An Ergonomic Customized-Tool Handle Design for Precision ... - MDPI

applied sciences Article

An Ergonomic Customized-Tool Handle Design for Precision Tools using Additive Manufacturing: A Case Study Alfonso González González 1, * Alonso Sánchez Ríos 3 ID 1 2 3

*

ID

, David Rodríguez Salgado 2 , Lorenzo García Moruno 3

ID

and

Campus of Mérida City, Department of Mechanical, Energy, and Materials Engineering, University of Extremadura, 06800 Mérida, Spain Campus of Badajoz City, Department of Mechanical, Energy, and Materials Engineering, University of Extremadura, 06071 Badajoz, Spain; [email protected] 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

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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 motors, show that while requirements for and the functional of workers’ the tool (duration, resulting in numbness or paraesthesia (“pins needles”)parts in the fingers.making it impossible to damage the motor’s installation, etc.) were taken into account in the design, ergonomic Hand size is a determining factor in how precision tools, in particular laparoscopic graspers, requirements for the gripping area of the tool were not. Prolonged use of tools with poor ergonomic are used [8]. Small-handed experience more grip problems than those large hands, and are design was shown to surgeons cause discomfort resulting in numbness or paraesthesia (“pinswith and needles”) in forced to hold the handle differently from what was originally considered in its design phase [8]. Current the workers’ fingers. Hand sizetools is a determining factorin in how precisionsize, tools,and in particular laparoscopic are surgical laparoscopic usually come a standard the surgeon must graspers, adapt accordingly by used [8]. Small-handed surgeons experience more grip problems than those with large hands, and holding and gripping them in certain ways, which a priori depend on the size of his or her hand. are forced to hold the handle differently from what was originally considered in its design phase [8]. The Current conventional laparoscopic surgery graspers shownsize, in Figure 1 incorporate a pistol grip surgical laparoscopic tools usually come in a standard and the surgeon must adapt mechanism with finger rings,and and a mechanism that ways, allows fullarotation of the of the shaft (upper accordingly by holding gripping them in certain which priori depend on tip the size of his her hand. The three images in the figure show different forms of gripping the instrument part of theorgraspers). surgery graspers shown in Figure 1 incorporate a pistol grip depending onThe theconventional size of thelaparoscopic user’s hand. In the case of Figure 1a, a surgeon with a small hand holds mechanism with finger rings, and a mechanism that allows full rotation of the tip of the shaft (upper the handle without being able to encompass of the In Figure 1b, part of the graspers). The three images in theall figure showinstrument’s different forms grasping of gripping elements. the instrument the opposite case ison revealed: with a large hand is 1a, unable to make depending the size ofA thesurgeon user’s hand. In the case of Figure a surgeon with asimultaneous small hand holdsuse of most the handle without beingthe ablehandle to encompass all of the instrument’s grasping In grip Figurewould 1b, of those elements, and grips in a completely different way. elements. The ideal be that the opposite case is revealed: A surgeon with a large hand is unable to make simultaneous use of shown in Figure 1c, in which all the grasping elements fit the size of the hand perfectly. It is important most of those elements, and grips the handle in a completely different way. The ideal grip would be to note that grips in Figure are not elements arbitrary, rather reflect situations brought thatthe shown in represented Figure 1c, in which all the1grasping fit but the size of the hand real perfectly. It is about when the size the hand and the dimensions of the do notbut correspond. important to of note that the grips represented in Figure 1 arehandle not arbitrary, rather reflectThese real different situations brought about when the of the de hand and the Invasión dimensionsJesús of theUsón handle(CCMIJU) do not grips were observed in the Centro de size Cirugía Mínima which correspond. These different grips were observed in the Centro de Cirugía de Mínima Invasión Jesús collaborated in the development of the present study. 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 forms of gripping the surgical laparoscopic tool according thethe surgeon’s hand The most irregular ones for this grip are the first two (a,b). These usually appear to when size size. The most irregular ones for this grip aresurgeon’s the firsthand. twoThe (a,b). usually appearand when of the tool is not adapted to the size of the thirdThese (c) is the most common, the the size of provided directly indicate that itThe caused the least the tool isinformation not adapted to the sizeby ofthe thesurgeons surgeon’s hand. third (c) isinjuries. 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 their design. The single size ofstudies minimally invasive surgery[9–12], (MIS) instruments means that surgeons At present, as various recent have observed the instruments used in laparoscopic have to adapt to the instruments, and different surgeons show different patterns of adaptation surgery are characterized by being of a single size (as mentioned above) and with little ergonomy in depending on their hand size. In spite of this adaptation, neither small- nor large-handed surgeons their design. The asingle size ofzone minimally invasive surgery (MIS) instruments that surgeons have can find comfortable to grip and manipulate laparoscopic grasping tools. means This is especially to adapt to the and different surgeons patterns true forinstruments, actioning the opening and closing mechanismshow of the different grasper. This problem of hasadaptation been broughtdepending to lightsize. in various studies such adaptation, as that of Berguer and Hreljac who surveyed userssurgeons of these can find on their hand In spite of this neither small-[5], nor large-handed instruments, finding that both those with large hands and those with small hands found them hard a comfortable zone to grip and manipulate laparoscopic grasping tools. This is especially true for to use. actioning the Given opening and closing mechanism of the This problem has analysing been brought to light this situation, several research papers havegrasper. been published in recent years the in variouscorrespondence studies suchthat as must that of Berguer Hreljac [5], who characteristics surveyed users of these instruments, exist betweenand a user’s anthropometric and the precision instruments they use, which need to be ergonomically adapted to thehands user’s hand. Sancho-Bru et al.to [13]use. finding that both those with large hands and those with small found them hard used a biomechanical model of the hand to study the appropriate diameter of a handle with Given this situation, several research papers have been published in recent years analysing the cylindrical grip for men and women. Other studies indicate that the shape of the handle should be

