Biomedical subjects

T Steffen

Publications and source records attributed to T Steffen.

At least 19 recordsLinked to original sources

PubMed2005

The in vitro stabilising effect of polyetheretherketone cages versus a titanium cage of similar design for anterior lumbar interbody fusion.

UNLABELLED: This biomechanical study was performed to test the primary segmental in vitro stabilising effect of a standard and large footprint radiolucent poly-ether-ether-ketone (PEEK) box cage versus a titanium box cage for anterior lumbar interbody fusion. Eighteen L2-L3 and sixteen L4-L5 cadaveric motion segments were divided into three groups and received a titanium cage or a radiolucent PEEK cage with standard or large footprint. All specimens were tested in three testing conditions: intact, stand-alone anterior cage and finally with supplemental translaminar screw fixation. Full range of motion and neutral zone measurements were determined and anterior cage pull out force was tested. The titanium design was significantly more effective in reducing the range of motion only in axial rotation. The larger footprint radiolucent cage did not increase stability as compared to the standard footprint. The titanium cage pull out force was significantly (P=0.0002) higher compared to both radiolucent cage constructs. CLINICAL RELEVANCE: Supplemental posterior fixation is strongly recommended to increase initial stability of any anterior interbody fusion cage construct. Although the biomechanical stability necessary to achieve spinal fusion is not defined, the radiolucent designs tested in this study, with a standard footprint as well as with a larger footprint, may be insufficiently stabilised with translaminar screws as compared to the titanium implant. Supplemental pedicle screw fixation may be required to obtain adequate stabilisation in the clinical setting.

Benzophenones↗

PubMed2005

A new cannula to ease cement injection during vertebroplasty.

One of the main limitations of vertebroplasty is the excessive pressure required to inject a sufficient amount of cement into a vertebral body. Based on previous work that shows that approximately 95% of the injection pressure is required to deliver the cement through the cannula, we proposed a new cannula design with a larger internal diameter in the proximal section. The objective of this study is to determine whether the new cannula geometry significantly reduces the delivery pressure and eases cement injection during vertebroplasty. Two different methods were employed to examine the delivery pressure in a conventional and two redesigned cannulae: (1) analytical model: Hagen-Poisseuille's flow through a tube was used to predict the pressure drop in the cannulae; (2) experiment: first a Newtonian silicone oil and then an acrylic bone cement was injected through the cannulae at a constant rate of 4 cc/min, and the delivery pressure was recorded. Both the experimental and analytical findings confirmed that the redesigned cannula reduces the delivery pressure significantly. Specifically, when the internal diameter of the proximal section was increased by a factor of two, which is clinically feasible, the delivery pressure dropped by about 63%. The redesigned cannula appears to have the potential to improve vertebroplasty. The key benefits are that (1) it eases cement injection, (2) it can be easily integrated into the existing procedure, and (3) it is cost-effective.

Acrylates↗

PubMed2004

Influence of mixing method on the cement temperature-mixing time history and doughing time of three acrylic cements for vertebroplasty.

Acrylic cements are increasingly being used to augment osteoporotic vertebrae in a procedure called vertebroplasty. Two significant factors that may complicate the use of acrylic cements are: (a) short handling time, which may result in insufficient filling of the vertebra; and (b) exothermic setting (curing) behavior, which may result in thermal damage of the surrounding tissue. It has been previously reported that mixing the cement components under oscillation, as compared to manual mixing, increases the handling time. More specifically, it seems that oscillatory mixing slows down the cement polymerization process and, consequently, widens the time window during which cement is injectable. However, the effect of oscillatory mixing on the exothermic setting behavior of cement undergoing polymerization has not been examined. In this study, the exothermic setting behavior of three commercially available acrylic cements--Antibiotic Simplex, DP-Pour&trade, and Vertebroplastic--were examined for both manual and oscillatory mixing methods. For each combination of cement and mixing method, the parameters that were measured were the exothermic setting curve (and hence the cement setting temperature and setting time) and the cement doughing time. It was found that oscillatory mixing had no significant effect on any of these parameters. Based on the results of this study, it can be concluded that, for the tested cements, the setting process is a reaction-controlled process rather than a diffusion-controlled one. Clinically, this implies that oscillatory mixing may be used to increase the working period for acrylic cements without increasing the risk of thermal damage to surrounding tissue.

