Early response of cartilage to abnormal factors as seen in the meniscus of the dog knee after cruciate ligament section.

Ultrastructural changes in the medial meniscus of the knee were studied following section of the anterior cruciate ligament in 7 dogs. As compared with the contralateral control knee, collagen fibrils became abnormally widely spaced and disoriented from 1 month after operation and amorphous material on the (femoral) articular surface increased in thickness. In superficial cells, granular endoplasmic reticulum and Golgi membranes were more profuse and lipid droplets increased in number from 1 week. Both superficial and deeper cells were very active at 1 and 2 months after operation and the nuclear fibrous lamina had increased in thickness. Some cell degeneration occurred in the superficial zone from 1 month. At 15 months both matrix and cells appeared to have returned to normal. These changes are compared with those in articular cartilage after cruciate ligament section and with the effects of intravenous papain on cartilage.