A medical hand tool physical interaction evaluation approach for prototype testing using patient care simulators

The purpose of this study was to develop and test a physical ergonomics assessment approach for medical device handles. The method assesses wrist posture and force of exertion simultaneously by task element. Electrogoniometers and EMG sensors were connected through a data acquisition module for synchronization with video recordings of trials. Task analysis of video recordings were performed offline with Observer XT software. Average posture and force data across several repetitions of individual task elements were calculated and presented in a format suitable for informing product designers of specific issues during a test trial. A handle comfort questionnaire is proposed to survey subjective responses. The evaluation approach was applied to an endoscope needle in sampling a biopsy from the stomach wall using a gastrointestinal track simulator with ten physician surrogates. The results showed that for all task elements the wrist was in extension (33(°)-45(°)). Peak muscle forces ranged from 28% to 68% MVC across the three muscles studied. Muscle peak forces were above ACGIH HAL maximum threshold limits for four of the seven task elements, and above the action limit for all seven task elements for two muscles. The handle comfort questionnaire data also supported the high muscle force findings, and also on force distribution on the handle due to contact stresses. This combined approach could be used to collect and report detailed early stage ergonomics data from user trials on patient care simulators. The approach is proposed for use by medical device designers at the design stage of new products using prototypes, but it could also be used on existing products with real patients.

Design of an Endoscopic Biopsy Needle With Flexural Members

As a minimally invasive means of extracting a tissue sample from a patient, current endoscopic biopsy needles generally do not preserve tissue histology and often require multiple attempts to obtain a tissue sample. This paper presents an endoscopic biopsy needle with internal flexures that enables tissue to enter the hollow needle and then be severed from the surrounding tissue when the needle is withdrawn. Using force-deflection and sample weight data from 10× scaled prototypes, variations of a flexural design captured 1.1grams of a tissue phantom on average, as compared to wedge-type designs that averaged 0.7-0.8grams. Sample mass exhibited an increase in mass as the feature angle decreased. Peak entrance forces (P2) for the flexure design were lower than for both wedge and extended wedge designs, and resistance forces (S2) were higher upon needle extraction. A low-angle (15 and 30deg) feature also produced a lower entrance friction (S1) and higher exit resistance (S2) compared with 45 and 60deg features. These results suggest that a biopsy needle with 15deg flexures could increase sample length and mass as well as sampling success rates for core biopsy procedures. Future tests of the flexural biopsy needle design will use this information to determine dimensions for laser cut features of 1× scale needles.