Ultrastructure of solitary enchondromas.

Solitary enchondromas obtained from the small bones of the hand were studied with transmission electron microscopy. Three cell types were seen as follows: (1) young looking, active cells with extensive dilated rough endoplasmic reticulum and well defined Golgi and mitochondria; (2) older looking, degenerating cells with dilated rough endoplasmic reticulum, well defined Golgi, glycogen masses, vacuoles containing tropocollagen, lipid and myelin figures; and (3) dying cells showing loss of cell membrane and lysosomal-like bodies. A young chondroblastic cell may try to mature, become a normal chondrocyte that produces normal matrix but it does not succeed and dies. Enchondromal cells are not capable of forming tropocollagen or synthesizing proteoglycans for the matrix.

Operative treatment of the acutely ruptured lateral ligament of the ankle.

Twenty-seven patients with acute inversion injuries of the ankle were treated surgically during the past ten years. Instability indicative of rupture of the lateral collateral ligament was demonstrated by anteroposterior stress inversion roentgenograms. Ruptures of a component or components of this ligament were found at operation in every case. The ligament and capsule were repaired and the ankle was immobilized by a plaster of Paris cast for six to eight weeks. Of 26 patients available for follow-up examination, none complained of instability although nine had minor residual symptoms. Postoperative stability was demonstrated by roentgenograms in 13 patients. In the other 13, clinical examination showed that the ankles were stable on forcible inversion of the foot and ankle. Our results indicate that surgical repair offers the best prospect for successful treatment when definite passive instability can be demonstrated by properly performed stress inversion roentgenograms.

The ultrastructure and biomechanical significance of the tidemark of articular cartilage.

Thirty specimens of human articular cartilage obtained at surgery were examined by scanning electron microscopy to determine the ultrastructure of the tidemark, the junction of the non-calcified and calcified portions of mature articular cartilage. Three distinct variations of the collagen framework of the tidemark were observed: (1) A band of randomly oriented compacted fibrils that appeared to be continuous with those of the non-calcified and calcified zones. (2) A band of flattened fibrils paralleling the undulating surface of the calcified cartilage. (3) A band of perpendicularly oriented fibrils having a distinct continuous transition between the non-calcified and calcified zones, the amount of calcified material applied about the fibrils rapidly increasing as the fibrils entered the calcified zone. The tidemark may serve to provide a tethering mechanism for the relatively flexible and perpendicularly oriented collagen fibrils of the deepest portion of the non-calcified articular cartilage and may prevent them from being sheared at their point of anchorage to the calcified zone. The undulating pattern of the tidemark affords a strong geometric pattern in providing resistance to the shearing action of articulation. Small gaps present in the tidemark may provide pathways for the passage of nutrients into the deep non-calcified zone of articular cartilage from the subchondral bone.