1. When a growing epiphysis is subjected to a stress, the rate or direction of the growth of that epiphysis or both are modified so as to yield to that stress.
2. Pressures applied in directions parallel to the direction of epiphyseal growth inhibit the rate of such growth. While considerable pressures are necessary to stop cartilaginous growth completely, slight or even intermittent pressures can slow or hinder it. The gravitational pressures of normal weight-bearing seem to slow cartilaginous growth in vertical weight-bearing bones; escape from normal weight-bearing stresses results in overgrowth.
3. Pressures applied in directions perpendicular to the direction of epiphyseal growth deflect the direction of such growth, resulting in lateral or spiral (torsional) displacement of the newly laid-down bone.
4. The ease with which angular or torsional deformities may be produced in a growing bone varies inversely with its diameter. The narrower the bone, the greater its "plasticity".