Wounds or defects in articular cartilage are repaired by fibrous or
osseous tissue derived from the subjacent cancellous spaces.
_Transplantation of Bone--Bone-grafting._--Clinical experience is
conclusive that a portion of bone which has been completely detached
from its surroundings--for example, a trephine circle, or a flap of bone
detached with the saw, or the loose fragments in a compound
fracture--may become, if replaced in position, firmly and permanently
incorporated with the surrounding bone. Embedded foreign bodies, on the
other hand, such as ivory pegs or decalcified bone, exhibit, on removal
after a sufficient interval, evidence of having been eroded, in the
shape of worm-eaten depressions and perforations, and do not become
united or fused to the surrounding bone. It follows from this that the
implanting of living bone is to be preferred to the implanting of dead
bone or of foreign material. We believe that transplanted living bone
when placed under favourable conditions survives and becomes
incorporated with the bone with which it is in contact, and does not
merely act as a scaffolding. We believe also that the retention of the
periosteum on the graft is not essential, but, by favouring the
establishment of vascular connections, it contributes to the survival of
the graft and the success of the transplantation. Macewen maintains that
bone grafts "take" better if broken up into small fragments; we regard
this as unnecessary. Bone grafts yield better functional results when
they are immovably fixed to the adjacent bone by suture, pegs, or
plates. As in all grafting procedures, asepsis is essential.
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