Bone Substitutes↗

PubMed2004

Influence of oscillatory mixing on the injectability of three acrylic and two calcium-phosphate bone cements for vertebroplasty.

Injecting acrylic and, increasingly, calcium-phosphate cements into the porous bone structure is an emerging procedure, referred to as vertebroplasty, for the augmentation of osteoporotic vertebrae. Despite the benefits of vertebroplasty, it has limitations. The limitations of interest in this study are the injectability of bone cements and their mixing variability (i.e., low reproducibility of resulting viscosity). The objective of this study is to investigate the effect of oscillatory versus manual mixing on cement viscosity and mixing variability. Five cements are tested: (a) Vertebroplastic, (b) DP-Pour, (c) Antibiotic Simplex, (d) chronOS Inject, and (e) Biopex. Compared to manual mixing, oscillatory mixing significantly decreased the mean viscosity and the mixing variability, which was inferred from the coefficient of variation. For example, under oscillatory mixing, the viscosity and the variability for Vertebroplastic decreased to one-third of the corresponding values for manual mixing. Similar results were obtained for the other cements. The decrease in viscosity is attributed to the pseudo-plastic behavior of bone cements. The decrease in the variability of cement viscosity was attributed to greater dispersive mixing of the cement components under oscillatory mixing. The decrease in viscosity eases the injection by reducing the pressure required. The decrease in the variability of cement viscosity increases reproducibility of the cement injection. Oscillatory mixing appears to have the potential to contribute to improving vertebroplasty.

Bone Substitutes↗

PubMed2004

Experimental and theoretical investigation of directional permeability of human vertebral cancellous bone for cement infiltration.

The use of acrylic polymers in infiltrating the porous bone structure is an emerging procedure for the augmentation of osteoporotic vertebrae. Although this procedure is employed frequently, it is performed based on empirical knowledge, and therefore, does not take into consideration the porosity-dependent permeability of human vertebral cancellous bone. The purpose of this study was to: (a). experimentally and theoretically investigate interdependence of the vertebral cancellous bone permeability and porosity, and (b). examine if the bone permeability of spinal cancellous bone can be predicted using bone mineral density measurements. If these relations can be established, they can be useful in optimizing the injection conditions for predicable cement infiltration. To determine the porosity-dependent and directional permeability, 34 bone cores-20 samples in the superior-inferior (SI) direction and 14 in the anterior-posterior (AP) direction-were cut from 20 lumbar vertebrae and infiltrated with silicone oil with a viscosity matching that of PMMA. The permeability of the cores was determined based on Darcy's law. The mean permeability of SI and AP cores was 4.45+/-1.72 x 10(-8) and 3.44+/-1.26 x 10(-8)m(2), respectively. An interesting finding of this study was that the permeability of the AP cores was approximately 78% of that of SI cores, though the porosity of the SI and AP cores taken from the same vertebra was approximately equal. In addition, we provided a theoretical model for the porosity-dependent permeability that accurately described non-linear dependency of the bone permeability and porosity in both directions. Although the relation of the bone permeability and porosity was established, bone mineral density was a weak predictor of the bone permeability. The experimental and theoretical results of this study can be used to understand polymer flow in cement infiltration procedures.

Adsorption↗

PubMed2004

Injection biomechanics of bone cements used in vertebroplasty.

