Introduction: The biological activity of autologous grafts is due to a number of proteins (growth factors) that control bone cell differentiation, proliferation and expression. Several of these have been isolated including; bone morphogenetic proteins 2 and 7. These are commercially available and regularly used with the intention of accelerating fracture healing, repairing critical sized defects and combating bone mineral loss. Whilst it is commonly recognised that multiple growth factors are present at differing times in the healing cascade, the usual delivery, both in the clinic and the laboratory, is of one growth factor delivered over a very short and early time period. Commonly growth factors are delivered in solution or from a collagen sponge and are quickly metabolised in the proteolytic wound healing environment. The physiological need for BMPs is later than the acute delivery at the time of surgery. The aim of this study is to develop a granular protein delivery system that enables controlled release of multiple proteins at a variety of time points.

Methods: A series of homogenous polymer granules 8mm3 were prepared by photo-polymerising 12uL of mixtures of methacrylated adipic acid anhydride (MAAA) and methyl methacrylate (MMA) or MAAA and butyl methacrylate (BMA) with molar ratios ranging from 100- 55 % (MSAA). Into each granule 5ug of a model drug, carmoisine was loaded and 1%w/w of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) photoinitiator was added per granule. The granules were exposed to UV light at 390nm for 14 minutes. Multilayered granules were prepared photo-polymerising 4uL layers of different monomer compositions in a similar method to the single layered method above. The composition of the multilayered granules was chosen to optimise the release profile. Carmoisine release profiles were determined by UV-visible spectroscopy.

Results: Homogenous granules composed of 100% MAAA released 90% of their payload by 24hrs, those composed of 90:10 MAAA:MMA released by 48hrs those composed of 70:30 MAAA:MMA released by 80hrs those composed of 60:40 MAAA:MMA released by 170hrs those composed of 70:30 MAAA: BMA released by 288hrs and those composed of 60:40 MAAA:BMA released by 456hrs. The multilayered granule had a sustained release of the model drug over the test period of 19 days.

Discussion: The limitation of most drug delivery systems, such as microspheres or collagen, is poor control over the release profile. The drug is ether released instantly or well after it is required. This multilayered composite drug delivery system enables the controlled release of different bioactive compounds at different time points between 0 and 19 days. By altering the drug loading in each layer we were able to sustain the release of one compound over this time period. This technology enables us to switch compounds at a given time points for example delivery of angiogenic factors for one week, proliferative factors for the second week and differentiation factors for the third week. This technology enables the pre-programmed release of multiple growth factors at times in the healing cascade when they meet the physiological need. A controlled release of growth factors at the appropriate time should improve bone healing rates.

Introduction: Acute neurological damage from spinal cord injuries is believed to be localised, however it initiates a cascade of secondary events which usually leads to extensive and permanent neurological deficit. The secondary damage begins with the disruption of the blood-spinal cord barrier which unleashes a protracted inflammatory response. This prolonged inflammatory response is the catalyst for the secondary neurodegeneration and limited repair response that occurs in the chronic phase of a spinal cord injury. In this study it was proposed that the acute delivery of the angiogenic growth factors vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) would mediate inflammation and restore the blood spinal cord barrier. This would minimise the formation of glial scar and reduce the extent of secondary degeneration caudal and cranial to the lesion site.

Methods: Adult male Wistar rats (400g) were anesthetised. Complete laminectomies were performed at T10 and the animals were subjected to T10 hemisection. Animals were randomised to a treatment group (Lesion Control (LC), Gel Control (GC) and Angiogenic Gel (AG)) after the spinal cord was cut. Each treatment group had 6 animals sacrificed 3 months post injury. Sections were stained with antibodies to neurofilament 200, glial fibrillary acidic protein, smooth muscle actin (SMA), and fluorescent secondary antibodies and mounted with DAPI. The lesion size was measured from horizontal histological sections of the midline from 5 animals in each group using Axiovision version 4.6.1.0 (Carl Zeiss Imaging Solutions, Germany).

Results: The mean lesion size for the lesion control group was 2.09mm2, 1.97mm2 for the gel control group and 0.45mm2 for the active gel group. A t-test was used to confirm that the differences between the active gel and the two control groups were statistically significant (AG vs LC p= 0.021 AG vs GC p= 0.026). Histology showed a marked improvement of the morphology of the astrocytes in the treatment group over the control groups indicating that the treatment affected the population of reactive astrocytes. SMA staining showed an increased level of revascularisation in the treated lesions.

