The truss structure of cancellous bone. Morphological basis of the function of load transmission of the synovial joint.

The structure of cancellous bone of synovial joints was studied under the scanning electron microscope in 4 young cadavers. It was discovered that in all specimens, the cancellous bone beneath the whole coverage of the articular cartilage had a honeycomb pattern in appearance formed by many arched trabeculae running in different directions, and that the major orientation of the arched trabeculae was toward the articular surface. The arms of one arched trabecula extended in different directions, forming the tops of other arched trabeculae; the direction of the collagen fibers conformed circumferentially with that of the arch, but the collagen fibers at the intermediate part of the common arm of the adjacent arched trabeculae crossed in a woven pattern, passing from one trabecula to another. It enables the whole end of the articular bone to have the capacity of integral deformation. That is the foundation of the character of compliance which is essential to the contact of the articular surfaces changing from incongrouity to total congrouity during normal load transmission. This special type of construction is just like the truss structure in the architectural engineering, and therefore the authors suggest to name it the "Truss Structure" of the cancellous bone. The relationship between integral deformation and the following two factors, compliance and incongrouity of the articular surface provides an explanation that the truss structure of the cancellous bone is the morphological basis of high load-bearing capacity and character of compliance of the synovial joint.