Aims: The main purpose of this study was to evaluate hemiplevis replacements in patients with periacetabular tumours in terms of the functional results and implant survivorship of the prosthesis. The second aim was to evaluate the complications and how they might be prevented in the future.

Methods: Case notes, hospital databases and radiographs were reviewed in 51 patients treated in a 16 year period with a custom made hemipelvis replacement (Stanmore Implants Worldwide). There were 13 deaths and 4 were lost to follow up. Of the remaining 34 patients there were 18 males and 16 females with a mean age of 48.6 (range 14 – 71).

Results: At a mean follow-up of 78 months (range 7 – 204), 70% of patients were still alive and the most common diagnosis was chondrosarcoma (17 cases). There were 2 cases of prosthesis failure and 22 of the 34 patients had one or more complications (12 cases of infection (8 deep and 4 superficial), 4 nerve palsies, 2 dislocations and 7 others). 13 patients had to have a second operation. The mean MSTS score was 63.8% and the TESS score was 59.8%

Conclusion: Infection was the most common complication and was the most significant reason for reoperation. This method of reconstruction is associated with a high morbidity rate and should be performed only at specialist centres, but the functional and oncological outcomes are satisfactory.

Introduction: Many mini compression screws are now available for fixation in procedures such as metatarsal osteotomies or arthrodeses of the foot.

The aim of the current study is to compare the compression forces achieved by mini compression screws on cortical and cancellous bone models.

Material and Methods: The screws that were tested are listed in the table below. The compression forces were tested by inserting a pressures load measurement cell between longitudinally-split sheep tibia as a cortical bone model and longitudinally split retrieved femoral heads as a cancellous bone model.

Results: The Headed AO 3.5 mm cortical screw gave the best compression force and the Bold was the weakest, both in cortical and cancellous bone. The relative compression forces of the other tested screws were different between cortical and cancellous bone. Compression with the headless screws was lost as soon as the screw penetrated through the cortex in the cortrical bone model.

Conclusions: The indications for using headless self-tapping screws should be reserved for fixation of cancellous bone or of metatarsal or Akin osteotomies where compression is not required for union. When compression is important, such as in MPJ, tarso-metatarsal or talonavicular arthrodeses, Headed AO 3.5 mm or 2.7 mm cortical or 4 mm cancellous screws, which give better compression, should be used.

Introduction: Intraosseous Transcutaneous Amputation Prostheses (ITAP) could overcome the problems associated with conventional stump-socket prostheses for amputees (pressure sores, pain, infections and unnatural gait), by attaching the external prosthesis directly to the skeleton via a skin penetrating abutment. Despite this, the skin breach introduces a potential route for infection. For success, a biological seal at the skin-ITAP interface is essential.

The protein Laminin-5 (L-5) is a ‘biological glue’, which is integral to epitheial cell adhesion. Covalently bonding L-5 to the ITAP titanium alloy (Ti6Al4V), may enhance the strength of the skin-ITAP interface.

Silanisation, a chemical technique that covalently bonds proteins to metals, could be used to bond L-5 to Ti6Al4V. We have assessed the characteristics L-5 silanised Ti6Al4V as a potential substrate for ITAP.

Method: To determine the maximum quantity of L-5 that could be silanised to Ti6Al4V, and its relative stability when soaked in foetal calf serum (FCS) over time; polished Ti6Al4V discs were silanised by immersing in aminopropyltriethoxysilane followed by glutaraldehyde. Radiolabelled rat laminin-5-I125 was then added. Discs were immersed in FCS for 4 days (37 C) and analysed at 24 hour intervals in a liquid scintillation counter. Un-silanised discs were used as controls.

Results: L-5 was successfully covalently bound to Ti6Al4V. 10ng, 100ng, 250ng and 500ng droplets yielded significantly more silanised L-5 (p< 0.05), but no difference was observed between 750ng and 1000ng. Percentage L-5 covalently bound ranged from 33% and 65%.

A small decrease in bound L-5 occurred after 24 hours of FCS soaking (p< 0.05), but subsequent to this no significant reduction was observed for 4 days (p< 0.05). Controls showed a significantly larger reduction after 24 hours (p< 0.05).

Conclusion: Covalently bonding L-5 to Ti6Al4V by silanisation can be achieved with predictable results. Large enough quantities can be immobilised to influ-ence cellular function. L-5 silanised to Ti6Al4V remains stable in vitro over time and is not removed. Following the study of cellular interactions with silanised L-5, a stable skin seal may be achieved at the transcutaneous portion of the ITAP.

Aim: To study the remodelling of cortical bone around the passive growing component of an expandable endoprosthesis.

Introduction: When inserting the passive component of an expandable prosthesis a polyethylene sleeve is commonly used. The sleeve migrates towards the lateral cortex and causes a cortical reaction and hence the use of the sleeve has been discarded recently. This study quantifies the amount of cortical reaction and degree of cortical drift in patients that had sleeves and those that did not.

