Ceramics such as hydroxyapatite are routinely used in fracture repair. However, their effects could be significantly improved as its bioavailability is incredibly poor (issues including low solubility, anionic charge, tendency to agglomerate). Nanoscale hydroxyapatite are gaining much interest, demonstrating increased effectiveness when compared to their micro-sized counterpart. In this study, we have developed a bioactive cargo–polymer-based system that allowed for the sustained, localised non-viral delivery of hydroxyapatite nanoparticles using an amphipathic peptide as a capping agent. The nanoparticles were delivered from a polycaprolactone nanofibre reinforced novel Alg-co-PNIPAAm thermoresponsive hydrogel. The bioactive cargo–polymer-based system was characterised in terms of its physiochemical properties, in vitro properties and in vivo performance using a subcutaneous mouse model. From this study, we have demonstrated that osteogenesis and bone regeneration were significantly increased when our novel capping agent was used to limit the particle size distribution and optimised the physiochemical characteristics of nanoscale hydroxyapatite (i.e. reducing risk of agglomeration and increasing its bioavailability). Additionally, the dual functionality of the thermoresponsive hydrogel as a scaffold for bone regeneration and as a vehicle for the sustained, local delivery of hydroxyapatite nanoparticles over an extended period was successfully demonstrated.

This study aimed to assess the effect of flexion and external rotation on measurement of femoral offset (FO), greater trochanter to femoral head centre (GT-FHC) distance, and neck shaft angle (NSA). Three-dimensional femoral shapes (n=100) were generated by statistical shape modelling from 47 CT-segmented right femora. Combined rotations in the range of 0–50° external and 0–50° flexion (in 10° increments) were applied to each femur after they were neutralised (defined as neck and proximal shaft axis parallel with detector plane). Each shape was projected to create 2D images representing radiographs of the proximal femora.

As already known, external rotation resulted in a significant error in measuring FO but flexion alone had no impact. Individually, neither flexion nor external rotation had any impact on GT-FHC but, for example, 30° of flexion combined with 50°of external rotation resulted in an 18.6mm change in height. NSA averaged 125° in neutral with external rotation resulting in a moderate increase and flexion on its own a moderate decrease. However, 50° degrees of both produced an almost 30 degree increase in NSA.

In conclusion, although the relationship between external rotation and FO is appreciated, the impact of flexion with external rotation is not. This combination results in apparent reduced FO, a high femoral head centre and an increased NSA. Femoral components with NSAs of 130° or 135° may historically have been based on X-ray misinterpretation. This work demonstrates that 2D to 3D reconstruction of the proximal femur in pre-op planning is a challenge.

Unknown femur orientation during X-ray imaging may cause inaccurate radiographic measurements. The aim of this study was to assess the effect of 3D femur orientation during radiographic imaging on the measurement of greater trochanter to femoral head centre (GT-FHC) distance.

Three-dimensional femoral shapes (n=100) of unknown gender were generated using a statistical shape model based on a training data of 47 CT segmented femora. Rotations in the range of 0° internal to 50° external and 50° of flexion to 0° of extension (at 10 degree increments) were applied to each femur. A ray tracing algorithm was then used to create 2D images representing radiographs of the femora in known 3D orientations. The GT-FHC distance was then measured automatically by identifying the femoral head, shaft axis and tip of greater trochanter.

Uniaxial rotations had little impact on the measurement with mean absolute error of 0.6 mm and 3.1 mm for 50° for pure external rotation and 50° pure flexion, respectively. Combined flexion and external rotation yielded more significant errors with 10° around each axis introducing a mean error of 3.6 mm and 20° showing an average error of 8.8 mm (Figure 1.). In the cohort we studied, when the femur was in neutral orientation, the tip of greater trochanter was never below the femoral head centre.

Greater trochanter to femoral head centre measurement was insensitive to rotations around a single axis (i.e. flexion or external rotation). Modest combined rotations caused the tip of greater trochanter to appear more distal in 2D and led to deviation from the true value. This study suggests that a radiograph with the greater trochanter appearing below femoral head centre may have been acquired with 3D rotation of the femur.

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Anterior-posterior (AP) x-rays are routinely taken following total hip replacement to assess placement and orientation of implanted components. Pelvic orientation at the time of an AP x-ray can influence projected implant orientation.¹However, the extent of pelvic orientation varies between patients.²Without compensation for patient specific pelvic orientation, misleading measurements for implant orientation may be obtained. These measurements are used as indicators for post-operative dislocation stability and range of motion. Errors in which could result in differences between expectations and the true outcome achieved. The aim of this research was to develop a tool that could be utilised to determine pelvic orientation from an AP x-ray.