Discussion: Spinal cords do not heal because of prolonged inflammation which leads to secondary necrotic events, scar formation and the inhibition of regeneration. In this study we present a method for regulating the post lesion inflammatory signals, significantly reducing post-lesion scar formation. We propose the delivery of VEGF/PDGF significantly increases the permeability of the blood spinal cord barrier to neutrophils and macrophages and promotes angiogenesis observed in the lesion site. This may have two major effects on the progression of the spinal cord injury. Firstly, by increasing the initial influx of inflammatory cells it enables the faster removal of damaged tissue and phagocytosis of apoptotic cells thereby restoring the balance in favour of regulated inflammation and results in a finite and reduced inflammation time. Secondly, combination of VEGF and PDGF provides a robust angiogenic response and reduces ischemia, the population of reactive astrocytes and the capacity to form glial scars. These growth factors appear to moderate the secondary degenerative changes that result from the prolonged inflammation and thus promote the inherent capacity for regeneration.

This presentation introduces a new tool to be used in the cementing of acetabular components in total hip arthroplasty, the ‘Rim Cutter’. The Rim Cutter is designed to cut a ledge in the rim of the acetabulum into which a flanged cup can be cemented. The flange is trimmed such that it fits precisely into the ledge cut in the acetabulum. We present the in vitro pilot study of the effect of using this tool on the intra-acetabular cement mantle pressure during cup insertion and also the effect on the depth of cement penetration as the cup is inserted. A significant improvement in both cement pressure and cement penetration over conventional flanged and unflanged cups is noted. Improved cement penetration around the rim of the acetabulum in THR has implications for reducing the rate of aseptic loosening. The pilot study also suggests other beneficial features of using the rim cutter such as improved cup centralisation, control of orientation and the prevention of the cup ‘bottoming out’. Further in vivo studies are required to better assess its efficacy.

To regenerate the complex tissue such as bone-cartilage construct using tissue engineering approaches, controllable differentiation of mesenchymal stem cells (BMSCs) into chondrogenic and osteogenic lineages is crucially important. Although bilayered scaffolds have been investigated in vitro and in vivo, no culture system is available to test BMSCs differentiation into bone and cartilage simultaneously in bilayered scaffolds. This study investigated a defined culture media, which supported osteoblast and chondrocyte differentiation depending on growth factors implemented in biomaterials. In 2-dimensional culture, BMSCs differentiated to chondrocytes when transforming growth factor-beta 3 (TGF-β3) was added to the defined media, whereas osteogenic differentiation was induced by adding bone morphogenetic protein 7 (BMP-7). BMSC differentiation to osteogenic and chondrogenic lineages was further strengthen in 3-dimensional culture. Proteoglycan formation, type II collagen, and aggrecan were upregulated in the defined media when BMSCs were mixed with fibrin gel impregnated with TGF-β3. Mineralization and the expression of osteogenic markers such as alkaline phosphatase, osteopontin, and osteoclacin were noticeable when BMSCs cultured in hydroxyapatite-tricalcium phosphate (HA/TCP) scaffolds coated with BMP-7.

This study generated and tested a growth media, which could induce osteogenic and chondrogenic differentiation of BMSCs in one culture system. These results will help the development of tissue substitutes for multi-complexed tissues such as subchondral replacement.

Bone Tissue Engineering Program, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia

Adult mesenchymal stem cells (MSCs) are a topic of immense research interest in the field of tissue engineering. Since, depletion of multipotent cells has been implicated in degenerative joint diseases, cell based therapies have been proposed for tissue regeneration, especially for cartilage repair. The aim of the present study is to focus on the possibility of deriving and expanding multipotential MSCs from the heterogeneous bone marrow stromal samples of patients with osteoarthritis (OA) by characterising MSCs at the single cell level.

Single cell clonal cultures were established by limiting dilution of marrow stromal cells from three OA patients. A total of 14 clones with a wide variation in their cell doubling time were isolated. The clones were grouped into fast-growing and slow-growing clones. All except one of the fast-growing clones were tripotential. However the slow-growing clones showed limited differentiation potential and morphological changes associated with cellular senescence with extended duration in culture. Flow cytometric analysis did not depict any difference in the expression of the selected putative MSC cell surface markers CD29, CD44, CD90, CD105 and CD166 between fast-growing and slow-growing clones indicating a strong need to investigate for novel cell-surface markers. Further, proteomic analysis to understand the sub-cellular processes responsible for the existence of varying sub-populations identified 11 differentially expressed proteins. These proteins were reported to be associated with cellular organization, signal transduction, energy pathways and stress related proteins. Identification of signaling pathway proteins and cell cycle related proteins, such as calmodulin and caldesmon in the clonal populations, suggest that high-throughput proteomic technologies like two dimensional liquid chromatography (2D LC) coupled with mass spectrometry (MS) may facilitate the discovery of therapeutically useful biomarkers.

