Migration of polyethylene debris along well-fixed cemented implants.

Implants, consisting of smooth Inox cylinders, were cemented into the lower femur and upper tibia of nine sheep to study the distal migration of polyethylene particles. Some implants had a titanium-bead porous coat at the proximal end. These were of three types: In the first type, the porous coat was covered with hydroxyapatite to obtain a bony seal; the second type was prepared for a polymethylmethacrylate seal; in the third type, the porous zone was surrounded by a 2-mm-thick space to allow the formation of a fibrous seal. Small polyethylene particles were injected into the knees once a week during the third and fourth months after implantation. The animals were euthanized 2 months later. Major longitudinal sections of the implants and the surrounding bone were examined under a polarized light microscope. Birefringent particles were counted at the cement-bone and cement-implant interfaces. Osteolysis was not observed. None of the seals significantly decreased the migration of particles around the cemented part of the implants. Particles were observed in cement fissures and vacuoles. They migrated at both interfaces and in the bone itself. They were visible in marrow spaces between bone trabeculae.

[Patellar reconstruction during total knee arthroplasty after previous patellectomy]. / Reconstruction patellaire au cours d'une arthroplastie totale sur genou patellectomisé

PURPOSE OF THE STUDY: In order to limit the consequences of prior total patellectomy on knee function after total knee arthroplasty, we propose an original technique using an en bloc patellar graft to reconstruct the quadriceps lever arm. The purpose of this work was to describe the technique and present preliminary results obtained in seven patients. PATIENTS AND METHODS: Seven en bloc patellar grafts were performed in seven patients (6 women and 1 man) during total knee arthroplasty procedures for femorotibial degenerative joint disease after prior patellectectomy (mean 13 years before arthroplasty, range 5-20 years). We implanted three posterior stabilized prostheses, one ultracongruent prosthesis, two prostheses preserving the posterior cruciate ligament, and one bi-cruciate prosthesis. The patella was reconstructed with an autologous bone graft fashioned from the tibial plateau in six cases, and with a homologous graft fashioned from a bone-bank femoral head in one. Transosseous sutures were used to fix the graft to the extensor system. A polyethylene button was cemented on five of the grafts. RESULTS: Active extension was defective in five knees prior to the patellar graft and in only one knee after patellar reconstruction. The IKS knee score improved from 41 points (range 35-45) before surgery to 78 points (range 55-95) after grafting and the IKS function score from 35 (range 5-50) to 72 (range 40-100). Four of the seven grafts were removed (eight weeks to five years after implantation, mean two years) mainly due to failure of fixation leading to progressive migration. Follow-up varied from eight weeks to six years. Mean follow-up for the three grafts still in place was 4.6 years (4-6 years). After removing the patellar graft (4 knees) the IKS knee score decreased to 68 points (20-95) and the IKS function score to 62 points (30-100). Lack of active extension reappeared in three of the knees after removing the patellar graft but was not observed in the three knees with the patellar graft in place (and flexion was at least 110 degrees ). Microradiography of the patellar graft explanted after two years revealed peripheral corticalization with areas of living bone tissue seen on the pathology specimens. Inversely, the autografts explanted at eight weeks and at five years exhibited bone necrosis. CONCLUSION: This preliminary study shows that patellar autograft can improve the performance of total knee arthroplasty on patellectomized knees. The fixation technique must be improved using transosseous transverse sutures in addition to peripheral sutures in order to limit secondary migration of the graft. A patellar autograft fixed into the extensor system can remain viable two years after implantation. This technique can be proposed when total knee arthroplasty is indicated for a patellectomized knee, particularly in patients with lack of active extension.

Influence of polymeric additives on the biological properties of brushite cements: an experimental study in rabbit.

