Educational Review

Factors involved in abdominal wall closure and subsequent incisional hernia

P.J. O’Dwyer 
C.A. Courtney
University Department of Surgery, Western Infirmary, Glasgow, G11 6NT, UK

Correspondence to: Professor P.J. O’Dwyer, University Department of Surgery, Western Infirmary, Glasgow, G11 6NT, UK

Introduction Choice of incision Suture type Method of closure

Continuous versus interrupted Suture to wound length ratio Conclusion References

Keywords: Abdominal, closure, hernia, chronic pain, sinus
Surg J R Coll Surg Edinb Irel., 1 February 2003, 17-22

Incisional hernia is a frequent complication of abdominal wall closure with a reported incidence of between 5% and 15% following vertical midline incisions at one-year follow-up. Evidence from randomised clinical trials and meta-analysis indicate that a continuous running non-absorbable or slowly absorbed suture such as polydioxanone is the method of choice for abdominal wall closure. Continuous polydioxanone has a similar incisional hernia rate to its non-absorbable counterparts but causes less chronic pain and wound sinuses. Evidence from randomised clinical trials indicates that a lateral paramedian incision is associated with a lower incidence of incisional hernia when compared with other abdominal incisions. Transverse abdominal incisions have no advantage over midline incisions in reducing incisional hernia rate. Although experimental and clinical evidence indicate that a greater number of stitches with a suture length to wound ratio of at least 4:1 is associated with a lower incidence of incisional hernia, there is no evidence from randomised clinical trials to support this. Intuitively one may think that putting as little tension as possible on the closure is important, but there is no evidence for this. Clinical trials evaluating these factors would be difficult to undertake making it important that surgeons continue to audit incisional hernia rates following abdominal closure

INTRODUCTION
Incisional hernia is a common complication of abdominal wall closure with rates of between 5% and 15% reported at one-year follow-up in prospective studies of vertical midline incisions.^1-7 This rate, however, is likely to under-represent the true incidence by a significant factor in that a 10-year prospective study by Mudge and Hughes (1985) demonstrated that less than 50% of incisional hernias occur in the first year after surgery while 35% appear five years or more after surgery.⁸ Although many are asymptomatic approximately one-third of incisional hernias are associated with pain, incarceration and/or strangulation. Twenty per cent require surgical repair with a high rate of failure after repair, varying between 20% for mesh repair to 40% for non-mesh repair.⁹ Chronic pain and chronic wound sinuses are also significant problems following abdominal wall closure. The purpose of this review was to examine the surgical related factors which contribute to incisional hernia and other chronic wound problems after laparotomy in order to provide an evidence-based approach to abdominal wall closure.

The electronic database MEDLINE was searched with use of appropriate terms for abdominal wall closure and incisional hernia. Trials were also identified from the reference lists of reports from known published trials.

CHOICE OF INCISION
Although many factors influence the choice of an abdominal incision, foremost amongst these is the type of operation being undertaken. The common choices are between vertical midline, medial paramedian, lateral paramedian or transverse incisions. For most major abdominal operations a vertical midline incision offers rapid and easy access and is straightforward to close. Alternatives take a little longer to perform and are associated with more blood loss.^10,11

For vertical midline incisions, incisional  hernia rates of between 5% and 15% are reported in prospective trials with similar results for the conventional ‘medial’ paramedian incision.^1-7 In contrast, the ‘lateral’ paramedian incision has been consistently shown to achieve incisional hernia rates of less than 1%.¹² This incision is made by incising both the anterior and posterior rectus sheaths in the same sagittal plane at a point not less than two-thirds of the width of the rectus sheath from the midline. The rectus muscle is then retracted laterally and it is thought that the wide ‘shutter’mechanism thus conferred after closurecontributes to the inherent stability of this incision. There have been three randomised controlled trials published comparing the lateral paramedian incision to the midline incision.^4,5,7 All of these included a wide range of general surgical procedures and all demonstrate the superiority, OR 0.09 (95% CI 0.03-0.27),of this incision¹³ (Table 1). A further randomised trial by Brennan et al (1987) demonstrated the importance of performing a lateral incision in both the anterior and posterior rectus sheaths.6 Medial incision of the anterior rectus sheath and lateral incision of the posterior sheath resulted in an incisional hernia rate of 2.9%, while the reverse, lateral incision of the anterior rectus sheath and medial incision of the posterior sheath, had an incisional hernia rate of 4.6% in a randomised trial. Lateral incision of both had a 0% incisional hernia rate.

