Stephen Naumann

A three-dimensional kinematic and dynamic model of the lower limb

A model describing the kinematics and dynamics of the lower limb is presented. The lower limb is modeled as a sequence of four rigid links connected by three universal rotary joints representing the hip, knee and ankle joints. Each joint is modeled as a sequence of three single axis rotational joints thus ascribing to the lower limb a total of 12 degrees of freedom. A method is described to measure the gait variables so that all nine angles can be computed based on the positions of nine markers placed on the subject during a gait study. The gait variables are then used in an iterative Newton-Euler formulation to compute the moments exerted about the axes of each joint during gait.

Evaluation of selective dorsal rhizotomy for the reduction of spasticity in cerebral palsy: a randomized controlled trial

Selective dorsal rhizotomy (SDR) is widely used to treat spasticity in children with diplegic cerebral palsy (CP) but has never been shown conclusively to improve functional outcome. The study was designed to measure changes in gross motor function in children 1 year following rhizotomy compared with a control group receiving equivalent physiotherapy. (PT) and occupational therapy (OT) with the exception that the rhizotomy group initially underwent a 6‐week postoperative in‐patient therapy program. Twenty‐four children (mean age 58 months) with mild to moderate CP with spastic diplegia were randomly assigned to a therapy‐only control group (CG) (N=12) or rhizotomy and therapy group (RG) (N=12). The Gross Motor Function Measure (GMFM) was administered at the baseline, 6‐, and 12‐month assessments. Extremity tone, range of motion (ROM), biomechanics of the ankle‐stretch reflex, isometric contraction, and temporal gait components were also evaluated. GMFM scores in the RG improved by 12.1 percentage points versus 4.4 percentage points in the CG (P<0.02). RG knee arid ankle tone was significantly reduced (P<0.005), associated with increased passive ankle ROM (P<0.001), and decreased soleus EMG reflex activity on forced dorsiflexion (P<0.008). Foot‐floor contact pattern improved in the RG compared with the CG (P<0.05). In conclusion, SDR combined with PT and OT leads to significantly greater functional motor improvement at 1 year following surgery compared with PT and OT alone. This was achieved in part through reduced knee and ankle tone, increased ankle dorsiflexion ROM, and more normal foot‐floor contact during walking.

Outcomes measurement of assistive technologies: an institutional case study.

The assistive technology (AT) community has been challenged to effectively measure the outcomes of AT services. There has been much discussion recently in the literature about how to conceptualize and respond to this challenge. In this paper, we suggest that these objectives are best accomplished when AT services are understood within the contexts of the total rehabilitation of AT users and the institutional culture in which services are delivered. We provide examples of outcome priorities we have identified and the tools and approaches we have used. These include projects in the areas of clinical, functional, and psychosocial outcomes assessment of ATs.

Application of quality function deployment in rehabilitation engineering

Rehabilitation engineers are highly dependent upon input from consumers, service clinicians and other technical professionals to guide them in the product development process. Designers of assistive devices are consistently striving to improve their products to remain competitive. New designs or modifications to current products that are cost effective yet truly reflective of the priorities of consumers and clinicians are often difficult to identify. A design strategy called Quality Function Deployment provides a method of organizing and structuring these priorities to focus the energies of the design team. A case study is presented that describes the application of Quality Function Deployment to the modification of the design of myoelectric prosthetic hands. >

Dual-channel electrical stimulators for use by children with diplegic spastic cerebral palsy

The paper describes the design of two dual-channel constant-current electrical stimulators for use by children with diplegic spastic cerebral palsy. One stimulator for correction of equinus gait. The technique used to isolate the two stimulus output channels permits expansion to multiple stimulus channels using a single DC/DC convertor. False triggering of the functional stimulator by footswitches has been accounted for electronically. Examples reflecting the use of the device in the course of gait studies are presented.

Design characteristics of pediatric prosthetic knees

We examined whether pediatric prosthetic single-axis knees can theoretically provide the beneficial functional characteristics of polycentric knees and the design considerations needed to realize this. Five children and their parents provided subjective opinions of the relative importance of functional requirements (FRs) for the knee. FRs related to comfort, fatigue, stability, and falling were found to be of high importance, while sitting appearance and adequate knee flexion were of lower importance. Relationships were drawn between these FRs and deductions were made regarding the importance of associated design parameters. Stance-phase control was rated to be of greatest importance followed by toe clearance. Models were developed for five knees including four- and six-bar knees, corresponding to two commercially available components, and for three configurations of a single-axis knee. Stance-phase control, specifically stability after heel-strike and swing-phase initiation at push-off, and toe clearance were simulated. The results suggest that a single-axis knee design incorporating stance-phase control will mutually satisfy the identified set of highly and moderately important FRs.

