Capsule contracture in animals can be characterized by gross deformation of prostheses and surrounding tissue

Gel-filled miniprostheses were implanted in rats, recovered, and reimplanted in fresh animals. Experimental contracture characterized by severe, visually detectable distortion of hemispherical prosthesis mounds into pointed ovoid structures oriented laterally was observed. This finding confirms the existence in rats of a phenomenon similar in appearance to clinical contracture in humans. The incidence of contracture was higher than in the first implantation of these prostheses, which suggests that some property of the prosthesis is critical in the occurrence of contracture, and that this property can be altered by prolonged implantation in the tissue so that contracture is more likely. Implants that were overfilled by injection of extra fluid into the gel showed no contracture, but capsules around these implants did not differ from contracted capsules in protein, collagen, glycosaminoglycan composition, weight, thickness, histological appearance, or incidence of myofibroblasts.