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

Introduction. The main symptoms in multiple myeloma are the result of skeletal destruction mainly the vertebral column. The current treatments for multiple myeloma include radiotherapy and chemotherapy but unfortunately it is still incurable. However, the symptoms and quality of life of these patients can be improved by cement augmentation which has gained popularity in the recent years. Aim. To analyse the efficacy and safety of cement augmentation and to assess the survival and outcome of the patients with vertebral fractures secondary to multiple myeloma. Material and Methods. In this retrospective study, we reviewed the data over the last 3 years. Medical records review included correction of vertebral angle (VA), assessment of disability, survival and postoperative improvement in pain and functional status. Results. We reviewed 12 patients with 48 vertebral compression fractures including 9 male and 3 female patients. Mean age was 62.5 years (41–85). 5 patients had single vertebral involvement while 7 had multiple fractures at different levels in thoracolumbar spine. Average length of follow-up was 20.3 months (14–33 months). Based on Modified Tokuhashi score, the expected survival was less than 12 months in 2 patients and more than 12 months in the remaining patients. 11 patients are alive till date with average survival of 26 months (18–42 months) while 1 patient died, 23 months after the initial correction surgery. Prior to correction, the average vertebral angle (VA) was 10.60 (2.30 to 25.20) and after cement augmentation the average VA was 7.00 (1.60–22.80). Mean correction achieved was 3.60. There was no loss of vertebral height in any patient until their latest follow-up. Karnofsky performance score was more than 70 in 5 patients, 50–70 in 6 and less than 50 in 1 patient preoperatively while it improved to more than 70 in all patients postoperatively which indicates improvement in their functional status. All patients reported improvement in their pain level after surgery. No cement leakage or major complication occurred in these patients. Conclusion. Cement augmentation is a safe and effective way of treating the symptoms of multiple myeloma which occur due to vertebral metastases. It results in excellent pain control and improvement in quality of life

Hip fractures constitute the most debilitating complication of osteoporosis with a steadily increasing incidence in an aging population. Intramedullary nailing of osteoporotic proximal femoral fractures can be challenging because of poor implant anchorage in the femoral head. Recently, cement augmentation of PFNA blades with Polymethylmethycrylate (PMMA) has shown promising results by enhancing the cutout resistance in proximal femoral fractures. The aim of this biomechanical study was to assess the impact of cement augmentation on the fixation strength of TFNA blades and screws within the femoral head, and compare its effect with head elements placed in a center or antero–posterior off–center positions. Eight groups were formed out of 96 polyurethane foam specimens with low density, simulating isolated femoral heads with severe osteoporotic bone. The specimens in each group were implanted with either non–augmented or PMMA–augmented TFNA blades or screws in a center or antero–posterior off–center position, 7 mm anterior or 7 mm posterior. They were mechanically tested in a setup simulating an unstable pertrochanteric fracture with lack of postero–medial support and load sharing at the fracture gap. All specimens underwent progressively increasing cyclic loading until catastrophic construct failure. Varus–valgus and head rotation angles were monitored by an inclinometer mounted on the head. A varus collapse of 5° or a 10° head rotation were defined as the clinically relevant failure criterion. Load at failure for specimens with augmented TFNA head elements (screw center: 3799 N ± 326 (mean ± SD); blade center: 3228 N ± 478; screw off–center: 2680 N ± 182; blade off–center: 2591 N ± 244) was significantly higher compared to the respective non–augmented specimens (blade center: 1489 N ± 41; screw center: 1593 N ± 120; blade off–center: 1018 N ± 48; screw off–center: 515 N ± 73), p<0.001. In both non–augmented and augmented specimens, the failure load in center position was significantly higher compared to the respective off–center position, regardless of head element, p<0.001. Non–augmented TFNA blades in off–center position revealed significantly higher load at failure versus non–augmented screws in off–center position, p<0.001. Cement augmentation clearly enhances fixation stability of TFNA blades and screws. Non–augmented blades outperformed screws in antero–posterior off–center position. Positioning of TFNA blades in the femoral head is more forgiving than TFNA screws in terms of failure load. Augmentation with TFNA has not been approved by FDA

