Cancer associated bone pain (CIBP) is a common event in patients with advanced disease with bone metastases (BM), significantly impairing their quality of life. Treatment options are limited and mainly based on the use of opioids with unacceptable side effects. Local acidosis is a well-known cause of pain since it directly stimulates nociceptors that express acid-sensing ion channels and densely innervate bone. In BM, local acidosis derives from osteoclast bone resorption activity and from the acidification by glycolytic tumor cells. Here we speculated that the pH lowering of intratumoral interstitial fluid also promotes nociceptors sensitization and hyperalgesia through the activation of cells of mesenchymal origin in BM microenvironment that might release inflammatory and nociceptive mediators.

As a model of breast cancer that can metastatise to the bone we used MDA-MB-231 (MDA), and a subclone with a higher tendency to form osteolytic BM (bmMDA). We evaluated the basal expression of proton pumps/ion transporters by Real-Time PCR (Q-RT-PCR). To evaluate the effect of extracellular acidosis on mesenchymal tumor-associated stroma, we used human osteoblast primary cultures from healthy donors and cancer-associated fibroblasts isolated with specific immunobeads from the tumor biopsies of patient with BM. We exposed the cells to pH 6.8 medium at different time points (between 3 to 24 hours). After the short-term incubation with acidosis, for the expression of and acid-sensing ion channels, inflammatory cytokines and nociceptive mediators that can produce hyperalgesia, we used both a wide screening through a deep-sequencing approach and Q-RT-PCR, and ELISA. Xenograft for osteolytic BM induced by intratibial injection of bmMDA were treated with Omeprazole and monitored for CIBP through several cognitive tests.

We found a significantly higher extracellular proton efflux and expression of proton pumps/ion transporters associated with the acid-base balance, the monocarboxylate transporter 4 (MCT4), the carbonic anhydrase (CA9), and the vacuolar ATPase (V-ATPase) V₁G₁ subunit, and V₀c subunitin bmMDA, a subclone that is prone to form BM in respect to the parental cell line MDA-MB-231. In mesenchymal stromal cells, osteoblasts and cancer-associated fibroblasts, the incubation with pH 6.8 induced the expression of the achid-sensing ion channels AISC3/ACCN3 and AICS4/ACCN4, as well as of the nociceptive modulators nerve growth factor (NGF), Brain-derived neurotrophic factor (BDNF), and of the inflammatory cytokines interleukin 6 (IL6) and 8 (IL8), and Chemokine (C-C motif) ligand 5 (CCL5). Furthermore, the targeting of V0c subunit to inhibit intratumoral acidification significantly reduced CIBP in mice model of BM.

In this study we demonstrated for the first time that, in addition to the direct acid-sensing neuronal stimulation, the acidic microenvironment of BM causes hyperalgesia through the activation of an inflammatory reaction in the tumor-associated mesenchymal stroma at the tumor site, thereby offering as a new target for palliative treatment in advanced cancer.

Recent emphasis in total knee arthroplasty has been on accelerated rehabilitation and recovery. Minimally invasive and quadriceps sparing techniques have been developed to expediate return to normal function. The aim of this study was to evaluate the effect of the tourniquet on post-operative pain and quadriceps function in total knee arthroplasty.

This study involved a randomised, blinded, prospective trial of 20 patients undergoing total knee arthroplasty by a single surgeon. All patients received a general anaesthetic, identical prosthesis and post-operative protocol. Patients were randomly allocated to one of two group: (a) tourniquet group or (b) no tourniquet group. A standard surgical tourniquet was applied to all patients but only inflated in the tourniquet group.

Outcomes included Oxford knee scores, post-operative pain scores, post-operative drainage and transfusion requirements, thigh and knee circumference measurements, range of motion, and surface EMG measurements at intervals of two weeks, six weeks, six months and twelve months.

The study included 16 male and four female patients with 11 right and nine left knees. There was no significant difference pre-operatively between groups in age, degree of deformity or range of motion.

