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Bone & Joint Research
Vol. 6, Issue 3 | Pages 144 - 153
1 Mar 2017
Kharwadkar N Mayne B Lawrence JE Khanduja V

Objectives. Bisphosphonates are widely used as first-line treatment for primary and secondary prevention of fragility fractures. Whilst they have proved effective in this role, there is growing concern over their long-term use, with much evidence linking bisphosphonate-related suppression of bone remodelling to an increased risk of atypical subtrochanteric fractures of the femur (AFFs). The objective of this article is to review this evidence, while presenting the current available strategies for the management of AFFs. Methods. We present an evaluation of current literature relating to the pathogenesis and treatment of AFFs in the context of bisphosphonate use. Results. Six broad themes relating to the pathogenesis and management of bisphosphonate-related AFFs are presented. The key themes in fracture pathogenesis are: bone microdamage accumulation; altered bone mineralisation and altered collagen formation. The key themes in fracture management are: medical therapy and surgical therapy. In addition, primary prevention strategies for AFFs are discussed. Conclusions. This article presents current knowledge about the relationship between bisphosphonates and the development of AFFs, and highlights key areas for future research. In particular, studies aimed at identifying at-risk subpopulations and organising surveillance for those on long-term therapy will be crucial in both increasing our understanding of the condition, and improving population outcomes. Cite this article: N. Kharwadkar, B. Mayne, J. E. Lawrence, V. Khanduja. Bisphosphonates and atypical subtrochanteric fractures of the femur. Bone Joint Res 2017;6:144–153. DOI: 10.1302/2046-3758.63.BJR-2016-0125.R1


Objectives. The annual incidence of hip fracture is 620 000 in the European Union. The cost of this clinical problem has been estimated at 1.75 million disability-adjusted life years lost, equating to 1.4% of the total healthcare burden in established market economies. Recent guidance from The National Institute for Health and Clinical Excellence (NICE) states that research into the clinical and cost effectiveness of total hip arthroplasty (THA) as a treatment for hip fracture is a priority. We asked the question: can a trial investigating THA for hip fracture currently be delivered in the NHS?. Methods. We performed a contemporaneous process evaluation that provides a context for the interpretation of the findings of WHiTE Two – a randomised study of THA for hip fracture. We developed a mixed methods approach to situate the trial centre within the context of wider United Kingdom clinical practice. We focused on fidelity, implementation, acceptability and feasibility of both the trial processes and interventions to stakeholder groups, such as healthcare providers and patients. Results. We have shown that patients are willing to participate in this type of research and that surgeons value being part of a team that has a strong research ethos. However, surgical practice does not currently reflect NICE guidance. Current models of service delivery for hip fractures are unlikely to be able to provide timely total hip arthroplasty for suitable patients. Conclusions. Further observational research should be conducted to define the population of interest before future interventional studies are performed. Cite this article: C. Huxley, J. Achten, M. L. Costa, F. Griffiths, X. L. Griffin. A process evaluation of the WHiTE Two trial comparing total hip arthroplasty with and without dual mobility component in the treatment of displaced intracapsular fractures of the proximal femur: Can a trial investigating total hip arthroplasty for hip fracture be delivered in the NHS? Bone Joint Res 2016;5:444–452. DOI: 10.1302/2046-3758.510.BJR-2015-0008.R1


Bone & Joint Research
Vol. 7, Issue 6 | Pages 430 - 439
1 Jun 2018
Eggermont F Derikx LC Verdonschot N van der Geest ICM de Jong MAA Snyers A van der Linden YM Tanck E

