Introduction: Unstable inter-trochanteric fractures are increasing in incidence and stable fixation can improve outcome by leading to earlier mobilisation and reduced mortality. The appropriate choice of implant is vital to ensure a satisfactory outcome.

Objectives: The objective of this study was to determine the load at which different intramedullary device constructs failed.

Materials and Methods: Nine identical 3rd generation composite Sawbones were used and prepared with reverse obliquity cuts made to the femoral necks. Three different types of trochanteric entry intramedullary nail were then inserted using manufacturer’s guidelines. The nine constructs were loaded to failure using a Dartec 9500 servo hydraulic testing machine.

Results: The average failure loads were 3954±952N for the DePuy nail, 2420±281N for the Synthes nail and 3810±377N for the Stryker nail. In eight of the nine constructs the Sawbone failed at the medial side of the fracture. One of the DePuy nails failed at 5041N in the area of the distal locking screws.

The Stryker nail constructs were significantly stronger than the Synthes constructs (p=0.008); although the DePuy constructs were similar in strength to the Stryker constructs (p=0.83) they were not significantly different from the Synthes constructs (p=0.098).

Conclusion: There must be a balance between movement at the fracture site to allow compression but enough stability that the fracture may heal.

Our study showed that the Synthes nail failed at a significantly lower load than the DePuy or the Stryker nails. The Synthes construct failed at a typical walking load, around three times body weight for an 80kg patient.

Introduction: Acrylic bone cement (ABC) manufacturers vary their products by using different proportions of the principle ingredients to optimize handling time or mechanical properties.

There is limited research showing the effect that varying the monomer to polymer ratio (independent from other constituents) has on thermal and mechanical properties of ABC.

Materials and Methods: The formula for CMW1 (DePuy) was reproduced using original ingredients obtained separately from different suppliers. The commercially available CMW1 monomer/polymer ratio is approximately (0.6 ml/gm). Six variants of CMW1 bone cement were prepared with varying monomer/polymer ratio (0.4–1 ml/gm). The specimens were cured and aged in an incubator for 7 days at 37°C.

Thermal characteristics of the polymerization reaction such as maximum polymerization reaction temperature (Tmax) and setting time (ts) were recorded using a Picolog digital data recorder.

Compressive mechanical properties (Young’s modulus and yield stress) were measured using a TestexpertII Universal Testing System from Zwick Roell implementing ISO5833 test criteria.

SPSS 14 for Windows software was used for calculating statistics and data analysis.

Results: An increase in monomer/polymer ratio was associated with a significant (p= 0.00) increase in setting time (5.3–11.3 minutes) with a strong correlation (r2=0.988). However, there seemed to be no effect on Tmax (p=0.792).

Compression tests showed a significant (p=0.022) decrease in E-modulus (2.63 to 2.22 GPa) with a strong Pearson correlation negative coefficient (r2= −0.827).

Similarly, yield compressive stress showed a significant (p=0.002) decrease (121.83–101.19 MPa) with a strong negative correlation (r2= −0.93)

Conclusion: This experimental study shows that varying the ratio of monomer to polymer independently from other constituents in acrylic bone cement significantly affects setting time and compressive mechanical properties. Setting time can be prolonged to increase handling time; however this will occur at the expense of a reduction in compressive stiffness and strength.

This study aims to evaluate the accuracy of sheer off self limiting screw drivers and to assess repeatability with age.

It has been reported that overzealous tightening of halo pins is associated with co-morbidity. Our unit has recently received a tertiary referral where the patient over tightened a pin leading to intracranial haematoma, hence our interest in this subject. The torque produced by six new and nine old screw drivers was tested using an Avery Torque Gauge and a Picotech data recorder. These devices are designed to produce a torque of 0.68 Nm, any greater than this is potentially hazardous. Accepted error for each device was +/− 10%. The average torque produced by the new screw drivers was 0.56 Nm with a range of 0.35–0.64 Nm (SD 0.120). The older screw drivers produced an average torque of 0.67 Nm ranging from 0.52–0.85 Nm (SD 0.123).

