Orthopaedic implants are often fixed into place using bone cement. The degradation of the cement mantle has been implicated as playing a major role in the loosening of these implants, and this often necessitates revision surgery. The present work has used the non-destructive acoustic emission (AE) technique to monitor the initiation and evolution of fatigue damage in bone cement constructs. Using this technique, it should be possible to gain an understanding of failure progression in cemented orthopaedic devices. Previous work in this area has focused on AE activity originating from the eventual failure location in order to identify those signatures associated with critical fatigue cracks. This usually involves analysing AE signatures associated with the final stages of failure; however, there have been limited investigations that have looked at the damage that takes up most of the crack propagation life of the sample, (i.e. microcracking formation and development), that occurs away from the failure site, but could still play a role in final failure.

In this study, dog-bone-shaped specimens of bone cement were subjected to uniaxial tensile fatigue loading, with damage monitored along the length of specimens using AE. Where specimens exhibited AE activity at locations away from the fracture site, they were sectioned and subjected to synchrotron tomography, which enabled high resolution images of these regions to be obtained. Microcracks of the order of 20 microns were observed in areas where AE had identified early, non-critical damage; in contrast, no microcracking was observed in areas that either remained unloaded or exhibited no AE. To further corroborate these observations, and characterise the damage mechanisms involved, scanning electron microscopy (SEM) was applied to the sectioned samples. In those locations where significant yet non-critical AE occurred, there was evidence of crack-bridging, suggesting that crack closure mechanisms may have slowed down or even arrested crack propagation within the bone cement.

These findings further validate the use of AE as a passive non-destructive method for the identification and understanding of damage evolution in cemented orthopaedic devices.

During hip replacement surgery the hip centre may become offset from its natural position and it is important to investigate the effect of this on the musculoskeletal system. Johnston et al [1] found that medialisation of the hip centre reduced the hip joint moment, hip contact and abductor force using a musculoskeletal model with hip centre displacements in 10mm increments. More recently an in vivo study found that the range of displacement of the hip centre of rotation was from 4.4mm laterally to 19.1mm medially [2]. To investigate the hypothesis that medialisation of the hip centre reduces the hip contact force, a musculoskeletal model of a single gait cycle was analysed using three scenarios with the hip in the neutral position and with it displaced by 10mm medially and laterally.

The lower limb musculoskeletal model included 162 Hill type muscle units in each leg and uses a muscle recruitment criterion based on minimising the squared muscle activities, where the muscle activity is the muscle force divided by the muscle’s maximum potential force. The maximum potential force is affected by the length of the muscle unit and the muscle’s tendons each are calibrated to give the correct length in its neutral position. The same gait analysis data from one normal walking cycle was applied to each modelled scenario and the resultant hip joint moment, hip contact force and muscle forces were calculated. The abductor muscles forces were summed and the peak force at heel strike reported. The peak resultant hip moments and the peak hip contact forces at heel strike are also reported and compared between the different scenarios. The scenarios were each run twice, once with the muscle tendon lengths calibrated for the hip in the altered position and subsequently with the muscle tendon lengths maintained from the neutral hip position.

For the medialising of the femoral head, the hip contact force and the peak abductor force were reduced by 4% and 2% respectively compared the neutral position. However if the tendon lengths of the muscles were maintained from the neutral position, the medial displacement model had a 3% higher hip contact force and a 6% larger abductor force than calculated for the neutral position. Although the peak resultant hip joint moment increases with a lateral displacement by 3%, the peak abductor force and peak hip contact force have a reduced force of 3% compared to the neutral hip. Using the muscle tendon lengths calibrated for the hip in the original position produces a 3% increase in the hip contact and abductor force for the lateralised femoral head.

This study has shown that the hip contact force and abductor force depend on the calibration of the muscle’s tendon lengths. Using the model with muscles calibrated for the altered hip centre produced the hypothesed reduction in hip contact force. However, maintaining the tendon lengths from the neutral position had a significant effect the calculated forces. The hip contact and abductor forces increased in the models with the original tendon lengths and the effect was also found to be greater when the hip was displaced medially.

Clinical management of ankle injuries often involves use of braces to provide pain relief and stability. Individuals with braced ankles may be at more risk of injury while turning. The aim of this study was to evaluate the biomechanical effects of one of the commonly prescribed pneumatic ankle braces on gait parameters while turning.

