Congenital discoid medial semilunar cartilage.

Since the original description ofa dissecting-room specimen ofa congenital discoid lateral cartilage by Young of Glasgow in 1889, numerous publications have appeared on the subject. The stage has now been reached when it is recognised to be fairly common. Abnormalities of the medial cartilage on the other hand are rare. In this report three examples are described. Smillie (1948), in a contribution of twenty-nine cases of discoid lateral cartilage, reported the various lesions found in these abnormal structures and classified them as primitive, intermediate and infantile. In the primitive type the cartilage exists as a complete disc; the infantile approaches the normal but is abnormally broad. It is on the basis of this arbitrary classification that the literature is reviewed and discussed. The first reference to an anomalous medial cartilage is that of Watson-Jones (1930), who described a ring-shaped cartilage at a meeting ofthe Royal Society ofMedicine. The illustration however shows longitudinal striations on both central and peripheral parts of the “ ring,” which suggest that this specimen was probably a normal cartilage, the subject of a complete longitudinal (bucket-handle) tear with the central part displaced and altered by time and pressure. This view is supported by Elmslie’s comments at the meeting. The first record of an undisputed discoid medial cartilage is that of Cave and Staples (1941). Of the two specimens they described, one is undoubtedly discoid, with an anterior split and a notch such as is characteristic of lateral discs (Smillie 1948). This is an intermediate type of discoid cartilage. The other specimen was said to be “ incompletely discoid “ and to have a “ bucket-handle “ split. This is probably an example of the infantile type. Dwyer and Taylor (1945) reported a discoid medial cartilage which was virtually a complete disc and, without question, of the primitive type. This specimen demonstrated the characteristic “ horizontal cleavage “ as described by Smillie (1948), who reported a similar specimen encountered in 1943. This exhibited cystic degeneration in addition to horizontal cleavage, almost the entire under surface being worn away. Jeannopoulos (1950) reported the removal of discoid cartilages from the knee of a girl of ten, the medial in 1938 and the lateral in 1942. The medial cartilage was “ abnormally wide, pear-shaped “ and measured 5 centimetres by 2’7 centimetres by 08 centimetre. The upper surface showed a transverse ridge, the inferior was roughened and horizontal cleavage was present. This specimen, though not illustrated, was, from the description, probably infantile. A case of” ring-shaped medial semilunar cartilage” was published by Basmajian (1952). The specimen was similar to that of Watson-Jones (1930) and cannot be accepted as a discoid cartilage. In the opinion of Professor R. I. Harris, who saw the specimen, which had been removed from a dissecting-room male subject, it represents an old longitudinal tear with complete displacement of the medial fragment. De Palma (1954) described and illustrated a specimen which at the posterior horn was abnormally broad. The rest of the cartilage, however, was of normal dimensions and showed a longitudinal tear and a pedunculated tag. Though this specimen is unusual it is probably an example of the infantile type. CASE REPORTS Case 1-An engine driver aged forty-three complained of pain in his right knee. He gave a history of a twist of unknown direction, and one incident of instability subsequently. There was no history of locking, clicking or effusion. On examination the only abnormality to be found was a loud medial cartilage click in both knees. A precise diagnosis could not be