Design and quantitative evaluation of a stance-phase controlled prosthetic knee joint for children

The aims of this study were to demonstrate a theoretical basis for the design of a stance-phase controlled paediatric prosthetic knee joint, clinically test prototypes of the knee, and use a questionnaire to evaluate its efficacy. Biomechanical models were used to analyze the stance-phase control characteristics of the proposed knee, and those of three other commonly prescribed paediatric knee joint mechanisms, which were also the conventional knee joints used by the six participants of this study (mean age 10.8 years). A questionnaire pertaining to stance-phase control was designed and administered twice to each child; once for the evaluation of the prototype knee joint and once for the conventional knee joint. Stance-phase modeling results indicated decreased zones of instability for the new knee as compared to other paediatric knee joints. Questionnaire results revealed a decrease in the frequency of falls with the prototype compared to other knees, especially in highly active children. The children also reported worrying less about the knee collapsing during walking. No differences were evident for stance-phase stability during running, walking on uneven terrain, ambulating up and down stairs and inclines, fatigue, and types of activities performed.

Systematic characterisation of silicon-embedded accelerometers for mechanomyography

Silicon soft suction sockets (roll-on sleeves) currently used in passive prostheses for below-elbow amputees could also be used in externally powered prostheses, enhancing their functionality and comfort. However, as it is extremely difficult to hold currently used electromyography (EMG) sensors in place reliably within a silicon socket, an alternative measurement of muscular activity as the control input is necessary. Mechanomyography (MMG) is the epidermal measurement of the low-frequency vibrations produced by a contracting muscle. MMG sensors do not have to be in direct contact with the skin. Moreover, the embedding of sensors in the roll-on sleeve may also solve attachment issues, making sensor placement flexible. Therefore the objective was to determine the feasibility of recording MMG signals using silicon-embedded, micro-machined accelerometers. Fifteen embedded accelerometers were excited with predefined vibration patterns. The signal-to-noise ratio (SNR) and frequency response of each sample were measured and compared with those of non-embedded accelerometers. The SNR of embedded samples (≊19 dB) was significantly higher than that of non-embedded samples (≊12 dB), owing to the considerable mechanical damping effect of the silicon in the 300–900 Hz bandwidth (p=0.0028). This has implications for the application of silicon-embedded accelerometers for externally powered prosthesis control.

Optimization of the signal-to-noise ratio of silicon-embedded microphones for mechanomyography

Soft silicon sockets enhance mobility and comfort of artificial limbs for below-elbow amputees compared to acrylic resin laminated hard sockets. However, standard electromyographic (EMG) sensor attachment issues prevent their use with electrically powered prostheses. Mechanomyography (MMG) may facilitate the use of soft silicon sockets with electrically powered prostheses. Unlike EMG sensors, MMG sensors can be reliably placed distally over the patients stump, by embedding them into the silicon socket. Our experiments focused on maximizing the signal-to-noise ratio (SNR) of silicon-embedded microphones for MMG. Optimal dimensions were obtained for the cylindrical air chamber enclosed within the embedding capsule (13mm diameter, 2mm height). Furthermore, shores 20A and 65A were identified as the optimal silicon hardness values for the embedding case and driving membrane, respectively. Embedded microphones provided, on average, a 6dB SNR enhancement over previously reported embedded accelerometers.

Development of an integrated wheelchair tray system for augmentative communication.

This paper describes the development of a wheelchair tray system for persons with physical disabilities who require an augmentative communication system. The tray system offers advantages over existing systems by providing a convenient anterior/posterior tilt feature, a means for stowing the tray when not in use, and a method of accommodating communication systems and powered wheelchair controls. Caregivers of seven subjects fitted with the prototype system assessed its performance through the completion of questionnaires provided at the end of 6-week field trials. The technical performance of the systems was also monitored. The prototype system was favorably received by six participants. Several recommendations are made to further increase consumer acceptance of the final tray design.