A study in vivo of the effects of a static compressive load on the proximal tibial physis in rabbits
ABSTRACT The effect of compression on the physis is generally defined by the Hueter-Volkmann principle, in which decreased linear growth of the physis results from increased compression. This investigation examined whether mechanically induced compression of rabbit physes causes changes in gene expression, cells, and extracellular components that promote physeal resilience and strength (type-II collagen and aggrecan) and cartilage hypertrophy (type-X collagen and matrix metalloprotease-13).
Static compressive loads (10 N or 30 N) were applied for two or six weeks across one hind limb proximal tibial physis of thirteen-week-old female New Zealand White rabbits (n = 18). The contralateral hind limb in all rabbits underwent sham surgery with no load to serve as an internal control. Harvested physes were divided into portions for histological, immunohistochemical, and quantitative reverse transcription-polymerase chain reaction analysis. Gene expression was statistically analyzed by means of comparisons between loaded samples and unloaded shams with use of analysis of variance and a Tukey post hoc test.
Compared with unloaded shams, physes loaded at 10 N or 30 N for two weeks and at 10 N for six weeks showed histological changes in cells and matrices. Physes loaded at 30 N for six weeks were decreased in thickness and had structurally disorganized chondrocyte columns, a decreased extracellular matrix, and less intense type-II and X collagen immunohistochemical staining. Quantitative reverse transcription-polymerase chain reaction analysis of loaded samples compared with unloaded shams yielded a significantly (p ≤ 0.05) decreased gene expression of aggrecan and type-II and X collagen and no significant (p > 0.05) changes in the matrix metalloprotease-13 gene expression with increasing load.
Compressed rabbit physes generate biochemical changes in collagens, proteoglycan, and cellular and tissue matrix architecture. Changes potentially weaken overall physeal strength, consistent with the Hueter-Volkmann principle, and lend understanding of the causes of pathological conditions of the physis.
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ABSTRACT: The growth plate (physis) is responsible for long bone growth through endochondral ossification, a process which can be mechanically modulated. However, our understanding of the detailed mechanical behavior of physeal cartilage occurring in vivo is limited. In this study, we aimed to quantify the time-dependent deformational behavior of physeal cartilage in intact knees under physiologically realistic dynamic loading, and compare physeal cartilage deformation with articular cartilage deformation. A 4.7T MRI scanner continuously scanned a knee joint in the sagittal plane through the central load-bearing region of the medial compartment every 2.5min while a realistic cyclic loading was applied. A custom auto-segmentation program was developed to delineate complex physeal cartilage boundaries. Physeal volume changes at each time step were calculated. The new auto-segmentation was found to be reproducible with COV of the volume measurements being less than 0.5%. Time-constants of physeal cartilage consolidation (1.31±0.74min) and recovery (1.63±0.70min) were significantly smaller than the values (5.53±1.78/17.71±13.88min for consolidation/recovery) in articular cartilage (P<0.05). The rapid consolidation and recovery of physeal cartilage may due to a relatively free metaphyseal fluid boundary which would allow rapid fluid exchange with the adjacent cancellous bone. This may impair the generation of hydrostatic pressure in the cartilage matrix when the physis is under chronic compressive loading, and may be related to the premature ossification of the growth plate under such conditions. Research on the growth plate fluid exchange may provide a more comprehensive understanding of mechanisms and disorders of long bone growth.Journal of Biomechanics 04/2013; 46(9). DOI:10.1016/j.jbiomech.2013.03.026 · 2.75 Impact Factor
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ABSTRACT: Abstract Of more than 2 million segmental bone defects repaired annually with bone autografts and allografts, 15-40% fail. Improving healing rates may be approached with tissue engineering and use of periosteum overlying an allograft. The present study documents gene expression in human periosteum-allograft constructs compared to allografts alone. Strips of human cadaveric periosteum (26 years, f, distal femur) were sutured about sterilized human femoral cortical strut bone allograft (54 years, m) segments. After construct incubation (M199 supplemented medium) for 8 d, constructs and allografts alone were implanted in nude mice. At 10 and 20 weeks, constructs (N = 4, each group) and allografts (N = 2, each group) were retrieved and placed in RNAlater for quantitative PCR to determine expression of human- and murine-specific genes relevant to remodeling. Specimens were frozen-ground to powders and RNA was extracted, purified, reverse-transcribed, and amplified. Ribosomal protein (P0) was used to normalize sample quantities. Fold change plots were generated following statistical analyses comparing 20- to 10-week gene expression data. Allografts alone yielded no human-specific gene expression. Notable fold changes of human-specific alkaline phosphatase, bone sialoprotein, type I collagen, decorin, RANKL, RANK, cathepsin K, and osteocalcin in 20-week compared to 10-week specimens were found. Murine-specific expression of genes indicative of host mouse vascularization (RANK, type I collagen) was detected in both allograft alone and periosteum-allograft samples. Gene data confirm viable periosteum in constructs after 20 weeks. Relatively higher fold-change values of RANK, RANKL and cathepsin K indicate activities of osteoclast precursors, osteoclasts and osteoblasts involved in allograft remodeling during implantation. All additional genes of interest indicate osteoblast activity in new bone matrix formation. Gene data are directly correlated with previous and present histology work. The results of this study suggest that further investigations could help to establish whether autologous periosteum-allograft constructs could be used for the repair of bone defects.Connective Tissue Research 08/2014; 55(S1):146-149. DOI:10.3109/03008207.2014.923851 · 1.61 Impact Factor
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ABSTRACT: This in vivo study aimed at investigating the effects of dynamic compression on the growth plate. Rats (28 days old) were divided into three dynamically loaded groups, compared with two groups (control, sham). A device was implanted on the 6th and 8th caudal vertebrae for 15 days. Controls (n = 4) did not undergo surgery. Shams (n = 4) were operated but not loaded. Dynamic groups had sinusoidal compression with a mean value of 0.2 MPa: 1.0 Hz and ±0.06 MPa (group a, n = 4); 0.1 Hz and ±0.2 MPa (group b, n = 4); 1.0 Hz and ±0.14 MPa (group c, n = 3). Growth rates (µm/day) of dynamic groups (a) and (b) were lower than shams (p < 0.01). Growth plate heights, hypertrophic cell heights and proliferative cell counts per column did not change in dynamic (a) and (b) groups compared with shams (p > 0.01). Rats from dynamic group (c) had repeated inflammations damaging tissues; consequently, their analysis was unachievable. Increasing magnitude or frequency leads to growth reduction without histomorphometric changes. However, the combined augmentation of magnitude and frequency alter drastically growth plate integrity. Appropriate loading parameters could be leveraged for developing novel growth modulation implants to treat skeletal deformities. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.Journal of Orthopaedic Research 09/2014; 32(9). DOI:10.1002/jor.22664 · 2.99 Impact Factor