
 simulation - based medical education has been widely used in medical skills training;simulation - based surgical training can be of immense help in acquiring and maintaining surgical skills in safe environments without exposing patients to risk;several bench models have been described for cutaneous surgical - skill training ; however , so far , none of them is complete . 
  simulation - based medical education has been widely used in medical skills training ; simulation - based surgical training can be of immense help in acquiring and maintaining surgical skills in safe environments without exposing patients to risk ; several bench models have been described for cutaneous surgical - skill training ; however , so far , none of them is complete . in the last few years , the number of cases of cutaneous lesions managed by primary care physicians has increased . in order to manage such lesions , it is necessary to perform simple cutaneous surgical procedures . in this scenario and
taking into account that most of the general practitioners performing minor surgical procedures do not have any formal surgical training , as well as that basic surgical fundamentals are not acquired by a large percentage of medical students despite the relevance of the topic , teaching and learning the principles of cutaneous surgery ( e.g. , closure of skin incision and excision of skin lesion ) have become important components in the training of both undergraduates and newly graduates . also considering that surgical - skill training on live patients infringes medical , legal and ethical aspects , that the practice on fresh human cadavers and on live animals is associated with high costs , risk for infections , the need for specialized facilities as well as with legal and ethical aspects , and that the use of virtual reality simulators is hampered by its high cost and lack of access , learning technical skills on inanimate bench models has been widely used in medical education .
however , although several inanimate bench models have been described,[714 ] none of them allows for developing all basic surgical skills .
therefore , this study aimed at proposing , describing , and outlining a simulation - based cutaneous surgical skill training by using a chicken - wing , -thigh , or -trunk , bench model which , since it is an educational , simple , versatile , portable , easy - to - assemble and inexpensive tool , enables medical students to practice basic surgical skills in a safe , controlled , risk - free setting before applying the techniques in real practice situations .
the design in the present proposal is based on the performance of various training sessions ( days , weeks , or months ) intercalated with resting periods and encompassing three different teaching and learning sessions [ figure 1 ] .
the basic structure of each training session is oral teaching based on teaching materials ( text books , on - line texts , and on - line narrated expert - demonstration videos ) for the group of students followed by instructor - directed training on the chicken - skin bench model in an individualized fashion and by self - directed training on the chicken - skin bench model outside the classroom ( e.g. , at home ) .
such proposal must be integrated to the educational program , and it can be adapted and distributed so as to complement the established curriculum .
the chicken - skin bench model training can be incorporated as a teaching and learning tool for both novice medical students and others that partly master basic surgical skills , but need to perfect them .
it can also be applied within the context of different courses in the medical program , such as in instrumental technique , ambulatory surgery , surgical clinic , plastic surgery , dermatology , and others .
design of the proposed simulation - based cutaneous surgical - skill training on a chicken - skin bench model : basic structure of each teaching session students must practice in an individual , deliberate , repetitive and participative fashion .
learning goals must be clearly defined ; teaching objectives must be listed in an increasing order of difficulty [ figure 2 ] and distributed in different training sessions ; as a medical student acquires easier skills , the level of difficulty must be increased . with this regard , the training must be student - centered .
in the subsequent sessions , the proposals must vary according to the differences shown in skill development by the trainees .
the principles of cutaneous surgery proposed and outlined in this study include basic training on the techniques for incisions , suture , biopsies , and reconstruction .
each of these procedures must be taught separately to medical students so that they can learn each technical skill as thoroughly as possible .
learning targets in an increasing order of difficulty for the principles of cutaneous surgery training , chicken trunks , wings , or thighs must be bought from food stores ( e.g. , supermarkets ) , and preference must be given to fresh pieces with skin .
additionally , the following will be necessary for training : a glass ( or wooden ) plate , which will serve as support , needle - felt thread , a needle holder , rat tooth tweezers , scissors , a number-15 surgical blade with a scalpel handle , and a marking pen [ figure 3 ] .
