Aim of Study and Background. The vertebral endplate (VEP) is characterised as a bilayer of cartilage and bone, acting as a boundary between the disc and the vertebra. The disc being the largest avascular tissue in the body, relies primarily on the nutritional pathways from the vascular network in the adjacent VEP. Disruption of this nutrient supply has been identified as a major contributor to disc degeneration, yet the 3D topology of the network is poorly understood. The aim of this work is the characterisation of this vascular network to further understand the physiology of the vascular network and the correlation between disc degeneration and nutrient supply. Methods and Results. Caudal and cranial VEP sections were sampled from lumbar ovine spines and imaged using high-resolution micro-computed tomography (micro-CT) at 4.92 µm pixel size. The diameter, length, orientation and depth from the VEP surface were measured for individual canals using 3D canal centreline models using ScanIP. The results showed higher concentration of canals in the central regions of the VEP and in caudal VEP to the disc. Large transverse canals were identified running parallel to the VEP surface connected to both the disc and the vertebra, and depth-dependence of the length and diameter of the canals was recorded. Conclusion. This work demonstrates that the micro-CT, coupled with centreline models is an extremely useful tool for the characterisation of the vascular network in the VEP. Further study is required to evaluate the effect of degeneration on the observed patterns and to assess reliability of these results when compared with human VEP. No conflicts of interest. No funding obtained

Introduction. Dual energy X-ray absorptiometry (DEXA) is the gold standard for assessing bone mineral density (BMD) and fracture risk in vivo. However, it has limitations in the spine because vertebrae show marked regional variations in BMD that are difficult to detect clinically. This study investigated whether micro-CT can provide improved estimates of BMD that better predict vertebral strength. Methods. Ten cadaveric vertebral bodies (mean age: 83.7 +/− 10.8 yrs) were scanned using lateral-projection DEXA and Micro-CT. Standardised protocols were used to determine BMD of the whole vertebral body and of anterior/posterior and superior/inferior regions. Vertebral body volume was assessed by water displacement after which specimens were compressed to failure to determine their compressive strength. Specimens were then ashed to determine their bone mineral content (BMC). Parameters were compared using ANOVA and linear regression. Results. Measures of volumetric BMD obtained from Micro-CT were significantly higher than those obtained by DEXA (P<0.001), and estimates using the two techniques were not significantly correlated. DEXA measurements were strongly predictive of compressive strength, with areal BMD of the anterior vertebral body being the best predictor (R. 2. = 0.722, P = 0.002). Micro-CT measurements did not predict strength. Vertebral body BMD (derived from ash weight) correlated more highly with volumetric BMD values obtained from DEXA (R = 0.88) than those obtained from micro-CT (R = 0.72). Conclusion. BMD assessed by lateral DEXA predicted strength and BMC of osteoporotic vertebrae more accurately than micro-CT measures. Poor correlation between BMD measurements from DEXA and micro-CT suggests that ‘phantoms’ used in Micro-CT may require fine-tuning in order to better represent osteoporotic vertebrae

Aims. Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques. Methods. Micro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S. 4. ). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads. Results. Experimental pull-out strengths were excellently correlated to the µFE pull-out stiffness of the ROI (R. 2. > 0.87) and FV (R. 2. > 0.84) models. No significant difference due to screw design was observed. Cement augmentation increased pull-out stiffness by up to 94% and 48% for L and R screws, respectively, but only increased bending stiffness by up to 6.9% and 1.5%, respectively. Cementing involving only one screw tip resulted in lower stiffness increases in all tested screw designs and loading cases. The stiffening effect of cement augmentation on pull-out and bending stiffness was strongly and negatively correlated to local bone density around the screw (correlation coefficient (R) = -0.95). Conclusion. This combined experimental, µCT and µFE study showed that regional analyses may be sufficient to predict fixation strength in pull-out and that full analyses could show that cement augmentation around pedicle screws increased fixation stiffness in both pull-out and bending, especially for low-density bone. Cite this article: Bone Joint Res 2021;10(12):797–806