The resorbability and ability of calcium phosphate hydraulic cements to promote new bone formation was investigated in vivo. The effects of two hydrosoluble polymeric additives (hyaluronic acid, and xanthan gum,) on the biological response of two brushite cement formulations (BHC-A vs BHC-B) was investigated. The brushite cements differed in P/Ca (0.71 vs 0.98) and S/Ca (0.10 vs 0.005) atomic ratios and by the presence of calcium sulfate hemihydrate in BHC-A. Polymer-free cements were used as controls. Cement specimens were injected in cylindrical bone defects manually drilled in the distal condyle of rabbit femora. The implants were harvested at 12 and 24 weeks after implantation and subjected to quantitative histomorphometry. The study showed a significantly lower resorption rate for cement BHC-A, which induces the formation of well-mineralized bone in close apposition to the residual material. In contrast, cement BHC-B showed a significant increase of bone formation period and the formation of a thick layer of unmineralized osteoid tissue at the bone/residual cement interface. The presence of xanthan gum made the biological response even worse, particularly in the case of cement BHC-B. The presence of hyaluronic acid has little effect, except for a slight decrease in initial resorption rate, in the case of cement BHC-A.

Bone colonization of beta-TCP granules incorporated in brushite cements.

Injectable calcium phosphate hydraulic cements are known to have a high clinical potential in bone reconstruction for mini-invasive orthopaedic surgery, interventional radiology, and rheumatology. Previous in vivo experiments in rabbit have shown that the presence of beta-TCP granules in injectable bone cement help maintain the transient biomechanical function of the implanted bone and promote the formation of good-quality new bone. Histomorphometric analysis of two brushite hydraulic cement (BHC) mixtures selected from previous results (referred to in this work as BHC-A and BHC-B) was performed at three postoperative delays (0, 12, and 24 weeks): histomorphometric analysis of bone colonization within beta-TCP shows that, just before implantation, the beta-TCP granule area is significantly higher in BHC-B; the residual granule area decreases steadily over time in BHC-A, whereas it goes through a maximum of 30% at 12 weeks in BHC-B; the residual granule porosity increases steadily up to 35% in BHC-A, whereas it goes through a maximum of 35% at 12 weeks and decreases somewhat until 24 weeks in BHC-B. New bone formation within granules appears higher in BHC-A (58% Area) compared to BHC-B (38% area) at 12 weeks. At 24 weeks bone colonization levels off in both cements at about 50% area. Irrespective of the cement matrix composition, beta-TCP granules contribute actively to the conduction of new bone formation.

Porous HA ceramic for bone replacement: role of the pores and interconnections - experimental study in the rabbit.

Hydroxyapatite (HA) porous ceramics are increasingly used in biomedical applications. Their physical characteristics, such as porous volume, require perfect control of the pore shape, as well as the number and the size of their interconnections. The aim of our study was to evaluate a new HA ceramic using polymethylmethacrylate microbeads (PMMA) as the porous agent. Four interconnection sizes (30, 60, 100 and 130 microm) with a 175-260 microm pore size and three pore sizes (175-260, 260-350 and 350-435 microm) for a 130 microm interconnection size were tested. Various HA implants were appraised by microscopic evaluation in a 4.6 x 10 mm rabbit femur cancellous bone defect 12 weeks after implantation. The best osteoconduction result was obtained in the center of the ceramic by means of a 130 microm interconnection size and a 175-260 microm mean pore size. Bone formation obtained within the pores was double that obtained in our previous study where naphtalen microbeads were used as the porous agents.

Tissue engineering and skeletal diseases.

Tissue engineering, a cross between the science of the living organism and that of engineering, aims to replace, maintain or improve human tissue functions, by means of tissue substitutes containing living elements. Thus, it is about production of artificial tissue, using (alone or in combination) cells, matrix or bioactive factors. Their association gives rise to a hybrid biomaterial combining biological components (cells, growth factors or adhesion proteins) and materials (polymers, ceramics). The applications are wide-ranging, from the skin, to the liver, or to the cornea as well as to the locomotor system. Bone tissue engineering has advanced the most in this field, partly because of the progress made by research into bone substitutes, although cartilage and tendons are also concerned. This technology requires cell culture (committed cells or more often bone marrow stem cells), biomaterials (porous materials with controlled architecture and cements), growth factors (such as 'Bone Morphogenetic Proteins'), the proteins implicated in cell adhesion (such as fibronectin or the aminoacid sequences specifically recognised by integrin subunits) or gene therapy (notably using transfected stem cells). Tissue engineering and regenerative stimulation of tissue are now booming on experimental and industrial levels and clinical applications are increasingly numerous. Considering the potential of these technologies, they should continue to develop widely.