chicken - skin bench model and materials prepared for the principles of cutaneous surgery training incision and suture techniques can be practiced simultaneously . to that end , the trainees place a mark on the chicken - skin bench model and then make an incision in the marked tissue by using the appropriate technique ( smooth movements with the scalpel , cutting angle from 30 to 60 , no movements of  aliasing  , and no movement sideways ) . in sequence ,
the created defects are repaired by stitches as well as by applying important technical aspects to promote good wound healing and cosmesis , such as instrument handling , correct needle positioning in the needle holder , angle for needle insertion in the skin , needle withdrawal at an equidistant point from the insertion point for both bites , approximation of wound edges with an appropriate level of tension , eversion and apposition of the wound edges , and meticulous tissue handling . such process can be repeated innumerous times and hence , linear , circular , vertical , and horizontal incisions as well as different sutures , such as simple interrupted sutures , vertical mattress sutures , horizontal mattress sutures , half - buried mattress sutures , subdermal interrupted sutures , running simple suture , running locked suture , and running subcuticular suture , can be practiced [ figure 4 ] . chicken - skin bench model simulating ( a - b ) linear , circular , and elliptic patterns of incision and ( c - d ) simple interrupted suture and running locked suture the practice of surgical excisions with previously determined safety margins ( excision biopsy ) , which is considered to be the cornerstone of cutaneous surgical practice and therefore , should be part of the cutaneous surgical armamentarium ,
for instance , for the practice of the classic elliptical excisional skills [ figure 5 ] , students receive the following instructions : 
 ellipse design  the ellipse should be formed by tracing two arcs of a circle on the skin ; the arcs , which are symmetrical with respect to the midline axis separating them , intersect at their ends to form a convex shape ; the curvature used leads to a 3:1 to 4:1 length - width ratio between the long and short axes of the ellipse formed ; the 30elliptical angle was used at the ends ( intersection of the arcs).[161921]safety margins  the two arcs of a circle should be placed around the periphery of the skin tumor to delineate the required safety margins .
the extent of safety margins ranges from 2 to 10 mm according to the recommendations for surgical resection of most non - melanoma skin cancers.incision of the ellipse  smooth movements with the scalpel ; cutting angle ( 30 - 60 ) ; cuts to  subcutaneous tissue  with 1 or 2 strokes avoiding stair casing ; and avoids cross - hatching the tips of the ellipse.excision of the ellipse  cuts in the same plane while removing tissue , leaving the same amount of tissue on all areas of the postoperative wound and handling tissue delicately , thus avoiding damage to the epidermis . 
 
ellipse design  the ellipse should be formed by tracing two arcs of a circle on the skin ; the arcs , which are symmetrical with respect to the midline axis separating them , intersect at their ends to form a convex shape ; the curvature used leads to a 3:1 to 4:1 length - width ratio between the long and short axes of the ellipse formed ; the 30elliptical angle was used at the ends ( intersection of the arcs).[161921 ] safety margins  the two arcs of a circle should be placed around the periphery of the skin tumor to delineate the required safety margins .
the extent of safety margins ranges from 2 to 10 mm according to the recommendations for surgical resection of most non - melanoma skin cancers .
incision of the ellipse  smooth movements with the scalpel ; cutting angle ( 30 - 60 ) ; cuts to  subcutaneous tissue  with 1 or 2 strokes avoiding stair casing ; and avoids cross - hatching the tips of the ellipse .
excision of the ellipse  cuts in the same plane while removing tissue , leaving the same amount of tissue on all areas of the postoperative wound and handling tissue delicately , thus avoiding damage to the epidermis .
learning goals must be clearly defined ; teaching objectives must be listed in an increasing order of difficulty [ figure 2 ] and distributed in different training sessions ; as a medical student acquires easier skills , the level of difficulty must be increased . with this regard
in the subsequent sessions , the proposals must vary according to the differences shown in skill development by the trainees .
the principles of cutaneous surgery proposed and outlined in this study include basic training on the techniques for incisions , suture , biopsies , and reconstruction .
each of these procedures must be taught separately to medical students so that they can learn each technical skill as thoroughly as possible . learning targets in an increasing order of difficulty
for the principles of cutaneous surgery training , chicken trunks , wings , or thighs must be bought from food stores ( e.g. , supermarkets ) , and preference must be given to fresh pieces with skin .
additionally , the following will be necessary for training : a glass ( or wooden ) plate , which will serve as support , needle - felt thread , a needle holder , rat tooth tweezers , scissors , a number-15 surgical blade with a scalpel handle , and a marking pen [ figure 3 ] .
