To identify the change of mechanoreceptor of anterior cruciate ligament (ACL) in fixed knee and injured ACL.

Eighteen rabbits were divided into three groups as control, fixed knee, and injured ACL groups. Both knee of all fixed knee group were fixed with K-wire on the first day. The ligaments of the injured ACL group were cut at tibial attatchment site on the first day. Two rabbits of each group were sacrificed for the evaluation of mechanoreceptor at the 1st, 3rd, and 5th week. Histologic studies were performed by modified gold-chloride stain for the mechanoreceptors.

The types of mechanoreceptor in normal ACL were type I, type II, and type III. There was no difference in the appearance rate of each type. In the fixed knee group, the frequency of appearance decreased significantly at 5th week compared with that of the control group. In the injured ACL group, the frequency of appearance decreased at 1st week and showed no difference at 3rd week in comparison with 1st week, and zero at 5th week. In morphology the degree of degradation of mechanoreceptor increased with time in both experimental group, and showed more severe in the injured ACL group than in the fixed knee group. Most of all mechanoreceptors were located in the subsynovial region, and degraded with synovial degeneration and synovial inflammation.

Mechanoreceptors were changed with the change of intra-articular condition and ligament itself. Therefore the duration of immobilization shoud be shortened if possible and the torn ACL should be repaired anatomically, if indicated, as soon as possible to preserve the mechanoreceptors.