Volume effect on biological properties of a calcium phosphate hydraulic cement: experimental study in sheep.

Injectable calcium phosphate hydraulic cements (CPHC) are a new family of bone substitutes within the class of bone reconstruction biomaterials. In this work, CPHC were tested in two consistencies (preset blocks or liquid paste) in an experimental model of cancellous bone defect in sheep. The defects were eight times larger than those investigated previously in rabbits. Three delays (12, 24, and 52 weeks) were used. Before death, a double label of oxytetracycline and alizarine was made intravenously. The distribution of implants was randomized, histomorphometric evaluation was performed and compared with micrographic observation, and optical microscopy of stained sections was performed either under visible, ultraviolet, or polarized light. The results were compared with spontaneous healing of empty defects and with a control group of normal cancellous bone from sheeps of the same age. No significant difference has been observed between premolded and injected implants. In the sheep model, the degradation and new bone formation rates are three times slower, compared with those observed previously in rabbits. New bone formation increased from 5.9% (12 weeks) up to 11.0% (24 weeks) in the empty defect group. In the cement groups, 28.3% new bone was obtained at 12 weeks, which seemed then to level off (27.8% new bone at 24 weeks). Cement residues appear as radio-opaque cylinders on microradiographs. In all cases, a radiolucent layer was observed at the cement/bone interface at 24 weeks. Stained sections showed the formation of a fibroconnective capsule around the residual cement, which presumably slows down new bone formation. Nevertheless, quantitative bone remodeling was accelerated in the cement group; mineral apposition as well as adjusted apposition rates were higher, and the formation period as well as the mineralization of osteoid tissue were faster compared with empty cavities and controls. These results point to higher osteoblast activity and better exchange with surrounding tissues in the defects filled with cement.

Association of porous hydroxyapatite and bone marrow cells for bone regeneration.

The preparation of hybrid material with osteoinductive capacity may be achieved by association of cultured autologous bone cells with a porous ceramic vehicle. We optimized culture conditions for rabbit marrow stromal stem cells (MSCs), notably by selection from batches of fetal calf serum. Rabbit MSCs formed colony-forming unit-ribroblastic (CFU-Fs) in vitro. Their alkaline phosphatase (ALP) activity was doubled in the presence of dexamethasone. Autologous rabbit serum allowed the formation of ALP-positive CFU-Fs, but results were highly variable depending on the rabbit. We tested the osteogenic potential of autologous cultured (with or without dexamethasone addition in the culture medium) and noncultured rabbit MSCs associated with a porous hydroxyapatite ceramic after a dorsal intramuscular implantation. Nucleated cells (10(7) or 10(8)/mL) were used for the preparation of autologous hybrid material. A significantly higher number of implants containing bone was obtained with a suspension of 10(7) cells/mL cultured in the presence of 10(-8) M dexamethasone. Some positive implants were also obtained with a suspension of 10(8) noncultured cells/mL. We demonstrated the feasibility of preparing rabbit autologous hybrid materials following a process for controlling culture conditions, cell characterization and cell/material association.

Raman microspectrometry studies of brushite cement: in vivo evolution in a sheep model.