Objectives. In this prospective cohort study, we investigated whether patient-specific finite element (FE) models can identify patients at risk of a pathological femoral fracture resulting from metastatic bone disease, and compared these FE predictions with clinical assessments by experienced clinicians. Methods. A total of 39 patients with non-fractured femoral metastatic lesions who were irradiated for pain were included from three radiotherapy institutes. During follow-up, nine pathological fractures occurred in seven patients. Quantitative CT-based FE models were generated for all patients. Femoral failure load was calculated and compared between the fractured and non-fractured femurs. Due to inter-scanner differences, patients were analyzed separately for the three institutes. In addition, the FE-based predictions were compared with fracture risk assessments by experienced clinicians. Results. In institute 1, median failure load was significantly lower for patients who sustained a fracture than for patients with no fractures. In institutes 2 and 3, the number of patients with a fracture was too low to make a clear distinction. Fracture locations were well predicted by the FE model when compared with post-fracture radiographs. The FE model was more accurate in identifying patients with a high fracture risk compared with experienced clinicians, with a sensitivity of 89% versus 0% to 33% for clinical assessments. Specificity was 79% for the FE models versus 84% to 95% for clinical assessments. Conclusion. FE models can be a valuable tool to improve clinical fracture risk predictions in metastatic bone disease. Future work in a larger patient population should confirm the higher predictive power of FE models compared with current clinical guidelines. Cite this article: F. Eggermont, L. C. Derikx, N. Verdonschot, I. C. M. van der Geest, M. A. A. de Jong, A. Snyers, Y. M. van der Linden, E. Tanck. Can patient-specific finite element models better predict fractures in metastatic bone disease than experienced clinicians? Towards computational modelling in daily clinical practice. Bone Joint Res 2018;7:430–439. DOI: 10.1302/2046-3758.76.BJR-2017-0325.R2


Bone & Joint Research
Vol. 12, Issue 2 | Pages 138 - 146
14 Feb 2023
Aquilina AL Claireaux H Aquilina CO Tutton E Fitzpatrick R Costa ML Griffin XL

Aims

Open lower limb fracture is a life-changing injury affecting 11.5 per 100,000 adults each year, and causes significant morbidity and resource demand on trauma infrastructures. This study aims to identify what, and how, outcomes have been reported for people following open lower limb fracture over ten years.

Methods

Systematic literature searches identified all clinical studies reporting outcomes for adults following open lower limb fracture between January 2009 and July 2019. All outcomes and outcome measurement instruments were extracted verbatim. An iterative process was used to group outcome terms under standardized outcome headings categorized using an outcome taxonomy.


Bone & Joint Research
Vol. 12, Issue 7 | Pages 423 - 432
6 Jul 2023
Xie H Wang N He H Yang Z Wu J Yang T Wang Y

Aims

Previous studies have suggested that selenium as a trace element is involved in bone health, but findings related to the specific effect of selenium on bone health remain inconclusive. Thus, we performed a meta-analysis by including all the relevant studies to elucidate the association between selenium status (dietary intake or serum selenium) and bone health indicators (bone mineral density (BMD), osteoporosis (OP), or fracture).

Methods

PubMed, Embase, and Cochrane Library were systematically searched to retrieve relevant articles published before 15 November 2022. Studies focusing on the correlation between selenium and BMD, OP, or fracture were included. Effect sizes included regression coefficient (β), weighted mean difference (WMD), and odds ratio (OR). According to heterogeneity, the fixed-effect or random-effect model was used to assess the association between selenium and bone health.


Bone & Joint Research
Vol. 11, Issue 6 | Pages 342 - 345
1 Jun 2022
Hall AJ Clement ND MacLullich AMJ Simpson AHRW White TO Duckworth AD

Research into COVID-19 has been rapid in response to the dynamic global situation, which has resulted in heterogeneity of methodology and the communication of information. Adherence to reporting standards would improve the quality of evidence presented in future studies, and may ensure that findings could be interpreted in the context of the wider literature. The COVID-19 pandemic remains a dynamic situation, requiring continued assessment of the disease incidence and monitoring for the emergence of viral variants and their transmissibility, virulence, and susceptibility to vaccine-induced immunity. More work is needed to assess the long-term impact of COVID-19 infection on patients who sustain a hip fracture. The International Multicentre Project Auditing COVID-19 in Trauma & Orthopaedics (IMPACT) formed the largest multicentre collaborative audit conducted in orthopaedics in order to provide an emergency response to a global pandemic, but this was in the context of many vital established audit services being disrupted at an early stage, and it is crucial that these resources are protected during future health crises. Rapid data-sharing between regions should be developed, with wider adoption of the revised 2022 Fragility Fracture Network Minimum Common Data Set for Hip Fracture Audit, and a pragmatic approach to information governance processes in order to facilitate cooperation and meta-audit. This editorial aims to: 1) identify issues related to COVID-19 that require further research; 2) suggest reporting standards for studies of COVID-19 and other communicable diseases; 3) consider the requirement of new risk scores for hip fracture patients; and 4) present the lessons learned from IMPACT in order to inform future collaborative studies.