An algorithm based on comparing projections of a statistical shape model of the pelvis (n=20) with the target X-ray was developed in MATLAB. For each iteration, the average shape was adjusted, rotated (to account for patient-specific pelvic orientation), projected onto a 2D plane, and the simulated outline determined. With respect to rotation, the pelvis was allowed to rotate about its transverse axis (pelvic flexion/extension) and anterior-posterior axis (pelvic adduction/abduction). Minimum root mean square error between the outline of the pelvis from the X-ray and the projected shape model outline was used to select final values for flexion and adduction. To test the algorithm, virtual X-rays (n=6) of different pelvis in known orientations were created using the algorithm described by Freud et al.³The true pelvic orientation for each case was randomly generated. Angular error was defined as the difference between the true pelvic orientation and that selected by the algorithm.

Initial testing has exhibited similar accuracy in determining true pelvic flexion (x̄_error = 2.74°, σ_error=±2.21°) and true pelvic adduction (x̄_error = 2.38°, σ_error=±1.76°). For both pelvic flexion and adduction the maximum angular error observed was 5.62°. The minimum angular error for pelvic flexion was 0.37°, whilst for pelvic adduction it was 1.08°.

Although the algorithm is still under development, the low mean, maximum, and standard deviations of error from initial testing indicate the approach is promising. Ongoing work will involve the use of additional landmarks for registration and training shapes to improve the shape model. This tool will allow surgeons to more accurately determine true acetabular orientation relative to the pelvis without the use of additional x-ray views or CT scans. In turn, this will help improve diagnoses of post-operative range of motion and dislocation stability.

Vertebroplasty is a minimal invasive surgical procedure for treatment of vertebral compressive fractures, whereby cement is injected percutaneously into a vertebral body. Cement viscosity is believed to influence injectability, cement wash-out and leakage. Altering the liquid to powder ratio can affect the viscosity, level of cohesion and extent cement fill within the vertebral body and the ultimately strength and stiffness of the cement-vertebra composite. The association of these combined factors remains unclear. The aim of this study was to determine the relationship between cement viscosity and the potential augmentation of strength and stiffness in a model simulating in-vitro prophylactic vertebroplasty of osteoporotic vertebral bodies.

Samples of synthetic bone (Sawbone) representing osteoporotic bone were manually injected with 1mL of calcium phosphate cement using a 11G cannulated needle. Calcium phosphate cement was produced by mixing alpha-tricalcium phosphate, calcium carbonate and hydroxyapatite with an aqueous solution of 5 wt% disodium hydrogen phosphate. Three liquid to powder ratio (LPR) representing different viscosity levels were used; i.e. 0.5mL/g (low viscosity), 0.45mL/g (medium viscosity) and 0.35mL/g (high viscosity). Cement filled samples were then placed in an oven (37oC) for 20 min and then immersed in Ringer's solution (37oC) for 3 days. Samples of synthetic bone without cement injection were used as controls.

Potential for leakage and wash-out was determined using gravimetric analysis. Extent of cement fill was determined using computer tomography (CT).

Samples were tested under axial compression at a rate of 1 mm/min and the strength and stiffness determined. Statistical significance against controls was determined using a one-way analysis of variance (p<0.05).

Low viscosity cement showed more cement leakage (p=0.512) and increased cement wash-out after 3 days in Ringer's solution (p=0.476). Qualitative assessment of cement fill within the vertebral body using CT imaging supported the wash-out results. The strength (p<0.05-0.01) and stiffness (p<0.01) of samples significantly increased by cement injection in comparison to control, the extent of this increase was greater with increasing cement viscosity.

Linear correlation analysis showed a definite association between the mechanical properties and viscosity of injected cement and was dependent on the amount of cement retained within the synthetic bone post-setting.

Introduction: Computational modelling of the spine offers a particularly difficult challenge to analysts due to its complex structure and high level of functionality. Previous studies [Wijayathunga, 2008; Jones, 2007] have shown that finite element (FE) predictions of vertebral stiffness are highly sensitive to the applied boundary conditions and therefore validation requires careful matching between the experimental and simulated situation. The aim of this study was to develop and experimentally validate specimen specific FE models of porcine vertebrae in order to accurately predict the stiffness of single vertebra specimens.

