applied sciences Article An Ergonomic Customized-Tool Handle Design for Precision Tools using Additive Manufacturing: A Case Study Alfonso González González 1,* ID , David Rodríguez Salgado 2, Lorenzo García Moruno 3 ID and Alonso Sánchez Ríos 3 ID 1 Campus of Mérida City, Department of Mechanical, Energy, and Materials Engineering, University of Extremadura, 06800 Mérida, Spain 2 Campus of Badajoz City, Department of Mechanical, Energy, and Materials Engineering, University of Extremadura, 06071 Badajoz, Spain; [email protected] 3 Department of Graphical Expression, University of Extremadura, 06800 Mérida, Spain; [email protected] (L.G.M.); [email protected] (A.S.R.) * Correspondence: [email protected]; Tel.: +34-924-28-93-00 Received: 12 June 2018; Accepted: 18 July 2018; Published: 22 July 2018 Abstract: A study was carried out with 135 surgeons to obtain a surgical laparoscopic grasper handle design that adapts to the size of each surgeon’s hand, in a functionally appropriate way, and has the sufficient ergonomics to avoid generating the problems detected nowadays. The main conclusion of the work is the practical 3D parametric design obtained for a laparoscopic surgical graspers handle that is scalable to fit each particular surgeon's hand size. In addition, it has been possible to determine that the anthropometric measure of the surgeon's hand defined as Palm Length Measured (PLM) allows the design of the 3D parametric model of the surgical handle to be conveniently scaled. The results show that both additive manufacturing and the application of ergonomics criterion provide an efficient method for the custom design and manufacture of this type of specialised tool, with potential application in other sectors. Keywords: parametric design; anthropometric; custom handle design; rapid prototyping; 3D CAD 1. Introduction Universal object designs try to fit all users using the criterion known as “design for all” [1]. This criterion is included in the “Universal Design” guide, which in turn lists the “7 principles of universal design” [2]. One of these principles is to facilitate “flexibility in use”. The proposal by Mace et al. [2] was further developed by Story et al. [3], in order to make the use of products designed for the greatest number of people, accessible [4]. To comply with this principle, hand tools in particular should satisfy a number of guidelines in their design. These include overcoming such obstacles as age, sex, dexterity, motor skills, etc., and whether the user is right- or left-handed, so that the handles can be adapted to different hand sizes and shapes. One of the fundamental problems in hand tool design is in trying to optimize the dimensions of the tool relative to the hand anthropometry. Another fundamental challenge is faced when trying to make sure that the shape and dimensions of the design are consistent with the type and specific functionality of each instrument type [5]. For the instruments used in laparoscopic surgery, Alleblas et al. [6] notes the need to assess expert opinions regarding the current designs of their handles. This is done in order to determine surgeons’ needs and expectations with respect to the laparoscopic instruments they currently use and the possibility of the future implementation of haptic feedback in their design. Other studies, such as that of Stoklasek et al. [7] on tools used for the assembly of electric motors, show that while Appl. Sci. 2018, 8, 1200; doi:10.3390/app8071200 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 1200 2 of 13 requirements for the functional parts of the tool (duration, making it impossible to damage the motor’s installation, etc.) were taken into account in the design, ergonomic requirements for the gripping area Appl. Sci. 2018, 8, x FOR PEER REVIEW 2 of 14 of the tool were not. Prolonged use of tools with poor ergonomic design was shown to cause discomfort resulting inmotors, numbness show that or paraesthesiawhile requirements (“pins for andthe functional needles”) parts in the of workers’the tool (duration, fingers. making it Handimpossible size is to a damage determining the motor factor’s installation, in how etc.) precision were taken tools, into account in particular in the design, laparoscopic ergonomic graspers, requirements for the gripping area of the tool were not. Prolonged use of tools with poor ergonomic are used [8design]. Small-handed was shown to surgeonscause discomfort experience resulting more in numbness grip problems or paraesthesia than those (“pins withand needles large” hands,) in and are forced to holdthe workers the handle’ fingers. differently from what was originally considered in its design phase [8]. Current surgical laparoscopicHand size tools is a determinin usuallyg come factor inin how a standard precision size, tools, and in particular the surgeon laparoscopic must graspers, adapt accordingly are by holding andused gripping [8]. Small them-handed in surgeons certain ways,experience which more a grip priori