Metallic implants are widely used in orthopedic, oral and maxillofacial surgery. Durable osseous fixation of an implant requires that osteoprogenitor cells attach and adhere to the implant, proliferate, differentiate into osteoblasts, and produce mineralized matrix. We previously observed that human mesenchymal stem cells (MSCs) adherent to smooth tantalum (Ta) surfaces demonstrated superior biocompatibility compared with titanium (Ti) coatings.

The aim of the present study was to investigate the interactions between MSCs and smooth surfaces of Ta and by means of whole-genome microarray technology.

Immortalized human mesenchymal stem cells were cultivated on smooth surfaces of Ti and Ta. Total RNA was extracted after culturing for 1, 2, 4, and 8 days and hybridized to Affymetrix whole-genome microarrays (N=16). Replicate arrays were averaged and the ratios of gene expression by MSCs cultivated on Ta versus Ti coating were calculated. Absolute fold differences were also calculated and lists of upregulated genes were generated. Moreover, gene Ontology (GO) annotation analysis of differentially regulated genes was performed.

For both Ta and Ti coatings, the vast majority of genes were upregulated after 4 d of cultivation. Genes upregulated by MSCs cultivated on Ta coating for 4 d were annotated to relevant GO terms. Ti-regulated GO annotation clusters were predominantly transcription-related. By using the K-means clustering algorithm, 10 clusters containing more than 5 genes were identified. Moreover, various genes related to osteogenesis and cell adhesion were upregulated by MSCs exposed to Ta surface.

Microarray analysis of MSCs exposed to smooth metallic surfaces of both Ta and Ti generally showed a huge increase in transcriptional activity after 4 d of cultivation. According to GO annotation analysis Ta coating may induce increased adhesion and earlier differentiation of MSCs compared to Ti surface making Ta a promising biocompatible material for bone implants.

Impacted bone allograft is often used in revision joint replacement. Hydroxyapatite granules have been suggested as a substitute or to enhance morcellised bone allograft. We hypothesised that adding osteogenic protein-1 to a composite of bone allograft and non-resorbable hydroxyapatite granules (ProOsteon) would improve the incorporation of bone and implant fixation. We also compared the response to using ProOsteon alone against bone allograft used in isolation. We implanted two non-weight-bearing hydroxyapatite-coated implants into each proximal humerus of six dogs, with each implant surrounded by a concentric 3 mm gap. These gaps were randomly allocated to four different procedures in each dog: 1) bone allograft used on its own; 2) ProOsteon used on its own; 3) allograft and ProOsteon used together; or 4) allograft and ProOsteon with the addition of osteogenic protein-1.

After three weeks osteogenic protein-1 increased bone formation and the energy absorption of implants grafted with allograft and ProOsteon. A composite of allograft, ProOsteon and osteogenic protein-1 was comparable, but not superior to, allograft used on its own.

ProOsteon alone cannot be recommended as a substitute for allograft around non-cemented implants, but should be used to extend the volume of the graft, preferably with the addition of a growth factor.

Introduction Circumferential fusion has become a common procedure in lumbar spinal fusion, both as a primary and salvage procedure. However, the claimed advantages of circumferential fusion over conventional posterolateral fusion lack scientific documentation. The aim of the present study was to analyse the long-term outcome; functional disability, pain and general health of circumferential lumbar fusion in comparison to instrumented posterolateral lumbar fusion.

Methods From April 1996 to November 1999 a total of 148 patients with severe chronic low back pain were randomly selected for either posterolateral lumbar fusion (titanium Cotrel-Dubousset) or circumferential lumbar fusion (instrumented posterolateral fusion with anterior intervertebral support by a Brantigan cage). The primary outcome measure was the Dallas Pain Questionnaire (DPQ). The secondary outcome measures were, the Oswestry Disability Index, the SF-36 instrument and the Low Back Pain Rating Scale. All measures assessed the end-point outcomes at 5–9 years postoperatively.

