Background

Wound dehiscence is an unusual complication of abdominal surgery with high morbidity and a reported mortality rate as high as 25% [1,2,3,4]. Wound dehiscence is defined as the separation of the sutured edges of the abdominal fascia after surgery [5]. There are four principal pathogenic mechanisms resulting in wound dehiscence: rupture of the suture, knot failure, slack suture, or sutures cutting through the fascia. The last-named is considered the most common [6,7,8]. Wound dehiscence can be subclinical with a small dehiscence of the fascia detectable only by radiology. This form of fascial dehiscence can easily be overlooked or ignored in the early stage, but may later lead to incisional hernia formation [3]. Extensive wound dehiscence is clinically evident, with secretion from the wound and sometimes dramatic protrusion of abdominal content through the fascia, a condition known as burst abdomen. Depending on the size of the fascial defect, there is a risk for incarceration and ischaemia of the protruding viscera [9]. Wound dehiscence usually develops on days 3–7 postoperatively [10, 11] but the diagnosis is often delayed. Symptomatic wound dehiscence is unusual, with an incidence of approximately 1 % of patients undergoing elective abdominal surgery [12]. Hospital stay is significantly longer for patients suffering from wound dehiscence [13] and it is associated with considerable postoperative mortality [14]. Clinically evident wound dehiscence requires emergency surgery, which is often complicated by suboptimal condition of the patient after the index surgical procedure. At clinical examination, early wound dehiscence presents with secretion from the wound and can be mistaken for an infection. More severe cases may be diagnosed by CT scan showing dehiscence of the fascia and protrusion of viscera into the subcutaneous tissue.

There is still uncertainty regarding which patient-related factors lead to the development of wound dehiscence. There are studies that have examined risk factors for wound dehiscence [14, 15], but most of these are old and performed before meticulous suturing of the abdominal wall was introduced.

The aim of the present study was to analyse the incidence of wound dehiscence after colorectal cancer surgery based on a population-based national register, to identify risk factors for wound dehiscence, and to analyse mortality after wound dehiscence.

Methods

This study was based on colorectal cancer procedures performed in 2007–2013. Data were obtained from the Swedish Colorectal Cancer Registry (SCRCR) [16]. All patients diagnosed with rectal cancer since 1995 and colon cancer since 2007 are registered in the SCRCR. The register includes data on age, gender, treatment, and postoperative follow-up. Completeness for the SCRCR is over 98% for both colon and rectal cancer, and validity compared to reabstracted data has an average agreement of 90% [17]. In addition to the SCRCR, we also used data from the National Patient Register (NPR) [18]. The NPR contains data on all hospital admissions in Sweden since 1987, including outpatient specialist care and outpatient emergency care. The validity of the NPR is estimated to be 85–90% [19]. Diagnoses from all admissions and visits prior to the colorectal cancer surgical procedure (identified by the ICD code) were also retrieved from the NPR. The diagnoses obtained from the NPR as potential risk factors were liver cirrhosis, chronic kidney disease, diabetes with secondary complications, chronic obstructive lung disease, and generalised inflammatory disease. We also included variables such as age, gender, duration of surgery, and preoperative radiation therapy in the analyses. Cross-matching between the SCRCR and the NPR was performed using the Swedish Personal Registration Number, which is a ten-digit identity number unique for each Swedish citizen.

Reoperation for wound dehiscence is registered in the SCRCR by the surgeon responsible for the procedure. In the NPR, on the other hand, the procedure code for wound dehiscence surgery (JWA00) is recorded by the surgeon responsible for the patient at the time of discharge and then transferred to the NPR. Wound dehiscence in the present study was defined as wound dehiscence registered in the SCRCR and/or the NPR, i.e. any wound dehiscence irrespective of the need for reoperation.

Ethics statement

This study was approved by the Regional Ethics Review Board in Stockholm, ref. 2014/1351-31/5.

Statistics

Statistical calculations were performed using SPSS 22.0 (Chicago, IL). Analyses were performed to assess the impact of each investigated risk factor and to estimate the incidence of wound dehiscence. Surgery for wound dehiscence was defined as discharge note or outpatient visit with the ICD code JWA00. Age, BMI, comorbid disease, presence of distant metastases, and operative time as risk factors for wound dehiscence were analysed using uni- and multivariable logistic regression analysis. Survival after reoperation for wound dehiscence was analysed with the Cox proportional hazard analysis. In a multivariate Cox proportional hazard analysis, an adjustment was made for all covariates found to increase the risk for development of wound dehiscence. The multivariate model was based on stepwise selection, with entry testing based on the significance of the score statistic and removal testing based on the probability of a likelihood ratio statistic based on the maximum partial likelihood estimates.

Results

During the study period of 2007–2013, 39,984 patients were registered in the SCRCR. After excluding patients not undergoing surgery, laparoscopic procedures, patients where data on the procedure were missing, appendectomies, transluminal endoscopic mucosectomies, and local excisions, 30,505 patients remained in the study group. The study cohort assembly flow chart is shown in Fig. 1. Baseline characteristics of the study population are shown in Table 1.