problems depend than on those the sizewith oflarge his hands, or her and hand. are forced to hold the handle differently from what was originally considered in its design phase [8]. TheCurrent conventional surgical laparoscopic tools surgery usually come graspers in a standard shown size, in Figureand the1 surgeon incorporate must adapt a pistol grip mechanismaccordingly with finger by holding rings, and and gripping a mechanism them in certain that ways, allows which full a rotationpriori depend of the on tipthe size of the of his shaft (upper part of theor graspers).her hand. The three images in the figure show different forms of gripping the instrument depending onThe the conventional size of the laparoscopic user’s hand. surgery In the graspers case ofshown Figure in Figure1a, a surgeon1 incorporate with a apistol small grip hand holds mechanism with finger rings, and a mechanism that allows full rotation of the tip of the shaft (upper the handlepart without of the graspers). being ableThe three to encompass images in the allfigure of theshow instrument’s different forms graspingof gripping elements.the instrument In Figure1b, the oppositedepending case is on revealed: the size of Athe surgeon user’s hand. with In the a large case of hand Figure is 1a, unable a surgeon to make with a simultaneoussmall hand holds use of most of those elements,the handle without and grips being the able handle to encompass in acompletely all of the instrument different’s grasping way. elements. The ideal In gripFigure would 1b, be that shown inthe Figure opposite1c,in case which is revealed: all the A grasping surgeon with elements a large hand fit the is sizeunable of to the make hand simultaneous perfectly. use It isof important most of those elements, and grips the handle in a completely different way. The ideal grip would be to note thatthat the shown grips in representedFigure 1c, in which in Figure all the1 graspingare not arbitrary,elements fit but the rathersize of the reflect hand realperfectly. situations It is brought about whenimpo thertant size to ofnote the that hand the grips and therepresented dimensions in Figure of the1 are handle not arbitrary, do not but correspond. rather reflect These real different grips weresituations observed brought in theabout Centro when the de size Cirug of theía dehand M íandnima the Invasidimensionsón Jes of úthes Ushandleón (CCMIJU) do not which collaboratedcorrespond. in the developmentThese different grips of the were present observed study. in the Centro de Cirugía de Mínima Invasión Jesús Usón (CCMIJU) which collaborated in the development of the present study. (a) (b) (c) Figure 1. Different forms of gripping the surgical laparoscopic tool according to the surgeon’s hand Figure 1. size.Different The most forms irregular of grippingones for this the grip surgical are the first laparoscopic two (a,b). These tool usually according appear towhen the the surgeon’s size hand size. The mostof the tool irregular is not adapted ones for to the this size grip of the are surgeon the first’s hand. two The (a, bthird). These (c) is the usually most common, appear and when the the size of the tool isinformation not adapted provided to the directly size by of th thee surgeons surgeon’s indicate hand. that it The caused third the least (c) is injuries. the most common, and the information provided directly by the surgeons indicate that it caused the least injuries. At present, as various recent studies have observed [9–12], the instruments used in laparoscopic surgery are characterized by being of a single size (as mentioned above) and with little ergonomy in At present,their design. as various The single recent size of studies minimally have invasive observed surgery [ 9(MIS)–12], instruments the instruments means that used surgeons in laparoscopic surgery arehave characterized to adapt to the by instruments, being of aand single different size surgeons (as mentioned show different above) patterns and with of adaptation little ergonomy in depending on their hand size. In spite of this adaptation, neither small- nor large-handed surgeons their design.can find The a single comfortable size of zone minimally to grip and invasive manipulate surgery laparoscopic (MIS) instrumentsgrasping tools. meansThis is especially that surgeons have to adapt totrue the for instruments, actioning the opening and different and closing surgeons mechanism show of the differentgrasper. This patterns problem ofhas adaptation been broughtdepending on their handto light size. in various In spite studies of thissuch adaptation,as that of Berguer neither and Hreljac small- [5] nor, who large-handed surveyed users surgeons of these can find a comfortableinstruments, zone finding to grip that and both manipulate those with large laparoscopic hands and those grasping with small tools. hands This found is them especially hard true for to use. actioning theGiven opening this situation, and closing several mechanism research papers of thehave grasper.