To determine whether spinal facet osteoblasts at the curve apex display a different phenotype to osteoblasts from outside the curve in patients with adolescent idiopathic scoliosis (AIS). Intrinsic differences in the phenotype of spinal facet bone tissue and in spinal osteoblasts have been implicated in the pathogenesis of AIS. However, no study has compared the phenotype of facet osteoblasts at the curve apex with the facet osteoblasts from outside the curve in patients with AIS. Facet bone tissue was collected from three sites, the concave and convex side at the curve apex and from outside the curve from three female patients with AIS (aged 13–16 years). Micro-CT analysis was used to determine the density and trabecular structure. Osteoblasts were then cultured from the sampled bone. Osteoblast phenotype was investigated by assessing cellular proliferation (MTS assay), cellular metabolism (alkaline phosphatase and Seahorse Analyser), bone nodule mineralisation (Alizarin red assay), and the mRNA expression of Wnt signalling genes (quantitative RT-PCR). Convex bone showed greater bone mineral density and trabecular thickness than did concave bone. The convex side of the curve apex exhibited a significantly higher proliferative and metabolic phenotype and a greater capacity to form mineralised bone nodules than did concave osteoblasts. mRNA expression of SKP2 was significantly greater in both concave and convex osteoblasts than in non-curve osteoblasts. The expression of SFRP1 was significantly downregulated in convex osteoblasts compared with either concave or non-curve. Intrinsic differences that affect osteoblast function are exhibited by spinal facet osteoblasts at the curve apex in patients with AIS

We evaluated the efficacy of Escherichia coli-derived recombinant human bone morphogenetic protein-2 (E-BMP-2) in a mini-pig model of spinal anterior interbody fusion. A total of 14 male mini-pigs underwent three-level anterior lumbar interbody fusion using polyether etherketone (PEEK) cages containing porous hydroxyapatite (HA). Four groups of cages were prepared: 1) control (n = 10 segments); 2) 50 μg E-BMP-2 (n = 9); 3) 200 μg E-BMP-2 (n = 10); and 4) 800 μg E-BMP-2 (n = 9). At eight weeks after surgery the mini-pigs were killed and the specimens were evaluated by gross inspection and manual palpation, radiological evaluation including plain radiographs and micro-CT scans, and histological analysis. Rates of fusion within PEEK cages and overall union rates were calculated, and bone formation outside vertebrae was evaluated. One animal died post-operatively and was excluded, and one section was lost and also excluded, leaving 38 sites for assessment. This rate of fusion within cages was 30.0% (three of ten) in the control group, 44.4% (four of nine) in the 50 μg E-BMP-2 group, 60.0% (six of ten) in the 200 μg E-BMP-2 group, and 77.8% (seven of nine) in the 800 μg E-BMP-2 group. Fusion rate was significantly increased by the addition of E-BMP-2 and with increasing E-BMP-2 dose (p = 0.046). In a mini-pig spinal anterior interbody fusion model using porous HA as a carrier, the implantation of E-BMP-2-loaded PEEK cages improved the fusion rate compared with PEEK cages alone, an effect that was significantly increased with increasing E-BMP-2 dosage. Cite this article: Bone Joint J 2013;95-B:217–23

Background. We have reported an injectable L-pNIPAM-co-DMAc hydrogel with hydroxyaptite nanoparticles (HAPna) which promotes mesenchymal stem cell (MSC) differentiation to bone cells without the need for growth factors. This hydrogel could potentially be used as an osteogenic and osteoconductive bone filler of spinal cages to improve vertebral body fusion. Here we investigated the biocompatibility and efficacy of the hydrogel in vivo using a proof of concept femur defect model. Methods. Rat sub-cut analysis was performed to investigate safety in vivo. A rat femur defect model was performed to evaluate efficacy. Four groups were investigated: sham operated controls; acellular L-pNIPAM-co-DMAc hydrogel; acellular L-pNIPAM-co-DMAc hydrogel with HAPna; L-pNIPAM-co-DMAc hydrogel with rat MSCs and HAPna. Following 4 weeks, defect site and organs were histologically examined to determine integration, repair and inflammatory response, as well as Micro-CT to assess mineralisation. Results. No inflammatory reactions or toxicity were seen in any animal. Enhanced bone healing was observed in aged exbreeder female rats where hydrogel was injected with increased deposition of collagen type I. Integration of the hydrogel with surrounding bone was observed without the need for delivered MSCs; native cell infiltration was also seen and bone formation was observed within all hydrogel systems investigated. Conclusion. This novel hydrogel is biocompatible, facilitates migration of cells, promotes increased bone formation and integrates with surrounding bone. This system could be injected to fill spaces within and surrounding spinal cages to aid in cage fixation and spinal fusion without the need for harvesting of bone autografts, thus reducing operative risk and surgical cost. Conflicts of Interest: None. Source of Funding: BMRC, MERI Sheffield Hallam University