Material And Methods: We reviewed X-rays and case notes of all patients that had an expandable endoprosthesis in a 20 year period. The thickness of medial and lateral cortices of the tibial diaphysis was measured at 6 months and on the last follow up radiograph. The distance from the edge of the sleeve (or prosthesis) from the cortical edge was also compared. Retrieved components also had their histology reviewed.

Results: The sleeve shifted laterally on average by 2mm (range 0.5 – 3mm) and touched the cortex. This was associated with an increase in lateral cortical thickness by 2.27mm (range 1 – 3mm). When the sleeve was used the prosthesis was inserted in the mid-line. When the sleeve was not used the tibial component tended to be inserted in valgus.

Conclusions: The presence of a sleeve is associated with a cortical reaction and the sleeve tends to migrate laterally. The clinical implications of this and the evolution of the design will be discussed in the meeting.

Introduction: The current practice of impaction allograft to fill large defects in revision total hip replacements is sometimes useful but clinical results are inconsistent. Other studies have shown that addition of mesenchymal stem cells (MSC) in blocks of hydroxyapatite (HA) scaffold can enhance new bone formation in a critical sized defect. However, no study has been conducted on combined MSCs with morselised allograft and HA granules. It is hypothesized that impaction of allograft or HA granules seeded with MSCs or osteoprogenitors will enhance new bone formation compared with the groups without MSCs.

Materials and Methods: Six sheep were used for the study. Each sheep received 8 scaffolds which were embedded in both paraspinal muscles. Groups were: 1) 3.5g allograft, 2) 3.5g allograft with MSCs, 3) 3.5g allograft with osteoblasts; 4) 3.5g of 50:50 allograft/ HA, 5) 3.5g of 50:50 allograft/HA with MSCs, 6) 3.5g of 50:50 allograft/HA with osteoblasts; 7) a block of HA, 8) a block of HA with MSCs. The experimental scaffolds were seeded with either 10x106 MSCs/ml or 10x106 MSC-derived osteoprogenitors/ml, in 3ml autologous plasma. Grafts were impacted twenty times at 3KN. At eight weeks, samples were sectioned for histology analysis. Areas of new bone formation were measured as percentage to total available spaces. ANOVA was used for statistical analysis.

Results: Addition of MSCs increased new bone formation in allograft (4.98%), allograft/HA (5.15%) and HA block (7.09%) compared with their controls at 2.24%, 1.96% and 1.96% respectively. Statistical study showed significant increase in 50:50 allograft/HA with MSCs compared with 50:50 allograft/HA only (p=0.046) and 50:50 allograft/HA with osteoprogenitors (p=0.028). No difference was found in allograft groups. For the HA block groups, addition of MSCs showed a significant new bone increase compared to the control (p=0.028).

Conclusion: Addition of MSCs to the allograft and HA granules will enhance new bone formation after impaction which can be used for revision total hip replacements, especially when allograft and HA is mixed. However, addition of osteoprogenitors has not achieved the similar results. This study encourages a further clinical investigation of impaction tissue-engineered graft to repair bone defects in revision total joint replacements.

Introduction: Since 1975, 6 types of extendable endo-prostheses have been developed at Biomedical Engineering, UCL, and Stanmore Implants Worldwide in conjunction with the surgeons at this centre.

Aims: To establish whether developments in design have had the desired effect of improving both implant survivorship and functional outcome.

Methods: This was a retrospective study using case notes, hospital databases and a radiological review, combined with contemporary functional outcome assessments (MSTS, TESS, SF36).

Results: 161 consecutive prostheses in 138 paediatric patients, between the years of 1983 – 2005, were implanted for primary bone tumours. Mean age was 10.3 (3 – 18), 81 were males and 57 females. There were 136 primary procedures and 25 revisions.

6 prostheses that used ball bearings to achieve length (designed in 1981) were implanted, 3 (50 %) were revised due to mechanical failure.

19 prostheses that utilised external C-washes (1998) to achieve length were implanted, 6 (32 %) were revised, half of these for mechanical failure.

Of the 98 minimally invasive prostheses (1992) that utilized an Allan key and screw-jack mechanism to lengthen, 14 (14 %) were revised, half of these for infection.

17 non-invasive extendable endoprostheses (2001) that are lengthened by electromagnetic coupling have been implanted so far. There has only been 1 (6 %) revision. This was due to full extension being reached.

Conclusions: Design improvements in growing endoprostheses since 1983 have led to improved survivorship. Initially this led to a reduction in mechanical failure and latterly to a reduction in infection, as indications for revision.

Key Words: Bone tumour, children, endoprosthesis, survivorship.

Bone grafts are frequently used to augment bone healing. Autologous bone graft is the gold standard for osteogenesis but is limited by availability and donor site morbidity. The processing required to lower the immunogenicity of allograft also reduces the osteogeneic properties. Bone marrow contains mesenchymal stem cells (MSCs) which differentiate into osteoblasts, forming bone. Our study examined the use of bone marrow to enhance the osteogenic properties of allograft.

