the story of catgut - postgraduate medical...

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THE STORY OF CATGUTBy ELDRED J. HOLDER, PH.D., B.PHARM., PH.C.(Edin.)

HistoricalThe dictionary definition of catgut is 'a tough

cord made from the intestines of animals, es-pecially sheep.' There may or may not followan indication of its uses.

Mention catgut to a surgeon and he thinks ofa suture material; to a musician, he recalls themellow tones of the violin or cello; to a sportsmanand he wonders if he remembered to replace thethe press on his tennis racquet. Catgut, to Every-man, prompts speculation as to its feline origin.There is, however, in fact no evidence that theintestine of the cat has ever been used to producecatgut strings. The name can be traced back tothe Arabic cither, an early stringed instrument.The same root is seen in the old name for thedancing master's fiddle, a kit. From kitgut tocatgut is an easy etymological step.No aid to surgery has had such a chequered

career as catgut. It has been in and out of favour,sworn by and sworn at, over a period of some 75years. Catgut for suturing has been ' going out offashion' since the writer first took interest in itsome I7 years ago. Nevertheless, more is beingmanufactured and used today than ever before.Why should this be so ? The answer lies in onespecial feature-its absorbability in living animaltissues.

Although this absorbability was not realizeduntil comparatively recently, the use of animalintestine as a ' string' dates back as far as thereare records of mankind. Indeed, it is reasonable toassume that its utility would have been recognizedlong before there was evolved the art of twistingvegetable fibres or hairs into thread. The use ofdried intestine as a suture is undoubted even sofar back in history as the Papyrus of Ebers, circa3750 B.C. Egyptian surgeons at that time appearto have acquired considerable skill in woundrepair.

Susruta, a Hindu writer who lived about 1500B.C., refers to the use of cotton, drawn copper,horsehair and animal intestines as ligatures.Ferrara, an Italian, at the end of the i6th centuryused intestines of tortoises amongst other suturematerials; he seems to have had some precognitionof the need for sterilizing because he is said to havestored his sutures in wine before use. In Francethe importance of catgut makers was recognized in

I656 by Louis XIV, who granted letters patent tothe Guild whose members supplied racquetmakers, clockmakers, musicians, cross-bow makersand surgeons.A short digression may be permissible to make

reference to a natural means of wound closurewhich has been known for hundreds of years,namely the use of the mandibles of certain speciesof biting ants. The edges of a wound are broughttogether manually, the ant is held by its body andallowed to bite across the wound edges; themoment it has done so the body is twisted awayfrom the head which, with the jaws, is left actinglike a modern metal clip. This procedure is stillused by the aboriginal natives of central Australiaand there are records of its use up to recent timesin Greece, Serbia and Algeria.To return to catgut, it was in i868, the year

before he came to Edinburgh University asProfessor of Clinical Surgery, that Joseph Listerexperimentally tied catgut round the right carotidartery of a 1l. Thirty days later the animal waskilled and Lister examined the ligature. At firsthe thought that it was unchanged, but closer in-vestigation revealed the fact that the catgut was nolonger present but had been replaced by a ring ofliving tissue. Though Lister is mainly rememberedfor his introduction of antisepsis into surgery, hisrecognition of the absorbability of catgut has beenof fundamental importance in the successfulmodern use of this material.He quickly realized also the risk of introducing

infection into wounds by the use of' raw' catgut.There are records that in I869 he was using anaqueous solution of phenol as a sterilizing agentfor catgut. This would be fairly efficient as asterilizing agent (except for resistant spores) butwould leave the sutures in a waterlogged andweakened condition. Apparently with the ideaof overcoming these defects, Lister then used asolution of phenol in olive oil. This would un-doubtedly obviate loss of tensile strength butwould be even less efficient in sterilization, thoughthe catgut would be 'antiseptic' and far lessdangerous than untreated material. He furtheranticipated the modern process for 'hardening'catgut, that is for delaying its rate of absorptionin the tissues, by chromicizing by the use ofmixtures of phenol and chromic acid solution in

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428 POST GRADUATE MEDICAL JOURNAL September I949

which the catgut was steeped for varyingperiods.