The incidence of osteoporotic bone fractures is growing exponentially as the western population ages and as life expectancy increases. Vertebroplasty, where acrylic or calcium phosphate cement is injected into the weakened vertebrae to augment them, is an emerging procedure for treating spinal fragility fractures. However, cement injection is currently limited because there are no clear standards for a safe, reproducible and predictable procedure. The purpose of this paper is to examine the role that bone cements play in the underlying bio-mechanisms that affect the outcomes of cement injection. Our most important finding after combining clinical, laboratory and theoretical research is that the process of cement injection poses conflicting demands on bone cements. The cements are required to be more viscous and less viscous at the same time. The challenge therefore is to develop biomaterials, techniques and/or devices that can overcome or manage the conflicting demands on cement viscosity.

Biomechanical Phenomena↗

PubMed2003

Load shift of the intervertebral disc after a vertebroplasty: a finite-element study.

Infiltrating osteoporotic cancellous bone with bone cement (vertebroplasty) is a novel surgical procedure to stabilize and prevent osteoporotic vertebral fractures. Short-term clinical and biomechanical results are encouraging; however, so far no reports on long-term results have been published. Our clinical observations suggest that vertebroplasty may induce subsequent fractures in the vertebrae adjacent to the ones augmented. At this point, there is only a limited understanding of what causes these fractures. We have previously hypothesized that adjacent fractures may result from a shift in stiffness and load following rigid augmentation. The purpose of this study is to determine the load shift in a lumbar motion segment following vertebroplasty. A finite-element (FE) model of a lumbar motion segment (L4-L5) was used to quantify and compare the pre- and post-augmentation stiffness and loading (load shift) of the intervertebral (IV) disc adjacent to the augmented vertebra in response to quasi-static compression. The results showed that the rigid cement augmentation underneath the endplates acted as an upright pillar that severely reduced the inward bulge of the endplates of the augmented vertebra. The bulge of the augmented endplate was reduced to 7% of its value before the augmentation, resulting in a stiffening of the IV joint by approximately 17%, and of the whole motion segment by approximately 11%. The IV pressure accordingly increased by approximately 19%, and the inward bulge of the endplate adjacent to the one augmented (L4 inferior) increased considerably, by approximately 17%. This increase of up to 17% in the inward bulge of the endplate adjacent to the one augmented may be the cause of the adjacent fractures.

Biomechanical Phenomena↗

PubMed2003

[Old age as risk factor for complications of malaria in non-immune travellers].

BACKGROUND: Malaria plays an important role as a dangerous imported infection in Europe. In addition, the number of elderly travellers is increasing. We examined the hypothesis, whether age can be considered as a risk factor for the development of complications in malaria. PATIENTS AND METHODS: We examined retrospectively 134 case records of patients of all age groups with a plasmodial infection. We analysed personal data, travel details and patient histories, the neurological status, respiratory function, as well as haematological, biochemical and parasitological parameters. RESULTS: There is significant evidence for a correlation between age and the frequency of complications in malaria like cerebral involvement, respiratory failure, renal failure, anaemia, and hyperparasitaemia. Out of 132 patients over 15 years of age, 49 (37.1 %) developed a severe course of malaria. In the age group of 60 years and above this percentage increased to 61.5 %. The age distribution in the group with severe malaria was significantly shifted towards the elderly (p = 0.016 in Mann-Whitney test). The duration of hospitalisation also increased with age from an average of five days for the group below 45 years to 21 days for the elderly of 60 years and above. CONCLUSION: Our findings suggest a higher risk for a severe course of malaria in the elderly. For this reason, extensive advice on the correct use of exposure- and chemoprophylaxis of malaria is especially important for travellers above the age of 60.

Adolescent↗

PubMed2003

How to determine the permeability for cement infiltration of osteoporotic cancellous bone.

