Michael Patkin's

Heuristics of surgical dissection
Part 1: What and why

Publication history, Reflections & comments



Surgery & ergonomics


Information design

Editorials, book reviews




Heuristics are rules of thumb used by experts, of which they are usually unaware, or which seem trivial to them or not worth stating formally. Many of them apply to ill-defined manual or perceptual skills that in this case are used during surgical dissection. The aim of this study is to make these heuristics more explicit.

This study is presented in two parts. This first part describes the historical context for changes in surgical dissection in the past two centuries, the mechanical basis of how tissues actually separate and some of the methods used to identify and study heuristics. The second part1 describes heuristics used by expert surgeons. These are meant as a basis for improving dissection (accuracy, safety, time taken) and shortening the learning curve for new procedures and for trainees. It also discusses future methods of teaching dissection and other applications.


Traditional teaching of surgical skills by apprenticeship is being replaced by a formal structured approach in workshops and skills labs over recent decades. There are powerful reasons for improving teaching of operating skills of surgeons - pressure of time, less clinical experience, dissatisfaction with "see one, do one, teach one", more complex surgery, less dexterity among children because of fewer manual hobbies and similar activities in their everyday life, more concern about outcomes and complications, wider clinical audit, and of course litigation.

This does not exhaust the list. Both trainees and experienced surgeons are strongly motivated to do their work better, both to improve their results and for the satisfaction of feeling they are working skilfully. Fellow-workers have higher regard for those who operate in less time provided they do so safely. Longer operating times mean higher staff costs, cancelled procedures and longer waiting lists for patients.

A less obvious but powerful reason is that we are now also in the era of Post-Modern Surgery2 , a time when traditional skills used for direct handling of tissues are no longer sufficient. The concept of Eras of Surgery, together with a possible fourth one, requires a brief explanation (Table 1).

TABLE 1. Eras in surgical history

Pre Modern Surgery To 1846 Quick brutal procedures
Modern Surgery From 1846 General anaesthesia
Post-Modern Surgery From 1960s Layers of technology
interposed between
surgeon and patient, for
imaging & manipulation
Programmable surgical actions
? soon right-click mouse-controlled actions
Autonomous computer systems
? 2010 intelligent agents and new-generation
haptic and other sensors


Pre Modern Surgery ended with the introduction of general anaesthesia for surgery in 1846. Modern Surgery, over the next 125 years, was concerned with cutting and stitching of tissue which became increasingly complex. Although this was a time of huge innovation and expansion in surgery, surgeons still handled tissues directly or with tools held in the hands in traditional ways. (This classification blurred somewhat as tools and devices such as orthopaedic implants and techniques for example heart-lung bypass became more complex and needed special training.)

The distinctive feature of today's third era of Post-Modern Surgery is a complex layer of technology interposed between the operator and the tissues. It began in the late 1960s with operating microscopes and instruments with tiny working ends, expanded in the 1990s as minimally invasive surgery using flat images lacking depth, and instruments with long thin shafts constrained by a fulcrum at each port-site. Such a fulcrum adjacent to a single hinge mechanism reduced the usually available degrees of freedom2 from 33 at the fingertips to only four or five. The ordinary hand-skills associated with traditional types of tools, already inadequate, are no longer sufficient.

During this third era of surgery the children who will become surgeons have not developed the hand skills of former generations. They fail to learn the gentle handling and graduated forces needed for manipulating fragile or complex structures. Instead, they are used to snap-click toys such as Leggo, electronic keyboards controls with binary on-off functions and a few multiple settings defined by click détentes. They learn to write using ball-point pens which may take 5 or 10 times the force of traditional ink pens to use, and as a result develop tense hand-grips and tense habits of working with their hands unsuitable for working with delicate material3.

