Analysis of the stress-strain state of the spine model with posterior fusion in the treatment of scoliotic deformities in children

Background. Mathematical modeling of the correction of scoliotic deformities of the spine makes it possible to analyze the effectiveness of various methods of treatment without surgical intervention. In the study of traction, mainly experimental methods were used. The purpose was to investigate the stress-strain state of the spine models with varying degrees of scoliotic deformity during posterior spinal fusion. Materials and methods. Deformities of the spine of 40, 70 and 100° were modeled, with posterior spondylodesis of the Th1-Th12 vertebrae. A load of 300 N was used. Results. With a deformity of 40°, the most stressed are the areas of frontal plane curve. For the upper vertebrae Th1-Th4, a more even distribution of stress over the vertebral body is observed. For Th5-Th10 vertebrae, the concave side of the vertebral bodies is more stressed. In the thoracic spine, the more stressed vertebrae are Th2 and Th5. The main load is borne by the fixing structure, in which the level of stress is significantly higher than in the bone structures of the vertebrae. In the posterior supporting complex of the vertebrae, the stress concentration areas are located at the points where fixing screws enter the bone. An increase in the magnitude of the scoliotic deformity of the spine up to 70° causes an increase in the level of stresses in all elements of the model, with the exception of Th9-Th10 vertebrae. With a deformity of 100° in the posterior supporting complex of the vertebrae, the stress concentration areas are located at the points where fixing screws enter the bone. The stress level of 116.0 MPa exceeds the ultimate strength of the cortical layer of the bone tissue of the spine, which can lead to microdamage of the bone tissue and loosening of the screws. Conclusions. For all values of scoliotic deformity of the spine, the most stressed are Th4 and Th5 vertebrae. A decrease in the degree of deformity has a significant effect on the stress-strain state of the spinal column. In the Th4 vertebral body, the level of stresses with a deformity of 100° is more than twice as high as with a deformity of 70°, and more than 4 times higher than with a deformity of 40°. In the body of the Th5 vertebra, the stress level with a deformity of 70° is 1.5 times less than with a deformity of 100°, and with a deformity of 40°, it is 3 times less. The level of stress in the Th1-Th5 vertebral bodies is higher than that of Th6-Th12. In the posterior supporting complex, at the points where screws enter the bone, the maximum stress value at a deformity of 40° is 34.0 MPa, which is not critical for the bone tissue. With a deformity of 70°, the stresses are 85.0 MPa, which can exceed the ultimate strength for the cortical bone and lead to microdestruction of the bone tissue in the screw-bone contact area. With a deformity of 100°, the stresses are equal to 116.0 MPa, which exceeds the ultimate strength for the cortical bone and can lead to microfracture in the screw-bone contact area.

Heparin Enriched-WPI Coating on Ti6Al4V Increases Hydrophilicity and Improves Proliferation and Differentiation of Human Bone Marrow Stromal Cells

Titanium alloy (Ti6Al4V) is one of the most prominent biomaterials for bone contact because of its ability to bear mechanical loading and resist corrosion. The success of Ti6Al4V implants depends on bone formation on the implant surface. Hence, implant coatings which promote adhesion, proliferation and differentiation of bone-forming cells are desirable. One coating strategy is by adsorption of biomacromolecules. In this study, Ti6Al4V substrates produced by additive manufacturing (AM) were coated with whey protein isolate (WPI) fibrils, obtained at pH 2, and heparin or tinzaparin (a low molecular weight heparin LMWH) in order to improve the proliferation and differentiation of bone-forming cells. WPI fibrils proved to be an excellent support for the growth of human bone marrow stromal cells (hBMSC). Indeed, WPI fibrils were resistant to sterilization and were stable during storage. This WPI-heparin-enriched coating, especially the LMWH, enhanced the differentiation of hBMSC by increasing tissue non-specific alkaline phosphatase (TNAP) activity. Finally, the coating increased the hydrophilicity of the material. The results confirmed that WPI fibrils are an excellent biomaterial which can be used for biomedical coatings, as they are easily modifiable and resistant to heat treatments. Indeed, the already known positive effect on osteogenic integration of WPI-only coated substrates has been further enhanced by a simple adsorption procedure.

Indigenous built structures and anthropogenic impacts on the stratigraphy of Northern Australian rockshelters: insights from Malarakk 1, north western Arnhem Land

Malarrak 1 is currently the northernmost excavated rockshelter on the Australian mainland, located in the Wellington Range in north western Arnhem Land. The site contains a rich late Holocene deposit, with extensive contact rock art, stone artefacts, shell, bone, contact materials, ancestral human remains, and other cultural material. Excavation of the Malarrak 1 rockshelter and analysis of its sediments revealed many impacts on site formation processes within the deposit. We attribute the disturbance to possible erosion or sediment deposition during periods of intense rainfall and also to the construction of timber structures within the site. This is supported by modern and historical observations and is the focus of this paper. The extent of the disturbance to Malarrak 1 provides a cautionary tale for other excavations in the region that may be affected by similar Indigenous site occupation, as these anthropogenic activities enhance the risk of further impacts arising from biological and geomorphological processes that can impinge on the stratigraphic integrity of the cultural deposits.