These trials also addressed some of the criticisms of the lateral paramedian incision. In a randomised trial the mean time to open and close a lateral paramedian incision was 22 minutes (range 11-31 minutes), as opposed to 18 minutes (range 10-27 minutes) for mass closure of a midline incision.⁵ Wound infection rates were similar in all groups and although blood loss was not measured it is reasonable to assume that with the use of electrocautery this would be low in both groups.¹⁴

The use of the transverse incision for laparotomy has been less widely studied. There have been two randomised trials of note on this subject.^10,11 Ellis et al (1984) compared transverse to midline to medial paramedian incisions in a series of 96 laparotomies and found no particular advantage in either with incisional hernia rates of 17% in the medial paramedian group and 14% in the transverse group.¹¹ Greenall et al (1980) who reported that the transverse incision took longer to perform randomised 579 patients undergoing laparotomy to either midline or transverse incisions.¹⁰ At a follow-up of not less than six months 7% of the midline versus 6.4% of the transverse incisions had an incisional hernia.

SUTURE TYPE
The desirable features of a suture material include a product that maintains high tensile strength until the wound has healed, has a low reactivity, is absorbable and easy to handle. Throughout the years many different materials have enjoyed popularity in the closure of laparotomy wounds, the choice for the modern surgeon, however, is generally between absorbable and non-absorbable sutures. There have been many randomised trials comparing the relative merits between these two classes of suture, often with conflicting results. ^1,2,3,15,17 These trials have recently been subjected to a meta-analysis by Hodgson et al (2000), the main findings of which were that the incidence of incisional hernias was reduced by 32% (95% CI 13%-48%) when a non-absorbable material was used regardless of incision type.¹⁸ This finding is in broad agreement with a previous meta-analysis by Weiland et al (1998) where the authors concluded that continuous closure with a nonabsorbable suture should be used to close most abdominal wounds.¹⁹

Hodgson et al (2000) also demonstrated that polydioxanone (PDS), unlike all other absorbable sutures, did not have an increased risk of incisional hernia.¹⁸ Polydioxanone is a slowly absorbable monofilamentsuture which retains its tensile strengthfor up to six weeks post-operatively. In addition to having an incisional hernia rate comparable to non-absorbable sutures (Table 2) PDS is associated with less chronic wound pain and suture sinuses than its non-absorbable counterparts.^1,2,3,15 Meta-analyses of the three large randomised or quasi randomised trials with one year followup reveal that 40 (4.5%) of 891 patients in the PDS group developed chronic pain compared with 79 (8.7%) of 912 in the nylon group OR 0.53 (95% CI 0.36 - 0.79).¹³ Excluding the trial by Israelsson and Jonsson (1994) where suture type was employed to patients operated on in consecutive weeks did not significantly affect the odds ratio or confidence intervals.³ The figures for chronic suture sinus formation were 12 (1.3%) of 891 versus 25 (2.7%) of 912, OR 0.47, (95% CI 0.24 - 0.83), respectively.

Another reported drawback of non-absorbable suture material is the incidence of ‘buttonhole’ incisional hernia formation.²⁰ This appears to be a late complication which is thought to be due to the cheesewire effect of the permanent suture material against the rectus sheath at the site of stitch penetration leading to multiple small incisional hernias.

