The present population-based study shows that the incidence of incisional hernias following gynecological surgery is relatively low. In the Swedish Registry for Ventral Hernias 12.2% of incisional hernia operations were performed after gynecological and obstetrical surgery. A diagnosis or surgery for incisional hernia is a surrogate marker for the actual incidence of incisional hernias and is likely a low estimate. However, these numbers reflect the incidence of clinically relevant incisional hernias. The group of excluded patients (12,496) may hide several incisional hernias.
There are patient categories that face an increased risk of incisional hernia. The variables with the highest impact on development of an incisional hernia were obesity and a midline incision.
Obesity is a great problem in case of surgery. In 2001–2002 Sweden had an obesity (BMI > 30) prevalence of 10% and in 2014 the prevalence had increased to 14% . Obesity is increasing all over the world and it is unfortunate that this group is additionally burdened by an increased incidence of incisional hernias. Israelsson et al. observed that the surgeon tends to use larger tissue bites with greater intervals between stitches on obese patients . Current evidence favors small tissue bites with small intervals using a suture to wound ratio of at least 4:1 [8, 9]. It seems as if we unwittingly increase the risk of incisional hernias in these patients. Furthermore, it can be difficult to palpate incisional hernias in obese patients. A hernia in a Pfannenstiel incision can be even more difficult to palpate and can go unnoticed by the patient.
The Pfannenstiel incision was developed to reduce the incidence of incisional hernias  and to this day remains superior to the midline incision in that respect . Unfortunately, the Pfannenstiel and Cohen incisions are not always appropriate, e.g., in extensive oncological surgery where access to the abdomen must be prioritized. The Pfannenstiel incision can also be used successfully in general surgery, e.g., in laparoscopically assisted colectomy for extracting the specimen . However, nerve entrapment is a complication to this incision, especially when extended laterally. This must be taken into consideration when choosing the appropriate incision .
Age is also a considerable risk factor in univariate analysis but not so much in multivariate analysis, perhaps due to the fact that comorbidity tends to increase with age.
The reported proportion of smokers in the GynOp Register was 15.8%. Data were missing for 30% of all women. In 2006, 17% of Swedish women smoked daily , 11% in 2014 . Therefore, it is reasonable to assume that the self-reported frequency of smoking in the GynOp Register is accurate. We found that smoking was the third most important risk factor in the development of incisional hernias. This is consistent with earlier findings . Preoperative anti-smoking programs have been shown to have beneficial effects on postoperative complications . Many clinics in Sweden have implemented such programs.
We chose to eliminate women who had multiple surgeries from the statistical analysis. This may have reduced the incidence of incisional hernias found in our study. It is known that repeated incisions carry a higher risk of development of an incisional hernia.
The incidence of incisional hernia depends not only on patient- and surgeon-related factors but also on the method of detection. Henriksen et al. reported an incidence of 25.9% on patients who were examined by an experienced surgeon , whereas J Nilsson et al. reported an incidence of 30.5% on patients regularly examined with CT scans after surgery for liver metastases of colorectal cancer . The women in our study were not screened for incisional hernia. Therefore, the incidence of incisional hernia is likely underestimated.
Tecce et al. have recently performed a cost-analysis on incisional hernias after hysterectomy. In their material, women with an incisional hernia had fourfold more readmissions, fivefold added hospital length of stay and significantly higher index procedure costs .
In conclusion, our study shows that there is much to be gained if patients can cease smoking and lose weight before undergoing abdominal surgery. Many departments specializing in hernia surgery strive to optimize their patients preoperatively through weight loss regimens and anti-smoking programs . This could and should be applied to all patients undergoing elective abdominal surgery. The Pfannenstiel incision results in fewer incisional hernias compared to a midline incision and should be considered whenever possible.