Introduction Cement leakage into adjacent structures is the main complication during vertebroplasty. The majority of these leaks are asymptomatic, but pulmonary cement embolism has been reported to cause cardiovascular disturbances and even death (1,2). Furthermore, the use of calcium phosphate (CaP) cements for vertebroplasty may aggravate cardiovascular deterioration in the event of cement embolism by stimulating coagulation [3].

The cardiovascular effects of pulmonary cement embolism were investigated using an animal model.

Methods In 18 skeletally mature sheep, 2.0ml cement was injected into the pulmonary trunk during general anaesthesia (approved by Animal Ethics Committee). Three different cements were used: 1) PMMA (Simplex P, Stryker); 2) PMMA with 10% hydroxyapatite (PMMA & HA) (Vertecem, Synthes); 3) Experimental injectable CaP cement (Synthes). The following cardiovascular parameters were recorded continuously (endpoint: 60min post-injection): arterial, central venous, pulmonary arterial pressures and cardiac output. Blood gases and coagulation parameters (antithrombin, D-dimer, prothrombin fragments I & II) were measured pre-injection, 10, 30 and 60min post-injection. Postmortem, lungs were removed intact and submitted to computer tomography (CT) imaging.

Results There were no fatalities. After 1min, mean pulmonary arterial pressure had increased by 9%, 14% and 21% from pre-injection value in the PMMA, PMMA & HA and CaP group respectively. Differences in pulmonary arterial pressure between the three material groups were not statistically significant. Pulmonary arterial pressure stayed elevated for the duration of the experiment (i.e. 60min post-injection). There were no other significant changes in cardiovascular, blood gas or coagulation parameters from pre- to post-injection values. Three dimensional reconstructions of the CT images showed a tendency of the CaP cement to break up into multiple smaller pieces whereas the two other cements did not.

Discussion Cement embolism led to mild pulmonary hypertension in all material groups. Present results are in contrast to earlier reports (pig model) of fulminant cardiovascular deterioration after CaP cement embolism (3). Present changes were not as severe and there was no evidence of thromboembolism. This discrepancy may have been due to differences in the cement formulations or the animal model.

Pulmonary hypertension was more severe in the CaP cement group. This may have been due to the disintegration of the CaP cement resulting in blockage of more pulmonary vessels compared to the PMMA cements.

Introduction Reported clinical results suggest that vertebroplasty is a safe and effective technique for providing pain relief. However, information about the long-term effect of PMMA on the adjacent intervertebral discs and the augmented bone is lacking. Adjacent intervertebral discs may be at higher risk of degeneration due to nutritional constraints. Bone loss in augmented vertebrae may occur due to mechanical stress-shielding or toxicological effects.

The aim of the present study was therefore to investigate the effect of PMMA augmentation on intervertebral disc and bone tissue after 6 and 12 months, using an animal model.

Methods In 12 skeletally mature sheep, 2.0ml PMMA (Simplex P) was injected into three lumbar vertebrae (approved by Animal Ethics Committee). Two injection holes were drilled into the middle of three vertebrae at a distance of 5.0mm from the cranial and caudal endplate and 1.0ml PMMA was injected into each hole. Four weeks before euthanasia, animals received an injection of tetracycline for bone labeling.

Postmortem, T1- and T2-weighted sagittal and axial MR images were taken prior to fixation in 80% ethanol. Spines were cut into specimens containing one intervertebral disc and half of the two adjacent vertebrae. The discs which were two levels above the first augmented vertebra served as controls. Microsections were stained with H& E, Goldner, Alcian blue-PAS and Safranin O. MRI signal intensity and morphology of discs were evaluated qualitatively. Histomorphological analysis of discs and endplates was conducted using published criteria [1]. Presence of bone remodeling, fibrous tissue and foreign body reaction in the vertebrae was also recorded.

Results There was no distinguishable loss of MRI signal intensity in the discs in between augmented vertebrae. Cement injection resulted in blocking 50–75% of the endplate lengths. Most discs that were in between augmented vertebrae showed signs of degeneration (chondrocyte proliferation, necrosis) after 6 (80%) and 12 months (88%). Inflammatory reaction to PMMA was observed in some specimens (approximately 25%). Cement had been covered with fibrous tissue in all augmented vertebrae, but tetracycline labeling revealed new bone formation in the vicinity of PMMA.