Cite this article: Bone Joint Res 2022;11(6):342–345.


Bone & Joint Research
Vol. 11, Issue 6 | Pages 398 - 408
22 Jun 2022
Xu T Zeng Y Yang X Liu G Lv T Yang H Jiang F Chen Y

Aims

We aimed to evaluate the utility of 68Ga-citrate positron emission tomography (PET)/CT in the differentiation of periprosthetic joint infection (PJI) and aseptic loosening (AL), and compare it with 99mTc-methylene bisphosphonates (99mTc-MDP) bone scan.

Methods

We studied 39 patients with suspected PJI or AL. These patients underwent 68Ga-citrate PET/CT, 99mTc-MDP three-phase bone scan and single-photon emission CT (SPECT)/CT. PET/CT was performed at ten minutes and 60 minutes after injection, respectively. Images were evaluated by three nuclear medicine doctors based on: 1) visual analysis of the three methods based on tracer uptake model, and PET images attenuation-corrected with CT and those not attenuation-corrected with CT were analyzed, respectively; and 2) semi-quantitative analysis of PET/CT: maximum standardized uptake value (SUVmax) of lesions, SUVmax of the lesion/SUVmean of the normal bone, and SUVmax of the lesion/SUVmean of the normal muscle. The final diagnosis was based on the clinical and intraoperative findings, and histopathological and microbiological examinations.


Bone & Joint Research
Vol. 11, Issue 7 | Pages 465 - 476
13 Jul 2022
Li MCM Chow SK Wong RMY Chen B Cheng JCY Qin L Cheung W

Aims

There is an increasing concern of osteoporotic fractures in the ageing population. Low-magnitude high-frequency vibration (LMHFV) was shown to significantly enhance osteoporotic fracture healing through alteration of osteocyte lacuno-canalicular network (LCN). Dentin matrix protein 1 (DMP1) in osteocytes is known to be responsible for maintaining the LCN and mineralization. This study aimed to investigate the role of osteocyte-specific DMP1 during osteoporotic fracture healing augmented by LMHFV.

Methods

A metaphyseal fracture was created in the distal femur of ovariectomy-induced osteoporotic Sprague Dawley rats. Rats were randomized to five different groups: 1) DMP1 knockdown (KD), 2) DMP1 KD + vibration (VT), 3) Scramble + VT, 4) VT, and 5) control (CT), where KD was performed by injection of short hairpin RNA (shRNA) into marrow cavity; vibration treatment was conducted at 35 Hz, 0.3 g; 20 minutes/day, five days/week). Assessments included radiography, micro-CT, dynamic histomorphometry and immunohistochemistry on DMP1, sclerostin, E11, and fibroblast growth factor 23 (FGF23). In vitro, murine long bone osteocyte-Y4 (MLO-Y4) osteocyte-like cells were randomized as in vivo groupings. DMP1 KD was performed by transfecting cells with shRNA plasmid. Assessments included immunocytochemistry on osteocyte-specific markers as above, and mineralized nodule staining.


Bone & Joint Research
Vol. 11, Issue 4 | Pages 239 - 250
20 Apr 2022
Stewart CC O’Hara NN Bzovsky S Bahney CS Sprague S Slobogean GP

Aims

Bone turnover markers (BTMs) follow distinct trends after fractures and limited evidence suggests differential levels in BTMs in patients with delayed healing. The effect of vitamin D, and other factors that influence BTMs and fracture healing, is important to elucidate the use of BTMs as surrogates of fracture healing. We sought to determine whether BTMs can be used as early markers of delayed fracture healing, and the effect of vitamin D on BTM response after fracture.

Methods

A total of 102 participants aged 18 to 50 years (median 28 years (interquartile range 23 to 35)), receiving an intramedullary nail for a tibial or femoral shaft fracture, were enrolled in a randomized controlled trial comparing vitamin D3 supplementation to placebo. Serum C-terminal telopeptide of type I collagen (CTX; bone resorption marker) and N-terminal propeptide of type I procollagen (P1NP; bone formation marker) were measured at baseline, six weeks, and 12 weeks post-injury. Clinical and radiological fracture healing was assessed at three months.


