Biomechanical analysis of different osteosyntheses and the combination with bone substitute in tibial head depression fractures

Background Tibial head depression fractures demand a high level of fracture stabilization to prevent a secondary loss of reduction after surgery. Elderly individuals are at an increased risk of developing these fractures, and biomechanical investigations of the fractures are rare. Therefore, the aim of this study was to systematically analyze different types of osteosyntheses in combination with two commonly used bone substitutes. Methods Lateral tibial head depression fractures were created in synthetic bones. After reduction, the fractures were stabilized with eight different treatment options of osteosynthesis alone or in combination with a bone substitute. Two screws, 4 screws and a lateral buttress plate were investigated. As a bone substitute, two common clinically used calcium phosphate cements, Norian® Drillable and ChronOS™ Inject, were applied. Displacement of the articular fracture fragment (mm) during cyclic loading, stiffness (N/mm) and maximum load (N) in Load-to-Failure tests were measured. Results The three different osteosyntheses (Group 1: 2 screws, group 2: 4 screws, group 3: plate) alone revealed a significantly higher displacement compared to the control group (Group 7: ChronOS™ Inject only) (Group 1, 7 [p < 0.01]; group 2, 7 [p = 0.04]; group 3, 7 [p < 0.01]). However, the osteosyntheses in combination with bone substitute exhibited no differences in displacement compared to the control group. The buttress plate demonstrated a higher normalized maximum load than the 2 and 4 screw osteosynthesis. Comparing the two different bone substitutes to each other, ChronOS™ inject had a significantly higher stiffness and lower displacement than Norian® Drillable. Conclusions The highest biomechanical stability under maximal loading was provided by a buttress plate osteosynthesis. A bone substitute, such as the biomechanically favorable ChronOS™ Inject, is essential to reduce the displacement under lower loading

The Transcriptional Profile of Mesenchymal Stem Cell Populations in Primary Osteoporosis Is Distinct and Shows Overexpression of Osteogenic Inhibitors

Primary osteoporosis is an age-related disease characterized by an imbalance in bone homeostasis. While the resorptive aspect of the disease has been studied intensely, less is known about the anabolic part of the syndrome or presumptive deficiencies in bone regeneration. Multipotent mesenchymal stem cells (MSC) are the primary source of osteogenic regeneration. In the present study we aimed to unravel whether MSC biology is directly involved in the pathophysiology of the disease and therefore performed microarray analyses of hMSC of elderly patients (79-94 years old) suffering from osteoporosis (hMSC-OP). In comparison to age-matched controls we detected profound changes in the transcriptome in hMSC-OP, e.g. enhanced mRNA expression of known osteoporosis-associated genes (LRP5, RUNX2, COL1A1) and of genes involved in osteoclastogenesis (CSF1, PTH1R), but most notably of genes coding for inhibitors of WNT and BMP signaling, such as Sclerostin and MAB21L2. These candidate genes indicate intrinsic deficiencies in self-renewal and differentiation potential in osteoporotic stem cells. We also compared both hMSC-OP and non-osteoporotic hMSC-old of elderly donors to hMSC of similar to 30 years younger donors and found that the transcriptional changes acquired between the sixth and the ninth decade of life differed widely between osteoporotic and non-osteoporotic stem cells. In addition, we compared the osteoporotic transcriptome to long term-cultivated, senescent hMSC and detected some signs for pre-senescence in hMSC-OP. Our results suggest that in primary osteoporosis the transcriptomes of hMSC populations show distinct signatures and little overlap with non-osteoporotic aging, although we detected some hints for senescence-associated changes. While there are remarkable inter-individual variations as expected for polygenetic diseases, we could identify many susceptibility genes for osteoporosis known from genetic studies. We also found new candidates, e.g. MAB21L2, a novel repressor of BMP-induced transcription. Such transcriptional changes may reflect epigenetic changes, which are part of a specific osteoporosis-associated aging process

Functional clustering of differentially expressed genes of hMSC-OP, hMSC-old and hMSC-senescent when compared to hMSC-C.

<p>arrows pointing downward = at least 2fold reduced expression in comparison to hMSC-C; arrows pointing upward = at least 2fold enhanced expression in comparison to hMSC-C;</p>W<p> = gene associated with WNT signaling;</p>B<p> = gene associated with BMP signaling;</p>*<p> = probesets that refer to the gene are not identical in the indicated comparisons.</p

Human MSC populations used for microarray hybridization.

<p>hMSC-C = control hMSC; hMSC-OP = osteoporotic hMSC; hMSC-old = hMSC of non-osteoporotic, elderly donors; hMSC-senescent = long term-cultivated hMSC in the state of replicative senescence; standard deviations are indicated by ±; n = number; f = female; m = male; P = passage; Px = senescent passage.</p

Differentially expressed genes in hMSC-OP in comparison to hMSC-old with known association to BMD or fracture risk.

<p>FC = fold change; FDR = false discovery rate.</p

Differential gene expression of osteoporotic and aged hMSC.

<p>(A) Microarray comparison of hMSC-OP of elderly patients suffering from primary osteoporosis to age-matched control group hMSC-old. The numbers indicate the number of gene products with enhanced expression (red) and reduced expression (green) in hMSC-OP (for gene names see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045142#pone.0045142.s001" target="_blank">Table S1</a>). Black numbers mark expressed gene products without significant change in expression. (B) Quantitative PCR of relative change in gene expression of <i>SOST</i> (Sclerostin) and <i>MAB21L2</i> (Mab-21-like 2) in hMSC-old and osteoporotic hMSC-OP in comparison to hMSC-C. Complementary DNA of hMSC-OP of patients suffering from primary osteoporosis (n = 12, including 4 samples also used for microarray hybridization; age 84.2±6.3), hMSC-old from non-osteoporotic donors of advanced age (n = 13, including 4 samples also used for microarray hybridization; age 82.3±3.6) and hMSC-C of middle-aged, healthy donors (n = 11, including one sample also used for microarray hybridization; age 41.6±2.6) was used. Asterisks indicate significant differences as analyzed by Mann-Whitney U test (*p<0.05, **p<0.01, ***p<0.001). (C–D) Comparison of differential gene expression patterns of hMSC-OP, hMSC-old and hMSC-senescent when compared to hMSC-C of middle-aged, healthy donors by microarray analyses. The numbers indicate the number of gene products (GP) with significantly enhanced (C) or reduced (D) expression, respectively (for gene names see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045142#pone.0045142.s002" target="_blank">Table S2</a>).</p

Heat map of microarray results of osteoporotic and aged hMSC.

<p>Color-coded microarray hybridization signals (green to red = low to high signals) of hMSC-OP, hMSC-old and hMSC-senescent. The 998 gene products depicted showed at least 2fold differential gene expression (630 enhanced, 368 reduced; FDR<10%) in SAM comparison of hMSC-OP versus hMSC-C (for gene names see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045142#pone.0045142.s002" target="_blank">Table S2</a>).</p