THE INFLUENCE OF FLANGE COMPLIANCE AND MECHANICAL LOADING ON THE TISSUE-RESPONSE TO PERCUTANEOUS DEVICES

The failure of most percutaneous devices (PD) is caused by infection i nitiated by a lack of a tight seal at the skin-device interface. This interface can be disrupted by both extrinsic and intrinsic forces. Man y stress reduction methods have been proposed, the most common being t he application of a subcutaneous flange. It is widely believed that th e bending compliance of the flange plays a significant role in the suc cess or failure of a PD. A study was conducted to observe the effect o f flange compliance on local host response in both a functional and no nfunctional setting. Two PDs having flanges with different bending rig idities were implanted percutaneously in goats (n = 8). After a healin g period of 2 weeks, half of these devices were externally stimulated with a random load. All the implants were retrieved after 4 weeks and evaluated histologically. The tissue capsule was significantly thicker and the incidence of severe fibrosis and/or necrosis was higher at th e flange rim of the functional implants, irrespective of flange compli ance. The more compliant devices were encapsulated with a thick fibrou s capsule more frequently than the less compliant ones, irrespective o f functional status. The more compliant devices also had a greater inc idence of foreign body giant cells in the corner region and elicited s evere acute inflammation at the corner and top of the flange more freq uently than the less compliant implants. Numerous areas of degeneratin g foreign body giant cells accompanied with fibroblastic proliferation and dystrophic mineralization were identified in many -of the capsule s beneath the flanges. It was concluded that the rigid implants elicit ed a more desirable tissue response than the compliant implants while the functional implants elicited a less desirable response than the no nfunctional ones. There was no synergistic or antagonistic relationshi p between the functional status of the device and flange compliance.