Aims. Fixation of osteoporotic proximal humerus fractures remains challenging even with state-of-the-art locking plates. Despite the demonstrated biomechanical benefit of screw tip augmentation with bone cement, the clinical findings have remained unclear, potentially as the optimal augmentation combinations are unknown. The aim of this study was to systematically evaluate the biomechanical benefits of the augmentation options in a humeral locking plate using finite element analysis (FEA). Methods. A total of 64 cement augmentation configurations were analyzed using six screws of a locking plate to virtually fix unstable three-part fractures in 24 low-density proximal humerus models under three physiological loading cases (4,608 simulations). The biomechanical benefit of augmentation was evaluated through an established FEA methodology using the average peri-screw bone strain as a validated predictor of cyclic cut-out failure. Results. The biomechanical benefit was already significant with a single cemented screw and increased with the number of augmented screws, but the configuration was highly influential. The best two-screw (mean 23%, SD 3% reduction) and the worst four-screw (mean 22%, SD 5%) combinations performed similarly. The largest benefits were achieved with augmenting screws purchasing into the calcar and having posteriorly located tips. Local bone mineral density was not directly related to the improvement. Conclusion. The number and configuration of cemented screws strongly determined how augmentation can alleviate the predicted risk of cut-out failure. Screws purchasing in the calcar and posterior humeral head regions may be prioritized. Although requiring clinical corroborations, these findings may explain the controversial results of previous clinical studies not controlling the choices of screw augmentation

Introduction

Pedicle screw pullout or loosening is increased in the osteoporotic spine. Recent studies showed a significant increase of pullout forces especially for PMMA-augmentation. With application of conventional viscosity PMMA the risk of cement extravasation is associated. This risk can be reduced by using radiofrequency-responsive, ultrahigh viscosity bone cement.

Posterior internal fixation systems undergo internal constraints resulting in high load bearing requirement for the pedicular screw/bone interface. Only few studies deal with the impact of the vertebral augmentation on the migration of pedicular screws. In this study, the impact of the pedicular screw augmentation has been investigated under physiological load for osteoporotic vertebras. The data have been proceeded to reduce the influence of vertebral geometry, which generally leads to results devoid of statistical meaning

In 8 osteoporotic vertebrae, two screws have been inserted in each vertebra: a non-augmented on one side and an augmented one on the contralateral side.

Compression tests have been performed (two consecutive 50 cycles load steps -100N and 200N-) to observe the displacement of the screw’s head. Two different setups have been employed: a free connection (FC) and a blocked connection (BC). A load step is successful if the migration between two consecutive cycles tends to zero. To reduce the impact of the vertebras’ geometry, the screws’ migration have been compared contra-laterally using the migration ratio (MR). MR of vertebrae is defined as the division of the augmented screw’s migration with the non-augmented screw’s migration.

All the augmented screws survived both test setups whereas the non-augmented failed the 200N FC load step. Significant differences are observable only for the highest successful load steps for each test setup: T-tests (P=0.039 and P=0.007 respectively) put into evidence that the results are statistically smaller than one. It is observable as well, that the BC induced fewer loads into the vertebrae: even non-augmented screw can withstand 200N load step.

As expected, augmentation of pedicular perforated screws increases their stability in osteoporotic vertebras undergoing large physiological load. This could be explained by the fact that the presence of PMMA increases the load transfer interface improving screw/PMMA complex bearing capacity. Smaller loads induce only small differences that are not significant.

INTRODUCTION

Over 85% of patients with multiple myeloma (MM) have bone disease, mostly affecting thoraco-lumbar vertebrae. Vertebral fractures can lead to pain and large spinal deformities requiring application of vertebroplasty (PVP). PVP could be enhanced by use of Coblation technique to remove lesions from compromised MM vertebrae prior to cement injection (C-PVP).

The purpose of this study was to determine the effect of cement mixing time on fixation augmentation in both healthy and simulated osteoporotic canine bone. In a canine diaphyseal model, screw insertion into liquid cement achieves greater bending stiffness and resists a greater load to failure than cement inserted as a paste. Bone cement in its liquid state may provide increased structural support in the setting of an osteoporotic fracture, possibly due to increased interdigitation of the cement with the screw threads and bone.

An inconsistency exists among orthopaedic surgeons with regards to the appropriate mixing time for bone cement to achieve optimal results. The purpose of this study was to determine the effect of cement mixing time on fixation augmentation in both healthy and simulated osteoporotic canine bone.

In a canine diaphyseal fracture model, screw insertion into liquid cement achieves greater bending stiffness and resists a greater load to failure than insertion into cement with the consistency of a paste.