This study demonstrated the existence of a fast-growing multipotential MSC population from bone marrow samples of patients with OA. Therefore, despite a supposedly smaller stem cell compartment in these patients, we demonstrate here that they can still yield a potentially therapeutically useful source of syngeneic MSCs.

Synthetic biodegradable polymers have been utilized increasingly in pharmaceutical, medical and biomedical engineering. Control of the interaction of living cells and biomaterials surfaces is one of the major goals in the design and development of new polymeric biomaterials in tissue engineering.

In this study, a novel amphiphilic tri-block copolymer, methoxy-terminated poly (ethylene glycol) (MPEG) – polyL-lactide (PLLA) – polylysine (PLL) was synthesized. Various molecular compositions of tri-block copolymers were prepared via optimising the parameters and characterized through Nuclear Magnetic Resonance and Gel Permeation Chromatography. The tri-block copolymer was then mixed with high molecular weight PLLA to form a flat film. The surface properties measured by X-ray Photoelectron Spectroscopy and Atomic Force Microscopy demonstrated high content of the PLL on the surface of PLLA film, which indicated self-segregation of MPEG-b-PLLA-b-PLL on PLLA surface. No cytotoxicity was detected in triblock copolymers, and compared to pure PLLA and diblock copolymers, the triblock copolymers were much more effective for cell adhesion and proliferation. It was noted that the hydrophilic chain of PEG and PLL stretched out and formed an outer layer, especially under the aqueous environment, which resulted in enhanced cell attachment and proliferation. The self-segregation behaviour of MPEG-b-PLLA-b-PLL triblock copolymer shows a potential application in scaffold preparation of tissue engineering.

Interactions between cells and polymers are mediated by proteins, which are either secreted by cells and immobilized on the biomaterial surface, or absorbed from the medium. Poly (lactic acid) (PLA) is widely used in tissue engineering as a scaffold material, however anchorage-dependent cells such as osteoblasts do not attach, grow, and differentiate well on a hydrophobic surface. In this study, a hydrophilic polymer-poly (ethylene glycol) (PEG) was used to develop diblock polymers, Methoxy-terminated poly (ethylene glycol)-Poly (lactic acid) (MPEG-PLA) to investigate cell-biomaterial interactions. Osteoblasts were cultured on different composition of PEG-PLA films in serum free or serum condition. Lactate dehydrogense (LDH) assay was used to assess the cytotoxicity of the copolymers and cell attachment and proliferation on the polymer surfaces; furthermore cell morphology was visualized by Crystal Violet stain.

The results showed that MPEG-PLA films induced early osteoblast attachment in serum free condition and the higher content of PEG in the MPEG-PLA films the more cell attachment was noticed. No significant difference of cell attachment was observed on MPEG-PLA films between serum free and 10% serum culture condition. Crystal Violet stain demonstrated the same trend in the cell-spreading characteristics on the polymer surface.

In conclusion MPEG-PLA copolymer can enhance osteoblast attachment under serum-free condition, which implies a potential application in cell delivery therapy due to the restriction in animal products for human therapeutically goods.

In both physiological and pathological processes, periosteum plays a determinant role in both bone formation and fracture healing. However, no specific reports are available so far focusing on the detailed structural and major cellular differences between the periostea covering different bone surface areas in relation to ageing. The aim of this study is to compare the structural and cellular differences in diaphyseal and epiphyseal periostea in different-aged rats using histological and immunohistochemical methods.

Four female Lewis rats from each group of juvenile (7-week old), mature (7-month old) and aged groups (2-year old) were sacrificed and the right femur of each rat was retrieved, fixed, decalcified and embedded. 5μm thick serial sagittal sections were cut and stained with Hematoxylin and Eosin, Stro-1 (stem cell marker), F4/80 (macrophage marker), TRAP (osteoclast marker) and vWF (endothelial cell marker). 1mm length of middle diaphyseal and epiphyseal periosteum were selected for observation. The thickness, total cell number and positive cell number for each antibody in each periosteal area and different-aged groups were measured and compared. The results were subjected to ANOVA and SNK-q tests.

