Failure Mode of Depressive Osteochondral Fracture under Maximum Compressive Load: Studies of Normal, Osteoporotic, and Osteosclerotic Subchondral Bones

Abstract

Objective : To determine the failure mode of depressive osteochondral fracture under the maximum compressive load.
Design : An experimental cadaveric study. A compressive load was applied through an indenter on a femoral condyle to create a depressive osteochondral fracture until the maximum load was reached.
Background : Most depressive osteochondral fractures occur without a gross articular cartilage injury because a large amount of load is reabsorbed by the surrounding tissues, especially the subchondral bone under the cartilage. We asked what the mode of depressive osteochondral fracture is. It might function as a load adsorber from the articular cartilage.
Methods : Three groups of depressive osteochondral fractures were studied. Croup 1 consisted of 12 pieces of middle third of normal median and lateral femoral condyles. Groups 2 and 3 consisted of 12 pieces of osteoporotic and osteosclerotic middle of both femoral condyles. Using a universal testing machine, a depressive osteochondral fracture was created by applying a uniaxial compressive load through an indenter until the load rose to the maximum level. At that point, the load applied was stopped in order to minimize the extent of subchondral trabeculae fracture. Maximum load was recorded. Pressure and stiffness were calculated. The pattern of depressive fracture was studied histologically.
Results : The failure mode of depressive osteochondral fracture wan such that the bone under the articular cartilage had a subchondral plate fracture, an interlacing of bone trabeculae under the plate, and a few fractures of the bone trabeculae. The interlacing of subchondral bone trabeculae was most evident in the normal bone as compared with the osteoporotic and osteosclerotic bones. The osteosclerotic bone failed at the highest load, while the osteoporotic bone failed at the lowest.
Conclusion : The subchondral plate fracture and the interlacing of subchondral bone trabeculae under the plate are the characteristics of the failure mode of depressive ostechondral fracture. This failure mode occurs before there is a discernible fracture of the subchondral bone trabeculae. The amount of load causing fracture depends on the quality of the bone.
Relevance : The failure mode, especially the interlacing of subchondral bone trabeculae, night function as a load absorber from the articular cartilage. Therefore, the quality of subchondral bone is important for protection of the articular cartilage from compressive load injury.