The impact of walking on the perception of multichannel electrotactile stimulation in individuals with lower-limb amputation and able-bodied participants.

BACKGROUND: One of the drawbacks of lower-limb prostheses is that they do not provide explicit somatosensory feedback to their users. Electrotactile stimulation is an attractive technology to restore such feedback because it enables compact solutions with multiple stimulation points. This allows stimulating a larger skin area to provide more information concurrently and modulate parameters spatially as well as in amplitude. However, for effective use, electrotactile stimulation needs to be calibrated and it would be convenient to perform this procedure while the subject is seated. However, amplitude and spatial perception can be affected by motion and/or physical coupling between the residual limb and the socket. In the present study, we therefore evaluated and compared the psychometric properties of multichannel electrotactile stimulation applied to the thigh/residual limb during sitting versus walking. METHODS: The comprehensive assessment included the measurement of the sensation and discomfort thresholds (ST & DT), just noticeable difference (JND), number of distinct intervals (NDI), two-point discrimination threshold (2PD), and spatial discrimination performance (SD). The experiment involved 11 able-bodied participants (4 females and 7 males; 29.2 ± 3.8 years), 3 participants with transtibial amputation, and 3 participants with transfemoral amputation. RESULTS: In able-bodied participants, the results were consistent for all the measured parameters, and they indicated that both amplitude and spatial perception became worse during walking. More specifically, ST and DT increased significantly during walking vs. sitting (2.90 ± 0.82 mA vs. 2.00 ± 0.52 mA; p < 0.001 for ST and 7.74 ± 0.84 mA vs. 7.21 ± 1.30 mA; p < 0.05 for DT) and likewise for the JND (22.47 ± 12.21% vs. 11.82 ± 5.07%; p < 0.01), while the NDI became lower (6.46 ± 3.47 vs. 11.27 ± 5.18 intervals; p < 0.01). Regarding spatial perception, 2PD was higher during walking (69.78 ± 17.66 mm vs. 57.85 ± 14.87 mm; p < 0.001), while the performance of SD was significantly lower (56.70 ± 10.02% vs. 64.55 ± 9.44%; p < 0.01). For participants with lower-limb amputation, the ST, DT, and performance in the SD assessment followed the trends observed in the able-bodied population. The results for 2PD and JND were however different and subject-specific. CONCLUSION: The conducted evaluation demonstrates that electrotactile feedback should be calibrated in the conditions in which it will be used (e.g., during walking). The calibration during sitting, while more convenient, might lead to an overly optimistic (or in some cases pessimistic) estimate of sensitivity. In addition, the results underline that calibration is particularly important in people affected by lower-limb loss to capture the substantial variability in the conditions of the residual limb and prosthesis setup. These insights are important for the implementation of artificial sensory feedback in lower-limb prosthetics applications.

A review of user needs to drive the development of lower limb prostheses.

BACKGROUND: The development of bionic legs has seen substantial improvements in the past years but people with lower-limb amputation still suffer from impairments in mobility (e.g., altered balance and gait control) due to significant limitations of the contemporary prostheses. Approaching the problem from a human-centered perspective by focusing on user-specific needs can allow identifying critical improvements that can increase the quality of life. While there are several reviews of user needs regarding upper limb prostheses, a comprehensive summary of such needs for those affected by lower limb loss does not exist. METHODS: We have conducted a systematic review of the literature to extract important needs of the users of lower-limb prostheses. The review included 56 articles in which a need (desire, wish) was reported explicitly by the recruited people with lower limb amputation (N = 8149). RESULTS: An exhaustive list of user needs was collected and subdivided into functional, psychological, cognitive, ergonomics, and other domain. Where appropriate, we have also briefly discussed the developments in prosthetic devices that are related to or could have an impact on those needs. In summary, the users would like to lead an independent life and reintegrate into society by coming back to work and participating in social and leisure activities. Efficient, versatile, and stable gait, but also support to other activities (e.g., sit to stand), contribute to safety and confidence, while appearance and comfort are important for the body image. However, the relation between specific needs, objective measures of performance, and overall satisfaction and quality of life is still an open question. CONCLUSIONS: Identifying user needs is a critical step for the development of new generation lower limb prostheses that aim to improve the quality of life of their users. However, this is not a simple task, as the needs interact with each other and depend on multiple factors (e.g., mobility level, age, gender), while evolving in time with the use of the device. Hence, novel assessment methods are required that can evaluate the impact of the system from a holistic perspective, capturing objective outcomes but also overall user experience and satisfaction in the relevant environment (daily life).

Changes in Vestibular Function Following Pediatric Cochlear Implantation: a Prospective Study.