The results showed that the thickness and cell number in diaphyseal periosteum decreased with age (p< 0.001). In comparison with diaphyseal area, the thickness and cell number in epiphyseal periosteum were much higher (p< 0.001). There were no significant differences between the juvenile and aged groups in the thickness and cell number in cambial layer of epiphyseal periosteum (p> 0.05). However, the juvenile rats had more Stro1+, F4/80+ cells and blood vessels and few TRAP+ cells in different periosteal areas compared with other groups(p< 0.001). The aged rats showed much less Stro1+ cells, but more F4/80+,TRAP+ cells and blood vessels in the cambial layer of epiphyseal periosteum (p< 0.001).

In conclusion, the age-related structure and cell population in diaphyseal and epiphyseal periostea are different, especially in aged rats. The epiphyseal periosteum of aged rats seems more destructive than diaphyseal part and other age groups. Macrophages in the periosteum play a dual important role in osteogenesis and osteoclastogenesis.

Bone Tissue Engineering Program, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, QLD 4059, Australia.

Osteophytes are the most remarkable and consistently distinct feature of osteoarthritis (OA). Their formation may be related to pluripotential cells in the periosteum responding to stimulus during OA. This study aimed to isolate stem cells from osteophyte tissues, and characterise their phenotype, proliferation and differentiation potential, and immuno-modulatory properties.

Osteophyte derived cells were isolated from five osteophyte tissue samples collected during knee replacement surgery. These cells were characterised by the expression of cell surface antigens, differentiation potential into mesenchymal lineages, growth kinetics and modulation of allo-immune responses.

Multipotential stem cells (MSCs) were identified from all osteophyte samples namely osteophyte derived MSCs (oMSCs). The surface antigen expression of oMSCs was consistent with that of mesenchymal stem cells, such as lacking the haematopoietic and common leukocyte markers (CD34, CD45) while expressing those related to adhesion (CD29, CD166, CD44) and stem cells (CD90, CD105, CD73). The longevity of oMSCs in culture was superior to that of bone marrow derived MSC (bMSCs), and they readily differentiated into tissues of the mesenchymal lineages. oMSCs also demonstrated the ability to suppress allogeneic T-cell proliferation, which was associated with the expression of tryptophan degrading enzyme indoleamine 2,3 dioxygenase (IDO).

Our results showed that osteophyte derived cells had similar properties to mesenchymal stem cells in the expression of antigen phenotype, differential potential and suppression of allo-immune response. Furthermore, when compared to bMSCs, oMSCs maintained a higher proliferative capacity, which may offer an alternative source for therapeutic stem cell based tissue regeneration.

Introduction: Although there are several accepted methods of surgical treatment for single level cervical radiculopathy, the choice depends on the surgeon’s preference. The techniques may vary in perioperative morbidity, short and long term outcome, but no study so far has analysed their cost-effectiveness. To compare the outcome and cost-effectiveness of four techniques commonly used for degenerative cervical disc pathology.

Methods: We conducted a observational cohort study from two spinal units. Between 1999 and 2004, 60 patients underwent surgery for single level anterior cervical disc pathology. Out of this 30 patients underwent their surgery in centre A the other 30 in centre B. Centre A used two ACDF techniques-group 1- plate and tricortical graft, group 2- plate, cage and bone substitute (BCP granules). Centre B used two other techniques- group 3- cage alone with autologous locally harvested graft, group 4- disc arthroplasty. We had 15 patients in each of the above four groups. Operating time, blood loss, duration of stay, donor site morbidity, analgesia requirements, and total cost incurred per patient were recorded. All patients were followed up at 6 weeks, 3 months, 6 months, 1 year and 2 years. The clinical outcome and pain assessment were done using the SF12 and VAS.

Results: The three Fusion groups had a similar radiological outcome. With appropriate statistical analysis, there were no differences in physical and mental domains of the SF12 or pain scores between the groups. The average operative time in the group 1 was 160 minutes, group 2 was 100 minutes, group 3 was 90 minutes and group 4 was 105 minutes. Average blood loss was minimal in all groups. The average hospital stay was of 5, 2.7, 2.5, 2 days for groups 1–4 respectively. The average total cost per patient in the group 1 (surgery+stay+plate) was £2790, group 2 (surgery+stay+plate+cage+BCP) was £2400, group 3 (surgery+stay+cage) was £1900, and group 4(surgery+stay+disc implant) was £2350.

