Mechanical integrity of subchondral bone in osteochondral autografts and allografts

To assess the influence of osteochondral graft preservation techniques on post-transplant biomechanics of graft and host subchondral bone in the knee joint.

An experimental animal model (sheep), specifically the weight-bearing articular surface of the medial femoral condyle of the knee joints.

Each sheep received, in the ipsilateral knee, an allograft that was (a) frozen without dimethyl sulfoxide (DMSO), (b) snap-frozen in liquid nitrogen or (c) frozen with DMSO. The contralateral knee received an autograft that was (a) snap-frozen, (b) treated with DMSO or (c) left untreated (fresh).

Mechanical and material properties of bone, including maximal compression stress, modulus of elasticity and bone cores (from the graft centre and surrounding host bone).

No significant differences were found in the mechanical properties of the subchondral bone under the graft, but there were significant changes in surrounding bone. Bone surrounding the grafts that were snap-frozen or frozen without DMSO was significantly stronger than the normal control bone. However, bone surrounding fresh autografts and cryoprotected allografts was not significantly different from normal control bone. CONCLUSIONS; The changes in the mechanical behaviour of the host bone may be associated with graft cell viability. The great stiffness of the subchondral host bone may have consequences for long-term graft integrity and for the development of degenerative osteoarthritis.