Calcium phosphate hydraulic cements are promising synthetic bone grafting materials. Brushite-based cements were implanted for 6 and 12 months in the distal condyle of sheep femur, and their in vivo evolution was investigated by Raman microspectrometry. This new technique can probe small volumes in the cubic micrometer range. Its resolution allows a very fine analysis of crystalline changes in calcium phosphate mixtures at the microscopic level. First, Raman spectra of pure brushite, monetite, and beta-tricalcium phosphate (beta-TCP) were recorded, in order to set a data base for the basic components of brushite cements. These spectra show significant differences in the vibration mode v1 for the phosphate ion (988 and 878 cm(-1) for brushite, 988 and 900 cm(-1) for monetite, 968 and 948 cm(-1) for beta-TCP). These differences are strong enough as to allow the qualitative and quantitative analysis of these crystalline phases in the cement. Implanted sheep femur samples were harvested after 24 and 52 weeks post-op, and prepared for Raman analysis in the form of 1-mm-thick sections. Implants at 24 weeks show a core of residual cement isolated from the surrounding bone by fibroconnective tissue. No trace of brushite was detected by micro-Raman analysis in this area, but instead, a mixture of beta-TCP and Type-B carbonated apatite, the latter being very close in composition and structure to the mineral fraction of normal bone in the vicinity of the implant. Implants recovered after 52 weeks show a decrease of the bone/residual cement perimeter, whereas new trabeculations are formed in the implanted zone; the small amounts of residual cement still present are substantially transformed into Type-B carbonated apatite containing small amounts of proteins. In the same area, some beta-TCP particles are also detected showing that, contrary to brushite, the excess beta-TCP originally present in the cement is not completely metabolized. In the implanted zone already converted into trabecular bone, Raman microspectrometry shows the characteristic spectrum of normal bone.

Role of interconnections in porous bioceramics on bone recolonization in vitro and in vivo.

The interconnections in a porous biomaterial are the pathways between the pores. They conduct cells and vessels between pores. Thus they favour bone ingrowth inside ceramics. The aim of our study was to determine the effect on bone ingrowth of interconnections in two ceramics: hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) with the same porosity of about 50% and a mean pores size of 100-300 microm and a mean interconnection size of 30-100 microm. In vitro, four discs for osteoblast culture were studied after 14 and 28 days of incubation. The results show that human osteoblasts can penetrate interconnections over 20 microm in size, and colonize and proliferate inside macropores, but the most favourable size is over 40 microm. In vivo, eight cylinders were implanted in the middle shaft of both rabbit femurs for 12 or 24 weeks. The histomorphometric results show that interconnections in porous ceramics favour bone ingrowth inside the macropores. In the HA group the rate of calcification and bone ingrowth do not differ, and chondroid tissue is observed inside pores. But in beta-TCP, the calcification rate and the bone ingrowth increased significantly. At week 12 significant correlation between new bone ingrowth and the size of the interconnections is observed between new bone ingrowth and the density of pores. In conclusion we notice that in vivo a 20 microm interconnection size only allows cell penetration and chondroid tissue formation; however the size of the interconnections must be over 50 microm to favour new bone ingrowth inside the pores. We propose the concept of "interconnection density" which expresses the quantity of links between pores of porous materials. It assures cell proliferation and differentiation with blood circulation and extracellular liquid exchange. In resorbable materials, pore density and interconnection density are more important than their size, contrary to unresorbable materials in which the sizes and the densities are equally important.

Histological aspects in bone regeneration of an association with porous hydroxyapatite and bone marrow cells.

The osteogenic potential of an association of two kinds of hydroxyapatite (HA) porous ceramics with autologous bone marrow cells cultured with or without dexamethasone (10(-8)M) addition in the culture medium and non-cultured rabbit marrow stromal stem cells (MSCs) was tested after 4 weeks of implantation in the dorsal muscles of spine in rabbit. A significantly higher number of rabbits with implants containing bone tissue inside pores were obtained with 10(7) cells ml(-1) cultured treated with Dex. In the HA porous ceramic using naphtalen as porogen agent, the bone recolonization remains only at the periphery of implants and in the second row of pores, while in the HA porous ceramic using polymethacrylate (PMMA) microbeads as porogen agent, the bone recolonization is observed in the depth of implants. In the PMMA HA group, the Krüskal-Wallis variance analysis between the rabbits is significantly different with the percentage of number of occupied pores and occupied pores with bone tissue is different (p<0.05).