Surgical dissection differs from the usual kind of work which has been studied in industry. There, such tasks consist of short cycles of highly repeatable activity using material whose properties are consistent from one item to the next, unaffected by processes like inflammation, infiltration, or scarring. Mostly the workers are putting manufactured components together rather than separating or shaping them according to subtle differences in the material. They cut them to specific measurements rather than variable or arbitrary landmarks within the material.

By contrast the substrate in surgical dissection is non-uniform and unpredictable, and has an elastic gluggy texture discussed later. Dissection in surgery has lacked a formal task analysis at a high level of detail, a large gap in the study of surgical skills which needs to be filled. Unlike most industrial work the actions in surgery can often not be reversed without damage. There is nothing comparable to the "undo" button on a computer, and the penalties for error are truly considerable at times.

The separation between operator's fingers and tissues will grow further as movements and functions are taken over by computer. Studies into heuristics may be important or essential not only for present day surgeons and present day technology, but also for surgery of the future to be carried out by robots.
A possible fourth era of surgery, emerging from the present hybrid human-computer systems using voice commands and tele-manipulation, may emerge along the lines now imagined as science fiction, but undreamed of by older futurists such as HG Wells and Jules Verne. Such systems will also need to incorporate the sophisticated tissue management in the present study.
Defining heuristics

In a surgical context, a heuristic is defined here as "a rule of thumb used by experts to do something effectively, which they are often unaware of and therefore can't teach, or a rule which seems to lack the seriousness of something important enough to teach". It comes from the same root as the Greek "Eureka!" ("I have discovered it!"). It is also used as a technical term with special meanings in other fields such as diagnosis and decision-making in medicine, computer programming and philosophy. A heuristic may sometimes be kept as a trade secret. Chamberlen, credited with the invention of the obstetrical forceps, refused to describe the instrument publicly, intending to use it in securing financial success for himself and his descendants5 .

Heuristics of surgical dissection of the kind discussed in Part 2 of this paper1 are rarely stated formally. They may be mentioned in conversation across an operating table or over a cup of coffee, incidentally in a sentence in an article or book on surgical technique, or learned by unconscious imitation. They are most often unconscious and informal. Heuristics are discovered or invented as a result of individual experience, a happy chance discovery ("serendipity"), formal observations including video analysis (discussed later), or deliberate design of tasks.

Nature versus nurture

An old argument continues about whether people with particular skills are born with the capacity for them or whether anyone can be trained to achieve the same result. One determinant is how old you are when you learn. You can generally identify where a speaker grew up by their accent. If you are in Paris, you hear small children babbling away expertly in French. A teenage lab technician can be taught to do mouse renal transplants in a few weeks. A member of the fourth generation of the Barraquez ophthalmic surgery dynasty carried out his first cataract extraction at the age of ten (Personal communication Barraquez 1978). Maybe laparoscopic surgeons should start learning their skill at the same age as children learn to ride skateboards, and spend similar amounts of time on them. Surgeons have different views about being able to predict how well trainees will turn out as operators. Some feel there are no predictive tests, others think it is possible to tell early if someone will be "good with their hands". It would be interesting to survey the opinions of a representative group of surgeons.
Before considering them further some examples of heuristics should make their nature clearer:

" If cutting with one blade then do so at right angles to lines of tension. You need to pull limp material from side to side and then cut across it. (This is different to the usual mechanism by which scissors cut 3).
" In tearing tissue apart along a tissue plane, tear slowly enough to avoid losing the plane and tearing into other structures
" Increase the accuracy of movement by supporting hands, fingers or instruments on a fulcrum close to the work.

A heuristic differs from a theory, principle, or algorithm, the last being a formally stated series of steps in a procedure. Heuristics are the elements of a skill rather than the total performance, the elements of separating tissue rather than the whole dissection. Over time, some heuristics become explicit (carpenters say "measure twice, cut once") and later on they gain a basis in theory. By contrast the original "Eureka!" experience attributed to Archimedes was sudden rather than gradual, conscious, and like the "aha!" experience discussed by Arthur Koestler6 . Today's Heuristics are tomorrow's Principles. Before that transition occurs they need to be stated explicitly. In this study we add an extra dimension by also presenting their possible physical basis, thus presenting a "hypothesis", to be followed by "theory".

