A biomechanical analysis of cervical and bony fixation methods for laparoscopic apical fixation in a porcine model 

The incidence of apical uterine prolapse increases with age. After conservative treatment options have been exhausted, surgical correction with the use of alloplastic material often follows. Laparoscopic apical mesh fixation is often performed, and different materials (tacks or sutures) can be used to fix the mesh material either to the vaginal apex (cervix) or sacral bone (promontory) for apical fixation.
The aim of this ex-vivo study was to compare the biomechanical properties for fixation of a synthetic mesh (PVDF, polyvinylidene-fluoride) to the fresh cadaver porcine cervix and sacral spines. Primary endpoints were biomechanical properties maximum load (N), displacement at failure (mm) and stiffness (N/mm). Mode of failure was evaluated as a secondary endpoint. 
In addition, autologous fascia (rectus fascia) of the pig was also examined in the same way.

The biomechanical ex-vivo testing was performed on porcine, non-embalmed, fresh and unfrozen cadaver uteri and sacral spines (Fig. 1). In a two-column material testing machine (Instron 5565®) a total of 28 trials were conducted in three groups on fresh porcine uteri. Each group evaluated the cervical mesh fixation with a different fixation device: Group 1 (n=10) evaluated three interrupted sutures, group 2 (n=10) three titanium tacks (ProTack), and group 3 (n=8) three absorbable tacks (AbsorbaTack) (Fig. 2). The mesh used for cervical fixation are composed of nonabsorbable, biostable polyvinylidene-fluoride (PVDF) monofilaments. 
Additionally, in a total of 30 trials of fresh cadaver sacral spines, the mesh was fixed with two single sutures (group 4), with three titanium tacks arranged in a row (group 5), with three titanium tacks arranged in a triangle (group 6) on the anterior longitudinal ligament.

Fascia interpositions from fresh, unfrozen pig cadavers were prepared to a length of 1.5 x 8 cm and suture-fixed to porcine cervices. The rectus fascia interpositions were examined in 4 groups: Group 1 (along the fiber direction, single), Group 2 (along the fiber direction, doubled), Group 3 (across the fiber direction, single), and Group 4 (across the fiber direction, doubled) (Fig. 3).

All trials were conducted until failure of the mesh, tissue or fixation device occurred. Primary endpoints were biomechanical properties maximum load (N), displacement at failure (mm) and stiffness (N/mm). Mode of failure was evaluated as a secondary endpoint.

Significant differences were found between all three groups of the cervical fixation methods in terms of maximum load: Group 1 (three single-button sutures) showed a maximum load of 64 ± 15 N, Group 2 (three titanium tacks) 41 ± 10 N and Group 3 (three absorbable tacks) reached a maximum load of 15 ± 8 N. The most common mode of failure for group 1 and 2 was a net tear or rip under 80-times of maximum load. In group 3, the limiting factor in all tests was a pull-out of the absorbable tacks. 
Regarding the sacral spines fixation, the maximum load for group 4 (two single sutures) was 65 ± 12 N, for group 5 (three titanium tacks arranged in a row) it was 25 ± 10 N and for group 6 (three titanium tacks arranged in a triangle) it was 38 ± 12 N. There was a significant difference between all three groups (4-6). The most common failure mode was a “mesh failure” in 9/10 trials for group 4-6.
All porcine rectus fascial interpositions (groups 1-4) withstood the physiological load of 10 N and showed a high resistance.

Cervical fixation of the PVDF-mesh with three single-button sutures is superior to fixation with three titanium tacks as well as absorbable tacks in terms of maximum load. The suture carries 1.5 times the load of titanium tacks and 4.2 times the load of absorbable tacks. All three fixation options can withstand the physiological load of 10 N, but absorbable tacks are the weakest cervical fixation methods. 
The PVDF-mesh fixation with two single sutures at the sacral spine endures 2.6 times more load than titanium tacks arranged in a row and 1.7 times more load than titanium tacks arranged in a triangle.
Regarding the porcine rectus fascia, it was noticeable that the doubled fascial interpositions were more resistant.

Single-button sutures are the significantly stronger and less expensive but could increase operating time (when fixating the mesh) by factor 9 compared to tacks. Possible risks of the tacks are not considered in this ex-vivo analysis. 
Due to the necessary abdominal access route, the rectus fascia may be an obvious option or alternative.

Ludwig S, Alina J, Fabinshy T, Dominik R, Axel S, Jens H, Kilian W, Claudia R, Leonidas K, Julia R, Nadja T, Christian E. Arch Gynecol Obstet. 2022 Nov 20.
Jansen AK, Ludwig S, Malter W, Sauerwald A, Hachenberg J, Pahmeyer C, et al. Tacks vs. sutures: a biomechanical analysis of sacral bony fixation methods for laparoscopic apical fixations in the porcine model. Archives of Gynecology and Obstetrics. 2021
Hachenberg J, Sauerwald A, Brunke H, Ludwig S, Scaal M, Prescher A, et al. Suturing methods in prolapse surgery: a biomechanical analysis. International Urogynecology Journal. 2021;32(6).