In-vivo time-dependent articular cartilage contact behavior of the tibiofemoral joint.

OBJECTIVE The purpose of this study was to investigate the in-vivo time-dependent contact behavior of tibiofemoral cartilage of human subjects during the first 300 s after applying a constant full body weight loading and determine whether there are differences in cartilage contact responses between the medial and lateral compartments. DESIGN Six healthy knees were investigated in this study. Each knee joint was subjected to full body weight loading and the in-vivo positions of the knee were captured by two orthogonal fluoroscopes during the first 300 s after applying the load. Three-dimensional models of the knee were created from MR images and used to reproduce the in-vivo knee positions recorded by the fluoroscopes. The time-dependent contact behavior of the cartilage was represented using the peak cartilage contact deformation and the cartilage contact area as functions of time under the constant full body weight. RESULTS Both medial and lateral compartments showed a rapid increase in contact deformation and contact area during the first 20s of loading. After 50s of loading, the peak contact deformation values were 10.5+/-0.8% (medial) and 12.6+/-3.4% (lateral), and the contact areas were 223.9+/-14.8 mm(2) (medial) and 123.0+/-22.8 mm(2) (lateral). Thereafter, the peak cartilage contact deformation and contact area remained relatively constant. The respective changing rates of cartilage contact deformation were 1.4+/-0.9%/s (medial) and 3.1+/-2.5%/s (lateral); and of contact areas were 40.6+/-20.8 mm(2)/s (medial) and 24.0+/-11.4 mm(2)/s (lateral), at the first second of loading. Beyond 50 s, both changing rates approached zero. CONCLUSIONS The peak cartilage contact deformation increased rapidly within the first 20s of loading and remained relatively constant after approximately 50 s of loading. The time-dependent response of cartilage contact behavior under constant full body weight loading was significantly different in the medial and lateral tibiofemoral compartments, with greater peak cartilage contact deformation on the lateral side and greater contact area on the medial side. These data can provide insight into normal in-vivo cartilage function and provide guidelines for the improvement of ex-vivo cartilage experiments and the validation of computational models that simulate human knee joint contact.