Types of heuristics in surgery

Three main types of heuristic can be considered in relation to surgical dissection - motor, perceptual and cognitive (Table 2).

TABLE 2. Types of heuristics in surgery

Motor Handling tissues
Perceptual Recognizing tissues
Cognitive Tools for thought, checklists, mental programs

The three examples given in the previous section are all of motor heuristics which are considered in detail later. The other two types are discussed briefly here Perceptual heuristics (and perceptual skills) are as important as motor ones. These represent the "trained eye" of experts, but of course it is really their mind and brain, with millions of nerve cell connections re-forming in the visual cortex, memory, and analytical and motor parts of the brain every second of time, overlying the strengthening of synapses that occurs through memory and training7 . The trained eye is needed to recognize the presence and site of structures and their individual properties, where "eye" is a synecdoche for brain, mind, innate capacity, training, experience and much more. To dissect structures safely and effectively the surgeon must perceive them in sufficient detail and complexity before working on them.

People see things differently according to their expertise and experience. A geologist, a land developer, and a painter viewing the same landscape will see different aspects of it, like the legend of the six blind Hindu scholars each running their hands over a different part of an elephant8 . The same view at operative surgery will yield more information to the expert than the tyro. Where is the iliac vein under the veil of connective tissue, or the common bile duct, or the outside or the lumen of the rectum on palpation?

Surgeons use a variety of little tricks to make structures more conspicuous, for example inducing movement in them. Peristalsis of the ureter may be spontaneous, or brought on by gentle stroking. A structure may be more visible if moved by something attached to it, like moving the stomach from side to side at laparoscopy to show the shifting highlights over the oesophagus. A catheter or stent makes the ureter easier to feel with the finger, an illuminated endoscope makes it easier to see the location of the oesophagus, or a range of dyes or radioactive markers can serve similar purposes. Perceptual heuristics are discussed elsewhere (in preparation), including the roles of senses such as haptics (touch, texture, shape) and smell and noise in surgery.

The third type of heuristic is cognitive, what has been termed a "tool for thought" by Waddington9 . Planning a movement before carrying it out is a cognitive skill, for example "you have to set up a line of tension, so that you can then cut at right angles to it." Of course this is usually subconscious. There are many cognitive heuristics which are concepts rather than plans for movement, and these can be found in other areas of work and in daily life. Rudyard Kipling, who was a working journalist as well as a great writer of stories, described his "six little servants" for preparing a news item as "who, what, why, how, when, where".10.

Surgery has many examples of "tools of thought" such as the "surgical sieve" for the possible causes or nature of a lump. Traditionally this is stated as "congenital, traumatic, inflammatory, neoplastic, vascular, or constitutional", though these days a student reciting the list is likely to peter out uncertainly towards the end. An expanded checklist for 15 features of a lump might be: Site, size, shape, colour contour, consistency, temperature, tenderness, translucency, skin, surrounds, structures deeper, regional nodes, rest of the patient, relevant tests.

The history of such checklists goes back at least to Aristotle's Categories11 in which he lists ten qualities of matter. In modern times they have been extended to tools such as flow-charts, critical path method and problem solving techniques. Perhaps there is also a fourth group of heuristics or skills which relate to managing an organization or a complex system. The best surgeons, military leaders, and engineers have been good intuitive ergonomists, understanding the particular needs for organising people, their working environment and their tools of work. Examples are managing and training an Operating Room (OR) team, a department, hospital, or health service. Some people have intuitive skills in this area, or know some simple rules ("there are no bad soldiers, only bad officers", "praise not punish", "let people know what's happening"). They may have studied management effectively or had opportunities for developing leadership skills in other circumstances.


