Reply to “In vivo polypropylene mesh degradation is hardly a myth”

We appreciate the comments provided by Thompson et al. in their Letter to the Editor, regarding our study BThe myth: in vivo degradation of polypropylene-based meshes^ . However, we question the motives of the authors, who have notably disclosed that they provide medicolegal testimony on behalf of the plaintiffs in mesh litigation, for bringing their courtroom rhetoric into this discussion. Thompson et al. grossly erred in claiming that we only analyzed the exposed surface of the explants, and not the flaked material that had been removed when cleaning the explants (Bremoved material^) and ended up in the cleaning solution. As stated in our paper, however, the flaked material was analyzed using light microscopy (LM), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) microscopy before cleaning and after each of the five sequences of the overall cleaning process. Analyzing the cleaning solution would be redundant and therefore serve no purpose, i.e., the material on the surface was already analyzed and then ended up in the cleaning solution. Based on our chemical and microscopic analyses (LM, SEM, and FTIR), we concluded that the explanted Prolene meshes that we examined did not degrade or oxidize in vivo. Thompson et al. noted that that there are Bwell over 100 peer-reviewed articles, accepting or describing the degradation of PP [polypropylene] in variable conditions and degradation of other implantable polymers in the body .̂ They also claimed that they are not aware of any other peer-reviewed journal articles supporting the notion that PP does not degrade in the body. As stated in our paper, it is well documented that unstabilized PP oxidizes readily under ultraviolet (UV) light and upon exposure to high temperatures. However, as we also discuss and cite to in our paper, properly formulated PP is stable in oxidizing media, including elevated temperatures, in in vivo applications, and to a lesser extent, under UV light. Thompson et al. further claimed that our study Bdoes not explain the multiple features of PP degradation reported in the literature.^ This is an erroneous statement because they must have either failed to review or chose to ignore the discussion of the literature in our paper. For instance, the literature is replete with the chemistry of PP degradation, confirming simultaneous production of carbonyl groups and loss of molecular weight. It is well known chemistry that oxidative degradation of PP produces carbonyl groups and if there is no carbonyl group formation, there is no oxidative degradation. To further highlight this point, Clavé et al.  have often been cited as supporting the notion that PP degrades in vivo, and as discussed in our manuscript, their findings and statements in the study confirmed that they were unable to prove the existence of PP degradation from any of their various tests. They further failed to include that Liebert’s investigation reported explicitly that stabilized PP, such as Prolene, did not degrade. Thompson et al. also claimed that the degradation process for PP continues until no more PP can be oxidized, with the corresponding appearance of external surface features and hardening and shrinkage of the material. The fallacy of their statement, in the context of the explanted meshes that we examined, is highlighted by the clean fibers that retained their manufacturing extrusion lines and the lack of a wide range of crack morphology (e.g., varying crack depths into the core of the PP fibers) for a given explant and across explants from different patients with different implantation durations. This reply refers to the comment available at doi:10.1007/s00192-016-3233-z.