There was no significant difference detected between Oxford knee scores up to twelve months, days to discharge, post-operative drainage and range of motion. However, the pain scores were significantly higher in the tourniquet group. Surface EMG as a measurement of quadriceps activation showed a significant difference between the groups and between time points. The no tourniquet group can support more energy in their quads muscle than the tourniquet group

The use of a tourniquet in total knee arthroplasty has no effect on overall knee function at twelve months as measured by the Oxford knee score and range of motion; however tourniquet use results in higher initial pain scores and reduction in quadriceps function as measured by surface EMG.

The Birmingham Hip Mid Head Resection (BMHR) was designed to accommodate patients with lower quality bone in the proximal half of the femoral head. It is a relatively new conservative hip implant with promising early results. Finite element modelling may provide an insight into mid-term results.

A cadaveric femur was CT scanned and 3D geometry of the intact femur constructed. The correctly sized BMHR implants (with and without visual stop) were positioned and these verified by a surgeon; hence constructing the post-operative models. Walking loads were applied and contact surfaces defined.

Stress analyses were performed using the finite element method and contact examined. Also, a strain-adaptive bone remodelling analysis was run using 45% gait hip loading data. Virtual DEXA images were computed and were analysed in seven regions of the bone surrounding the implants.

The BMHR was found to be mechanically stable with all surfaces indicating micromotion less than the critical 150 microns. Stress distribution was similar to the intact femur, with the exception of the head-neck region where some stress/strain shielding occurs. This is mirrored in the bone remodelling results, which show some bone resorption in this region. The visual stop, which is designed to ensure that the stem is not overdriven during implantation, did not affect the stress/strain results; only on a very local scale.

There is minimal data available in the literature regarding conservative hip implants and no data regarding the BMHR. This study is the first to look at the mechanical response of the bone to this implant.

The advantages of unicompartmental knee arthroplasty (UKA) include its bone preserving nature, lower relative cost and superior functional results. Some temporary pain has been reported clinically following this procedure. Could this be related to bone remodeling? A validated bone remodeling algorithm may have the answers…

A 3D geometry of an intact human cadaveric tibia was generated using CT images. An all poly unicompartmental implant geometry was positioned in an inlay and onlay configuration on the tibia and the post-operative models created. An adaptive bone remodeling algorithm was used with finite element modeling to predict the bone remodeling behavior surrounding the implant in both scenarios. Virtual DEXA images were generated from the model and bone mineral density (BMD) was measured in regions of interest in the AP and ML planes. BMD results were compared to clinical results.

The bone remodelling algorithm predicted BMD growth in the proximal anterior regions of the tibia, with an inward tendency for both inlay and onlay models. Looking in the AP plane, a maximum of up to 7% BMD growth was predicted and in the ML plane this was as high as 16%. Minimal BMD loss was observed, which suggests minimal disturbance to the natural bone growth following UKA.

Positron emission tomography (PET) scans showed active hot spots in the antero- medial regions of the tibia. These results were consistent with the finite element modeling results.

Bone remodeling behavior was found to be sensitive to sizing and positioning of the implant.

The adaptive bone remodeling algorithm predicted minimal BMD loss and some BMD growth in the anterior region of the tibia following UKA. This is consistent with patient complaint and PET scans.

Introduction: Cemented hip resurfacing component orientation may, in part, be associated with femoral neck fracture. Orientation offset may be introduced due to the cement setting prior to achieving a completely seated component. Varus/valgus orientation error may occur due to surgical error or poor instrumentation design. We modeled a number of different orientations and investigated bone mineral density change using the finite element method.

Methods: CT scans were used to reconstruct the femoral geometry and create a finite element model. The boundary conditions applied were hip muscle forces at the 45% position of the gait cycle. Two models were created, a preoperative (reference) and a postoperative (reconstructed) model. The post operative model was reconstructed using the Birmingham Hip Replacement (BHR). Implant offsets and varus/valgus orientations were analysed. The bone mineral density (BMD) changes at nine positions along the superior and inferior aspects of the alignment stem were analyzed.