Conclusion: All the techniques gave similarly satisfactory clinical outcomes but using cages alone could be more cost-effective than using iliac crest auto-graft for fusion. The disc arthroplasty was comparable to cage with bone substitute and plate in terms of outcome and may giev the surgeon an alternative choice in patients who are not keen on/ unfit for fusion.

AIM: To compare the outcomes between two different surgical techniques for cervical myelopathy (skip laminectomy vs laminoplasty).

METHODS: Cervical skip laminectomy is a new technique described by Japanese surgeons in 2000. The advantage of this procedure over the other conventional techniques is it addresses multilevel problem in a least traumatic way without need for instrumentation.

We are comparing the above two techniques with 25 patients in each group operated by 3 surgeons. The first group had conventional laminoplasty and the second group underwent the skip laminectomy. The groups were comparable in age, sex, pathology and clinical presentation. Both these group had clinical outcome measurements using SF 12 questionnaires, pre and postoperative clinical assessment with standard tools performed by independent surgeon and a specialist spinal physiotherapist. We also routinely performed pre and postoperative MRI scans to assess the adequacy of decompression.

RESULTS & CONCLUSION: There was no significant difference in the outcome of these patients in terms of the operative technique, hospital stay, clinical and radiological outcome. However skip laminectomy is relatively a easier procedure to perform, while the laminoplasty does need instrumentation.

Introduction: Dislocation remains one of the most common orthopaedic complications of hip replacement. Surgical technique, implant design and patient factors have been suggested as risk factors. The 2005 AOA Joint Registry recorded data on 101, 952 hip procedures between 1999 and 2004. We analyzed risk factors for early revision in this group of patients.

Methods: Ethics approval was obtained then a formal application was made to the Australian Joint Registry to release the required data. All primary hip replacements between 1/09/1999 – 31/12/2004 were studied. Statistical analyses of traditional risk factors including initial diagnosis, sex, age and head size were performed. We also studied the effect of fixation method on revision for dislocation.

Results: A total of 65,992 primary hip replacements across all diagnoses groups recorded were investigated with regard to diagnosis. The only initial diagnoses with significantly increased relative risk (RR) of revision for dislocation compared to osteoarthritis was fractured neck of femur (RR 2.25, p< 0.0001) and rheumatoid arthritis (RR 1.9, p< 0.01).

58,109 primary hip replacements for osteoarthritis were investigated for effect of age group, sex and fixation method. Age group and sex were not significant risk factors in revision for dislocation. Studying fixation method, cementless acetabular components were implanted more frequently (49,027, 84%) than cemented (9,082, 15.6%). In total, there were 428 (0.7%) revisions for dislocation, 369(0.8%) with a cementless acetabulum and 59 (0.6%) with cemented. Relative risk (cementless v cemented acetabulum adjusted for age group, sex and head size) of 1.59 (CI 1.19 to 2.12, p< 0.01). Head sizes of > 30mm, 28mm, 26mm and 22mm had significantly increasing relative risk (p< 0.001).

Discussion: The results from this large database indicate rheumatoid patients and those after fractured neck of femur have increased risk of revision for dislocation compared to osteoarthritis. Many of the traditional groups thought to be at higher risk of dislocation were not associated with an increased risk of revision for dislocation. These included age group, sex, avascular necrosis, developmental dysplasia and failed internal fixation. Cementless acetabuli have a higher rate of revision for dislocation. This has not been previously reported. Further investigation is needed to identify the cause of this finding.

Introduction/Aims: Early results of a prospective randomised control trial suggested improved position of components implanted during primary hip replacement. The aim of this study is to definitively show the benefit of computer aided navigation in hip arthroplasty with regard to acetabular component position, stem position and leg length.

Method: Eighty consecutive patients were prospectively recruited. Patients were quasi-randomised, on an alternating basis, to undergo hip arthroplasty conventionally or with imageless computer navigation. Postoperatively, a CT scan was performed of the pelvis and lower limb. Using a dynamic CT planning software package, the cup and stem position was measured and compared to the position expected by the three operating surgeons in control cases and the position given by the navigation unit in the study group. Change in leg length was measured clinically and compared with the navigation predicted leg length change. Statistical analysis was performed by a statistician.

Results: Thirty nine navigated hips (29 female, 10 male) and forty one control hips (26 female, 15 male) were recruited. In the navigated group, the mean age was 65.7 and mean BMI was 29.1. In the control group, the mean age was 64.7 and the mean BMI was 29.4 in the control group. Uncemented, securfit/trident hips were used in 18 navigated cases and 20 control cases, with all other cases being cemented Exeter stems and contemporary cups. None of these differences were significant using the Mann-Whitney test. The mean operating time was 128 minutes for navigated hips and 84 minutes for controls, the difference significant at p< 0.005 using t-test.