Bone & Joint Research
Vol. 11, Issue 2 | Pages 102 - 111
1 Feb 2022
Jung C Cha Y Yoon HS Park CH Yoo J Kim J Jeon Y

Aims

In this study, we aimed to explore surgical variations in the Femoral Neck System (FNS) used for stable fixation of Pauwels type III femoral neck fractures.

Methods

Finite element models were established with surgical variations in the distance between the implant tip and subchondral bone, the gap between the plate and lateral femoral cortex, and inferior implant positioning. The models were subjected to physiological load.


Bone & Joint Research
Vol. 11, Issue 2 | Pages 49 - 60
1 Feb 2022
Li J Wong RMY Chung YL Leung SSY Chow SK Ip M Cheung W

Aims

With the ageing population, fragility fractures have become one of the most common conditions. The objective of this study was to investigate whether microbiological outcomes and fracture-healing in osteoporotic bone is worse than normal bone with fracture-related infection (FRI).

Methods

A total of 120 six-month-old Sprague-Dawley (SD) rats were randomized to six groups: Sham, sham + infection (Sham-Inf), sham with infection + antibiotics (Sham-Inf-A), ovariectomized (OVX), OVX + infection (OVX-Inf), and OVX + infection + antibiotics (OVX-Inf-A). Open femoral diaphysis fractures with Kirschner wire fixation were performed. Staphylococcus aureus at 4 × 104 colony-forming units (CFU)/ml was inoculated. Rats were euthanized at four and eight weeks post-surgery. Radiography, micro-CT, haematoxylin-eosin, mechanical testing, immunohistochemistry (IHC), gram staining, agar plating, crystal violet staining, and scanning electron microscopy were performed.


Aims

Exosomes derived from bone marrow mesenchymal stem cells (BMSCs) have been reported to be a promising cellular therapeutic approach for various human diseases. The current study aimed to investigate the mechanism of BMSC-derived exosomes carrying microRNA (miR)-136-5p in fracture healing.

Methods

A mouse fracture model was initially established by surgical means. Exosomes were isolated from BMSCs from mice. The endocytosis of the mouse osteoblast MC3T3-E1 cell line was analyzed. CCK-8 and disodium phenyl phosphate microplate methods were employed to detect cell proliferation and alkaline phosphatase (ALP) activity, respectively. The binding of miR-136-5p to low-density lipoprotein receptor related protein 4 (LRP4) was analyzed by dual luciferase reporter gene assay. HE staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemistry were performed to evaluate the healing of the bone tissue ends, the positive number of osteoclasts, and the positive expression of β-catenin protein, respectively.


Bone & Joint Research
Vol. 5, Issue 5 | Pages 191 - 197
1 May 2016
Kienast B Kowald B Seide K Aljudaibi M Faschingbauer M Juergens C Gille J

Objectives. The monitoring of fracture healing is a complex process. Typically, successive radiographs are performed and an emerging calcification of the fracture area is evaluated. The aim of this study was to investigate whether different bone healing patterns can be distinguished using a telemetric instrumented femoral internal plate fixator. Materials and Methods. An electronic telemetric system was developed to assess bone healing mechanically. The system consists of a telemetry module which is applied to an internal locking plate fixator, an external reader device, a sensor for measuring externally applied load and a laptop computer with processing software. By correlation between externally applied load and load measured in the implant, the elasticity of the osteosynthesis is calculated. The elasticity decreases with ongoing consolidation of a fracture or nonunion and is an appropriate parameter for the course of bone healing. At our centre, clinical application has been performed in 56 patients suffering nonunion or fracture of the femur. Results. A total of 39 cases of clinical application were reviewed for this study. In total, four different types of healing curves were observed: fast healing; slow healing; plateau followed by healing; and non-healing. Conclusion. The electronically instrumented internal fixator proved to be valuable for the assessment of bone healing in difficult healing situations. Cost-effective manufacturing is possible because the used electronic components are derived from large-scale production. The incorporation of microelectronics into orthopaedic implants will be an important innovation in future clinical care. Cite this article: B. Kienast, B. Kowald, K. Seide, M. Aljudaibi, M. Faschingbauer, C. Juergens, J. Gille. An electronically instrumented internal fixator for the assessment of bone healing. Bone Joint Res 2016;5:191–197. DOI: 10.1302/2046-3758.55.2000611


