Aims. In recent conflicts, most injuries to the limbs are due to blasts resulting in a large number of lower limb amputations. These lead to heterotopic ossification (HO), phantom limb pain (PLP), and functional deficit. The mechanism of blast loading produces a combined fracture and amputation. Therefore, to study these conditions, in vivo models that replicate this combined effect are required. The aim of this study is to develop a preclinical model of blast-induced lower limb amputation. Methods. Cadaveric Sprague-Dawley rats’ left hindlimbs were exposed to blast waves of 7 to 13 bar burst pressures and 7.76 ms to 12.68 ms positive duration using a shock tube. Radiographs and dissection were used to identify the injuries. Results. Higher burst pressures of 13 and 12 bar caused multiple fractures at the hip, and the right and left limbs. Lowering the pressure to 10 bar eliminated hip fractures; however, the remaining fractures were not isolated to the left limb. Further reducing the pressure to 9 bar resulted in the desired isolated fracture of the left tibia with a dramatic reduction in the fractures to other sites. Conclusion. In this paper, a rodent blast injury model has been developed in the hindlimb of cadaveric rats that combines the blast and fracture in one insult, necessitating amputation. Experimental setup with 9 bar burst pressure and 9.13 ms positive duration created a fracture at the tibia with total reduction in non-targeted fractures, rendering 9 bar burst pressure suitable for translation to a survivable model to investigate blast injury-associated diseases. Cite this article: Bone Joint Res 2021;10(3):166–173

Aims. The involvement of cyclin D1 in the proliferation of microglia, and the generation and maintenance of bone cancer pain (BCP), have not yet been clarified. We investigated the expression of microglia and cyclin D1, and the influences of cyclin D1 on pain threshold. Methods. Female Sprague Dawley (SD) rats were used to establish a rat model of BCP, and the messenger RNA (mRNA) and protein expression of ionized calcium binding adaptor molecule 1 (IBA1) and cyclin D1 were detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot, respectively. The proliferation of spinal microglia was detected by immunohistochemistry. The pain behaviour test was assessed by quantification of spontaneous flinches, limb use, and guarding during forced ambulation, mechanical paw withdrawal threshold, and thermal paw withdrawal latency. Results. IBA1 and cyclin D1 in the ipsilateral spinal horn increased in a time-dependent fashion. Spinal microglia proliferated in BCP rats. The microglia inhibitor minocycline attenuated the pain behaviour in BCP rats. The cyclin-dependent kinase inhibitor flavopiridol inhibited the proliferation of spinal microglia, and was associated with an improvement in pain behaviour in BCP rats. Conclusion. Our results revealed that the inhibition of spinal microglial proliferation was associated with a decrease in pain behaviour in a rat model of BCP. Cyclin D1 acts as a key regulator of the proliferation of spinal microglia in a rat model of BCP. Disruption of cyclin D1, the restriction-point control of cell cycle, inhibited the proliferation of microglia and attenuated the pain behaviours in BCP rats. Cyclin D1 and the proliferation of spinal microglia may be potential targets for the clinical treatment of BCP. Cite this article: Bone Joint Res 2022;11(11):803–813

Aims. Dystrophic calcification (DC) is the abnormal appearance of calcified deposits in degenerating tissue, often associated with injury. Extensive DC can lead to heterotopic ossification (HO), a pathological condition of ectopic bone formation. The highest rate of HO was found in combat-related blast injuries, a polytrauma condition with severe muscle injury. It has been noted that the incidence of HO significantly increased in the residual limbs of combat-injured patients if the final amputation was performed within the zone of injury compared to that which was proximal to the zone of injury. While aggressive limb salvage strategies may maximize the function of the residual limb, they may increase the possibility of retaining non-viable muscle tissue inside the body. In this study, we hypothesized that residual dead muscle tissue at the zone of injury could promote HO formation. Methods. We tested the hypothesis by investigating the cellular and molecular consequences of implanting devitalized muscle tissue into mouse muscle pouch in the presence of muscle injury induced by cardiotoxin. Results. Our findings showed that the presence of devitalized muscle tissue could cause a systemic decrease in circulating transforming growth factor-beta 1 (TGF-β1), which promoted DC formation following muscle injury. We further demonstrated that suppression of TGF-β signalling promoted DC in vivo, and potentiated osteogenic differentiation of muscle-derived stromal cells in vitro. Conclusion. Taken together, these findings suggest that TGF-β1 may play a protective role in dead muscle tissue-induced DC, which is relevant to understanding the pathogenesis of post-traumatic HO. Cite this article: Bone Joint Res 2020;9(11):742–750

