The regeneration. of´the injured articular cartilage has been a controversial subject among many authors. but ~it is generally agreed´ as to the basic concepts that the injuries of the hyaline cartilage heal with formation of eitber fibrous tissue, fibrocartilage or hyaline cartilage depending on the depth and size of rthe articular damage.
There have appeared in the literatures,~however. no detailed reports pertaining to the effects of irradiation on the repair of injured articular cartilages.
The author therefore has undertaken an experimental study in order to observe comparatively the histological changes occurring in the injured articular cartilages of the patella of rabbit following operative defects and x-irradiation.
Material and method:
Seventy five rabbits, weighing 500 to 800 gm. were evenly divided into 3(A. B, C) groups dependin~ on the depth of the injury created on the patella. s
A surgical defect was made on the articular cartilage of both patellas of each rabbit, parallel to the long axis of the bone and one half to three quarters in width of the cartilage surface. The depth of damage varied in each group as follows:
Group A: The defect was made through the entire layer of the cartilage exposing the subchondral bone.
Group B: The defect extended to the intermediate or radiate zone of cartilage.
Group C: The defect was created to the calcified zone of tbe cartilage and the subchondial
bone was not exposed.
Only the right knee of each rabbit was locally irradiated to 500 R(air), twice a week for 3 weeks at maximum from the day following operation. The technique of irradiation was as follows:at 100 I:VP, 10 mA, 0.5 millimeter copper filter, 25 centimeter target-skin distance, and delivery rate of 120 R. per minute. Five animals of each group were sacrificed 1. 2. 4. 8 and 12 weeks after the operative procedure and tben both patellas were removed, decalcified and stained with bematoxylin eosin for microscopic examination.
The summary of the histological findings is as follows:
a) In non-irradiated group:
1. In the new growing tissues formed at the site of the cartilage defect, it was possible to distinguish fibrous tissue, fibrocartj~ge and immature hyaline cartilage.
2. When the defect was extended deeply to expose subchondral bone, the granulation tissue first derived from the subchondral intertrabecular tissues .developed to the cellular fibrous tissues which in turn underwent metaplasia to form immature hyaline ca~lage.
3. In the superficial defect involving the intermediate or partial radiate zone of the articular cartilage, the new hyaline cartilage was formed by cellular proliferation from adjacent superficial zone of the cartilage or it was found to be directly filled from adjacent margins of the remaining cartilage. - - ,
4. When the defect was~made relatively deep leaving only calcified zone unaffected, no new tissue development was observed.
5. Growth of new tissues was most vigorous in the cases in which the defect extended to the subchondral bone.
6) In the irradiated group:
1. The new growing hyaline cartilage in the full thickness defect exposing the subchondral bone showed.no changes ifi quality but marked decrease in quantity. The attributable reason was that the intertrabecular tissues, to be parent body of the new tissue on the defect, were decreased in number secondary to irradiation.
2. The formation of new growing hyaline cartilage in the superficial defect involving the intermediate or partial iadiate zone was either meager or absent. This may be attributable to the fact that the remaining cartilage cells were damaged by irradiation in contradistinction to the nonirradiated group.
3. In the defect with only the calcified zone preserved, formation of new tissues was not obsertcd as in non-irradiated group. ~
4. The remaining articular cartilage cells were damaged after irradiation. After completion of irradiation, recovey began at 5 weeks, and completed by 9th wee]:.
5. The marrow cells were slightly decreased in number after exposure to 1000 R. and markedly diminished following 3000 R. of s-ray. Tl~c marrow cells increased from 5t}1 wee´_+ after irradiation E but fibrous tissues were abundantly laid down between intertrabecular spsces. The trabeculae ha~e become thickened following irradiation.
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