Arthroscopic anatomy of the infrapatellar plica.

The infrapatellar plicae, ligamentum mucosum, were examined by arthroscopy in 200 knees. They were classified into five patterns according to the characteristics of the morphologic findings: separate type in 121 cases (60.5%), split type in 27 cases (13.5%), vertical septum type in 21 cases (10.5%), and fenestra type in 2 cases (1.0%). The remaining 29 cases (14.5%) did not have any infrapatellar plica, which were defined as absent type. Hence, the incidence of the infrapatellar plica was 85.5% of the 200 knees examined. There was no significant difference between right and left knees in the distribution pattern of the plica types. The incidence of the infrapatellar plicae decreased as the age increased. Both knees showed the same pattern in the 9 of 16 cases in which a bilateral comparison of the infrapatellar plicae was made.