correspondence that must exist between a user’s anthropometric characteristics and the precision instruments they use, which need to be ergonomically adapted to the user’s hand. Sancho-Bru et al. [13] used a biomechanical model of the hand to study the appropriate diameter of a handle with cylindrical grip for men and women. Other studies indicate that the shape of the handle should be designed to optimize the performance of the tasks in which the tool is to be used [9], maximize the ease of use and contact area between the hand and the handle [10,14], and to distribute pressure so as to minimize

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discomfort [11,12]. Other anthropometric studies have had the aim of determining laparoscopic surgery instrument dimensions that adapt to different hand sizes [8,15–18]. However, it should be noted that these last works defined three or four sizes for the handle, but listed no criterion for the design of a handle customized for each surgeon. There are many ergonomic directives and guides in the literature for the design of everyday products. Examples include “Ergonomics and Design. A Reference Guide” [19] for the development of products to improve workplace environments and the “Office Ergonomics. Guidelines for Preventing Musculoskeletal Injuries” [20] which gives a series of guidelines to make working with computers more comfortable. A few even appear in the healthcare sector, such as “Ergonomics Guidelines” [21] for surgical instruments, although none specifically discuss laparoscopic graspers. Most of these ergonomic design guides are too generic for specific applications, and there is a clear need to develop more specific guidelines for the ergonomic design of precision MIS tools [6,22–25]. The ever more widespread application of MIS has brought to the forefront the problem of specific injuries related to the use of laparoscopic tools. Although the techniques of MIS have already attained a relatively high level of development, the ergonomic characteristics of the tools it uses are still deficient [17,26–31]. Surgeons frequently complain of pressure, pain, and fatigue in their hands while using these instruments, which frequently result in lesions [26,28,29,32–37]. According to Trejo et al. [36], these lesions can be attributed to the repetitive and prolonged use of unergonomic instruments. Park et al. [37] found that 87% of surgeons who regularly perform laparoscopic surgery suffer lesions, and that the main cause is this lack of ergonomy. Therefore several firms in the medical sector, such as Dimeda-Surgical Instruments and WISAP Medical Technology GmbH in Germany, Medtronic in the US, and Endomexico in Mexico, have been working to overcome the problems with the design of MIS tools. In the circumstances, the main purpose of this paper was to design an ergonomic handle for laparoscopic surgery tools that adapted to each surgeon based on the anthropometry of their hands. The basis would be a parametric design of the handle that includes all the specifications needed for it to be more ergonomic and functional than current handles. The work involved the participation of a total of 135 surgeons, and most of it was carried out in coordination with the CCMIJU. 2. Methods 2.1. Introduction The experimental phase of this work was conducted with surgeons in the CCMIJU. The basic shape of the handle that was worked with to determine an ergonomic and customized design for laparoscopic surgery graspers is shown in Figure 2. It was the result of the ERGOLAP project [38], and is patented (Patent Number EP2471473A1). The ERGOLAP project was carried out by the authors of the present work in coordination with the CCMIJU and with the Institute of Biomechanics of Valencia (IBV). 2.2. Participants The study population comprised 135 surgeons. Their ages ranged from 20 to 70 years (mean age = 39.7 years; SD = 9.78 years), and the distribution of the sample population by sex was 69 female and 66 male. The main anthropometric data of the participants are presented in Table 1. Table 1. Anthropometric data of the study’s participants (n = 135). Characteristics

Mean (SD)

Range

Age (years) Hand length (mm) Palm length measured (mm) Hand breadth digitized (mm)

39.7 (9.78) 178.9 (13.08) 96.5 (8.79) 79.9 (6,98)

20–70 159.3–194.4 87.6–111.6 71.1–86.5

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2.3. Experimental Task and the Parametric Prototype Handle 2.3. Experimental Task and the Parametric Prototype Handle The design and development of the handle shown in Figure 2 was based on a study of the The design and development of the handle shown 2 was based on a techniques study of the ergonomic preferences of 135 surgeons during their periodinofFigure training in laparoscopic in ergonomic preferences of 135 surgeons during their period of training in laparoscopic techniques in the CCMIJU. Two of the handle design criteria were a large palmar grip surface and the combination the CCMIJU.and Two of the ability. handle These designcriteria criteriaeliminated were a large gripof surface anddesign the combination of precision turning thepalmar possibility a handle with rings. of precision and turning ability. These criteria eliminated the possibility of a handle design with rings.