Results: Results suggest bone loss decreases with increasing offset distances. Femoral offset distance is defined as the perpendicular distance from the center line of the femoral shaft to the center of the femoral head. Greater femoral stem offsets increases the abductor moment arm and this decreases the abductor force need for walking as well as the overall articulating reactive force at the articulating surface. As the BHR orientation deviates away from the an extreme valgus to a more varus position, the volume of bone that will decrease in BMD increases.

Discussion: There is minimal difference between the 1mm and 3mm offsets and their respective bone remodeling volumes. The 5mm offset has a larger bone volume where the BMD will increase; this is due to the larger moment applied to the proximal femur and is not an advisable surgical position as there may be a large density gradient at the mouth of the resurfacing component and could predispose the femoral neck to fracture. There is also not a lot of difference in bone remodeling volume between the extreme valgus, 5° and 10° cases. However, the extreme valgus case does present a “notching” risk. The objective of this study was to implement a consistent theoretical adaptive bone remodelling rule that may, in part, give an understanding as to how a femoral resurfacing component’s orientation would influence and simulate BMD changes in the proximal femur.

Introduction: Squeaking is reported ceramic-on-ceramic hip bearings in association with acetabular component malposition – particularly too much or too little anteversion. Acoustic analysis of squeaking hips with modular ceramic-titanium acetabular components suggests that there may be dynamic uncoupling of the ceramic insert from the titanium shell with edge loading of the ceramic. The aim of this study was to investigate edge loading of a modular ceramic-titanium acetabular component during gait at different positions of anteversion using the finite element (FE) method.

Methods: An intact and reconstructed 3D FE model of a human pelvis was generated using PATRAN. Bone properties extracted from the CT data were applied using FORTRAN subroutines. A generic acetabular titanium shell and ceramic liner were modelled and placed in the pelvis in two different positions: ideal anteversion and 18 degree excess anteversion. The contact conditions simulated a fully osseointegrated acetabular shell and a matched taper junction with a friction coefficient of 0.2. We ran FE analysis with ABAQUS software to determine the stress distribution and surface separation of shell and liner at toe-off.

Results: The separation distance between the ceramic liner and the acetabular shell for the anteverted component (40mm) was an order of magnitude greater than that for the ideally positioned component (4mm). There was “tilting” of the ceramic liner out of the acetabular shell in both cases.

Discussion: Based on clinical observations, the toe-of phase of gait is a common position for squeaking to occur. Clinical retrievals also show evidence of edge loading wear and contralateral taper interface separation with the “tilting” of the liner out of the acetabular shell. It is envisaged that the “tilting” of the liner in the acetabular shell may allow forced vibrations associated with the squeaking phenomena, possibly in combination with edge loading.

Introduction: Bone resorption at the bone-implant interface is still a problem, leading to pain, poor function and the possibility of bone fracture. This loss of supporting bone tissue is due to resorption and impaired bone formation. Loosening of an implant is often not clinically or radiographically apparent for 8–10 years. It would be beneficial if these potential failures could be identified early so that revision surgery can be avoided. The aim of this study was to investigate the influence of implant material property changes and its influence on the trabecular loading patterns of the underlying supporting bone structure.

Methods: An intact and reconstructed 3D finite element (FE) model of a human femur was developed. The model was generated using PATRAN and CT scans. This was used to determine the stress, strain and interface sliding of a knee implant at heel-strike and stair climbing phases of gait. FE analysis of the model was performed using ABAQUS software. The materials properties of the bone were extracted from the CT data and applied using FORTRAN subroutines. Implant-bone interfaces were simulated using cementless fixation concepts. Sliding contact conditions were applied to simulate the immediate post-operative period.

