In seven knee joints of dogs, the internal semilunar cartilages were freed, to a varying extent, from their attachments to the synovial membrane and capsule peripherally. Within a few days, the dogs walked and ran about in a normal way; no locking of the joints was produced. After a period of time (two weeks to three and a half months), the animals were sacrificed and the joints were examined. In each case, the cartilage was firmly healed in normal anatomical position.
In thirteen joints, the semilunar cartilages were incised longitudinally. In each case the incision did not communicate with the synovial membrane and varied in its position in the cartilage. With one exception (Dog 14), the two fragments of the semilunar cartilages remained closely apposed although no postoperative fixation was used. In spite of this close apposition, there was not the slightest evidence of healing between the fragments during the period of observation (three weeks to two months).
In seven joints, the longitudinal incision was carried through the convex edge of the meniscus to the synovial membrane. In each case, the peripheral end of the incision healed by connective tissue arising from the synovial membrane and capsule. In one instance (Dog 3), the entire incision was filled with scar tissue.
When the semilunar cartilage was divided transversely (in six joints), the two fragments were separated a short distance. The free space thus produced was obliterated by an ingrowth of connective tissue from the synovial membrane, linking the two fragments firmly together. This connective tissue, which grossly resembled fibrocartilage, contained no cartilage cells.
Our experiments indicate that:
1. Tears which are limited to the semilunar cartilage probably never heal.
2. A torn meniscus can be healed by connective tissue if the tear communicates with the synovial membrane laterally.
3. A complete transverse or oblique tear results in some separation of the fragments, but the intervening space fills in with connective tissue arising from the synovial membrane. This connective tissue is quite firm in three weeks, which suggests the length of time necessary for complete fixation in these cases.
4. If the meniscus is partially torn from its peripheral attachment, it heals in normal anatomical position without difficulty.