Figure 2. The The laparoscopic laparoscopic tool tool handle developed in the ERGOLAP project. Figure

The resultinghandle handledesign design has been studied further analyzed the work of González et The resulting has been studied andand further analyzed in theinwork of González et al. [18]. al. [18].study, In thata study, a first approach was to define ahandle grasper handle size that would best suit the In that first approach was to define a grasper size that would best suit the surgeon’s surgeon’s hand size, but without attempting to customize the design as this is the purpose of the hand size, but without attempting to customize the design as this is the purpose of the paper at paper at hand, considering designs based on four hand sizes (XS, S, M, and L). The results of hand, considering designs based on four hand sizes (XS, S, M, and L). The results of that workthat are work are summarized 2. It should be noted in addition to this study Gonzálezet et al. al. [18], summarized in Tablein2.Table It should be noted that, that, in addition to this study ofofGonzález [18], other workers have proposed different sizes for surgical handles and hand tools, specifically other workers have proposed different sizes for surgical handles and hand tools, specifically by by defining defining three three sizes sizes [5,16,39–41]. [5,16,39–41]. Nonetheless, Nonetheless, given given the the precision precision required required in in surgery surgery and and the the many many hours together with technological means hours that that some some operations operations last last [36], [36], together with the the technological means available available today today such such as as additive manufacturing and the development of 3D parametric design software [42], a personalized additive manufacturing and the development of 3D parametric design software [42], a personalized solution solution would would seem seem to to be be called called for, for, with with the the handle handle being being designed designed to to have have the the size size ergonomically ergonomically best suited to the anthropometric dimensions of each surgeon’s hand. Recent studies, such best suited to the anthropometric dimensions of each surgeon’s hand. Recent studies, such as as that that of of Zanetti et al. [43], show that the use of 3D printing can bring substantial benefits, such as Zanetti et al. [43], show that the use of 3D printing can bring substantial benefits, such as customization, customization, optimization and the very complex geometries. optimization and the manufacture ofmanufacture very complexofgeometries. Table 2. Optimal size categories. categories. Table 2. Optimal for for each each of of the the hand hand size

Hand Size XS

Hand Size XS

S S

M

M

L

L

% % 26% 26% 11.1% 11.1% 18.5% 18.5% 24.4% 24.4% 6.7% 6.7% 13.3% 13.3%

Sex Mean Diameter (mm) Sex Mean Diameter (mm) Both sexes 29.4 Both sexes 29.4 M 32.9 32.9 FM 31.7 F 31.7 M 36.4 36.4 FM 33.1 F 33.1 Both sexes 37.9 Both sexes

37.9

The final design of the handle used in this study (Figure 2) allowed us to resolve a series of The final design that of the handle used in this study (Figure 2) allowed us to a series of ergonomic problems existed with other types of MIS handles which did notresolve meet the design ergonomic problems that existed with otherit types handles which not palm meetof the criteria obtained in ERGOLAP. In this sense, shouldofbeMIS noted that, since thedid entire thedesign hand criteria obtained in in gripping ERGOLAP. this sense, it should be noted that, since the entire the is now involved theIn handle, it is easier to achieve a neutral position of thepalm wrist.ofThis hand is now involved gripping thelesions. handle,Hence, it is easier to achieve a neutralinposition of the wrist. reduces fatigue and theinrisk of thenar the grip was designed such a way that the This reduces fatigue andevenly the riskbetween of thenarthe lesions. thefingers. grip wasAllowing designedgreater in such contact a way that pressure is distributed palmHence, and the of the pressurewith is distributed between the palm thestretching fingers. Allowing contact the handle handle the wholeevenly hand avoids flexing the and wrist, tendons,greater distending theofelbow, and with the shoulder whole hand avoids flexing the wrist, tendons, distending the elbow,relative and limiting limiting movement. The length of thestretching handle and its diameter were increased to the handles traditionally used in MIS, as this provides a better fit for different hand sizes, and the fingers have a larger contact surface thus reducing the pressure on localized areas, especially the thumb.

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shoulder movement. The length of the handle and its diameter were increased relative to the handles traditionally used in MIS, as this provides a better fit for different hand sizes, and the fingers have a larger contact surface thus reducing the pressure on localized areas, especially the thumb. Regarding the geometry of the handle design developed in the ERGOLAP project (Figure 3a), there are three significant parameters. These are identified as the “inferior diameter” (DI ), “median diameter” (DM ), and “superior diameter” (DS ). The median diameter (DM ) coincides with the diameter defined at the point of inflection of the curvature of the handle (Figure 3a). It also defines the position of the hand relative to the handle during grasping, since for all the surgeons this diameter coincides with the line defined between the third and fourth (Figure 3b). Similarly, DS and DI correspond to the narrowest and the broadest parts of the handle design, respectively. These diameters, as shown in Figure 3b, in turn coincide with the lines defined between the second and third phalanges in the case of DI and the fourth and fifth phalanges in the case of DS . Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 14

(a)

(b)

Figure 3. (a) Parameters used in the study; (b) directives for determining the handle position. Figure 3. (a) Parameters used in the study; (b) directives for determining the handle position.