Results: Three material property cases were analysed, with respect to the intact bone, at 100%, 25% and 2.5% of cobalt chrome’s (CoCr) Youngs modulus. At heel-strike, for the 100% case, higher stress was found at anterior flange while lower stress dominated around the pegs and intercondylar notch. For the 25% case, lower stresses were found in the intercondylar notch and higher stresses above the pegs. For the 2.5% case, stresses resembled that of intact bone, higher stresses were found above the pegs and lower stress in the intercondylar notch. In stair-climbing, for the 100% case, lower stresses were found around the pegs and in the intercondylar notch. For the 25% case, lower stresses were found in the intercondylar notch and higher stresses in areas above the pegs. For the 2.5% case, higher stresses were found at the distal condyles and lower stresses were observed in the intercondylar notch.

Discussion: The analysis presented changes in the trabecular loading and subsequently resulted in stress shielding. The general trend showed that the majority of stress shielding is occurring at the posterior flange and medial condyle while increased trabecular loading occurred at the anterior flange and lateral condyle regions. As the stiffness of the implant decreases from 100% to 25%, the differences in trabecular loading are extremely small. Both these implant material properties are very stiff in comparison to the underlying trabecular bone. However, as CoCr stiffness is decreased to 2.5% this yields a more homogenous stress distribution at the contact interfaces.

Introduction: Prevalence of femoral neck fracture in resurfacing hip arthroplasty continues to question if failure is technique-related or due to the inherent bone quality. This study aimed to correlate cement penetration profile during resurfacing hip with inherent bone density. The hypothesis is that osteoporotic bone is unable to support the prosthesis leading to fatigue failure.

Methods: Fifteen patients scheduled for total hip replacement (THR) were recruited to undergo resurfacing arthroplasty prior to THR. Each patient was implanted with a resurfacing femoral component (BHR, Smith & Nephew, Memphis, TN). Antibiotic simplex cement was inserted one minute after mixing at 18°C to fill 10% of the femoral component volume. The femoral head-implant section was removed and kept in buffered formalin. The patients then proceeded with standard THR. The femoral head-cement-prosthesis section was separated using electrical discharge (ED) machining technique and CT-scanned. The depth and volume of cement penetration were measured from the CT scans and correlated with femoral neck bone densities.

Results: Cement penetration was compared for three groups of bone density: normal, osteopenic, osteoporotic. Average cement thickness were found to be 0.36 ± 0.16mm (proximal), 0.28 ± 0.11 mm (centre) and 0.12 ± 0.05 mm. During hip resurfacing, cement is forced into the porous structure, e.g. the trabeculae and airspaces when the femoral component is fixed onto the head of the femur. In normal bone, the trabeculae is dense and air spaces occupy a small volume of the bone. Greater cement penetration was expected in osteopenic and osteoporotic bones. However, no significant difference was found between cement thickness and volume against inherent patient bone density (p> 0.05). High viscosity of the cement may have prevented more cement to penetrate the bone. While the exterior cortex of the femoral head is strengthened by a cement layer, the interior structure of the femoral neck is still susceptible to fracture at high loads. In addition, increased bone necrosis due to the exothermic reaction during cement fixation may predispose patients to fracture.

Discussion: Resurfacing hip replacement is a viable technique if the fracture risk can be reduced by gaining the best possible cement penetration. This would provide continuous cement stiffness with the bone.

Introduction: The process of impacting cemented hip resurfacing components may, in part, be associated with femoral neck fracture. The impaction process may introduce fractures due to the impact shock wave passing through the bone during the setting of the implant and achieving a completely seated position. The aim of this study was to measure the impaction loads during hip resurfacing surgery and correlate the measured loads to theoretical calculations.

Methods: Following ethical approval 3 patients have been enrolled out of 24 patients in a pilot study. A surgical mallet was manufactured and instrumented with a calibrated impact load cell. During the impaction procedure the impact loads are recorded to a laptop using Labview software. An Excel spreadsheet has been written using the finite difference method to calculate the impact loads based on a mass (hammer, impactor and implant) and spring system (compression only) defining each part of the surgical instrumentation used to impact the resurfacing component onto the femoral head.

