A hernia is defined as a protrusion of a viscus through an opening in the wall of the cavity in which it is contained. The first description of the inguinal anatomy and repair was by that of Sir Astley Cooper in 1804 [1]. In 1939, Chester McVay described a technique of approximation of the conjoined tendon to Cooper’s ligament with a relaxing incision to reduce tension on the repair [1]. The Cooper ligament repair remains the only open repair that can treat all groin hernias to include femoral, indirect, and direct. Hernia repair advanced to the Lichtenstein repair in 1984 with the use of polypropylene mesh to provide a tension-free repair without the necessity of a relaxing incision [1].

A posterior (preperitoneal) approach was discovered in 1876 by Annandale. This approach has undergone several modifications over the years to include emphasis on an iliopubic tract repair by Condon in 1960 and further elaborated by Nyhus [2]. It is the combination of the McVay (Cooper ligament repair) and the work by Nyhus (iliopubic tract repair) that lead to a protocol for laparoscopic repair of groin hernias in 1991. The advent of laparoscopic surgery provided a technique of repair that was associated with less postoperative pain and decreased recovery time [3]. Laparoscopic inguinal hernia repair also has the advantage of intra-operative diagnosis and treatment of a contralateral inguinal hernia as well as the ability to treat all groin hernias.

Inguinal hernia repair is one of the most commonly performed procedures in the USA today. Approximately 800,000 cases are performed annually, with 89 % of those being on an outpatient basis [3]. Laparoscopic inguinal hernia repair only accounted for 14 %, whereas 86 % were open repair [3]. Laparoscopic surgery, however, is felt to be more costly resulting in preference of open inguinal hernia repair.

The effect of obesity on inguinal hernia repair is not known though it is felt to be a risk factor for ventral hernia recurrences and wound infections [4]. This study proposes that an open inguinal hernia may save hospitals on initial cost, but in patients with an obese body mass index (BMI), there will be longer operating times, longer hospital stays, and more complications that will impose higher costs to the facility and the patient. This study aims to define the ideal BMI at which a laparoscopic inguinal hernia repair will be advantageous over open inguinal repair.

Methods

Study design

This is a retrospective comparative analysis of the National Surgical Quality Improvement Program (NSQIP) database. The database provides information based on clinical data rather than claim data from medical billing [5]. No patient identifiers were associated with the data collected for this study.

The patient population included all male and female patients undergoing initial unilateral inguinal hernia repair between the ages 18–65 in the time frame of 2005–2012 (Table 1). Patients with a history of previous inguinal hernia repair on the same operative side were excluded as repeat operations may endure longer operating times and increase risk of operative and postoperative complications. Patients undergoing bilateral inguinal hernia repair were also excluded as this procedure may also involve a longer operating time.

Table 1 Demographics
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Chi-square tests and Fisher’s exact tests were used to assess associations between type of operation and categorical variables including demographics, risk factors, and 30-day outcomes. t tests and nonparametric Wilcoxon rank-sum tests were used to assess unadjusted differences between types of operation for continuous variables such as operating time. All tests are two-sided with a significance level of 0.05.

Multivariable logistic regression analyses were done to estimate adjusted odds ratios. Models were based on stepwise selection with p < 0.05 for inclusion. Interactions between type of operation and BMI were evaluated to see if odds ratios for mortality, morbidity, and complications differ by level of BMI to include Class I obesity (BMI 30–34.9), Class II obesity (BMI 35–39.9), and Class III obesity (BMI > 40). The overweight category (BMI 25–29.9) was also analyzed, and it was compared to normal-weight individuals (BMI 18.5–24.9). Analysis of covariance was used to evaluate differences in operating times between treatments adjusted for significant risk factors. All p values and odds ratios were adjusted for age, sex, functional status, ASA class, sepsis, bleeding disorder, renal failure, ascites, and patients receiving chemotherapy.

Cost data

The Healthcare Cost and Utilization Project (HCUP) was used to compare the cost outcomes of laparoscopic and open hernia repairs. HCUP is the largest collection of longitudinal hospital care data in the USA with collection beginning in 1988 [6]. Databases include research of a broad range of health policy issues, including cost and quality of health services, medical practice patterns, access to healthcare programs, and outcomes of treatments at the national, state, and local levels [6]. Goals of HCUP are to create a source of national, state, local all-payer healthcare data to conduct and translate research to inform decision-making professionals and improve healthcare delivery [6].

Both unweighted and weighted data were obtained. Weights are usually required to obtain unbiased estimates of descriptive statistics. Unweighted means will almost equal weighted means on outcomes for which there is little variation. Hospital-level statistics are the average occupancy rate and the average volume of hospital procedures. Average occupancy rate and the average procedure volume would be estimated using a hospital-level file and hospital-level weights. The average length of stay and total number of procedures performed per discharge are patient-level statistics. These would be estimated using discharge-level file and discharge weights.