In conclusion, sheer off self limiting screw drivers are not accurate devices. The older devices are more likely to produce a torque exceeding a safe range and therefore we would recommend the use of new devices only.

Ethics approval: none audit.

Interest statement: none local grant.

Introduction: Restoration of vertebral height for burst fractures can be achieved either anteriorly, posteriorly or combined.

Aim: To biomechanically assess and compare stiffness of 1) posterior pedicle screws with Synex, 2) Synex+ Double screw+rod Ventrofix 3) Synex+ Double screw+ Single rod and 4) Synex+ Single screw+ Single rod in reconstructing an unstable burst fracture following anterior corpectomy.

Method: Fresh frozen calf lumbar spines (L3–L5) were dissected and L4 corpectomy performed. L3 and L5 were mounted on a plate and fixed. Loads were applied as a dead weight of 2Nm. The range of movement was measured using the Qualisys motion analysis system using external marker clusters attached to L3 and L5. Bony landmarks were identified with marker clusters as baseline. The movement was measured between the 2 marker clusters.

Five specimens were implanted for each group 1) with pedicle screw (into L3 and L5) and tested with/without Synex (expandable) cage anteriorly, 2) implanted with a Synex cage and Double screw+rod Ventrofix system, 3) Synex cage and Double screw+ Single rod Ventrofix construct and 4) Synex cage and Single screw+ Single rod Ventrofix system.

Results: Reconstruction of the anterior column with the combination of Synex and double rod Ventrofix produces a stiffer construct than the pedicle screw system in all planes of movement (p= 0.001 in rotation).

The double screw/ single rod system is less effective than the Ventrofix System but is comparable to the pedicle screw construct.

The single screw/ single rod construct leads to unacceptable movement about the axis of the inferior screw particularly in extension with a ROM much greater than the intact spine (p< 0.001)

Conclusion: Thus biomechanically we recommend Synex and double rod Ventrofix construct to reconstruct the anterior vertebral column following corpectomy for unstable burst fractures.

Introduction and aim: prosthesis displacement while attempting closed reduction of a dislocated total hip or during dislocation itself is a rare but significant complication. We have come across three cases and there are at least six case reports in the literature. The aim of our study is to conduct an in vitro biomechanical study to assess, whether application of bone cement over the shoulder of the stem confers any additional advantage in the pull out strength of the implant.

Materials and Methods: We used fourteen saw bones and cemented seven bones with a standard cementing technique and another seven bones with additional cement over the shoulder of the implant. A tensile testing machine was used to assess the pull out force needed in both groups. A comparision was done between both groups.

Results: The mean pull out force in the routine cementing technique was 2066N(S.D. 256.65) and for the group with the cement on the shoulder was 3220N(S.D. 312.22). The mean difference was 1154N. The results were analysed with two-tailed t- test, unequal variance and the difference was statistically significant with p value of 0.00045.

Conclusion: Our experiment confirms that application of the bone cement over the shoulder of the implant does give additional axial stability and should be practised routinely to reduce this complication.