Results: Clinically, upto 19 impacts are used to seat the resurfacing implant onto the femoral head. Loads upto 24kN were recorded. The finite difference model was calibrated to the clinical measurements. The Pearson’s R correlation coefficient for the net force on the mallet was 0.91 and for the impulse was 0.98

Discussion: This study has investigated the clinical impaction loads imparted onto an implant during resurfacing surgery and developed a finite difference model of the process. The finite difference approach can be used to better understand the loads applied to not only the implant, but the underlying bone. This may, in part, give the surgeon a better understanding as to whether the bone has been predisposed to fracture following the high impact loads and thereby affecting the long-term integrity of the joint replacement.

To determine the effect of experience of the operator and the effect of type of anaesthesia used on re-manipulation rates of fracture distal radius manipulated in A& E, a retrospective review of distal radius fractures manipulated in A& E between January 2000 and January 2001. Operators were divided into two categories: junior (SHO grade) and senior (higher grade) doctor.

54 patients with fracture distal radius had manipulation in A& E. 15 male and 39 female patients with mean age of 61 years (52 for males and 63 for females) were included.

42 (78%) fractures were manipulated under haematoma block (18 by junior, 23 by senior doctor) and 12 (22%) fractures were manipulated under Bier block (1 by junior, 11 by senior doctor). Operator’s grade was not clearly mentioned in one case. 13 out of 54 patients (24%) needed fracture re-manipulation under general anaesthesia. 12 out of 42 fractures manipulated under haematoma block (30%) needed re-manipulation compared to only one out of 12 fractures (8%) manipulated under Bier block (p=0.25). 9 out of 19 fractures manipulated by junior doctors needed re-manipulation compared to only 4 out of 34 fractures manipulated by senior doctors (p=0.007). Haematoma block was used for 18 out of 19 cases by junior doctors and for 23 out of 34 cases by senior doctors (p=0.038). Average number of fracture clinic follow-ups was 4 (range 2 to 8).

Junior doctors had significantly higher preference for haematoma block and significantly higher re-manipulation rate. Re-manipulation rates were higher with fractures manipulated under haematoma block compared to Bier block.

Adequate training and supervision should be provided for SHOs while performing such procedures in A& E. Use of Bier block as a regional anaesthesia for manipulation of distal radius fractures in A& E should be encouraged.

Introduction: The biomechanical properties of tendon and ligament have long been the subject of intense research. The understanding of the ultrastructure as it relates to the biomechanical function and clinical demands have often considered the ultimate properties at failure alone. Tendons and ligaments are predominately loaded in-vivo at subfailure loads and often in the initial toe region. To date, little work has focussed on the viscoelastic properties of the tendon in the initial toe region. The biomechanical behaviour at these low loads may reflect the unique mechanical interactions between the fasciles and collagen fibrils. This study examined stress relaxation of ligaments in the initial non-linear portion of the load vs. displacement curve.

Methods: Six flexor tendons (2.5 mm wide x 1mm thick) were harvested from 18 month cross bred whethers and stored in 0.145 M NaCl until testing. Tensile testing was performed on a MACH 1 Micromechanical Testing Machine (BIOSYNTECH, Laval, Quebec, Canada) in 0.145M phosphate buffered saline at room temperature. Tendons (gauge length 30mm) were displaced to 0.5, 1 and 5% strain at a loading rate of 50 microns/sec and stress relaxation measured over a period of 300 seconds and repeated for 4 sequences. Data was analysed using an analysis of variance.

