Aims

The “2 to 10% strain rule” for fracture healing has been widely interpreted to mean that interfragmentary strain greater than 10% predisposes a fracture to nonunion. This interpretation focuses on the gap-closing strain (axial micromotion divided by gap size), ignoring the region around the gap where osteogenesis typically initiates. The aim of this study was to measure gap-closing and 3D interfragmentary strains in plated ovine osteotomies and associate local strain conditions with callus mineralization.

Intramedullary nails (IMNs) are the current gold standard for treatment of long bone diaphyseal and selected metaphyseal fractures. Their design has undergone many revisions to improve fixation techniques, conform to the bone shape with appropriate anatomic fit, reduce operative time and radiation exposure, and extend the indication of the same implant for treatment of different fracture types with minimal soft tissue irritation. The IMNs are made or either titanium alloy or stainless steel and work as load-sharing internal splints along the long bone, usually accommodating locking elements – screws and blades, often featuring angular stability and offering different configurations for multiplanar fixation – to secure secondary fracture healing with callus formation in a relative-stability environment. Bone cement augmentation of the locking elements can modulate the construct stiffness, increase the surface area at the bone-implant interface, and prevent cut-through of the locking elements. The functional requirements of IMNs are related to maintaining fracture reduction in terms of length, alignment and rotation to enhance fracture healing. The load distribution during patient's activities is along the entire bone-nail interface, with nail length and anatomic fit being important factors to avoid stress risers

The course of secondary fracture healing typically consists of four major phases including inflammation, soft and hard callus formation, and bone remodeling. Callus formation is promoted by mechanical stimulation, yet little is known about the healing tissue response to strain stimuli over shorter timeframes on hourly and daily basis. The aim of this study was to explore the hourly, daily and weekly variations in bone healing progression and to analyze the short-term response of the repair tissue to well-controlled mechanical stimulation. A system for continuous monitoring of fracture healing was designed for implantation in sheep tibia. The experimental model was adapted from Tufekci et al. 2018 and consisted of 3 mm transverse osteotomy and 30 mm bone defect resulting in an intermediate mobile bone fragment in the tibial shaft. Whereas the distal and proximal parts of the tibia were fixed with external fixator, the mobile fragment was connected to the proximal part via a second, active fixator. A linear actuator embedded in the active fixator moved the mobile fragment axially, thus stimulating mechanically the tissue in the osteotomy gap via well-controlled displacement being independent from the sheep's functional weightbearing. A load sensor was integrated in the active fixation to measure the force acting in the osteotomy gap. During each stimulation cycle the displacement and force magnitudes were recorded to determine in vivo fracture stiffness. Following approval of the local ethics committee, experiments were conducted on four skeletally mature sheep. Starting from the first day after surgery, the daily stimulation protocols consisted of 1000 loading events equally distributed over 12 hours from 9:00 to 21:00 resulting in a single loading event every 44 seconds. No stimulation was performed overnight. One animal had to be excluded due to inconsistencies in the load sensor data. The onset of tissue stiffening was detected around the eleventh day post-op. However, on a daily basis, the stiffness was not steadily increasing, but instead, an abrupt drop was observed in the beginning of the daily stimulations. Following this initial drop, the stiffness increased until the last stimulation cycle of the day. The continuous measurements enabled resolving the tissue response to strain stimuli over hours and days. The presented data contributes to the understanding of the influence of patient activity on daily variations in tissue stiffness and can serve to optimize rehabilitation protocols post fractures

Objectives. Secondary fracture healing is strongly influenced by the stiffness of the bone-fixator system. Biomechanical tests are extensively used to investigate stiffness and strength of fixation devices. The stiffness values reported in the literature for locked plating, however, vary by three orders of magnitude. The aim of this study was to examine the influence that the method of restraint and load application has on the stiffness produced, the strain distribution within the bone, and the stresses in the implant for locking plate constructs. Methods. Synthetic composite bones were used to evaluate experimentally the influence of four different methods of loading and restraining specimens, all used in recent previous studies. Two plate types and three screw arrangements were also evaluated for each loading scenario. Computational models were also developed and validated using the experimental tests. Results. The method of loading was found to affect the gap stiffness strongly (by up to six times) but also the magnitude of the plate stress and the location and magnitude of strains at the bone-screw interface. Conclusions. This study demonstrates that the method of loading is responsible for much of the difference in reported stiffness values in the literature. It also shows that previous contradictory findings, such as the influence of working length and very large differences in failure loads, can be readily explained by the choice of loading condition. Cite this article: A. MacLeod, A. H. R. W. Simpson, P. Pankaj. Experimental and numerical investigation into the influence of loading conditions in biomechanical testing of locking plate fracture fixation devices. Bone Joint Res 2018;7:111–120. DOI: 10.1302/2046-3758.71.BJR-2017-0074.R2

Secondary fracture healing processes are strongly influenced by interfragmentary motion. Shear movement is assumed to be more critical than axial movement, however experimental results are controversial. Numerical fracture healing models allow to simulate the fracture healing process with variation of single input parameters and under comparable normalized mechanical conditions. Therefore, a direct comparison of different in vivo scenarios is possible. The aim of this study was to simulate fracture healing under several axial and shear movement scenarios and compare their respective time to heal. We hypothesize that shear movement is always more critical than axial loading. For the presented study, we used a corroborated numerical model for fracture healing in sheep. Numerous variations of the movement amplitude, the fracture gap size and the musculoskeletal loads were simulated for comparable axial compressive and shear load cases. In all simulated cases, axial compressive load had less inhibitory influences on the healing process than shear load. Therefore, shear loading is more critical for the fracture healing outcome in general. Thus, our findings suggest osteosynthesis implants to be optimized to limit shear movements under musculoskeletal loading

