Michael Patkin's

Ergonomics and the operating microscope
(Singapore 1977

Publication history, Reflections & comments



Surgery & ergonomics


Information design

Editorials, book reviews



The small scale of microsurgery provides the two special problems of fine manipulation and fine perception of detail, made more critical by the delicacy of tissue with a breaking strain sometimes below the normal threshold for touch. Because of both the critical nature of the task and the short history of clinical microsurgery unhampered by entrenched traditions, it is possible to make a basic analysis of many aspects of technique less readily accepted in older branches of the mainstream of general surgery.

Such a basic analysis can be derived from a study of the capacities and limitations of the human operator in terms of the science of 'ergonomics' [Murrell, 1965], also known as `human factors' in the United States. While scientific analysis of man at work was established before the present century, the main impetus to its development came during the Second World War, when groups of scientists from different disciplines were brought together to create effective weapon systems.

Since then, most industrial countries have had organisations appearing in this field, bringing together engineers, psychologists, doctors, architects, lighting engineers, and many others concerned with the man-machine interface. Such studies received a particularly strong stimulus from the aerospace programme in the United States, but many fields of human activity have derived benefit from application of the very large growing body of knowledge in this field.

However little formal application of such knowledge to surgery has occurred, and unifying concepts have been scarce [Patkin, 1967a, 1977]. The present study is meant to bring together information of basic importance to the microsurgeon. The five main areas to be covered will be:
(1) visual perception; (2) tremor control and fine manipulation; (3) hand grips; (4) the process of skill acquisition, and (5) microsurgical instrument design, considered in detail in the companion paper at this workshop.

Visual Feedback

As the scale of work becomes smaller, tactile feedback becomes less helpful in controlling dissection and suture, so that increasing and finally total reliance must be placed on visual feedback. The factors determining and controlling visual feedback may be considered in some detail (table 1).

Table I. Factors affecting visual acuity

Normal visual health, age, fatigue
Trained perception
Moulding effect of directional lighting
Lighting intensity

Contrast (colour and brightness)
Colour rendering


The early experience of seeing living tissues under magnification is dramatic for the new insights it gives into apparently familiar territory. The interpretation of these new appearances needs training and experience, whose role in skill acquisition is analysed later in this paper. Operating the mechanism of the microscope will not be considered in further detail here, though the importance of its design features should become increasingly apparent in this study.

Lighting Intensity

Over a wide range, the brighter the lighting, the more that fine detail can be seen, a principle familiar from reading fine print, or trying to thread a needle or identify an obscure structure in poor light [LYTHGOE, 1932]. Laboratory studies have amply confirmed this common-sense impression.


The closer a glare source to the line of sight, the more that visual acuity suffers [Luckiesh and Guth, 1946]. While this is familiar from such everyday experiences as driving into the sunset and failing to see the road ahead clearly, glare is also important in surgical practice when it is reflected from highly polished instruments at operation. Manufacturing processes to dull such glare include matt finish, satinising, black chroming, and anodising.

Colour Contrast

The safety yellow raincoats of children in wintry weather show up strikingly against the grey background of a wet road. Yellow or blue plastic strips behind vessel anastomoses show them up more clearly than a background of tissue of similar colour. Suture colour is important for the same reason. Selective colouring of tissues is well established in other fields of surgery, such as painting the vagina with Bonney's blue, putting methylene blue into conduits and fistulae, staining vaginal adenosis with iodine, and the use of various blue dyes for demonstrating lymphatics, parathyroid, and pancreatic cell tissue. Claims of demonstrating vagal fibres with leucomethylene blue [LEE, 1969] have unfortunately not been substantiated. Under the microscope, vas epithelium stains brightly with Codman's skin marking pencil, but whether there is safe absence of scarring is not yet studied. Other dyes to show up tissues, particularly the perineurium for nerve suture, may have a most important role to play in future operative microsurgery. Coloured filters are already used in retinal examination, and the `colour temperature' of lighting is important, for example in masking cyanosis with `cool' fluorescent lighting.

Directional Lighting

The moulding effect of directional lighting, when it avoids troublesome shadows, also increases visual feedback.

Other Visual Factors

These include binocularity, visual health and fatigue. It is worth noting that perspiration can fog the eyepiece, which clears with evaporation, and this provides a second reason for resting one's eyes away from the microscope from time to time during dissection.

Disadvantages of Magnification

While magnification makes microsurgery possible, it also has drawbacks, for example (1) loss of area and depth of visual field; (2) loss of reference points; (3) errors in positioning instruments and sutures; (4) fatigue; (5) intrusion of the bulk of the microscope into the operating area; (6) a need for planning and practice by the microsurgical team; (7) cost and organisation of a microsurgical service. For several of these reasons, it is important to use the lowest level of magnification necessary at each stage of a procedure, for example, zooming in to insert sutures, but zooming out to tie the knot.

