Impact of incisional hernia on abdominal wall strength

Introduction

Incisional hernias are a common condition after abdominal wall incisions, with varying incidence rates and significant associated costs^1,2. The rates tend to increase over time, reaching approximately 12.8% 2 years after the initial surgery², though they can be considerably higher when patient-related factors (obesity, uncontrolled diabetes, active smoking, malnutrition, etc.), hernia characteristics (hernia defect size, contaminated surgical field) or the type of surgical repair (closure technique, mesh placement, etc.) are taken into account^3–5.

Furthermore, recurrence after incisional hernia repair increases to reach 50% in the long term, also elevating the risk of other postoperative complications^4,6.

Patients with incisional hernia often experience symptoms that adversely affect their quality of life (QoL)^7,8. These symptoms include pain, swelling, discomfort, and urinary and gastrointestinal issues^9,10. The presence of incisional hernias can also impact domains of general health such as social functioning, mental health and physical performance¹¹. However, reports assessing the effects of incisional hernias on abdominal wall strength and functional performance are scarce.

Muscle strength, particularly hand grip strength and lower limb strength, is widely recognized as a critical determinant of overall population health^12,13. Extending this principle, it is reasonable to posit that abdominal wall strength may similarly influence an individual’s health and overall QoL.

Therefore, the aim of this study was to analyse abdominal muscle strength in patients with incisional hernia compared with healthy control subjects.

Methods

A prospective case-control study (July 2022–June 2023) included midline incisional hernia patients (W2-3 per European Hernia Society classification, larger than 4 cm) in a 1:1 match with healthy controls, aligning for sex, BMI, age and body composition (variables related to abdominal wall strength)¹⁴ (Supplementary methods).

Exclusion criteria included lateral hernias, prior abdominal surgery and patient refusal. The control group included healthy subjects (hospital staff and patients’ relatives) matched for biometric criteria with the patients’ group.

The primary aim was to compare abdominal muscle strength, while secondary objectives involved analysing strain gauge kinetic measurements and identifying predictive variables for abdominal wall strength.

Approved by the Andalusian Biomedical Research Ethics Portal (PEIBA), the study followed STROBE guidelines¹⁵. Data included demographics, body composition, hernia defect width, and strength measurements using bioelectrical impedance analysis and a strain gauge (Chronojump, Barcelona, Spain: Boscosystem®). Isometric contractions at 90° and 45° were assessed, and three repetitions were performed with a 60 second rest between each, as detailed elsewhere¹⁴.

Results

Of 42 recruited patients with hernia, two were excluded (incorrect test performed). Their mean(s.d.) hernia diameter was 6.6(1.5) cm. Forty healthy subjects were included. The mean(s.d.) age was 57.9(9.8) years, and female patients represented 62.5%. No differences were observed in the demographic characteristics and body composition between groups (Table S1).

Abdominal wall strength measurements

Regarding the maximal force generated, significant differences close to 20% were observed between the incisional hernia group and the control group in both 90° for rectus abdominis muscles and 45° for lateral musculature (P = 0.001 and P < 0.0001). The force generation rates were also lower in the incisional hernia group, with mean differences ranging from 168 to 290 N·s⁻¹ (P = 0.003 and P < 0.0001). Detailed strength data comparing both groups can be found in Table 1.

A multivariable analysis included age, sex, BMI and hernia diameter. Both models for 90° and 45° were statistically significant, with R-square values of 0.43 for 90° and 0.39 for 45°, indicating a strong explanatory power.

Our findings indicate that sex was the most influential factor in the regression model (Table 2). On average, male patients exhibited approximately 50 Newtons more strength than their female counterparts (both at 90° and 45°). Additionally, according to our model, an increase of each centimetre in hernia size reduced the peak force by 5 Newtons. Age was an independent factor for abdominal strength at 45° only. Finally, BMI also emerged as an independent predictor of peak force both at 90° and 45°.

Discussion

The study primary outcome revealed that individuals with incisional hernias larger than 4 cm exert approximately 20% less force in abdominal wall muscle function compared with those without abdominal wall defects, when matched for sex, age, BMI and body composition. It is evident that patients with incisional hernia show significantly reduced abdominal strength compared with healthy individuals. Identifying this early could have an impact on perioperative management, improving their overall QoL.

Previous research indicated reduced muscle strength with larger hernias¹⁶, while the findings of this study extend this association to hernias larger than 4 cm. The prevalence of W2 hernias suggests a substantial population with compromised abdominal strength. Jensen et al.'s validation study¹² observed a decline of strength in patients with hernia, but without substantial sample or comparable groups, leading to potential biases.

While the isokinetic dynamometer is considered the ‘standard’ for strength assessment¹⁷, its cost makes it impractical for clinical use. This study proposes the strain gauge as a cost-effective, clinically practical alternative for assessing abdominal muscle strength, overcoming limitations of other devices. The use of a strain gauge in the trunk region presents additional challenges, such as the difficulty in isolating the musculature of the abdominal wall from other accessory muscle groups.

Several variables emerged as independent predictors of abdominal functional capacity in our study. The most prominent predictor was sex, with the size of the hernia defect also playing a significant role. Moreover, the observed differences in peak force at 45° with age imply a more substantial impact of ageing effects on the lateral musculature. A previous report¹⁸ linked sex to abdominal wall strength, but not age nor BMI, although these were studies with a small number of subjects. In this regard it is well established that both age and BMI exert a direct influence on the onset of sarcopenia, which is implicated in functional decline and the occurrence of adverse health events¹⁹. Consequently, these new findings enable us to identify potential risk groups that could benefit from specific therapies aimed at preventing the decline in abdominal wall function.

The generation of this strength is accompanied by the speed at which it is produced, assessed by means of the rate force development (RFD), which correlates with physical function and neuromuscular health²⁰. According to the results of the present study, hernia patients exhibited a significant decrease in RFD values compared with the control group. A possible explanation could be the presence of a limiting psychological factor, such as fear of movement in patients with some type of hernia, especially when generating force rapidly. However, the present study did not evaluate the fear factor, thus potential future directions of research could establish the relationship between fear or kinesiophobia and the rapid generation of force.

Finally, this study has some limitations. First, the baseline level of physical activity for both groups was not factored in; therefore, the findings are solely grounded on demographics and body composition data. Since only patients capable of performing the strength test were included, a selection bias in that regard cannot be excluded. Despite the relatively small sample size, it outperforms previous studies. Back pain, which could affect the performance of the tests, was not taken into account.

Funding

The authors have no funding to declare.

Acknowledgements

The authors thank all the study participants and the University of Seville and University Hospital Virgen del Rocío for providing the infrastructure and logistics necessary to conduct the study. The authors also thank all the members of the research group for their ongoing advice and support, and for their hard work and commitment.

Disclosure

The authors declare no conflict of interest.

Supplementary material

Supplementary material is available at BJS Open online.

Data availability

The data that support the findings of this study are available from the corresponding author (A.F.M.) upon reasonable request.

Author contributions

Alejandro Sánchez Arteaga (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), Jose Luis Gil Delgado (Data curation, Methodology, Resources, Software, Validation, Writing—original draft), Adrián Feria Madueño (Conceptualization, Methodology, Software, Validation, Visualization, Writing—review & editing), Luis Tallon-Aguilar (Conceptualization, Investigation, Supervision, Writing—review & editing), Borja Sañudo (Conceptualization, Project administration, Resources, Supervision, Validation, Writing—review & editing) and Javier Padillo Ruiz (Supervision, Validation, Writing—review & editing)

References