Regarding the geometry of the handle design developed in the ERGOLAP project (Figure 3a), ◦ (Figure 3b). features of thisparameters. handle are These that the of the as handle with thediameter” shaft is 45(D there Other are three significant areangle identified the “inferior I), “median This is a design constraint thatdiameter” must remain unchanged, regardless size of the handle or size of diameter” (DM), and “superior (DS). The median diameterof (Dthe M) coincides with the diameter the surgeon’s hand of since it is theofvalue recommended previous studies was approved by defined at the point inflection the curvature of the by handle (Figure 3a). It[23] alsoand defines the position allthe thehand surgeons whotoparticipated in the ERGOLAP project. of relative the handle during grasping, since for all the surgeons this diameter coincides To define a 3D parametric model of the handle, we chose as the scaling parameter the median with the line defined between the third and fourth (Figure 3b). Similarly, DS and DI correspond to the diameter (D ), since this is the most characteristic diameter of the design. It is defined as the line of M narrowest and the broadest parts of the handle design, respectively. These diameters, as shown in the hand between the third and fourth phalanges, and which must pass through the point of inflexion Figure 3b, in turn coincide with the lines defined between the second and third phalanges in the case of D the curvature of the handle during grasping. The other parameters that have to be modified to of I and the fourth and fifth phalanges in the case of D S. properly the of handle to the surgeon’s hand size (Figure 3b). The other S , DI , Rwith 1 , and Otheradapt features this handle are that the angle ofare theDhandle theR2shaft is 45° (Figure 3b). parameters are kept invariant, affecting neither the scalability of the model nor the functionality of This is a design constraint that must remain unchanged, regardless of the size of the handle or size of the design, as we explain below. We reached this result by modifying in various ways the physical the surgeon’s hand since it is the value recommended by previous studies [23] and was approved by model generated by participated additive manufacturing [42,44], and testing it on a large number of surgeons. all the surgeons who in the ERGOLAP project. Physical models were manufactured for each subject using rapid prototyping technology their To define a 3D parametric model of the handle, we chose as the scaling parameter the for median subsequent evaluation. were manufactured a 3D printer using white plastic diameter (DM ), since thisAll is the the handles most characteristic diameterwith of the design. It is defined asABS the line of and a smooth surface finish. the hand between the third and fourth phalanges, and which must pass through the point of inflexion simplicity 3D parametric CAD handle we found itthat possible the values of theFor curvature of of thethe handle during grasping. The model, other parameters have to torelate be modified to of D , D , R , and R , to the value of D . The ratios between D and the other parameters are listed in S I 1 2 M M properly adapt the handle to the surgeon’s hand size are DS, DI, R1, and R2 (Figure 3b). The other Table 3. parameters are kept invariant, affecting neither the scalability of the model nor the functionality of the design, as we explain below. We reached this result by modifying in various ways the physical model generated by additive manufacturing [42,44], and testing it on a large number of surgeons. Physical models were manufactured for each subject using rapid prototyping technology for their subsequent evaluation. All the handles were manufactured with a 3D printer using white ABS plastic and a smooth surface finish. For simplicity of the 3D parametric CAD handle model, we found it possible to relate the values of DS, DI, R1, and R2, to the value of DM. The ratios between DM and the other parameters are listed in Table 3.

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Table 3. Constants which relate the parameters of the handle to DM . Parameter (mm)

Parametric Ratio

DM DI DS R1 R2

1 0.80 1.15 1.25 4.48

2.4. Anthropometric Relationship between the Surgeon’s Hand and the Size of the Handle In this subsection, we shall describe the study that we carried out to relate the anthropometry of the hand to the size of the handle. The aim was to determine which hand measurements are related to the size of the surgical handle developed in this paper to scale the parametric model of the handle to the size most appropriate for each surgeon’s hand. To this end, we started from the base of previous studies of anthropometric dimensions of the hand for the optimal design of everyday utensils. In this sense, one of the most thorough-going works is entitled “Hand Anthropometry of U.S. Army Personnel” [45]. This reports the statistical results of data collected in an anthropometric study of the hands of US Army personnel in 1987 and 1988. The population of that study consisted of 1003 men and 1304 women. The 86 hand dimensions analyzed in the report consisted of 64 measurements obtained photometrically, and 22 direct measurements. Figure 4 shows some of these dimensions which have been widely used in anthropometric and ergonomic studies of the hand [5,16,41,46,47]. Greiner’s study is of great importance given the sparsity of the literature that includes any analyses of such a large number of anthropometric parameters of the hand. Such is the case for the design of hand tools whose design can make use of a large number of anthropometric parameters such as the finger length, the width of the hand, and the length of the hand [5,16,41,46–48]. As a complement to this anthropometric study, we also analyzed papers that studied the relationship of the dimensions of the hand with the ergonomic use of hand tools. For example, Matern and Waller [49] presented a detailed analysis of the concave surface of the hand with respect to its longitudinal and lateral dimensions which has a correspondence with the generatrix used in the present work (Figure 3b). Using data from the work of Greiner [45], DiMartino et al. [16] defined three categories of hand tools (small, medium, and large) in accordance with hand length. To reduce the number of anthropometric data that we needed to employ in this study, we carried out a comparative study of the different lengths studied by Greiner [45] and those studied by González et al. [18]. In accordance with the aspects indicated above in Section 2.3 that the handle design must meet, the following two criteria were established to determine the most appropriate hand measurements to be analyzed:

•

•

Measurements related to the palm support of the handle—these correspond to the importance of having greater contact between hand and handle, and are therefore related to the breadth of the hand. Measurements related to the diameter of the handle—these correspond to the handle appropriately fitting the different types of hand, allowing the fingers to have a greater contact surface, and are therefore related to the total length of the hand and the length of the palm.

