Growth plate explants respond differently to in vitro static and dynamic loadings

Abstract

This study aimed at investigating the effects of static and dynamic compression applied on growth plate explants using matched compressive strains. Growth plate explants from 4-week-old swine ulnae were submitted to in vitro static (10% strain) or dynamic (oscillating between 7% and 13% at 0.1 Hz) unconfined compression for 48 h. The total growth plate height, the combined proliferative and hypertrophic thickness and the resulting ratio between these two thicknesses were evaluated. Standard immunohistochemistry was used to analyze the protein expression of key components of the extracellular matrix: aggrecan, type II collagen, type X collagen, and MMP13. In the statically loaded samples, the columnar organization of the cells was preserved but with slight columns deviation from the growth axis. Decreases in all histomorphological parameters were important and a notable loss of aggrecan, type II and type X collagens expressions was denoted. In the dynamically loaded samples, a severe loss of columnar arrangement was observed in the proliferative and hypertrophic zones. However, dynamic compressive loads preserved the proliferative and hypertrophic zones ratio and contributed to the synthesis of aggrecan and type II collagen in the extracellular matrix. The exact response of the growth plate to mechanical stresses along with optimal loading parameters could help improve the current treatment approaches or develop new treatment approaches for the underlying progressive musculoskeletal deformities. ß

BMP‐6 and BMPR‐1a are up‐regulated in the growth plate of the fractured tibia

“…This apparent “cross‐talk” between the two bones could be mediated by mechanical stress imposed as the contra‐lateral bone assumes a greater weight‐bearing role after fracture. The complex mechanism of mechanotransduction and the influence of mechanical forces on longitudinal bone growth has been subject of several investigations but has not been clarified yet 29, 47. Indeed one can assume that the concomitant enhanced expression of BMP‐6 and BMPR‐1a in the contra‐lateral bone on Day 29 could represent a natural means of limiting leg length discrepancies under natural circumstances when the non‐injured limb is immediately exposed to increased weight‐bearing stress, with associated survival advantage through preservation of mobility.…”

Investigation for Effects of Cyclical Dynamic Compression on Matrix Metabolite and Mechanical Properties of Chondrocytes Cultured in Alginate

“…and proteoglycan are main composition characteristic of cartilage extracellular matrix, which play an important role in the biomechanical function such as resistant to compression and deformation 11) . In this context, recent investigations of loaded physeal extracts from four-week swine ulnae showed losses by immunohistochemistry in Agg, Col-2 and Col-10 under static compressive loading 12) . In this study, chondrocytes were isolated from the rabbits knee articular cartilage and cultured in alginate under cyclical dynamic compression with pulses of 20 kPa at a frequency of 0.5 Hz.…”

Compressive mechanical modulation alters the viability of growth plate chondrocytes in vitro

“…Few in vivo and in vitro studies have previously investigated the effects of compressive static and dynamic modulation on bone growth rate, histomorphology, and protein expression . During mechanical modulation, growth plate chondrocytes undergo mechanical stimulation; they need to survive this mechanical stimulus in order to maintain their matrix integrity, which in turn will determine the resulting mechanical properties of the tissue.…”

“…Few in vivo and in vitro studies have previously investigated the effects of compressive static and dynamic modulation on bone growth rate, 1,3,10 histomorphology, 3,10 and protein expression. 1,11 During mechanical modulation, growth plate chondrocytes undergo mechanical stimulation; they need to survive this mechanical stimulus in order to maintain their matrix integrity, which in turn will determine the resulting mechanical properties of the tissue. Based on previous studies on articular cartilage, which is very similar to growth plate in terms of structure and biocomposition, chondrocytes viability in explants modulated in vitro was found dependent on the mode of loading (static or dynamic), 12 magnitude, 13,14 duration, 13,14 and zone, 13,14 but non-dependent on frequency.…”