Discussion Augmentation of three adjacent vertebrae initiated degenerative changes of intervertebral discs in between two augmented vertebrae. This is in contrast to previous animal studies [2] where no degenerative changes after cementing endplates were observed. Current investigations were performed with the specific aim to block the endplates. Clinically, endplates may not get blocked as effectively. On the other hand, discs in older patients are nutritionally constrained due to end-plate calcification and even partial blockage may lead to degenerative changes as documented presently.

The risk of degenerative changes of intervertebral discs should be considered in patients undergoing vertebroplasty.

Cementless implants have gained popularity in modern orthopaedic practice. The type implants and surface characteristics on fixation has been extensively investigated, however there is insufficient data on the effect of the host bone bed status on implant fixation. This study aims to determine if there is a correlation between the fixation strength of cementless press-fit implants and bone mineral density (BMD) of the host bone bed.

Implants coated with pure titanium, Hydroxyapatite (HA) with or without Hyaluronic Acid (HY) and implants coated with bone growth factors – Bone Morphogenetic Protein 2 (BMP-2) were inserted into tibiae and femora of 32 skeletally mature ewes (109 implants) for a period of 1, 2 and 4 weeks. Mechanical pull-out testing was performed after each time interval to evaluate the ultimate load of failure (Nmm⁻²). The BMD (gcm⁻³) surrounding the implant site was measured using a CT scanner.

The mean BMD (S.D.) was 1.515gcm⁻³ (0.147gcm⁻³). The mean (S.D.) mechanical pull-out strength at 1, 2 and 4 weeks was 0.37 (0.31), 3.14 (0.17) and 9.74 (2.31) Nmm⁻² respectively. The overall correlation co-efficient between BMD and pull out strength is 0.31.

Early fixation strength of implants is independent of BMD, however, the strength of fixation increases with time in a ‘normal’ sheep population. This suggests that the fixation of implants is dependent on the type of implant and surface coating used rather than the density of the host bone bed.

Purpose: To investigate the effect of pressurizing vertebral bodies during vertebroplasty using different materials in the development of fat embolism (FE) and any associated cardiovascular changes.

Polymethylmethacrylate (PMMA) is the material of choice for vertebroplasty (VP). However, PMMA has several disadvantages such as exothermic curing, uncertain long-term biomechanical effects and biocompatibility. As a result alternative materials are being developed to overcome these problems.

In order to determine the role of PMMA in the generation of cardiovascular changes following vertebroplasty we compared injection of cement with wax in an animal model.

Method: In twenty sheep, four vertebral bodies were augmented either with PMMA or bone wax. Heart rate, arterial, central venous and pulmonary artery pressure, cardiac output and blood gas values were recorded. At postmortem the lungs were subjected to histological evaluation.

Results: The consecutive augmentation of four vertebral bodies with PMMA induced cumulative fat embolism causing significant deterioration of baseline mean arterial blood pressure (MABP) and blood gas values. Injection of bone wax resulted in similar cardiovascular changes and amount of intravascular fat in the lungs.

Conclusion: In this animal model cardiovascular complications during multiple VP happen regardless of the augmentation material used. The deteriorating baseline MABP during VP is associated with the pressurization and displacement of bone marrow/fat into the circulation rather than caused by polymethylmethacrylate.

Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation.

Purpose: The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite coated implants.

Method: Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated either by light microscopy or by pullout tests after 1, 2 and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep.

Results: The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at 4 weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Introduction Polymethylmethacrylate (PMMA) has been widely used in orthopaedic procedures for fixation of joint replacements or enhancing the fixation of implants. However, the use of PMMA has been associated with cardiovascular deterioration and even death. More recently, PMMA has also been used for augmenting osteoporotic vertebral bodies which have fractured or are at risk of fracture. The main complication is PMMA leakage into adjacent structures. Transient hypotension and fatal fat embolism (FE) have also been reported.