Tremor Control

It is normal to have a tremor. In the outstretched hand, normal tremor has an amplitude of 0.5-3 mm and irregular frequency of about 7-30 vibrations/sec [VOIGT, 1963]. This is modified greatly by a number of factors that can be looked at in more detail, particularly the use of support to the limb and the instrument being used.

The closer the area of support to the end of the limb or the instrument, the more that fine movement can be controlled. The ultimate simple device for this purpose is a ruler for drawing a straight line. Support can come from the material being worked on itself, provided it is rigid, which is not the case with the delicate tissues encountered in microsurgery.

An important principle in using mechanical guides for movement is the concept of `funnelling', with support from a broad area gradually narrowed to give more accurate critical control. I have termed this process funnelling because of the analogy of pouring liquid into the broad open end of a funnel which narrows into a much smaller hole. In much the same way a peg which is tapered partly to a point is much easier to place into a hole than one that is cut off square at the end, while the same result can be achieved for a cylinder by a flared hole. While it is proverbially difficult to put a square peg into a round hole, it is also hard to guide a perfectly cylindrical peg into an exactly corresponding cylindrical cavity. Establishing a `hierarchy' or programme of priority of movements from the general and less demanding to the specific and more exact will be looked at in the analysis of skill and its refinement.

The physiological basis for tremor is still not certain [Lippold, 1971 ], though it is probably a `hunting' phenomenon at the level of the spinal cord. For the present purpose what is of crucial importance is attention to the factors which modify it. They can be considered as long-term, intermediate, and short-term (table II), and of these it is the short-term factors in particular which must be controlled each time in the working microsurgical situation.

Table 2. Factors affecting tremor

Physiological tremor

Amplitude: 0.5-3 mm
Frequency: 7-20 H

Long-term factors


Intermediate term factors

Skill - training, experience
Social poisons - nicotine, caffeine, alcohol

Short-term factors

Point of limb support
Direction of movement
Design for rotability
Strenuous exertion
Stress, heat, digestion
Cold temperature

Neutral Body Posture

The barrier to prolonged work under high magnification is partly psychological. In American industry numerous workers use bench microscopes for much of the working week. However, for prolonged work they must be positioned, with the spinal column straight, the bench height at elbow joint level with the arms along the trunk, the forearms and hands fully supported, and the chair height allowing the thighs parallel to the ground, without the seat edge digging in. The axes of the binocular telescopes have to be correctly aligned for the resting position of the extraocular muscles, as otherwise pain is referred from these structures to the neck [Tichauer, pers. common.].

Support for the Hand, Fingers and Forearm

This should extend along the forearm and ulnar digits and under the tips of some of the fingers. Laboratory studies have clearly demonstrated the progressive way in which tremor is increasingly dampened as support is provided to more distal segments of the limb. In everyday terms this is familiar from the maulstick of the signwriter and the difficulty in writing well low down on a vertical blackboard, where contact of the ulnar edge of the hand with the surface is lost while the chalk still touches. Special arm supports have been described by O'Brien et al. [1970], and in industrial situations it is common to have a part of the bench cut away for the trunk, so that the elbows can be supported alongside the body and not anterior to it.

Direction of Movement

Least tremor occurs in a hand movement towards the opposite shoulder than at right angles to this direction [Woodson et al., 1966). This will help determine the best position of the operator in relation to a suture line, though modified by the details of the hand grip to be adopted, discussed later. Partly this is because movement in the more favourable direction takes place at more distal joints in the limb, controlled by more highly trained and richly innervated smaller muscles.

Preceding Muscular Exertion

It is commonplace that one's signature in a hotel register is shaky if one has just carried heavy suitcases in. The effect of strenuous exertion is to aggravate tremor significantly for up to 24 hours afterwards, confirmed in laboratory studies as well as by personal experience [Simon et al., 1965]. For the microsurgeon it is important not to precede fine work with heavier tasks, such as a hip replacement for an orthopaedic surgeon, or wrestling with obstinate mechanical equipment. Some recent evidence suggests that splinting to rest the forearm and hand completely for some time before fine manipulation is an advantage [Tichauer, pers. commun. ].

Muscle Loading

Evidence from two sources suggests that exerting a force greater than 50 g with the index finger increases tremor. This was found in a study of electrical component assemblers by Voigt [1963]. In 1976, at a Microsurgery Workshop in Sydney, I asked five experienced microsurgeons to select the preferred instrument from a range of needleholders closing with various amount of force applied to the handles. All choices were in the range of 45-60 g contrasting with commercially available needleholders which take a force of 1.5-10 times this level to close. Instruments sold for the same purpose 5 years earlier had closing pressures which ranged from 0.5 to > 1 kg, and the change in standards for manufacture is an interesting evolution. The question of instrument standards is analysed further in the companion paper on instrument selection and care.

