The Treatment Effect Of Porous Titanium Alloy Rod On The Early Stage Of Talar Osteonecrosis

BackgroundONT (Osteonecrosis of the Talus) is a kind of chronic disease which is able to resultin severe ache and disablity of the ankle joint. The treatment of ONT is still controversialat present.The main aetiological agent of ONT comes from traumatic damage of the anklejoint, and other causes are relatively less, such as some systemic disease, corticalhormone, and insobriety and so on. To treat the traumatic ONT, reduction and internalfixation are always used for those cases preserved proper blood supply; nevertheless,arthrodesis is the first choice for those cases with severe fracture of the bone and poorblood supply. However, as far as the atraumatic ONT is concerned, there exist manypuzzles in surgical treatment because of the evolution of the disease is subtle andnecrobiotic. Such as when and how to operate are both difficulties which perplex thesurgeons. Presently, there are several surgical methods including simple and complicatedways in treating ONT, and the clinical experiences suggest that complicated ways are farfrom the idea methods for the curative effects are sometimes abjective. Therefore, toexplore a simple and effective operative approach is very necessary and positive in clinic.Among the diseases of osteonecrosis, ONFH (Osteonecrosis of the Femoral Head)and ONT are especially dangerous for they always lead to functional incapacitation of ankles. However, the present researches mainly focus on the ONFH nowadays. Theresearches on ONT are really superficial particularly in the field of novel implants. Thetrabecular metal (porous tantalum) has been applied in clinic for treating the ONFH sincethe year of2000. This kind of implant possesses well function of internal support andcore decompression for its tantalum metal and porous structure. Our research group havestudied this kind of porous metal and found that it had some advantages such as lowmodulus of elasticity, high friction factor and capability to stimulate the bone repair. Butit was not perfect as an implant to treat the osteonecrosis. The main problem is that thebioactivity was poor, the pore size was too tiny and dense, the process was difficult, veryexpensive and the clinical results were not very well. Moreover, there exist greatdifference between femoral head and talus as far as the biomechanics is concerned. So,on considering these backgrounds, to treat the ONT by designing a novel porous titaniumalloy may bring a surprise result, because the titanium alloy possesses excellentbiocompatibility and easy to molding. To this day, there are none of the reports have evermentioned this treatment.ObjectiveTo establish the first animal model of ONT through experiments in vivo, andimplant a newly designed porous titanium alloy rod to treat the early-stage ONT based onthis animal model and the curative effect will be tested and verified by comparing to thetreatment of core decompression. To explore the concise and valid operative approach byimplant this kind of porous titanium alloy rod into the human cadaveric talus.Methods1. Animal model of ONT: After number the animals randomly; they were dividedinto4groups evenly. The right tali of the sheep were used as experimental group toinduce the osteonecrosis and the untreated left tali were treated as control group. Allsamples were harvested2,4,12and24weeks after operation. The ONT was induced byintraosseous injection of pure ethanol, and the surgical site was located in the central ofthe medial talar heads. The assessment methods included macro observation, lateral filmof the X-ray, CT scan, and histological examination and so on.2. The preparation of the porous titanium alloy rods: Firstly, design the threedimensional model of the rod by CAD and input the data into EBM S12system; Secondly, the Ti6Al4V powder are melt layer-by-layer in the machine according to theCAD model and the sample of the rod prepared; Last, blow away the residual powderwith high pressure draft and disinfect the rod.3. To treat the ONT by implanting the porous titanium alloy rods into the tali ofsheep in vivo: The animals were evenly divided into experimental and control groupsrandomly. A month after animal model of ONT were induced and the osteonecrosis wereconfirmed by X-ray and CT scan, the porous titanium alloy rods of the experimentalgroup were implanted into the tali, and the curative effect was compared to the controlgroup which treated by core decompression. The samples were harvested one and threemonths after intervention. The assessment methods included macro observation, theX-ray, CT scan, Micro-CT, histological examination and so on.4. The exploration of operative approach by implanting the porous titanium alloyrods into the human cadaveric tali: Implanting the porous titanium alloy rods into thehuman cadaveric tali by minimally invasive surgery, and to observe the location byanterioposterior and lateral film of X-ray postoperatively. The BMD and thebiomechanical compression strength of the talus were detected.Results1. Animal model of ONT: All of the animals recovered to normal physicalconditions two weeks postoperatively. A case of superficial infection occurred andrecovered two weeks later after careful debridement. No other complications occurredduring the whole experimentation.1) Macro observation： The samples of early-stage (2weeks and4weekspostoperatively) kept normal contour. However, the cartilage degeneration and colobomaof small area on the talar surface appeared12weeks after the surgery, and thisphenomenon get worse at the time of24weeks postoperatively. The section view of thenecrotic parts showed that parts of the trabeculae inside the tali degenerated2weeks aftersurgery. After4weeks, lacunar defect of about4mm×4mm×3mm formed in most