Results The available follow-up rate was 93%. The circumferential group showed a significantly better improvement (p< 0.05) in comparison to the posterolateral group with respect to all four DPQ categories: daily activities, work/leisure, anxiety/depression and social interest. The Oswestry Disability Index supported these results (p< 0.01) in the circumferential group where as no significant difference was found with respect to mental health compared to the posterolateral group. The circumferential group showed significantly less back pain (p< 0.05) in comparison to the posterolateral group. No significant difference was found regarding leg pain.

Discussion Circumferential lumbar fusion demands more extensive operative resources compared to posterolateral lumbar fusion. However, 5–9 years after surgery the circumferentially fused patients had a significantly improved outcome compared to posterolateral fusion alone. These new results underline the superiority of circumferential fusion in the complex pathology of the lumbar spine and are strongly supported in all validated questionnaires.

Introduction: In the pathogenesis of steroid-associated femoral head necrosis only intra- and extravascular factors have been discussed. This study investigated the effect of long term glucocorticoid treatment on contraction of intraosseous femoral head arteries in a porcine model.

Materials and Methods: From 24 immature female Danish Landrace pigs from 12 litters, 12 animals received 100 mg methylprednisolone daily for 3 months. Their 12 sister pigs served as controls and received no steroids. Resistance arteries (diameter approximately 250 μm) were isolated from the femoral head epiphyseal cancellous bone and mounted as ring preparations on a small vessel myograph for measurement of isometric force development.

Results: Increasing doses of endothelin-1 evoked significantly stronger vasoconstriction after 3 months of methylprednisolone treatment. The vasocontractory response to increasing doses of noradrenaline was not altered by the previous methylprednisolone treatment. After submaximal precontraction by noradrenaline, vasorelaxation by bradykinin was not altered by methylprednisolone treatment.

Discussion: The vasocontractory response of isolated intraosseous femoral head epiphyseal arteries to endothelin-1 after long term glucocorticoid treatment in the pig was enhanced. Enhanced contraction of FH lateral epiphyseal arteries can diminish femoral head blood flow as vessel diameter decreases. This may be a relevant cofactor in the early pathogenesis of steroid-associated femoral head necrosis.

Introduction: In the attempt to improve fusion rates in spondylodesis surgery, focus has been applied on numerous factors, including surgical strategies, instrumentation-devices and –material, technical preparation of the fusion bed, stringency of radiological outcome criteria, patient-related factors such as age, sex, tobacco consumption, and severity of underlying pathology. In recent years the development of new techniques for exploring mechanisms in cellular and molecular biology have further directed focus toward more advanced biological techniques and considerations. To the authors’ knowledge, little or no attention has been focused on one of the basic and important factors in the attempt to achieve fusion, ie the impact of bone graft quantity placed at the fusion bed.

The aim of this study was to investigate the influence of autologous bone graft quantity in posterolateral instrumented spinal fusion (PLF) in respect to fusion rates.

Methods and results: A prospective clinical study in 76 patients, in which CD-instrumented posterolateral lumbar or lumbosacral spine fusion surgery was performed. The quantity of autologous bone graft applied at the fusion bed was recorded peroperatively. Spinal fusion rates were assessed by AP/lateral radiographs at one-year follow-up by two independent observers, according to our strict classification system. The impact of bone graft quantity, tobacco consumption, age and sex of the patients were analysed in respect to fusion-rates by logistic regression.

According to our classification “fusion” was seen in 76% of the patients, “non-union” in 12.7% and “doubtful”fusion in 11.3%. In “fusion” segments, the median amount of bone used was 24.4 (13–53) g and 14.7 (12.5–23.4) g in “non-union” segments. The “non-union” rate was 7.1% for non-smokers in contrast to 21.4% for patients who smoked during the first six post-operative months. The impact on fusion rates by graft quantity and cigarette smoking were significant, p< 0.006 respectively 0.035. Age and gender did not influence fusion rates. Thirty-three percent of patients with “non-union” had a corresponding failure of the implant.