Results and Discussion: Peak loads at 0.5 % strain ranged from 50 g (sequence 1) to 130 g (sequence 4) while at 5 % strain peak loads reached upwards to 1600 g. These loads are well within the initial toe region of the load-displacement behaviour of the ligament. The MACH 1 testing system provide a reliable and highly accurate system to control micron level displacements and mg load resolution. Recently, Yamamoto and coworkers reported the stress relaxation behavior and strain rate effects of collagen fascicles differed greatly from those of bulk tendons. The differences in tensile and viscoelastic properties between fascicles and bulk tendons may be attributable, in part, to ground substances, mechanical interaction between fascicles, and the difference of crimp structure of collagen fibrils. The present study supports an important role of tissue ultra-structure at low loads with regard to stress relaxation. Subtle changes in ground susbtance, water content or biochemical consituents not evident in testin

Introduction: Various plating devices and screw systems are available for single and multi-level cervical fusions. Recent reports regarding screw migration under torsional load and a “windshield wiper effect” has brought to light the importance of plate and screw design as well as the choice of graft.

Aim: This study examined the relative stability of cervical plating systems under pure bending and axial-torsional fatigue using the Cloward type graft.

Methods: Five fresh-frozen human cervical and 10 porcine spines assessed by dual-energy x-ray absorptiometry (DEXA) scanning and then reconstructed at the C_2–3 and levels using the anterior Cloward technique. C_4–5 Two different plating systems (a solid plate and a hollow plate) were used and alternated between the C2–3 and C4–5 levels. Strain gauges placed on the plates themselves. The systems were subjected to pure bending and torsional loading.. Five kilogram loads were used to apply bending moments to the spine and did not differ between the two systems evaluated. Bending moments and displacement angles were recorded for the pure bending loading regime and torque versus time was recorded for the torsional fatigue loading.

Results: Strain gauge analysis revealed minimal strains on the plates under the loading conditions. Torque versus time was measured, and the decay constant was calculated from the decay curves. The hollow plating system decayed quicker than the solid plating system. Angular displacement under pure bending was minimal. The hollow system plate system resisted greater torque compared with the solid system. The decay curves eventually reached an asymptote for the both systems. This implied that the systems become stable under fatigue loading. The X-rays illustrated no failure at the screw/ bone interface (i.e. No “wiper” effect) after torsional fatigue.

Introduction: Unicomparmental knee replacements have a long clinical history of success as well as failure. Recently, in Australia some 40% of knee surgery performed consists of unicompartmental knees for the treatment of medial compartment OA. This increased use of unicompartmental knees is in part due to advances in surgical technique through a minimally invasive approach. Loading conditions at the tibia-implant interface will play an important role in the stress/strain distributions at the proximal tibia. The use of an all PE tibial insert versus a metal backed component may provide a different strain disribution to the proximal tibia. This study examined the influence of metal backed and polyethylene tibial components in unicompartmental knee replacements with and without cement fixation on the initial strain distributions under various loading conditions.

Materials and Methods: Three cadaveric tibias (mean age 47 years old) were cleaned of all soft tissue and strain gauged. Rosette strain gauges (TML Ltd., Tokyo, Japan) were placed at 2 levels on the tibial cortex. The intact tibia were embedded in a low melting point alloy at a standard height and tested using an MTS 858 Bionix testing machine (MTS Systems, Min., MI). The tibia were tested in nuetral, varus and valgus positions at zero and sixty degrees of flexion. A 1500N was applied for 15 seconds and the strains measured. A K-Scan sensor (Tekscan, Boston, MA) was used to confirm the varus and valgus loading positions and to obtain a contact footprint and pressure for the intact and reconstructed tibias under the loading conditions (Fig. 1). Following intact testing, the tibias were templated and reconstructed by a surgeon familiar with the technigue. The implants were investigated with and without cement fixation and compared to their respective all polyethylene component if it was available using the same loading regime as the intact tibias. Principal strains were calculated.

Results: Tibial cortical strain distributions were significantly different at the proximal and distal sites under the loading conditions examined. The strain distribution for metal backed components was greater than the all PE design. Increasing flexion angle shifted the peak strains posteriorly. Metal backing and all PE tibial inserts presented different strain distributions on the medial side under nuetral and varus loading. Lateral compartment strains did not differ between designs, were higher proximal and decreased dramatically at the distal gauges. Cementless fixation tended to overload compared to the intact condition. Figure 2 presents the strain distribution for a typical metal backed and all poly unicompartmental knee in the nuetral position.