Cement augmentation is an emerging surgical procedure in which bone cement is used to infiltrate and reinforce osteoporotic vertebrae. Although this infiltration procedure has been widely applied, it is performed empirically and little is known about the flow characteristics of cement during the injection process. We present a theoretical and experimental approach to investigate the intertrabecular bone permeability during the infiltration procedure. The cement permeability was considered to be dependent on time, bone porosity, and cement viscosity in our analysis. In order to determine the time-dependent permeability, ten cancellous bone cores were harvested from osteoporotic vertebrae, infiltrated with acrylic cement at a constant flow rate, and the pressure drop across the cores during the infiltration was measured. The viscosity dependence of the permeability was determined based on published experimental data. The theoretical model for the permeability as a function of bone porosity and time was then fit to the testing data. Our findings suggest that the intertrabecular bone permeability depends strongly on time. For instance, the initial permeability (60.89 mm(4)/N(*)s) reduced to approximately 63% of its original value within 18 seconds. This study is the first to analyze cement flow through osteoporotic bone. The theoretical and experimental models provided in this paper are generic. Thus, they can be used to systematically study and optimize the infiltration process for clinical practice.

Aged↗

PubMed2003

Material changes in osteoporotic human cancellous bone following infiltration with acrylic bone cement for a vertebral cement augmentation.

Bone cement infiltration can be effective at mechanically augmenting osteoporotic vertebrae. While most published literature describes the gain in mechanical strength of augmented vertebrae, we report the first measurements of viscoelastic material changes of cancellous bone due to cement infiltration. We infiltrated cancellous core specimen harvested from osteoporotic cadaveric spines with acrylic bone cement. Bone specimen before and after cement infiltration were subjected to identical quasi-static and relaxation loading in confined and free compression. Testing data were fitted to a linear viscoelastic model of compressible material and the model parameters for cement, native cancellous bone, and cancellous bone infiltrated (composite) with cement were identified. The fitting demonstrated that the linear viscoelastic model presented in this paper accurately describes the mechanical behaviour of cement and bone, before and after infiltration. Although the composite specimen did not completely adopt the properties of bulk bone cement, the stiffening of cancellous bone due to cement infiltration is considerable. The composite was, for example, 8.5 times stiffer than native bone. The local stiffening of cancellous bone in patients may alter the load transfer of the augmented motion segment and may be the cause of subsequent fractures in the vertebrae adjacent to the ones infiltrated with cement. The material model and parameters in this paper, together with an adequate finite-element model, can be helpful to investigate the load shift, the mechanism for subsequent fractures, and filling patterns for ideal cement infiltration.

Bone Density↗

PubMed2001

Feasibility, safety, and efficacy of injectable heroin prescription for refractory opioid addicts: a follow-up study.

BACKGROUND: Heroin-assisted substitution treatment for severely opioid-dependent drug users has been available in Switzerland since 1994. Our aim was to ascertain the feasibility, safety, and efficacy of this treatment. METHODS: We did a cohort study in 21 community outpatient treatment centres. We assessed 1969 opioid-dependent drug users, who began heroin-assisted substitution treatment between January, 1994, and December, 2000, to ascertain admission and discharge patterns, and patient characteristics. We also followed up a subset of 237 patients who began treatment between Jan 1, 1994, and March 31, 1995, and who stayed with the programme for at least 18 months. We used questionnaires, interviews, and medical examinations done at entry and after 6, 12, and 18 months to assess somatic and mental health, social integration, and treatment outcomes. FINDINGS: More than 70% (1378) of patients remained in treatment for more than a year. Treatment showed positive effects with respect to health and social outcomes. A long stay in treatment was related to a higher chance of starting abstinence-oriented therapy than a short stay. INTERPRETATION: Heroin-assisted substitution treatment might be an effective option for chronically addicted patients for whom other treatments have failed.

Adult↗

PubMed2001

Porous tricalcium phosphate and transforming growth factor used for anterior spine surgery.