Bone cement in its liquid state may provide increased structural support in the setting of an osteoporotic fracture, possibly due to increased interdigitation of the cement with the screw threads and bone.

Baseline stiffness for fourteen pairs of cadaveric canine femora was determined. A transverse diaphyseal osteotomy was created and fixed using an eight-hole DC plate and 3.5 mm screws. A 1cm gap was created at the osteotomy site simulating loss of bone. In the left femora, cement was mixed for one minute (liquid) prior to injection into pre-drilled holes; in the right femora, cement was mixed for five minutes prior to injection (thick paste). In each mixing time group, seven specimens were treated with a plate and properly sized pre-drilled and tapped holes (2.5mm), and seven received over-drilled holes (3.2 mm) to simulate osteoporotic bone. Four-point bending stiffness was determined for each plated construct, and normalized to baseline stiffness. Specimens were then loaded to failure.

Within the properly sized holes, there were no statistically significant differences (SSD) in bending stiffness with or without a gap. The liquid cement had a force to failure 77% greater than that of cement as a paste (p< 0.05). Within the over-sized holes, there was no SSD between liquid and paste without a gap. With a gap, liquid cement demonstrated an increased bending stiffness of 24 % (p< 0.05) and force to failure was 92% higher (p< 0.05).

Introduction and Aims: Bone cement (Polymethylmethacrylate) is commonly used to augment internal fixation in osteoporotic bone. An inconsistency exists among surgeons regarding the appropriate mixing time for bone cement to achieve optimal screw purchase. The study addresses the effect of cement viscosity on fixation augmentation in both healthy and simulated osteoporotic canine bone.

Method: Fourteen canine femora were plated using eight-hole DC plates and 3.5mm screws, repairing transverse diaphyseal osteotomies with and without a gap. In the left femora, cement was mixed for one minute (liquid) prior to injection into drilled and tapped holes that were either properly sized (2.5mm) or over-drilled (3.2mm) to simulate osteoporotic bone. In the right femora, cement was mixed for five minutes prior to injection (thick paste). Four-point bending stiffness for each plated construct was normalised to baseline stiffness, followed by failure loading.

Results: Within the properly sized holes, there were no significant differences in bending stiffness with or without a gap at the fracture site. The liquid cement had a force to failure 77% greater than that of cement as a paste (p< 0.05).

Within the over-sized holes simulating osteoporotic bone, there was no difference between liquid and paste without a gap. With a gap, liquid cement demonstrated an increased bending stiffness of 24% (p< 0.05) and force to failure was 92% higher (p< 0.05).

Bone cement in its liquid state may provide increased structural support in the setting of an osteoporotic fracture, possibly due to increased interdigitation of the cement with the screw threads and bone.

Conclusion: In a canine diaphyseal fracture model, screw insertion into liquid cement achieves greater bending stiffness and resists a greater load to failure than insertion into cement with the consistency of a paste.

Introduction and Objective. Trochanteric fractures are associated with increasing incidence and represent serious adverse effect of osteoporosis. Their cephalomedullary nailing in poor bone stock can be challenging and associated with insufficient implant fixation in the femoral head. Despite ongoing implant improvements, the rate of mechanical complications in the treatment of unstable trochanteric fractures is high. Recently, two novel concepts for nailing with use of a helical blade – with or without bone cement augmentation – or an interlocking screw have demonstrated advantages as compared with single screw systems regarding rotational stability and cut-out resistance. However, these two concepts have not been subjected to direct biomechanical comparison so far. The aims of this study were to investigate in a human cadaveric model with low bone density (1) the biomechanical competence of cephalomedullary nailing with use of a helical blade versus an interlocking screw, and (2) the effect of cement augmentation on the fixation strength of the helical blade. Materials and Methods. Twelve osteoporotic and osteopenic femoral pairs were assigned for pairwise implantation using either short TFN-ADVANCED Proximal Femoral Nailing System (TFNA) with a helical blade head element, offering the option for cement augmentation, or short TRIGEN INTERTAN Intertrochanteric Antegrade Nail (InterTAN) with an interlocking screw. Six osteoporotic femora, implanted with TFNA, were augmented with 3 ml cement. Four study groups were created – group 1 (TFNA) paired with group 2 (InterTAN), and group 3 (TFNA augmented) paired with group 4 (InterTAN). An unstable pertrochanteric OTA/AO 31-A2.2 fracture was simulated. All specimens were biomechanically tested until failure under progressively increasing cyclic loading featuring physiologic loading trajectory, with monitoring via motion tracking. Results. T-score in groups 3 and 4 was significantly lower compared with groups 1 and 2, p=0.03. Stiffness (N/mm) in groups 1 to 4 was 335.7+/−65.3, 326.9+/−62.2, 371.5+/−63.8 and 301.6+/−85.9, being significantly different between groups 3 and 4, p=0.03. Varus (°) and femoral head rotation around neck axis (°) after 10,000 cycles were 1.9+/−0.9 and 0.3+/−0.2 in group 1, 2.2+/−0.7 and 0.7+/−0.4 in group 2, 1.5+/−1.3 and 0.3+/−0.2 in group 3, and 3.5+/−2.8 and 0.9+/−0.6 in group 4, both with significant difference between groups 3 and 4, p<=0.04. Cycles to failure and failure load (N) at 5° varus in groups 1 to 4 were 21428+/−6020 and 1571.4+/−301.0, 20611+/−7453 and 1530.6+/−372.7,21739+/−4248 and 1587.0+/−212.4, and 18622+/−6733 and 1431.1+/−336.7, both significantly different between groups 3 and 4, p=0.04. Conclusions. From a biomechanical perspective, cephalomedullary nailing of trochanteric fractures with use of helical blades is comparable to interlocking screw fixation in femoral head fragments with low bone density. Moreover, bone cement augmentation of helical blades considerably improves their fixation strength in poor bone quality