Conclusions: The quantity of graft used at the fusion bed is critical for successful fusion. Based on the results presented here, we recommend a minimum of 24 g of autogenous bone graft at each intervention segment in auto-grafted posterolateral spinal spondylodesis surgery. In addition, this study underlines the importance of tobacco arrest, in at least the first six post-operative months. The data presented here strongly support the importance of quantifying or optimally standardising the amount of graft placed at each intervention segment.

Introduction: Lumbar spine fusion is now an evidence based treatment principle of low back pain. However, much controversy still exists on the choice of surgical technique. Since the source of pain may be located in the intervertebral disc, a disc removal seems logical. Instrumented and non-instrumented fusion as well as PLIF have failed to restore lumbar lordosis.

Aim: The aim of the present study was to study fusion rates, functional outcome, lumbar lordosis and complications in a RCT design using radiolucent cages and titanium instrumentation.

Materials and methods: 148 patients were bloc randomised to either PLF (72) or ALIF + PLF (76) from April 1996 to February 2000. Inclusion criteria were disc degeneration or spondylolisthesis groups 1 and 2; Age> 20 years and < 65 years. Life quality was assessed pre-operatively, one and two years post-operatively by Dallas Pain Questionnaires and by Back and Leg Pain rating scales from 0 to 10.

Results and discussion: A preliminary follow-up at one year post-op of 56 patients in each group showed no difference in admission or blood loss (921/1008 ml) and peroperative morbidity, although the operation time was significantly longer in the ALIF+ group (mean 219/344 minutes). Sagittal lordosis was restored and maintained in the ALIF+ group (p< 0.01), in contrast to the PLF group. There was no difference in functional outcome. Average back pain lasting 14 days scored 4.5 in each group, and leg pain 3.2 in the ALIF+ group versus 4 in the PLF group (NS). The re-operation rate was significantly higher in PLF after both one and two years with 9% refusion versus no refusion in the ALIF+ group. Global patient satisfaction was equal in both groups: 78% versus 76% at one year and at two years 75% versus 80% in PLF and ALIF+ groups.

Conclusion: ALIF+ fusion demands higher operative resources compared to PLF, however ALIF+ restores lordosis and provides the highest union rate and significantly fewer reoperations. A cost/effectiveness analysis after long-term follow-up may also favour the ALIF+ treatment due to improved lordosis and perhaps less degeneration of adjacent motion segments.

We have studied the beneficial effects of a hydroxyapatite (HA) coating on the prevention of the migration of wear debris along the implant-bone interface. We implanted a loaded HA-coated implant and a non-coated grit-blasted titanium alloy (Ti) implant in each distal femoral condyle of eight Labrador dogs. The test implant was surrounded by a gap communicating with the joint space and allowing access of joint fluid to the implant-bone interface. We injected polyethylene (PE) particles into the right knee three weeks after surgery and repeated this weekly for the following five weeks. The left knee received sham injections. The animals were killed eight weeks after surgery. Specimens from the implant-bone interface were examined under plain and polarised light.

Only a few particles were found around HA-coated implants, but around Ti implants there was a large amount of particles. HA-coated implants had approximately 35% bone ingrowth, whereas Ti implants had virtually no bone ingrowth and were surrounded by a fibrous membrane.

Our findings suggest that HA coating of implants is able to inhibit peri-implant migration of PE particles by creating a seal of tightly-bonded bone on the surface of the implant.

Treatment with corticosteroids is a risk factor for non-traumatic avascular necrosis of the femoral head, but the pathological mechanism is poorly understood. Short-term treatment with high doses of methylprednisolone is used in severe neurotrauma and after kidney and heart transplantation. We investigated the effect of such treatment on the pattern of perfusion of the femoral head and of bone in general in the pig.

We allocated 15 immature pigs to treatment with high-dose methylprednisolone (20 mg/kg per day intramuscularly for three days, followed by 10 mg/kg intramuscularly for a further 11 days) and 15 to a control group. Perfusion of the systematically subdivided femoral head, proximal femur, acetabulum, humerus, and soft tissues was determined by the microsphere technique. Blood flow in bone was severely reduced in the steroid-treated group. The reduction of flow affected all the segments and the entire epiphysis of the femoral head. No changes in flow were found in non-osseous tissue. Short-term treatment with high-dose methylprednisolone causes reduction of osseous blood flow which may be the pathogenetic factor in the early stage of steroid-induced osteonecrosis.

