Histomorphometric Analysis of Callus Formation Stimulated by Axial Dynamisation in a Standardised Ovine Osteotomy Model.

The cyclic axial dynamisation of a stabilised fracture is intended to promote callus formation and bone healing. Most studies focused on biomechanical properties or the quantity of new bone formation. Far less is known about the quality of newly formed callus tissues, such as tissue distribution and arrangement within the callus. The aim of this current study was to investigate the effect of cyclic, axial dynamisation on the quantity and quality of callus in an established delayed fracture healing model. In 41 sheep transverse osteotomies with a gap size of 3 mm were stabilised with a unilateral external fixator. In 32 of these, fracture ends were axially stimulated with displacement amplitudes of 0.8 mm, 0.4 mm, 0.2 mm, or 0.0 mm, respectively, for six weeks. In the remaining 9 sheep of the control group, an additional external fixator was mounted to achieve almost total rigidity. Animal material originating from a past animal experiment was reanalysed in this study. Histological thin-ground sections were histomorphometrically analysed regarding the histological structure and composition of the defect region. A slight tendency towards an increase in size of total callus area, area of new bone (nB.Ar), and cartilage (Cg.Ar) was detected with increasing displacement amplitudes compared to the control group. At the anterior callus side nB.Ar and Cg.Ar were significantly larger than at the posterior side in all groups independent of treatment. Regarding the quality of callus, areas of very compact bone were predominant in the treatment groups whereas in the control group a slight shift to more porous bone was observed. No difference of callus compactness was observed between the anterior and the posterior side. The established method to assess the local compactness of callus areas is a useful tool to quantitatively determine the spatial distribution of new bone tissue within the callus. The application of this method in combination with biomechanical testing might reveal interesting relations between tissue distribution and bone strength that, with traditional histomorphometry, cannot be identified.

The incidence rate of colectomy for medically refractory ulcerative colitis has declined in parallel with increasing anti-TNF use: a time-trend study.

BACKGROUND: Medical therapy is standard treatment for ulcerative colitis with colectomy reserved for medically refractory disease or malignancy. The introductions of ciclosporin in 1994 and anti-TNF therapy in 2005 have extended medical management options. AIM: To determine whether the colectomy incidence rate for medically refractory ulcerative colitis has changed since the introduction of anti-TNF therapy. METHODS: Adult patients with a diagnosis of ulcerative colitis and who subsequently underwent an urgent or elective colectomy for medically refractory disease in Edmonton, Canada between 1 January 1998 and 31 December 2011 were identified. Log-linear regression was used to estimate the annual percent change in the total colectomy incidence rate (urgent and elective combined) and the urgent and elective incidence rates individually, before and after 2005, the year infliximab was approved for use in ulcerative colitis. Temporal trends of drug utilisation in this study population were also described. RESULTS: During 1998-2011, 481 patients with ulcerative colitis underwent a colectomy for medically refractory disease. There was negligible change in the total colectomy incidence rate from 1998 to 2005, with an annual percent change of 4.4% (95% confidence interval (CI): -1.12% to 10.16%). From 2005-2011, following the approval and increasing use of anti-TNF therapy, the total colectomy incidence rate decreased by 16.1% (95% CI: -21.32% to -10.54%) every year to 0.9 per 100 ulcerative colitis patients in 2011. CONCLUSION: The total incidence rate of colectomy for medically refractory ulcerative colitis has declined substantially since 2005, paralleling the increased use of anti-TNF therapy in this patient population.

Atrophy of the residual alveolar ridge following tooth loss in an historical population.

OBJECTIVES: To study the natural aetiopathology of jaw atrophy after tooth loss, unaltered by prosthetic procedures, an historical population without modern dental treatment was examined. METHODS: Based on the hypothesis that there are predictable changes in shape during jaw-atrophy, frequency and degree of atrophy as well as clinical aspects of bone quality and resorption were determined in the skeletal remains of 263 individuals. The potential association between age and frequency/severity of atrophy was analysed. RESULTS: Atrophy in at least one jaw segment was present in 45.2% of the analysed jaw specimens. The residual ridge underwent a series of changes in shape and height following the pattern of resorption described for modern populations. The severity of these alterations was associated with the age of the individual and the region within the jaw. Atrophy was frequently related to structural degradation of the covering cortical layer. CONCLUSIONS: These findings prove that atrophy of the jaw evidently does occur, displaying similar patterns of resorption in a population without modern prosthetics, where the negative effect of ill-fitting dentures is excluded. The basic information about alterations of shape and the cortical layer covering the residual crest might help to provide a deeper insight into aetiopathological mechanisms of this common oral disease.