Introduction. Spine is a common site for haematological malignancies. Multiple myeloma affects the spine in 70% of cases. New guidelines were published in 2015 to help manage spinal haematological malignancies. Despite neural compression or spinal instability, instrumentation of the spine should be avoided. Surgery carries significant risks of wound complications and more importantly delaying the definitive chemotherapy and radiotherapy. Cement augmentation and bracing for pain and prevention of deformity is key to the new strategies. We aimed to evaluate the different treatment modalities adopted in the spine unit at St George's hospital for spinal haematological malignancies. We compared our practice to the current guidelines published in 2015. Methods. Retrospective review of all spinal haematological malignancy patients who were discussed in the spinal MDT and managed through the spine unit at St George's hospital in the period between April 2019 and February 2021. We analysed the demographics of the patients treated in this period and compared the management modalities adopted in the unit to the current British haematological guidelines. Results. 139 patients were included in this study, 61.9% of them were male. 70 cases came through the MSCC pathway. 15 patients had their spinal involvement in the lumbar spine only below the conus. The Bilsky Grades of the other 124 cases were B0: 35.97 % 1a: 4.31%%, 1b: 7.19%, 1c: 3.59%, 2: 5.75% 3: 32.37%. 43 patients (30.9 %) had neurological deficits on presentation. 70 cases were treated conservatively (50.35%), 21 were treated with brace only (15.1%), 25 had BKP (17.98%) and 23 were treated with instrumentation (16.54%). The number of instrumented cases was small and trending down and cement augmentation and bracing were more frequently chosen for these patients. This comes in accordance to the British haematological guidelines. Conclusion. Utilising BJH 2015 guidelines we have reduced our instrumented operative case load. There is a higher percentage of BKP and Bracing in accordance to the algorithm

Femoroplasty is the process of injecting cement (cement augmentation) into the proximal femur to prevent osteoporotic hip fractures. Femoroplasty increases the strength and energy to failure of the femur and can be performed in a minimally-invasively manner with lower hospitalization costs and reduced recovery. Our hypothesis was that efficient cement augmentation strategies can be identified via computational optimization. Therefore, using patient-specific planning we can minimize cement volume while increasing bone strength and reducing the risk of fracture. We proposed an in-silico methodology that was validated with in vitro experiments. A discrete particle model for cement infiltration was used to determine the optimum volume and filling pattern of the cement such that the best outcome was achieved. Several artificial bones were scanned before and after cement augmentation to applied previous in silico methodology. Then those femurs were mechanically tested (non-augmented and augmented). Therefore, in silico methodology was validated. Cement augmentation significantly increased the yield load. Predicted yield loads correlated well with the experiments. Results suggest that patient-specific planning of femoroplasty reduces the risk of hip fracture while minimizing the amount of cement required

