[Histological and immunohistochemical study of capsular contracture in an animal model--a comparison of two implants according to a modification of Wilflingseder's classification].

[BACKGROUND] The influence of silicone implants on the formation of a periprosthetic capsule can be well examined in animal studies. New implant materials have been developed to reduce capsular contracture. In order to evaluate the capsule formation, Wilflingseder et al. developed a histological score system. Because of new knowledge in the development of capsular contracture, the Wilflingseder classification is no longer appropriate. Current references are not considered so that a modification is required.

[MATERIAL AND METHOD] In a randomised, experimental animal study 31 mini-implants were implanted into the dorsum of female Wistar rats [17 smooth, 10 mL saline-filled silicone implants (Group A) and 14 titanium coated silicone implants (Group B)]. After 12 (group A/B12) or 36 (group A/B36) weeks, surgical removal of the implants with subsequent histomorphological and immunohistochemical examination of periprosthetic capsule formation was performed by 2 independent investigators in a double-blind manner.

[RESULTS] An analysis of the studies showed that the inner synovia metaplasia and the infiltration by inflammatory cells such as lymphocytes, histiocytes, plasma cells and granulocytes are of crucial importance in the development of a fibrotic capsule. The occurrence of these factors correlated significantly with each other and influenced also significantly the capsule architecture depending on implant surface. An adjustment of the existing Wilflingseder classification system was evaluated. The current rating system contains the following parameters: capsule thickness and cell layers of the capsule, the thickness of the inner synovial metaplasia, collagen structure, presence of histiocytes and the incidence of inflammatory cells. According to this classification, titanium-coated implants show an advantage in terms of the formation of capsular contracture.

[CONCLUSION] In 1974 Wilflingseder et al. developed a classification system for capsular contracture which is no longer appropriate, since current histological and immunohistochemical findings are not mentioned. Our study presents a new system which includes the latest insights into the development of capsular contracture and provides an objective classification of histological changes. Furthermore, we were able to show that titanium-coated implants are a promising approach in the reduction of capsular contracture.