The assumptions in this present study are:

1. In operative dissection, heuristics explain some important differences in skill between individuals and what stage they may be at on the learning curve.
2. Heuristics are not taught because both experts and teachers have been unaware of them or have not taken them seriously.
3. Once heuristics are stated they can be taught and learned more quickly and used more effectively than otherwise. Expertise is also taught, learned and developed more quickly and to a higher standard.

Proving the last assumption requires a comparison between two groups, taught without or with incorporation of heuristics, and measuring their subsequent performance as has been done in proving the value of imagery and mental rehearsal of skills12 . This assumption seems intuitive and there is a risk of accepting it uncritically or overstating it at a cost to other aspects of surgery. However, evidence for the importance of heuristics, or at least of some crucial factors in learning or aptitude, is obvious both from the learning curves for a wide range of surgical procedures, and the obvious differences in skill between one surgeon and another. Perhaps one should experiment on identical twins, where one twin has been taught a relevant heuristic and both are given the same task to do.

Differences between expert & non-expert

Several questions arise. What is expertise, and what differences are there between the expert and the non-expert, how can they be identified, and how can they be learned by the non-expert? An expert doesn't make quicker movements. If anything, movements appear unhurried and may even be slower, but they are performed only once so the task as a whole is performed in less time. By contrast the novice makes repeated ineffective movements. These are defined as "movements that do not advance the dissection or the progress of the operation, or that hinder it by needing extra corrective work". Typically a non-expert spends a lot of time in such repetition or correction.

Recognizing expertise can be easy or it may need knowledge of the field it is practised in, and then more knowledge to say what it consists of. It needs to be defined more precisely than the circular definition of "what experts do", and is derived from the adjective with its two connotations of (1) being skilful and (2) being regarded by others as performing distinctively well. A formal definition of expert performance by Ericsson and Lehmann13 is "consistently superior performance on a specified set of representative tasks for a domain". Apart from recognition by others, in the context of tissue dissection expertise consists of recognizing tissue features in detail, recognizing the tasks to perform, doing them accurately and safely in minimum time without hurry, and using fewest resources without stinting. Expertise in operating is not the same as being an expert surgeon, which needs additional skills of judgment, communication and values.
Psychologists and ergonomists have studied skills and expertise in many areas such as work, sport, and the arts. In the factory workplace, expertise has described as the result of experience - ten years, 10 000 hours, and 100 000 repetitions, for example in as apparently mundane a task as rolling cigars14 . A useful schema for considering the features of expertise, which now follows, is given by Abernethy15 .

Characteristics of experts

Experts do not have keener eyesight than others. Indeed their ability to see fine detail on a test chart is likely to be two to four times less than that of trainees because of normal age changes in the eye. However the expert has significant advantages in 4 other areas :

" perception, based (like the other factors that follow) on experience and learning and a rich mental library of images and patterns,
" planning of movements - more complex, and grouped together ("chunked") by the expert
" attention resources, with the expert carrying out much more at a subconscious level ("on automatic pilot"), and therefore able to devote more attention to conscious processes, and fine-tuning or adjusting to abnormal circumstances
" Feedback from tasks as they are performing them, recognizing small mistakes as they go, and correcting them or altering their actions for a better result..

The studies on expertise previously quoted suggest that though there are global skills such as intelligence and ability to co-ordinate movement, many skills are task specific. A good gastric surgeon may not be a good thyroid surgeon. The great Sir Heneage Ogilvie of Guy's Hospital once told his then registrar WJ Ferguson to never let him again do a thyroid operation (related by Ferguson to the author at the West Middlesex Hospital, 1964). It would be a double disaster for a surgeon and anaesthetist to try swapping their roles in the OR, even though each has been so close to the other's work.

Analysing skills in surgery

Ergonomic analysis of surgical skill has previously been applied to improving control of fine movement and hand tremor in microsurgery16 . This was based on the Glencross model of skill acquisition17 which was simplified, renaming his three stages more briefly as coding, ordering and timing.

