A review of assistive devices for arm balancing.

Due to neuromuscular disorders (e.g., Duchenne Muscular Dystrophy) people often loose muscle strength and become wheelchair bound. It is important to use muscles as much as possible. To allow this, and to increase independency of patients, an arm orthosis can be used to perform activities of daily life. The orthosis compensates for the gravity force of the arm, allowing people to perform movements with smaller muscle forces. For patients, the aesthetics of the orthosis is one of the critical issues. This paper presents the state-of-the-art in passive and wearable active arm orthoses, and investigates how to proceed towards a suitable structure for a wearable passive arm orthosis, that is able to balance the arm within its natural range of motion and is inconspicuous; in the ideal case it fits underneath the clothes. Existing devices were investigated with respect to the body interface, the volume, and the workspace. According to these evaluation metrics it is investigated to what extent the devices are wearable and inconspicuous. Furthermore, the balancing principle of the devices, the architecture, force transmission through the devices, and alignment with the body joints are investigated. It appears that there is only one wearable passive orthosis presented in literature. This orthosis can perform throughout the natural workspace of the arm, but is still too bulky to be inconspicuous. The other passive orthoses were conspicuous and mounted to the wheelchair. Except one, the wearable active orthoses were all conspicuous and heavy due to a large backpack to enclose the actuators. They also could not achieve the entire natural workspace of the human arm. A future design of an inconspicuous, wearable, passive arm orthoses should stay close to the body, be comfortable to wear, and supports pronation and supination.

Experimental approach to study arthroscopic irrigation.

The view during arthroscopic operations is kept clear by means of irrigation. The purpose was to determine dominant parameters on irrigation performance from which design considerations were formulated for optimization of joint irrigation. An experimental approach was chosen. The set up consisted of a human joint phantom with normal operative equipment for irrigation. Disturbances of the view were simulated with blue colored ink. With this, an objective and quantitative outcome measure was defined as the time from ink injection till complete clear view (irrigation time). The irrigation times for varying parameters were evaluated: pressure and flow, configuration of in- and outflow portals, location of bleeding, two- versus three-dimensionally shaped joint space, direction and location of inflow, and presence of an instrument. Apart from the level of pressure and flow (F(5,34)=245, p<0.05), the configuration of in- and outflow portals had a dominant significant influence on the irrigation time (F(2,23)=69, p<0.05) achieving a decrease of up to 64% and 77%, respectively. The experimental approach resulted in formulation of design criteria for new sheaths: cross-sectional area as large as possible, and stimulation of a turbulent inflow. The method can be used as a standard testing protocol for new arthroscopic devices and instruments.

Behavior of arthroscopic irrigation systems.

In the literature, no consensus exists about optimal irrigation of joints during arthroscopic operations. The goal of this paper is to study the behavior of irrigation systems resulting in the proposal of guidelines for optimal irrigation. To this end, optimal irrigation is defined as the steady state of irrigation of a joint in which a sufficient positive intra-articular pressure and a sufficient flow are maintained. A model of the complete irrigation system was created to schematically elucidate the behavior of pump systems. Additionally, clinical experiments were performed during arthroscopic knee operations in which the pressure at different locations and the irrigation flow were measured. The combination of model prediction and clinical results could well be used to derive guidelines, since the clinical results, which showed considerable variation, were used to verify the model, and the model could be used to explain the typical trends. The main findings are twofold the set pressure is always higher than the intra-articular pressure, and the scope-sheath combination has a significant influence on irrigation control, because of its large restriction. Based on the results, we advice to increase the set pressure during active suction, and to include the sheath-scope combination in the control loop.

Clinically-driven approach to improve arthroscopic techniques.

In this paper, a clinically-driven approach is introduced as the starting point for the improvement of arthroscopic techniques. The approach was divided into two phases. Phase 1 consisted of a combination of observations and discussions that resulted in the definition of clinically-relevant research topics. Phase 2 consisted of an interview which aimed at analysis of the general opinion on arthroscopy, and which assigned a priority ranking to the topics. Six research topics were defined. Based on the information collected, the conclusion is that the surgeons are satisfied with current arthroscopic techniques. A majority gives priority to the optimization of cartilage treatment and to the design of a steerable arthroscopic cutter. A minority gives priority to the expansion of arthroscopic techniques. The two-phase approach was fruitful in terms of establishing clinical problem areas, and of involving surgeons in the technical improvement of arthroscopic techniques.

Translational stiffness of the replaced shoulder joint.