Introduction. Decreasing endplate porosity has been proposed as a risk factor for intervertebral disc degeneration, because it interferes with disc metabolite transport. However, endplate porosity has recently been shown to increase with age and disc degeneration. We hypothesise that this increase reflects adaptive remodelling in response to altered loading from adjacent discs. Methods. Nineteen cadaver motion segments (61–98 yrs) were compressed to 1kN while a pressure-transducer was pulled across the mid-sagittal diameter of the disc. Stress profiles indicated nucleus (intradiscal) pressure (IDP) and maximum stress in the anterior and posterior annulus. Subsequently, micro-CT was used to evaluate endplate porosity along the antero-posterior diameter of the adjacent endplates. Data were analysed using ANOVA and linear regression. Results. Endplate porosity averaged 67% centrally (where IDP averaged 0.85MPa) and decreased steadily to 48% and 53% in the anterior and posterior periphery, where maximum stresses were 1.37MPa and 1.33MPa, respectively. In each region, porosity was inversely related to IDP (or maximum stress) with R. 2. = 0.49, 0.32 and 0.31 respectively (P<0.001 in each case). Porosity was 3% higher in the inferior (weaker) endplate of the disc compared to the superior endplate (P=0.07). Conclusion. In old spines, strong correlations between endplate porosity and stress in each anatomical region indicate mechanically-adaptive remodelling. Regional differences in endplate porosity (across the antero-posterior diameter) probably reflect the varying nutritional demands of nucleus and annulus, as well as adaptations to loading from an adjacent decompressed disc. In younger age-groups, high loading could possibly reduce endplate porosity, promoting disc degeneration

Introduction. Disc degeneration is often scored using macroscopic and microscopic scoring systems. Although reproducible, these scores may not accurately reflect declining function in a degenerated disc. Accordingly, we compared macroscopic and microscopic degeneration scores with measurements of disc function. Methods. Thirteen cadaveric motion segments (62–93 yrs) were compressed to 1kN while a pressure-transducer was pulled across the mid-sagittal diameter of the disc. Resulting stress profiles indicated intradiscal pressure (IDP), and maximum stress in the anterior (MaxStress_Ant) and posterior (MaxStress_Post) annulus. Macroscopic grade (1–4) of disc degeneration was based on visual examination of mid-sagittal sections, using subscales that yielded a maximum score of 48. Microscopic grade (1–4) was based on histological sections of the disc + vertebral body taken from anterior annulus, nucleus pulposus and posterior annulus, using subscale scores that totalled 108. Cartilage endplate thickness (CEP_thickness) was measured histologically, and porosity of the bony endplates was measured using micro-CT. ANOVA was used to compare between grades, and regression was used to establish dependence on scores. Results. IDP and CEP_thickness both decreased with increasing macroscopic grade (1–4) of degeneration (P= 0.021 & 0.022 respectively). Also, IDP, CEP_thickness and MaxStress_Ant decreased with increasing macroscopic score (1–48) (R. 2. = 0.39, P = 0.022; R. 2. = 0.36, P = 0.03; R. 2. = 0.30, P = 0.04 respectively). IDP and MaxStress_Ant decreased with increasing microscopic grade (1–4) of degeneration (P=0.05 & 0.005 respectively) and increasing microscopic score (1–108) (R. 2. = 0.36, P = 0.02; R. 2. = 0.47, P = 0.009 respectively) whereas inferior endplate porosity increased with increasing microscopic grade (P = 0.05) and score (R. 2. = 0.36, P = 0.03). Conclusion. Macroscopic and microscopic ‘degeneration’ scores both reflect changes in disc function and endplate integrity