Sampled from the State Inpatient Databases (SID), HCUP’s Nationwide Inpatient Sample (NIS) contains all discharge data from more than 1000 short-term and non-federal hospitals each year, which approximates a 20-percent stratified sample of US community hospitals. For 2011, these states comprise over 97 % of the US population [6]. The NIS contains charge information on individuals covered by Medicare, Medicaid, or private insurance, as well as those who are uninsured. The NIS can be used to identify, track, and analyze national trends in healthcare utilization, access, charges, quality, and outcomes. Unweighted, it contains data from approximately eight million hospital stays each year [6]. Weighted, it estimates roughly 40 million hospitalizations [6]. The Agency for Healthcare Research and Quality (AHRQ) and policy makers use the NIS to identify, track, and analyze national trends in healthcare utilization, access, charges, quality, and outcomes. It should be possible, for example, to estimate diagnosis-related group (DRG)-specific average lengths of stay across all US hospitals using weighted average lengths of stay, based on averages or regression coefficients calculated from the NIS. Ideally, relationships among outcomes and their correlates estimated from the NIS should accurately represent all US hospitals.

Chi-square tests and Fisher’s exact tests were used to assess associations between type of operation and categorical variables to include length of stay and costs between the years of 2008 and 2011. All tests are two-sided with a significance level of 0.05. Interactions between type of operation and costs/length of hospital stay were evaluated.

Results

There were 17,919 patients in the laparoscopic group and 46, 582 patients in the open group. The majority of patients were male, Caucasian, and American Society of Anesthesiologists (ASA) Class II. In both groups, 18.9 % of patients were obese. In the open group, 44.2 % of patients were overweight compared to 45.9 % in the laparoscopic group. The open repair group had significantly more patients that were diabetic requiring medication. The open repair group also had more patients with renal failure, ascites, tobacco dependence, chronic obstructive pulmonary disease (COPD), using steroids, bleeding disorder, congestive heart failure (CHF), hypertension (HTN), coronary artery disease (CAD), peripheral vascular disease (PVD), received radiotherapy in past 90 days, sepsis, and on dialysis. Inpatient status occurred for 6.3 % of the open repair group and 5.8 % in the laparoscopic group. Outpatient status accounted for 93.7 % of the open repair group and 94.2 % of the laparoscopic group (Table 1).

Comparing open versus laparoscopic procedures

When adjusted for risk, the overall morbidity, surgical site infection (SSI), complications [including wound disruption, failure to wean from the ventilator, and urinary tract infection (UTI)] were greater in the open repair group compared to the laparoscopic group (Table 2). The return to operating room was greater in the open repair group than in the laparoscopic group (p < 0.01).

Table 2 Thirty-day outcomes between open and laparoscopic procedure groups for all BMI categories ages 18–65
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Comparing laparoscopic versus open procedures in the obese patients

There was no statistical significance in the odds ratios between the open technique and the laparoscopic one when comparing obese versus normal-weight patients (p = 0.684) (Table 3). Similarly, there is no significant difference between an open repair and a laparoscopic one when comparing obese and overweight patients versus normal-weight patients (p = 0.472).

Table 3 Thirty-day outcomes between open and laparoscopic procedure groups for obese (≥30) BMI
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Comparing obese patients in open and laparoscopic procedures

Overall morbidity in obese patients is significantly higher in the open repair group (OR 1.76, p < 0.01) compared to normal-weight individuals (Table 4a). The overall morbidity of obese patients in the laparoscopic group was not significant (OR 1.39, p = 0.163) compared to normal-weight individuals (Table 4a). When obese and overweight patients were compared to normal-weight patients, the open repair group still had a significantly higher risk of complications (OR 1.32, p = 0.014). When obese and overweight patients were compared to normal-weight patients in the laparoscopic group, there was not a significant increase in morbidity (OR 1.12, p = 0.553) (Table 4b).

Table 4 Odds ratios for morbidity between both open and laparoscopic procedures for A. Obese versus normal BMI and B. Obese/overweight versus normal BMI categories ages 18–65
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In the overweight population, there was a difference in surgical site infection in the open repair group. Deep incisional surgical site infections were more common in the overweight (BMI 25–30) open repair group when compared to the overweight laparoscopic group with p = 0.026 (Table 5).

Table 5 Thirty-day outcomes between open and laparoscopic procedure groups for overweight (25–29.9) BMI
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There were no differences in surgical site infection between the open and laparoscopic groups in obese patients. There were no statistically significant findings in the normal/underweight BMI category (BMI < 24.9) (Table 6).