Bioactive proteins within allogenic bone graft stimulate marrow-derived MSCs to differentiate into osteoblasts, thereby increasing the osteogenic nature of the graft.

After informed consent, bone marrow aspirates were taken from five patients during orthopaedic operations. Freeze-dried ethylene oxide treated allograft, from a number of donors, was obtained from the bone bank. MSCs isolated from each marrow aspirate were grown on eight samples of test allograft. Further allograft was heated to 70°C to denature the osteogenic proteins and MSCs from each aspirate were grown on 8 samples, as a negative control. Osteoblastic differentiation of MSCs cultured on the types of allograft was compared.

Scanning electron microscopy confirmed that MSCs covered the allograft after 14 days. Transmission electron microscopy showed that cells on the test allograft were characteristic of osteoblasts and produced collagen extracellular matrix. The levels of osteoblastic proteins, ALP, osteopontin and Type I pro-collagen, produced by cells on test allograft were significantly greater compared with heat-treated control (P< 0.005), after days 7 and 14.

Our study showed that marrow-isolated MSCs could be successfully cultured on allograft. As the levels of osteoblastic proteins increased significantly when MSCs were grown on allograft, osteogenic proteins within allograft caused MSCs to change into osteoblasts. This confirms that autologous marrow MSCs could be grown on allograft to increase its osteogenic prior to grafting, resulting in increased rate of bony healing.

Endoprosthetic reconstruction as a form of limb salvage in the management of malignant disease is common. We present our experience with custom-made distal femoral replacement as a form of limb salvage in the absence of malignancy.

49 cases of distal femoral replacement were identified using the unit database. There were 18 males and 31 females, with a mean age at operation of 62.3 years (range 26–86). There were 29 cases of failed total knee replacements, 8 cases of fracture associated with bone loss, non-union or deformity, 7 periprosthetic fractures, 3 aneurysmal bone cysts, and one case each of avascular necrosis and Gorham’s disease. Clinical and radiographic review of all available patients, including a functional assessment with the Musculoskeletal Tumour Society (MSTS) Score and Toronto Extremity Salvage (TES) score was undertaken.

The average follow-up was 5.4 years (range 1 to 29 years). Three types of endoprosthesis were used, rotating hinge, fixed hinge and arthrodesis prosthesis. One patient required amputation at 2 months following post-operative wound infection with methicillin-resistant staphylococcus aureus and subsequent inability to provide adequate soft tissue coverage. There was one revision at 16 months for deep prosthetic infection. 21 patients were available for functional follow-up. The mean MSTS score was 63.7 (range 16.0–86.7) and the mean TES score was 59.4 (range 9.4–87.5).

Custom-made distal femoral replacements have an established role in limb-salvage surgery for malignant disease. This series demonstrates the reconstructive capability of custom prostheses in non-malignant disease, where deformity causes functional embarrassment or when massive bone loss would normally lead to amputation.

The purpose of this study was to determine whether the low rate of mechanical loosening of the SMILES rotating hinge distal femoral endoprosthesis relates to the hydroxyapatite (HA)-coated, grooved collar of the femoral component.

A database was used to identify two groups of cases of primary distal femoral replacement with a custom-designed and manufactured SMILES endoprosthesis at our unit; those with the collared femoral component (“collar group”), and those without a collar (“non-collargroup”). From these two groups, patients were pair-matched for age and length of bone resection. A retrospective review of serial biplanar pairs of radiographs of each patient, assessing radiolucent lines and extracortical bone pedicle.

11 matched pairs were identified, (14 females, 8 males), with a mean age of 36 years, (range 16–66). The pathology was primary bone tumour in 20 cases, (17 malignant, 3 benign), and metastatic disease in 2 cases. Mean length of follow-up was 85 months, (range 27–122). Radiolucent line score (RLS) progression over time was significantly lower in the collar group, (0.01 vs 0.73, p=0.001) (fig. 1 & 2), as was the mean final RLS, (2.72 vs 7.81, p=0.02). Mean RLS per radiographic quadrant was 0.56 in cases in which a bony pedicle was ingrown onto the prosthesis, (exclusively in the collared-group), 2.41 in cases in which the pedicle was not ingrown, (most prevalent in the non-collared group), and 1.02 in those cases without any pedicle formation, (ANOVA analysis, p=0.0002).

This study demonstrates that the HA-coated, grooved collar significantly reduces the progression of radiolucent lines, and consequently the overall RLS, explaining the reduced rate of mechanical loosening of the collared endoprosthesis. A bony pedicle that does not incorporate onto the prosthesis surface may be associated with an increase in radiographic loosening.