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

Introduction. In complex primary and revision total knee replacement (TKR) the operating surgeon may encounter proximal tibial bone defects. The correct management of such defects is fundamental to both the initial stability and long-term survival of the prosthesis. Cement or metal augments have been used to address some such type II unconstrained defects [1]. Aim. The aim of this finite element (FE) study was to analyse the comparative behaviour of cement and metal based augments and quantify the stresses within these different augments and underlying cancellous bone. Materials and methods. A three-dimensional FE model was constructed from a computer tomography (CT) scan of the proximal tibia using SIMPLEWARE v3.2 image processing software. The tibial component of a TKR was implanted with either a block or wedge-shaped augment made of either metal or cement. The model was axially loaded with a force of 3600N and testing was conducted with both evenly and eccentrically distributed loads. Results. Upon loading the FE model, the von-Mises stresses in the cancellous bone underneath the augments were found to be higher with cement based augments in comparison their metal based counterparts. This was evident with both block and wedge-shaped augments. The FE model demonstrated that compressive stresses within the metal based augments were greater than those within the cement based augments. This was evident with both block and wedge designs. Upon even loading the maximum recorded compressive stresses within the metal augments were 5 times less than the endurance limit of the material [3]. However, the maximum recorded compressive stresses within cement augments were only half the endurance limit of the material [4] and upon eccentric loading compressive stresses in excess of the endurance limit were recorded. Discussion. The FE model has demonstrated that cement based augments undergo a greater deformation when loaded and therefore transfer greater loads to the underlying cancellous bone. This is a result of the inherent flexibility of the cement based augment in comparison to the stiffer metal counterparts. The greater transference of load to cancellous bone with cement based augments may reduce the possibility of stress shielding. However, the compressive stresses within cement based augments are too close to the endurance limit of the material and with uneven loading even exceed it. This would imply that cement based augments are more prone to fatigue failure than their metal counterparts. Conclusion. This FE study supports the use of metal based augments over cement based augments in augmented and revision TKR surgery

Intramedullary nailed high proximal tibial fractures rely on the proximal screw-bone interface to provide stability, which can be insufficient in low-density bones. This study investigated the biomechanics of proximal screw cement augmentation in intramedullary nailing of high proximal tibial fractures. Mechanical stability in flexion/extension, varus/valgus and torsion was tested on six pairs of cadaveric proximal tibiae, with/without cement augmentation. Cement augmentation significantly increased construct stability in torsion and demonstrated a trend towards improved varus/valgus stabilization. Surprisingly, cement augmentation significantly decreased stability in flexion/extension, suggesting the potential benefits of cement augmentation may be limited in intramedullary nailed high proximal tibial fractures. This study assessed the biomechanical effects of augmenting proximal screws with cement in intramedullary nailing of high proximal third tibial fractures. While increased biomechanical stability was seen in torsion and varus/valgus, the reduction in stability in flexion/extension suggests that there may be limited benefit in cement augmentation in the nailing of high proximal tibia fractures. High proximal tibial fractures fixed with intramedullary nailing rely primarily on proximal screw fixation to provide stability. Cement augmentation of the proximal screws may provide needed increased construct stability in low-density tibiae. Cement augmentation provided a significant increase in construct stability in torsion (37.5% ± 8.0%, p< 0.05), with a trend toward increased stability in varus/valgus (25.5% ± 36.2%, p=0.08). Conversely, stability in flex-ion/extension was significantly decreased with the use of cement (25.9% ± 13.0%, p< 0.05). Reamed intramedullary nails (Zimmer, MDN) were implanted into six pairs of elderly cadaveric fresh-frozen proximal tibiae and secured using four proximal screws (two transverse, two oblique, 4.5mm diameter). Bone cement was injected into the screw holes just prior to screw insertion to augment the bone-screw interface in one tibia from each pair. Specimen stability was tested in flexion/extension and varus/valgus loading to 12Nm and in torsion to 7Nm. Displacement data was generated and analyzed using a repeated measures design. We hypothesized that intramedullary nail-bone construct stability would be increased with cement augmentation, particularly in low-density specimens. While construct stability was improved in torsion and varus/valgus, surprisingly stability consistently decreased in flexion/extension