Surgical catgut is not easy to make. The rawmaterial, sheep's intestine, varies from animal toanimal in quality, width and toughness ; it variesaccording to age, to feeding and so on, and cannotbe bulked in order to obtain uniformity. In itsnatural state it is loaded with bacteria, bothpathogenic and non-pathogenic. The problemlies in its complete sterilization without thedestruction of the natural properties of the gut. Itis manufactured in this country only underGovernment licence, and the conditions and in-spections required leave no doubt as to thebacteriological safety of the final product. Its rateof absorption in the human body is hard tocontrol; the same strand divided into two piecesand implanted in similar locations in two in-dividuals may have different absorption periodsdue to idiosyncrasy, sensitivity, vitamin deficiencyor cachexia.Many arguments have been used for and against

non-absorbable suture materials. They are oftenless expensive and more easily sterilized than cat-gut, they can be of absolutely standard size andtensile strength. If buried, however, they remainpermanently in the tissues and may at any timesubsequently become a focus for infection.Two further points regarding non-absorbable

sutures are worth noting. First, the harshness ofmonofilaments such as silk-worm gut. Harshness,that is, to the patient, for if the stitches are on thesurface the cut ends tend to harden and may catchin the dressings; if such materials are used forburied sutures there is a grave risk of the sharppoints of the cut ends doing damage to adjacenttissues, particularly to blood vessels. The otherpoint concerns the softer and generally preferablebraided materials such as braided silk. Even ininterrupted sutures of such materials there is thepossibility of bacteria finding refuge in their inter-stices, whilst in continuous sutures the movementof serum along the suture material by capillaryaction favours the spread of any incidental in-fection. If, to eliminate this wick-like action, thebraided material has been rendered non-capillary,the disadvantage disappears and gives probably theideal form of non-absorbable suture.The ideal suture material is one which will

retain its holding power until healing is completeand will then disappear with a minimum of dis-turbance to the tissues. Until a substitute isfound, either natural or synthetic, which hassuperior physical qualities as well as absorbability,catgut is likely to remain the most popular andvaluable of all suture and ligature materials.

For a detailed and comprehensive history ofsutures, and especially of catgut, through the ages,

the reader is confidently referred to ' Le Catgut'by Dr. A. Fandre (I944).ManufactureThere are two main stages in the production of

a sterile suture; first the manufacture of thestrand, then its sterilization and preparation foruse at operation.A cross section of sheep's intestine reveals three

main layers; the outer mesenteric coat wherebythe intestine is ' slung' within the abdominalcavity; the middle (sub-mucous and muscular)layer which is thin, elastic and muscular; andthe inner, absorptive mucous layer.

In preparation the gut is split longitudinally intoribbons and by carefully controlled scraping opera-tions the outer mesenteric and inner mucous coatsare removed. The sub-mucous, muscular rib-bons are twisted, sometimes singly, more oftenin twos, threes or fours, then stretched and driedto form an almost solid filament. Thereafter thestrings must be polished to give uniformity ofdiameter along the strand and a smooth surface,but not too smooth or the knot may slip aftersuturing with the risk of a disaster such as a'burst abdomen.' Finally the strands are sortedinto gauges to agree with the size standards in theBritish Pharmaceutical Codex and the UnitedStates Pharmacopoeia.

Until I944 British manufacturers each had theirown catgut size standards with the result that onemaker's No. I might be equivalent to anothermaker's No. 3, and so on. During the recent war,standards for gauge and tensile strength weredrawn up and included in the Sixth Supplement,I944, to the British Pharmaceutical Codex, 1934edition. The B.P.C. size standards are nearlyidentical with those of the United States Pharma-copoeia which, in addition to reducing confusionamongst British makes, was a useful contributiontowards international co-operation.

Deliberate hardening to delay the rate ofabsorption in the tissues is referred to later and isusually done during manufacture of the raw catgutstrings.SterilizationA phrase often used by makers and users of

surgical catgut is ' the catgut problem.' This ex-expression summarizes the difficulty of devising asterilizing process which is rigorous enough to killthe most resistant sporing organisms without alsodamaging the tensile strength of the strand.What is the bacteriological flora of unsterilized

catgut ? Primarily it is that of the contents of theintestine in the living animal. The non-sporingorganisms, staphylococci, streptococci, B. coli, etc.,may be disregarded. Whatever their pathological



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September I949 HOLDER : The Story of Catgut 429

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Chromic catgut stitches in dorso-lumbar muscle of rabbit ten days afterimplanting.Note freedom from local reaction.

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Thick, plain catgut stitches seven days after operation showing accumula-tion of detritus.



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430 POST GRADUATE MEDICAL JOURNAI. Septembet I949

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September I949 HOLDER : The Story of Catgut 431

significance in human ailments, they are com-paratively easy to kill in catgut. Even if they sur-vived other processes of manufacture, the alcoholicfluid normally present in the sealed tube contain-ing the finished suture would kill all but sporingorganisms.

