OBJECTIVE.After surgical resection or repair of a torn meniscus, the healed area may have areas of abnormal signal Intensity on MR images.

In vitro monolayer cultures of growth plate chondrocytes isolated from newborn calf costochondral junctions were subjected to capacitively coupled electrical fields for 48 h. In part A, the electrical signal was a 60-kHz sine wave applied at different voltages so as to produce electrical fields at the pericellular level of 7, 20, 50, and 126 mV/cm. Incorporations of [3H]thymidine and [35S]sulfate were assayed to determine the effect of the above fields on cells proliferation and matrix synthesis, respectively. Proliferation was increased by 47% in the 20 mV/cm field whereas the same field decreased [35S]sulfate incorporation by 21%. These changes were significant at p less than 0.05 in both instances. In part B, the 20 mV/cm field was applied in a pulsed fashion to produce daily duty cycles of 100, 25, 2, and 0.25%. Incorporation of [3H]thymidine, [35S]sulfate, and [14C]proline per DNA were assayed. Results indicated that the 100, 25, and 0.25% percent duty cycles showed significantly (p less than 0.01-0.05) increased proliferation, whereas the 0.25% signal (5 ms on/495 ms off for 6 h/day) significantly decreased [14C]proline incorporation. We conclude that the biologic response of cells in vitro is signal specific, and that the total amount of electrical energy required to stimulate the growth plate chondrocyte to increased proliferation is very small since the total time the 0.25% duty cycle signal was only 3.6 min of a 24-h period.

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Summary:Growth plate chondrocytes isolated from the proliferative and hypertrophic zones of bovine costochondral junctions were grown in vitro in the presence of various oxygen tensions ranging from 3 to 60%. Using [35S] sulfate as an index of glycosaminoglycan synthesis, incorporation was found to be maximal at 21% 0,. In contrast, proteoglycan aggregation under the same conditions was found to be maximal at 3% 0,. There were no consistent differences in response between cells from the different morphologic zones even though they are exposed to different oxygen tensions in situ. These results show that proteoglycan synthesis and aggregation in growth plate chondrocytes in vitro are differentially affected by the ambient oxygen environment. Key Words: Oxygen tension-Chondrocytes-Growth plateProteoglycan aggregation-Proteoglycan synthesis.Chondrocytes in the growth plate exhibit characteristic morphologic and metabolic changes as they mature through proliferative and hypertrophic stages. For example, proliferative chondrocytes in situ are relatively small and rapidly divide, whereas hypertrophic cells are at least five times larger (8) and do not divide (19,31). Moreover, chondrocytes in the two zones differ markedly in their cellular morphology and metabolism (3), and in the nature of their extracellular matrix (9,25,28,33). With respect to the latter, for example, a number of studies have shown that proteoglycan aggregation is less in the hypertrophic zone (HZ) as compared with the