Fyi. Lee et al., Micromechanical properties of epiphyseal trabecular bone and primary spongiosa around the physis: An in situ nanoindentation study, J PED ORTH, 18(5), 1998, pp. 582-585
The elastic modulus and hardness of the mineralized bone around the growth
plate was measured to determine its regional micromechanical properties. Mu
ltiple nanoindentation tests, >10 sessions, with depths ranging from 100 to
1,000 nm at loading rates of 12.5 and 750 mu N/s, were performed on the tr
abecular bone in the epiphysis, trabecular bone at the junction of the phys
is and epiphysis, primary spongiosa in the metaphysis, and surrounding cort
ical bone of the distal femur of 300-gm Sprague-Dawley rats. The indentatio
n load-displacement data obtained in these tests were analyzed to determine
the elastic modulus and hardness of the tissues. The nanoindentation resul
ts highlighted the regional variations in the material properties of the mi
neralized tissues around the growth plate. The primary spongiosa had a lowe
r elastic modulus and hardness than both epiphyseal trabecular and cortical
bone (p < 0.01). A relatively well-defined thick trabecular band at the ph
yseal-epiphyseal junction had modulus and hardness values comparable to tho
se of cortical bone (p > 0.05). These findings support the hypothesis that
the primary spongiosa has micromechanical properties that are significantly
lower than the epiphyseal trabecular bone. On this basis, it is speculated
that the fracture patterns commonly seen in patients with physeal injuries
are influenced by the micromechanical properties of these tissues, as well
as by the nature and direction of the applied force.