We inserted two hydroxyapatite (HA)-coated implants with crystallinities of either 50% (HA-50%) or 75% (HA-75%) bilaterally into the medial femoral condyles of the knees of 16 dogs. The implants were allocated to two groups with implantation periods of 16 and 32 weeks. They were weight-bearing and subjected to controlled micromovement of 250 μm during each gait cycle. After 16 weeks, mechanical fixation of the HA-50% implants was increased threefold as compared with the HA-75% implants. After 32 weeks there was no difference between HA-50% and HA-75%. Fixation of HA-75% increased from 16 to 32 weeks whereas that of HA-50% was unchanged. HA-50% implants had 100% more bone ingrowth than HA-75% implants after 16 weeks. More HA coating was removed on HA-50% implants compared with HA-75% implants after both 16 and 32 weeks. No further loss of the HA coating was shown from 16 to 32 weeks.

Our study suggests that the crystallinity of the HA coating is an important factor in its bioactivity and resorption during weight-bearing conditions. Our findings suggest two phases of coating resorption, an initial rapid loss, followed by a slow loss. Resorbed HA coating was partly replaced by bone ingrowth, suggesting that implant fixation will be durable.

The clinical use of hydroxyapatite (HA) coating is controversial especially in regard to the long-term performance of the coating and the effects of resorption. In each of 15 consenting patients we inserted two implants, coated with either HA or fluorapatite (FA) into the iliac crest. They were harvested at a mean of 13.6 ± 0.6 months after surgery.

Histological examination showed that bone ongrowth on the HA-coated implants was significantly greater (29%) than that on the FA-coated implants. When bone was present on the coating surface the HA coating was significantly thicker than the FA coating. When bone marrow was present, the HA coating was significantly thinner than the FA coating. The reduction in coating thickness when covered by bone or bone marrow was 23.1 ± 9.7 μm for HA and 5.1 ± 1.7 μm for FA (p < 0.01) suggesting that FA is more stable than HA against resorption by bone marrow.

The findings suggest that in man the osteoconductive properties of HA coating are superior to those of FA. Resorption rates for both coatings were approximately 20% of the coating thickness per year. Bone ongrowth appears to protect against resorption whereas bone marrow seems to accelerate resorption. No adverse reaction was seen in the surrounding bone.

Bone growth into cementless prosthetic components is compromised by osteoporosis, by any gap between the implant and the bone, by micromotion, and after the revision of failed prostheses. Recombinant human transforming growth factor-β1 (rhTGF-β1) has recently been shown to be a potent stimulator of bone healing and bone formation in various models in vivo.

We have investigated the potential of rhTGF-β1, adsorbed on to weight-loaded tricalcium phosphate (TCP) coated implants, to enhance bone ongrowth and mechanical fixation. We inserted cylindrical grit-blasted titanium alloy implants bilaterally into the weight-bearing part of the medial femoral condyles of ten skeletally mature dogs. The implants were mounted on special devices which ensured stable weight-loading during each gait cycle. All implants were initially surrounded by a 0.75 mm gap and were coated with TCP ceramic.

Each animal received two implants, one with 0.3 μg rhTGF-β1 adsorbed on the ceramic surface and the other without growth factor. Histological analysis showed that bone ongrowth was significantly increased from 22 ± 5.6% bone-implant contact in the control group to 36 ± 2.9% in the rhTGF-β stimulated group, an increase of 59%. The volume of bone in the gap was increased by 16% in rhTGF-β1-stimulated TCP-coated implants, but this difference was not significant. Mechanical push-out tests showed no difference in fixation of the implant between the two groups. Our study suggests that rhTGF-β1 adsorbed on TCP-ceramic-coated implants can enhance bone ongrowth.