Spores are normally not killed by alcohol(Williams, I936) which to them is merely anotherkind of anhydrous state, and it is precisely for sucha condition that the dormant spore stage isdesigned. This point may still not be fullyappreciated as is apparent from the continuedpopularity of rinsing with alcohol or ether as ameans of' sterilizing' hypodermic syringes.

Theoretically, if the faecal and pre-faecal con-tents of the intestine could be entirely removed atthe moment of death, the gut should be sterile.In practical slaughterhouse conditions this is im-possible as is shown by cultures obtained from rawcatgut strings. Both anaerobic and aerobic sporesmay be present, the most spectacular and alarmingbeing Clostridium tetani.The presence of tetanus bacilli in bowel con-

tents has been demonstrated often enough. Yetthousands of samples of raw catgut strings can betested without finding it. Moreover, in manyyears of experience the writer has yet to find a caseof tetanus in which imperfectly sterilized catgutcould reasonably be blamed as the source of theinfection. Nevertheless, the wise manufacturertreats every strand as though it were loaded withthe most resistant spores known.

Other pathogenic anaerobes such as Cl. welchii,CI. sporogenes and C1. oedematis maligni are com-monly present in unsterilized catgut.The sporing aerobes, which are mostly non-

pathogenic, include in addition to varieties ofB. subtilis, B. mesentericus ruber which is sometimescalled the ' catgut bacillus,' being very commonand giving, in broth culture, a distinctive off-whitepellicle with a red line running through it. Fromexperimental work it has been found that aerobicspores are more resistant than those of anaerobes.In control bacteriological tests on sterile catgut itis, however, necessary to test both aerobically andanaerobically.From the end of the last century when Lister,

who first demonstrated the absorbability of catgut,sterilized his sutures by immersion in a strongphenol solution, until catgut offered for sale assterile came within the purview of the TherapeuticSubstances Act, many methods of 'sterilization'used were as unreliable as they were numerous.They included the use of phenol, mercury com-pounds, essential oils, peroxide of hydrogen,iodine, silver salts, formaldehyde and heating inoil or alcohol (Holder, I939).The main faults included failure to kill spores

(phenol, mercury compounds, essential oils);causticity (phenol); inhibition, giving an apparentbut false sterility (mercury compounds); damageto the catgut (silver salts; iodine: acidity andwater-logging; hot oil or alcohol: 'cooking' ofthe gut); unintentional increase in resistance toabsorption (iodine and formaldehyde).Under the Therapeutic Substances Act, I93 I,

and subsequent regulations, manufacturers offer-ing sterile surgical catgut for sale must be licensedby the Ministry of Health or by the Department ofHealth for Scotland. By the terms of the licence,the authorities must approve the premises inwhich sterilization is performed, the qualificationsof the technical personnel and the processes used,whilst samples from every batch sterilized must besubmitted to approved bacteriological test beforethe remainder may be sold.A fundamental difficulty in sterilizing catgut is

that the contaminating spores are not all on thesurface of the strand. It will be remembered thatin manufacturing raw catgut strings, ribbons ofgut are twisted to form the strand. Spores presenton the surface of the ribbons are thereby sealedinto the interior of the string. The sterilizingagent, whether chemical or heat, must thereforereach and destroy the resistant spore envelopeswithout damaging the sensitive collagen of thecatgut through which it must first pass.

Chemical sterilization is practicable under care-fully controlled conditions, iodine sterilizationhaving been employed for many years to givesterile catgut of excellent tensile strength andpliability. A serious objection to this method isthat it is uneconomical, taking many weeks fromstart to finish and requiring much space and con-stant supervision to obtain optimum results.Another objection is that although no uncombinediodine need be left in the catgut, a change takesplace in its chemical constitution which greatlyprolongs the period required for absorption by thetissues (Holder, I946). Although this was lessserious than having the sutures absorbed tooquickly, it was not uncommon to find fragments ofcatgut stitches expelled to the surface of a woundweeks after healing had taken place.

Heat sterilization has now largely replaced thechemical method. It has the great advantage ofbeing a quick process which has little effect uponthe absorption rate of the product and it has beenimproved to a stage which gives sterile catgut ofexcellent tensile strength and pliability.