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Figure 4. (a) Hand Length Digitized (58); (b) Hand Length Measured (59); (c) Palm Length Measured

Figure 4. (a) Hand Length Digitized (58); (b) Hand Length Measured (59); (c) Palm Length Measured (61); (d) Hand Breadth from Digitizer (62); (e) Hand Breadth Measured (63); (f) Crotch 1 Height (69); (61); (d) Hand Breadth from Digitizer (62); (e) Hand Breadth Measured (63); (f) Crotch 1 Height (69); (g) Crotch 2 Height (70); (h) Crotch 3 Height (71); (i) Crotch 4 Height (72). (g) Crotch 2 Height (70); (h) Crotch 3 Height (71); (i) Crotch 4 Height (72). Based on the above and on the anthropometric measurements of the hand that have already been analyzed other and works ergonomics, in the present work we analyzed the following three Based on the in above ononthe anthropometric measurements of the hand that have already anthropometric parameters of the hand: been analyzed in other works on ergonomics, in the present work we analyzed the following three

anthropometric parameters of the hand: • Hand Length from Digitizer (HLD) (Figure 4a).

• • •

• Palm Length Measured (PLM) (Figure 4c). Length from Digitizer (HLD) •Hand Hand Breadth from Digitizer (HBD)(Figure (Figure4a). 4d).

Palm Length Measured (PLM) (Figure 4c). To investigate the correspondence between hand size and handle size, we analyzed the Hand Breadth from Digitizer (HBD) (Figure 4d). anthropometric data for the 135 surgeons who participated in this study, as summarized in Table 1.

From the values obtained, we first calculated HLD, PLM, and HBD (Table 4, columns 3 to 5) for each To investigate the correspondence between hand size and handle size, we analyzed the sex and each hand type as defined in González et al. [18], and then, in order to have parameters that anthropometric data for the 135 surgeons who participated in this study, as summarized in Table 1. are very similar in value for any hand size, calculated the ratios between these three sets of Fromanthropometric the values obtained, we first calculated HLD, PLM, and HBD (Table 4, columns 3 to 5) for each values and the optimal median diameter of the handle (Table 4, last three columns). sex and each hand type as defined et al. [18], and then, in order to have parameters that are The last two rows of Tablein4González give the mean values and standard deviations of these ratios very weighted similar inaccording value fortoany size, calculated three of anthropometric thehand population of each sexthe andratios hand between type (see these Table 2). Onesets observes that, of values theanthropometric optimal median diameter the (a handle (Table 4, last columns). theand three ratios, that of of PLM measure of the innerthree length of the palm) has the smallest We therefore concluded that this ratio of would the most The last standard two rowsdeviation of Table 4(0.0113021). give the mean values and standard deviations theseberatios weighted appropriate to use to relate a surgeon’s hand size with the best handle size of a laparoscopic grasper, according to the population of each sex and hand type (see Table 2). One observes that, of the three and hence ultimately theof best custom handle of design. anthropometric ratios, that PLM (a measure the inner length of the palm) has the smallest standard

deviation (0.0113021). We therefore concluded that this ratio would be the most appropriate to use to relate a surgeon’s hand size with the best handle size of a laparoscopic grasper, and hence ultimately the best custom handle design.

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Table 4. Relationships between thethe Hand Length from Digitizer (HLD), Palm Length Measured (PLM), andand Hand Breadth from Digitizer (HBD) dimensions andand Table 4. Relationships Relationships between the Hand Length from Digitizer (HLD), Palm Length Measured (PLM), and Hand Breadth from Digitizer (HBD) dimensions and Table 4. between Hand Length from Digitizer (HLD), Palm Length Measured (PLM), Hand Breadth from Digitizer (HBD) dimensions the optimal median diameters of a laparoscopic surgery handle. the optimal median diameters of a laparoscopic surgery handle. the optimal median diameters of a laparoscopic surgery handle. the optimal median diameters of a laparoscopic surgery handle. optimal median diameters a laparoscopic surgery handle. thethe optimal median diameters of aoflaparoscopic surgery handle.

Table 4. Relationships between the Length Hand Length from Digitizer (HLD), Palm Length Measured (PLM), and Hand Breadth from Digitizer (HBD) dimensions Table 4. Relationships between Hand Length from Digitizer (HLD), Palm Length Measured (PLM), Hand Breadth from Digitizer (HBD) dimensions Table 4. Relationships between thethe Hand from Digitizer (HLD), Palm Length Measured (PLM), andand Hand Breadth from Digitizer (HBD) dimensions andand and8 of 13 Appl. Sci. 2018, 8, 1200

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Ø Table 4. Relationships between the Hand Length from Digitizer (HLD), Palm Length Measured (PLM), and Hand Breadth from Digitizer (HBD) dimensions and the Hand Length Palm Length Hand Breadth Optimum Hand Length Palm Length Hand Breadth Optimum Hand Length Palm Length Hand Breadth Optimum Hand Length Palm Length Hand Breadth Optimum Hand Length Palm Length Hand Breadth Optimum Hand Length Palm Length Hand Breadth Optimum optimal median diameters of a laparoscopic surgery handle.