Introduction VEGF is a well known angiogenic peptide which has been shown to be central to endochondral ossification. Secondary fracture healing involves a combination of intramembranous and endochondral ossification. VEGF has been recently shown to be chemotactic for osteoblasts and chondroclasts. We therefore set out to examine the temporal and spatial expression of VEGF and its receptors in fracture healing. We report here the preliminary findings of our study. Methods A closed mid-shaft fracture was produced in the right femora of nine 12 week old Sprague Dawley rats, stabilised by an intramedullary K-wire. The rats were sacrificed at one, two and four weeks. Through the use of immunohistochemistry, RT-PCR and in situ hybridisation. Results We show that at each of the time points, VEGF is expressed in all of the cell types involved in fracture healing; the inflammatory cells, the osteo-progenitor cells,chondroblasts,chondrocytes,osteoblasts and osteoclasts as well as fibroblasts. We further show that there is persistent expression of VEGF in chondrocytes at four weeks. Conclusions Our findings are consistent with the hypothesis that events in fracture healing reflect the processes that take place at the growth plate during embryonic development

Introduction: The addition of recombinant human bone morphogenetic protein-2 (rhBMP-2) showed significant reduction of secondary intervention, fracture healing time and infection rates compared with intramedullary nailing alone in open tibia fractures. However, the upfront price of approx. 3000 € is a barrier to its regular use. The goal of the study was to determine potential cost savings and cost-effectiveness of rhBMP-2 in grade III open tibia fractures from the perspective of the UK National Health Service (NHS) and the German Health Care System and to derive conclusions for other European health care systems. Materials and Methods: Clinical data from a previously published randomised controlled study with 450 patients (“BESTT study”) were used to generate total treatment costs for each patient for the control and the 1.5 mg/ml BMP-2 group based on the current German-DRG and the NHS for UK. The analysis was performed from a health care system and a societal perspective for a one year time horizon. Furthermore, assessment of the cost-effectiveness of BMP-2 was done by utility analysis. Results: The use of BMP-2 for grade III open tibia fractures is leading to cost savings of 3183 € per case and, therefore, to net savings for the German health care system. The main driver for cost savings is faster fracture healing with faster resumption of work and reduced expenses for sickness leave payments. For the UK rhBMP-2 is a cost-effective strategy with a cost-effectiveness ratio of approx. £11,000/QALY which is well below the standard £30,000 benchmark for the NHS. From a societal perspective, rhBMP-2 is a cost-saving treatment. Conclusions: BMP-2 leads to net savings in grade III open tibia fractures in Germany which can be expected for other European countries where sickness payments are provided by health care insurers. For countries like UK where sickness are provided by third parties BMP-2 is a cost-effective treatment strategy from a health care system perspective and a cost-saving treatment from a societal perspective

Purpose: Inverted pediculated fasciocutaneous flap is an alternative to microanastomosed free flap for cover of tissue loss of the lower third of the leg in trauma victims. We report our experience in fourteen patients. Material and methods: Fifteen fasciocutaneous inverted pediculated island flaps were performed in fourteen trauma victims with major tissue loss of the lower limbs. Mean age was 42 year (range 24 – 70). There were thirteen men and one woman. The fracture was located on the lower third of the leg and involved the diaphysome-taphyseal junction in thirteen patients (associated with loss of heal tissue on one), the fibular malleolus in one and the tibial column in one. The Gustilo classification was two grade 0, three grade I, eight grade IIIB, and one grade IIIC. Four patients were given first-intention treatment. For the referral patients treated secondarily, three had a dehiscent wound with an exposed fixation plate. A supramalleolar lateral flap was used in six patients (40%), a sural neurocutaneous flap with a distal pedicle in seven (47%), and a sural neurocutaneous flap with a distal pedicle in two (13%). Seven patients (50%) had a bone graft. Results: Wound healing was achieved in thirteen patients, with three infectious complications. The one failure involved a sural neurocutaneous flap (grade IIIC fracture). The fixation plate was preserved under the flap in one patient who developed secondary nonunion. Fracture healing was achieved in all cases. Discussion: Use of island fasciocutaneous flaps with a distal pedicle for the treatment of tissue loss of the lower third of the leg has grown steadily since the introduction of the concept. The principal advantage, beyond the simplicity of the flap procedure, is to spare locoregional vessel and muscle stock. Our series confirmed that this method can give good results if the flaps are carefully planned. This method should not be recommended as an emergency procedure. Combining two fasciocutaneous flaps could be a salvage solution in certain cases where the trauma context implies less concentration in the aesthetic and sensorial result. Conclusion: Use of fasciocutaneous flaps with a distal pedicle is a first choice solution for covering tissue loss of the lower third of the leg and foot. This method should not be proposed as an emergency procedure

This paper reviews the current literature concerning the main clinical factors which can impair the healing of fractures and makes recommendations on avoiding or minimising these in order to optimise the outcome for patients. The clinical implications are described.