Activation of G proteins mediates flow-induced prostaglandin E2 production in osteoblasts.

Interstitial fluid flow may play a role in load-induced bone remodeling. Previously, we have shown that fluid flow stimulates osteoblast production of cAMP inositol trisphosphate (IP3), and PGE2. Flow-induced increases in cAMP and IP3 were shown to be a result of PG production. Thus, PGE2 production appears to be an important component in fluid flow induced signal transduction. In the present study, we investigated the mechanism of flow-induced PGE2 synthesis. Flow-induced a 20-fold increase in PGE2 production in osteoblasts. Increases were also observed with ALF4-(10mM) (98-fold), an activator of guanidine nucleotide-binding proteins (G proteins), and calcium ionophore A23187 (2 microM) (100-fold) in stationary cells. We then investigated whether flow stimulation is mediated by G proteins and increases in intracellular calcium. Flow-induced PGE2 production was inhibited by the G protein inhibitors GDP beta S (100 microM) and pertussis toxin (1 microgram/ml) by 83% and 72%, respectively. Chelation of extracellular calcium by EGTA (2 mM) and intracellular calcium by quin-2/AM (30 microM) blocked flow stimulation by 87% and 67%, respectively. These results suggest that G proteins and calcium play an important role in mediating mechanochemical signal transduction in osteoblasts.

Functional reach in wheelchair users: the effects of trunk and lower extremity stabilization.

Our purpose was to compare the effects of using wheelchair trunk and lower extremity stabilization on sitting trunk mobility and functional reach of wheelchair users. Seven subjects with paraplegia who averaged 35.6 years of age and nine able-bodied control subjects with an average age of 26.0 years participated in this study. Each subject's functional reach in the transverse and sagittal planes was video-recorded in each of three conditions, randomized in order: (1) without a belt; (2) with a neoprene chest belt; and (3) with a webbing thigh belt. The area circumscribed by each subject's functional reach under each condition was processed using the Motion Analysis Expert Vision Flextrak program. Functional reach in each belting condition was compared within each subject and between able-bodied controls and subjects with high and low thoracic levels of paraplegia. This study showed that in the sagittal plane, subjects with both high and low thoracic levels of paraplegia were able to substantially increase the area of their functional reach when using a chest belt when compared with the thigh belt or no-belt condition. The mean area of their sagittal plane functional reach increased by over 50% by stabilizing the chest to the wheelchair using a neoprene belt. However, in the transverse plane, only those individuals with lower thoracic paraplegia (T8 to L1) gained substantial benefit from chest strapping, increasing the area of their functional reach by a mean of 24%. In contrast, able-bodied control subjects gained no benefit in functional reach from either belting condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C mediates flow-induced prostaglandin E2 production in osteoblasts.

Interstitial fluid flow generated by skeletal loading may be responsible for load-induced bone remodeling. Production of prostaglandin E2 (PGE2), a potent mediator of bone remodeling, is augmented in osteoblasts exposed to fluid flow. Exposure to fluid flow resulted in a slight initial increase in PGE2 production (1-2 hour), followed by a dramatic increase (2-8 hours). The initial phase of only slightly increased PGE2 production was dependent on substrate availability. H7, a protein kinase C inhibitor, strongly inhibited flow-induced prostaglandin E2 production at all time points examined without effecting production in stationary cultures. Blocking protein synthesis with cycloheximide resulted in a 56% reduction in long-term flow-induced PGE2 production. Thus, the later phase appeared to be the result of an increased number of enzymes as well as increased activity of existing enzymes or increased substrate availability. In conclusion, fluid flow increases PGE2 production in osteoblasts via a protein kinase C-dependent pathway involving de novo protein synthesis.