Interventional MRI provides a novel non-invasive method of in-vivo weight-bearing analysis of the talo-calcaneal joint. Six healthy males (mean 28.8 years) underwent static right foot weight bearing MRI imaging at 0o, 15o inversion, and eversion. Using known radiological markers the motion of the talus and calcaneum were analysed.

The calcaneum externally rotates, plantar-flexes and angulates into varus. The talus shows greater plantarflexion with similar varus angulation, with variable axial rotation. Relative talo-calcaneal motion thus involves, 6o relative talar internal rotation, 3.2o flexion and no motion in the frontal plane. Concurrently the talus moves laterally on the calcaneum, by 6.5mm, with variable translations in other planes.

The calcaneum plantar-flexes, undergoes valgus angulation, and shows variable rotation in the axial plane. The talus plantar-flexes less, externally rotates, and shifts into varus. Relative motion in the axial and saggital plane reverses rotations seen during inversion. The 8o of relative valgus talo-calcaneal angulation is achieved through considerable varus angulation of the talus, in a direction opposite to the input motion. This phenomenon has not been previously reported. From coronal MRI data, comparative talo-calcaneal motion in inversion is prevented by high bony congruity, whereas during eversion, the taut posterior tibio-talar ligament appears to prevent talar valgus angulation.

We have demonstrated that Interventional MRI scanning is a valuable tool in analysing the weight-bearing motion of the talo-calcaneal joint, whilst approaching the diagnostic accuracy of stereophotogammetry. We have also demonstrated consistent unexpected talar motion in the frontal plane. Talo-calcaneal motion is highly complex involving simultaneous rotation and translation, and hence calculations of instantaneous axes of rotation cannot effectively describe talo-calca-neal motion. We would suggest that relating individual and relative motion of the talus / calcaneum better describes subtalar kinematics.

The purpose of this study was to evaluate the results of custom-made endoprosthetic reconstruction for both tumourous and non-tumourous conditions around the elbow joint.

28 consecutive cases of endoprosthetic elbow reconstruction, performed between 1989 and 2003, were identified using the unit database. There were 12 males and 16 females, with a mean age 48.9 years, (range 14–84). There were 16 cases of malignant tumour (10 primary, 6 secondary), 3 cases of benign tumour (one each of giant cell tumour, osteoblastoma and pigmented villonodular synovitis) and 10 non-oncological cases, (5 cases of fracture, 3 failed total elbow replacements and 1 infected synostosis). A distal humeral prosthesis was used in 16 patients, distal humeral and proximal ulna in 10 patients, proximal ulna with a humeral component in one patient and proximal radial replacement in one patient. Clinical and radiographic review of all available patients, including a functional assessment with The Toronto Extremity Salvage score (TESS) was undertaken.

28 consecutive cases of endoprosthetic elbow reconstruction, performed between 1989 and 2003, were identified using the unit database. There were 12 males and 16 females, with a mean age 48.9 years, (range 14–84). There were 16 cases of malignant tumour (10 primary, 6 secondary), 3 cases of benign tumour (one each of giant cell tumour, osteoblastoma and pigmented villonodular synovitis) and 10 non-oncological cases, (5 cases of fracture, 3 failed total elbow replacements and 1 infected synostosis). A distal humeral prosthesis was used in 16 patients, distal humeral and proximal ulna in 10 patients, proximal ulna with a humeral component in one patient and proximal radial replacement in one patient. Clinical and radiographic review of all available patients, including a functional assessment with The Toronto Extremity Salvage score (TESS) was undertaken.

Endoprosthetic reconstruction around the elbow joint is effective in a wide range of pathologies, allowing in most cases a reasonable level of function, even following two-stage revision for infection.

For the treatment of malignant bone tumours in immature patients, extending prostheses are used to maintain growth in the affected limb. This new prosthesis allows the implant to be lengthened by using electromagnetic coupling that is simple and easy to use.

Because of bone tumour, fourteen patients between the age of 8 and 15 years underwent bone replacement treatment and a further two patients, both male 18 and 61 years, received the same treatment to restore limb length discrepancy. These implants consisted of a telescoping shaft where the expansion is done by a power screw driven by a gearbox connected to a NdFeB magnet. This prosthesis is capable of being extended under an axial load of up to 1350N. This is in line with 76 distraction force measurements taken in 43 patients with growing prosthesis where extension was achieved by invasive procedure and where a force of up to 1513N for an extension of 6mm was recorded. Once implanted, the non-invasive prosthesis is extended by placing the limb through an external drive unit. As the drive unit is turned on, it produces a rotating magnetic field capturing the implant magnet causing it to rotate in synchronisation. At full speed, the implant grows at a rate of 0.23mm per minute.

Of the sixteen patients, seven have been extended with one to its full capacity of 63mm. During extension, the patients have no sensations of vibration, heat, stretching or any other kind although the faint vibrations could be heard by placing a stethoscope on bony protrusions such as greater trochanter. At each sitting, the patients were extended by approximately 4mm during normal outpatient clinics and were able to walk as before immediately after the treatment. Patients with knee joint were functionally assessed before and after the treatment and showed approximately 10° to 15° of reduction in knee flexion/extension.

