Biotribology of Osteochondral Grafts in the Knee

Osteochondral grafts as a regenerative early intervention therapy provide a solution for the repair of osteochondral defects and in the long-term may prevent the requirement for total knee replacement. The successful application of osteochondral grafts and novel regenerative solutions is heavily reliant on the biomechanical, tribological and biological properties of the constructs. In order to successfully deliver novel early intervention solutions, there is a requirement to develop robust and stratified preclinical test methods. The aims of the project were twofold; firstly, using simple geometry biomechanical and biotribological models, investigate the stability, friction and wear of osteochondral grafts post implantation in the knee. Secondly, develop a method for the preclinical, functional assessment of friction and wear following osteochondral implantation in a natural knee simulation model.
Initial biomechanical evaluation of osteochondral grafts indicated that the most significant factor determining graft stability post implantation was the ratio between graft and defect length and tissue species used. Porcine grafts and grafts implanted into defects longer than the graft length, were less inherently stable and subject to subsidence below congruency at lower loads. A simple geometry pin-on-plate reciprocating friction model was used to investigate the effects of osteochondral grafts on the tribology of the opposing articulating cartilage surface. Osteochondral grafts were compared with the native state (negative control), cartilage defects and stainless steel pins inserted both flush and proud of the cartilage surface (positive controls). The ability of osteochondral grafts to restore a congruent, low friction and wear articulation was evaluated. The simple geometry study demonstrated that osteochondral grafts have the potential to restore the articular surface without significantly disrupting the local tribology.
A whole joint natural knee simulator capable of reproducing the physiological conditions in the knee was used to develop a novel preclinical test method to evaluate the friction and wear properties of osteochondral grafts in a porcine knee model. In summary, increased wear levels did not correlate with significant increases in shear force; osteochondral grafts demonstrated the potential to restore a low friction and wear articulation with no significant differences to the native state. The development of the simulation model represents a significant step in the preclinical testing of osteochondral grafts and may be applied to test regenerative osteochondral interventions, disease models and aid in the development of stratified interventions.