Three-dimensional gait data was collected using a 7 camera, VICON 612 (Oxford Metric, UK) motion analysis system (120 HZ) synchronised with a single Kistler force plate embedded in the floor and set at a sampling frequency of 600HZ. Sixteen retro-reflective markers were attached to anatomical landmarks on both lower limbs and pelvis using wig tape. In the case of the braced ankle, markers were attached on the brace over the respective body landmarks.

Out of ten trials, five were performed with and the other five without brace. Comparative results were produced between braced and un-braced ankle during turning at 90 degrees with the right foot landing on the force plate and turning right. Results show that use of brace is effective in reducing gross moments about the ankle joint even at the time of turning but it does not totally eliminate motion.

Both conditions showed different rotation moments at knee but hip rotation moments were not affected by the brace. Knee rotation moment without brace was mainly in internal rotation (0.301Nm/kg) towards the terminal stance phase and it reduced to 0.128Nm/kg by bracing the ankle.

A new type of turning strategy was identified where the subject pre-planned the turn in late swing phase before landing on the ground probably to avoid a fall. It is important that patients with ankle injuries receive supervised gait training to improve their turning confidence during their rehabilitation therapy.

Aim: To investigate the training of civilian Orthopaedic Trainee’s in complex trauma management.

Methods: A web-based survey of orthopaedic trainees utilising three scenarios for investigating complex trauma management. 225 responses obtained, achieving a < 0.05 error rate with 90% confidence.

Results:

Pelvic packing in exanguinating pelvic trauma:

2.2% fully confidentto manage such a case. A positive correlation exists between increasing training and confidence. 58.9% have never seen such a case. No correlation exists between time in training and exposure. 62.8% report training in this case inadequate. A positive correlation exists between time in training and perceived inadequacy of ability to manage such a case.

Junctional traum with non-compressible groin haemorrhage:

0.4% fully confident. A positive correlation exists between time in training and confidence. 73.0% have never seen such a case. 67.9% report training in this case inadequate. No correlation was found between time spent in training and perceived training adequacy.

Blood product resuscitation in trauma:

11.6% were fully confident. 18.8% have never seen such a case. No correlation exists between time in training and confidence or exposure. 45.0% report training as inadequate in this case. No correlation seen between time in training and perceived training adequacy.

Conclusion: Current training provides limited opportunities for exposure to significant trauma.

The quality of care afforded to service personnel and civilians in recent conflict is unsurpassed and it is essential that the lessons learnt by deployed surgeons form a continuum to their successors.

For military orthopaedic trainees this reinforces the need for closely supervised secondments on deployment; attendance at established military surgical training courses and appropriate fellowships to maximise exposure prior to first consultant deployment.

Aim: To establish confidence and perceived adequacy of training of UK Orthopaedic Specialist Trainees in assessment of limb viability and amputation.

Methods: A web based survey of orthopaedic trainees using scenarios centred around limb viability assessment and amputation resultant from trauma. 225 responses obtained, achieving a < 0.05 error rate with 90% confidence.

Results:

Limb viability:

27.8% were fully confident. A positive correlation exists between training year and fully confident reports. 68.6% encounter such injury either every six months or less frequently. 18.6% regard their training in these cases inadequate. No correlation seen between experience and perceived adequacy of training.

Amputation:

10.3% were fully confident. A positive correlation exists between time in training and perceived fully confident reports.

57.3% encounter such injury either every six months or less frequently. 36.3% regard their training in these cases inadequate. No correlation seen between experience and exposure to cases or perceived adequacy of training.

Conclusion: Current training provides limited opportunities for decision making in limb viability and amputation. Confidence in dealing with such cases is seen to increase with training. Perceived adequacy of training did not change over time.

Military orthopaedic surgeons are providing injured service personnel and civilians with the best possible chance of successful rehabilitation from these injuries. It is fundamental that the experience of these individuals is accessible to their successors.

For military trainees, this reinforces the need for participation in closely supervised secondments on deployment, attendance at established military surgical training courses and appropriate fellowships to maximise exposure prior to completion of training and first consultant deployment.

A child with traumatic laceration of the tendo Achillis developed secondary infection after primary repair. This resulted in the loss of 5 cm of the distal part of the tendon and overlying soft tissue. The patient was treated with a free skin flap to cover the wound and to control the infection leaving reconstruction for a second-stage procedure.

However, when he was assessed two years after the skin-flap, delayed reconstruction proved to be unnecessary since he had regained normal ankle function spontaneously and could demonstrate equal function in both tendons.