Normally holding 15 to 20 per cent. of moisture,the catgut must be dried before a high temperatureis applied otherwise the water present in it wouldcause ' cooking' or partial hydrolysis with almostcomplete loss of tensile strength. The sterilizingtemperature is critical, less than 1500 C. being in-

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432 POST GRADUATE MEDICAL JOURNAL September 1949

sufficient for consistent sterility and more thanI55° C. tending to cause brittleness. The heat mustbe applied evenly throughout the strand and forthis reason hot air, which has a low heat con-ductivity factor, cannot be used for sterilizing.The customary procedure is for the catgut to be

coiled, placed in tubes open at one end, dried inovens at a moderate temperature and then im-mersed for sterilization in a heated inert anhydrousfluid wherein the required temperature and timeof exposure can be closely controlled.The tubes of catgut are usually processed in

suitable basket containers from which the oil canbe drained after sterilization and, maintainingstrictly aseptic conditions, a sterilized alcoholic re-conditioning fluid, containing a predeterminedproportion of water, is introduced and the openend of each tube is at once hermetically sealed.

Samples are taken from each batch. of sealedtubes, some for bacteriological and some forphysical tests, which must be passed before theremainder of the batch is released for sale.

' Multiple'"packings for sterile sutures, fromwhich successive portions may be withdrawn foruse on different occasions, are being discarded onsafety grounds. With the sealed glass tube pack-ing, any portion of the suture material not requiredon the occasion for which the tube was openedshould be thrown away, not kept for use laterwith the consequent risk of contamination.

In order to clean the outsides of the sealed tubesbefore opening in the theatre, they may be washedin soapy water and stored in jars of antisepticsolution. Tubes which can be boiled or placed inin the sterilizer with the instruments beforeoperation are obtainable, but most makers do notrecommend this 'boilable' pack. In order toavoid damage to the catgut during boiling orsteam sterilizing the storage fluid in the tubes mustbe completely anhydrous; catgut taken from suchtubes is therefore brittle and wiry and its correctreconditioning in weak alcohol or physiologicalsaline is a difficult procedure to control in theoperating theatre.

AbsorptionThe rate of absorption of catgut in the body is

usually determined in normal muscle such as therectus abdominis.

Catgut which has not been specially treated toprolong its resistance to digestion lasts from 7 to15 days in normal muscle; such catgut is known as'plain.' In practice the, process of manufactureof raw catgut strings tends to harden them a littleand most commercial 'plain' catgut lasts from14 to 2z days in normal muscle.When used to suture the bowel, catgut usually

lasts only one-third to one-quarter of its duration

in muscle. Samples of hardened catgut, insertedthrough the gastric wall in rabbits and being incontact with the stomach contents, were absorbedin less than four days (Holder, '946). Althoughwounds of the stomach wall heal with greatrapidity, these experiments suggest that anabsorbable suture may be contra-indicated wherethe stitches come into contact with the gastric juice.

It is customary for much of the catgut used insuturing to be hardened to prolong its absorptionperiod. This is commonly achieved by the actionof chrome salts, preferably in the ribbon stage ofmanufacture. Catgut containing the equivalent ofapproximately one-half per cent. Cr2O, lasts for20 to 30 days in normal muscle and for five to tendays in intestinal tissue. More resistant catgutmay be obtained containing up to I per cent.Cr203.

Manufacturers usually control the absorptionrate of their catgut by routine in vitro tests. Thesemay take the form of hydrolysis time-checks in hotaqueous solutions or of enzyme digestion-periodsof catgut strands under tension, using pepsin orbetter an alkaline-acting enzyme such as papain ortrypsin. The ideal control is the implanting ofcatgut into living animal tissue (Holder, 1946).This may be performed by closing an incision inthe dorso-lumbar muscle of rabbits with in-terrupted stitches and observing, at re-operation ata later date, the breaking strain of the stitches withthe aid of an accurate spring balance.The loss of strength of catgut stitches by

digestion, when plotted against time, gives astraight-line graph so that the date after whicheffective holding power (which may be regarded as450 gm. or I lb.) would be lost can be calculated.Generally speaking, it is safer to have catgut resistabsorption for too long rather than for too short atime.

It is often recommended that only plain catgutshould be used in subcutaneous or fatty tissue.This, however, leads to another interesting point,namely the reaction of the tissues to the intro-duction of catgut stitches. The significant factorsare:-the more truly ' plain' the catgut and thethicker the strand, the greater is the local reaction(Jenkins, I942).The first reaction in the tissues after implanting

catgut is a concentration of polymorphonuclearleucocytes. If the catgut is quite unhardened,digestion proceeds at such a pace that there is soona marked collection of detritus, formed largely ofdisintegrated leucocytes. If the catgut is moreresistant than the plain variety, little or no detritusis observable and digestion proceeds mainly by theingrowth of giant-cells. Such reaction as takesplace is greater with a thick suture than with afine one, particularly with plain catgut.