This new extending mechanism in these prostheses has provided the patients a treatment, which reduces trauma infection and discomfort. The mechanism of extension is reliable and effective.

Introduction: External fixation is used widely in the management of fractures, despite a relatively high incidence of complication, arising from pin loosening and infection. Diamond like carbon (DLC) is a low surface energy coating that can be applied to external fixator pins and may reduce biofilm formation and infection resulting in a lower incidence of pin loosening. Hydroxyapatite (HA) is well established as a coating to enhance fixation of external fixator pins. This study tests the hypothesis that HA and DLC coatings on stainless steel (SS) external fixator pin shafts modify integration of the implant with soft/hard tissues.

Materials and Methods: An Orthofix external fixator was used to stabilise a tibial osteotomy with 6 self-drilling/tapping 6mm pins in 32 skeletally mature Friesland ewes. Animals were divided into four groups; SS, DLC, HA partially coated (threads only) and HA fully coated (threads and pin shaft). Pin insertion torque was measured using a torque wrench and extraction torque similarly obtained at 10 weeks when animals underwent euthanasia. Pin performance indices (PPI) were calculated as a ratio of extraction to insertion torque x100%. Pin site 2 was preserved for hard grade resin histology and subsequent pin tissue integration analysis. Pin site 3 was used for analysis of the soft tissue pin shaft interface using transmission electron microscopy. Pin site 5 was examined for the presence of biofilm formation using scanning electron microscopy. Pin site 6 was swabbed for microbiological analysis.

Results: SS and DLC pins achieved significantly higher insertion torques compared to HA partially coated pins (p=0.001, 0.002). Both groups of HA coated pins demonstrated a significantly higher, extraction torque and therefore PPI for all pin site positions compared to SS and DLC (p< 0.001– 0.025). The epithelium was found not to be in contact with the pin shaft in all cases. No significant differences were found between the different pin groups for epidermal down growth and dermal contact. Both groups of HA coated pins showed a significantly higher percentage of new bone in direct contact with the embedded threads compared to SS and DLC pins (p< 0.001, p=0.004). The proportion of soft tissue in contact and within the thread, of fully coated HA pins was significantly lower compared to stainless steel (p=0.003, p=0.017), DLC (p=0.004, p=0.002) and HA partially coated pins (p=0.006, p=0.02). Biofilms were evident on all pins except those coated with DLC. More bacteria were observed on the fully HA coated pins. DLC had significantly lower number of bacterial colonies in culture compared to SS (p=0.028) and fully coated HA pins (p=0.005).

Discussion: Coatings of DLC and HA do have a significant affect on hard/soft tissue reactions. However coatings do not have a significant effect on epidermal down growth or dermal attachment to the pin shaft surface. DLC coated pins had the cleanest surface with no bio-film present and significantly lower numbers of bacteria present. Fully HA coated pins despite evidence of bio-film formation, bacteria and high microbiological counts had significantly higher PPI. In addition fully coated HA pins demonstrated significantly reduced amounts of soft tissue at the pin bone interface. Therefore soft tissue reactions may affect bone integration.

Introduction: One of the most common complications following total joint surgery is aseptic loosening. Improving the bone-cement interlock may increase implant longevity. An ideally prepared bony surface is dry; clean; free from marrow, fat and debris; free from active bleeding; and free from micro-organisms. Lavage removes debris, blood and fat from the interstices of the bone surface so as to allow optimal penetration of the cement. The hypothesis that we investigated in this study was that lavage with a detergent solution obtains a greater depth of cement penetration into bone compared with lavage using 0.9% saline, hydrogen peroxide or an alcohol solution.

Methods: The cancellous bone of ovine femoral condyles were cut into 10×10×13mm blocks. Lavage solutions were delivered via a pulsatile system and directed towards one side of the bone block. All blocks were swabbed dry. A high viscosity cement was manually mixed and applied to the sandblasted surface of titanium alloy plate (10×10mm, weight 0.9g ±0.01g). The titanium plate and cement were placed on the irrigated bone block, and a known weight applied to achieve pressurisation. Time, temperature and method were controlled. The prosthesis-cement-bone composite was sectioned perpendicularly, and image analysis used to quantify penetration depths. 10 readings were recorded per block with 6 blocks per lavage group.

Results: Cancellous bone porosity averaged 75.2% (±4.0) . The mean penetration depth in the saline group averaged 3.39mm (± 0.77); 3.04mm (± 0.59) using a 2% alcohol solution; 3.33mm (±0.79) using a 3% hydrogen peroxide solution; and 5.41mm (± 1.30) when using the detergent lavage. There was no significant difference in cement penetration depth between hydrogen peroxide and saline irrigation (p> 0.05), nor with hydrogen peroxide and alcohol irrigation (p> 0.05). Irrigation with saline however, afforded statistically superior cement penetration than that of alcohol lavage (p < 0.012). Irrigation with detergent solution demonstrated significantly greater depth of penetration than all three other lavage groups (saline p< 0.05; alcohol p< 0.05; hydrogen peroxide p< 0.05).

