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    Ultrastructural analysis of the adaptation of articular cartilage to mechanical stimulation.

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    Ultrastructural analysis was conducted on samples of articular cartilage taken from both load-bearing and non-load-bearing areas with the aim of evaluating the morphologic adaptation of the articular cartilage to mechanical stimulation and identifying the mechanisms of interaction of the chondrocyte and the matrix. Through this analysis we were able to better define the adaptation process of the cartilage as well as the modalities of mechanical stress transmission. We believe that the complex formed by the chondrocyte, the pericellular matrix, and the pericellular capsule constitutes the biomechanical unit of the articular cartilage which serves as the sensor and transducer of mechanical stress. The arrangement of the collagen fibers and the proteoglycans which make up the pericellular capsule and membrane around the chondrocyte can be compared, from a mechanical standpoint, to a dynamic structure constructed in order to absorb the load stresses and protect the internal environment. From a biological standpoint, these are comparable to an extracellular-scaffold constructed with the aim of mediating the interaction between the chondrocyte and the territorial and inter-territorial compartments

    The effect of intra-articular ACL reconstruction on the growth plates of rabbits.

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    We performed intra-articular reconstruction of the anterior cruciate ligament (ACL) with the semitendinosus tendon placed in 2 mm diameter tunnels in 21 skeletally immature rabbits. The operation caused 11% damage to the physis of the femur on the frontal plane and 3% of its cross-sectional area but no alteration of growth or axial deviation of the bone resulted. In the tibia, the operation caused 12% damage to the physis in the frontal plane and 4% of the cross-sectional area. Two tibiae developed valgus deformities and one was shortened. Histological examination showed no areas of epiphysiodesis. There was no abnormality of growth-plate thickness in the two cases of tibia valga. Osseous metaplasia in the grafted tendons did not occur. The results suggest the need for careful evaluation of the percentage of damage to the growth plate before using intra-articular methods for reconstruction of the anterior cruciate ligament in adolescents. </jats:p
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