Comparative study of tissue reactions to calcium phosphate ceramics among cancellous, cortical, and medullar bone sites in rabbits.

In order to understand the influence of the implantation site on bone biomaterial evaluation, we implanted cylinders of HA and beta-TCP ceramics in the femoral diaphysis and condyle of rabbits. After 3, 8, 12, and 24 weeks of implantation, histological investigation and histomorphometry were performed on undecalcified samples. Our results show that spontaneous bone healing in the empty cavities is significantly different (p < 0.05) between cortical (SBH > 80%) and cancellous bone sites (SBH < 31%) and that no new bone is formed in marrow tissue. For both porous ceramics, the highest osteogenesis was obtained in the cortical site. Osteogenesis was intermediate in the cancellous site and weak in the medullar site. The material biodegradation was the strongest in the medullar site and higher in the cancellous site than in the cortical site. Both activities were better in the beta-TCP than in the HA (p > 0.05). The marrow tissue presents a foreign-body reaction more reliable, sensitive, and durable than other bone tissues. Therefore, the cancellous bone site is a good site for evaluation of the biofunctionality of biomaterials because of the equilibrium of the osteogenesis and the biodegradation activities, but marrow tissue seems to be better for testing material biocompatibility in vivo.

Intramural injection of biodegradable microspheres as a local drug-delivery system to inhibit neointimal thickening in a rabbit model of balloon angioplasty.

Restenosis remains the major limitation of coronary angioplasty. The objective of this study was to develop microspheres able to be delivered at the angioplasty site for long-term drug release and to test their effects in a model of balloon angioplasty. Polylactic-co-glycolide acid microspheres (5-10 microm in diameter) were prepared by using an oil-in-water emulsion-solvent evaporation method. In vitro experiments with hydrocortisone-loaded microspheres revealed a hydrocortisone release for 4 weeks. We studied the in vivo effect of injection of microspheres into the arterial wall of New Zealand White rabbits by using a perforated balloon. Deep penetration of microspheres in the arterial wall was documented immediately after angioplasty. Intimal hyperplasia was assessed in iliac arteries 4 weeks after angioplasty. The morphometric analysis was performed in four groups of animals; the first group was subjected only to conventional angioplasty (control, n = 10), whereas the other three groups after conventional angioplasty were received perforated balloon angioplasty with saline (n = 10), microspheres (n = 10), or hydrocortisone-loaded microspheres (n = 7). Intramural injection of saline did not induce greater intimal hyperplasia compared with control (0.17 +/- 0.03 vs. 0.18 +/- 0.03 mm2, respectively). Microspheres injection was associated with a trend toward a greater degree of intimal hyperplasia that did not reach statistical significance. Hydrocortisone-loaded microspheres were associated with a significant reduction in intimal hyperplasia compared with unloaded microspheres (0.16 +/- 0.02 vs. 0.26 +/- 0.03 mm2, respectively). The polylactic-co-glycolide acid microspheres are well tolerated, easily injected into the arterial wall, and the increase of intimal hyperplasia is easily inhibited by release of hydrocortisone for 4 weeks after initial injury.

Biomechanical characterization of a biodegradable calcium phosphate hydraulic cement: a comparison with porous biphasic calcium phosphate ceramics.

