INTERMITTENT COMPRESSION STIMULATES CARTILAGE MINERALIZATION

The effects of intermittent hydrostatic compressive force (ICF; 13 kPa applied at 0.3 Hz frequency), as a substitute for moderate loading in vivo, on ossifying bone organ cultures, were evaluated by means of (h isto)-morphometry. In earlier studies, biochemical tests have shown an increased Ca-45 intake and an increased alkaline phosphatase activity in bone organ cultures that received ICF, suggesting that ICF promote d matrix mineralization. The purpose of this study was to examine whet her an effect of ICF on mineralization can be described by means of hi stomorphometrical analysis, Fetal mouse metatarsal bone rudiments were cultured for 5 days in serum-free medium, with (experimental) or with out (control) ICF. Linear measurements taken during culture demonstrat ed that the dark zone in the center of the rudiment, representing mine ralized hypertrophic cartilage, became significantly longer in the gro up that received ICF when compared with the control group, This findin g was in conformation with the former studies, Histological sections o f the rudiments, stained with Goldner's trichrome method were used to study changes at the cellular level and to describe the position and r elative amount of mineralizing cartilage matrix (defined as Goldner-po sitive matrix [GPM]). Histomorphometry demonstrated that ICF treatment significantly increased the length of the hypertrophic cartilaginous zone and enhanced the amount of GPM between the mineralizing hypertrop hic chondrocytes, However, the total length of the zone containing GPM was not increased, nor was the future bone collar, consisting of a th in osteoid seam, lengthened by ICF, These data indicate that the cellu lar processes involved in chrondrocyte hypertrophy were accelerated by ICF, as well as the extracellular processes leading to matrix mineral ization, The study supports the earlier conclusion that embryonic bone rudiments are sensitive to mechanical stimulation and that moderate l oading promotes their ossification in vitro.