Table 6 Thirty-day outcomes between open and laparoscopic procedure groups for normal/underweight (≤ 24.9) BMI
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Further breakdown and comparison of patients with a BMI > 30 into obesity classes did not reveal statistical significance between the open and laparoscopic repair groups (Table 7). Class I (BMI 30–<35) obesity demonstrated a morbidity of 1.2 % in the open group compared to 1.0 % in the laparoscopic group (p = 0.448) (Table 7). Class II (BMI 35–<40) obesity patients had a morbidity of 2.3 % in the open group and 1.45 % in the laparoscopic group (p = 0.298). Lastly, Class III (BMI > 40) patients had a morbidity of 4.01 % in the open group and 3.7 % in the laparoscopic group (p = 1.000).

Table 7 Morbidity for Class I, II, and III obesity categories
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When looking at the total charges for a procedure based on the ICD9 codes between 2008 and 2011, laparoscopic cases appeared to be more expensive than open ones even when considering 75 % of the laparoscopic cases had total charges less than $36,777 with a maximum of $498,912 (Table 8). The open repair group had 75 % of the cases with total charges less than $33,052 with a maximum of $1,056,303. The median was used to ensure that the minimum and maximum charges did not skew the results. The median cost for laparoscopic procedure was $25,376 and for open procedures was $21,156.

Table 8 Total charges based on Healthcare Cost and Utilization Project data
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The length of stay was also evaluated based on the ICD9 code for the procedure and demonstrated that 75 % of patients undergoing laparoscopic repair had a stay less than 2.5 days with a maximum stay of 36 days (Table 9). In the open repair group, 75 % of patients had a stay less than 2.8 days with a maximum of 138 days. No analysis could be performed to determine a correlation between total charges and length of stay with BMI given the data sets available.

Table 9 Length of stay based on procedure from the Healthcare Cost and Utilization Project
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When reviewing the operating room times, the results demonstrated comparable times between the open and laparoscopic cases. The median operating times demonstrated that the laparoscopic procedures were 3–5 min longer than an open repair; however, this finding is not statistically significant. The operating room time increased with increasing BMI regardless of procedure type (Fig. 1).

Fig. 1
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Operating room times for open versus laparoscopic procedures by BMI category

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Discussion

The demographics demonstrate that inguinal hernia predominated in the male population for both the open and laparoscopic groups. Risk factors for inguinal hernia development in males include heavy lifting for long periods of time, chronic cough, drinking, and COPD [7]. Risk factors for developing an inguinal hernia in women include family history, chronic cough, umbilical hernia, old age, and constipation [7]. The data demonstrates that the percentage of patients in each category with these risk factors were more prevalent in the open repair group than in the laparoscopic group.

A prospective Swedish study examined the extent to which lifestyle factors (smoking and obesity) affect outcomes after inguinal hernia surgery and found that smoking does increase the postoperative complication rate and obesity will increase hospital stay (p < 0.001) [8]. Their obese group had a trend toward an increase in postoperative complications with p = 0.07. The data demonstrated that deep incisional surgical site infection was statistically significant for the open procedure group when comparing the overweight BMI categories. Smoking is a known factor attributing to surgical site infection development by causing vasoconstriction and adversely affecting connective tissue metabolism [9]. The CDC has found correlations between low subcutaneous concentrations of O2 and impaired lysosomal function of the neutrophils with smoking leading to vasoconstriction and thereby decreasing tissue oxygen tension [10]. Diabetes was also more common among our patients in the open procedure group. The CDC research has found that the incidence of postoperative SSI increased by 30 % for every 40 % increase in blood glucose over 110 mg/dL and recommends less than 180 mg/dL for a maximal glucose target [10]. Although we do not have the data on glucose control of our patient populations, our findings of an increase in SSI may be explained by the demographics demonstrating a significantly greater proportion of smokers and diabetics in the open procedure group than in the laparoscopic group. In our study, when patients were risk-stratified, the open group still had significantly more complications than the laparoscopic group.

In our study, we found that complications of open inguinal hernia repairs were greater than that of laparoscopic hernia repairs in all patients. Common early complications of inguinal hernia repair include seroma/hematoma formation, urinary retention, bladder injury, and superficial SSI. Late complications include persistent groin pain and neuralgia, testicular complications, deep SSI, recurrence, and mesh migration/erosion. Although the majority of complications were not found to be statistically significant, when comparing the obese and normal-weight patients, the trend demonstrated a higher percent of complications in the open repair group than in the laparoscopic one (Table 2). In the obese category, 76 % of patients will experience morbidity if undergoing the open repair compared to 39 % in the laparoscopic group (Table 4a). The OR remains significant when comparing obese/overweight to normal-weight individuals (p = 0.014). In the open repair group, 32 % of obese/overweight patients will experience morbidity, while only 12 % will in the laparoscopic group (Table 4b).