OBJECTIVES: Given the close interconnection between the auditory and vestibular end organs, the increasingly broad application of (bilateral) cochlear implantation (CI) in children raises concern about its impact on the vestibular function. Unfortunately, literature on this matter is inconclusive and subject to several limitations. Therefore, this study aimed to elucidate the impact of pediatric CI on the vestibular function in a large sample of children, representative for the current CI population. DESIGN: Fifty hearing-impaired children followed in the Ghent University Hospital were included in this prospective study. Twenty-seven patients underwent unilateral CI, and 23 were bilaterally implanted (9 sequentially, 14 simultaneously), adding up to 73 implanted ears. Children's median age at first implantation was 29 (range 8 to 194) months. Vestibular assessment was scheduled on average 2.8 months (SD: 3.6) before and 4.6 (SD: 4.0) months after implantation and consisted of video Head Impulse Testing of the lateral semicircular canals, rotatory testing (0.16, 0.04, and 0.01 Hz) and cervical vestibular evoked myogenic potential (cVEMP) testing with bone conduction stimulation. Caloric testing was added in children older than 3 years of age. RESULTS: Overall, group analysis in our sample of 73 CI-ears did not reveal any significant impact on the vestibular function, except for a significantly shortened ipsilateral N1 latency of the cVEMP responses (p = 0.027) after CI. Complete ipsilateral loss of function after implantation was seen in 5% (3/54) of all CI-ears on the video head impulse testing, in 0% (0/10) on the caloric test and in 2% (1/52) on the cVEMP, notably all patients deafened by a congenital cytomegalovirus infection. CONCLUSIONS: The impact of CI on the vestibular function in our dataset was limited. Therefore, the many advantages of simultaneous bilateral implantation may outweigh the risk for vestibular damage postoperatively. However, the impact on the vestibular function may be dependent on various factors (e.g., etiology of the hearing loss), and the clinical outcome is still difficult to predict. Vestibular assessment remains thus an important aspect in the pediatric CI population; first because the vestibular function should be considered in the decision-making process on (simultaneous or sequential bilateral) CI and second because it is essential to reveal a possible additional sensory deficit, allowing an opportunity for rehabilitation to improve the overall outcome of these children.

The Ototoxic Potential of Cobalt From Metal-on-Metal Hip Implants: Objective Auditory and Vestibular Outcome.

OBJECTIVES: During the past decade, the initial popularity of metal-on-metal (MoM) hip implants has shown a progressive decline due to increasingly reported implant failure and revision surgeries. Local as well as systemic toxic side effects have been associated with excessive metal ion release from implants, in which cobalt (Co) plays an important role. The rare condition of systemic cobaltism seems to manifest as a clinical syndrome with cardiac, endocrine, and neurological symptoms, including hearing loss, tinnitus, and imbalance. In most cases described in the literature, revision surgery and the subsequent drop in blood Co level led to (partial) alleviation of the symptoms, suggesting a causal relationship with Co exposure. Moreover, the ototoxic potential of Co has recently been demonstrated in animal experiments. Since its ototoxic potential in humans is merely based on anecdotal case reports, the current study aimed to prospectively and objectively examine the auditory and vestibular function in patients implanted with a MoM hip prosthesis. DESIGN: Twenty patients (15 males and 5 females, aged between 33 and 65 years) implanted with a primary MoM hip prosthesis were matched for age, gender, and noise exposure to 20 non-implanted control subjects. Each participant was subjected to an extensive auditory (conventional and high-frequency pure tone audiometry, transient evoked and distortion product otoacoustic emissions [TEOAEs and DPOAEs], auditory brainstem responses [ABR]) and vestibular test battery (cervical and ocular vestibular evoked myogenic potentials [cVEMPs and oVEMPs], rotatory test, caloric test, video head impulse test [vHIT]), supplemented with a blood sample collection to determine the plasma Co concentration. RESULTS: The median [interquartile range] plasma Co concentration was 1.40 [0.70, 6.30] µg/L in the MoM patient group and 0.19 [0.09, 0.34] µg/L in the control group. Within the auditory test battery, a clear trend was observed toward higher audiometric thresholds (11.2 to 16 kHz), lower DPOAE (between 4 and 8 kHz), and total TEOAE (1 to 4 kHz) amplitudes, and a higher interaural latency difference for wave V of the ABR in the patient versus control group (0.01 ≤ p < 0.05). Within the vestibular test battery, considerably longer cVEMP P1 latencies, higher oVEMP amplitudes (0.01 ≤ p < 0.05), and lower asymmetry ratio of the vHIT gain (p < 0.01) were found in the MoM patients. In the patient group, no suggestive association was observed between the plasma Co level and the auditory or vestibular outcome parameters. CONCLUSIONS: The auditory results seem to reflect signs of Co-induced damage to the hearing function in the high frequencies. This corresponds to previous findings on drug-induced ototoxicity and the recent animal experiments with Co, which identified the basal cochlear outer hair cells as primary targets and indicated that the cellular mechanisms underlying the toxicity might be similar. The vestibular outcomes of the current study are inconclusive and require further elaboration, especially with respect to animal studies. The lack of a clear dose-response relationship may question the clinical relevance of our results, but recent findings in MoM hip implant patients have confirmed that this relationship can be complicated by many patient-specific factors.