Introduction: The Pavlik harness is widely used in the management of developmental dysplasia of the hip and its efficacy in the treatment of instability and acetabular dysplasia is well established. There are some hips which although reducible consistently fail to stabilise in a harness irrespective of the age of application. We report three cases in which through altering the method of application of the harness, stability and subsequent normal development was achieved.

Method: Three patients age one week, six weeks and twelve weeks failed to stabilise in a harness applied in the conventional fashion. By rerouting the posterior “abduction strap” in front of the anterior “flexion” strap and attaching it as usual distally we observed improved abduction and more restriction of movement such that the unstable hip was held reduced. Reduction was confirmed by anterior ultrasound. The harness was converted back to the conventional application at four weeks by which time all of the hips had stabilised clinically. It was retained for a further eight weeks.

Results: Significant dysplasia was evident in all three hips at presentation ( alpha angles 32, 48 and 34). At average follow up of 23 months all hips were concentrically reduced with no significant persisting dysplasia nor evidence of avascular necrosis.

Discussion: Early reduction and stabilisation of the femoral head in DDH is important if subsequent intervention is to be minimised and it has been suggested that the more rigid Von Rosen splint is more effective than the Pavlik in achieving this. Our early experience with this simple modification has been successful in treating three unstable hips which would otherwise have failed splintage in our hands. We recommend it as an option to consider in the unstable hip, in conjunction with anterior ultrasound to confirm that reduction has been achieved from the outset.

Introduction: Reduction of ultra high molecular weight polyethylene (UHMWPE) wear in total knee replacement (TKR) bearings may delay the onset of osteolysis and subsequent loosening of components. This study used finite element (FE) modelling and in vitro simulator testing to investigate the effect of wear path geometry on UHMWPE surface wear.

Methods: The wear of PFC Sigma fixed bearing TKRs (DePuy) was investigated using a six-station force/ displacement controlled knee simulator (frequency 1 Hz) using previously developed methods [1]. High, intermediate and low kinematic inputs were simulated for up to five million cycles (Table 1) with identical flexion-extension and axial loading for all components. This kinematic data was also applied to a FE model of the PFC Sigma TKR and run using PAM-CRASH-SAFE software. The anterior-posterior (AP), medial-lateral (ML) and inferior-superior data were recorded and the resulting wear paths generated by selecting nodes from the contacting surface of the polyethylene relative to the femoral.

Results and Discussion: The mean wear rates with 95% confidence limits on the simulator when subjected to high, intermediate and low kinematics were 22.75 ± 5.95, 9.85 ± 3.7 and 5.2 ± 3.77 mm3 per million cycles, respectively. All FE models exhibited looped wear paths. An example wear path for the first 60% of the gait cycle for a lateral node is displayed in Figure I. The high kinematics model generated the greatest ML displacement and similar AP displacement to the intermediate kinematics model. The low kinematics model showed least ML and AP displacements. The AP displacements for medial wear paths differed little when subjected to the different kinematics. A looped wear path on the surface of UHMWPE results in greater cross shear transverse to the principal direction of motion, which is parallel to AP displacement in TKR and is the axis along which strain hardening occurs. This study revealed that increased AP displacement and tibial rotation kinematics generate more looped wear paths, increase ML and AP displacements on the surface of fixed bearing TKR and result in greater cross shear which ultimately increases UHMWPE surface wear.

Aims: To evaluate the effect of tapered pegs in reducing tibial tray tilt and subsidence in closed cell foam. Methods: 1. Foam validation was carried out using a load frame (Instron) to establish its static and fatigue behaviour. 2. Subsidence and tilt tests: Three brass peg sets of varying length and matching surface area were designed. Four identical pegs of each set were fixed with screws to an IBII tibial tray and testing was performed using the load frame and the closed cell foam. Results: Foam validation revealed an average strength of 0.65±0.01 MPa in compression and 1.53±0.02 MPa in tension and an average stiffness of 40.2±1.5 Mpa in compression and 50.4±1.06 Mpa in tension. Subsidence tests revealed a significant increase in the total load producing 0.2mm subsidence with pegs ( p< 0.0053) and no significant difference for 1 and 2mm (p> 0.1). Tilt tests revealed a significant increase in the total load producing 0.2mm tilt with the medium and short pegs ( p < 0.008 & < 0.042 respectively) and no significant difference for 1 and 2mm (p> 0.1). Conclusions: The foam analogue material shows similar behaviour to cancellous bone in both static and dynamic tests and suggests that polymer foams are a good analogue material to cancellous bone. The addition of tapered conical pegs to the tibial tray increases its resistance to initial subsidence while initial tilt resistance is increased only with the medium and short pegs. Combining tilt and subsidence resistance, the medium pegs perform most favourably.

