The experimental investigation of the effects of continuous compression of living articular cartilage was prompted by our clinical observation of joint degeneration associated with immobilization of a joint in a forced position. This observation was recognized as a problem, time explanation of which could not be found in a study of the relevant literature.
The hypothesis that was evolved, in an attempt to explain the problem, was that the joint degeneration under consideration could be explained on the basis of continuous compression of articular cartilage. As a test of the validity of this hypothesis, experiments were designed and conducted to study the effects of continuous compression of living articular cartilage in the monkey and in the rabbit. The compression was produced by a clamp in some animals and by simple immobilization of a joint in a forced position in others; 113 compressed joints were studied. No record could be found of any previous investigation of this aspect of articular cartilage. The results of the present experiments may be summarized as follows:
1. Lesions were observed in the compressed area of articular cartilage in all of the eighty-seven classifiable joints subjected to continuous compression for six days or longer. The lesions varied in extent from superficial necrosis to loss of the full thickness of articular cartilage.
2. The lesions produced by simple immobilization of a joint in a forced position were similar in nature to those produced by clamp compression.
3. The extent of the lesion varied directly with duration of continuous compression.
The articular lesion has been designated pressure necrosis of cartilage, and it has been concluded that it is the result of interference with the diffusion of nutritive fluid through the intercellular substance of the cartilage. Pressure necrosis of cartilage is probably an irreparable lesion and may interfere with growth of the epiphysis. It may also act as the starting point in the development of degenerative arthritis.
As a result of the present experiments a principle relating to articular cartilage has been formulated and may now be stated: Continuous compression of opposing joint surfaces, whether produced by a mechanical instrument, or by simple immobilization of the joint in a forced position, causes pressure necrosis of articular cartilage within six days. The similarity of articular cartilage in animals to articular cartilage in man and the observation of joint degeneration associated with immobilization of human joints in forced positions provide indirect evidence in support of the applicability of the principle to articular cartilage in man.
Clinically, the development of pressure necrosis of articular cartilage is difficult to detect because it is both painless and occult ; its prevention, therefore, is of considerable importance. Certain clinical situations in which we observed joint degeneration in association with immobilization of a joint in a forced position serve to relate the present investigation to clinical problems.
Finally, it is concluded that time principle formulated in this paper provides an explanation of the joint degeneration under consideration, and the suggestion is made that such joint degeneration might be prevented by avoiding immobilization of joints in forced positions.