ARTHROSCOPIC STUDIES OF VARIANTS OF THE ANTERIOR HORN OF THE MEDIAL MENISCUS

The objective of this study was to arthroscopically analyse the morpho logy and dynamics of variants of the anterior horn of the medial menis cus of the knee (VAMM) and to then consider the pathological significa nce of these variants. VAMM was defined as knees in which the anterior horn of the medial meniscus is not attached to the tibia. Between Apr il 1992 and March 1995, arthroscopy was performed on 953 knees of 903 patients. At the time of this examination, observation and probing wer e performed to determine the condition of the synovium, the synovial p lica, the cartilage in all compartments, the meniscus, the cruciate li gaments, and the popliteal tendon. In particular, detailed examination was made of the anterior horn of the medial meniscus with regard to t he point of insertion to the tibia and the degree of movement in knee flexion/extension. Cases of VAMM diagnosed on the basis of the arthros copic findings were classified into the following four categories: the ACL (anterior cruciate ligament) type, where the anterior horn of the medial meniscus was attached to the ACL; the transverse ligament type , where the anterior horn of the medial meniscus was attached to the t ransverse ligament; the coronary ligament type, where the anterior hor n of the medial meniscus was attached to the coronary ligament; and th e infrapatellar fold type, where the anterior horn of the medial menis cus was attached to the infrapatellar synovial fold. These patients we re then analyzed with regard to the arthroscopic findings and the intr a-articular lesions other than VAMM. In 98 (10.9%) of the total patien ts, 103 knees were classified as VAMM. Classification of those 103 kne es using the above criteria showed 39 ACL type knees, 51 transverse li gament type knees, 11 coronary ligament type knees, and 2 infrapatella r fold type knees. The arthroscopic findings indicated that the anteri or horn of the medial meniscus was not attached directly to the tibia in any of these knees. Probing and flexion/extension of the knee revea led hypermobility at the anterior horn of the medial meniscus. In this study, anterior knee pain syndrome was diagnosed in 12 (11.7%) of the 103 VAMM knees. In addition, there was no clear history of trauma in 20 of 23 knees found to have an isolated medial meniscus tear. In thes e cases, even detailed arthroscopic observation proved the causes of t he symptoms or injury. On the basis of these findings, we surmised tha t the anterior portion shows hypermobility at the time of flexion/exte nsion of the knee, regardless of the type of VAMM. In this study, we d iscussed the possibility that the existence of VAMM may become the cau se of pain or injury to the meniscus.