[Experimental study of chondromalacia patellae (author's transl)].

There are many theories concerning the etiology of chondromalacia patellae, as well as many points which have not been fully investigated yet. Using rabbits experimentally, shortening and elongation of the 3 mm patellar ligament were performed, producing the changes of contact surface and pressure on the patellar cartilage, and the patellar cartilage and the subchondral bone were studied sequentially. In the group of shortening, after the course of 16 weeks, no particular changes were recognized in the cartilage and the subchondral bone, compared with the control. In the group with elongation, 2-4 weeks after the operation, thinning of the trabecular and the subchondral bone, proliferation of blood vessels in the subchondral bone and their invasion into the calcified cartilage, were seen, without abnormality in the articular cartilage. After 4 weeks, irregularity or disappearance of the tide mark and degeneration of the ground substance toward the deep layer of the cartilage began to be recognized. After 8 weeks fasciculation was produced in the ground substance from the deep to the middle layers of the cartilage. After 12 weeks, degeneration extended to the superficial layer of the cartilage, producing blister formation, fibrillation and fissura, and finally proceeding to the desquamation of the superficial layer, degeneration and decrease in the thickness of the cartilage. These findings are similar to the histological findings of chondromalacia patellae, and seem to be different from those of arthrosis deformans in the bony changes. It is further suggested that decrease of contact surface and pressure on the cartilage can be considered to be one of the causes for chondromalacia patellae.