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Sex Sex Sex Sex Sex Sex

HSC

from Digitizer Measured from Digitizer Diameter from Digitizer Measured from Digitizer Diameter from Digitizer Measured from Digitizer Diameter from Digitizer Measured Measured from from Digitizer Diameter from Digitizer Measured from Digitizer Diameter from Digitizer Digitizer Diameter (HLD) (PLM) (HBD) of handle (HLD) (PLM) (HBD) of handle (HLD) (PLM) (HBD) handle (HLD) (PLM) (HBD) of of of handle (HLD) (PLM) (HBD) handle (HLD) (PLM) (HBD) handle Hand Length Palm Length Hand Breadth Øof Optimum DM M Mof Sex from Digitizer Measured from Digitizer Diameter D DMD M DD M (HLD)

(PLM)

(HBD)

Units mm Units in mm Units in mm Units in mm Units mm Units ininin mm

handle DM

Units in mm

XS Both sexes XSXS Both Both sexes XS Both sexes Both sexes XS Both sexes XS sexes XS Both sexes Male Male Male Male Male Male Male S SS SS S SFemale Female Female Female Female Female Female Male Male Male Male Male Male Male MM MMMM M Female Female Female Female Female Female Female Both sexes Both sexes sexes Both sexes Both sexes LLL LL L Both sexes L Both Both sexes

159.3 159.3 159.3 159.3 159.3 159.3 159.3 174.1 174.1 174.1 174.1 174.1 174.1 174.1 170.2 170.2 170.2 170.2 170.2 170.2 170.2 188.8 188.8 188.8 188.8 188.8 188.8 188.8 182.1 182.1 182.1 182.1 182.1 182.1 182.1 194.9 194.9 194.9 194.9 194.9 194.9 194.9

87.6 87.6 87.6 87.6 87.6 87.6 87.6 97.6 97.6 97.6 97.6 97.6 97.6 97.6 94.3 94.3 94.3 94.3 94.3 94.3 94.3 107.8 107.8 107.8 107.8 107.8 107.8 107.8 98.2 98.2 98.2 98.2 98.2 98.2 98.2 111.6 111.6 111.6 111.6 111.6 111.6 111.6

71.1 71.1 71.1 71.1 71.1 71.1 71.1 79.1 79.1 79.1 79.179.1 79.1 79.1 72.5 72.5 72.5 72.5 72.5 72.5 72.5 86.5 86.5 86.5 86.586.5 86.5 86.5 78.9 78.9 78.9 78.9 78.9 78.9 78.9 86.5 86.5 86.5 86.586.5 86.5 86.5

Anthropometric Relationship Factor Anthropometric Relationship Factor Anthropometric Relationship Factor Anthropometric Relationship Factor Anthropometric Relationship Factor Anthropometric Relationship Factor Anthropometric Relationship Factor

𝑯𝑳𝑫 𝑯𝑳𝑫 𝑯𝑳𝑫 𝑯𝑳𝑫 𝑯𝑳𝑫 𝑯𝑳𝑫 HLD 𝑫 𝑫 𝑫 𝑫 𝑫𝑴𝑫𝑴𝑴 𝑴𝑴 D𝑴

𝑷𝑳𝑴 𝑷𝑳𝑴 𝑷𝑳𝑴 𝑷𝑳𝑴 𝑷𝑳𝑴 𝑷𝑳𝑴 PLM 𝑫 𝑫 𝑫 𝑫D𝑴𝑫𝑴𝑴𝑴𝑫 𝑴𝑴

𝑯𝑩𝑫 𝑯𝑩𝑫 𝑯𝑩𝑫 𝑯𝑩𝑫 𝑯𝑩𝑫 𝑯𝑩𝑫 HBD 𝑫 𝑫 𝑫 𝑫 𝑫 𝑫 𝑴𝑴 D 𝑴𝑴𝑴𝑴

5.418 5.418 5.418 5.418 5.418 5.418 5.418 5.292 5.292 5.292 5.292 5.292 5.292 5.292 5.369 5.369 5.369 5.369 5.369 5.369 5.369 5.187 5.187 5.187 5.187 5.187 5.187 5.187 5.502 5.502 5.502 5.502 5.502 5.502 5.502 5.142 5.142 5.142 5.142 5.142 5.142 5.142 5.308 5.308 5.308 5.308 5.308 5.308 5.308 0.1173040 0.1173040 0.1173040 0.1173040 0.1173040 0.1173040 0.1173040

2.980 2.980 2.980 2.980 2.980 2.980 2.980 2.967 2.967 2.967 2.967 2.967 2.967 2.967 2.975 2.975 2.975 2.975 2.975 2.975 2.975 2.962 2.962 2.962 2.962 2.962 2.962 2.962 2.967 2.967 2.967 2.967 2.967 2.967 2.967 2.945 2.945 2.945 2.945 2.945 2.945 2.945 2.967 2.967 2.967 2.967 2.967 2.967 2.967 0.0113021 0.0113021 0.0113021 0.0113021 0.0113021 0.0113021 0.0113021

