Animal model for evaluation of soft tissue ingrowth into various types of porous coating

Results from several studies have suggested that soft tissue ingrowth into porous coating can serve as a biologic containment mechanism to prevent particulate debris migration by sealing off the effective joint space. Therefore, a rabbit animal model was developed to investigate soft tissue ingrowth into various types of metallic rods. After implantation of several types of coated and smooth rods within the thigh musculature of rabbits, a thick encapsulation of soft tissue was observed around porous-coated rods whereas a nonadherent pseudosynovial-lined cavity was observed around smooth rods. Within 3 weeks, soft tissue had grown into the three different types of porous coating on the rods. Histologic evaluation verified that maturation of this ingrowth tissue occurred by 12 weeks. Incomplete soft tissue ingrowth occurred into the depths of large-bead (590-840 mm) porous-coated surfaces. Soft tissue separation from the bead surfaces was observed at 12 weeks in the porous-coated implants that also had been coated with a thin layer of tricalcium phosphate. These findings suggest that soft tissue ingrowth can be expected to occur into the porous coatings tested, but that tricalcium phosphate should not be used as an additional surface coating to obtain long-term adherence of circumferential soft tissue ingrowth.