The pathomechanism of cardiovascular deterioration after the injection of PMMA (i.e. FE) remains a highly controversial subject. The exact role of PMMA in the development of FE remains unclear. The aim of the present study was to elucidate the acute effects of injecting PMMA compared with bone wax into vertebral bodies on the cardiovascular system using an established animal model for vertebroplasty (VP) (Aebli, N, et al. Spine. 2002).

Methods In 8 skeletally mature mixed-bred ewes (2–4 years) 6.0ml PMMA (CMW3-Depuy) or bone wax (Bone Wax, Ethicon) were injected unilaterally, through an open approach into the L1 & L2 pedicles. Blood pressure, heart rate, and cardiac output were measured.

Results The major difference between the cardiovascular response of the PMMA and that of the bone wax group was the recovery in Pulmonary Artery Pressure (PAP) and Pulmonary Vascular Resistance (PVR). Three minutes post-injection, PAP had fully recovered to baseline values in the wax group. However in the PMMA group, PAP had only recovered by 52% after 3 min and fully recovered after 10 min.

Discussion The augmentation of vertebral bodies resulted in transient cardiovascular changes regardless of the material used. However, the recovery of PAP and PVR values took significantly longer with the PMMA group. The peak response was a result of pulmonary vasoconstriction triggered by a reflex reaction to the embolisation of bone marrow particles or by vasoactive cytokines. The peak response was therefore mainly associated with the increase in intraosseous pressure during the augmentation causing release of bone marrow contents into the and not the cement monomer. The cement monomer however plays a role in the cardiovascular complications during FE. The delayed recovery of PAP and PVR in the PMMA group may be due to a vasoconstriction effect of the cement monomer on the pulmonary vascular system.

Potentially serious cardiovascular complications may occur during VP regardless of the material used. The injection of PMMA may cause prolonged pulmonary hypertension during vertebro- and also arthroplasty. Continuous invasive cardiovascular monitoring may be required in patients with impaired cardiovascular and pulmonary function

Introduction Locking plates are the most used devices for achieving anterior cervical spinal fusion and offer considerable advantages such as faster and easier implantation and fewer implant-related failures than older plate systems. Recently polyaxial locking screws were introduced to make the implantation of these plates even easier by facilitating the implantation of the screw in all directions. However polyaxial screws may have the disadvantage of losing the angular stability with subsequent failure of the plate. The aim of this study was the radiological follow up of the patients with polyaxial screw and to compare them with the conventional looking plates.

Methods Patients underwent anterior cervical discectomy and fusion in which either ventral cervical locking plates or a polyaxial locking screw were used for indications including cervical spondylotic radiculopathy, disc herniation, trauma, and myelopathy. Patients underwent anterior cervical discectomy and interbody fusion and / or corpectomy. Preoperative and postoperative radiographic data included sagittal angle, translation, and settling of the graft.

Results One hundred and forty patients were investigated (mean age of 49 years) with an average follow up period of 21.5 months (range from 4 to 50 months). All underwent anterior cervical plate fusion as a component of the surgical treatment for symptomatic degenerative cervical spinal disease (55%) or for vertebral destruction caused by trauma (45%).100 (71%) of patients were treated with a conventional locking plate and 29 % with a plate with polyaxial screw fixation. Besides plate fixation, 4 of the 140 patients had a combined ventrodorsal fusion. In 46 cases (25%), one or more vertebral bodies were removed and replaced with either iliac bone graft (two levels, 21% of all cases) or fibula strutgraft (4%). In the group with conventional locking plates no patient had to be revised, 3 showed a subluxation (up to 1/3 of the vertebral body diameter) and 2 screw back out posteriorly without clinical relevance. In the group with the plate with polyaxial screw fixation two patient had to be revised (posterior stabilisation) because of subluxation due to loss of angular stability of the screws and one patient developed subluxation of 1/3 of the vertebral body also due to loss of angular stability.

Discussion The complication rate and the revision rate for anterior cervical discectomy and fusion with plates with and without polyaxial screw fixation were similarly low. Polyaxial screw may have the theoretical disadvantage of loosening with loss of the angular stability and subsequent failure necessitating revision.

