Mechanical stimulation of bone induces new bone formation in vivo and increases the metabolic activity and gene expression of osteoblasts in culture. We investigated the role of the actin cytoskeleton and actin-membrane interactions in the transmission of mechanical signals leading to altered gene expression in cultured MC3T3-E1 osteoblasts. Application of fluid shear to osteoblasts caused reorganization of actin filaments into contractile stress fibers and involved recruitment of β1-integrins and α-actinin to focal adhesions. Fluid shear also increased expression of two proteins linked to mechanotransduction in vivo, cyclooxygenase-2 (COX-2) and the early response gene product c-fos. Inhibition of actin stress fiber development by treatment of cells with cytochalasin D, by expression of a dominant negative form of the small GTPase Rho, or by microinjection into cells of a proteolytic fragment of α-actinin that inhibits α-actinin-mediated anchoring of actin filaments to integrins at the plasma membrane each blocked fluid-shear-induced gene expression in osteoblasts. We conclude that fluid shear-induced mechanical signaling in osteoblasts leads to increased expression of COX-2 and c-Fos through a mechanism that involves reorganization of the actin cytoskeleton. Thus Rho-mediated stress fiber formation and the α-actinin-dependent anchorage of stress fibers to integrins in focal adhesions may promote fluid shear-induced metabolic changes in bone cells.

Mechanical force applied to bone produces two localized mechanical signals on the cell: deformation of the extracellular matrix (substrate strain) and extracellular fluid flow. To study the effects of these stimuli on osteoblasts, MC3T3-E1 cells were grown on type I collagen-coated plastic plates and subjected to four-point bending. This technique produces uniform levels of physiological strain and fluid forces on the cells. Each of these parameters can be varied independently. Osteopontin (OPN) mRNA expression was used to assess the anabolic response of MC3T3-E1 cells. When fluid forces were low, neither strain magnitude nor strain rate was correlated with OPN expression. However, higher-magnitude fluid forces significantly increased OPN message levels independently of the strain magnitude or rate. These data indicate that fluid forces, and not mechanical stretch, influence OPN expression in osteoblasts and suggest that fluid forces induced by extracellular fluid flow within the bone matrix may play an important role in bone formation in response to mechanical loading.

Osteoblasts subjected to fluid shear increase the expression of the early response gene, c-fos, and the inducible isoform of cyclooxygenase, COX-2, two proteins linked to the anabolic response of bone to mechanical stimulation, in vivo. These increases in gene expression are dependent on shear-induced actin stress fiber formation. Here, we demonstrate that MC3T3-E1 osteoblast-like cells respond to shear with a rapid increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) that we postulate is important to subsequent cellular responses to shear. To test this hypothesis, MC3T3-E1 cells were grown on glass slides coated with fibronectin and subjected to laminar fluid flow (12 dyn/cm(2)). Before application of shear, cells were treated with two Ca(2+) channel inhibitors or various blockers of intracellular Ca(2+) release for 0. 5-1 h. Although gadolinium, a mechanosensitive channel blocker, significantly reduced the [Ca(2+)](i) response, neither gadolinium nor nifedipine, an L-type channel Ca(2+) channel blocker, were able to block shear-induced stress fiber formation and increase in c-fos and COX-2 in MC3T3-E1 cells. However, 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, an intracellular Ca(2+) chelator, or thapsigargin, which empties intracellular Ca(2+) stores, completely inhibited stress fiber formation and c-fos/COX-2 production in sheared osteoblasts. Neomycin or U-73122 inhibition of phospholipase C, which mediates D-myo-inositol 1,4,5-trisphosphate (IP(3))-induced intracellular Ca(2+) release, also completely suppressed actin reorganization and c-fos/COX-2 production. Pretreatment of MC3T3-E1 cells with U-73343, the inactive isoform of U-73122, did not inhibit these shear-induced responses. These results suggest that IP(3)-mediated intracellular Ca(2+) release is required for modulating flow-induced responses in MC3T3-E1 cells.

Objective To investigate the efficacy of the minimally invasive clamp reduction technique via the anterior approach in the treatment of irreducible intertrochanteric femoral fractures. Methods From January 2015 to January 2021, 115 patients (48 males and 67 females) with irreducible intertrochanteric femoral fractures were treated. The average age of the patients was 78.7 (45–100 years old). The types of injuries were falls (91 cases), traffic accidents (12 cases), smashing (6 cases), and high falling (6 cases). The duration between injury and surgery ranged from 1 to 14 days, with an average of 3.9 days. The distribution of AO classification was as follows: 31-A1 in 15 cases, type 31-A2 in 67 cases and 31-A3 in 33 cases. Results All patients achieved good reduction, with fracture reduction times ranging from 10 to 32 min (mean of 18 min), and were followed up for 12–27 months after surgery (mean of 17.9 months). Two patients with pronation displacement of the proximal fracture segment died of infection or hypostatic pneumonia after internal fixation failure; one patient with failed internal fixation switched to joint replacement. After internal fixation, the lateral wall of six reversed intertrochanteric femoral fractures showed repronation and abduction displacement, but all fractures achieved bony healing. The rest of the patients did not lose fracture reduction, and all fractures achieved bony healing with a healing time ranging from 3 to 9 months (mean of 5.7 months). While two patients died and one patient exhibited failed internal fixation and thus switched to joint replacement, 91 of the remaining 112 patients had an excellent Harris score of the hip joint function at the final follow-up, while 21 patients had a good Harris score. Conclusion The minimally invasive clamp reduction technique via the anterior approach for the treatment of irreducible intertrochanteric femoral fractures is simple, effective and minimally invasive. In the case of irreducible intertrochanteric femoral fractures associated with lateral wall displacement, the lateral wall needs to be strengthened after clamp reduction and intramedullary nail fixation to avoid loss of reduction and failure of internal fixation.