To investigate and compare the biomechanical characteristics of Bipedicular versus Unipedicular Vertebroplasty in cadaveric vertebra. Cadaveric single level vertebra were used to evaluate Bipedicular versus Unipedicular Vertebroplasty as an intervention for vertebral compression fractures. Cadaveric vertebra were assigned to two arms: Arm A simulated a wedge fracture followed by bipedicular cement augmentation; Arm B simulated a wedge fracture followed by unipedicular cement augmentation. Micro-CT imaging was performed to assess vertebral dimension, cement fill volumes and bone mineral density. All augmented specimens were then compressed under a static eccentric flexion load to failure. Pre and post augmentation failure load and stiffness were used to compare the two groups. Results suggest, when compared with actual failure strength, that the product of bone mineral density and endplate surface area gave a good prediction of failure strength for specimens in both arms. The mean cement volume fill of augmented vertebral bodies was 22.8% ± 7.21%. The bipedicular group showed a reduction in stiffness but an increase in post augmentation failure load of 1.09. The unipedicular group also showed a reduction in stiffness but showed a much greater increase in post augmentation failure load of 1.68. Preliminary data from this study suggests there is a significant reduction in stiffness following both bipedicular and unipedicular vertebroplasty. There is a significant increase in failure load post augmentation in the unipedicular group

To investigate whether restoration of mechanical function and spinal load-sharing following vertebroplasty depends upon cement distribution. Fifteen pairs of cadaver motion segments (51-91 yr) were loaded to induce fracture. One from each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Various mechanical parameters were measured before and after vertebroplasty. Micro-CT was used to determine volumetric cement fill, and plane radiographs (sagittal, frontal, and axial) to determine areal fill, for the whole vertebral body and for several specific regions. Correlations between volumetric fill and areal fill for the whole vertebral body, and between regional volumetric fill and changes in mechanical parameters following vertebroplasty, were assessed using linear regression. For Cortoss, areal and volumetric fills were significantly correlated (R=0.58-0.84) but cement distribution had no significant effect on any mechanical parameters following vertebroplasty. For PMMA, areal fills showed no correlation with volumetric fill, suggesting a non-uniform distribution of cement that influenced mechanical outcome. Increased filling of the vertebral body adjacent to the disc was associated with increased intradiscal pressure (R=0.56, p<0.05) in flexed posture, and reduced neural arch load bearing (F. N. ) in extended posture (R=0.76, p<0.01). Increased filling of the anterior vertebral body was associated with increased bending stiffness (R=0.55, p<0.05). Cortoss tends to spread evenly within the vertebral body, and its distribution has little influence on the mechanical outcome of vertebroplasty. PMMA spreads less evenly, and its mechanical benefits are increased when cement is concentrated in the anterior vertebral body and adjacent to the intervertebral disc

Introduction. Although the association between osteoporosis and adolescent idiopathic scoliosis (AIS) has become widely accepted, the mechanism behind the development of osteoporosis and AIS remains unknown. To elucidate this relationship, we investigated the radiological and histological changes in a model of scoliosis in chickens, focusing on the cervical vertebrae that are not affected by scoliosis. Methods. 40 newly hatched broiler chickens were divided randomly into four equal groups: sham-operated chickens serving as control (CNT); pinealectomised chickens (PNX); and sham-operated (CNT+MLT) and pinealectomized chickens (PNX+MLT) that received intraperitoneal administration of MLT (8 mg/kg) at 2200 h daily. Pinealectomies were done at the age of 3 days. Before killing the chickens at 2 months of age, blood samples were collected at midnight and MLT concentrations were measured by radioimmunoassay. Post-mortem radiographs were examined for the presence of scoliosis, and microcomputed tomography (micro-CT) images were taken to assess the microstructure of the cervical vertebrae. Histological specimens of the scanned cervical vertebra were prepared, and a mid-sagittal section was stained with haematoxylin and eosin (HE) and tartrate-resistant acid phosphatase (TRAP) to assess the numbers of osteoblasts and osteoclasts, respectively. Results. Scoliosis developed at the thoracic spine in all chickens in the PNX group and in two of the PNX+MLT group. MLT concentrations in the PNX group were substantially reduced, whereas normal concentrations were restored in the PNX+MLT group and were normal in the CNT and CNT+MLT groups. Micro-CT data showed that chickens in the PNX group had a greater degree of generalised osteoporosis than did those in the other groups. The number of osteoblasts was significantly decreased in the PNX group, whereas we recorded no significant difference between the CNT, CNT+MLT, and PNX+MLT groups. The number of osteoclasts was similar in all groups. Conclusions. Our results suggest that MLT deficiency reduces osteoblast proliferation and leads to the development of scoliosis and osteoporosis. The restoration of MLT prevented the development of scoliosis and osteoporosis, indicating that MLT concentrations might be crucial to the development of scoliotic deformity and osteoporosis in AIS