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Fragility fractures have a limited capacity to regenerate, and impaired fracture healing is a leading cause of morbidity in the elderly. The recent identification of a highly purified bona fide human skeletal stem cell (hSSC) and its committed downstream progenitor cell populations provides an opportunity for understanding the mechanism of age‐related compromised fracture healing from the stem cell perspective. In this study, we tested whether hSSCs isolated from geriatric fractures demonstrate intrinsic functional defects that drive impaired healing. Using flow cytometry, we analyzed and isolated hSSCs from callus tissue of five different skeletal sites (n = 61) of patients ranging from 13 to 94 years of age for functional and molecular studies. We observed that fracture‐activated amplification of hSSC populations was comparable at all ages. However, functional analysis of isolated stem cells revealed that advanced age significantly correlated with reduced osteochondrogenic potential but was not associated with decreased in vitro clonogenicity. hSSCs derived from women displayed an exacerbated functional decline with age relative to those of aged men. Transcriptomic comparisons revealed downregulation of skeletogenic pathways such as WNT and upregulation of senescence‐related pathways in young versus older hSSCs. Strikingly, loss of Sirtuin1 expression played a major role in hSSC dysfunction but re‐activation by trans‐resveratrol or a small molecule compound restored in vitro differentiation potential. These are the first findings that characterize age‐related defects in purified hSSCs from geriatric fractures. Our results provide a foundation for future investigations into the mechanism and reversibility of skeletal stem cell aging in humans. [ABSTRACT FROM AUTHOR]

Critical bone defects pose a formidable orthopaedic problem in patients with bone loss. We developed a preclinical model based on the induced membrane technique using a synthetic graft to replace autograft for healing critical bone defects. Additionally, we used a novel osteoconductive scaffold coupled with a synthetic membrane to evaluate the potential for single‐stage bone regeneration. Three experimental conditions were investigated in critical femoral defects in rats. Group A underwent a two‐stage procedure with insertion of a polymethylmethacrylate (PMMA) spacer followed by replacement with a 3D printed polycaprolactone(PCL)/β‐tricalcium phosphate (β‐TCP) osteoconductive scaffold after 4 weeks. Group B received a single‐stage PCL/β‐TCP scaffold wrapped in a PCL‐based microporous polymer film creating a synthetic membrane. Group C received a single‐stage bare PCL/β‐TCP scaffold. All groups were examined by serial radiographs for callus formation. After 12 weeks, the femurs were explanted and analyzed with micro‐CT and histology. Mean callus scores tended to be higher in Group A. Group A showed statistically significant greater bone formation on micro‐CT compared with other groups, although bone volume fraction was similar between groups. Histology results suggested extensive bone ingrowth and new bone formation within the macroporous scaffolds in all groups and cell infiltration into the microporous synthetic membrane. This study supports the use of a critical size femoral defect in rats as a suitable model for investigating modifications to the induced membrane technique without autograft harvest. Future investigations should focus on bioactive synthetic membranes coupled with growth factors for single‐stage bone healing. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

Fracture healing is a complex process of many coordinated biological pathways. This system can go awry resulting in nonunion, which leads to significant patient morbidity. The Hedgehog (Hh) signaling pathway is upregulated in fracture healing. We hypothesized that the Hh signaling pathway can be pharmacologically modulated to positively affect fracture healing. Diaphyseal femur fractures were created in elderly mice (18 months, C57BL/6 females), which have a blunted and delayed healing response compared to younger mice, and were stabilized with intramedullary pins. To activate the Hh pathway we targeted the receptor Smoothened using an agonist (Hh‐Ag1.5 [Hh‐Ag]) and compared this to a vehicle control. Expression of Hh target genes were significantly increased in the fracture callus of the agonist group compared to controls, indicating pathway activation. Expression of osteogenic and chondrogenic‐related genes was greatly upregulated in fracture callus versus intact femora, although Hh agonist treatment did not consistently enhance this response. Blindly graded, radiographic callus healing scores were significantly higher in the Hh‐Ag groups at post operative day (POD) 14, indicating earlier callus bridging. On microCT, Hh‐Ag treatment led to greater callus volume (+40%) and bone volume (+25%) at POD21. By day 14, callus vascularity, as assessed by 3D microCT angiography vessel volume, was 85% greater in the Hh‐Ag group. Finally, mechanical strength of the calluses in the Hh‐Ag groups was significantly greater than in the control groups at POD21. In conclusion, systemic administration of a Hh agonist appears to improve the osseous and vascular healing responses in a mouse fracture healing‐impaired model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

