Effect of aging on tensile mechanical properties of the rabbit distal femoral growth plate

Tensile tests to failure were performed on the distal femoral growth plate of rabbits. The measured tensile forces, together with animal weight and dimensional measurements of the femur, were used to develop a noninvasive method of predicting growth failure loads and to examine the effects of age on the tensile strength of the growth plate. Growth plate failure load correlated with rabbit weight, (r = 0.93), femoral length, (r = 0.91), and contoured growth plate surface area, (r = 0.74). Regression analysis for these relationships allowed for failure load prediction if animal weight, femoral length, or growth plate surface area was known. Nominal stress (failure load/surface area) was calculated and correlated with animal weight (age) for each distal femoral growth plate utilizing two surface area estimating techniques: growth plate surface contour and growth plate cross-sectional enlargement. A strong association was found with either technique. The growth and maturation of growth plate cartilage is of major importance in pediatric orthopaedics. This study demonstrate that the age-dependent increases in tensile mechanical properties of the growth plate do not result merely from growth plate enlrgement or conformational changes. The changing tensile mechanical properties of the growth plate may explain why transphyseal distraction used clinically has produced varied and somewhat unpredictable results. Our study suggests that dose-response investigations are needed to define safe and optimal transphyseal distraction tensions before further clinical application is pursued.