(1) "Coding" is learning to relate a particular movement to a particular end result such as pressing a particular key to type a character or to play a particular musical note.

(2) "Ordering" is putting the coded actions into the correct sequence for a desired outcome. The performance may still be bumpy and lack a smooth rhythm.

(3) "Timing" is either establishing a personal rhythm, following internal constraints such as time needed for thinking or reacting, or avoiding build-up of fatigue, or external constraints such as movements by other members of a team, or the time taken by a physical or biological event.

Good timing, so that events are separated by the necessary time intervals or so they will coincide in time and space, needs anticipation but not hurry. Like the earlier stages of learning a skill it also requires rehearsal. Sometimes members of an operating team only get together for the first time during a procedure. A musical group or a football team would never plan to play together without rehearsing first. This study is concerned primarily with the first stage of coding, whose usually untaught elements correspond to our definition of heuristics, though one instance of timing is considered in Part 2 of this study.

Properties of tissue affecting dissection

Most materials in engineering are uniform over a large scale or their variation is predictable and within a narrow range. Their fine structure and gross structure are simple. Tissues dealt with in surgery are different. Quality control can not apply to human tissues in the same way and exclude those which fall outside a limited range of standards caused by normal variation or pathology. (However there is obvious value in improving general fitness or local properties such as changes from inflammation or other pathology by suitable treatment or delay for natural processes.) Their mechanical properties of strength and stretch vary much more widely

Artificial mechanisms frequently have a click-stop component, with defined settings. By contrast, tissues behave in a graded way, with slow displacement and stretching when handled or showing processes such as inflammation. (exceptions to this are sudden events such as perforations, tears, haemorrhage, emboli, dislocations and fractures.)

Such special biological properties vary over quite different time scales. Liability to infection differs hugely from deterioration by rusting or weathering, and healing is a unique biological property, though ageing affects both. (There are now self- repairing computer programs as well as self-curing puncture-proof tires). Rules for timing during dissection are considered later as an important group of heuristics.
With the exception of bone and tough tissue, dissection is through materials which are visco-elastic, gluggy and harder to identify. Structures are veiled by connective tissue, closely packed together, intermingled and intertwined, and merge into other structures. This confusion increases with inflammation and infiltrations, for example by fat in obesity. Confusion and error during dissection are decreased by better mental maps, experience, and perceptual heuristics already referred to.

There is an old joke that says patients are much easier to operate on if their viscera are all colour-coded and labelled like electronic circuits. Tissues and structures can generally be identified more easily by factors mentioned earlier such as better lighting, magnification, use of dyes, internal illumination, indwelling stents to make palpation easier, mechanical or electrical stimulation and other manoeuvres that are part of the craft of operative surgery.
Dissection is a non-ballistic and non-rhythmic skill

Ballistic skills are those in which the momentum of the body part or an external object precludes correcting or revising it halfway through based on feedback, for example throwing a ball. A phrase of music played at 16 notes per second can only be sampled intermittently because of limitations of the human brain. It takes almost 100 milliseconds to see something, process this information, and make a simple move in response to it - about a quarter of a second in total. The same applies to read-ahead in typing, where the chunk of commands have already gone to lower layers in the central nervous system and can not be cancelled or modified mid-course, and in a surgical example to elemental steps of tying knots at normal speed.

By contrast, dissection has to be more cautious and deliberate with feedback after each step, small enough and slow enough to allow recognition of vulnerable structures before the next step. Elaborate feedback is needed according to the size of the margin for error, and in particular possible irregularities from abnormal anatomy, scarring or other pathological change.