Objectives. Cement augmentation of pedicle screws could be used to improve screw stability, especially in osteoporotic vertebrae. However, little is known concerning the influence of different screw types and amount of cement applied. Therefore, the aim of this biomechanical in vitro study was to evaluate the effect of cement augmentation on the screw pull-out force in osteoporotic vertebrae, comparing different pedicle screws (solid and fenestrated) and cement volumes (0 mL, 1 mL or 3 mL). Materials and Methods. A total of 54 osteoporotic human cadaver thoracic and lumbar vertebrae were instrumented with pedicle screws (uncemented, solid cemented or fenestrated cemented) and augmented with high-viscosity PMMA cement (0 mL, 1 mL or 3 mL). The insertion torque and bone mineral density were determined. Radiographs and CT scans were undertaken to evaluate cement distribution and cement leakage. Pull-out testing was performed with a material testing machine to measure failure load and stiffness. The paired t-test was used to compare the two screws within each vertebra. Results. Mean failure load was significantly greater for fenestrated cemented screws (+622 N; p ⩽ 0.001) and solid cemented screws (+460 N; p ⩽ 0.001) than for uncemented screws. There was no significant difference between the solid and fenestrated cemented screws (p = 0.5). In the lower thoracic vertebrae, 1 mL cement was enough to significantly increase failure load, while 3 mL led to further significant improvement in the upper thoracic, lower thoracic and lumbar regions. Conclusion. Conventional, solid pedicle screws augmented with high-viscosity cement provided comparable screw stability in pull-out testing to that of sophisticated and more expensive fenestrated screws. In terms of cement volume, we recommend the use of at least 1 mL in the thoracic and 3 mL in the lumbar spine. Cite this article: C. I. Leichtle, A. Lorenz, S. Rothstock, J. Happel, F. Walter, T. Shiozawa, U. G. Leichtle. Pull-out strength of cemented solid versus fenestrated pedicle screws in osteoporotic vertebrae. Bone Joint Res 2016;5:419–426

Aim. The aim of this FE study was to analyse the comparative behaviour of cement and metal based augments in TKR and quantify the stresses within these different augments and underlying cancellous bone. Materials and methods. A three-dimensional FE model was constructed from a CT scan of the proximal tibia using SIMPLEWARE v3.2 image processing software. The tibial component of a TKR was implanted with either a block or wedge-shaped augment made of either metal or cement. The model was axially loaded with a force of 3600N and testing was conducted with both evenly and eccentrically distributed loads. Results. Upon loading the FE model, the von-Mises stresses in the cancellous bone underneath the augments was higher with cement based augments in comparison their metal counterparts. When evenly loaded the maximum recorded compressive stresses within the metal augments were 5 times less than the endurance limit of the material, whilst the stresses within cement augments were only half the endurance limit of the material. Upon eccentric loading compressive stresses within the cement based augments in excess of the endurance limit were recorded. Discussion. The FE model has demonstrated that cement based augments undergo greater deformation when loaded and transfer greater loads to the underlying cancellous bone thus reducing the possibility of stress shielding. However, the compressive stresses within cement based augments are too close to the endurance limit of the material and with uneven loading even exceed it. This would imply that cement based augments are more prone to fatigue failure than their metal counterparts. Conclusion. This study supports the use of metal over cement based augments in augmented and revision TKR surgery

Purpose: The objectives of this study were to determine the effect of posterior instrumentation extension and/or cement augmentation on immediate stabilization of the instrumented level and biomechanical changes adjacent to the spinal instrumentation. Methods: This study was designed for repeated measures comparison, using 12 T9-L3 human cadaveric segments, to test the effects of posterior rod extension and cement augmentation following T11 corpectomy. The spine was stabilized with a vertebral body replacement device and with posterior instrumentation from T10 to T12. The T12 pedicle tracts were over-drilled to simulate loosened screws in an osteoporotic spine. The T10 screws were not over-drilled but cemented so as to keep the superior segments constant. Flexibility tests were first carried out on the intact specimen, followed by 3 randomized surgical conditions without cement and lastly the 3 conditions after cement augmentation. The 3 conditions were: 1) no posterior extension rods to L1, 2) flexible extension rods, and 3) rigid extension rods. A combined testing/analysis protocol that used both the traditional flexibility method and a hybrid technique [Panjabi 2005] was adopted. Flexibility tests with +/−5 Nm pure moments in flexion-extension, axial rotation and lateral bending were carried out and vertebral bodies’ motion in 3-D were collected. Two-way repeated measures ANOVA analyses were carried out on ROM between cement augmentation (factor 1) and the posterior rod extension (factor 2) on each flexibility test direction. An alpha of 0.05 was chosen. Newman-Keuls post-hoc analyses were carried out to compare between surgical techniques. Results: Using the flexibility protocol, a reduction in ROMs at the destabilized level was observed with cement augmentation of screws or extension with rigid or flexible posterior rods to adjacent distal level. With the hybrid protocol, ROMs at adjacent level (T12-L1) were reduced with rod extension, but not with cement. Conclusions: The results of this study suggest that cement augmentation would enhance stabilization, but create possible adjacent level effects due to increased motion and strain, while additional flexible extension rods would reduce biomechanical changes at the level of extension. Funding: 2 Funding Parties: CIHR

