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

Aims

The aim of this study was to compare outcomes after growth-friendly treatment for early-onset scoliosis (EOS) between patients with skeletal dysplasias versus those with other syndromes.

Introduction. Adolescent idiopathic scoliosis (AIS) is associated with low bone mineral density, which could be related to its etiopathogenesis. Apart from bone density, bone micro-architectures are equally important for better understanding of disease initiation and progression in AIS. Quantitative assessment of bone quality is hampered by the invasive nature of investigations, until recently when the high-resolution pQCT (XtremeCT) became available for revolutionary in-vivo microimaging and derivation of bone micro-architectural parameters. Our objective was to use this powerful instrument to study bone qualities in AIS and compare findings with those from healthy controls. Methods. 48 girls with AIS and 84 sex-matched healthy controls were recruited. Cobb angle was measured with standing radiographs, and imaging of the non-dominant distal radius was captured with XtremeCT according to a standard protocol. Results. The mean age was 13·48 years for controls and 13·54 years for patients with AIS (p=0·773). The mean Cobb's angle for AIS was 32·7° (SD 5·8°). Volumetric bone density, cortical thickness, trabecular bone density, meta-trabecular density, inner-trabecular density, bone volume fraction, and trabecular thickness were all lower in patients with AIS than in controls, and differences were statistically significant (p<0·05). Conclusions. This is the first report describing the differences in radiographic bone micro-architectures between patients with AIS and controls. All significant parameters were lower in the AIS group, indicating deranged bony quality that could have an important role in disease initiation or progression in AIS. The exact biomechanical process and how this is related to the etiopathogenesis of AIS warrant further studies. Acknowledgments. This study is supported by RGC-HKSAR (project number 467808 and 468809)

Introduction. The main challenge in management of adolescent idiopathic scoliosis (AIS) is to predict which curve will progress so that appropriate treatment can be given. We previously reported that low bone mineral density (BMD) was one of the adverse prognostic factors for AIS. With advancement in imaging technology, quantitative ultrasound (QUS) becomes a useful method to assess bone density and bone quality. The objective of this study was to assess the role of QUS as a radiation-free method to predict curve progression in AIS. Methods. 294 girls with AIS were recruited at ages 11–16 years and followed up until skeletal maturity. 269 age-matched healthy girls were recruited as controls. They provided the normal reference for calculation of Z score for QUS parameters. QUS measurements, including BUA (broadband ultrasound attenuation), VOS (velocity of sound) and SI (stiffness index) of the calcaneum, BMD of femoral neck, menarche history, ages, and Cobb angle of the major curve were recorded at baseline as independent variables. The predictive outcome was curve progression defined as an increase of Cobb angle of 6° or more. Logistic regression model and the ROC curve were used for statistical analysis. Results. Mean follow-up was 3·4 years (SD 1·57). At baseline, mean age was 13·4 years (1·23), 73 (24·8%) patients were premenarchal, and mean Cobb angle was 26·3° (SD 8·2°). 202 (68·7%), 194 (66%), and 202 (68·7%) of patients with AIS had Z score of BUA, VOS, and SI of 0 or less, respectively. Initial univariate analysis indicated all independent variables had p values less than 0.2. Logistic regression analysis indicated that the p values of their regression coefficients were: age (p<0·001), menarchal status (p<0·001), Cobb angle (p=0·008), BMD (p=0·084), BUA (p=0·722), VOS (p=0·112), and SI (p=0·027). SI, age, menarchal status, and Cobb angle were therefore included in the final prediction equation. The adjusted odds ratio for Z score of SI of 0 or less was 2·00 (95% CI 1·08–3·71). The area under the ROC curve was 0·831(95% CI 0·785–0·877). The predictive model had a sensitivity of 0·847 and a specificity of 0·665 at a probability cutoff of 0·368. Conclusions. We recorded evidence of deranged bone density and bone quality in AIS, as indicated by QUS investigation. SI is an independent and significant prognostic factor for AIS. It can be used as a radiation-free parameter to predict curve progression in combination with initial Cobb angle, age, and menarchal status, especially when DXA is not available. Acknowledgments. This study is supported by Research Grant Council—The government of HKSAR (project number CUHK4498/06M)

Introduction/Aim. Intra-operative localisation of thoracic spine levels can be difficult due to anatomical constraints such as scapular shadow, patient's size and poor bone quality. This is particularly true in cases of thoracic discectomies in which the vertebral bodies appear normal. We describe a simple and reliable technique to identify the correct thoracic spine level. Methods. After induction of general anaesthesia, the patient is placed prone and the pedicle of interest is identified using fluoroscopy. A ‘K’ wire is then inserted percutaneously into this pedicle under image guidance (confirmed in the antero-posterior (AP) and lateral views). The ‘K’ wire is then cut flush and the patient is then positioned laterally and the intended procedure is performed. Results. We routinely use this technique in all our thoracic discectomies. Placing the ‘K’ wire into a fixed point like the pedicle, facilitates rapid intra-operative viewing of the level of interest and is removed easily at the conclusion of surgery. Conclusion. Per-operative placement of the ‘K’ wire avoids the patient undergoing two procedures as some of the other invasive techniques have described in the literature for correct level identification. Furthermore, this technique is simple and requires no more ability than placing an implant in the pedicle under fluoroscopy. It has the added advantage of reducing anaesthetic, surgery and fluoroscopy time