Discussion: Metal backed unicompartmental components overloaded the proximal cortex of the tibia. All polyethylene tibial inserts did not overload the proximal cortex and had similar strain distribution to the intact tibia. Cemented fixation allows the transfer of load to the distal tibial cortex via the proximal cortex and subchondral bone, provided that the bone cement has inter-digitised the subchondral bone.

Introduction: The stress and strain in the proximal femur after total hip arthroplasty are influenced by the geometry of the implant in addition to its materials properties and applied loading. The addition of a third taper in the medio-lateral plane may provide additional stability and improved load transmission.

Aim: To examine the relative stability of double and triple tapered stems in two finite element (FE) models.

Methods: The geometry of a polished, double-tapered and a triple-tapered stem were scanned using a three dimensional technique. Two FE models of the stems were created using PATRAN. The models were analysed using the ABAQUS. Tied and sliding contact conditions were allowed between the implants and the cement mantle. The interface at the distal tip of the stem was removed to represent the scenario with a distal centraliser present.

Results: When tied contact was assumed, both stems displayed similar von Mises’ stress distributions. The peak stresses remained constant in the double tapered stem, with a marked translation of regions of high stress towards the distal tip with the introduction of sliding contact conditions. Peak stresses in the triple tapered stem decreased, but displayed a more continuous distribution along the implant with sliding contact. Torsional loading of the stems reduced the magnitude of the distal tip stresses.

Conclusions: The triple-tapered geometry displayed a more even distribution of stresses along the length of the implant. The double-tapered geometry displayed a high stress state at the distal tip of the implant.

Introduction: Proximal bone resorption is a common problem after total hip arthroplasty. This has been attributed to stress shielding and has been reported to be more pronounced for cemented than for uncemented implants.

Aim: To investigate the cortical strain distribution of a new proximal “fit and fill” cementless, titanium, femoral, hip prosthesis based on the SROM design.

Methods: Strain gauges were mounted on five fresh-frozen cadaveric and five saw-bone femora and checked against a template for the prosthesis. The strain gauges were placed at four levels on the anterior, posterior, medial and lateral cortices corresponding to the Gruen zones. Two extra strain gauges were placed on the proximal posteromedial cortex. Loading was applied to the intact and reconstructed femora in the ISO 7206–4 orientation and single legged stance in an MTS servo-hydraulic testing machine. Data were analysed using analysis of variance.

Results: The strain distributions following reconstruction and multi-axis loading (ISO 7206–4 orientation) approximated the strains in an intact femur in the diaphysis. The proximal posteromedial cortical strains were approximately 50% of those of the intact femur.

Conclusions: The strains observed in the proximal femur following reconstruction in the present study are considerably higher than most others reported in the literature. A number of factors may contribute to the high proximal strains observed. This study has illustrated that geometric design and material selection along with surgical technique may allow for greater loading to proximal bone and enhance the long term integrity of this type of implant.

Introduction: A tibial tubercle osteotomy can be used in the exposure of severe articular deformity and the tight knee in total knee arthroplasty, especially revision surgery. This osteotomy has been popularised by Dr. L. Whiteside [1] who described transosseous wiring to secure the osteotomy following joint reconstruction. Other fixation techniques including the use of cables and screws may provide options for this technique. The current study exmained 3 different fixation methods for tibial tubercle osteotomy using an in-vitro sheep model.