Harvesting autologous bone graft from the iliac crest is associated with considerable secondary morbidity. Bone graft substitutes such as porous ceramics are increasingly used for spinal surgery. This paper presents the results of an animal study in which beta-tricalcium phosphate (beta-TCP) bone substitutes were used for anterior spinal surgery in sheep and baboons. The presented baboon study also investigated the effect of impregnating the ceramic material with transforming growth factor (TGF). In the first study, using the sheep model, a stand-alone instrumented anterior fusion was performed. The animals were randomized into three treatment groups: autologous bone, beta-TCP granules, and sham group. The results were analyzed biomechanically and histologically at three survival intervals: 8, 16 and 32 weeks. An additional animal group was added later, with ceramic pre-filled implants. In the second study, a baboon model was used to assess the osteointegration of a 15-mm-diameter porous beta-TCP block into the vertebral body. The experiment was partially motivated by a new surgical procedure proposed for local bone graft harvest. Three treatment groups were used: beta-TCP plug, beta-TCP plug impregnated with TGF-beta3, and a sham group with empty defect. The evaluation for all animals included computer tomograms at 3 and 6 months, as well as histology at 6 months. In the sheep model, the mechanical evaluation failed to demonstrate differences between treatment groups. This was because massive anterior bone bridges formed in almost all the animals, masking the effects of individual treatments. Histologically, beta-TCP was shown to be a good osteoconductor. While multiple signs of implant micromotion were documented, pre-filling the cages markedly improved the histological fusion outcomes. In the baboon study, the beta-TCP plugs were completely osteointegrated at 6 months. For the group that used ceramic plugs impregnated with TGF-beta3, no incremental advantage was seen as a result of this particular application. However, TGF-beta3 is a potent growth factor at a very low dose. Not only does it speed up the ceramic material resorption, but it is also responsible for massive regional new bone formation. More experiments are required to better understand the biological effects of this growth factor in relation to bone formation, and to be able to take clinical advantage of them.

Animals↗

PubMed2001

Infectious diseases and public health: risk-taking behavior during participation in the Swiss program for a medical prescription of narcotics (PROVE).

The medically controlled prescription of narcotics program (PROVE) followed a uniform protocol from January 1, 1994 until December 31, 1996. The program included 800 slots for heroin prescription, 200 slots for intravenous methadone prescription, and 200 slots for intraveneous morphine. Admission criteria were age 20 and above, minimum 2-year duration of daily heroin consumption, failure in at least two previous treatments, and documented social and/or health deficits. There was a very high seroprevalence of hepatitis B (73%) and hepatitis C (82%) among the 1035 entrants. The rate of HIV (15%) was also high compared with prevalence of infection in other therapy programs (methadone program, inpatient therapy). The prevalence of HIV and hepatitis B/C increased with the duration of drug dependence and cocaine use. During treatment, use of street heroin and cocaine could be reduced substantially. After 18 months of continued participation in the program, 74% of patients reported no illegal heroin consumption, and the rate of cocaine abstinence increased from 15% at entry to 41%. Significant declines in visits to the drug scene, illegal income, and needle sharing were also observed. The high prevalence of HIV and hepatitis B and C confirm that a group of drug dependence with severe medical problems was reached in accordance with the admission criteria for the studies. During treatment, a significant reduction in risk-taking behavior was observed in a target population of heroin-dependent persons who failed in previous treatments.

Adult↗

PubMed2001

HIV and hepatitis virus infections among injecting drug users in a medically controlled heroin prescription programme.

BACKGROUND: In Switzerland, 1,035 patients were accepted for admission to the medically controlled prescription of narcotics programme (PROVE) from 1 January 1994 until 31 December 1996. Heroin, methadone, and morphine were prescribed. This paper presents the prevalence and incidence of HIV and hepatitis B/C infections in the sociomedical context of the participants. METHODS: Admission criteria were a minimum age of 20 years, at least a two-year duration of daily heroin consumption, a negative outcome of at least two previous treatments, and documented social and health deficits as a consequence of their heroin dependence. The patients were examined at admission and every six months. A serological test was carried out at the same time for HIV and hepatitis B/C. RESULTS: Serological testing on admission could be performed in more than 80% of the entrants and documented a very high seroprevalence of antibodies against HBcore (73%) and HCV (82%). The prevalence of HIV and hepatitis B/C increased with duration of drug intake. In the follow-up analysis of seronegative individuals, a halving of the risk of viral hepatitis infection was shown when comparing the first six months with the period greater then six months after PROVE entry. CONCLUSION: The tests conducted showed high prevalence and incidence rates of HIV and hepatitis B/C among patients who had consumed intravenous drugs for years. The descriptive analysis in heroin-assisted treatment showed a reduction in infection risk for viral hepatitis corresponding to the lower risk behaviour of patients.