A circadian rhythm matched to the phase and period of the day-night cycle has measurable benefits for land plants. We assessed the contribution of circadian period to the phasing of cellular events with the light : dark cycle. We also investigated the plasticity of circadian period within the Arabidopsis circadian oscillator., We monitored the circadian oscillator in wild-type and circadian period mutants under light : dark cycles of varying total duration. We also investigated changes in oscillator dynamics during and after the transition from light : dark cycles to free running conditions., Under light : dark cycles, dawn and dusk were anticipated differently when the circadian period was not resonant with the environmental period (' T cycle'). Entrainment to T cycles differing from the free-running period caused a short-term alteration in oscillator period. The transient plasticity of period was described by existing mathematical models of the Arabidopsis circadian network., We conclude that a circadian period resonant with the period of the environment is particularly important for anticipation of dawn and the timing of nocturnal events; and there is short-term and transient plasticity of period of the Arabidopsis circadian network. [ABSTRACT FROM AUTHOR]

Displaced acetabular fractures are best treated with open reduction to achieve anatomic reduction and maximize the chance of a good functional outcome. Because of the anatomic complexity and often limited visualization, fracture reduction can be difficult. Virtual planning software can allow the surgeon to understand the fracture morphology and to rehearse reduction maneuvers. The purpose of this study was to determine the effect of a novel virtual fracture reduction module on time and accuracy of reduction. Four acetabular fracture patterns were created in synthetic pelves, which were implanted with fiducial markers and were registered with CT scan. Ten surgeons used virtual fracture reduction software or conventional 2D planning methods and immediately reduced the fractures blindly in a viscous gel medium. 3D imaging was again performed and the accuracy of reduction was assessed. The average malreduction was significantly improved following planning with the virtual software compared to the standard technique. The time taken for reduction was also significantly less for two of the four fracture patterns. Virtual software may be useful for visualizing and planning treatment of fractures of the acetabulum, potentially leading to more accurate and efficient reductions, and may also be an effective educational tool. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:547-552, 2008 [ABSTRACT FROM AUTHOR]

Successful outcomes following high tibial osteotomy (HTO) require precise realignment of the mechanical axis of the lower extremity. The inability to accurately assess the weight-bearing axis intraoperatively may account for inappropriate degrees of correction with the osteotomy. We tested the hypothesis that axial loading of the limb affects alignment during an HTO procedure. A custom mechanical load apparatus was developed to simulate weight-bearing conditions intraoperatively. Fixation to the trunk was achieved by supraacetabular pins and an external fixation device, which allowed the pelvis to be rigidly fixed relative to the apparatus while axial load was applied to the foot. Ten fresh cadavers were used for testing. The baseline mechanical axis was determined by a navigation system. HTO was then performed, and varying degrees of valgus correction were obtained and stabilized. For each correction, one quarter, one half, or full body weight was applied axially to the foot, and the axis deviation was measured. Subsequently, the MCL was sequentially released to determine the effect of ligament incompetence. Prior to osteotomy, load application did not produce significant axis deviations. Following osteotomy, the mechanical axis deviation shifted significantly in all trials, increasing as load magnitude and degree of correction increased. With complete sectioning of the MCL, a further significant shift in the axis occurred. Deviations of mechanical axis occur on weight bearing in lower limbs following HTO. These shifts must be considered and possibly quantified to achieve the desired axis correction and maximize the chance at a successful long term outcome. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:553-561, 2008 [ABSTRACT FROM AUTHOR]

The mechanical environment at a fracture site can influence the course of healing. Intermittent parathyroid hormone (PTH) has been shown to accelerate fracture healing. Intact bone models show that mechanical loading and PTH have a synergistic beneficial effect on osteogenesis. We hypothesized that PTH and mechanical loading would have a similar synergistic effect on fracture healing. Eighty mice underwent surgical osteotomy and intramedullary nailing of the tibia. The mice were divided into four groups: one underwent daily loading, one received daily subcutaneous PTH injections (30 µg/kg/day), one received both loading and PTH, and a control group received sham loading and vehicle injection. Daily loading was applied to the ends of the tibia with an external loading device for 2 weeks. Fracture healing was assessed by microcomputed tomography, histology, and biomechanical testing. The group with both loading and PTH had increased osteoblast and osteoclast activity and was the only group with a significantly larger callus mineral density and bone volume fraction. The PTH only group had significantly more osteoid in the callus compared to the control group, indicating enhanced early osteoblast activity. This group also had a significantly higher bone mineral content and total bone volume compared to controls. The group that received loading as the only intervention had significantly greater osteoclast activity versus controls. The contribution of loading and PTH administration to the fracture healing cascade indicates a synergistic effect. This finding may be of potential clinical utility when weight bearing is utilized to stimulate lower extremity fracture healing. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1474-1480, 2007 [ABSTRACT FROM AUTHOR]