Bone & Joint Research
Vol. 6, Issue 8 | Pages 481 - 488
1 Aug 2017
Caruso G Bonomo M Valpiani G Salvatori G Gildone A Lorusso V Massari L

Objectives. Intramedullary fixation is considered the most stable treatment for pertrochanteric fractures of the proximal femur and cut-out is one of the most frequent mechanical complications. In order to determine the role of clinical variables and radiological parameters in predicting the risk of this complication, we analysed the data pertaining to a group of patients recruited over the course of six years. Methods. A total of 571 patients were included in this study, which analysed the incidence of cut-out in relation to several clinical variables: age; gender; the AO Foundation and Orthopaedic Trauma Association classification system (AO/OTA); type of nail; cervical-diaphyseal angle; surgical wait times; anti-osteoporotic medication; complete post-operative weight bearing; and radiological parameters (namely the lag-screw position with respect to the femoral head, the Cleveland system, the tip-apex distance (TAD), and the calcar-referenced tip-apex distance (CalTAD)). Results. The incidence of cut-out across the sample was 5.6%, with a higher incidence in female patients. A significantly higher risk of this complication was correlated with lag-screw tip positioning in the upper part of the femoral head in the anteroposterior radiological view, posterior in the latero-lateral radiological view, and in the Cleveland peripheral zones. The tip-apex distance and the calcar-referenced tip-apex distance were found to be highly significant predictors of the risk of cut-out at cut-offs of 30.7 mm and 37.3 mm, respectively, but the former appeared more reliable than the latter in predicting the occurrence of this complication. Conclusion. The tip-apex distance remains the most accurate predictor of cut-out, which is significantly greater above a cut-off of 30.7 mm. Cite this article: G. Caruso, M. Bonomo, G. Valpiani, G. Salvatori, A. Gildone, V. Lorusso, L. Massari. A six-year retrospective analysis of cut-out risk predictors in cephalomedullary nailing for pertrochanteric fractures: Can the tip-apex distance (TAD) still be considered the best parameter?. Bone Joint Res 2017;6:481–488. DOI: 10.1302/2046-3758.68.BJR-2016-0299.R1


Bone & Joint Research
Vol. 1, Issue 11 | Pages 310 - 314
1 Nov 2012
Griffin XL Achten J Parsons N Boardman F Griffiths F Costa ML

Fractures of the proximal femur are one of the greatest challenges facing the medical community, constituting a heavy socioeconomic burden worldwide. The National Hip Fracture Audit currently provides a framework for service evaluation. This evaluation is based upon the assessment of process rather than assessment of patient-centred outcome and therefore it fails to provide meaningful data regarding the clinical effectiveness of treatments. This study aims to capture data from the cohort of patients who present with a fracture of the proximal femur at a single United Kingdom Major Trauma Centre. Patient-centred outcomes will be recorded and provide a baseline cohort within which to test the clinical effectiveness of experimental interventions


Bone & Joint Research
Vol. 9, Issue 7 | Pages 368 - 385
1 Jul 2020
Chow SK Chim Y Wang J Wong RM Choy VM Cheung W

A balanced inflammatory response is important for successful fracture healing. The response of osteoporotic fracture healing is deranged and an altered inflammatory response can be one underlying cause. The objectives of this review were to compare the inflammatory responses between normal and osteoporotic fractures and to examine the potential effects on different healing outcomes. A systematic literature search was conducted with relevant keywords in PubMed, Embase, and Web of Science independently. Original preclinical studies and clinical studies involving the investigation of inflammatory response in fracture healing in ovariectomized (OVX) animals or osteoporotic/elderly patients with available full text and written in English were included. In total, 14 articles were selected. Various inflammatory factors were reported; of those tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 are two commonly studied markers. Preclinical studies showed that OVX animals generally demonstrated higher systemic inflammatory response and poorer healing outcomes compared to normal controls (SHAM). However, it is inconclusive if the local inflammatory response is higher or lower in OVX animals. As for clinical studies, they mainly examine the temporal changes of the inflammatory stage or perform comparison between osteoporotic/fragility fracture patients and normal subjects without fracture. Our review of these studies emphasizes the lack of understanding that inflammation plays in the altered fracture healing response of osteoporotic/elderly patients. Taken together, it is clear that additional studies, preclinical and clinical, are required to dissect the regulatory role of inflammatory response in osteoporotic fracture healing.

