Why is the adolescent joint particularly susceptible to osteochondral shear fracture?

A biomechanical investigation of the dynamic shear failure of the osteochon dral region of immature, adolescent, and mature bovine cartilage bone lamin ates was performed, The osteochondral junction was loaded in pure shear und er impact conditions through the cartilage layer only. The results indicate the adolescent tissue fails at a nominal shear stress of 2.0 MPa, whereas the immature and the mature tissues fail at 3.8 MPa and 2.6 MPa, respective ly, The adolescent tissue had a significant reduction in the fracture tough ness of its osteochondral junction compared with that of the immature or ma ture tissues. The fracture toughness, describing the energy required to ini tiate and propagate a crack to failure, was 3.6 kN/m, 2.3 kN/m, and 10.2 kN /m for the immature, adolescent, and mature bovine tissues, respectively. T his significant reduction associated with the adolescent osteochondral junc tion is explained in terms of the structural changes occurring within this important anchoring region during maturation. These findings question the w isdom of subjecting the adolescent joint to high levels and rates of loadin g.