Adult↗

PubMed2000

[Development of skin diseases in intravenous drug dependent patients treated with heroin substitution].

Drug addiction is linked with increased prevalence of various illnesses. Of major importance are skin diseases which often have a powerful influence on the health. Analysis of the situation in Switzerland at the outset of the 1990s showed that not all drug addicts could be reached with the existing range of treatments. For this reason, heroin-supported treatment was examined as a new therapy option from 1994 on. The influence on the skin's health are examined in this study. The minimum age of those admitted was set at age 20. Heroin addiction had to date back at least two years, and several treatment efforts had to have failed. Data of 1,035 patients was based on tests at admission and after six, 12, and 18 months of treatment. Some 18% of drug consumers indicated abcesses at admission, and almost 30% showed phlegmones. The prevalence of all skin diseases examined show significant declines over the 18 months of treatment. The relative risk resulting from puncture points fell to 0.35 (SD: 0.26-0.47), from phlegmones to 0.24 (SD: 0.14-0.41), from absesses to 0.31 (SD: 0.15-0.60). This study shows that skin diseases are a frequent and important complication among intravenous drug addicts. Heroin-supported treatment led to favourable progress of the dermatological situation among patients.

Abscess↗

PubMed2000

Segmental stability and compressive strength of posterior lumbar interbody fusion implants.

STUDY DESIGN: Human cadaveric study on initial segmental stability and compressive strength of posterior lumbar interbody fusion implants. OBJECTIVES: To compare the initial segmental stability and compressive strength of a posterior lumbar interbody fusion construct using a new cortical bone spacer machined from allograft to that of titanium threaded and nonthreaded posterior lumbar interbody fusion cages, tested as stand-alone and with supplemental pedicle screw fixation. SUMMARY OF BACKGROUND DATA: Cages were introduced to overcome the limitations of conventional allografts. Radiodense cage materials impede radiographic assessment of the fusion, however, and may cause stress shielding of the graft. METHODS: Multisegmental specimens were tested intact, with posterior lumbar interbody fusion implants inserted into the L4/L5 interbody space and with supplemental pedicle screw fixation. Three posterior lumbar interbody fusion implant constructs (Ray Threaded Fusion Cage, Contact Fusion Cage, and PLIF Allograft Spacer) were tested nondestructively in axial rotation, flexion-extension, and lateral bending. The implant-specimen constructs then were isolated and compressed to failure. Changes in the neutral zone, range of motion, yield strength, and ultimate compressive strength were analyzed. RESULTS: None of the stand-alone implant constructs reduced the neutral zone. Supplemental pedicle screw fixation decreased the neutral zone in flexion-extension and lateral bending. Stand-alone implant constructs decreased the range of motion in flexion and lateral bending. Differences in the range of motion between stand-alone cage constructs were found in flexion and extension (marginally significant). Supplemental posterior fixation further decreased the range of motion in all loading directions with no differences between implant constructs. The Contact Fusion Cage and PLIF Allograft Spacer constructs had a higher ultimate compressive strength than the Ray Threaded Fusion Cage. CONCLUSIONS: The biomechanical data did not suggest any implant construct to behave superiorly either as a stand-alone or with supplemental posterior fixation. The PLIF Allograph Spacer is biomechanically equivalent to titanium cages but is devoid of the deficiencies associated with other cage technologies. Therefore, the PLIF Allograft Spacer is a valid alternative to conventional cages.

Bone Screws↗

PubMed2000

Harvesting the intact cadaveric cervical spine (C0-Th1).