incision and suture techniques can be practiced simultaneously . to that end , the trainees place a mark on the chicken - skin bench model and then make an incision in the marked tissue by using the appropriate technique ( smooth movements with the scalpel , cutting angle from 30 to 60 , no movements of  aliasing  , and no movement sideways ) . in sequence ,
the created defects are repaired by stitches as well as by applying important technical aspects to promote good wound healing and cosmesis , such as instrument handling , correct needle positioning in the needle holder , angle for needle insertion in the skin , needle withdrawal at an equidistant point from the insertion point for both bites , approximation of wound edges with an appropriate level of tension , eversion and apposition of the wound edges , and meticulous tissue handling . such process can be repeated innumerous times and hence , linear , circular , vertical , and horizontal incisions as well as different sutures , such as simple interrupted sutures , vertical mattress sutures , horizontal mattress sutures , half - buried mattress sutures , subdermal interrupted sutures , running simple suture , running locked suture , and running subcuticular suture , can be practiced [ figure 4 ] . chicken - skin bench model simulating ( a - b ) linear , circular , and elliptic patterns of incision and ( c - d ) simple interrupted suture and running locked suture
the practice of surgical excisions with previously determined safety margins ( excision biopsy ) , which is considered to be the cornerstone of cutaneous surgical practice and therefore , should be part of the cutaneous surgical armamentarium , can also be performed on the chicken - skin bench model .
for instance , for the practice of the classic elliptical excisional skills [ figure 5 ] , students receive the following instructions : 
 ellipse design  the ellipse should be formed by tracing two arcs of a circle on the skin ; the arcs , which are symmetrical with respect to the midline axis separating them , intersect at their ends to form a convex shape ; the curvature used leads to a 3:1 to 4:1 length - width ratio between the long and short axes of the ellipse formed ; the 30elliptical angle was used at the ends ( intersection of the arcs).[161921]safety margins  the two arcs of a circle should be placed around the periphery of the skin tumor to delineate the required safety margins .
the extent of safety margins ranges from 2 to 10 mm according to the recommendations for surgical resection of most non - melanoma skin cancers.incision of the ellipse  smooth movements with the scalpel ; cutting angle ( 30 - 60 ) ; cuts to  subcutaneous tissue  with 1 or 2 strokes avoiding stair casing ; and avoids cross - hatching the tips of the ellipse.excision of the ellipse  cuts in the same plane while removing tissue , leaving the same amount of tissue on all areas of the postoperative wound and handling tissue delicately , thus avoiding damage to the epidermis . 
 
ellipse design  the ellipse should be formed by tracing two arcs of a circle on the skin ; the arcs , which are symmetrical with respect to the midline axis separating them , intersect at their ends to form a convex shape ; the curvature used leads to a 3:1 to 4:1 length - width ratio between the long and short axes of the ellipse formed ; the 30elliptical angle was used at the ends ( intersection of the arcs).[161921 ] safety margins  the two arcs of a circle should be placed around the periphery of the skin tumor to delineate the required safety margins .
the extent of safety margins ranges from 2 to 10 mm according to the recommendations for surgical resection of most non - melanoma skin cancers .
incision of the ellipse  smooth movements with the scalpel ; cutting angle ( 30 - 60 ) ; cuts to  subcutaneous tissue  with 1 or 2 strokes avoiding stair casing ; and avoids cross - hatching the tips of the ellipse .
excision of the ellipse  cuts in the same plane while removing tissue , leaving the same amount of tissue on all areas of the postoperative wound and handling tissue delicately , thus avoiding damage to the epidermis .
the chicken - skin bench model provides the opportunity for the simulated practice of cutaneous reconstruction , such as grafting and flaps .
transposition flaps ( rhomboid flaps , z - plasty , w - plasty , banner flap , and bilobed flap ) , rotation flaps , and advancement flaps ( v - y plasty , and t - plasty ) can be simulated on the chicken - skin bench model .
for example , in face of a cutaneous defect , the performance of a flap ( flap outlining ) is planned with basis on schemes from teaching materials .
next , the markings are incised and the flap should be carefully separated from the underlying tissue attachments . in the sequence ,
the flap is moved to fill the defect and sutures should carefully fix the flap in place , avoiding tension on the pedicle [ figure 6 ] .
after practicing the techniques for incisions , sutures , biopsies , and reconstruction , the students can practice the management of cutaneous lesions . for this phase of the simulated learning
, different cutaneous lesions must be drawn on the chicken - skin bench model so that students can make the respective diagnoses and/or treatments by using the previously learned principles and then the surgical repair .
it is important to describe the phases to be followed by students if they do not yet master decision - making clinical concepts ; for example , when simulating a non - melanoma skin cancer , the trainee must then mark the safety margins by forming an ellipse , make the incision in the margins , the careful tissue excision and the primary closure of the defect created by placing stitches or the defect repair with the transposition , rotation or advancement of the flap or graft placement [ figures 7 and 8 ] .
chicken - skin bench model simulating a  non - melanoma skin cancer  and its diagnosis and treatment .
