Despite the general belief that cartilage contact pressures are elevated near articular surface incongruities, there are no data which directly link the degree of geometric incongruity with the degree of pressure elevation. Nor are there data linking the degree of pressure elevation with the quality of defect repair. The governing hypothesis of our application is that the ability of hyaline cartilage to repair and/or avoid degeneration, due to local defect, progressively diminishes in accordance with the severity of elevations of contacts pressure (and/or pressure gradient) near the defect. To date, techniques have been lacking for measuring cartilage contact stresses at spatial resolutions appropriate for the high- gradient regions that often surround local incongruities. Recent success with digital image scanning of magnified Fuji-film recordings now makings such measurements feasible. After briefly expanding upon our preliminary studies to further document the reliability and precision of the new pressure mapping technique, we first propose (specific Aim 1) to perform in-vitro pressure mappings for three established human intra- articular fracture models (tibial plateau, acetabulum, and ankle). The objective of this part of the study is to show that despite substantial differences in the amount of geometric incongruity that can be tolerated clinically, these functions involve approximately equivalent local pressure elevations near their respective geometric tolerance limits. We also propose to study the influence of local pressure aberrations on the quality of cartilage repair, using a canine model with full-thickness circular defects in the femoral condyle. We will perform in-vitro pressure mapping studies (Aim 2) to determine the specific defect sizes necessary to achieve three specific levels of pressure elevation at the defect rim. We then will conduct a prospective in-vivo study (Aim 3), in which each of our three graded local pressure elevations is created in a group of eight dogs, all of which will be allowed to heal their defects over a ten-month period. The success of defect repair in these 24 dogs will be assessed by numerical histomorphic grading, supplemented by indentation testing.