Discussion: Detergents can physically remove particulate matter and emulsify and remove fats, thereby acting to maximise porosity of the cancellous bone network and optimise space for occupation by intruding cement. This study has proven the ability of a detergent solution to provide a clean, debris free cancellous network, which consequently provides a significantly greater depth of cement penetration than other commonly used irrigating agents. It was noted that cement penetration into cancellous bone followed the line and depth of cleaning from lavage. In conclusion, the hypothesis can be accepted, and lavage with a detergent solution affords a statistically greater depth of cement penetration into bone than that of the universally used 0.9% saline lavage.

Introduction: Periprosthetic bone loss, brought about by wear particle induced osteolysis, presents a major challenge and compromises outcome in revision Total Hip Replacement. Poor bone stock at revision hip replacement is the main indication for impaction allografting. There are well documented limitations in the use of bone graft. Autogenous bone graft is osseoinductive, though donor site morbidity and the limited amount available restrict its use. An alternative is allogenic bone graft from cadaveric femoral heads. The drawbacks of using allograft are a limited supply and the risk of disease transmission. An alternative may be the use of bone substitute materials. Usually these are used in conjunction with allograft and therefore a number of drawbacks still apply. This study investigates the use of impaction grafting without bone graft. In this study we tested Apopore, 60% porosity, 2–5 mm hydroxyappatite (HA) granules (ApaTech Ltd) in an animal impaction model with allograft as control. Hypothesis Impaction using porous granular HA induces a similar volume of new bone compared with impaction using allograft.

Methods and Materials: Cylindrical defects of 15mm diameter were created in the medial femoral condyles of 12 sheep (6 sheep in each group) and filled with 3.5 grams of either morselised ovine allograft, washed and defatted according to North London Tissue Bank protocols, or porous HA granules impacted with a specially designed impactor, 20 times with a force of 3 KN. This force was similar to that measured during impaction grafting in clinical cases. After 6 weeks the sheep were euthanized, samples embedded in resin and the amount of bone formation measured by histomorphometric analysis.

Results: Under the impaction forces used the HA graft was more impacted than allograft. In the impacted HA graft the average pore size was smaller than for impacted allograft. After 6 weeks more new bone formation was observed at the host implant interface than the middle of the implant in both groups. At the implant host interface there was 26.64% (± 2.13%) new bone formation in the allograft and 21.13% (± 4.51%) new bone formation in the HA implant. In the middle of the implants allograft produced 11.01% (± 2.07%) new bone whilst the HA produced 7.23% (± 4.05%) new bone. Two tailed t-test showed no significance in either region, p=0.28 at the interface and p=0.40 in the middle. Allograft underwent resorption, from 39.37% at time zero to 5.66% (± 2.04%) at 6 weeks, a total reduction of 85%, where as the volume of HA granules remained the same and was 49% at time zero and 48.59% (± 1.69%) at 6 weeks. Two tailed t-test showed a significant difference (p< 0.0001) between allograft and HA at 6 weeks.

Conclusions: This study shows that granular porous HA induced a similar level of bone formation as compared with allograft. Resorption of allograft in this model allowed greater ingrowth of fibrous tissue. This makes the structural scaffold much more porous, compromising stability of the construct. The HA was not resorbed after 6 weeks and hence may be more stable. HA also has the advantage of being readily available. This study demonstrates that a bone substitute material does not need to be mixed with allograft.

Introduction: The main problem facing the longevity of total hip replacements (THR) is wear particle induced osteolysis, particularly around the acetabular component. The articulating surfaces produce wear particles that migrate in the fibrous tissue membrane along the acetabular implant-bone interface causing osteolysis and subsequent implant loosening. The hypothesis that we investigated was that uncemented acetabular interfaces are more effective than cemented implants at resisting progressive osteolysis through bone attachment and the formation of a biological seal.

Methods: THR surgery was performed in an ovine model. Implants remained in vivo for 1 year. Femoral heads were roughened in order to generate wear debris and aseptic loosening of the acetabular component. Sheep were randomly assigned to one of three experimental groups: cemented polyethylene, grit blasted or plasma sprayed porous acetabular components with a polyethylene insert. Ground Reaction Force (GRF) data was collected pre-op and at 12, 24, 36 and 52 weeks post op. Retrieved specimens were analysed radiographically, histologically and using Scanning Electron Microscopy (SEM). A mould was made of the polyethylene liner and head penetration rates quantified using a shadowgraph technique. Thin sections through the acetabuli were prepared and image analysis used to quantify fibrous tissue (FT) thickness at the bone-implant interface. Mann-Whitney U tests were used for comparative statistical analysis where p< 0.05 were classified as significant.