METHOD OF CLOSURE
Once a suitable material has been chosen the surgeon must employ an appropriate surgical technique to achieve satisfactory fascial closure and maintain the extrinsic strength of the wound until it develops its own intrinsic strength. The variables of importance in closure technique are continuous versus interrupted modifications of the continuous running suture and suture-to-wound length ratio. Layered closure or closure of the peritoneum in vertical midline incisions plays no significant role in the healing of laparotomy wounds.²¹

* Follow-up six months, all other studies have a one year follow-up with between 21-24% dead or lost to follow-up
** Suture material was employed exclusively to patients operated on in alternative weeks

CONTINUOUS VERSUS INTERRUPTED
While most surgeons use continuous mass closure there have been trials of continuous versus interrupted closure. Wissing et al (1987) carried out a randomised prospective trial of almost 1500 patients comparing continuous closure with polygalactin, with nylon or PDS interrupted closure with polygalactin.² They found the highest rate of incisional hernias with continuous polygalactin and the lowest with continuous nylon. In their metaanalysis of abdominal fascial closure Hodgson et al (2000) looked at six trials comparing these two-closure types and found continuous closure to be superior overall. Richards et al (1983), in a study of 571 laparotomy wounds, found no significant difference in the rates of wound dehiscence and incisional  hernia formation using these two different techniques. This finding was confirmed by Gislason et al (1995) who found no difference in incisional hernia formation, when comparing continuous with interrupted closure and found the former to be significantly quicker.²³ It is postulated that continuous closure should offer theoretical advantages by evenly distributing the tension on the wound across the whole suture line rather than on individual stitches. It is certainly true that it has advantages in terms of ease and expediency of closure and in terms of cost benefit as less suture material is required.

Some authors have attempted to develop alternative suture techniques to replace the continuous running suture (CRS). One such method was a continuous double loop closure technique (CDLC) described by Niggebrugge et al (1999). This is basically a continuous mattress suture which incorporates inner and outer loops.²⁴ The theoretical advantage proposed by the authors was that stress on the outer loop causes tightening of the inner loop which in theory should allow the wound to resist high intraabdominal pressures and still maintain close tissue approximation. It became apparent, however, halfway through the study that patients in the CDLC group were experiencing a significantly higher rate of pulmonary complications and post-operative mortality, 5.4% vs 17.2% (p = 0.0002) and 8.3% vs 21% (p = 0.0004), respectively. This technique, therefore, was quickly abandoned. It is thought that the decreased compliance of the abdominal wall leads to sustained increased intra-abdominal pressure. It is imperative, therefore, that any closure technique has enough ‘give’ or elasticity to accommodate the raised intra-abdominal pressure which inevitably occurs after laparotomy.

SUTURE TO WOUND LENGTH RATIO
Although suture length-to-wound length ratio, (SL:WL) is thought to be important in the prevention of incisional hernia formation, there is no evidence from randomised controlled trials to support this. Jenkins (1976) was the first to define an ideal ratio on the basis of both clinical trials and a mathematical model. He recommended that for safe closure of laparotomy wounds a SL: WL ratio of at least 4:1 is necessary. ²⁵ It  is known that the size of the tissue bite and the diameter of the suture bear an inverse relationship to the distribution of forces at the tissue-suture interface.²⁶ In other words, large tissue bites taken with a thick suture have less tendency to cut through tissues. Recently, Jenkins’ mathematical model has been challenged by Varshney et al (1999) who proposed that an ideal SL:WL ratio should approach 6:1.27 They contend that Jenkins’ original model failed to take into account the three dimensional nature of the wound and that approximately 6cm of suture material is required per stitch when taking 1cm by 1cm bites.