Speed of Movement

Because technique under the microscope relies on visual and not kinaesthetic feedback, and the visual feedback and processing group is slower, especially with newly acquired skills, movements under the microscope must be made much more slowly. Buncke et al. (1974) suggest that the operator does not draw sutures faster than about 0.5 mm/sec to save losing it.

Anxiety and Confidence

Discussion of psychological aspects of tremor control is outside the scope of this paper, but the relation between the two factors can be critical to technique at times, and under conditions of stress it may be necessary to use every available trick of limb and instrument support to allow surgery to proceed, especially in the early phases of practice. With experience and practice there should be little opportunity given for the damaging type of operator stress to occur.

Miscellaneous Factors

These include a recent heavy meal, and doubtless other factors will emerge. The design of surgical instruments used has a great effect on accuracy of manipulation, and is best related to hand grip, next to be examined.

Hand Grips and Handle Design

Of the three main areas of hand function comprising mechanical activity movement and support, sensation, and gesture, it is one aspect of mechanical activity, that of hand grip, which will be studied further here. On the basis of previous studies [Patkin, 1962, 1969], hand grips can be classified into the four main types of power grip, external and internal precision grips, and storage grip. The external precision grip, used in writing with a pen or pencil, is the main one of interest here, and is analysed in more detail in the accompanying paper on instrument selection. Briefly, it represents more than a simple pinch by the fingertips, and includes also support for the instrument from the thumb cleft, and support for the hand and forearm along their u1nar edge. Instruments for this group must be approximately pen-shaped, and detailed criteria for this are also presented elsewhere.

One special aspect of hand function in using this grip I have termed `trigger function', signifying that the instrument used has a moving part, moved by just one or two digits, while the bulk of the instrument is held more securely in the rest of the hand. Everyday examples include the trigger of a gun and the end button of a handbrake. In surgery, examples include the use of forceps, clamps, and holders of all kinds, some of them requiring complex compression-rotation movements. In general surgery, the use of ratchets and locking devices relieves the need for forceful hand grip to some extent, but in microsurgery the jerking associated with release of a ratchet is a disadvantage which far outweighs the help of a mechanical grip, and general experience is that ratchets should be removed if they are present.

Because independent movement of one digit to open or close needleholders and scissors introduces some unsteadiness, various remote control devices have been tried, usually controlled by a foot pedal through a mechanism which is hydraulic, pneumatic, mechanical, or electrical. However, practical circumstances and experience has favoured simpler instruments held entirely within the hand, aided by careful attention to the details of the hand grip to be used.

Skill Acquisition

The acquisition of skill has been defined [Glencross, 1975, 1977] as learning to make -highly refined patterns of movement for a desired outcome. The learning and refining of microsurgical skills provides a valuable opportunity for examining these processes, but at the same time what is already known about skill acquisition can be of great value to microsurgeons.

The stages of skill acquisition have been divided by Glencross into coding, temporal organisation, and hierarchical organisation.

The first of these, coding, is learning to associate a particular movement with a specific outcome, such as playing middle C on the piano or closing the jaws of microsurgical forceps when these are viewed under the microscope. This paper, like the detailed and more valuable work by Buncke et al [1974], is concerned mainly with the stage of coding. Buncke, for example, spends almost a hundred words simply instructing the trainee operator about the length and position of the tail of a suture when it has been pulled through tissue. There are several dozen different elements of movement to be coded for the trainee microsurgeon, or for the experienced operator for that matter, and a formal list of these movements has not yet been compiled in detail.

The next stage of skill acquisition, that of temporal organisation, consists of linking the coded movements together in a rhythmic sequence. By contrast with single coded movements, feedback (whether visual or kinaesthetic) to correct errors in these movements is only intermittent in this phase. When a pianist is playing notes at the rate of 16 per second, it is the phrase rather than individual notes which is checked for correctness. In much the same way, tying the first hitch of a knot under the microscope is not corrected halfway through by the skilled rhythmic operator if he happens to err. Instead, the whole process of forming a loop round the points of the suture-holding instrument is started again from the beginning. This stage, like playing scales or music accurately on the piano, depends on a repertoire of correctly coded movements, closely comparable to the individual statements in a computer programme, with the powerful addition of flexibility to alter the setting of the variables on the programme according to sensory data being continuously received. Under the microscope, skilled movement is slowed down for three reasons. First, the role of non-visual feedback becomes much less helpful, compared with activity in sport, or in surgical steps such as dissecting out a prostate gland with the finger. Central processing time is almost twice as slow for visual as for kineasthetic sensory data received by the brain.

