The discovery of microRNA (miRNA) has revealed a novel type of regulatory control for gene expression. Increasing evidence suggests that miRNA regulates chondrocyte, osteoblast, and osteoclast differentiation and function, indicating miRNA as key regulators of bone formation, resorption, remodeling, and repair. We hypothesized that the functions of certain miRNAs and changes to their expression pattern may play crucial roles during the process of fracture healing. Standard healing fractures and unhealing fractures produced by periosteal cauterization at the fracture site were created in femurs of seventy rats, with half assigned to the standard healing fracture group and half assigned to the nonunion group. At post-fracture days 3, 7, 10, 14, 21, and 28, total RNA including miRNA was extracted from the newly generated tissue at the fracture site. Microarray analysis was performed with miRNA samples from each group on post-fracture day 14. For further analysis, we selected highly up-regulated five miRNAs in the standard healing fracture group from the microarray data. Real-time PCR was performed with miRNA samples at each time point above mentioned to compare the expression levels of the selected miRNAs between standard healing fractures and unhealing fractures and investigate their time-course changes. Microarray and real-time polymerase chain reaction (PCR) analyses on day 14 revealed that five miRNAs, miR-140-3p, miR-140-5p, miR-181a-5p, miR-181d-5p, and miR-451a, were significantly highly expressed in standard healing fractures compared with unhealing fractures. Real-time PCR analysis further revealed that in standard healing fractures, the expression of all five of these miRNAs peaked on day 14 and declined thereafter. Our results suggest that the five miRNAs identified using microarray and real-time PCR analyses may play important roles during fracture healing. These findings provide valuable information to further understand the molecular mechanism of fracture healing and may lead to the development of miRNA-based tissue engineering strategies to promote fracture healing.

The regeneration of articular cartilage damaged due to trauma and posttraumatic osteoarthritis is an unmet medical need. Current approaches to regeneration and tissue engineering of articular cartilage include the use of chondrocytes, stem cells, scaffolds and signals, including morphogens and growth factors. Stem cells, as a source of cells for articular cartilage regeneration, are a critical factor for articular cartilage regeneration. This is because articular cartilage tissue has a low cell turnover and does not heal spontaneously. Adult stem cells have been isolated from various tissues, such as bone marrow, adipose, synovial tissue, muscle and periosteum. Signals of the transforming growth factor beta superfamily play critical roles in chondrogenesis. However, adult stem cells derived from various tissues tend to differ in their chondrogenic potential. Pluripotent stem cells have unlimited proliferative capacity compared to adult stem cells. Chondrogenesis from embryonic stem (ES) cells has been studied for more than a decade. However, establishment of ES cells requires embryos and leads to ethical issues for clinical applications. Induced pluripotent stem (iPS) cells are generated by cellular reprogramming of adult cells by transcription factors. Although iPS cells have chondrogenic potential, optimization, generation and differentiation toward articular chondrocytes are currently under intense investigation.

Introduction: Osteopetrosis is a skeletal disorder characterized by increased osteodensity and a remodeling defect. The fragility of dense sclerotic bones may lead to an increased incidence of fractures. Although internal fixation can be performed, technical challenges may be experienced because of the increased bone density. Complications such as delayed union, nonunion, or implant failure may occur postoperatively. Presentation of case: We describe a patient with autosomal-dominant osteopetrosis type 2 who suffered a shaft fracture below a plate of his right femur. We performed osteosynthesis with a single locking plate. Union was delayed, and plate breakage occurred along with nonunion of the fracture. The nonunion was addressed using double locking plates, which secured fixation and allowed complete fracture healing. Discussion: There were three reasons of nonunion in our case. First, we left gaps between the fragments. Second, we used mainly cerclage wires, rather than screws, for plate fixation, which led to inadequate stability. Third, the patient was large (height 167 cm, weight 93.1 kg), so the single plate provided insufficient fixing force. We then used double locking plates and attained stronger internal fixation with complete fracture healing. Conclusion: Double plating with locking plates may be an effective treatment option for femoral fractures in patients with osteopetrosis. Highlights:

A Morel-Lavallee lesion (MLL) involves posttraumatic fluid collection around the greater trochanter. Many cases of MLL are missed at the initial evaluation, and the treatment of MLL is not well established. We present two cases in which MLL was missed at the initial evaluation.Case 1.A 65-year-old man was run over by a parade float. There was subcutaneous hematoma around the left greater trochanter, and no fracture was found. We diagnosed this injury as MLL on the 7th day after the trauma. Although we performed percutaneous drainage, the injured area was infected.Case 2.A 57-year-old man was hit by a train in a factory. There was an iliac wing fracture, but an MLL was not initially recognized. On the 6th day after the trauma, when performing open reduction and internal fixation for the iliac fracture, we recognized the lesion and performed percutaneous drainage simultaneously. This lesion also became infected. In these two cases, the wounds finally healed after a long duration of treatment. We suggest that it is important to keep this injury in mind and debride the lesion early and completely in the treatment course.

Bicondylar coronal plane fracture, eponymically named Hoffa fractures, is an extremely rare injury. We present a case of isolated unilateral bicondylar Hoffa fracture that was successfully treated with open reduction and internal fixation using headless compression screws with satisfactory results. We inserted posteroanteriorly oriented Acutrak screws perpendicular to the fracture plane via lateral parapatellar arthrotomy, which provided excellent compression across the fracture.

Mesenchymal progenitor cells (MPCs) play a critical role in fracture healing. Increasing evidence suggests that circulating MPCs in peripheral blood are mobilized during fracture healing and may contribute to fracture repair. However, to date, there have been no reports comparing the number of circulating MPCs in arterial blood (AB) with that in venous blood (VB) after fracture. In this study, we investigated the numbers of MPCs in AB, VB and bone marrow (BM) after fracture in rabbits via the colony‐forming unit–fibroblasts (CFU‐Fs) assay, and clarified the time‐course change. After femoral fracture in one side, the number of BM‐MPCs in the contralateral femur increased from day 1 to day 7. Correspondingly, the number of circulating MPCs in AB and VB increased. The number of circulating MPCs in AB was highest at post‐fracture day 4, whereas that in VB was highest at post‐fracture day 1, with significant difference compared to the control. Circulating MPCs in AB and VB after fracture may serve as new cell sources for bone tissue engineering. As the peaks of the number of circulating MPCs in AB and VB after fracture were different, our findings may provide new insights about when to collect circulating MPCs after fracture and from which blood to obtain them. Copyright © 2012 John Wiley & Sons, Ltd.