Results: GRF demonstrated functional hips. A gradual increase was seen until week 36 followed by a decrease until retrieval suggesting the onset of aseptic loosening. 42.86% of control, 60% of grit blasted and 50% of porous coated components were deemed radiographically loose. Mean linear penetration rates demonstrated significantly less penetration within the porous cups (p=0.003, control and p=0.036, grit blasted). SEM established that wear particles generated were < 1μm in size. Light microscopy of thin sections revealed the common mechanism of loosening involving a resorption wedge at the interface with progressive bone loss. In all cases, the FT layer was greatest at the rim of the cup and gradually decreased towards the apex. The grit blasted group had the thickest FT layer adjacent to the cup. Under polarised light, wear debris was seen packed within macrophages in all sections.

Discussion: GRF data demonstrated grit blasted cups to have least function. This was confirmed through histology as they had the thickest FT layer surrounding the acetabular shell suggesting increased aseptic loosening of its component due to wear particles being able to access the interface more easily. Data corroborates radiographic results. In conclusion, porous and control cups performed better than grit blasted cups. Acknowledgments: EPSRC.

Introduction: Human bone marrow stromal stem cells(BMSSC’s) have the ability to differentiate into a variety of mesenchymal cell types including osteoblasts, fibroblasts, adipiocytes and myocytes. These stromal cells are involved in the process of bone formation during the healing of fractures. Collagen lyophilisate is a sterile extract of bovine demineralised bone matrix. This material contains proteins removed from bone that may control the differentiation of osteoblasts from BMSSC’s. These proteins are localised within collagen type 1. The aim of this study was to determine the effects of collagen lyophilisate on the osteogenic differentiation of bone marrow stromal stem cells cultured in vitro.

Methods: Bone marrow was aspirated from the iliac crest of a human donor who was undergoing an unrelated elective orthopadic surgical procedure. Stromal stem cells were isolated from marrow, cultured and then characterised using immunofluorescent antibodies to Stro −1, a stromal stem cell marker. 3x10⁴ BMSSC’s were seeded into each of 3 culture wells and incubated with standard growth medium or standard medium with collagen lyophilisate diluted 1:50 or 1:100. Cells were cultured for a maximum duration of 30 days. At selected time intervals until day 30, osteogenic differentiation was assessed by determination of alkaline phosphatase, osteopontin, pro collagen carboxyterminal (type 1 collagen synthesis) and calcium in cultures using specific assays.

Results: Cells cultured in collagen lyophilisate displayed a polygonal morphology early in the culture period and later formed complex aggregates. Cells in control cultures maintained a fibroblstic morphology until confluence. On day 21 alkaline phosphatase activity was significantly higher in collagen lyophilisate containing cultures than control cultures. Osteopontin levels were not enhanced in the collagen lyophilisate containing cultures. Type 1 collagen synthesis was higher in the collagen lyophilisate 1:50 group than all other groups at day 14. No differences in type 1 collagen synthesis were detected between cultures at other time periods. Calcium was not detected in any of the control cultures for the duration of the culture period. In contrast, calcium was detected in collagen lyophilisate containing cultures on day 15.

Conclusion: Collagen lyophilisate resulted in changes in cellular morphology and arrangement. The ability of collagen lyophilisate to enhance alkaline phosphatase activity, increase collagen type 1 expression and stimulate the deposition of calcium in stromal stem cell cultures provides evidence that it has osteogenic properties.

Introduction: Impaction allografting is a technique that is used at revision where the bone stock in the femur is poor. Femoral heads are ground to create morsellised bone, which is impacted down the femur prior to the cementing a new stem into the canal. The results of this technique are variable and there is a high incidence of stem migration. This variation in results may be due to the degree of bone loss or the techniques used to impact the graft. The aim of this study was to quantify the forces currently used in revision hip surgery with impaction allografting.

Methods: To enable these measurements the Exeter slap hammer (Stryker Howmedica) was altered to include a load washer. The load washer had a special cable welded to it so that sterilisation could still be conducted in an autoclave. During surgery the end of the load washer cable is passed to the operator, who is able to connect it to a laptop computer. A specially written Labview program is then used to store the data and determine the impaction forces. The load washer is mounted within the hammer at the point of impact between the sliding mass and the hammer, consequently it is reading the force transmitted to the hammer, not that transmitted to the graft chips. Calibration was performed in an in vitro experiment with a second load washer, which found that the force in the hammer is three times that in the impactor. The force is so much less because it is taken up in the hammer’s inertia.

Conclusions: The impaction forces have been measured during eight operations performed by three different surgeons. The study shows variability between surgeons, and variability between patients operated on by the same surgeon. These readings show that the forces travelling through the impactor range between three to eleven time body weight.