There was no significant correlation between clinical leg length change, measured in the operating theatre and the leg length change predicted by navigation. Accuracy of cup and stem placement was assessed by comparison of the homogeneity of variances, the Levene statistic, in the navigated and control groups. The range of cup inclination, cup version and stem version was significantly narrowed in the navigation group (p< 0.05).

Conclusion: Computer navigation improves the accuracy of component placement in hip arthroplasty with respect to cup version, cup inclination and stem version with either cemented or uncemented hips.

Purpose: To compare two different techniques of inter-body fusion in treatment for single level degenerative spondylolisthesis with symptomatic spinal stenosis.

Methods: Retrospective review of patients with degenerative spondylolisthesis and spinal stenosis treated with decompression and instrumented posterior interbody fusion with and without cages. Between 1996 and 2003 there were 59 patients with single level degenerative spondylolisthesis and spinal stenosis. Of these 32 were treated with complete laminectomy, interbody grafting and pedicle screw fixation. In the second group of 27 patients, the technique was modified by the incorporation of an interbody cage in an attempt to improve the restoration of lordosis. Both groups were comparable in terms of pathology, age, sex, intraoperative technique and were treated by the same surgeon. All patients were followed up at 6, 12, 26 and 52 weeks with radiographs and were assessed for fusion and maintenance of lordosis at a minimum of 1 year.

Results: There was a statistically significant difference between pre and postoperative lordotic angles in both groups. There was no significant difference in clinical outcomes between the two groups, nor was there a statistical difference in postoperative lordotic angles at the end of 1 year between the two groups. We had 2 deep infections in the cage group. There was one implant failure in the no cage group.

Conclusion: We did not find any advantage in using interbody cages in treating single level degenerative spondylolisthesis.

Aim: To compare the outcomes between two different surgical techniques for cervical myelopathy (skip laminectomy vs laminoplasty).

Methods: Cervical skip laminectomy is a new technique described by Japanese surgeons in 2000. The advantage of this procedure over the other conventional techniques is it addresses multilevel problem in a least traumatic way without need for instrumentation.

We are comparing the above two techniques with 25 patients in each group operated by 3 surgeons. The first group had conventional laminoplasty and the second group underwent the skip laminectomy. The groups were comparable in age, sex, pathology and clinical presentation. Both these group had clinical outcome measurements using SF 12 questionnaires, pre and postoperative clinical assessment with standard tools performed by independent surgeon and a specialist spinal physiotherapist. We also routinely performed pre and postoperative MRI scans to assess the adequacy of decompression.

Results and Conclusion: here was no significant difference in the outcome of these patients in terms of the operative technique, hospital stay, clinical and radiological outcome. However skip laminectomy is relatively a easier procedure to perform, while the laminoplasty does need instrumentation.

Introduction Anterior column reconstruction and fusion remains the gold standard of treatment for a number of spinal pathologies. One of the challenges of interbody fusions cages is the footprint of the cage reducing the surface area of endplate available for fusion. Biodegradable polymer implants will over time present a greater area for fusion and may help to reduce problems such as stress shielding, particulate debris and retained foreign body response. Resorbable cages have been have been prepared from a number of different materials, including inorganic composites (eg hydroxyapatite / tricalcium phosphate) and polymers (Poly L-lactide-co-D,L-lactide (PDLLA)). However all of the current options for interbody fusion have reported deficiencies or complications. The synthesis, mechanical properties, and degradation behaviour of two novel biopolymers are presented and the applicability for use as materials in interbody fusion devices is discussed.

Methods Methacrylated adipic anhydride (MAA) and methacrylated sebacic anhydride (MSA) pre-polymers were synthesized by melt condensation. Conversion of the acid to the anhydride was confirmed using 1H nuclear magnetic resonance (NMR) (Bruker, Alexandria, NSW) and FT- Infrared spectroscopy (Nicolet, Waltham MA). These pre-polymers were subsequently co-polymerized with methyl methacrylate (MMA) and 0.25 wt% benzoyl peroxide at 65oC for 16hrs and post-cured at 120oC under vacuum for 2 hrs to form biodegradable networks. The co-polymerization behaviour was monitored by FT-Raman spectroscopy. The compressive mechanical properties of the polymer were determined using an Instron 5567 (Bayswater Vic.). The polymer networks were degraded in phosphate buffered saline (PBS) with various amounts of MAA and MSA.