( f ) repair of the defect by placing a skin graft chicken - skin bench model simulating a  non - melanoma skin cancer  and its diagnosis and treatment .
in the present proposal for a simulated training , it is important that all medical students individually receive instructor - administered concurrent ( or process ) and summary ( or outcome ) feedback , that is feedback must be provided during and on completion of each training phase . in order to standardize teaching and learning , it is recommended that one instructor should be available for each group of 4 students .
the instructors must evaluate each specific movement in the technique , searching for errors and deficiencies so that , by means for constructive feedback , students can perfect their skills based on their errors , practice repeatedly and consequently develop skills over time .
it is important that , during and on completion of the whole teaching and learning process for each one of the surgical skills proposed , an objective evaluation be applied in order to measure the level of development of the competencies taught . to that end
, the global rating scale can be used [ table 1 ] , as it evaluates students performances in eight major areas , each of which was rated on a behaviorally anchored 5-point scale with 1 being the minimum score and 5 the maximum score for a total maximum score of 40 . global rating scale to assess objectively all suture and biopsy performances the global rating scale can be used to follow performance during different teaching sessions as well as to ensure that most students have developed the surgical skills proposed .
additionally , the global rating scale can be applied as a certification tool ; for an individual task , the candidate must achieve a score of 24 or more to be considered competent .
thus , if a medical student meets the previously defined criteria based on the objective evaluation , he can participate in the next training phase ( basic skills to complex procedures ) . in case that does not occur , the learning process must be repeated with a focus on the specific deficits and then a new evaluation must be applied .
since the ability to close a wound correctly is an essential and important skill in a general - practice setting , and excision biopsy techniques have been described as a cornerstone of cutaneous surgical practice , it is necessary to teach the principles of cutaneous surgery to undergraduates . in this scenario ( cutaneous surgical skill training ) , the development of basic surgical skills outside an operating environment ( simulation - based training ) is recommended prior to procedures on live patients . in addition , it has been shown that the retention of surgical skills is more robust when they are acquired by means of a combination of self - directed training with instructor - administered feedback distributed in an intercalated fashion with resting periods ( several training sessions ) instead of being taught all at once .
thus , this teaching form must be adopted with the purpose to retain and perfect the surgical skills learned .
however , some factors such as high costs and scarce available time by experienced faculty surgeons have been described as limiting factors to the implementation of that teaching and learning method . in the last few years , in an attempt to reduce the costs related to teaching that subject by distributing them over a pre - established period of time ( days , weeks , or months ) , various alternative methodologies , such as training on low - cost inanimate bench models , have been proposed , discussed , and evaluated by several groups.[71431 ] based on this , the main focus of the present study is to propose the use of an alternative bench model made from chicken trunks , wings , and thighs as simulation platforms for complementing the learning of the principles of cutaneous surgery in medical undergraduate programs .
chicken tissue was used as a model owing to its similarity , in echotexture and consistency , to human tissue . in the literature on simulation - based training ,
similar bench models made from chicken parts postmortem have been previously used with different indications , such as legs for teaching how to change needle angles , microneurosurgical and microvascular surgery and bedsidedetection of glass in wounds;[3335 ] thigh , wings , esophagus and trachea for microsurgical surgery training;[3640 ] the gizzard , posterior trunks , crop and esophagus for laparoscopic training;[4143 ] and others.[44 - 45 ] to the best of our knowledge , there are few studies on the application of the chicken - skin bench models in medical undergraduate programs , and the way of utilizing the bench model outlined in this study provides the opportunity to teach novice medical students and as medical students develop simple skills ( pre - established requirements ) , the training can be enhanced by simulating more complex procedures on the model itself or on other bench models .
bench models using hoops ( fabric ) and latex gloves are simple , easily available and inexpensive ; however , they do not allow for training on three - dimensional procedures , such as in some types of sutures , biopsies , and reconstructions .
synthetic materials , such as various simulated tissue produced and commercialized by different companies ( 3b scientific , simulab , life / form , all pro , simulation , 3-dmed , limbs and things , and others ) , can be used for practicing suture , biopsy , and three - dimensional skills ; however , they are difficult to purchase and expensive when compared to chicken trunks , wings , and thighs
. surgical skill practice could be performed on bench models , such as discarded surgical pieces , in case they did not need to be donated with consent from patients and/or their relatives .