The purpose of this study was to determine if routine x-ray exposure produced any chemical oxidation of Ultra High Molecular Weight Polyethylene (UHMWPE), used for joint arthroplasty.

Three different polyethylene polymers were obtained from Biomet, Depuys and Howmedica. These samples had undergone sterilisation and packaging methods. Rectangular shapes of polymer were cut according to the standards specified by the ASTM (American Society For Testing and Materials). Eight samples of each polymer were obtained and divided randomly in to test and control subgroups. The test samples were exposed to ten x-rays with the standard dose used for the hip joint.

Polyethylene oxidation was measured using Fourier transform infrared spectroscopy. This technique can assess the incorporation of oxygen within the carbonyl region. Radiated and non-irradiated samples were compared in each polymer group.

Oxidation from the Fourier transform infrared spectroscopy was quantified by calculating the area under a signature absorption peak for UHMWPE (methylene band at 1370 cm-1) and an oxidation absorption peak (carbonyl band at 1720 cm-1). The ratio of the area of the oxidation peak to the area of the signature peak yields the carbonyl content, or oxidation, relative to the amount of polyethylene. There was no significant difference in oxidation after exposure to x-rays between test and control UHMWPE samples.

Although numerous studies have looked in to the effects of high dose radiation exposure on polyethylene, effects of routine x-rays have not been studied before. It is common practice to follow-up patients with joint replacements over a long period with xrays at each visit. Present study examined the effects of routine x-rays on oxidation of polyethylene. However there was no detectable oxidation after exposure to x-rays. This study paves way for further research in this direction.

We have compared the survival and radiological outcome at ten years after total hip replacement using two techniques for preparing the femoral canal. The same prosthesis was used throughout and all operations were performed by the same surgical team. In technique 1 the canal was over-reamed by 2 mm and in technique 2 it was reamed to the same size as the prosthesis. Technique 1 was performed on 92 patients and technique 2 on 97 patients.

The survival at ten years was 97.2% (90.6 to 99.2) for technique 1 and 98.8% (92.9 to 99.8) for technique 2. Vertical migration was greater in technique 1 (1.8 mm versus 1.0 mm at five years; p = 0.36). There were significantly more lytic lesions and radiolucent lines at five years (p = 0.0061) with technique 1. We conclude that technique 2 is not worse and may produce better long- term results than current teaching suggests.

Purpose: Posters of study: To produce a virtual reality model of prosthetic knee joint motion, giving detail regarding contact area and contact pressures during the process of walking.

Method: Using serial CT scans and data regarding the material properties of bone, cartilage, ligaments and other soft tissue structures a computational “virtual reality model” of the knee has been constructed. This computational model which is a 3D dynamic representation of a human knee joint, may be programmed to replicate the standard gait pattern of the human knee.

This study details the development of this model and its validation against the accepted Stenmore Test Rig for modelling of knee joint movement and knee prosthetic wear. The validation results will be presented,

The model allows the calculation and representation of contact pressures and contact areas in the knee joint as it moves through the gait cycle. This study also shows the effect of uni-condular loading and varus mal-positioning which may occur at surgery and the effect this has on the contact area and contact pressures of a prosthetic knee in ambulation. The resultant gait pattern produced by uni-condular loading and exhibited by the virtual knee closely resembles that seen in In Vivo Kinematic Studies reported by other authors.

In conclusion we present this as a valid computational dynamic model of knee prosthetic wear and kinematics which represents an enormous advantage over standard mechanical testing and presents possibilities for rapid analysis in new knee joint designs and the effect of abnormalities of gait and wear.

Inter-observer agreement and reproducibility of opinion were assessed for the radiographic diagnosis of union of scaphoid fractures on films taken 12 weeks after injury. Weighted kappa statistics were used to compare the opinions of eight senior observers reviewing 20 sets of good quality radiographs on two occasions separated by two months. There was poor agreement on whether trabeculae crossed the fracture line, whether there was sclerosis at or near the fracture and on whether the proximal part of the scaphoid was avascular. As a consequence, agreement on union also was poor; it appears that radiographs taken 12 weeks after a scaphoid fracture do not provide reliable and reproducible evidence of healing.