Results The formation of the pre-polymer was confirmed with the observation of NMR peaks at 5.8 and 6.2 ppm and FT-IR peaks at 1637cm-1. Copolymerization was followed with consecutive FT-IR acquisitions with 100% conversion achieved between 10 and 30 hrs depending on the ratio of MMA to MSA or MAA. Increasing the fraction of methacrylated anhydride slowed the reaction rate.

The compressive strength of the MAA and MSA based copolymers was measured as a function of anhydride concentration. Compressive strength for MMA increased (90±9 to 140±10 Mpa) in an approximately linear manner for MAA concentrations from 10 to 40 wt.% but decreased markedly for MAA concentration of 45% (62±14 Mpa). The compressive strength of MSA decreased exponentially for concentrations ranging from 10 to 45 wt.% (140±18 to 39±1 Mpa).

Discussion The use of poly-L-lactic acid in lumbar interbody cages has been shown to be mechanically feasible with the mechanical strength of the cage material reported to be 93 Mpa (1). The material described here has controlled mechanical properties in the required range as well as a degradation behaviour that lends itself better to spinal applications than current materials

Computer aided joint replacement surgery has become very popular during recent years and is being done in increasing numbers all over the world. The accuracy of the system depends to a major extent, on accurate registration and immobility of the tracker attachment devices to the bone. This study was designed to assess the forces needed to displace the tracker attachment devices in the bone simulators.

Bone simulators were used to maintain the uniformity of the bone structure during the study. The fixation devices tested were 3mm diameter self drilling, self tapping threaded pin, 4mm diameter self tapping cortical threaded pin, 5mm diameter self tapping cancellous threaded pin and a triplanar fixation device ‘ortholock’ used with three 3mm pins. All the devices were tested for pull out, translational and rotational forces in unicortical and bicortical fixation modes. Also tested was the normal bang strength and forces generated by leaning on the devices.

The forces required to produce translation increased with the increasing diameter of the pins. These were 105 N, 185 N, and 225 N for the unicortical fixations and 130N, 200N, 225 N for the bicortical fixations for 3mm, 4mm and 5 mm diameter pins respectively. The forces required to pull out the pins were 1475N, 1650N, 2050N for the unicortical, 1020N, 3044N and 3042N for the bicortical fixated 3mm, 4mm and 5mm diameter pins. The ortholock translational and pull out strength was tested to 900N and 920N respectively and still it did not fail. Rotatory forces required to displace the tracker on pins was to the magnitude of 30N before failure. The ortholock device had rotational forces applied up to 135N and still did not fail. The manual leaning forces and the sudden bang forces generated were of the magnitude of 210 N and 150 N respectively.

The strength of the fixation pins increases with increasing diameter from three to five mm for the translational forces. There is no significant difference in pull out forces of four mm and five mm diameter pins though it is more than the three mm diameter pins. This is because of the failure of material at that stage rather than the fixation device. The rotatory forces required to displace the tracker are very small and much less than that can be produced by the accidental leaning or bang produced by the surgeon or assistants in single pins. Although the ortholock device was tested to 135 N in rotation without failing, one has to be very careful not to put any forces during the operation on the tracker devices to ensure the accuracy of the procedure.

Aims: Surgery for degenerative lumbar spondylolisthesis may entail both decompression and fusion. The knee-chest position facilitates decompression, but fixation in this position risks fusion in kyphosis. This can be avoided by intra-operative re-positioning to the prone position. The aim of our study was to quantify restoration of lordosis achieved by intra-operative repositioning and to assess clinical and radiological outcome.

Patients and method: Thirty-six patients with degenerative lumbar spondylolisthesis and stenosis were treated by posterior decompression and interbody fusion with pedicle screw fixation. The decompression, interbody grafting and screw insertion were performed with the patient in the knee-chest position. The patient was repositioned to the prone position for fusion. Sagittal plane angles were measured pre, intra and post-operatively. Clinical assessment was performed using SF-36 scores and visual analogue scores for back and leg pain.

Results: The median pre-operative sagittal angle between fused spinal segments was 16.0 degrees lordosis. Intra-operatively in the knee-chest position the sagittal angle was median 13.5 degrees and after changing to the prone position increased to median 27.1 degrees. On the initial post-operative lumbar radiographs the sagittal angle was 23.1 and this was maintained at 6 months post-operatively (22.5 degrees). Overall there was a mean increase in lordosis angle after repositioning of 7.1 degrees per operative level (p< 0.01). The SF-36 scores improved for 7 out of 8 domains and the physical score improved from 29% to 40% (p< 0.05). Mean pain scores improved from 7.5 to 3.8 for back pain and from 7.6 to 3.7 for leg pain (p< 0.001).

