Regression

Abstract

The basic radiological signs of König’s phase of regression are as follows. The bones forming the joint are very porotic. The uniform porosis, which in stages 1 and 2 is manifested as acute atrophy and in which the epiphyseal structure almost disappears, progresses in stage 3 into a picture characteristic of chronic atrophy. The spongy bone structure can be identified, although the bone trabeculae are considerably rarified and thickened and are situated as required by functional adaptation. The compact substance is thinner and the tubular bones are narrowed and hypoplastic along their entire length. With the destruction of the cartilage, the chondral space is narrowed, sometimes it is only virtual, but osseous ankylosis is rare. The narrowing of the articular space is morphologically different from that seen in the stage of panarthritis. While in the latter stage it is uneven and variable, in regression it becomes more uniform, as a result of restorative processes, indicating that the previously severely eroded subchondral bone contours have more or less regenerated, and a smooth, continuous contour has newly formed. In our opinion, it is very important and characteristic of this stage that the numerous subchondral cysts formed in the 2nd stage slowly disappear, giving place to a chronic atrophic structure. The intensive subchondral sclerosis also disappears. Pseudoosteophytes are not so prominent now because the eroded areas have been partly filled up. However, the coarse bone destruction cannot be entirely restored, thus, the epiphyses remain more or less deformed.