ADVERSE-EFFECTS ON RABBIT ANTERIOR CRUCIATE LIGAMENT AFTER KNEE IMMOBILIZATION - CHANGES IN PERMEABILITY OF HORSERADISH-PEROXIDASE

Changes in the permeability of horseradih peroxidase (HRP) and the his tology of the rabbit anterior cruciate ligament (ACL) caused by knee i mmobilization were studied. The knees of adult rabbits were immobilize d for 2-8 weeks by a long leg cast with the knee flexed at 120 degrees , and some joints were allowed to be remobilized for 4 weeks after 6 o r 8 weeks' immobilization. After 1 mi of HRP was injected into the kne e joint and allowed to permeate into the ACL, the degree of permeation at the mid-portion of the ACL between femur and tibia was visualized with diaminobenzidine tetrahydrochloride. The ACL was examined histolo gically by light and transmission electron microscopy. Although the HR P permeated into almost the entire area of the transverse section of t he non-immobilized normal ACL, as the period of immobilization increas ed, the extent of permeation gradually decreased. The decrease was sig nificant from week 4 to week 6 and from week 6 to week 8. Degenerative change with necrosis of cells at the central area of the ACL was note d in the 6-week immobilization group, and the 8-week period of immobil ization increased the extent of this degeneration. Although the permea tion recovered in both the 6-week and 8-week immobilization groups 4 w eeks after remobilization, there were fewer cells with a normal morpho logy in the central area in the 8-week immobilization group than in th e control. These results suggest that long-term immobilization adverse ly affects the ACL.