The Development of Goat Models to Evaluate the Effectiveness of Negative Pressure in Promoting Tissue Ingrowth into Porous Metal Implants

Abstract

The repair of large segmental bone defects is problematic with a high risk of infection, large amounts of soft tissue damage, and fracture stabilization difficulties. This preliminary study evaluates three large animal caprine models. These models will be used in future studies to examine the effects of negative pressure to induce bone and soft tissue growth into porous metal implants for the repair of large segmental defects. In Aim #1 bilateral surgery was performed on 6 goats, attaching one large porous titanium implant to the lateral side of each femur. One leg of each animal served as the control while the other side was treated with Negative Pressure Wound Therapy (NPWT) at either -125 mmHg or -200 mmHg. Tissue ingrowth for each negative pressure was examined at 6, 9, and 12 days. After gross examination, 6 of 6 animals showed improved tissue adhesion to the implant treated with NPWT when compared to the implant not treated with NPWT. Two pilot animals were added to the original protocol in order to explore the iliac crest as a better implant location for soft tissue study. The iliac crest was easier to access, maintain cleanliness of the surgical site, and maintain fixation over the greater trochanter and is recommended as the preferred location for future soft tissue studies. In Aim #2 unilateral surgeries were performed on 8 goats, replacing a 35 mm diaphyseal segment on the tibia with a porous titanium cylinder (20 mm diameter) and using orthogonal plates to provide rigid fixation. Four goats received no additional therapy and served as the controls while the other 4 goats received NPWT at -125 mmHg directly on the implant for 24-72 hours. Two goats from each group were sacrificed at 6 weeks and 12 weeks and examined qualitatively and iomechanically. Longer durations of therapy need to be examined to determine the effects of negative pressure therapy on bone growth.