Introduction and Aims: Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation. The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite-coated implants in an animal model.

Method: Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated by light microscopy and pullout tests after one, two and four weeks of unloaded implantation in the cancellous bone of 18 sheep.

Results: The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at four weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Introduction and Aims: Polymethylmethacrylate (PMMA) has been widely used in orthopaedic surgery including more recently vertebroplasty. The reported rate of complications following vertebroplasty is low and mainly related to PMMA leakage.

The aim of this study was to elucidate the acute cardiovascular effects of PMMA or bone wax in a vertebroplasty animal model.

Method: Eight skeletally mature sheep were used and PMMA or bone wax were injected unilaterally into L1 and L2 at 10-minute intervals. Arterial, central venous, pulmonary artery and left ventricular pressures were recorded using Statham pressure transducers and Swan Ganz catheters were used for monitoring cardiac output.

Results: Augmentation resulted in a two-phase response regardless of which material was used. First the mean arterial blood pressures started to drop after approximately two seconds. Secondly the pulmonary artery pressure and central venous pressure increased after approximately 11 seconds, whereas cardiac output and left ventricular pressure decreased. There was no significant change in heart rate for both groups. There was a significant difference (p< 0.05) in the pulmonary artery pressure values in the PMMA group compared to the basal values at one, three and five minutes, whereas in the wax group the pulmonary artery pressure recovered within three minutes.

Conclusion: Augmentation resulted in a two-phase cardiovascular response regardless of which material was used. Peak responses were similar for both groups, but pulmonary artery pressure and cardiac output recovered quicker in the wax group. The late recovery of pulmonary artery pressure and cardiac output in the PMMA group may be due to a vasoconstriction effect of the cement monomer.

To investigate the effect of pressurizing vertebral bodies during vertebroplasty using different materials in the development of fat embolism (FE) and any associated cardiovascular changes.

Polymethylmethacrylate (PMMA) is the material of choice for vertebroplasty (VP). However, PMMA has several disadvantages such as exothermic curing, uncertain long-term biomechanical effects and biocompatibility. As a result alternative materials are being developed to overcome these problems.

In order to determine the role of PMMA in the generation of cardiovascular changes following vertebroplasty we compared injection of cement with wax in an animal model.

In twenty sheep, four vertebral bodies were augmented either with PMMA or bone wax. Heart rate, arterial, central venous and pulmonary artery pressure, cardiac output and blood gas values were recorded. At postmortem the lungs were subjected to histological evaluation.

The consecutive augmentation of four vertebral bodies with PMMA induced cumulative fat embolism causing significant deterioration of baseline mean arterial blood pressure (MABP) and blood gas values. Injection of bone wax resulted in similar cardiovascular changes and amount of intravascular fat in the lungs.

Conclusion: In this animal model cardiovascular complications during multiple VP happen regardless of the augmentation material used. The deteriorating baseline MABP during VP is associated with the pressurization and displacement of bone marrow/fat into the circulation rather than caused by polymethylmethacrylate.

The ability to assess the blood flow to a bone (IBF) is important for orthopaedic surgeons when deciding the fate of an injured or diseased bone. Currently there is no easy and effective method for quickly assessing the blood flow status of a bone. There is accumulating evidence that suggests that IBF may be correlated to intraosseous pressure (IOP).

Therefore, we aimed to investigate whether the two variables are correlated so that the orthopaedic surgeon could confidently use IOP as an indicator of IBF.

Using 8 mature female ewes (B.W. ~56 kg) we measured cardiovascular (eg. arterial blood pressure – ABP), and intraosseous (ie. IOP and IBF) responses to nor-adrenaline (0–1.5 μg/kg/min. i.v.) and nitroglycerine (0–80 μg/kg. i.v.) IBF was measured using semi-quantitative technique of laser Doppler flowmetry (LDF).

Our results revealed that changes in ABP were directly correlated to changes in IOP (p < 0.001). Due to technical difficulties that were encountered when using LDF, the collected IBF data were limited. However, there was compelling evidence that there is a positive and direct correlation between IBF and IOP.

