The enhancement of periosteal chondrogenesis in organ culture by dynamic fluid pressure

Cartilage repair by autologous periosteal arthroplasty is enhanced by conti nuous passive motion (CPM) of the joint after transplantation of the perios teal graft. However, the mechanisms by which CPM stimulate chondrogenesis a re unknown. Based on the observation that an oscillating intra-synovial pre ssure fluctuation has been reported to occur during CPM (0.6-10 kPa), it wa s hypothesized that the oscillating pressure experienced. by the periosteal graft as a result of CPM has a beneficial effect on the chondrogenic respo nse of the graft. We have developed an in vitro model with which dynamic fl uid pressures (DFP) that mimic those during CPM can be applied to periostea l explants while they are cultured in agarose gel suspension. In this study periosteal explants were treated with or without DFP during suspension cul ture in agarose, which is conducive to chondrogenesis. Different DFP applic ation times (30 min, 4 h, 24 h/day) and pressure magnitudes (13, 103 kPa or stepwise 13 to 54 to 103 kPa) were compared for their effects on periostea l chondrogenesis. Low levels of DFP (13 kPa at 0.3 Hz) significantly enhanc ed chondro-genesis over controls (34 +/- 7% vs 14 +/- 5%; P < 0.05), while higher pressures (103 kPa at 0.3 Hz) completely inhibited chondrogenesis, a s determined from the percentage of tissue that was determined to be cartil age by histomorphometry. Application of low levels of DFP to periosteal exp lants also resulted in significantly increased concentrations of Collagen T ype II protein (43 +/- 8% vs 10 +/- 5%;P < 0.05). New proteoglycan synthesi s, as measured by S-35-sulphate uptake was increased by 30% in periosteal e xplants stimulated with DFP (350 +/- 50 DPM vs 250 +/- 75 DPM of S-35-sulph ate uptake/mug total protein), when compared to controls though this differ ence was not statistically significant. The DFP effect at low levels was do se-dependant for time of application as well, with 4 h/day stimulation caus ing significantly higher chondrogenesis than just 30 min/day (34 +/- 7 vs 1 2 +/- 4% cartilage; P < 0.05) and not significantly less than that obtained with 24 h/day of DFP (48 +/- 9% cartilage, P > 0.05). These observations m ay partially explain the beneficial effect on cartilage repair by CPM. They also validate an in vitro model permitting studies aimed at elucidating th e mechanisms of action of mechanical factors regulating chondrogenesis. The fact that these tissues were successfully cultured in a mechanical environ ment for six weeks makes it possible to study the actions of mechanical fac tors on the entire chondrogenic pathway, from induction to maturation. Fina lly, these data support the theoretical predictions regarding the role of h ydrostatic compression in fracture healing. (C) 2001 Orthopaedic Research S ociety. Published by Elsevier Science Ltd. All rights reserved.