The results of this study demonstrate that IGF-1 and TGF-beta1 can act in combination to regulate proliferation and differentiation of periosteal mesenchymal cells during chondrogenesis.
Stable fixation and a high rate of union of complex distal humeral fractures can be achieved when a principle-based surgical technique that maximizes fixation in the distal segments and stability at the supracondylar level is employed. The early stability achieved with this technique permits intensive rehabilitation to restore elbow motion.
Periosteum contains undifferentiated inesenchymal stem cells that possess the potential for chondrogenesis during cartilage repair and in fracture healing. With aging, the chondrogenic potential of periosteum declines significantly. An organ-culture model was used to investigate the relationship between the chondrogenic potential of periosteum and aging. A total of 736 periosteal explants from the proximal medial tibiae of 82 rabbits, aged 2 weeks to 2 years, were cultured in agarose suspension conditions conductive for chondrogenesis, and analyzed using histomorphometry, collagen typing, wet weight measurement, jH-thymidine and "S-sulfate uptake, autoradiography, and PCNA immunostaining. The rabbits were skeletally mature by 6 months and stopped increasing in weight by 12 months. Chondrogenesis declined significantly with age ( P < 0.0001) and was maximal in the 1.5-2 month-old rabbits, Explants from the 6 month-old rabbits formed 50% less cartilage, and by 12 months chondrogenesis reached a steady state minimal level. In parallel with this decrease in chondrogenic potential similar decreases were measured in 'H-thymidine uptake ( P < 0.0001 ). "S-sulfate uptake ( P = 0.01 17), as well as the thickness ( P < 0.0001) and the total number of cells in the cambium layer of the periosteum ( P < 0.0001 ). Autoradiography with 'H-thymidine and PCNA immunostaining confirmed the measured decrease in proliferative activity in the cambium layer where the chondrocyte precursors reside, although the percentage of proliferating cells did not change significantly with age. The most dramatic change was the marked decrease (87"h) in the thickness and total cell number in the cambium layer of the perisoteum between the 2 and 12 month-old rabbits ( P < 0.05). These data confirm a decline in the chondrogenic potential of periosteum with aging. Thus, one possibility for improving cartilage formation by periosteal transplantation after skeletal maturity would be to stimulate an increase in the total number of cells in the chondrocyte precursor pool early during chondrogenesis.
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