talarheads. By the end of week12, the lacunar defect slightly decreased but there were somesoft tissue proliferated around the defect. Until the end of week24, the comprehensive necrotic defect had formed inside all of the samples.2) Image examination: The lateral film of X-ray showed a small scale of lowdensity image inside the talar heads after2weeks of the animal model were induced. Thelow density image extended and the image of trabeculae ruptured after4weekspostoperatively. The low density image enlarged obviously by the end of week12, alsodegeneration and cartilage damage appeared on the talar heads by the end of week24.The three-dimensional reconstruction of the CT data showed the visualized sections andthe quantitative analysis suggested that the necrosis of the talar heads progressed withtime.3) Histological examination: Many lacunas appeared inside the trabeculae of thenecrotic parts after2weeks of the animal model were induced. The quantity of thelacunas increased obviously and the living osteocytes remarkably decreased inside thetrabeculae after4weeks. By the end of week12, there were still huge number of lacunasexisted but a small scale of new bone and fibrosis proliferated around the trabeculae. Bythe end of week24, the quantity of the trabeculae obviously decreased and a great deal offibrosis infiltrated into the talar heads. The statistic analysis showed that the percentageof the living trabeculae decrease progressively with time between every twoneighbouring group and mostly statistical significance, except for week4vs week12(p=0.051).2. The preparation of the porous titanium alloy rods: Two standard porous titaniumalloy rods were prepared. One was4mm in diameter and12mm in length, the other was8mm in diameter and20mm in length. Their porosity was about70%and the pore sizewas about1mm.3. To treat the ONT by implanting the porous titanium alloy rods into the tali ofsheep in vivo: All of the experiment sheep got a little lameness after surgery and thewound healed a week later. There were no complications such as infection, implants falloff and breakage or pathologic fracture appeared during the whole study.1) Macro observation：All talar samples showed ordinary appearance a month aftersurgical intervention. The samples which simply carried out surgery of core decompression appeared cartilage degeneration with defect about5mm×6mm on thepulley of the talar heads. Whereas, the samples which implanted with porous titaniumalloy rods still kept normal contour.2) Image examination: The lateral film of X-ray showed very clear low densityimage of the talar heads a month after core decompression, and the low density imagebecame thin but enlarged in scale2months later. For the samples implanted with poroustitanium alloy rods, the density of talar heads kept uniform at each time. The quantitativeanalysis of micro-CT scan suggested that the reconstructed trabeculae of the experimentgroup were obviously prior to the control group at each time point both in quantity andquality.3) Histological examination: The cavities of the defective parts were very clear amonth after core decompression. Two months later, the trabeculae inside the taligenerally became very loosen and the structure of the trabeculae presented very irregular,what’s more, a great deal of lacunas were found in the trabeculae. As far as the samplesof implanting the porous titanium alloy rods were concerned, there were also littlereconstructed trabeculae founded a month after implantation, but a large number oftrabeculae grew into the porous titanium alloy scaffolds3months after implantation andthe trabeculae were tightly combined with the scaffolds. The statistic analysis showedthat the percentage of the reconstructed trabeculae had no significance (P＞0.05) a monthafter intervention, however, the reconstructed trabeculae of experiment group were1.7times more than the control group3months after intervention and the difference wasstatistical significance (p<0.051).4. The exploration of operative approach by implanting the porous titanium alloyrods into the human cadaveric tali: By using the minimally invasive surgery, the poroustitanium alloy rods were implanted into the human cadaveric tali and the anterioposteriorand lateral film postoperatively showed that the location of the rods were fine. The dataof BMD and the biomechanical compressive strength of all samples suggested thatmaximum compressive strength was not seriously influenced by the surgery ofimplantation or core decompression if the tali were normal, and the maximum compressive strength was generally direct proportional to the BMD of the tali.Conclusion:1. It’s feasible to induce the animal model of ONT by intraosseous injecting thepure ethanol and this method could induce the animal model from early stage to laterstage. This animal model is able to imitate the natural pathophysiological progress ofhuman ONT to some extent and people could explore novel diagnosis and treatmentsbased on this animal model.2. Limited by the observation time point, it’s very regret that our study has not gotthe long-term data about the treatment effect of porous titanium alloy rods on theearly-stage of ONT, and this experimental is awaiting our research group to makearduous efforts. Whereas, the porous titanium alloy rods were absolutely effective to treatthe early-stage ONT in short time based on present studies, and this exploratory work haslaid the foundation for the porous titanium alloy implant treating osteonecrosis in clinic.3. By implanting the porous titanium alloy rod into the talus to treat the ONT ispracticable, and the operative approach was completely under minimally invasive surgerybased on core decompression. This is a very concise surgery and has a very broadprospect in clinic after the correlational research has completed.