The periosteum in a long bone is apparently a thick layer of specialized dense connective tissue covering the entire bone surface, except for the articular cartilage and insertion site of the tendon or ligament.
In case of the ulna, its periosteum exists in the area between the bone and muscule tissue. It is composed of two or three parts. The cellular layer with its numerous cell components exists in contact with the bone aurface. This cellular layer has been generally regarded to have osteogenic capacity.
Most research indicates that the cellular layer is almost impossible to recognize upon reaching adulthood; therefore, the periosteum at this stage is considered to lack osteogenic capacity. However, the opposing view exists that the periosteum an adult maintains its osteogenic capacity, albeit accompanied by some time lag. To date, there are various opinions concerning the relationship between periosteal structure and its osteogenic capacity.
Research on the adult periosteal structure is especially insufficient, and many unanswered questions remain.
The present study was designed to obtain fundamental knowledge on structural differences of the periosteum in young and adult stages. We studied the ulnar periosteum of rabbits by light microscopy.
The results are summarized as follows:
The young periosteum can be divided into two parts: cellular and fibrous layers. The cellular layer with rich cell components was observed on the inner surface in contact with bone, indicating that this layer has osteogenic capacity. The fibrous layer, in contact with muscular tissue, consists of fibrous tissue containing few cells.
In the periosteum of adults, the existence of two layers cannot be discerned. The adult periosteum was devoid of a cellular layer rich in cells, and consisted mostly of fibrous tissue with a few spindle-shaped cells.
The thickness of the periosteum in young rabbits was nearly three times wider than that of adults.
Our observations agree with many previous reports and support then, except for a few minor differences. The adult periosteum therefore dose not have a cellular component and lacks osteogenic capacity or its is osteogenic potential is markedly inferior to that of the young periosteum.
However, it is interesting to observe structual changes of the adult periosteum induced by certain stimuli. The mechanisms of periosteal bone repair will be the subject of further studies.
