QUANTITATIVE MEASUREMENT OF VASCULARIZATION AND VASCULAR INGROWTH RATE OF CORALLINE HYDROXYAPATITE OCULAR IMPLANT BY TC-99M MDP BONE IMAGING

Complete fibrovascular ingrowth of the hydroxyapatite ocular implant is necessary for peg drilling, the secondary procedure that couples the mobile sphere to the ocular prosthesis providing it with motility, This study was conducted to determine the usefulness of the bone scan for the evaluation and relative quantification of the vascularization of coralline hydroxyapatite ocular implants. In 23 patients (32 scans), vascularization of the ocular implant was measured by three-phase bone scintigraphy. There were 16 patients with left, and 7 with right orbital implants. At followup 0.5 to 8 months after successful hydroxyapatite implantation, the mean implant to normal intraorbital activity ratio on delayed bone scans in anterior view was 2.73 +/- 0.73 (mean +/- SD) with a range of 1.42-4.2. The normal right to left and left to right intraorbital bone activity ratios determined in anterior view from 10 normal delayed bone scans were 0.98 +/- 0.05 (mean +/- SD) and 1.02 +/- 0.05 (mean +/- SD) respectively, with a range of 0.93-1.07. The difference of the activity (count) ratios among the successfully implanted group and normals was statistically significant (P < 0.0001), A hydroxyapatite ocular implant to contralateral intraorbital bone activity ratio of greater than 1.12 with a homogeneous tracer distribution throughout the implant suggests adequate and diffuse vascularization is present. The progressive increase in activity ratio of the orbital implants seen in the early postimplantation period, which is indicative of the progression of vascularization, reaches a plateau after 1 month and remains relatively stable thereafter. The authors report that by using their surgical technique, the bone scan characteristics at 1-2 months were similar to those at 6 months suggesting that the vascularization of the ocular hydroxyapatite implant may well be complete as early as 1-2 months after the implant surgery.