Of the several methods available for producing an experimental arthritis, authors adopted a relatively simple and constant method for the production of an experimental azthritis by infra-articular injection of formaldehyde, and gave a detailed description for its sequential change of articular cartilage as observed by gross examination and by light microscopy. A total of 15 growing white rabbits, weighing 1.5-1.6 kg, were used.
This animal were divided into two main groups, one designated as a clontrol and the other as experimental group. Experimental group was subdivided into three groups to produce three form of arthritis simulating clinical forms of rheumatoid arthritis.
Both knees were selected for the site of injection.
Four rabbits received a single infra-articulaz injection of formaldehyde, while the other eight received 5 doses, halves at daily interval and the other halves at one week interval.
The rabbits observed clinically during the course of the experiment. They were sacrificed at I month after last infra-articular injection. The knee joints were then opened and examined grossly. The proximal end of tibia with the adjacent synovium of the infrapat~llar region was excised ex bloc and examined. Sections were stained with hematoxylin and eosin.
Those joints were normal in control group, but formaldehyde induced arthritic joint had mild to severe change of articular cartilage.
A single infra-azticular injection could cause arthritis transiently but minimum cartilage destruction by pann ~s invasion at periphery.
Five daily successive injection could cause most severe progressive form of arthritis which persisted over 6 months and caused most mazked cartilage destruction in entire area but 5 successive injection at 1 week interval could cause intermediate form of arthritis persisting about 2 months after-last injection. Cartilage destruction were moderate at periphery.
Authors do not, however, as yet have a complete explanation for the longer perpetuati6n of the arthritis in the 5 doeses of successive daily injection group.
Severity of the joint destruction including cartilage seems to be responsible for the severity. of initial insult. The diseased synovium itself could be responsible for the continued joint damage and it´s severity including cartilage, perhaps by the release of proteolytic enzymes and the perpetuation of a chronic inflammatory response. Also it is postulated that many of the late changes in the cartilage are simply the end result of the initial injury to synovium and articular cartilage by formaldehyde.
|