Growth plate activity in the upper extremity.

Roentgenograms of 200 males and females were examined to determine the contribution of each growth center to the total length of the humerus, radius, and ulna. Subjects were healthy, middle-class Americans, mostly of northwest European descent. The nutrient foramen in the cortex provides the site of entry for the nutrient vessel and is a fixed point in the long bone. Growth occurring at each growth plate was measured in relation to the nutrient foramen. The proportion of growth from each upper extremity growth plate is not equal. Also, growth plate activity is not constant or average throughout the growth period. Growth occurs one or two years earlier in females than in males. Overall, approximately 80% of growth in the humerus occurs at the proximal growth plate. Before the age of two years, less than 75% of growth occurs at the proximal growth plate, increasing to 85% at the age of eight and remaining constant at 90% after the age of 11. For the ulna, approximately 85% of overall growth occurs at the distal growth plate, but by the age of five years, 90% of growth occurs distally. After the age of eight years, 95% of growth occurs at the distal growth plate. For the radius, approximately 80% of overall growth occurs distally. At the age of five years, the distal growth plate contributes 85% of total growth, increasing to 90% by the age of eight.