Secondly, the fragile nature of the tissues relative to the forces with which they split along tissue planes means that sensory input becomes important at much shorter intervals of dissection. Thirdly the limiting of vision to the optical field of the microscope deprives the operator of many peripheral visual cues and points of reference.

The third stage of skill acquisition, that of hierarchical organisation, is the combination of rhythmic sequences of movements into a total strategy for the operation. Much of this is manipulation of ideas, more suited to the blackboard than the holding of instruments, but which cannot succeed until the first two stages have been mastered by a process of trial and of errors which are corrected and learnt from continually.

In the wider field of general surgery, questions of analysing skill acquisition have not arisen within a system of learning by apprenticeship, or by trial and error. The beginner has to learn to code elements of operative procedures such as making a cut rather than a scratch in the skin, and learning the basic role of tension in stabilising tissues for display, or for incision at right angles to lines of tension. This is merely the beginning of a surgical procedure, well short of choosing successful strategies, necessary for a favourable outcome. The new and critical demands of microsurgical practice provide an opportunity for detailed analysis of this type, originally aimed at general surgery, but inhibited by an established tradition of technique.

Microsurgical Instrument Design and Care

This area, the fifth and last referred to in this paper, is discussed in a separate paper. What is important is the possibility of analysing the performance needs of instruments used in microsurgery, in particular handle design, closing pressures, security of needle grip, and sharpness of blades and needles. Many of these matters are already covered by recommendations in standards, which are documents published by organisations concerned with industrial standards in each country. Similarly, in hospital practice a fresh look can be taken at the various steps in acquisition and care for instruments.

Future Possibilities

If the application of an ergonomic method of study to operative surgery is valid, more data will be needed. Much of this will consist of simple but informed observation and analysis during the course of operations. Measurements of forces exerted on instruments and tissues can be made with equipment ranging from a five-dollar kitchen scale to electronic gauges of considerable price. Video-tape recording and playback of hand movements and tissue manipulation during the course of an operation can be carried out along the lines of motion study in industry. Quite likely the main conclusion from such studies will be that the best results come from having a continuing heavy work flow with the same operating team in a specific area of work, with all its implications for the organisation of medical practice.

In a growing area of activity such as surgery, there is a constant interplay between the two processes of complexity and simplification. One of the roles of analysis in this area must be to make work simpler, so that techniques which are initially difficult, complicated, and even awesome, become safe, reliable, and routine components of the management of the surgical patient.


Buncke, H. J.; Chester, N. L., and Szabo, Z.: The complete teaching manual of microvascular surgery (R. K. Davies Medical Centre, San Francisco 1974).
Glencross, D. J.: Information processing and skill training. Aust. J. Sports Med. 7: 48-51 (1975).
Glencross, D. J.: The control of skilled movements. Psychol. Bull. 84: 14-29 (1977). LEE, M.: Selective stain to detect the vagus nerve on the operation of Vagotomy. Br. J. Surg. 56: 10-13 (1969).
Ergonomics and the Operating Microscope 63
Lippold, O.: Physiological tremor. Scient.Am. 12: 65 (1971).
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Simon, J. R., et al.: Effects of physical exercise on hand steadiness. Laryngoscope 75: 1737 (1965).
Voigt, C.D.: Der Tremor and seine Auswirkungen auf feinmotorische Handlungen. Arbeitswissenschaft 6: 192 (1963).
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Visual feedback
Lighting intensity
Colour contrast
Directional lighting
Other visual factors
Disadvantages of magnification

Tremor control
Table of tremor factors
Neutral body posture
Support for the hand, fingers and forearm
Direction of movement
Preceding muscular exertion
Muscle loading
Speed of movement
Anxiety and confidence
Miscellaneous factors

Hand grips and handle design
Skill acquisition
instrument design and care
Future possibilities


This was one of two papers presented at International Workshops in Microsurgery held in Singapore by Dr. Arthur Lim for three years between 1977 and 1979. The papers were published by Karger in Advances in Ophthalmology as a separate volume.

This was during the phase of rapid development of microsurgery when it seemed the half-life of knowledge in microsurgery was about 6 months, or the time between any two major international congresses.

The personalities behind the scenes were far more intresting, for example Earl Owen and Bernard O'Brien of Australia, Rory of Canada, and Bob Acland from England who settled at Louisville, Kentucky , as part of the team of Kleinert and Koontz.

The intense rivalries of the time were recalled by the those around the world's first hand transplants 15 years later.

Published as:

Ergonomics and the Operating Microscope

Adv. Ophthal., vol. 37, pp. 53-63 (Karger, Basel 1978)

Dr. Michael Patkin, Ergon House, 92A Wood Terrace, Whyalla 5600 (South Australia)