Cite this article: Bone Joint Res 2020;9(7):368–385.


Bone & Joint Research
Vol. 9, Issue 7 | Pages 402 - 411
1 Aug 2020
Sanghani-Kerai A Coathup M Brown R Lodge G Osagie-Clouard L Graney I Skinner J Gikas P Blunn G

Aims

For cementless implants, stability is initially attained by an interference fit into the bone and osteo-integration may be encouraged by coating the implant with bioactive substances. Blood based autologous glue provides an easy, cost-effective way of obtaining high concentrations of growth factors for tissue healing and regeneration with the intention of spraying it onto the implant surface during surgery. The aim of this study was to incorporate nucleated cells from autologous bone marrow (BM) aspirate into gels made from the patient’s own blood, and to investigate the effects of incorporating three different concentrations of platelet rich plasma (PRP) on the proliferation and viability of the cells in the gel.

Methods

The autologous blood glue (ABG) that constituted 1.25, 2.5, and 5 times concentration PRP were made with and without equal volumes of BM nucleated cells. Proliferation, morphology, and viability of the cells in the glue was measured at days 7 and 14 and compared to cells seeded in fibrin glue.


Bone & Joint Research
Vol. 9, Issue 2 | Pages 71 - 76
1 Feb 2020
Gao T Lin J Zhang C Zhu H Zheng X

Aims

The purpose of this study was to determine whether intracellular Staphylococcus aureus is associated with recurrent infection in a rat model of open fracture.

Methods

After stabilizing with Kirschner wire, we created a midshaft femur fracture in Sprague-Dawley rats and infected the wound with green fluorescent protein (GFP)-tagged S. aureus. After repeated debridement and negative swab culture was achieved, the isolation of GFP-containing cells from skin, bone marrow, and muscle was then performed. The composition and viability of intracellular S. aureus in isolated GFP-positive cells was assessed. We suppressed the host immune system and observed whether recurrent infection would occur. Finally, rats were assigned to one of six treatment groups (a combination of antibiotic treatment and implant removal/retention). The proportion of successful eradication was determined.


Bone & Joint Research
Vol. 7, Issue 2 | Pages 139 - 147
1 Feb 2018
Takahara S Lee SY Iwakura T Oe K Fukui T Okumachi E Waki T Arakura M Sakai Y Nishida K Kuroda R Niikura T

Objectives

Diabetes mellitus (DM) is known to impair fracture healing. Increasing evidence suggests that some microRNA (miRNA) is involved in the pathophysiology of diabetes and its complications. We hypothesized that the functions of miRNA and changes to their patterns of expression may be implicated in the pathogenesis of impaired fracture healing in DM.

Methods

Closed transverse fractures were created in the femurs of 116 rats, with half assigned to the DM group and half assigned to the control group. Rats with DM were induced by a single intraperitoneal injection of streptozotocin. At post-fracture days five, seven, 11, 14, 21, and 28, 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 days five and 11. For further analysis, real-time polymerase chain reaction (PCR) analysis was performed at each timepoint.


Bone & Joint Research
Vol. 7, Issue 3 | Pages 232 - 243
1 Mar 2018
Winkler T Sass FA Duda GN Schmidt-Bleek K

Despite its intrinsic ability to regenerate form and function after injury, bone tissue can be challenged by a multitude of pathological conditions. While innovative approaches have helped to unravel the cascades of bone healing, this knowledge has so far not improved the clinical outcomes of bone defect treatment. Recent findings have allowed us to gain in-depth knowledge about the physiological conditions and biological principles of bone regeneration. Now it is time to transfer the lessons learned from bone healing to the challenging scenarios in defects and employ innovative technologies to enable biomaterial-based strategies for bone defect healing. This review aims to provide an overview on endogenous cascades of bone material formation and how these are transferred to new perspectives in biomaterial-driven approaches in bone regeneration.

Cite this article: T. Winkler, F. A. Sass, G. N. Duda, K. Schmidt-Bleek. A review of biomaterials in bone defect healing, remaining shortcomings and future opportunities for bone tissue engineering: The unsolved challenge. Bone Joint Res 2018;7:232–243. DOI: 10.1302/2046-3758.73.BJR-2017-0270.R1.