<0.001). Among the six modalities of stimulation channels, performance of 1C/SF was the best, which was similar to that of 1C/NF and 3C/SF; performance of 3C/NF was similar to that of 5C/SF; performance of 5C/NF was the worst. NASA-TLX scores indicated that mental workload increased as the number of stimulation channels increased. CONCLUSIONS: We quantified the difference between SF and NF, and the influence of different number of stimulation channels. SF was better than NF in general, but the practical issues such as the limited area of stumps could constrain the use of SF. We found that more channels increased the amount and richness of information to the amputee while fewer channels resulted in higher performance, and thus the 3C/SF modality was a good compromise. Based on this study, we provide possible solutions to the practical problems involving the implementation of tactile feedback for amputees. These results are expected to promote the application of SF and NF tactile feedback for amputees in the future.

Towards an assistive peripheral visual prosthesis for long-term treatment of retinitis pigmentosa: evaluating mobility performance in immersive simulations.

OBJECTIVE: The prospective efficacy of a future peripheral retinal prosthesis complementing residual vision to raise mobility performance in non-end stage retinitis pigmentosa (RP) was evaluated using simulated prosthetic vision (SPV). APPROACH: Normally sighted volunteers were fitted with a wide-angle head-mounted display and carried out mobility tasks in photorealistic virtual pedestrian scenarios. Circumvention of low-lying obstacles, path following, and navigating around static and moving pedestrians were performed either with central simulated residual vision of 10° alone or enhanced by assistive SPV in the lower and lateral peripheral visual field (VF). Three layouts of assistive vision corresponding to hypothetical electrode array layouts were compared, emphasizing higher visual acuity, a wider visual angle, or eccentricity-dependent acuity across an intermediate angle. Movement speed, task time, distance walked and collisions with the environment were analysed as performance measures. MAIN RESULTS: Circumvention of low-lying obstacles was improved with all tested configurations of assistive SPV. Higher-acuity assistive vision allowed for greatest improvement in walking speeds-14% above that of plain residual vision, while only wide-angle and eccentricity-dependent vision significantly reduced the number of collisions-both by 21%. Navigating around pedestrians, there were significant reductions in collisions with static pedestrians by 33% and task time by 7.7% with the higher-acuity layout. Following a path, higher-acuity assistive vision increased walking speed by 9%, and decreased collisions with stationary cars by 18%. SIGNIFICANCE: The ability of assistive peripheral prosthetic vision to improve mobility performance in persons with constricted VFs has been demonstrated. In a prospective peripheral visual prosthesis, electrode array designs need to be carefully tailored to the scope of tasks in which a device aims to assist. We posit that maximum benefit might come from application alongside existing visual aids, to further raise life quality of persons living through the prolonged early stages of RP.

More than 50% reduction of wear in polyethylene liners with alumina heads compared to cobalt-chrome heads in hip replacements: a 10-year follow-up with radiostereometry in 43 hips.

BACKGROUND AND PURPOSE: Excessive wear of acetabular liners in hip replacements may lead to osteolysis and cup loosening. Different head materials are currently used. We measured differences in wear between alumina and cobalt-chrome heads with the same polyethylene liner. PATIENTS AND METHODS: 39 patients (43 hips) with osteoarthritis were included in a study with 10-year follow-up. Wear was measured as proximal and 3D penetration of the head in the liner with radiostereometry (RSA). All the patients were followed clinically with Harris hip score (HHS) for up to 10 years. Radiolucent lines and osteolytic lesions were assessed on plain radiographs. RESULTS: With alumina heads, proximal wear (95% CI) after 10 years was 0.62 (0.44-0.80) mm as compared to 1.40 (1.00-1.80) mm in the cobalt-chrome group. For 3D wear, the results were 0.87 (0.69-1.04) mm for alumina heads and 1.78 (1.35-2.21) mm for cobalt-chrome heads. Median (range) HHS was 98 (77-100) in the alumina group and it was 93 (50-100) in the cobalt-chrome group (p = 0.01). We found no difference in osteolysis between the groups. INTERPRETATION: We found better wear properties with alumina heads than with cobalt-chrome heads. We recommend the use of alumina heads in patients in whom a high wear rate might be anticipated.

Prevention of voice prosthesis biofilms: current scenario and future trends in prolonging prosthesis lifetime.

Voice rehabilitation after a total laryngectomy is an important requisite for patients' rehabilitation. Oesophageal speech using tracheo-oesophageal-valved prostheses is now considered the state-of-art in postlaryngectomy voice rehabilitation. One of the major drawbacks of voice prostheses is their limited device lifetime. This is due to the deterioration of the silicone rubber material by different bacterial and yeast species, which are organised in the form of a biofilm resulting in internal leakage, increased airflow resistance, impeding speech, respiration and swallowing. The use of antimicrobials though easily applicable is associated with development of resistance if used on long-term basis. Other techniques in the form of modification of physicochemical properties of the silicon surface or covalent binding of antimicrobial agents to the silicon surface have been employed. This article reviews the different strategies investigated until now and the future trends in preventing biofilm formation for prolonging the lifetime of the silicon voice prostheses. Data was collected by conducting a computer aided search of the MED-LINE and PUBMED databases, supplemented by hand searches of key journals. Over 35 articles in the last two decades on the topic have been reviewed out of which 27 were found to be of relevant value for this article.

Wear and surface analysis of 38 mm ceramic-on-metal total hip replacements under standard and severe wear testing conditions.

