Experimental effects on surrounding fibrous capsule formation from placing steroid in a silicone bag-gel prosthesis...

Soft-gel miniprostheses of silicone were implanted subcutaneously into 75 male rats. Groups of prostheses were preinjected with saline, a commercial form of triamcinolone acetonide, or a suspension of crystalline triamcinolone acetonide. The softness of the prosthesis mound later was measured objectively, and the capsules surrounding the implants were analyzed by histology, SEM, and chemistry, at various intervals up to 120 days after implantation. The control implants developed a normal laminar capsule. With an incidence increasing up to 100 percent at 120 days, the steroid-treated implants were surrounded by capsules lacking an inner membrane. The inner membrane of the laminar capsule had a high protein content (relative to normal tissue) and a relatively reduced collagen content, while the diffuse capsule resulting from the TA treatment had a high protein content and a high collagen content (about the same as normal tissue). No differences were found in the softness of the mounds of the implanted prostheses. The effect of the TA treatment was explained on the basis of its collagenolytic effect, which could gradually erode the normal capsule membrane. Capsule firmness could not be related to the architecture or the protein or collagen content in our findings. We hypothesize that normal capsule firmness may be related to the amount and kind of interconnection between the loose outer zone of connective tissue and the surrounding tissue.