This opens an exciting possibility of using IOP for quickly and accurately assessing IBF as well as providing insight into the pathological mechanisms responsible for bone and joint disorders.

Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation.

The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite coated implants.

Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated either by light microscopy and pullout tests after 1, 2 and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep.

The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at 4 weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Introduction: Vertebroplasty using polymethylmethacrylate (PMMA) is an established technique in the treatment of osteoporotic fractures of the vertebra. Complications of vertebroplasty associated with PMMA leakage can include damage to the spinal cord. Previous studies have sought to investigate thermal changes in the paravertebral region, but used smaller volumes of cement than are used clinically¹, or used in vitro experimental techniques.² We have designed an in vivo sheep model to investigate the thermal changes after injection of clinically relevant volumes of PMMA, and to measure change in cord function associated with PMMA extrusion.

Methods: Five sheep were anaesthetised and 1.0ml of PMMA was injected into the spinal canal at the L1 level, with measurement of the temperature by thermocouple. The L2 to L5 vertebral bodies were then exposed and 9 thermocouples placed at points in and around the vertebra (superior and inferior endplate, disc above and below, central body, posterior wall, and spinal canal) to measure paravertebral temperature for a 10- minute period after injecting 6.0mls of PMMA. All animals were then humanely euthanased, and the T12 to L2 vertebrae harvested to examine the effect of temperature on the vertebral body and spinal cord using light microscopy.

Results: The experiments showed significant increases in the paravertebral temperature, especially at the end-plates (mean temperature 51.7°C, mean increase in temperature +16°C). This is contrary to studies using small cement volumes or in vitro conditions. Intradiscal and posterior wall temperature did not significantly rise. Spinal canal temperature reached a mean 75.4°C in the presence of “extruded” cement. Microscopic examination showed thermal damage to the spinal cord.

Discussion: The experiments indicate that neurological complications associated with vertebroplasty are likely to be thermally mediated, and that the analgesic effects of vertebroplasty are likely to be, at least in part, due to thermal damage to endplate neurological structures.

Introduction: Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. It has been shown that fat embolism (FE) with acute cardiopulmonary deterioration occurs during VP as in a variety of other orthopaedic procedures (e.g. knee and hip replacements). The aim of the study is to investigate cardiovascular changes during FE caused by multiple VP using an animal model.

Method: In six sheep, PMMA was injected unilaterally, into L1 – L6, with ten minutes in-between injections. Arterial, venous and pulmonary artery pressure, cardiac output and blood gas values were recorded pre injection and 1, 3, 5 and 10 minutes post injection. Post mortem lungs were harvested and the histopathologic score (percentage of lung fields occupied by intravascular fat globules as seen in the microscope) was calculated.

Results: The sequential injection of bone cement into six vertebral bodies from values pre injection of L1 to 10 minutes post injection of L6 resulted in: significant falls in arterial blood pressure (P< 0.0001), cardiac output (P< 0.0001) (P=0.0049), pO₂ and pH (P< 0.0001) and significant rises in pulmonary arterial pressure (P=0.0005) and pCO₂ (P< 0.0001),but no significant change in central venous pressure. The histopathological score was 19.1±1.94%.

Conclusion: This study clearly shows that multiple VP in sheep leads to FE with major cardiovascular reactions. Arterial blood pressure showed a stepwise, cumulative fall and was clearly the best parameter to demonstrate these reactions. This suggests, in human patients, particular attention should be paid to falls in arterial blood pressure during multiple VP.

We carried out a histological study of a proximally hydroxyapatite (HA)-coated femoral component, retrieved after 9.5 years of good function. The HA coating had completely degraded. Bone was in direct contact with the titanium surface in all the areas which had been coated, with no interposing fibrous tissue. There were no signs of particles, third-body wear, adverse tissue reactions or osteolysis. Bone remodelling was evident by the presence of resorption lacunae; tetracycline labelling showed bone laid down six years after implantation.

The loss of the HA-coating had no negative effect on the osseo-integration of the stem. We conclude that the HA coating contributes to the fixation of the implant and that its degradation does not adversely affect the long-term fixation.