Results after a total shoulder arthroplasty in rheumatoid patients are poor, indicated by loosening of especially the glenoid component, bad joint functionality and the possibility of a joint dislocation. The failure mechanisms behind this are multiple, including patient, surgical and design factors. These results must be improved. At present, the optimal geometrical prosthesis component design, focused on joint conformity and constraint, still has to be investigated. Proper understanding of the effect of geometrical design parameters on the theoretical relationship between joint translations and joint forces may contribute to improved designs. The main objective of this study is to theoretically describe this relationship and to investigate the joint translational stiffness, which can be used to investigate the effect of design parameters on joint motion. Joint translational stiffness is the gradient of the subluxation force with respect to the humeral head displacement. For this static analysis a potential field is introduced, as the result of a joint compressive force (muscle forces) and a subluxation force (external forces). The positive and negative stiffness during articulation inside and subluxation outside the glenoid cavity, lead to stable and unstable equilibrium joint positions, respectively. A most lateral position of the humeral head centre coincides with a zero subluxation force; at this position the humerus is dislocated and a restoring force is needed to relocate the humeral head. Joint conformity and compression force influence the joint translational stiffness during articulation inside the glenoid cavity, whereas during articulating outside the glenoid cavity this is influenced by the joint compression force and humeral radius of curvature. The glenoid radius of curvature influences the contact point and, in combination with the glenoid superior-inferior chord length, it also influences the constraintness angle, which influences the maximum allowable subluxation load to prevent a joint dislocation. This constraintness angle together with the joint conformity also influences maximum joint translations before articulation outside the glenoid cavity. Furthermore, the sign of the joint translational stiffness determines the stability of shoulder motion, which is stable and unstable if this stiffness is positive and negative, respectively.

Forces and displacements in colon surgery.

BACKGROUND: This study aims to find criteria for designing safer laparoscopic graspers for manipulation of delicate tissues. Since the experiment was performed in an open-surgery setup without any movement restrictions, the results are relevant to general surgery as well as laparoscopic. METHOD: Four surgeons were asked to apply via two clamps enough force to a pig's colon to stretch the mesocolon for dissection. Directions, magnitudes, and application points of the forces were recorded. RESULTS: The surgeons applied per clamp on average 2.5 N and maximally 5 N to the colon. These forces were at an angle of about 40 degrees to 70 degrees relative to the horizontal plane and approximately 60 degrees relative to each other. CONCLUSIONS: Safe laparoscopic graspers should be able to transmit at least a 5 N pull force to the tissue without damaging it. To minimize the forces used, the angles mentioned should be taken into account when placing the trocars.

Force-directed design of a voluntary closing hand prosthesis.

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.

Sensitivity of laparoscopic dissectors. What can you feel?

BACKGROUND: Sensory feedback is reduced considerably in minimally invasive procedures by the interposition of instruments, causing loss of direct manual contact with the tissue. The purpose of this study was to evaluate the feedback quality of commercially available reusable and disposable laparoscopic dissectors. METHODS: A total of 31 participants were asked to feel a simulated arterial pulse with their bare fingers and through laparoscopic dissectors, tweezers, an orthopedic forceps, and a laparoscopic low-friction prototype. The absolute sensory threshold was determined by the psychophysical method of limits. RESULTS: The sensory feedback quality was significantly better for the reusable dissectors tested than for the disposable dissector (p < 0.001). Nevertheless, the reusable dissectors were at least eight times less sensitive than bare fingers. Furthermore, sensitivity qualities were highly variable, depending on the dissector tested. CONCLUSIONS: This study showed that the overall sensitivity loss through instruments could be accurately assessed, proving that the sensory feedback for commercially available instruments was low compared to bare fingers. The good sensory feedback results of the prototype indicated that careful design could decrease the overall sensitivity loss.

Methods for reducing energy dissipation in cosmetic gloves.

For cosmetic reasons, hand prostheses are provided with cosmetic gloves. Their pleasing appearance, however, is accompanied by poor mechanical behavior, resulting in a negative influence on prosthesis operation. Glove stiffness is high and nonlinear, and internal friction in the glove material causes energy dissipation (hysteresis). In this article, two methods for reducing hysteresis in cosmetic gloves are proposed, that may be applied independently or in combination. Glove modification. Altering the mechanical properties of the glove itself is the first method that is presented. It was found possible to reduce both stiffness and hysteresis about 50% by forming grooves into the inside of the glove. Together with the evaluation of this method, several properties of the cosmetic glove were determined. Motion optimization. Additionally, a second method for reducing hysteresis was developed. The amount of hysteresis is influenced by the way the glove is forced to deform. The prosthesis mechanism, determining this deformation, was designed for minimum hysteresis and maximum cosmesis. For the prosthesis-glove combination used in this study, thumb motion optimization reduced hysteresis by about 65%.