Rhythm in a strict sense like dancing or juggling also does not apply. In some cases there is a regular repeated sequence of actions such as <clip-clip-cut-tie-tie-spread-forceps-to-open-next-window-in-mesentery> with more than one participant in synchrony, for example dividing the gastro-colic omentum, but too strict or too fast a tempo will cause mistakes. As in most human activities there is a trade-off between speed and accuracy, between ineffective or inaccurate movements and the need to repeat the attempt at accurate movement.
The special properties of tissue at surgery might benefit from a specialized vocabulary beyond everyday terms such as hard and soft, beyond the single adjective of "friable" or crumbly. Just as the Inuit people are reputed to have 15 or 25 words for different types of snow or whiteness (these are actually represented by phrases, but Greenlanders have a special vocabulary for types of ice), so the dissector needs words and phrases such as fluctuant, pulsatile, friable, like wet blotting paper, spatulate, appose, retract, fenestrate, and many more. Like the special vocabulary and notation for ballet movements, surgery needs a more elaborate language so its details can be better understood and taught.

A mechanical basis for understanding the heuristics of actions in surgery

Because most heuristics in surgery are unconscious, ignored, or not considered serious matters, their physical or other basis has not been inquired into. At risk of bothering a practical person or converting heuristics into Principles of Dissection a simple theoretical analysis might increase their utility, make them easier to remember, and help in the discovery of new ones..

Objects are divided or separated in five main ways—cutting, sawing, tearing, destroying or loosening (Table 3).

TABLE 3. Separating an object into parts or freeing it

1. Cutting
    a. Pushing into it (splitting if parallel to the grain)
    b. Crushing tissue against the second blade of scissors
    c. Cuts swiftly against the inertia of unsupported material
2. Sawing - moving a sharp blade transversely over it (perhaps to     and then fro) with some downward force
3. Tearing - pulling apart (splitting if parallel to the grain)
4. Destroying it along a narrow line (diathermy etc)
5. Loosening attaching structures or forces (melting, dissolving,     chemically attacking, demagnetising, grounding electrostatic     charge)

1. Cutting

A sharp blade is pushed against non-rigid limp tissue until one of the following occurs: (a) it meets the resistance of a firm underlying structure such as fibrous tissue or bone, or (b) it meets the edge of a second scissor blade, or (c) it moves swiftly enough so the inertia of the tissue provides resistance to movement - the legendary slicing of a delicate silk floating in the air with a rapid arc of his scimitar, shown to Richard the Lionheart by Saladin, the Saracen leader.
The act of cutting combines these and other methods of tissue separation in varying proportions, though one or another generally predominates. Cutting with a sharp blade and blunt dissection are the extremes of separating tissue by pulling.

2. Sawing.

A sharp blade which does not appear serrated to the naked eye acts as an extremely fine saw. Its tiny irregularities catch on similarly tiny irregularities in the surface of the material being cut, or they create indentations by pressing on to it. Where the individual saw teeth engage, they pull on the surface irregularity until it tears away or slips past ineffectively shaped teeth. An illustration is the failure of a straight kitchen knife to cut a firm tomato with a smooth slippery skin, compared with the success of a serrated blade. If a saw is cutting firm material such as wood or metal, or bone, it actually removes small pieces of material. When cutting elastic tissue, the mechanism is different. It pulls and then tears successive fibres defined by the size of teeth and the indentations they produce. The finer the teeth, the finer and weaker the structural components they engage with over a shallower depth. There is less drag and resistance to slicing with a sharper blade. Underlying this is a general rule which underlies the next method, that of tearing.

3. Tearing.

This occurs when the applied pull or push exceeds the limits of elastic and plastic deformation of the tissue. This may seem too obvious to state, but still not obvious enough for all surgeons to know intuitively (see Tearing Heuristic in Part 2. Also a tentative weaker pull may be needed to test or confirm the strength of the tissue). A corollary is that tension exposes fresh layers of uncut tissue (also discussed further).

4. Destroying a thin deepening line by agents such as ultrasonic scalpels, lasers, or chemicals.

Some modes need contact e.g. acoustic coupling, some need a small area of contact to minimise diffusion of energy, others that are focussed can act at a distance, and some need a gap to achieve an arcing current mentioned earlier. They must be controlled accurately, or insulated in some way to avoid unintended tissue damage. Preventing the "oops!" of an unwanted effect is considered in the heuristic for control of movement, in Part 21.