Fig. 1
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Flow chart of cohort assembly

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Table 1 Patient characteristics
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The overall incidence of reoperation for wound dehiscence after open colorectal cancer surgery was 2.9%. Uni- and multivariable logistic regression analyses of potential risk factors for wound dehiscence are presented in Table 2. In the multivariable regression model, age > 70 years, male gender, BMI > 30, history of chronic obstructive pulmonary disease, history of generalised inflammatory disease, and operation time less than 180 min were found to be independently and significantly associated with increased risk for wound dehiscence. The single strongest risk factor was male gender (odds ratio 3.00; 95% confidence interval 2.52–3.57). History of diabetes, chronic renal disease, liver cirrhosis, and distant metastases had no impact on the risk of wound dehiscence.

Table 2 Analysis of risk for wound dehiscence
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In the univariate Cox proportional hazard analysis, the hazard ratio for postoperative death was 1.24 (95% confidence interval 1.12–1.38, p < 0.001) for patients who underwent reoperation for wound dehiscence following the primary procedure. When adjusting for the factors found to have a significant association with wound dehiscence (age, gender, BMI, history of chronic obstructive pulmonary disease or generalised inflammatory disease, and operation time), the hazard ratio was 1.26 (95% confidence interval 1.11–1.43, p < 0.001).

Discussion

Although the incidence of wound dehiscence is reportedly only 1–2%, this remains a major, potentially lethal complication after abdominal surgery. In this study, we identified risk factors for wound dehiscence that can easily be used preoperatively to identify patients at risk for wound dehiscence in order to take prophylactic measures.

This study confirms that patients reoperated for wound dehiscence face a high risk of postoperative death. Male patients, those older than 70 years, patients with high BMI, or suffering from chronic obstructive pulmonary disease or generalised inflammatory disease have a higher risk for wound dehiscence than those in the general population. There is also an increased risk if the time taken at the index operation is less than 180 min.

During the study period of 2007–2013, surgery for colorectal cancer was mainly performed via a midline incision, and we therefore believe that this study provides a good estimate of the complication rate following midline incisions. This is also why we excluded laparoscopic surgery from the study.

There are, however, some limitations to this study. Surgery for colorectal cancer is performed on a heterogeneous group of patients. Our material includes acute, elective, curative, and palliative surgery. Most procedures are performed through a midline incision, but there could be cases in this cohort that were operated through an incision having a lower predicted incidence of complications such as a transverse or Pfannenstiel incision [20]. Furthermore, the length of the incision probably varied.

The surgical technique used to close the midline incision is probably a major risk factor for wound dehiscence. The modern technique introduced by Milbourn et al. [21,22,23] was introduced in Sweden during the study period, but no specific data on surgical technique were available in the SCRCR. The incidence of wound dehiscence after open colorectal cancer surgery in this study was 2.2% which is close to the findings of Kenig et al. [14] and Webster et al. [24] who reported the incidence to be 2% and 3%, respectively. In a study on 750 patients in 2009, Milbourn et al. [21] presented a modernised technique for closing midline incisions which has now become a standard [8]. In their study, there was only one case of wound dehiscence. Nicholas et al. [12] report the incidence of wound dehiscence to be 0.4–1.2% in elective surgery and 12% in acute surgery. This indicates that future studies on wound dehiscence must take surgical technique and acute or elective surgery into account. Our present study confirms the higher postoperative mortality rate for patients with wound dehiscence which is in accordance with previously reported studies such as those of Nicholas et al. [12]. From previous studies, we know that hospital stay is longer for patients with wound dehiscence [13]. Although wound dehiscence is an unusual complication, risk stratification and prophylactic measures are worthwhile since the suffering and cost of every case is so vast.

The study showed a hazard ratio of 1.26 for mortality risk when a wound dehiscence was registered. The actual increase in risk, however, is probably even higher. There may have been deaths in the early postoperative period where wound dehiscence was the main cause or contributing factor, but where no attempt to resuture the abdominal wall was made. In these cases, the wound dehiscence may not have been registered. This could explain the paradoxically higher survival for the first 7 days after surgery for patients who underwent surgery for wound dehiscence (Fig. 2).

Fig. 2
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Overall survival for patients undergoing and not undergoing reoperation for wound dehiscence

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Short operation duration as a risk factor for complication seems counter-intuitive and contradicts other studies [25]. A feasible explanation for this could be that palliative surgery and diagnostic surgery where you decide the tumour to be inoperable fall in this category. Operating time as a risk factor needs to be further investigated.

In conclusion, wound dehiscence is associated with a higher postoperative mortality rate. Patients at high risk for developing dehiscence may benefit from active prevention measures if these can be implemented in routine surgical practice. In this respect, the knowledge that male gender, age > 70 years, obesity, history of chronic obstructive pulmonary disease, and history of generalised inflammatory disease are risk factors makes identification of patients at risk possible.