Materials and Methods: Tibial tubercle osteotomies (5 cm in length) were performed in ten adult sheep tibias. The osteotomies were fixed sequentially using circumferential Dall-Miles cables (Howmedica, Ritherford, NJ) (Fig. 1), transosseous wires and lastly 2 AO screws. Testing of each fixation configuration was performed using an MTS 858 Mini Bionix servo hydraulic testing machine (MTS Systems Corporation, USA). The loading regime used a cyclic 200 N load applied along the line of the patellar tendon with micromotion measured at the osteotomy and adjacent bone using optical sensors (MEL, Bahnhofstr, Germany). Data was analyzed using ANOVA. Micromotion at the end of the osteotomy fragment was recorded for 150 cycles for each tibia following reconstruction with cables, wires, and screws in succession.

Results: Cable fixation provided the most stable construct followed by screws and wires respectively. Wire fixation had the greatest variation in micromotion (370 microns). The ovine tibia model provides a reproducible bone bed to evaluate different fixation strategies for tibial tubercle osteotomy. Clinically, differences may even be marked considering anatomic and bone quality issues as well as magnitude of the load that have not been addressed in this in-vitro study.

Discussion: Fixation of the osteotmoy is an important surgical technique. Wolff et al. found that major complications related to the surgical technique occurred in 23% of the knees performed in 26 cases [2]. Reis et al. [3] observed fixation with 3 or 4 titanium screws was sufficient after a follow-up period of 18 months. Twenty-nine of the osteotomies healed primarily. One patient developed postoperative displacement of the tibial tubercle requiring additional screw and suture fixation. This study has shown that micromotion of a tibial tubercle osteotomy fixation in sheep is dependent upon fixation technique. Cables provided the most stable fixation compared to screws and wires in an ovine tibial model.

Introduction: Uncemented humeral components rely heavily on initial stability and fixation as a function of the design of the implant. Concerns over initial torsional stability of humeral components have motivated the development of a variety of design concepts.

Aim: To investigate the torsional stability of two types of cementless humeral shoulder prostheses.

Methods: Twelve fresh-frozen cadaveric humeri were cleaned of all soft tissues and prepared for reconstruction with the two types of cementless humeral shoulder prostheses. The humeri were embedded in a low melting point alloy and tested in a servohydraulic-testing machine. The loading applied to the humeri was a controlled angle loading regime at ± 1.5 degrees for 150 cycles. Torque versus time was measured, and the exponential time constant was calculated.

Results: The Z implant displayed overall a tightening effect, and a positive time constant. Whereas the G implant displayed a negative time constant, i.e. a loosening of the implant.

Discussion: These differences reflect the initial stability achieved immediately following surgery and may have important implications for bone in-growth and long-term stability.

Introduction: Arthrodesis of the shoulder joint is appropriate for several conditions, including paralysis, degenerative disease, infection, and salvage of failed arthroplasty. Two common complications of shoulder fusion, non-union and unacceptable arm position, may reflect failure to achieve rigid fixation during the surgical procedure. Numerous fixation techniques have been described, including plate fixation, external fixation, and screw fixation.

Aim: To compare the biomechanics of five fixation techniques of shoulder fusion in a human cadaveric model.

Methods: Twenty-five shoulder fusions were carried out in fresh-frozen human cadaveric specimens with the following five techniques: screw fixation alone (n=5), external fixation alone (n=5), external fixation supplemented with screw fixation (n=5), single plate fixation (n=5), and double plate fixation (n=5). Each specimen was tested on a servo-hydraulic machine under repeated physiologic loads to determine the bending and torsional stiffness.

Results: There was a statistically significant difference in bending and torsional stiffness between all five fixation techniques (ANOVA, p< 0.05). Normalised bending (B) and torsional (T) stiffness, in descending order, were: double plate (B=1.0, T=1.0), single plate (B=0.77, T=0.89), external-fixation with screws (B=0.68, T=0.74), external-fixation alone (B=0.40, T=0.53), and screws alone (B=0.13, T=0.26).

Discussion & Conclusion: Statistically significant differences in bending and torsional stiffness have been identified using five different techniques of shoulder fusion. The risk of the most common complications of this surgical procedure, non-union and unacceptable arm position, may be minimised if these biomechanical findings are applied to surgical decision-making.