Fluid shear stress stimulates membrane phospholipid metabolism in cultured human endothelial cells.

There is evidence suggesting that fluid shear stress activates phospholipid turnover in endothelial cells, but it is not clear which phospholipids are involved in the transduction of the flow signal. Cultured human umbilical-vein endothelial cells were prelabeled with [14C]-arachidonic acid and subjected to laminar shear stresses of 0.4, 1.4 and 22 dyn/cm2 for times up to 30 min, after which the distribution of the radioactivity in the phospholipids was determined. We observed decreases in labeled phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid at 10-30 s, and increases in labeled diacylglycerol (DG) and free arachidonate, as well as a simultaneous elevation in inositol 1,4,5-triphosphate (IP3) levels. A second peak in IP3 levels was observed 10 min after the onset of shear. This is in contrast with agonist-stimulated endothelial cells, where IP3 levels go back to initial values within a few minutes after stimulation. The flow-induced IP3 response was the same in the presence or absence of ATP and serum in the perfusing medium. These results are consistent with the activation of phospholipase C, phospholipase A2 and DG lipase by shear stress. This suggests that several phospholipids are involved in the production of free arachidonic acid and DG, which are likely to be important mediators of the shear stress signal. In addition, flow may lead to a chronic stimulation of endothelial-cell metabolism.

Effect of flow on prostaglandin E2 and inositol trisphosphate levels in osteoblasts.

Osteoblasts in culture respond to mechanical strains. Fluid flow has been shown to increase intracellular adenosine 3',5'-cyclic monophosphate levels in cultured osteoblasts, and this response is mediated by prostaglandin synthesis. The signal transduction pathway of these cells exposed to fluid flow is still unknown. In the present study, we have demonstrated a 9- and 20-fold increase in the rate of prostaglandin E2 (PGE2) production in osteoblasts exposed to low (6 dyn/cm2) and high (24 dyn/cm2) steady shear, respectively. We further observed that fluid flow induced increases in the intracellular levels of inositol trisphosphate (IP3), another important second messenger. A shear stress of 24 dyn/cm2 increased IP3 levels dramatically for up to 2 h. Removal of flow resulted in a gradual return of IP3 to basal levels. The stimulation of IP3 levels was partially inhibited by 20 microM ibuprofen and 14 microM indomethacin, indicating that the IP3 response was partly dependent on flow-induced prostaglandin synthesis. The IP3 response was unaffected by daltroban, a specific thromboxane antagonist. These results show that fluid flow induced prostaglandin E2 production and increased intracellular levels of IP3 in osteoblasts. This suggests that flow may be the external signal produced by loading and that these messengers may be involved in the transduction of mechanical strain into a biochemical response.

Fluid shear stress as a mediator of osteoblast cyclic adenosine monophosphate production.

Effects of interstitial fluid flow on osteoblasts were investigated. Intracellular cyclic adenosine monophosphate (cAMP) levels were monitored in cultured osteoblasts subjected to shear rates ranging from 10 to 3,500 sec-1. Cyclic AMP levels were significantly increased at all shear rates from 1 pmole/mg protein to 10-16 pmole/mg protein. Osteoblasts subjected to a shear rate of 430 sec-1 for 0.5-15 minutes exhibited elevated levels (12-fold) of intracellular cAMP, which were sustained throughout the perfusion period. Osteoblasts were three times more sensitive to flow stimulation than human umbilical vein endothelial cells and baby hamster kidney fibroblasts, which also displayed higher cAMP levels (4-fold) after exposure to flow. To distinguish streaming potential effects from shear stress effects, viscosity was increased 5-fold by addition of neutral dextran to the perfusing medium. Shear stress is a function of viscosity, and streaming potentials are not for a given shear rate. The mechanism of this cellular response to flow was shown to be shear stress dependent. Inhibition of cyclooxygenase by 20 microM ibuprofen completely inhibited the flow-dependent cAMP response, indicating the cAMP response is mediated by prostaglandins. Our results suggest that fluid flow induced by mechanical stress may be an important mediator of bone remodeling.