additionally , educational institutions would require a collection and storage service , and there would be risk for infection .
others parts of postmortem animals ( e.g. , ox tongue , cattle digits and pig and rat skin[791112 ] ) have also been described with similar purposes , and some characteristics may hinder their use , including the material 's greater hardness ( frozen ) , which may cause the loss of needle - felt threads , the need for infra - structure , space and adequate conditions for their storage , in addition to risk for infection . with this regard ,
it is necessary to defrost the chicken trunks , wings , and thighs in advance to the training process .
furthermore , purchasing fresh pieces from shops that are rigorously supervised by the government can reduce risk for infection .
it is noteworthy that the chicken - skin bench model proposed in the present study should not necessarily replace the bench models used in different educational institutions .
in fact , the proposal is that this bench model be adapted ( or complementary ) to the teaching and learning program already established .
therefore , the chicken bench model can supplement training and consequently increase the available cutaneous surgical skill armamentarium of medical students in training . in addition to the financial cost involved in a training program with several teaching sessions
, time availability remains an issue for faculty surgeons as they are removed from the patient - care setting to teach in simulation environments .
computer - generated feedback could be an option to reduce learning time supervised by faculty surgeons , if computers were not so costly .
additionally , skill maintenance over time is significantly better when skills are learned with direct feedback from an instructor .
alternatively , the incorporation of residents , laboratory technicians or medical students could reduce the number of faculty experts that are transferred from their surgical practice to a simulation laboratory . increasing the intervals between training sessions and stimulating out - of - class practice ( e.g. , at home )
with regard to the simulated practice of surgical skills , the development of competencies must be evaluated by an objective method .
hence , in the present study , a previously validated certification and quantification tool was used ( global rating scale ) in order to objectively and quantitatively evaluate the surgical performances .
the proposal outlined in the present study was designed with basis only on the development of some principles of cutaneous surgery , and it does not meet all the needs of medical students in training , which must also include the learning of other surgical competencies .
because the simulated teaching and learning of cutaneous - surgery principles based on training on a bench model made from chicken trunks , wings , or thighs is reproducible , versatile , portable , available , easy to assemble and inexpensive ; it is a complementary alternative to the armamentarium of existing simulation platforms with the purpose to better prepare medical students prior to procedures on live patients . 

chicken - skin bench model is an educational , simple , versatile , portable , easy - to - assemble and inexpensive tool;this simulator allows medical students to practice cutaneous surgical skills in a safe , controlled , risk - free setting;this has an impact on the possibility of using this bench model according to the institutional availability . 
  chicken - skin bench model is an educational , simple , versatile , portable , easy - to - assemble and inexpensive tool ; this simulator allows medical students to practice cutaneous surgical skills in a safe , controlled , risk - free setting ; this has an impact on the possibility of using this bench model according to the institutional availability .
 background : because of ethical and medico - legal aspects involved in the training of cutaneous surgical skills on living patients , human cadavers and living animals , it is necessary the search for alternative and effective forms of training simulation.aims:to propose and describe an alternative methodology for teaching and learning the principles of cutaneous surgery in a medical undergraduate program by using a chicken - skin bench model.materials and methods : one instructor for every four students , teaching materials on cutaneous surgical skills , chicken trunks , wings , or thighs , a rigid platform support , needled threads , needle holders , surgical blades with scalpel handles , rat - tooth tweezers , scissors , and marking pens were necessary for training simulation.results:a proposal for simulation - based training on incision , suture , biopsy , and on reconstruction techniques using a chicken - skin bench model distributed in several sessions and with increasing levels of difficultywas structured . 
 both feedback and objective evaluations always directed to individual students were also outlined.conclusion:the teaching of a methodology for the principles of cutaneous surgery using a chicken - skin bench model versatile , portable , easy to assemble , and inexpensive is an alternative and complementary option to the armamentarium of methods based on other bench models described . 
Introduction
Design of the Proposed Simulation-Based Training
Learning goals
Preparing the chicken-skin bench model
Incision- and suture-technique training
Biopsy-technique training
Principles of Cutaneous-Reconstruction Training
Management of Simulated Cutaneous Lesions Using Cutaneous Surgical Skills
Instructor-Administered Feedback
Objective Evaluation on the Development of Cutaneous Surgical Skills
Discussion
Conclusion