2.418 2.418 2.418 2.418 2.418 2.418 2.418

M

29.4 29.4 29.4 29.4 29.4 29.4 29.4 32.9 32.9 32.9 32.9 32.9 32.9 32.9 31.7 31.7 31.7 31.7 31.7 31.7 31.7 36.4 36.4 36.4 36.4 36.4 36.4 36.4 33.1 33.1 33.1 33.1 33.1 33.1 33.1 37.9 37.9 37.9 37.9 37.9 37.9 37.9 𝑥 𝑥𝑥x𝑥𝑥 𝑥 𝑠 𝑠 𝑠 s𝑠𝑠 𝑠

M

M

2.404 2.404 2.404

2.404 2.404 2.404 2.404 2.287 2.287 2.287 2.287 2.287 2.287 2.287 2.376 2.376 2.376 2.376 2.376 2.376 2.376 2.384 2.384 2.384 2.384 2.384 2.384 2.384 2.282 2.282 2.282 2.282 2.282 2.282 2.282 2.362 2.362 2.362 2.362 2.362 2.362 2.362 0.0549504 0.0549504 0.0549504 0.0549504 0.0549504 0.0549504 0.0549504

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3.3.Results Resultsand andDiscussion Discussion The Themain mainresult resultof ofthis thiswork workhas hasbeen beento toobtain obtainthe the3D 3Dparametric parametricdesign design of ofaahandle handle for forthe the graspers the parameter parameter D DMMallows allowsthe thedesign designtotobebescaled scaled graspers used used in in laparoscopic laparoscopic surgery, in which the to to adaptthe thesize sizeofofthe thehandle handletotoeach each surgeon’s surgeon’s hand hand size. size. In In particular, it was adapt was found found that that the the anthropometric anthropometric measurement measurement of of the the hand hand that that isis most most appropriate appropriate to to relate relate the thehandle handle size size to tothe the surgeon’s surgeon’shand handsize sizeisisthat thatdefined definedby byPLM. PLM.To Toobtain obtainaa3D 3Ddesign, design,first firstthe thesurgeon’s surgeon’sPLM PLMvalue valueisis taken. taken. This This value value is is then then divided divided by by the the coefficient coefficient 2.967 2.967 (see (see Table Table4) 4)to togive givethe themost mostappropriate appropriate value valueof ofthe themedian mediandiameter diameterof ofthe thehandle handle(D (DMM).). With Withthis thisvalue, value,the the3D 3Dparametric parametricmodel modelof ofthe the handle is scaled to the surgeon’s hand size. Figure 5 shows some examples of 3D CAD models scaled handle is scaled to the surgeon’s hand size. Figure 5 shows some examples of 3D CAD models scaled to todifferent differentsurgeons surgeonsamong amongthe theparticipants participantsin inthis thisstudy. study.The Thecurve curvedrawn drawnin inaadashed dashedline lineon onthe the different differentcustomized customizedmodels modelsisisininthis thisway wayadapted adaptedto tothe thesurgeon’s surgeon’shand handas asshown shownby bythe theequivalent equivalent dashed dashedline linein inFigure Figure3b. 3b.

Figure Figure 5.5. Custom Custom 3D 3D Computer Computer Architectural Architectural Drawings Drawings (CAD) (CAD) models models of of the the surgical surgical handle handle depending on each surgeon’s PLM measurement. depending on each surgeon’s PLM measurement.

Tocheck checkthe theresults, results,several several CAD parametric designs different surgeons were fabricated To 3D3D CAD parametric designs forfor different surgeons were fabricated by by additive manufacturing (for different and hand 6 shows ofhandles these handles additive manufacturing (for different sexessexes and hand sizes).sizes). FigureFigure 6 shows one ofone these made made for a particular of PLM, and with therefore with a characteristic of Dthat M (a value that for a particular value of value PLM, and therefore a characteristic value of DMvalue (a value determines determines complete of the first thehand surgeon’s hand was to then the completethe design of thedesign handle). Forhandle). this, firstFor thethis, surgeon’s was scanned, to scanned, then obtain the obtain the palm length in thisa value case giving valueThe of 96.55 mm. The optimal diameterfrom was palm length (PLM), in this(PLM), case giving of 96.55a mm. optimal diameter was calculated calculated from theratio anthropometric ratio PLM/D M resulting in D a Mcustom of DM was = 32.54 mm, the anthropometric PLM/DM resulting in a custom value of = 32.54value mm, which used to which was used to generate the parametric model of the handle (Figure 6). generate the parametric model of the handle (Figure 6). Tobe befully fullyfunctional functionalfor forthe thevalidation validationtests, tests,the the3D 3DCAD CADmodel modelwas wasdesigned designedwith withaahollow hollow To interior.This Thisallowed allowedthe theshaft shaft(the (themetallic metallicclip) clip)to tobe beinserted insertedtogether togetherwith withthe theopening openingand andclosing closing interior. mechanismsof ofthe thegrasper grasperand andthe theshaft’s shaft’srotation rotationmechanism mechanism(Figure (Figure6). 6). mechanisms