METHOD: Nine single vertebra specimens were excised from the thoracolumbar region of two porcine spines. The specimens were mounted between two parallel PMMA housings and each specimen was imaged using a micro computed tomography (μCT) system (μCT80; Scanco Medical, Switzerland). In order to accurately match the experimental conditions, a radio-opaque marker was positioned on the specimen housing at the point of load application. The vertebrae were separated into two groups: a development set (set 1) consisting of three specimens and a validation set (set 2) of six specimens. Specimens from set 1 were used to establish the optimum method of conversion from image greyscale, to element material properties. The models in set 2 were used to assess the accuracy of the stiffness predictions for each model. The vertebrae were tested in a materials testing machine (AGS-10kNG; Shimadzu Corp., Japan) under axial compression and the stiffness for each specimen was calculated. The μCT data was imported into an image processing package (Scan IP, Simpleware, UK). The software enabled the images to be segmented and the vertebra, cement housings and position of load application to be identified. The segmented images were down-sampled to 1mm voxels, enabling a FE mesh to be generated (Scan FE; Simpleware, UK) based on direct voxel to element conversion. The Young’s modulus of each bone element was assigned, based on the greyscale of the corresponding image voxel. The PMMA housing plates were assigned homogeneous material properties (E = 2.45 GPa). Abaqus CAE 6.8 (Simula, Providence, Rhode Island, USA) was used for the processing and post-processing of all the models.

Results: The mean experimental stiffness was 4321 N/ mm (standard deviation = 415 N/mm). The optimum conversion factor was calculated for set 1, which yielded a root mean squared (RMS) percentage error of 7.5% when compared with the experimental stiffness. Using this optimised scale factor, FE models of specimens from set 2 were created. The predicted stiffnesses for set 2 were compared to the corresponding experimental values and yielded an RMS error of 10.1%.

Conclusion: The results indicate that specimen specific models can provide good agreement with the corresponding experimental specimen stiffness. In addition, the method employed in this study proved robust enough to be applied to vertebral tissue obtained from different animals of the same species. This method will now be developed to assess treatments for traumatic spinal injuries.

Introduction: It has been shown that acrylic bone cement is weakened by its porosity, which enhances the formation of micro-cracks that contribute to major crack propagation. It has also been observed, that mixing procedures play a significant role in determining the quality of bone cement produced. A high degree of porosity is found to exist in cement that is inadequately mixed.

Currently mixing system allow for the preparation of the bone cement under the application of a vacuum in a closed, sealed chamber by means of a repeatable mixing action. These systems are perceived to be repeatable, reliable, and operator independent. The objective of this study is to evaluate the quality and consistency of acrylic bone cement prepared by scrub staff in an orthopaedic theatre using a commercially available third generation vacuum mixing syringe, in terms of the level of voids within the cement microsturcture.

Materials and Methods: The mixing devices were stored at 23°C ± 1°C for a minimum of 24 hours prior to mixing. The acrylic bone cement (Palacos R® with gentamicin, Biomet Merck, UK) was stored at 4°C ± 1°C for a minimum of 24 hours prior to mixing.

Bone cement was mixed using a commercially available third generation mixing device (vacuum = −550mmHg) at Musgrave Park Hospital, Belfast, Northern Ireland. The cement was mixed according to the device manufacturers’ instructions for use. Mixing was carried out during a joint replacement surgery by a number of experienced theatre scrub staff (n = 35). The cement remaining at the end of the procedure was allowed to cure within the delivery nozzle, made from linear low-density polyethylene (LLDPE) and having an internal diameter of 10mm. 205 nozzles were collected post-operatively and stored at 23°C ± 1°C prior to testing. The percentage porosities were determined by measuring the apparent densities based on Archimedes principle and, as a direct result; it was possible to calculate the mean percentage porosities.

Discussion: It can be observed that the majority of the theatre nurses, ie 46.8% prepared bone cement using the vacuum mixing system containing a porosity of between 2% to 4%. A cement porosity of this range would be the accepted optimum content for acrylic bone cement. However, 6.4% of the theatre nurses prepared cement demonstrating a porosity content ranging from 8–16%, which is highly unsatisfactory when you consider that the cement mixing system is perceived to be a consistent and reliable mixing device that is operator independent.

Figure 2 illustrates a bar chart representing the bone cement porosity as a function of which orthopaedic theatre the cement was prepared. There was no significance difference when comparing the quality of the cement mixed in terms of porosity with the different theatres. The mean porosity values of the cement mixed ranged between 2.5% and 5.2% depending on which theatre was used.

Conclusions: Bone cement mixed using the commercially available third generation device in theatre by 35 scrub staff was found to have a high degree of variability. Thus demonstrating that even an alleged reproducible mixing system is independent on mixing technique when used in a clinical situation by a number of users. Thus illustrating the system is not wholly user independent.

As a consequence of this investigation it is recommended that the key to ensuring high quality bone cement, with a good mechanical strength, that can be consistently prepared in theatre by scrub staff are two fold.

The orthopaedic staff must be aware of the significance of cement mixing and how it is affected by a number of factors including the type of mixing system, vacuum level applied, and mixing technique.