Current Concepts of Surface Topography of Implants: A Review

Both the rate of osseointegration and its extent depend upon the characteristics of the implant surface.1 2 3 4 5 Depending on the surface of the implant determination of implant–bone contact area, the rate of bone formation around the implant can be done.6 Hence, the implant surface plays an important part in multiple ways in the osseointegration process.

An Efficient One-Step Moment Balancing Algorithm for Computing Medial and Lateral Knee Compartment Contact Forces

The knee adduction moment is associated with the progression of knee osteoarthritis (OA). The adduction moment reflects the net effect of muscles, passive tissues and bone-on-bone contact forces. Medial compartment OA is more common than lateral and therefore our ability to correctly partition bone-on-bones forces across the medial and lateral compartments is key to understanding mechanical factors associated with the onset and progression of knee OA. We have used frontal plane moment balancing to resolve medial and lateral compartment forces. In this technical brief we present an alternate and more efficient methodology, the 1-step approach, linking the sagittal and frontal planes in the determination of muscle forces. Muscle forces are the dominant contributors to knee joint loading and therefore our ability to predict compartmental contact is dependent on our ability to predict muscle forces. The 1-step approach introduces a penalty function limiting total compressive force from acting in the lateral compartment whenever the internal moment is net abduction (i.e., external knee adduction). Total compressive force in the lateral compartment implies greater lateral loading compared to medial, and this is inconsistent with what we know about the knee adduction moment and medial-to-lateral force distribution during gait. An EMG-driven musculoskeletal model with modified hamstrings EMG was implemented to demonstrate the 1-step methodology and compare results with frontal plane moment balancing. The 1-step approach is a more efficient methodology that can be used in place of frontal plane moment balancing.

Existing Bone-Derived Bone Morphogenetic Protein-2 Initiates Contact Osteogenesis on the Surface of a Titanium Implant

The dental implant relies on osseointegration and the response of bone to the implant surface. This process comprises bidirectional bone formation, including bone deposition on the implant surface toward the existing bone (contact osteogenesis) and vice versa (distance osteogenesis). It is unclear whether these processes are independent or whether contact osteogenesis is initiated by other factors. Therefore, this study aimed to identify the initiator of contact osteogenesis. We hypothesized that contact osteogenesis does not occur when it is physically isolated from distance osteogenesis, which would imply that some factors from the wounded bone normally promote contact osteogenesis. Using a rabbit tibial implant model, we tested the effects of human recombinant bone morphogenetic protein-2 (BMP-2) and plasma-rich plasma, which are possible initiators from bone and blood, respectively. Titanium implants with BMP-2 showed a better bone-to-implant contact (BIC) ratio. We concluded that BMP-2 initiated contact osteogenesis on the surface of titanium implants.

Hip implants can restore anatomical and medialized rotation centres in most cases

Aims Hip arthroplasty does not always restore normal anatomy. This is due to inaccurate surgery or lack of stem sizes. We evaluated the aptitude of four total hip arthroplasty systems to restore an anatomical and medialized hip rotation centre. Methods Using 3D templating software in 49 CT scans of non-deformed femora, we virtually implanted: 1) small uncemented calcar-guided stems with two offset options (Optimys, Mathys), 2) uncemented straight stems with two offset options (Summit, DePuy Synthes), 3) cemented undersized stems (Exeter philosophy) with three offset options (CPT, ZimmerBiomet), and 4) cemented line-to-line stems (Kerboul philosophy) with proportional offsets (Centris, Mathys). We measured the distance between the templated and the anatomical and 5 mm medialized hip rotation centre. Results Both rotation centres could be restored within 5 mm in 94% and 92% of cases, respectively. The cemented undersized stem performed best, combining freedom of stem positioning and a large offset range. The uncemented straight stem performed well because of its large and well-chosen offset range, and despite the need for cortical bone contact limiting stem positioning. The cemented line-to-line stem performed less well due to a small range of sizes and offsets. The uncemented calcar-guided stem performed worst, despite 24 sizes and a large and well-chosen offset range. This was attributed to the calcar curvature restricting the stem insertion depth along the femoral axis. Conclusion In the majority of non-deformed femora, leg length, offset, and anteversion can be restored accurately with non-modular stems during 3D templating. Failure to restore hip biomechanics is mostly due to surgical inaccuracy. Small calcar guided stems offer no advantage to restore hip biomechanics compared to more traditional designs. Cite this article: Bone Jt Open 2021;2(7):476–485.