Implication of region-dependent material properties of articular cartilage in the contact mechanics of porcine knee joint

Abstract

Background

The site-specific tissue properties of knee cartilage may play an essential role in knee joint mechanical function, and mitigate joint injury and cartilage degeneration. The present study aimed to determine the significance of tissue inhomogeneity in knee joint contact mechanics using a porcine model.

Methods

Finite element models were developed for a porcine knee with intact and total meniscectomy conditions to simulate whole-joint compression-relaxation tests under a 1.2-mm ramp-compression at 0.01, 0.1, or 1 mm/s. Two reference benchmarks were introduced for the implementation of poromechanical material properties of fibril-reinforced cartilage: Benchmark II consisted of 17 sets of cartilage properties, each for a region in the knee, representing site-specific inhomogeneity averaged from cartilage indentation maps of 14 porcine knees. Benchmark I was comprised of a single set of properties by taking the average properties of 17 regions in Benchmark II, assuming tissue homogeneity. To validate the modeling method, the reference benchmarks were used to produce results against whole-joint compression test data.

Results

Both benchmarks were able to approximate experimental force-compression data obtained from the same knee with intact menisci and total meniscectomy, provided that the average properties from 14 knees were appropriately scaled to account for individual joint differences. Noticeable differences in stress and pressure distributions were observed between the benchmarks. For instance, benchmark I generated higher peak contact and fluid pressures in the medial tibial cartilage, but benchmark II produced the higher ones in the lateral tibial cartilage. The load sharing asymmetry between the lateral and medial compartments was reduced in benchmark II which was more pronounced for higher compression rates. On the other hand, benchmark II produced a more uniform stress distribution or lower maxima. Meniscectomy caused a slight shift of the contact centers in the tibial plateaus as compared to the intact joint.

Conclusion

The modeling results demonstrated substantial differences in loading distributions in the joint between the homogeneous and nonhomogeneous models represented by the two benchmarks, indicating the role of tissue inhomogeneity in the joint contact mechanics. Region-dependent tissue properties may need to be implemented in joint mechanical modeling to evaluate the site of cartilage prone to injury or degeneration.

Keywords

Finite element, Joint mechanics, Porcine knee cartilage, Poromechanical model, Stress relaxation & Site-specific inhomogeneity.