STUDY DESIGN: Technical report on harvesting method for human cadaveric cervical spine. OBJECTIVES: Description of a new method for harvesting the intact cervical spine during routine autopsies, including the atlanto-occipital and cervico-thoracic joints, without visible disfigurement above the suprasternal notch. SUMMARY OF BACKGROUND DATA: Despite the need for cervical spine specimens, there are only few articles describing procedures for harvesting an intact cervical spine. Presently available techniques either do not preserve the atlanto-occipital joint or leave visible disfigurement. METHODS: The body was placed in a prone position with the head flexed, and a posterior midline incision was performed. The spine was separated from surrounding tissue, then the caudal end was cut off through the Th1/Th2 disc space. A circular craniotomy provided access to the cranial base. A square window surrounding the foramen magnum was cut at the cranial base (through the sella turcica, the internal occipital protuberance, and 5 cm parasagittal on either side), and the entire cervical spine extracted through the posterior incision. The defect was reconstructed using wood and plaster materials. RESULTS: Eighteen specimens were harvested to date using this method. The average time of harvesting the cervical spine was less than 30 minutes. Reconstruction using wood and plaster resulted in a nearly normal appearance of the neck. CONCLUSIONS: Using this technique, the nuchal ligament providing stability to the cervical spine can be preserved. The suggested method was found simple, efficient, and reproducible for harvesting the intact cervical spine, including the atlanto-occipital and cervico-thoracic joints, from any routine autopsy.

Atlanto-Occipital Joint↗

PubMed2000

The efficacy of interconnected porous hydroxyapatite in achieving posterolateral lumbar fusion in sheep.

STUDY DESIGN: An animal study was performed to evaluate lumbar spinal fusion radiologically and mechanically. OBJECTIVES: To assess the efficacy of interconnected porous hydroxyapatite in achieving posterolateral lumbar arthrodesis in sheep. SUMMARY OF BACKGROUND DATA: Posterolateral spinal arthrodesis with autologous bone graft is the gold standard procedure for lumbar fusion. The procedure for harvesting bone from the iliac crest increases morbidity. Interconnected porous hydroxyapatite has been used effectively as an alternative to cancellous bone graft material in metaphyseal bone defects. Little is known about the efficacy of interconnected porous hydroxyapatite in achieving lumbar spinal fusion. METHODS: Four groups of seven sheep underwent bisegmental posterolateral lumbar fusion with instrumentation using different intertransverse graft material. In group 1, no graft material was used. In group 2, autologous bone was used. Group 3 had interconnected porous hydroxyapatite. Group 4 had an equip of interconnected porous hydroxyapatite and autologous bone. The animals were killed at 20 weeks after surgery. Radiographs and computed tomography images were obtained. The fusion masses were graded for bone resorption and trabecular connectivity on the computed tomography images. Mechanical testing of the specimens was performed, and the three-dimensional segmental motion was measured in flexion/extension, axial rotation, and lateral bending. RESULTS: The radiographic images were difficult to interpret because of the radiodense interconnected porous hydroxyapatite granules. According to mechanical stability criteria, the fusion rate for the different groups was as follows: 100% (14/14) for the autologous bone group, 72% (10/14) for the bone/interconnected porous hydroxyapatite group, 50% (7/14) for the pure interconnected porous hydroxyapatite group, and 15% (2/14) for the sham group. CONCLUSIONS: Spinal arthrodesis using interconnected porous hydroxyapatite alone or mixed with bone as graft material reduced segmental motion. It was not, however, as effective as autologous bone graft material in achieving spinal arthrodesis. The sheep model using autologous bone achieved a 100% fusion rate. Because the nonunion rate for a single level in humans may be as high as 40%, the fusion rate with bone/interconnected porous hydroxyapatite in humans may be lower than the 72% found in the sheep model. The little resorption of the radiodense interconnected porous hydroxyapatite granules made the radiologic evaluation of the fusion masses difficult.

Animals↗