Experimental And Clinical MRI Study Of The Hydroxyapatite Orbital Implant Fibrovascularization

Objective To study the fibrovascular ingrowth progression of orbital hydroxyapatite implant in rabbits with MRI,and to assess its findings and characteristic of MRI.Methods Hydroxyapatite orbital implant into 12 New Zealand white rabbits, right orbits with the same surgery procedure,the orbital implants were implanted into-hole sclera shell.All rabbits after Hydroxyapatite placement who underwent MRI with plain and contrast enhancement at 1,2,3,4,5 and 6 weeks.The enhancement volume of HA orbital implant were measured,and the VE/VHA ratios were analyzed statistically by SPSS 10.0 using q test. At 2,4 weeks,2 implant were extracted and examined histopathologically.At 6 weeks,the others too.Result Of 9 rabbits, experiment were completed,because of 2 had present,of 1 had postoperative infection.MRI findings was difderent after HA insertion. MR images obtained 1 weeks after HA insertion ,1 had enhancement limited to the implant rim,8 had no enhancement. Of 9 rabbits undergoing MRI 2 weeks after HA placement, all rabbits had peripheral foci of enhancement. 3 weeks after HA placement,imllants had small noenhancement. 4 weeks after HA placement, 1 had not enhancement in all rabbits.. 5,6 weeks after HA placement,all rabbits had enhancement in full of all implants.The average VE/VHA ratios of the HA orbital implants added up weekly during the frist 4 weeks after HA placemen,the results were statistically differdent(F = 240.654,P = 0).While the average VE/VHA ratios of week 5 and week 6 were not higher than that of the week 4, the results had no statistically differdent(F = 0.686,P = 0.520).Implants fibrovascular tissue invade the pores of the HA orbital implant after 2 weeks,almost all implants were fully vascularized after 4 weeks and 6 weeks.Histtopathologic observation proved: The fibrovascular ingrowth progression was 2～3mm into implant at the 2th week,its was collagen fibers/blood capillary/collagenblastan and inflammatory cell. Implants had vascularization at the 4th week and 6th week. Conclusion MRI is a sensitive modality for assessing the process of vascularization in ocular HA implants. Hydroxyapatite orbital implant into rabbit,s orbits had vascularization after 4 weeks.AbstractⅡObjective To investigate the characteristic of MRI in hydroxyapatite(HA) orbital implants and explore the relation between the image and the vascularization at varying time intervals after implantation.Methods 28 patients who underwent an MR imaging study 1 to 14 months after HA orbital implant placemen were retrospectively.All patients undergoing gadolinium-DTPA T1-weighted MR imaging,and the enhancement degree of HA orbital implant were divlaed GradeⅠ～Ⅴ. The enhancement volume of HA orbital implant were measured,and the VE/VHA ratios were analyzed statistically by SPSS 10.0 using q test.Results MR images obtained 1 months after HA insertion in all 4 patients had enhancement limited to the implant rim (Grade I or less). Of 5 patients undergoing MRI 2 months after HA placement, 4 had peripheral foci of enhancement (Grade II), 1 had foci of enhancement extending to the center of the implant (Grade III). 3 months after HA placement, 5 patients had Grade III,.. 4 months after HA placement of the 7 patients, 4 had Grade III,3 had homogeneous enhancement throughout the implant (IV or V). From 5-14 months after surgery,2 had Grade IV,4 had Grade III. The average VE/VHA ratios of all groups:0.3648, 0.6265,0.9796, 1.00, 1.00.The Groups 1～3 were statistically differdent(F = 23.890,P = 0).Groups 3～5 were no statistically differdent(F = 0.686,P = 0.520)。Implants had vascularization after 3～4 months.Conclusion This study demonstrated consistent central HA orbital implant enhancement on MR imaging in the 3～4 months postoperative group.MRI is a sensitive modality for assessing the process of vascularization in ocular HA implants. The results of our study support the principle of performing orbital implant drilling and peg placement at least 5 to 6 months after HA implant insertion and may obviate MR imaging in some patients before implant drilling.