5. Other

The fifth and last group of methods considered here is destroying the attachments of a structure in some other way, a miscellaneous collection to which doubtless others can be added.

Learning heuristics

Before completing this section and then listing almost a dozen heuristics in Part 2 it is necessary to consider the various ways in which heuristics can be acquired, discovered or derived. Four groups of methods are listed (Table 4).

TABLE 4. Methods of finding or learning heuristics

1. Apprenticeship, formal teaching
2. Task analysis
3. Extraction of knowledge base for an expert system
4. Introspection, observation and experience

1. Apprenticeship, formal teaching

The traditional method of learning expertise was by apprenticeship to a master or by formal teaching. However as the demand for expertise has expanded in range and size of applications it has become both scarce and expensive. Industry has had to face the challenges of meeting these needs by a better understanding of expertise, improved methods of teaching it, and a move to replace part of human work with more reproducible mechanical work. The techniques it has developed most recently for this purpose are task analysis and construction of expert systems. To these two modern techniques should be added some simple older ones of personal experience and introspection, naked-eye observation and study of the writings of and about experts.

2. Task analysis

Task analysis is a method used in industry to study performance, efficiency and errors In the present study it is used in a more focussed and older sense of step-by-step motion analysis of movements and events. It was introduced almost 100 years ago using black and white movie film. Markers labeled the joints of the subject and an included clock allowed measurements of different movements of the trunk and limbs, usually to study the efficiency of tasks in industry carried out by different operators and in different ways and work-place arrangements. This has become easier and cheaper thanks to improved video cameras, more powerful computers with larger memories and hard disks, and better editing tools. A popular application is helping sportspeople improve their technique, for example the swing of golfers.

Formerly it was necessary to use complex software to analyze videos, because they had to be read from film or from Video Cassette Recorders linked to a computer. These are cumbersome and slow because they depend on serial access to a film or tape, needing to be wound and rewound rather than direct access to the tracks on the hard disk of a computer. Simple keyboard actions can switch between the window for playback view and a second window for entering the analyst's observations.

A study18 concurrent with this present report examines video recordings of one stage of dissecting the oesophagus free during laparoscopic fundoplication. Assessors examined successive short segments of the videos, rating effectiveness of movements according to whether or not they advanced the dissection and coding the movements in categories. The heuristics listed in the present study could then be understood better and new ones added to the list in Part 21

3. Extraction of knowledge base for an expert system

As described in the current Encyclopedia Britannica19 :

"An expert system is a computer program that uses artificial intelligence to solve problems within a specialized domain that ordinarily requires human expertise. … They have commercial applications in fields as diverse as medical diagnosis, petroleum engineering, and financial investing.

[It relies on two components: a knowledge base and an inference engine. …. Facts for a knowledge base must be acquired from human experts through interviews and observations [and] then usually represented in the form of "if-then" rules …

Human experts frequently employ heuristic rules, or "rules of thumb," [as well]. For example, a credit manager might know that an applicant with a poor credit history, but a clean record since acquiring a new job, might actually be a good credit risk. …. Nevertheless, expert systems remain supplements, rather than replacements, for human experts."

As part of a second concurrent study, a think-aloud protocol for analysing expertise in surgery was used20 in an attempt was made to extract expert knowledge from eight acknowledged experts in Nissen fundoplasty. Each responded to a request to "think aloud" as they mentally replayed their actions during the procedure over 30 to 45 minutes and said what they were thinking. The writer acted as interlocutor, prompted the interviewee with questions from time to time while recording the interview on a hand-held Dictaphone, and then transcribed the interview into a text file.

The text of the transcript was broken into paragraphs each associated with one event or concept. Keywords were highlighted and copied into an adjoining column of text, and emerging concepts and comments placed in a third column. As expected the heuristics which are the subject of this paper were rarely stated, but when raised as questions or comments they were generally confirmed as valid. Questions of interviewer bias and errors of analysis are still to be addressed.