Introduction: The Resurfacing Hip has been increasingly popular for younger patients. Femoral neck fractures are still the main complication. The problems associated with cement such as thermal necrosis, cement debris and lack of long-term biological fixation, combined with the general use of cementless fixation in young patients invite the question whether a cementless component can be used for resurfacing hip replacement. Given that the cement may reinforce the femoral head preventing collapse, an additional question regarding the effect of bone density in cemented and cementless fixation can be asked. The hypotheses of the study are that:

High bone density will increase the yield point and stiffness of the femoral head and therefore improve the implant fixation.

Materials and Methods: Thirty-six femoral head specimens were obtained from consented patients receiving routine hip arthroplasty. The heads were stored frozen at −20oC until use. pQCT was used to analyse trabecular bone density within each head. Specimens were ranked according to bone density and were assigned to high and low bone density groups. Cemented and cementless fixations were then alternatively assigned to individual heads in each group. Thus the 4 groups included in the study were: High density cemented, high density cementless, low density cemented, and low density cementless. Implantation of Birmingham resurfacing hips was carried out according to recommended surgical procedures. For cementing groups, surgical simplex P bone cement was used. Each sample was potted in a cylindrical polyethylene block for testing. A compressive load up to 5 or 10 KN using a Hounsfield Universal Testing Machine were applied on each sample at a rate of 1 mm min-1. Load versus displacement graphs were plotted for all tests. Yield point and stiffness were measured for each sample.

Results:

For yield point, there is no significant difference between cemented or cementless resurfacing (4169 ± 1420 N vs. 3789 ± 1461 N; P = 0.434). However, the high density heads provide a significantly higher yield point than low density heads (4749 ± 1145 N vs. 3208 ± 1287 N; P = 0.01).

Discussion: Bone density plays an important role in resurfacing hip arthroplasty. Higher bone density will reduce the incidence of fractures comparing with lower density. Therefore, resurfacing THR for the older patients and those with sub-optimal bone density should be used with caution. Consequently, it is suggested that a bone density scan should be routinely applied for those patients who are considered for resurfacing hip replacement. There is no difference between the cemented and cementless fixation in reducing femoral head failure, though cement will increase the stiffness of the bone. The study suggests that cementless resurfacing hip could be an alternative design with its clinical advantages of long-term osseointegration if implant is coated with bio-active materials.

Introduction: Normal limb use in amputees with made to measure external prostheses can be impaired by problems at the stump – socket interface. The development of an Intraosseous Transcutaneous Amputation Prosthesis (ITAP) would overcome the problems by protecting the soft tissues, whilst redistributing high stresses to bone. ITAP creates a breach in the skins protective barrier to infection, hence requires a sufficient soft tissue – implant seal to prevent implant failure. Deer antlers are natural analogues of ITAP, and successfully overcome the problems associated with skin penetrating implants such as infection, marsupilisation and avulsion. In this study, an ITAP device has been developed, with a successful soft tissue – implant interface, based on deer antler morphology. It is hypothesised that sub-epithelial dermal fibroblastic, but not epithelial layer adhesion, is directly responsible for the degree of downgrowth observed around ITAP.

Methods: Eleven pairs of deer antler were used to histologically evaluate the interface between the antler and pedicle, and the soft tissue seal around the antler-pedicle structure. The findings were used to develop a titanium alloy (Ti6Al4V) ITAP device in a goat model. Three to five transcutaneous pins were implanted into the medial aspect of the right tibia of skeletally mature female goats. Four implant designs were tested, Machine Finished Straight (MFS), Hydroxyapatite (HA) Coated MFS, Machine Finished Flanged (MFF) and HA Coated MFF. The 70μ thick HA coating was applied to the implant region abutting the sub-epithelium. The implants remained in situ for four weeks after which the histology of the resulting interfaces were analysed qualitatively and quantitatively for degrees of epithelial downgrowth (marsupilisation) and epithelial/sub-epithelial layer attachment to the implant surface.

Results: The histology of the deer antler showed there to be an extremely small area of epithelial attachment, with negligible downgrowth, arrested by soft tissue adhesion to the underlying pedicle surface. There was a significant increase in pore size and frequency in the pedicle structure (abutting the soft tissues), compared to the antler proper. The MFS ITAP implants were associated with significantly greater downgrowth and reduced epithelial and sub-epithelial layer attachment compared to all other implant designs. The HA coating, and porous flange structure significantly reduced downgrowth and increased sub-epithelial layer attachment. Regression correlation showed that there is a significant negative correlation between the extent of downgrowth and the degree of sub-epithelial dermal fibroblastic layer attachment observed around ITAP implants (All p values < 0.05).

Discussion: Deer antlers successfully overcome the potential problems for ITAP. By artificially recreating some of the aspects of the antler, including layering of porous and bioactive surfaces for tissue adhesion, we have successfully developed an ITAP implant that minimises downgrowth and actively encourages epithelial and sub-epithelial soft tissue adhesion.