Leucocytes represent a very important host defence against a number of invading pathogens and neoplasia. However, the activity of phagocytic leucocytes has been heavily implicated in the development of ischaemia-reperfusion injury, and as an aetiological factor in the pathology of other clinically important inflammatory conditions. Ischaemia-reperfusion injury occurs in diseases such as stroke and ischaemic heart disease (IHD), and during surgical procedures such as orthopaedic surgery. Investigations presented here employed a model of tourniquet-induced forearm ischaemia-reperfusion injury to investigate the effect on leucocyte adhesion and trapping (n=20). Neutrophil and monocyte leucocyte subpopulations were isolated by density gradient centrifugation techniques. Neutrophil and monocyte cell surface expression of the adhesion molecule CD11b was measured by labelling with fluorescent anti-CD11b monoclonal antibody via flow cytometry. Plasma concentrations of the soluble intercellular adhesion molecule-1 (sICAM-1) and soluble L-selectin (sL-selectin) adhesion molecules were measured using commercially available ELISA kits. Leucocyte trapping was investigated by measuring the concentration of leukocytes in venous blood leaving the arm. During ischaemia-reperfusion there was an increase in CD11b expression on neutrophils (p=0.040) and monocytes (p=0.049), a decrease in sL-selectin (p=0.387) and sICAM-1 (p=0.089) concentrations, and a decrease in peripheral blood leucocyte concentration (p=0.019). Evidence of increased leucocyte adhesion and trapping during ischaemia-reperfusion injury was supported by an increase in CD11b cell surface expression of neutrophils and monocytes. CD11b is expressed on phagocytic leucocytes and binds to ICAM-1 expressed on the surface of vascular endothelium. This increased expression of CD11b on leucocytes may therefore play a central role as the mechanism by which leucocyte trapping in the microcirculation occurs. The measured decrease in plasma concentration of sICAM-1 and sL-selectin suggests that these adhesion molecules retain their functional activity, and may bind to their corresponding cell surface ligands. It is therefore reasonable to believe that ICAM-1 expressed on the endothelium and L-selectin expressed on leucocytes is also binding to their corresponding cell surface ligands. A decrease in the number of leucocytes in the peripheral circulation may be due to increased trapping of leucocytes in the microcirculation. When leucocytes become trapped their concentration in blood leaving the microcirculation decreases, resulting in the measured decrease in leucocyte concentration. In conclusion, this study confirms the important role of leucocytes during ischaemia-reperfusion injury, which could allow for the possibility of future research that may provide therapeutic intervention for inflammatory conditions.

Introduction: Surface replacement of the hip has been proposed as an alternative to total hip replacement, particularly in young active patients. The suggested benefits include preservation of bone stock for future revision surgery and avoidance of proximal femoral stress protection, which can cause bone resorption. However, following femoral head resurfacing, femoral neck fracture can occur.

The aim of this study was to compare the strain pattern in intact and resurfaced femurs using validated third generation composite femurs and rosette strain gauges.

Methods: Rosette strain gauges were applied to an intact and a resurfaced third generation composite femur at three sites; narrowest part of the lateral surface of the neck, narrowest part of the medial surface of the neck and medial surface at the level of lesser trochanter. The femurs were loaded with axial loads of 600N, 800N and 1000N sequentially. The tests were repeated thrice for each femur. Maximum and minimum principal strains were calculated.

Further tests were carried out in which an abductor load was included in the model. Testing was done at 600N and repeated thrice for each femur. The principal strains were calculated and compared with the the principal strains without the abductor load.

Results: The maximum principal strains in the resurfaced femur were approximately 50% higher in the lateral surface of the neck and about 30% higher in the lesser trochanteric region when loaded without including an abductor force. Inclusion of the abductor force decreased the strain particularly at the lateral surface of the neck by approximately 45% in the intact femur and approximately 25% in the implanted femur. Even with the inclusion of the abductor load the strain in the resurfaced femur remained more than 50% higher at the lateral surface of the neck and 20% higher in the lesser trochanteric region.

Conclusion: Our study suggests that proximal femoral stress protection will not occur following surface replacement of the hip. The increased strain at the lateral surface of the neck could result in fracture, particularly if there is notching of the neck or if abductor function has been compromised, which can happen particularly with the direct lateral approach.

Controversy exists as to whether the biomechanical properties of a 360 lumbar fusion are influenced by the order in which the anterior and posterior components of the procedure are performed.

The fusion technique used Magerl screws to effect the posterior fusion and a Syncage implant (Stratec) to effect the anterior component of the fusion.

