Experimental Study On The Treatment Of Osteonecrosis Of The Femoral Head In Canine With Hydroxyapatite-coated Porous Titanium Implants

Objectives:1. To investigate the feasibility of usinghydroxyapatite-coated porous titanium implants to construct orthopedicmaterials.2. To compare the effects of using core decompression combined withhydroxyapatite-coated porous titanium rods and the head-neck junctiondecompression combined with hydroxyapatite-coated porous titanium screw inthe treatment of osteonecrosis of the femoral head.Methods: Twenty-two healthy adult beagle dogs were used in the experiment.Four dogs were randomly selected as normal control group (group E,4dogs,8femoral heads), and the rest18dogs were selected to creat ONFH animalmodels by using liquid nitrogen freezen method. At6th week after liquidnitrogen frozan,2dogs were randomly selected to test animal model and theremaining16dogs were randomly divided into4groups: the coredecompression combined with hydroxyapatite-coated porous titanium rodstreatment group(group A,4dogs,8femoral heads), the head-neck junctiondecompression combined with hydroxyapatite-coated porous titanium screwtreatment group(group B,4dogs,8femoral heads), the core decompressiongroup(group C,4dogs,8femoral heads), the necrosis control group(group D, 4dogs,8femoral heads). The dogs in Group A were planted withhydroxyapatite-coated porous titanium rods after core decompression, the dogsin Group B were planted with hydroxyapatite-coated porous titanium screwafter head-neck junction decompression, the dogs in group C were treated withcore decompression, the dogs in group D were treated with sham surgery andwere used to get primary information of ONFH, the dogs in group E weretreated with sham surgery and were used to get normal information of femoralhead.At6th and12th week after treatment, all groups were subjected toradiograph respectively, and were sacrificed respectively to take biomachanicsexamination and histology examination. Factorial design ANOVA was used tocompare the compressive strength in different times and in different groups, ttest method was used for pairwise comparison, LSD method was used formultiple comparison, so as to distinguish whether statistically significantdifference exists or not. Statistical significance exists when P＜0.05.Results:1. Imaging resultsAt6th week after establishment of osteonecrosis of the femoral headmodel via liquid nitrogen frozen, DR and CT showed the uneven density of thefemoral head, sclerosis, and low-density cystic shadow, but no collapse of thefemoral head.At6th week after treatment, DR and CT showed normal shape of the femoral head existed, uniform density of the femoral head was formed,sclerosis and cystic low density of the femoral head were disappeared in groupA and group B. At12th week after treatment, CT showed there was no collapseof the femoral head, porous titanium combined with the surrounding bonetissue, no loose and prolapse existed in group A and group B.At6th week after treatment, DR and CT showed normal shape of thefemoral head were formed, sclerosis and cystic low density of the femoralhead were disappeared in group C. DR showed low-density image caused bycore decompression channel in group C. At12th week after treatment, it ishard to distinguish the whole core decompression channel in DR in group C.CT showed low-density image caused by core decompression channel from6th to12th week in group C.At6th week after treatment, DR showed higher density, cystic lowdensity, sclerosis, and mild collapse of the femoral head in group D. At12thweek after treatment, DR showed Severe deform, missing, obviousmanifestations of osteoarthritis in group D. CT showed collapse, missing ofthe femoral head from6th to12th week in group D.2. appearances on the wholeAfter6weeks of modeling, the femoral heads were mildly deformed,cartilages lost their luster, surfaces became rough and were scattered withmacula, the majority of cartilages dropped in each group.At6th and12th week after treatment, the appearances of the femoral heads ruled, the cartilages were smooth, the colors were bright and transparent ingroup A, B and C.At6th week after treatment, the shapes of the femoral heads wereirregular and flat, part of the femoral heads were missing, the cartilages haddark yellow color and poor transparency, the collapse of the femoral headsstripped, cartilages dropped in group D. At12th week after treatment, most ofthe femoral heads were missing, left no cartilage in group D.3. The results of biomechanicsAt6th and12th week after treatment, compressive strength of the femoralheads improved in group A, B and C when comparing with that of group D,there was significant difference (P＜0.05). As time goes on the compressivestrength of the femoral heads gradually enhanced, but still not as good asGroup E (P＜0.05). The compressive strengths of different group lined inorder from lower to higher was of group D, group C, group A, group B andgroup E. The compressive strengths of the femoral heads of both group A andgroup B were significantly higher than that of group C, there was significantdifference (P＜0.05). But there was no significant difference between group Aand group B (P＞0.05). Compressive strengths of the femoral heads of6th and12th week after treatment had a significant difference (P＜0.05), as time goeson the compressive strength of the femoral heads gradually declined in groupD.4. The results of histology After6weeks of modeling, cartilages fractured and lost, trabecular boneswere thin, were partially fractured and arranged disorderedly, there were lotsof empty bone pits in each group.At6th week after treatment in group A and group B, cartilages werecomplete, bone trabeculars arranged regularly. There were a large number ofbone cells. Inflammatory cells could be seen infiltrating through the poroustitanium and bone interface. There were no obvious formation of new bone. At12th week after treatment, cartilages did not dropped, bone trabecularsarranged regularly, new organizations formed at the porous titanium and boneinterface, which were full of small amount of new cells.At6th week after treatment in group C, cartilages were complete, bonetrabeculars arranged regularly, pulp core decompression channels filled withgranulation tissue and connective tissue. At12th week after treatment in groupC, pulp core decompression channel partially filled with fibrous connectivetissues and bone tissues, which were scattered in trabeculars and bone cells.There were some ossifications.At6th and12th week after treatment, cartilages were missing, bonetrabeculars arranged disorderedly, focal necrosis existed, There were someempty bone pits, bone cells in the pits disappeared.Conclusion:1. Material built by hydroxyapatite-coated porous titanium implants hasmedical feasibility. 2. The treatments of both core decompression combined withhydroxyapatite-coated porous titanium rods and the head-neck junctiondecompression combined with hydroxyapatite-coated porous titanium screw,can improve the mechanical properties of the femoral head and promoterestoration of the femoral head. Their effects are better than that of coredecompression in the treatment of osteonecrosis of the femoral head.