INTRODUCTION: Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. It has been shown that fat embolism (FE) with acute cardiopulmonary deterioration occurs during VP as in a variety of other orthopaedic procedures (eg knee and hip replacements). The aim of the study is to investigate cardiovascular changes during FE caused by multiple VP using an animal model.

METHOD: In six sheep, PMMA was injected unilaterally, into L1 – L6, with ten minutes in between injections. Arterial, venous and pulmonary artery pressure, cardiac output and blood gas values were recorded pre injection and one, three, five and 10 minutes post injection. Post mortem lungs were harvested and the histopathologic score (percentage of lung fields occupied by intravascular fat globules as seen in the microscope) was calculated.

RESULTS: The sequential injection of bone cement into six vertebral bodies from values pre injection of L1 to 10 minutes post injection of L6 resulted in: significant falls in arterial blood pressure (P< 0.0001), cardiac output (P=0.0049), pO2 (P< 0.0001) and pH (P< 0.0001) and significant rises in pulmonary arterial pressure (P=0.0005) and pCO2 (P< 0.0001), but no significant change in central venous pressure. The histopathological score was 19.1±1.94%.

CONCLUSION: This study clearly shows that multiple VP in sheep leads to FE with major cardiovascular reactions. Arterial blood pressure showed a stepwise, cumulative fall and was clearly the best parameter to demonstrate these reactions. This suggests, in human patients, particular attention should be paid to falls in arterial blood pressure during multiple VP.

Introduction: Vertebroplasty (VP) is a relatively new procedure to treat osteoporotic compression fractures of vertebral bodies. During this procedure polymethyl-methacrylate (PMMA) is injected into vertebral bodies. However there is the concern, that fat embolism (FE) and acute hypotension could occur as in a variety of other orthopaedic procedures.

Aim: To investigate whether FE and acute hypotension are potential complications of VP using an animal model.

Methods: In six sheep, 6.0 ml PMMA were injected unilaterally into the L1 vertebral body. Transœsophageal echocardiography was used to monitor the pulmonary artery for bone marrow and fat particles until 30 minutes post-operatively. Pulse, arterial and venous pressures were also recorded. The lumbar spine and the lungs were harvested post mortem. The histopathologic score, (percentage of lung fields occupied by intravascular fat globules as seen through the microscope), was calculated.

Results: The first showers of echogenic material were visible approximately seven seconds after the beginning of the cement injection and lasted for about 2.5 minutes. The injection of bone cement caused a very rapid decrease in the heart rate after two seconds followed by a fall in the mean arterial pressure after 6.0 seconds. A maximum fall in heart rate was accompanied by a delayed fall in mean arterial pressure of 33.0 mmHg (P=0.0003) at 36seconds. The heat rate had returned to the baseline by 89 seconds and had increased by 10 beats/min (P=0.02) at 25 minutes. Mean arterial pressure had recovered by 209 seconds and was not different from the baseline at 25 minutes. Post mortem examination showed that no leakage of cement into the spinal cord had occurred. The histology revealed fat globules and bone marrow cells in the smaller and larger vessels throughout the lungs. The histopathologic score was 5.2 ± 0.9%.

Conclusions: This study clearly showed that VP resulted in FE with a two-phase decrease in heart rate and arterial blood pressure. The first phase was probably due to an autonomic reflex and the second phase was due to the passage of fat emboli through the right heart and obstructing the lungs.

Introduction: After more than 10 years of clinical experience, hydroxyapatite (HA) coated orthopaedic implants are now an established, viable alternative to porous coatings for achieving good implant fixation. However, developments are continuing to improve the nature and adhesion of the HA coating.

Aim: To investigate the biological attachment characteristics of titanium and highly crystalline HA implant coatings in the metaphysis of an animal model.

Method: Titanium alloy implants with a coating of commercially pure titanium (Ti) or highly crystalline HA were evaluated by light microscopy and pullout tests after one, two and four weeks of unloaded implantation in the tibial and femoral metaphyses of 18 sheep.