When the obese category was further divided into classes of obesity, there was no significant difference in morbidity (Table 7). The Class III obesity category did have a high incidence of morbidity; however, it was independent of type of procedure. Although it was not found to be statistically significant, there was a trend of increasing morbidity with increasing BMI for both types of procedures with twice the risk in obesity Class II as compared to normal-weight individuals.

A study performed by the Medical Research Council (MRC) Laparoscopic Groin Hernia Trial group to determine the operating room time threshold at which the laparoscopic repair is equivalent in cost to open hernia repair found that the two procedures became cost equivalent once the duration of laparoscopic repair was at a mean of 34 min [11]. They discovered that the use of disposable laparoscopic equipment would almost double in cost when compared to an open repair. Their results were adjusted for factors that could increase costs to include the learning curve associated with minimally invasive surgery as well as return to ‘usual activities.’ Another study performed by Lawrence et al. also found significant cost difference between open and laparoscopic repair with the laparoscopic group being higher than open due to the variable costs of staff and overhead, resulting in differences in operating time [12]. We found that the operating room times remain shorter in the majority of patients undergoing an open repair, and although it is not statistically significant, they do appear to be slightly shorter in obese patients undergoing a laparoscopic repair. Return to the operating room was found to be greater in the open procedure group than in the laparoscopic group, regardless of BMI category.

There were no laparoscopic cases reported in the HCUP database from 2005 to 2007 due to herniorrhaphies not being identified by the international classification of diseases (ICD9) procedure codes in the VA system [13]. The VA system relied heavily on current procedural terminology (CPT) codes, and mapping between CPT and ICD9 codes were incomplete during that time. As such, we only estimated cost based on the results from 2008 to 2011. The analysis shows that the overall cost of an open repair is still less than that of a laparoscopic one even if the cost of the added length of stay is considered. The results demonstrate that the laparoscopic cases do have higher costs, however, not statistically significant when compared to the open repair. The costs were calculated based on procedure, and although the open repair cases had a higher median length of stay, the median cost remained lower than that for the laparoscopic procedure.

The limitations of our study are that it is a retrospective review and is therefore subject to bias. There is an assumption that all laparoscopic surgeons are equivalent when there is a known learning curve and possibly limiting its practice. There is also a bias that most operations will be done using open technique because of surgeon skill set and comfort level. Relative risk was not calculated for this study population as the odds ratio is likely to overestimate relative risk. With the use of Fisher’s exact test and Chi-square, the odds ratio provided a ratio of the odds of an event happening versus not happening in two populations with low incidence of 30-day outcomes. The demographics demonstrated statistically significant differences between the two groups (open/laparoscopic), and this is likely due to the large difference in population size between the two groups with open repair accounting for 72.2 % of the population. These differences in demographics are thought to be statistically significant, however, not necessarily clinically significant due to the overall small incidence of each preoperative factor. The length of stay for both procedures was longer than expected for a same-day surgery with incarcerated/strangulated hernias being part of the exclusion criteria. Although all p values were adjusted, neither the NSQIP or HCUP databases were able to provide information on complications relating to their hospital course, nor whether they may have been a result of a preoperative comorbidity.

Furthermore, during this analysis time period, open inguinal hernia repair remained the predominant procedure performed for unilateral initial repair, accounting for 72.2 % of the patient population. Laparoscopic repair is recommended in the case of recurrent and bilateral hernias to avoid a previously operated field and facilitate simultaneous repair of bilateral hernias [4], which is one possible reason for the fewer number of cases. Also, laparoscopic inguinal hernia repair can be technically more challenging with a greater learning curve, therefore possibly limiting its practice. If the number of laparoscopic cases were higher, we may have seen a bigger difference with in the BMI categories when comparing the procedure types.

Conclusion

Laparoscopic unilateral de novo inguinal hernia repairs have less morbidity than open ones regardless of the patient’s size. Moreover, there does not appear to be an increase in morbidity using the laparoscopic approach in obese patients, as there is in open repairs. One may also consider using a laparoscopic approach in overweight patients as there appears to be fewer deep SSI. The initial cost of a laparoscopic inguinal hernia repair is significantly more expensive than the cost of an open one even when the cost for additional length of stay is considered. The percentage of patients in each type of complication/morbidity is the incidence based on the population, and although we see a trend in the expected direction, we would not expect a significant change in the data analysis if there were more patients in the laparoscopic group.