Interbody fusion aims to treat painful disc disease by demobilising the spinal segment through the use of an interbody fusion device (IFD). Diminished contact area at the endplate interface raises the risk of device subsidence, particularly in osteoporosis patients. The aim of the study was to ascertain whether vertebral body (VB) cement augmentation would reduce IFD subsidence following dynamic loading. Twenty-four human two-vertebra motion segments (T6–T11) were implanted with an IFD and distributed into three groups; a control with no cement augmentation; a second with PMMA augmentation; and a third group with calcium phosphate (CP) cement augmentation. Dynamic cyclic compression was applied at 1Hz for 24 hours in a specimen specific manner. Subsidence magnitude was calculated from pre and post-test micro-CT scans. The inferior VB analysis showed significantly increased subsidence in the control group (5.0±3.7mm) over both PMMA (1.6±1.5mm, p=.034) and CP (1.0±1.1mm, p=.010) cohorts. Subsidence in the superior VB to the index level showed no significant differences (control 1.6±3.0mm, PMMA 2.1±1.5mm, CP 2.2±1.2mm, p=.811). In the control group, the majority of subsidence occurred in the lower VB with the upper VB displaying little or no subsidence, which reflects the weaker nature of the superior endplate. Subsidence was significantly reduced in the lower VB when both levels were reinforced regardless of cement type. Both PMMA and CP cement augmentation significantly affected IFD subsidence by increasing VB strength within the motion segment, indicating that this may be a useful method for widening indications for surgical interventions in osteoporotic patients

Aims. Plating displaced proximal humeral fractures is associated with a high rate of screw perforation. Dynamization of the proximal screws might prevent these complications. The aim of this study was to develop and evaluate a new gliding screw concept for plating proximal humeral fractures biomechanically. Methods. Eight pairs of three-part humeral fractures were randomly assigned for pairwise instrumentation using either a prototype gliding plate or a standard PHILOS plate, and four pairs were fixed using the gliding plate with bone cement augmentation of its proximal screws. The specimens were cyclically tested under progressively increasing loading until perforation of a screw. Telescoping of a screw, varus tilting and screw migration were recorded using optical motion tracking. Results. Mean initial stiffness (N/mm) was 581.3 (. sd. 239.7) for the gliding plate, 631.5 (. sd. 160.0) for the PHILOS and 440.2 (. sd. 97.6) for the gliding augmented plate without significant differences between the groups (p = 0.11). Mean varus tilting (°) after 7500 cycles was comparable between the gliding plate (2.6; . sd. 1.9), PHILOS (1.2; . sd. 0.6) and gliding augmented plate (1.7; . sd. 0.9) (p = 0.10). Similarly, mean screw migration(mm) after 7500 cycles was similar between the gliding plate (3.02; . sd. 2.85), PHILOS (1.30; . sd. 0.44) and gliding augmented plate (2.83; . sd. 1.18) (p = 0.13). Mean number of cycles until failure with 5° varus tilting were 12702 (. sd. 3687) for the gliding plate, 13948 (. sd. 1295) for PHILOS and 13189 (. sd. 2647) for the gliding augmented plate without significant differences between the groups (p = 0.66). Conclusion. Biomechanically, plate fixation using a new gliding screw technology did not show considerable advantages in comparison with fixation using a standard PHILOS plate. Based on the finding of telescoping of screws, however, it may represent a valid approach for further investigations into how to avoid the cut-out of screws. Cite this article: Y. P. Acklin, I. Zderic, J. A. Inzana, S. Grechenig, R. Schwyn, R. G. Richards, B. Gueorguiev. Biomechanical evaluation of a new gliding screw concept for the fixation of proximal humeral fractures. Bone Joint Res 2018;7:422–429. DOI: 10.1302/2046-3758.76.BJR-2017-0356.R1