Isolated motion segments from calf spines were tested in each of two groups of five. In the first group the posterior fusion was performed first and in the second group the anterior fusion was performed first. Loads were applied as a dead weight of 2Nm in each range of movement of the spine (flexion/extension, lateral flexion and rotation). The range of movement was measured using the Qualisys motion analysis software linked to a set of five cameras, using external marker clusters attached to the vertebral bodies. Each motion segment was tested prior to instrumentation, post anterior or posterior instrumentation and with both anterior and posterior instrumentation.

Ranges of movement following 360 instrumentation were increased in all planes tested when posterior fixation was performed first; flexion/extension 26% v 55% (p=0.020), lateral flexion 18% v 34% (p=0.382), and rotation 18% v 73% (p=0.034).

It was concluded that posterior fixation should not be performed prior to anterior fixation as this results in a significant loss of stability in both flexion/extension and rotation

Objective: Controversy exists as to whether the biomechanical properties of a 360° lumbar fusion are influenced by the order in which the anterior and posterior components of the procedure are performed.

Methods: The fusion technique used Mager screws to effect the posterior fusion and a Syncage implant (Stratec) to effect the anterior component of the fusion. Isolated motion segments from five calf spines were tested in each of two groups. In the first group the posterior fusion was performed first and in the second group the anterior fusion was performed first. Loads were applied as a dead weight of 2Nm in each range of movement of the spine (flexion/extension, lateral flexion and rotation). The range of movement was measured using the Qualisys motion analysis system, using external marker clusters attached to the vertebral bodies. Each motion segment was tested prior to instrumentation, post anterior or posterior instrumentation and with both anterior and posterior instrumentation.

Results: Ranges of movement following 360° instrumentation were decreased in all planes. When posterior fixation was performed first; flexion/extension reduced to 55% compared to 26% with anterior fixation first (p=0.020), in lateral flexion 34% v 18% (p=0.382), and in rotation 73% v 18%(p=0.034).

Conclusions: The 360° fusion construct has reduced range of movement if the anterior first approach is used as compared to posterior first approach. Posterior fixation should not be performed prior to anterior fixation as this results in a significant loss of stability in both flexion/extension and rotation.

Interbody fusion is increasingly widely used as a treatment for intervertebral disc disorders, but the biomechanics of the procedure are not well understood. The compressive loads through the spine are largely carried by the implant or bone graft, which typically rests on a relatively small area of the vertebral body. As the compressive strength of the bone is very low, subsidence of the implants into the vertebral bodies is a common clinical complication.

Previous biomechanical studies of spinal fusion have concentrated on the stiffness of the constructs, which is important in promoting fusion. Preliminary studies have shown that there are large differences in compressive strength between different implant systems, and gave an insight into the biomechanical factors that are important in determining the strength of spinal fusion constructs. This paper reports part of a larger on going study comparing anterior and posterior fusion systems, with various methods of fixation.

A major problem in interpreting the results of these tests is to distinguish between initial settling of the implants and the onset of failure to construct. We have developed a novel technique using acoustic emission monitoring to detect microcracking in the bones, which allows the onset of failure to be distinguished from initial bedding in of the implants.

Two implant systems were tested, the Syncage and the Contact fusion cage. The cages were implanted into porcine lumbar spines at L4-L5, and the implanted motion segment was then dissected out. Steel plates were mounted on each end using bone cement to ensure an even distribution of load through the vertebral body. The complete constructs were then loaded in compression, using acoustic emission sensors to detect microcracking in the bones. The load was cyclically increased in o.5kN steps until failure occurred.

The acoustic emission technique gave a sensitive indication of the onset of damage in the bones and allowed the initial settling of the implant under load to be identified. Using cyclic unloading and reloading, it was possible to accurately identify whether this damage had weakened the construct or increased its strength by redistributing stress concentrations. Initial results indicate that the Contact fusion cage fails at a much lower load than the Syncage in this model; this is ascribed to the very small contact areas between the cage and the vertebral body, which results in high compressive stresses in the bone. Under large compressive loads it appears that the constructs become unstable, and fail by buckling and plastic collapse of the vertebral bodies. Various failure models are therefore possible depending on which part of the vertebral body starts to collapse first.