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(a) (a)

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(b) (b)

Figure 6. Prototype custom handle. (a) Details of the pieces; (b) assembled prototype. Figure 6. 6. Prototype Prototype custom custom handle. handle. (a) (a) Details Details of of the the pieces; pieces; (b) (b) assembled assembled prototype. prototype. Figure

Figure 7 shows a surgeon using the prototype (DM = 32.54 mm) during the validation test. At the Figure 7 shows a surgeon surgeon using using the the prototype prototype (D (DM M= = 32.54 32.54 mm) during the validation test. At the conclusion of the test, the surgeon confirmed that their experience using the handle was completely conclusion of the test, the surgeon confirmed that their experience using the handle was completely satisfactory [18]. Identical results were obtained with the surgeons whose handles corresponded to satisfactory satisfactory [18]. Identical Identical results results were obtained obtained with the surgeons whose handles corresponded to those illustrated in Figure 5. those illustrated in Figure 5.

Figure 7. Prototype custom handle used in a simulation test. Figure 7. Prototype custom handle used in a simulation test.

4. Conclusions 4. Conclusions The main finding of this work was confirmation that it is possible to obtain 3D parametric The main mainfinding findingofofthis this work confirmation that it is possible to obtain 3D parametric work waswas confirmation is possible parametric designs designs of a handle for laparoscopic graspers thatthat areit scalable totofitobtain each 3D surgeon’s hand size. designs of aforhandle for laparoscopic graspers that are scalable to fit each surgeon’s hand size. of a handle laparoscopic graspers that are scalable to fit each surgeon’s hand size. Furthermore, Furthermore, it was found that a single anthropometric factor—the “Palm Length Measured”—can Furthermore, it was found that a single anthropometric factor—the “Palm Length Measured”—can it found that aany single anthropometric factor—the “Palm Length Measured”—can used to relate bewas used to relate surgeon’s hand size to the optimal diameter of the handle. be Functional tests be used to relate anysize surgeon’s hand size to the of optimal diameter of the handle. Functional any surgeon’s hand to the optimal diameter the handle. Functional tests carried outadapts intests the carried out in the CCMIJU confirmed that the parametric design developed for the handles carried out in the CCMIJU confirmed that the parametric design developed for the handles adapts CCMIJU confirmed that the parametric design ergonomically to different surgeon’s hand sizes.developed for the handles adapts ergonomically to ergonomically to different surgeon’s hand sizes. different surgeon’s hand sizes. Thus, the specific contributions of this work include the following: Thus, the specific contributions of this work include the following: • A 3D parametric CAD design has been obtained for the handle of laparoscopic surgery graspers •• A 3D CAD design has obtained for the of surgery graspers A 3Disparametric parametric CAD designhand has been been forresulting the handle handle of laparoscopic laparoscopic graspers that scalable for different sizes.obtained All of the models personallysurgery customized for that is scalable for different hand sizes. All of the resulting models personally customized for that is scalable for different hand sizes. All of the resulting models personally customized for each surgeon complied with the ergonomic criteria for their use. each surgeon surgeon complied complied with with the the ergonomic ergonomic criteria criteria for for their their use. use. each • The results show that additive manufacturing and the application of ergonomics criterion • The results show that additive manufacturing and the application of ergonomics criterion provide an efficient method for the customized design and manufacture of this type of provide an efficient method for the customized design and manufacture of this type of specialized tools, being possible to be applicable to other sectors. specialized tools, being possible to be applicable to other sectors.

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•

•

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The results show that additive manufacturing and the application of ergonomics criterion provide an efficient method for the customized design and manufacture of this type of specialized tools, being possible to be applicable to other sectors. The relationship between the anthropometry of the surgeon’s hand and the most suitable size of the handle was determined, with the most suitable anthropometric parameter to measure being the “Palm Length Measured” (PLM).

Finally, the authors consider that the customization of the geometry of a surgical tool can serve as a reference for future research that addresses the optimal material and tools for their subsequent production through additive manufacturing techniques. Author Contributions: Conceptualization, A.G.G. and D.R.S.; Formal analysis, D.R.S. and A.S.R.; Investigation, A.G.G., D.R.S. and L.G.M.; Methodology, A.G.G.; Software, L.G.M.; Validation, A.G.G., D.R.S., L.G.M. and A.S.R.; Writing–review & editing, A.G.G. and D.R.S. Funding: This research received no external funding. Acknowledgments: The authors wish to acknowledge the support of this research work to the VI Regional Research Plan and the Regional Government of Extremadura and to the Fondo Social Europeo (FEDER) linked to the financial of the research groups Manufacturing Engineering (GR-18029) and INNOVA RNM020—Design, Sustainability and Added Value (GR-18015). The authors are grateful for the outstanding willingness to cooperate of the 135 surgeons who participated in the study, and for their interest in following through with the appropriate trials so as to obtain a satisfactory outcome. In particular, they all considered it of great importance to adapt the sizes of the handles of the tools they use to the size of their hands. Conflicts of Interest: The authors declare no conflicts of interest.

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