Israelsson and Jonsson (1994) performed numerous clinical and experimental studies on SL:WL ratio. In a large prospective trial they found that SL:WL ratio was an independent predictor for the development of an incisional hernia.3 The rate of incisional hernia could be reduced from 21% to 9% when a ratio of greater than 4:1 was achieved and was independent of suture type.³ In addition, they showed a decrease in incisional hernia formation at one-year from 19% to 11% when surgeons were presented with their own poor results and then made a conscious effort to achieve a suture to wound length ratio of 4:1 or more, in a series of 861 laparotomies.²⁸ The authors also demonstrated that although surgeons are aware of the importance of SL:WL ratio, not all employ an ideal technique.²⁹

Although there has been no randomised trial looking at SL:WL ratio, Kendall et al (1991), who compared mass and layered midline closure (fascia and peritoneum) in a randomised clinical trial, had a SL:WL ratio of 3.7:1 in the layered group and 5:1 in the mass closure group (p<0.001). Despite this there was no difference in incisional hernia rates at one-year follow-up and suggests that SL:WL may not be as critical as suggested by Israelsson and Jonsson (1994). Similarly, Weiland et al (1998) in their meta-analysis found that a SL:WL of >4 could not be validated by meta-analysis.¹⁹ A summary of studies examining SL:WL ratios are presented in Table 3.

There are several factors that can affect SL:WL ratio, not least being the tension applied by the surgeon as well as individual interpretation of the size and interval of fascial bites taken. The issue regarding the amount of tension to apply to a continuous running suture is unclear. In a randomised trial by Mayer et al (1981) comparing normal closure with a fixed compression of 5kg, incisional hernia rates of 10% were noted for the normal closure group, compared with 5.5% for the compression group.³⁰ This difference, however, only reached statistical significance when the Registrar applied the compression. No difference in post-operative pain or pulmonary function between the groups was noted. The mean length of suture used for each stitch in the normal group was 4.87cm, compared with 3.53cm for the compression group.

In a recent experimental study by Cengiz et al (2001), the authors found that wound bursting strength increases with the number of stitches used.³¹ They recommended that a SL:WL ratio of 4 is accomplished by placing many stitches in the wound rather than by using big tissue bites. One of the drawbacks of their study, however, was that the authors did not control for both factors and it may be that small tissue bites, 3mm as opposed to 10mm in a rodent model, and not the number of stitches was responsible for the increase in wound strength. While it is difficult to extrapolate to the human situation it might reasonably be assumed that a 1cm tissue bite in human fascia is a small bite and placing stitches every 5mm apart rather than 1cm may need to be considered.

CONCLUSION
There is good evidence from randomised clinical trials and meta-analysis that a continuous running non-absorbable or slowly absorbed suture is the method of choice of abdominal wall closure. Questions remain as to whether more stitches are better or not and the degree of tension that should be applied. Individual surgeons should continue to audit their incisional hernia rates.

REFERENCES
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2. Wissing J, van Vroonhoven Th JMV, Schattenkerk ME, Veen HF, Ponsen RJG, Jeekel J. Fascia closure after midline laparotomy: results of a randomised trial. Br J Surg 1987; 74: 738-41
3. Israelsson LA, Jonsson T. Closure of midline laparotomy incisions with polydioxanone and nylon: the importance of suture technique. Br J Surg 1994; 81: 1606-08
4. Cox PJ, Ausobsky JR, Ellis H, Pollock AV. Towards no incisional hernias: lateral paramedian versus midline incisions. J R Soc Med 1986; 79: 711-13
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13. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959; 22: 719-48
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20. Krukowski ZH, Matheson NA. ‘Button hole’ incisional hernia: a late complication of abdominal wound closure with continuous nonabsorbable sutures. Br J Surg 1987;74: 824-25
21. Ellis H, Heddle R. Does the peritoneum need to be closed at laparotomy? Br J Surg 1977; 64: 733-36
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24. Niggebrugge AH, Trimbos JB, Hermans J, Steup WH, Van de Velde JH. Influence of abdominal wound closure technique on complications after surgery: a randomised study. Lancet 1999; 353: 1563-67
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27. Varshney S, Manek P, Johnson CD. Six-fold suture: wound length ratio for abdominal closure; Ann R Coll Surg Eng 1999; 81: 333-36
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Copyright: 31 October 2002

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