Biomechanical properties of a biodegradable calcium phosphate hydraulic cement (CPHC) were tested with rabbits. The cement was composed of beta-tricalcium phosphate (beta-TCP), monocalcium phosphate monohydrate (MCPM), and calcium sulfate hemihydrate (CSH), beta-TCP-MCPM-CSH cement. Cylinders of 4.7 mm in diameter and 10 mm in length were put into bone cavities created in the distal epiphysis of femurs in rabbits. Cylinders of the same size of porous biphasic calcium phosphate ceramics (BCPC, 75% hydroxyapatite and 25% beta-TCP) were implanted as references. Two, 4, 12, and 16 weeks after the operation, the rabbits were sacrificed. Histomorphometry showed that the cement was resorbed, leaving only 7.67 +/- 1.81% of bone cavity after 12 weeks. Newly formed bone occupied 34.59 +/- 4.00% of the cavity. Cylindrical bone-material composites were cut out with a small dental burr. Compressive force was applied to the specimens and compressive strength, elastic modulus, and toughness were calculated. The same tests were performed on cylinders of normal bone from the same site, which served as controls. The compressive strength and the toughness of the cement-bone composite were higher than those of normal bone and porous ceramics 12 weeks after the operation (p < 0.05). At 16 weeks the compressive strength and the toughness returned to the normal bone values. The elastic modulus of the porous ceramic-bone composite was higher than the normal bone at 4, 12, and 16 weeks after surgery (p < 0.05). We found that the beta-TCP-MCPM-CSH cement is replaced by new bone and that the cement-new bone composite has similar or better mechanical properties than normal bone within 16 weeks. This study suggests the usefulness of a particular cement for filling bone defects or for temporary fixation of orthopedic implants.

[Development of a model which makes it possible to test injectable bone substitutes and evaluation of a calcium phosphate cement]. / Développement d'un modèle permettant de tester des substituts osseux injectables et mise au point d'un ciment phosphocalcique de comblement.

New percutaneous filling techniques are beginning to be used in bone tumor pathology. The purpose of this study was to develop a reproducible model for testing new injectable bone substitutes. A closed cancellous bone defect was created in the distal femoral condyles of rabbit. Bone defect was filled by a percutaneous injection. Several situations were tested: spontaneous evolution of unfilled cavities, evolution of cavities filled either with a conventional orthopedic cement (PMMA), either with a mixed collagen-hydroxyapatite material, either with a biomaterial derived from the vegetal protein zein, either with a calcium phosphate cement brushite type. The new bone formation was quantified in the defect for each group in which several delays were tested. A bone defect of reproducible size was obtained consistently. A partial bone formation was observed in the unfilled group. The best bone formation rate was obtained in the phosphate cement group. This model showed the interest of injectable biomaterials and more precisely the interest of the phosphate calcium cements as brushite.

Experimental evaluation of a percutaneous injectable biomaterial used in radio-interventional bone-filling procedures.

Interventional radiology is beginning to be used in bone pathology. An injectable biomaterial Ethibloc*, composed of alcohol and a vegetal protein (zein), has been successfully used for percutaneous treatment of benign bone lesions. The reasons for this success remained unknown and needed to be understood. In this study, using a rabbit model, an evaluation was made of bone formation and tissue reaction during the first weeks after the injection of this biomaterial. Ethibloc* was injected percutaneously into bone defects in rabbit distal femurs. Three time intervals were studied: 2, 4 and 8 wks. The three control groups constituted unfilled, polymethylmethacrylate (PMMA), and alcohol. Undecalcified bone technique was used for a qualitative analysis and histomorphometric evaluation. A low bone formation was found which was less than in the control groups (PMMA and unfilled). The "Ethibloc group" was characterized by an early inflammatory reaction. Good clinical results obtained with Ethibloc* probably arose, after an initial vascular thrombosis, from a secondary bone reaction and spontaneous osteogenesis obtained after the disappearance of vascular or hyperpression reaction.

[Fatigue rupture of a Harris-Galante shell in contact with an autograft of the femur head. Analysis of bone, mechanical and metallurgical factors]. / Rupture en fatigue d'une cupule de Harris-Galante au contact d'une autogreffe de tête fémorale. Analyse des facteurs osseux, mécaniques, et métallurgiques.