Purposes of the study. The most common fracture of the cervical spine in the elderly population is a fracture of the odontoid peg. Such fractures are usually not displaced and these are commonly treated non-operatively. Rarely though, peg fractures are displaced and then their management is less straightforward. This is in part because the group of patients who sustain them frequently have complex and pre-existing medical co-morbidities and in part because a new neurological injury may have been sustained as a result of the peg fracture itself. Many options for the management of displaced peg fractures, both operative and non-operative have been described in the literature and discussion continues as to which technique is superior and in which patient population. The purpose of this study was to follow-up those patients who were managed operatively in our unit between 2007 and 2009. Methods and Results. We present our case series of 4 patients who sustained significantly displaced fractures of the odontoid peg with accompanying neurological injury, who were treated with posterior stabilisation using the Harms technique. Conclusions. We have found this method to be safe and reliable. It not only yields a good surgical outcome, but allows patients' rehabilitation to be optimised, maximising functional improvement. We believe the technique is superior to anterior stabilisation in this patient population because it utilises superior posterior bone quality and mechanical fixation. The approach in our unit is to treat elderly patients with displaced odontoid peg fractures according to the same principles as would be followed in managing those that have disabling injuries such as fractures of the femoral neck; early stabilisation and early mobilisation in those patients whose co-morbidities allow it

Aims

Idiopathic scoliosis is the most common spinal deformity in adolescents and children. The aetiology of the disease remains unknown. Previous studies have shown a lower bone mineral density in individuals with idiopathic scoliosis, which may contribute to the causation. The aim of the present study was to compare bone health in adolescents with idiopathic scoliosis with controls.

Aims

We aimed to retrospectively assess the accuracy and safety of CT navigated pedicle screws and to compare accuracy in the cervical and thoracic spine (C2-T8) with (COMB) and without (POST) prior anterior surgery (anterior cervical discectomy or corpectomy and fusion with ventral plating: ACDF/ACCF).

Objectives

We performed a systematic review of the literature to determine the safety and efficacy of bone morphogenetic protein (BMP) compared with bone graft when used specifically for revision spinal fusion surgery secondary to pseudarthrosis.

Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis.

Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability.

The mean length of the odontoid peg was 39.76 mm (sd 2.68). The mean screw entry angle α was 59.45° (sd 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (sd 2.70), the maximum possible mean converging angle of two screws was 20.35° (sd 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (sd 0.84) for the inner diameter in the sagittal plane and 7.35 mm (sd 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (sd 0.91) in the sagittal plane and 11.77 mm (sd 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (sd 1.14) for the sagittal inner diameter and 5.50 mm (sd 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (sd 1.0) in the sagittal plane and 10.00 mm (sd 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible.

The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws.

Cite this article: Bone Joint J 2013;95-B:536–42.

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.

In patients with osteoporosis there is always a strong possibility that pedicle screws will loosen. This makes it difficult to select the appropriate osteoporotic patient for a spinal fusion. The purpose of this study was to determine the correlation between bone mineral density (BMD) and the magnitude of torque required to insert a pedicle screw. To accomplish this, 181 patients with degenerative disease of the lumbar spine were studied prospectively. Each underwent dual-energy x-ray absorptiometry (DEXA) and intra-operative measurement of the torque required to insert each pedicle screw. The levels of torque generated in patients with osteoporosis and osteopenia were significantly lower than those achieved in normal patients. Positive correlations were observed between BMD and T-value at the instrumented lumbar vertebrae, mean BMD and mean T-value of the lumbar vertebrae, and mean BMD and mean T-value of the proximal femur. The predictive torque (Nm) generated during pedicle screw insertion was [-0.127 + 1.62 × (BMD at the corresponding lumbar vertebrae)], as measured by linear regression analysis. The positive correlation between BMD and the maximum torque required to insert a pedicle screw suggests that pre-operative assessment of BMD may be useful in determining the ultimate strength of fixation of a device, as well as the number of levels that need to be fixed with pedicle screws in patients who are suspected of having osteoporosis.

Low bone mass and osteopenia have been described in the axial and peripheral skeleton of patients with adolescent idiopathic scoliosis (AIS). Recently, many studies have shown that gene polymorphism is related to osteoporosis. However, no studies have linked the association between IL6 gene polymorphism and bone mass in AIS. This study examined the association between bone mass and IL6 gene polymorphism in 198 girls with AIS. The polymorphisms of IL6-597 G→A, IL6-572 G→C and IL6-174 G→A and the bone mineral density in the lumbar spine and femoral neck were analysed and compared with their levels in healthy controls. The mean bone mineral density at both sites in patients with AIS was decreased compared with controls (p = 0.0022 and p = 0.0013, respectively). Comparison of genotype frequencies between AIS and healthy controls revealed a statistically significant difference in IL6-572 G→C polymorphism (p = 0.0305). There was a significant association between the IL6-572 G→C polymorphism and bone mineral density in the lumbar spine, with the CC genotype significantly higher with the GC (p = 0.0124) or GG (p = 0.0066) genotypes.

These results suggest that the IL6-572 G→C polymorphism is associated with bone mineral density in the lumbar spine in Korean girls with AIS.