Prior to PS matching, comparison of matching variables between laparoscopic IPOM and open sublay cohorts revealed statistically significant differences in age (p = 0.013), BMI, defect size, risk factors (p < 0.001 each), and EHS classification (p = 0.003). For example, compared with their laparoscopic IPOM counterparts, patients in the open sublay group had a significantly older age (mean age lap. IPOM 63.2 ± 12.8 years vs. sublay 63.8 ± 12.7 years), but lower BMI (mean BMI lap. IPOM 29.7 ± 5.7 vs. sublay 29.0 ± 5.6). Furthermore, the open sublay cohort had a significantly lower proportion of small defects (W1 < 4 cm lap. IPOM 36.0% vs. sublay 23.6%), a higher proportion of medial (EHS medial lap. IPOM 72.8% vs. sublay 74.7%), but lower proportion of combined defect localizations as per the EHS classification (EHS combined lap. IPOM 9.93% vs. sublay 7.95%) and a higher proportion of patients with risk factors (risk factors lap. IPOM 40.0% vs. sublay 44.0%).
PS matching was applied to match the 4110 patients who had undergone laparoscopic IPOM with the 5797 patients operated on with the open sublay technique. PS matching was applied to match the laparoscopic IPOM cohort (n = 4110) with the open sublay cohort (n = 5797).
Matching with the open sublay population was successfully applied for n = 3965 (96.5%) of the laparoscopic IPOM patients (Fig. 2).
In this matched sample with regards to the laparoscopic IPOM approach, the most frequently employed meshes (≥ 2%) were Parietex composite (27.2%), DynaMesh IPOM (21.1%), Parietene composite (9.1%), Parietex composite optimized (7.7%), Symbotex composite (5.3%), and TiMesh (5.2%). With the open sublay technique, the most frequently used meshes (≥ 2%) were Ultrapro (33.0%), Parietene ProGrip (7.0%), Parietex ProGrip (6.5%), Optilene Elastic (5.1%), Parietene light (4.7%), DynaMesh CICAT (4.6%), Prolene (3.9%), and TiMesh (2.2%).
Mesh fixation in the laparoscopic IPOM group was performed with tacker only in 55.9%, with tacker and suture in 36.6%, with suture alone in 4.3%, and other techniques in 3.2%. In the sublay group for mesh fixation in 78.6% only sutures, in 13.7% self-fixation, in 3.5% glue, in 3.6% suture and glue, and 0.6% other techniques were used. Defect closure in the laparoscopic IPOM group is only documented in 24.1% of the cases.
Figure 3 illustrates the standard differences between matching variables, both before (original sample) and after matching. Notably, the standardized differences before matching were already relatively small, thus affirming that the discrepancies in baseline characteristics of the two cohorts were not extreme.
Figure 4 summarizes the results of matched pairs analysis for laparoscopic IPOM versus open sublay, with respect to the various outcome parameters. Comparing the two surgical techniques, no statistically significant, systematic deviation was noted for recurrences [lap. IPOM 4.2% vs. sublay 4.1%, OR 1.037, 95% CI (0.830–1.296); p = 0.783], pain at rest [lap. IPOM 8.9% vs. sublay 8.9%; OR 1.006, 95% CI (0.865–1.169); p = 0.970], pain on exertion [lap. IPOM 15.4% vs. sublay 15.1%; OR 1.017, 95% CI (0.907–1.140); p = 0.796], and pain requiring treatment [lap. IPOM 6.8% vs. sublay 7.0%; OR 0.971, 95% CI (0.818–1.153); p = 0.765] after 1-year follow-up.
However, a significant deviation was observed to the disadvantage of the open sublay operation regarding the rate of surgical postoperative complications [lap. IPOM 3.4% vs. sublay 10.5%; OR 0.323, 95% CI (0.264–0.393); p < 0.001] (Table 1), mainly surgical site infection, seroma and bleeding (Table 2), complication-related reoperations [lap. IPOM 1.5% vs. sublay 4.7%; OR 0.314, 95% CI (0.229–0.423); p < 0.001), and general postoperative complications [lap. IPOM 2.5% vs. sublay 3.7%; OR 0.683, 95% CI (0.523–0.888); p = 0.004]. The complication-related reoperation rate for postoperative bleeding only showed also a significant deviation to the disadvantage of sublay repair [lap. IPOM 0.45% vs. sublay 1.6%; OR 0.281, 95% CI (0.124–0.579); p = 0.001].
On the contrary, a significant deviation was found to the disadvantage of the laparoscopic IPOM technique concerning the rate of intraoperative complications [lap. IPOM 2.3% vs. sublay 1.3%; OR 1.840, 95% CI (1.290–2.651); p ≤ 0.001] (Table 1), mainly bleeding, bowel, and other organ injuries (Table 2).
Main hospital stay showed again advantages for laparoscopic IPOM compared to open sublay with 4.35 ± 3.32 days versus 6.14 ± 5.29 days (p < 0.001).
A subgroup analyses of 339 matched pairs with laparoscopic IPOM and open sublay repair of incisional hernias with defect size ≥ 10 cm was also performed. The only significant disadvantage of the open sublay repair was found to be the postoperative complication rate [lap. IPOM 5.0% vs. sublay 18%; OR 0.279, 95% CI (0.153–0.483); p < 0.001] and the complication-related reoperation rate [lap IPOM 2.1% vs. sublay 7.7%; OR 0.269, 95% CI (0.099–0.637); p = 0.001] (Table 3). No significant deviation in the recurrence rate to the disadvantage for laparoscopic IPOM was identified.
In comparison to the outcome of the total patient population, this subgroup with larger defect sizes demonstrates higher perioperative complication, chronic pain, and recurrence rates for both surgical techniques.