Conclusion: Lumbar spondylolisthesis was found to be associated with a reduction of normal lumbar lordosis. The knee-chest position exacerbates this loss of lordosis. Intra-operative repositioning restores lordosis to greater than the pre-operative angle and was associated with a good clinical outcome.

Introduction and Aims: Reinfusion drains have been used to decrease the need for blood transfusion following total knee replacement. The aim of this study was to evaluate the degree of activation of platelets and leucocytes in both the blood that has been salvaged after total knee arthroplasty and the patients’ blood following reinfusion.

Method: A prospective series of 24 consecutive patients undergoing a primary total knee replacement in a case-control study were investigated. Post-operatively 12 patients received salvaged blood reinfusion and as a control, 12 patients underwent TKA with a standard drain. The reinfusion was initiated four hours after the operation. Blood samples were taken from all patients at three and five and a half to six hours post-operatively. A third sample was acquired in the treatment group from salvaged blood after reinfusion. Platelet, platelet-leucocyte and leucocyte activation markers were studied in both the drainage blood and the patients’ blood following reinfusion.

Results: Comparison between platelet, platelet-leucocyte and leucocyte activation markers in patients’ circulation prior to reinfusion compared to salvaged blood showed that almost all markers were significantly increased in salvaged blood. For example the platelet activation markers P-selectin (p< 0.01), Factor V (p< 0.01), CD40L (p< 0.01) and platelet derived microparticles (p< 0.01) were all significantly increased in the drainage blood. All studied platelet-leukocyte and leucocyte activation particles were also significantly increased. Following re-infusion of autologous salvaged blood there was no statistically measurable effect on activation markers of patients’ circulating platelets and leucocytes, but there was a slight drop in platelet count in the reinfused group compared to the control group. Levels of prothrombin fragment F 1+2 increased in the reinfused group compared to control indicating either activation of coagulation or simply the effect of addition of the high levels present in the salvage blood.

Conclusion: Blood from reinfusion drains showed a significant increase in activation of platelets and leukocytes indicating activation of coagulation. The reinfused blood did not lead to a difference in platelet and leukocyte activation but a decrease in platelets and an increase in fragment F1+2 suggests the possibility of activation of coagulation.

Introduction and aims: Surgical decompression for lumbar stenosis entails a risk of iatrogenic instability. Consequently, laminectomy has been largely superseded by the more conservative procedure of fenestration, but the decompression may be compromised. We describe an additional technique of undercutting laminectomy, which conserves stability while maximising decompression, and the results are presented.

Method: Forty-nine patients with lumbar spinal stenosis were treated by fenestration, medial facetectomy and removal with curved osteotomes of the ventral aspect of the lamina superior to the involved facets together with the attached ligamentum flavum. The results were assessed at a mean follow-up period of three years and four months using walking distance and a pain analogue scale as outcome measures, and surgical complications were recorded. The radiological results were assessed in 25 patients by measurement on MRI scan of the spinal canal cross-sectional area pre- and post-operatively.

Results: Ten patients had undercutting laminectomy at one level, 19 at two levels, 14 at three levels and four at four levels. Medical co-morbidity was present in most patients; 11 were ASA 1, 25 ASA2 and 11 ASA 3. Pre-operatively, all patients reported leg pain or numbness and 20 patients reported back pain. All but one had limited walking distance, the mean being 564 metres (range 5m–8000m). Post-operatively the mean pain score was 3.3 and the mean walking distance 762 metres. Forty-one patients said they felt the operation had been worthwhile and six said they did not. Surgical complications occurred in five patients, consisting of dural tear in four patients (repaired with no sequelae) and a wound haematoma requiring drainage in one patient. The mean spinal canal cross-sectional area at the level of maximal stenosis pre-operatively was 28mm² and postoperatively was 75mm², giving a mean increase of 133%. No patients had any evidence of iatrogenic instability as judged by the development of degenerative spondylolisthesis or scoliosis.

Conclusion: The technique described achieves excellent decompression of the stenotic lumbar canal as measured radiologically, while largely preserving the facet joints. In relation to published reports on fenestration and medial facetectomy alone, the clinical results are at least as good.