40. Understanding Periprosthetic Capsule Pathology in Pre-pectoral Versus Sub-pectoral Implant-based Breast Reconstruction: Development of a Rat Model

Abstract

PURPOSE: Clinical practices in implant-based breast reconstruction continue to evolve with ongoing innovation in both the surgical approach and implant design. Development of standardized models is increasingly important to evaluate the effect of these changes in the outcomes of implant-based reconstruction. In this study, we designed a physiological rat breast implant model to assess the effects of pre-pectoral and sub-pectoral implant placement on breast implant capsule formation. METHODS: Miniature silicone implants measuring 2cc in diameter were optimized for placement in the pre-pectoral and sub-pectoral planes bilaterally in Lewis rats for an internally controlled model. A submammary approach was simulated in rats by making skin incisions at the inferior aspect of the pectoralis muscle bilaterally. For sub-pectoral implant placement the lateral edge of the pectoralis muscle was elevated, a sub-pectoral plane was established with blunt dissection, and a sterile implant was secured in the sub-pectoral plane with complete pectoralis coverage. For pre-pectoral implant placement, blunt dissection was used on the contralateral side to establish a subcutaneous plane. A sterile implant was secured in this subcutaneous pocket. Samples were harvested at 12 weeks and histological analysis of capsule formation was performed with H&E and Trichrome staining. RESULTS: The rats showed immediate signs of bilateral forelimb use with walking and grasp following recovery from anesthesia. The surgical sites healed well over two-week follow-up with no signs of wound-site mutilation, discomfort, or dehiscence. Histological analysis demonstrated both pre-pectoral and sub-pectoral capsule formation compared to sham surgery samples. Prepectoral implant capsules showed lamellar collagen architecture whereas subpectoral implant capsules demonstrated increased thickness, hypercellularity and synovial metaplasia. CONCLUSIONS: This model demonstrates that a physiological approach with pre-pectoral and sub-pectoral implant placement to model breast implant reconstruction is feasible in rats and thus improves upon previous models that utilize dorsal subcutaneous pockets instead of pectoral planes. These earlier approaches do not replicate the anatomy and mechanics of the clinical prepectoral and subpectoral space. Additionally, this model demonstrates differences in the periprosthetic fibrotic processes in pre-pectoral and sub-pectoral approaches for implant placement. This model facilitates further mechanistic understanding of the physiology and pathology associated with breast implant reconstruction including outcomes such as capsular contracture and BIA-ALCL and will provide a valuable platform to test treatments and strategies that may mitigate them.