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September 1949 LE QUESNE : Hind-Quarter Amputation 433

A tendency to use thick catgut at operation isdue to an unfounded fear that fine stitches may beinsufficiently strong to hold the wound edges inapposition, Great force is not normally necessaryto keep a wound closed and even if considerablestrain is expected, as in retching or coughing afterlaparotomy, it is more likely that the sutures wouldcut out of the tissues than that the stitches them-selves would break.,The shearing strain of tissues, which is

analogous to their resistance to the cutting out ofstitches, is not so high as appears to be generallybelieved, varying from less than I lb. in softtissue, as for instance bowel, to no more than 24lb. in rectus muscle sheath. The minimumstandard breaking strain for No. 2/0 catgut, evenwhen knotted, is 3 lb. This bears out the ex-periments of various workers who advocate the useof fiher catgut sutures than those commonly used,with No. o for fascia as the thickest recommended,down to No. 3/0 or No. 4/0 for muscle, peritoneumand subcutaneous tissue (Howes, I929, I941).

Suspected infection in a wound need not be areason for using thick catgut; besides the additionof 'thick catgut reaction' to the bacterial dis-turbance, it is by no means certain that a moderateinfection speeds up the absorption of catgut ex-cessively. In a summary of a large number ofabdominal wound disruptions, it was found thatthe cases in which infection was present disruptedconsiderably later than the clean cases.

Furthermore, with the considerable improve-

ments in the manufacture of surgical catgut overrecent years resulting in greater tensile strength,there is no justification on this score for using thethicker sizes.

ConclusionTo summarize the points covered in this general

survey of catgut as a suture material :I. The fundamental advantage of catgut is its

absorbability.2. It has excellent tensile strength.3. Sterility, as taken from the sealed tubes, is

assured.4. A hardened or 'chromed,' catgut is pre-

ferable to the ' plain' variety.5. The finest possible sizes should be used in

preference to thicker sizes.In conclusion, the following quotation from

Mikulicz is offered with respect and sincerity:-'Je reconnais le bon chirurgien, non pas a la

fafon dont il coupe, mais a la faFon dont il saitrecoudre.'

BIBLIOGRAPHY

FANDRE, A. (i944), 'Le Catgut,' Masson et Cie, Paris.WILLIAMS, F. E. (1936), 'Alcohol and Sporing Organisms,'

Med. Jour. Australia.HOLDER, E. J. (I939), ' Surgical Sutures and Ligatures,' E. & S.

Livingstone, Edinburgh.HOLDER, E. J. (1946), 'Desirable Factors in Surgical Sutures,'

Wm. Blackwood & Sons, Ltd., Edinburgh.JENKINS, H. P., et al. (1942), Arch. Surg., 44, 88I, 984.JENKINS, H. P., et al. (1942), Ibid., 45, 74.JENKINS, H. P., et al. (1942), Ibid., 45, 323.HOWES, E. L., and HARVEY, S. C. (I929), New Eng. J. Med.,

200, I285.HOWES, E. L. ( 4x), Surg. Gyn. and Obst., 73, 319.

HIND-QUARTER AMPUTATIONBy L. P. LE QUESNE, M.A., F.R.C.S.

Second Assistant, Surgical Professorial Unit, Middlesex Hospital

Hind-quarter amputation was first performed ini891 by Billroth (1902), but it was not until i895that a successful result was obtained by Girard(I895). Since that time the operation has beenperformed by many surgeons with increasingsuccess. Pack and Ehrlich (1946) report that 132cases are recorded in surgical literature over thelast 50 years. Sir Gordon Gordon-Taylor, in I946,reported a personal series of 2I cases, and sincethat time has performed a further i i such opera-tions ; it is largely as a result of his work that thisformidable ablation has been established in thiscountry as a standard procedure in the surgicalmanagement of malignant disease.

In most cases the operation is performed forprimary malignant tumours of the bones or con-nective tissues of the pelvis, or for similar tumoursin the upper third of the thigh which have ex-'tended too far proximally to allow of disarticula-tion through the hip-joint; typical of the tumoursnecessitating this procedure are those illustrated inFigs. I and 2. On occasion the operation has beenperformed for extensive tuberculous or chronicinflammatory disease. of the hip and pelvic bones.By virtue of their less sinister pathologicalpotentialities, the best results are obtained in caseswhere the tumour is .essentially only of localmalignancy, such as infiltrating chondromas of the



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