The purpose of this study was to compare the wear of zirconia-toughened alumina (ZTA) and alumina femoral heads tested against as-cast CoCrMo alloy acetabular cups under both standard and severe wear conditions. A new severe test, which included medio-lateral displacement of the head and rim impact upon relocation, was developed. This resulted in an area of metal transfer and an area of increased wear on the superior-anterior segment of the head that were thought to be due to dislocation and rim impact respectively. While the wear of all ceramic heads was immeasurable using the gravimetric method, the wear rates for the metallic cups from each test were readily calculated. An average steady state wear rate of 0.023 +/- 0.005 mm3/10(6) cycles was found for the cups articulating against ZTA under standard wear conditions. A similar result had previously been obtained for the wear of cups articulated against alumina heads of the same size (within the same laboratory). Under severe wear conditions an increase in the metallic cup steady state wear rate was found with the ZTA and alumina tests giving 0.623 +/- 0.252 and 1.35 +/- 0.154 mm3/10(6) cycles respectively. Wear of the ceramic heads was detected using atomic force microscopy which showed, under severe wear conditions, a decrease in polishing marks and occasional grain removal. The surfaces of the ZTA heads tested under standard conditions were virtually unchanged from the unworn samples. Friction tests showed low friction factors for all components, pre and post wear.

[Large diameter femoral heads in primary alumina/alumina and XSPE/alumina total hip arthroplasty. A follow-up study of 50 hips after average 40 months and review of literature]. / Pierwotna calkowita bezcementowa endoprotezoplastyka stawów biodrowych--ceramika/ceramika i ceramika/polietylen XSPE z uzyciem glów o duzej srednicy. Ocena 50 bioder po okresie srednio 40 miesiecy i przeglad pismiennictwa.

INTRODUCTION: The aim of the study was a preliminary report of the use of large diameter alumina femoral heads in total hip arthroplasty. MATERIAL AND METHODS: In the years 2005-2008 50 THRs were implanted in 48 patients with the use of 36 mm alumina femoral heads. 5 women and 43 men in the age from 35 to 75 years (average 61 years) were operated on. Primary osteoarthritis was the cause of 41 arthroplasties, and AVN of femoral head of 9 surgeries. 18 alumina/alumina and 32 polyethylene/alumina THRs were implanted. The prospective study consisted of clinical examination with Harris Hip Score and X-ray evaluation. AP and lateral view X-rays were evaluated. The incidence of radiolucent lines around acetabular cups were noted with DeLee and Charnley zones and around stems with Gruen's zones. RESULTS: The follow up is from 24 to 58 months (average 40 months). There was an increase in Harris Hip Score from average 37 points (from 25 to 49 points) before operation to average 94 points (from 90 to 100 points) after the surgery. The incidence of postoperative dislocation have not been noted. Long-term postoperative X-ray examination have showed proper geometry of endoprostheses without radiolucent lines. Neither visible wear of bearing surfaces nor breakage of alumina components have been noted. CONCLUSIONS: 1) The use of 36 mm femoral heads in total hip arthroplasty decrease the risk of postoperative dislocation. 2) Innovative biomaterials: alumina ceramics and cross-linked polyethylene give chance for decrease the incidence of osteolysis.

Designing a thalamic somatosensory neural prosthesis: consistency and persistence of percepts evoked by electrical stimulation.

Intuitive somatosensory feedback is required for fine motor control. Here we explored whether thalamic electrical stimulation could provide the necessary durations and consistency of percepts for a human somatosensory neural prosthetic. Continuous and cycling high-frequency (185 Hz, 0.21 ms pulse duration charge balanced square wave) electrical pulses with the cycling patterns varying between 7% and 67% of duty cycle were applied in five patients with chronically implanted deep brain stimulators. Stimulation produced similar percepts to those elicited immediately after surgery. While consecutive continuous stimuli produced decreasing durations of sensation, the amplitude and type of percept did not change. Cycling stimulation with shorter duty cycles produced more persisting percepts. These features suggest that the thalamus could provide a site for stable and enduring sensations necessary for a long term somatosensory neural prosthesis.

Strength and reliability of alumina ceramic femoral heads: Review of design, testing, and retrieval analysis.

Ceramic components are used increasingly in total hip arthroplasty (THA). Compared with metallic components, ceramic femoral heads for THA have the potential advantage of lower wear rates in articulations with acetabular liners. However, the use of ceramic components is also associated with unique risks, including sudden fracture and intolerable bearing noise or squeaking. This review paper summarizes the published literature regarding alumina ceramic femoral heads and tries to identify areas where uncertainties remain. We will discuss the following topics: (1) the fracture mechanics of ceramic materials; (2) design-related stresses acting on the femoral head, especially at the interface between the stem trunnion and the head; (3) gradual loss of strength in service by fatigue or slow crack growth and simulation using a proof test; and (4) information that can be gathered from examination of fractured explants.

Two-dimensional finite element simulation of fracture and fatigue behaviours of alumina microstructures for hip prosthesis.

This paper describes a two-dimensional (2D) finite element simulation for fracture and fatigue behaviours of pure alumina microstructures such as those found at hip prostheses. Finite element models are developed using actual Al2O3 microstructures and a bilinear cohesive zone law. Simulation conditions are similar to those found at a slip zone in a dry contact between a femoral head and an acetabular cup of hip prosthesis. Contact stresses are imposed to generate cracks in the models. Magnitudes of imposed stresses are higher than those found at the microscopic scale. Effects of microstructures and contact stresses are investigated in terms of crack formation. In addition, fatigue behaviour of the microstructure is determined by performing simulations under cyclic loading conditions. It is shown that crack density observed in a microstructure increases with increasing magnitude of applied contact stress. Moreover, crack density increases linearly with respect to the number of fatigue cycles within a given contact stress range. Meanwhile, as applied contact stress increases, number of cycles to failure decreases gradually. Finally, this proposed finite element simulation offers an effective method for identifying fracture and fatigue behaviours of a microstructure provided that microstructure images are available.