Controlled, sinusoidally varying loading has been applied to the metacarpal bone in young adult sheep at a frequency of 24. cycles/min for two 1-hour periods per day for 28 days. The loading was applied through two Steinmann pins inserted in the metaphyses. After allowing for the bone reaction to surgery, several changes occurred in the mid-diaphysis:
- Peak compressive stresses in the range 2-8MPa caused new bone to be deposited on the periosteal surface, the amount being roughly proportional to the applied stress, with a maximum area increase of approximately 8%.
- The application of unidirectional bending moments, (with stresses up to 40 MPa) promoted significantly smaller amounts of periosteal proliferation than compressive loads.
- Osteonal remodelling activity in compressively loaded bones was significantly greater than in the contralateral controls, but no difference occurred with bending loads.
- Bone resorption, presumably the first stage in the apposition process, occurred on the periosteal surface of loaded bones. The average resorption for all test bones was of the order of 1.5 2.5% of the bone cross-sectional area.
The response of a bone to conditions of increased loading thus depends on the type of loading as well as its magnitude.