Objectives. The exact aetiology and pathogenesis of microdamage-induced long bone fractures remain unknown. These fractures are likely to be the result of inadequate bone remodelling in response to damage. This study aims to identify an association of osteocyte apoptosis, the presence of osteocytic osteolysis, and any alterations in sclerostin expression with a fracture of the third metacarpal (Mc-III) bone of Thoroughbred racehorses. Methods. A total of 30 Mc-III bones were obtained; ten bones were fractured during racing, ten were from the contralateral limb, and ten were from control horses. Each Mc-III bone was divided into a fracture site, condyle, condylar groove, and sagittal ridge. Microcracks and diffuse microdamage were quantified. Apoptotic osteocytes were measured using TUNEL staining. Cathepsin K, matrix metalloproteinase-13 (MMP-13), HtrA1, and sclerostin expression were analyzed. Results. In the fracture group, microdamage was elevated 38.9% (. sd 2.6. ) compared with controls. There was no difference in the osteocyte number and the percentage of apoptotic cells between contralateral limb and unraced control; however, there were significantly fewer apoptotic cells in fractured samples (p < 0.02). Immunohistochemistry showed that in deep zones of the fractured samples, sclerostin expression was significantly higher (p < 0.03) than the total number of osteocytes. No increase in cathepsin K, MMP-13, or HtrA1 was present. Conclusion. There is increased microdamage in Mc-III bones that have fractured during racing. In this study, this is not associated with osteocyte apoptosis or osteocytic osteolysis. The finding of increased sclerostin in the region of the fracture suggests that this protein may be playing a key role in the regulation of bone microdamage during stress adaptation. Cite this article: N. Hopper, E. Singer, F. Henson. Increased sclerostin associated with stress fracture of the third metacarpal bone in the Thoroughbred racehorse. Bone Joint Res 2018;7:94–102. DOI: 10.1302/2046-3758.71.BJR-2016-0202.R4

Aims

The use of 3D printing has become increasingly popular and has been widely used in orthopaedic surgery. There has been a trend towards an increasing number of publications in this field, but existing literature incorporates limited high-quality studies, and there is a lack of reports on outcomes. The aim of this study was to perform a scoping review with Level I evidence on the application and effectiveness of 3D printing.

Aims

Acquired heterotopic ossification (HO) is a debilitating disease characterized by abnormal extraskeletal bone formation within soft-tissues after injury. The exact pathogenesis of HO remains unknown. It was reported that BRD4 may contribute to osteoblastic differentiation. The current study aims to determine the role of BRD4 in the pathogenesis of HO and whether it could be a potential target for HO therapy.

Bone is a dynamic tissue with a quarter of the trabecular and a fifth of the cortical bone being replaced continuously each year in a complex process that continues throughout an individual’s lifetime. Bone has an important role in homeostasis of minerals with non-stoichiometric hydroxyapatite bone mineral forming the inorganic phase of bone. Due to its crystal structure and chemistry, hydroxyapatite (HA) and related apatites have a remarkable ability to bind molecules. This review article describes the accretion of trace elements in bone mineral giving a historical perspective. Implanted HA particles of synthetic origin have proved to be an efficient recruiting moiety for systemically circulating drugs which can locally biomodulate the material and lead to a therapeutic effect. Bone mineral and apatite however also act as a waste dump for trace elements and drugs, which significantly affects the environment and human health.

Cite this article: Bone Joint Res 2020;9(10):709–718.

Objectives

Up to 10% of fractures result in undesirable outcomes, for which female sex is a risk factor. Cellular sex differences have been implicated in these different healing processes. Better understanding of the mechanisms underlying bone healing and sex differences in this process is key to improved clinical outcomes. This study utilized a macrophage–mesenchymal stem cell (MSC) coculture system to determine: 1) the precise timing of proinflammatory (M1) to anti-inflammatory (M2) macrophage transition for optimal bone formation; and 2) how such immunomodulation was affected by male versus female cocultures.

Objectives

Long bone defects often require surgical intervention for functional restoration. The ‘gold standard’ treatment is autologous bone graft (ABG), usually from the patient’s iliac crest. However, autograft is plagued by complications including limited supply, donor site morbidity, and the need for an additional surgery. Thus, alternative therapies are being actively investigated. Autologous bone marrow (BM) is considered as a candidate due to the presence of both endogenous reparative cells and growth factors. We aimed to compare the therapeutic potentials of autologous bone marrow aspirate (BMA) and ABG, which has not previously been done.

During the last decades, several research groups have used bisphosphonates for local application to counteract secondary bone resorption after bone grafting, to improve implant fixation or to control bone resorption caused by bone morphogenetic proteins (BMPs). We focused on zoledronate (a bisphosphonate) due to its greater antiresorptive potential over other bisphosphonates. Recently, it has become obvious that the carrier is of importance to modulate the concentration and elution profile of the zoledronic acid locally. Incorporating one fifth of the recommended systemic dose of zoledronate with different apatite matrices and types of bone defects has been shown to enhance bone regeneration significantly in vivo. We expect the local delivery of zoledronate to overcome the limitations and side effects associated with systemic usage; however, we need to know more about the bioavailability and the biological effects. The local use of BMP-2 and zoledronate as a combination has a proven additional effect on bone regeneration. This review focuses primarily on the local use of zoledronate alone, or in combination with bone anabolic factors, in various preclinical models mimicking different orthopaedic conditions.

Cite this article: I. Qayoom, D. B. Raina, A. Širka, Š. Tarasevičius, M. Tägil, A. Kumar, L. Lidgren. Anabolic and antiresorptive actions of locally delivered bisphosphonates for bone repair: A review. Bone Joint Res 2018;7:548–560. DOI: 10.1302/2046-3758.710.BJR-2018-0015.R2.