4. Introspection, observation and experience

Like the interviews and analysis in the previous section, much of the present study is subjective. However some heuristics are supported by firmer evidence, for example control of hand tremor in microsurgery 16, based on physiological measurements of amplitude of hand tremor and factors which affect it.
Some of the conclusions in those earlier papers established de facto standards, for example the recommended stiffness range for micro instruments of 0.5 to 0.8 Newton. Others formed a logical basis for design standards for microsurgical instruments21 and for such innovations as lengthening the ocular tubes on Zeiss operating microscopes. Conversations with current leaders in microsurgery suggest that some of the elements of skill described then have also become part of the accepted wisdom in the field.

In conversation as well as publications most surgeons attest to general skills or specific expert manoeuvres they have devised or learned from specific individual teachers. Internationally famous surgical names that spring to mind are Norman Tanner of London, York Mason and Michael De Bakey of Houston, Texas, but there are many others and most hospitals boast local heroes of this type. The tragic loss is that often the details of these skills were not analyzed or recorded. Fortunately today opportunities are better than ever for recording and viewing the expertise of the later generations of surgeons, especially with tools and technology such as video analysis and expert systems just described.

Extraction of knowledge base for an expert system

In 1964-65 the author served a term as registrar to WJ Ferguson, surgeon at the West Middlesex Hospital, known widely at that time for his impeccable gastrectomy technique 22. This allowed direct observations of his skilled hand grips23 , used also by a few other surgeons, especially those using the large hand-needles which were popular for suturing at the time, for example at Norwich. The double-grip he used allowed him to maintain the desired tension on the suture himself, and improve surgical dexterity for suturing and handling tissues24 .
Papers dating back to the 1930s, when surgeons didn't have to devote time to molecular biology, lawyers, and management, described a few even more complicated grips, but with no assessment of their value. The second part of this study identifies a provisional list of a dozen heuristics used by expert surgeons and describes methods used in their identification.


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11. Aristotle's Categories http://classics.mit.edu/Aristotle/categories.mb.txt
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Nature versus nurture

Types of heuristics in surgery
Differences between expert & non-expert
Characteristics of experts
Analysing skills in surgery
Properties o ftissue affecting dissection

A mechanical basis
for heuristics of movements
   1. Cutting
   2. Sawing.
   3. Tearing.
   4. Destroying a thin        line     
   5. Other

Learning heuristics

   1. App'ship
   2. Task analysis
   3. Extraction of knowledge
   4. Introspec


In 2007, despite submission to three surgical journals these two papers had not been accepted for publication.

The subject matter had beend commended, in each case but the papers were regarded as too long.

The obvious way to shorten them would have been to omit part 1, which I was unwilling to do. Readers may or not agree.

The editor of the ANZ Journal of Surgery was sufficiently interested to undertake drastic shorteningby over four-fifths, and published a single paper in a special issue of the Journal which included eight other papers on heuristics in particvular specialties.


Heuristics of surgical dissection
Part 1: What and why

Michael Patkin FRACS
Departments of Surgery
Royal Adelaide Hospital & Flinders Medical Centre
mp at mpatkin.org


This study examines heuristics, defined here as rules of thumb used by surgeons, in dissection. Using such rules is an important difference between the working methods of experts and others. Because they are often subconscious or regarded as obvious or trivial they are not written down and rarely taught formally.

Heuristics are defined and described in detail, together with their mechanical basis. In a second accompanying paper, methods of deriving them are considered and twelve examples are presented. As the costs of surgery and operating time become more important, the possible contribution of heuristics to shortening learning curves and improving surgical skills becomes more important.

Experienced surgeons accumulate specific ways of doing things when operating, and they constitute "the tricks of the trade". Some are handed on by surgical mentors, others are copied from colleagues, and some just develop intuitively over time through trial and error. The term used here to describe them is "heuristics" of surgical dissection.