Drilling procedures are common in orthopedic surgery and are one specific task that may be aided by computer-assisted navigation. However, the inherent flexibility of drill bit bending may make this the limiting factor in achieving acceptable accuracy when using these systems. We designed an alignment device that was fit to a standard orthopedic drill that allowed an extension of the stabilizing point of a drill bit. In foam blocks with a similar density as cancellous bone, 208 total navigated drilling trials were performed, using four different sized drill bits (2.5, 3.2, 3.5, and 4.5 mm) with and without the alignment device. Drilling tracts of 80 mm were made towards an intended target on the other side of the block. Reduction in deviation from the intended target was significantly improved with the use of the guide, ranging from 33% to 45% for the four drill sizes. For the trails using the alignment device, the 2.5-mm drill bit was significantly less accurate than the three larger drills. Our results demonstrate that the use of external devices to augment drill bit stabilization can improve drilling accuracy. This may have particular importance when using navigation systems to drill into small anatomic confines. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:951-957, 2007 [ABSTRACT FROM AUTHOR]

Circadian clocks are signalling networks that enhance an organism's relationship with the rhythmic environment. The plant circadian clock modulates a wide range of physiological and biochemical events, such as stomatal and organ movements, photosynthesis and induction of flowering. Environmental signals regulate the phase and period of the plant circadian clock, which results in an approximate synchronization of clock outputs with external events. One of the consequences of circadian control is that stimuli of the same strength applied at different times of the day can result in responses of different intensities. This is known as ‘gating’. Gating of a signal may allow plants to better process and react to the wide range and intensities of environmental signals to which they are constantly subjected. Light signalling, stomatal movements and low-temperature responses are examples of signalling pathways that are gated by the circadian clock. In this review, we describe the many levels at which the circadian clock interacts with responses to the environment. We discuss how environmental rhythms of temperature and light intensity entrain the circadian clock, how photoperiodism may be regulated by the relationship between environmental rhythms and the phasing of clock outputs, and how gating modulates the sensitivity of the clock and other responses to environmental and physiological signals. Finally, we describe evidence that the circadian clock can increase plant fitness. [ABSTRACT FROM AUTHOR]

Abundant evidence exists that fracture healing can be influenced by mechanical loading. However, the specific loading parameters that are osteogenic remain unknown. We hypothesized that the bone healing response in mouse tibial osteotomies would be different with a short delay before loading compared to immediate load application, as well as with higher and lower load magnitudes applied. Eighty 12-week-old mice underwent osteotomy of the left tibia followed by intramedullary nailing. Mice were divided into six groups based on days delayed until application of load (0 days or 4 days) and amplitude of cyclic load (0.5N, 1N, or 2N). Loading regimens were applied at 1 Hz for 100 cycles per day, 5 days per week for 2 weeks, using an external device that applied axial compression to the tibia. Bone healing was assessed by both microcomputed tomography (CT) and four-point bend testing. A short delay followed by cyclic application of a relatively low load led to improved fracture healing, as determined by increased callus strength, but this enhancement disappeared as load amplitudes increased. Load initiation immediately following fracture inhibited healing, regardless of the magnitude of load applied. MicroCT measurements of calluses in the early healing stage did not predict the mechanical strength of the fractures. These findings confirm that controlled, noninvasive cyclic loading can improve the strength of healing callus. However, application of load immediately after fracture appears to be detrimental to healing. Load magnitude also plays a critical role, and must be taken into account in future studies and clinical applications. As the loading parameters necessary to enhance fracture healing become refined, external compression may be used as a potent stimulus for treating fractures with decreased biological capacity. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1679-1686, 2006 [ABSTRACT FROM AUTHOR]

Fracture healing is a complex process of many coordinated biological pathways. This system can go awry resulting in nonunion, which leads to significant patient morbidity. The Hedgehog (Hh) signaling pathway is upregulated in fracture healing. We hypothesized that the Hh signaling pathway can be pharmacologically modulated to positively affect fracture healing. Diaphyseal femur fractures were created in elderly mice (18 months, C57BL/6 females), which have a blunted and delayed healing response compared to younger mice, and were stabilized with intramedullary pins. To activate the Hh pathway we targeted the receptor Smoothened using an agonist (Hh‐Ag1.5 [Hh‐Ag]) and compared this to a vehicle control. Expression of Hh target genes were significantly increased in the fracture callus of the agonist group compared to controls, indicating pathway activation. Expression of osteogenic and chondrogenic‐related genes was greatly upregulated in fracture callus vs. intact femora, although Hh agonist treatment did not consistently enhance this response. Blindly graded, radiographic callus healing scores were significantly higher in the Hh‐Ag groups at post operative day (POD) 14, indicating earlier callus bridging. On microCT, Hh‐Ag treatment led to greater callus volume (+40%) and bone volume (+25%) at POD21. By day 14, callus vascularity, as assessed by 3D microCT angiography vessel volume, was 85% greater in the Hh‐Ag group. Finally, mechanical strength of the calluses in the Hh‐Ag groups was significantly greater than in the control groups at POD21. In conclusion, systemic administration of a Hh agonist appears to improve the osseous and vascular healing responses in a mouse fracture healing‐impaired model. This article is protected by copyright. All rights reserved [ABSTRACT FROM AUTHOR]