We observed, after 38 months of follow-up, the rupture of the metallic shell of a Harris-Galante cup implanted in a dysplastic acetabulum augmented with a femoral head autograft. Bone ingrowth was extended to 53% of the porous surface, but only in the areas in contact with the true acetabulum. No bone ingrowth was identified in the fiber mesh in contact with the autograft. The graft was necrotic on histologic examination and showed collapse radiographically. These last conditions were responsible for shear stress in the part of the cup that was in contact with the graft-acetabulum junction. These stresses were involved in the fatigue rupture mechanism identified on microscopic examination of rupture surfaces. We observed metallic structure anomalies in the failed cup by comparing with another Harris-Galante cup considered as a reference: larger alpha elements, reduction of the titanium equiaxial structure. These defects could be related to uncontrolled temperature during the sintering process utilized for fiber mesh fixation. These structural anomalies, by reducing the metallic fatigue strength, potentiated the deleterious effect of partial bone ingrowth and graft collapse.

[Structural MRI study of the Achilles tendon. Correlation with microanatomy and histology]. / Etude structurale du tendon d'achille en IRM. Corrélation avec la microanatomie et l'histologie.

On T1 and T2 weighted MR Imaging, normal Achilles tendon is generally described as a homogeneous low signal structure. However, punctuate and/or short linear high signal foci are often seen, especially on the anterior part of axial sections. These images are not artifacts. The aim of this study was to correlate MR images of 20 normal Achilles tendons with micro-anatomic and histologic studies of 2 cadaver tendons. Intratendinous vessels were found in connective tissue septa called mesotenon. Foci of high signals result from this mesotenon. On T1 weighted images, a normal Achilles tendon can present high signal images without any disease process.

Resorption of, and bone formation from, new beta-tricalcium phosphate-monocalcium phosphate cements: an in vivo study.

Hard cylinders (4.7 x 10 mm) of two kinds of beta-tricalcium phosphate-monocalcium phosphate monohydrate-calcium sulfate hemihydrate (beta-TCP-MCPM-CSH) cements with and without beta-TCP granules (500-1000 microns) were implanted into holes drilled in rabbit femoral condyles for up to 16 weeks. Empty cavities were used as control. Cement resorption and new bone formation in the cylinders were evaluated with contact microradiography and quantified through an automatic image analysis system. At 4 weeks, both kinds of cement cylinders were surrounded by new bone. At 8 weeks, except for beta-TCP granules, both cement cylinders were almost completely resorbed and replaced by bone tissue. At 16 weeks the bone in the cavities of both cements recovered a trabecular pattern, but only the bone trabeculae in the initial cavity of the cement with beta-TCP granules became thick and mature. However, the cavities of the empty control were still empty and large. These results show that the beta-TCP-MCPM-CSH cements stimulate bone formation and are rapidly replaced by bone tissue. When added with nonresorbable beta-TCP granules, this cement maintains bone formation for a longer time.

Experimental model of posterolateral spinal arthrodesis in sheep. Part 1. Experimental procedures and results with autologous bone graft.

OBJECTIVES: The authors evaluated the reliability in obtaining a posterolateral spinal arthrodesis (PSA) with autologous bone graft. SUMMARY OF BACKGROUND DATA: Posterolateral spinal arthrodesis using autogenous cancellous bone graft is the most simple and efficient technique to get a spinal graft. No extensive biomechanical study of PSA is available. Thus, an experimental model of PSA is needed. METHODS: Eleven sheep underwent lumbar autologous bone grafts and Cotrel-Dubousset instrumentations, and four sheep were used as controls. Sacrifice and biomechanical evaluation of the lumbar spines were performed after 1 year. RESULTS: All grafts appeared continuous. A large decrease of flexibility (in rotation and in translation) was found in grafted spines in every direction. Failure in extension occurred at a mean value of 35.26 +/- 3.71 Nm. CONCLUSION: A constant and homogenous PSA appears to be obtained in sheep under conditions close to the human surgery.