Results: The interface shear strength pullout increased from approximately 29N/cm2 at one week to approximately 326N/cm² at two weeks. At four weeks the pull-out strength for Ti and HA coated implants was 1,004.87 ± 189.82N/cm2 and 1,043.26 ± 260.61N/cm2 respectively. The pullout strength increased significantly over time up to four weeks, but the difference between the coatings was not statistically significant at any time interval.

Histomorphometric analysis showed an increase of bone-implant contact between one and two weeks from 0 to 15% for Ti and 0 to 20% for HA coated implants. At four weeks Ti and HA implants showed 44% and 60% bone-implant contact respectively. There was a significant increase in bone-implant contact over time for both coatings. HA implants had significantly higher bone-implant contact at two and four weeks. Light microscopy revealed that bone grew into HA coated surfaces in the form of feet, spreading over the surface. Whereas for Ti the newly formed bone looked like a bridge linking the original bone with the implant surface.

Conclusion: The different growth patterns of bone into Ti and HA surfaces resulted in different bone-implant contact areas. Highly crystalline hydroxyapatite coatings enhanced the osseointegration in the early stages of bone healing. However there was a discrepancy between the mechanical and histological results. This may suggest that the mechanical failure does not occur at the implant-bone interface.

Introduction: The aim of introducing mobile-bearing knee replacements was to improve long term survival by maintaining large areas of surface contact, while allowing motion to occur at the bearing-metal interface on the tibial and patellar components. Despite wide use of these implants, there are only a few intermediate or long-term follow-up studies.

Aims: To present the intermediate follow-up results of a cementless, posterior cruciate ligament retaining, low contact-stress, knee replacement system (LCS).

Methods: Between 1987 and 1991 the senior author (U.W.) performed 134 cementless LCS total knee arthroplasties in 121 patients. Twenty of the patients were male, 101 female, with an average age of 70 years (range: 49 years to 91years). In 40% of the cases the patella was resurfaced. The patients were evaluated with clinical knee rating (Insall score) and radiographic analysis, between six and nine years postoperatively.

Results: At the time of the follow-up 94 patients were alive. Twelve patients (10%; 14 prostheses) were contacted by phone after an average of 77 months. Evaluation was possible in 82 patients (68%; 91 prostheses) after an average of 74 months. Ninety percent of these patients had an Insall score of > 80 (good to very good). One patient had a score of < 70 (insufficient). Average flexion was 114 degrees (range: of 70 to 135 degrees). Two patients had flexion of < 90 degrees. There were no radiographic signs of aseptic loosening. The meniscal bearing of four prostheses and one patellar component were replaced. Complications like haematoma, fibrotic arthritis and infection due to endocarditis lenta lead to three revisions.

Conclusion: Our study has shown that the non-cemented posterior cruciate ligament retaining LCS knee replacement system produced very satisfactory results with few complications in the medium term.

Introduction: Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. It has been shown that fat embolism (FE) with acute cardiopulmonary deterioration occurs during VP as it does in a variety of other orthopaedic procedures (e.g. knee and hip replacements).

Aim: To investigate the cardiovascular changes during FE caused by multiple VP using an animal model.

Method: PMMA was injected unilaterally, into L1 – L6 in six sheep, with 10 minutes between injections. Arterial, venous and pulmonary arterial pressure, cardiac output and blood gas values were recorded before injection and again after the injection at one, three, five and 10 minutes. The lungs were harvested post mortem and the histopathologic score (percentage of lung fields occupied by intravascular fat globules as the field of the microscope) was calculated.

Results: The sequential injection of bone cement into six vertebral bodies from values before injection of L1 to 10 minutes after injection of L6 resulted in significant falls in arterial blood pressure (P< 0.0001), cardiac output (P=0.0049), pO² (P< 0.0001) and pH (P< 0.0001). There were also significant rises in pulmonary arterial pressure (P=0.0005) and pCO2 (P< 0.0001), but no significant change in central venous pressure. The histopathological score was 19.1±1.94%,

Conclusions: This study clearly showed that multiple VP in sheep leads to FE with major cardiovascular reactions. Arterial blood pressure showed a stepwise, cumulative fall and was clearly the best parameter to demonstrate these reactions. This suggests that in human patients, particular attention should be paid to falls in arterial blood pressure during multiple VP.