Evaluation of scintigraphy to assess incorporation of intercalary cortical bone grafts in sheep
ABSTRACT To evaluate scintigraphy, radiography, and histomorphometric analysis for assessing incorporation of intercalary bone grafts and to compare incorporation of cortical autografts and allografts by the recipient.
12 skeletally mature sheep.
A 5-cm tibial defect was filled with a cortical allograft (n = 6) or autograft (6) and stabilized with an interlocking nail. Radiography, scintigraphy, and fluorochrome bone labeling were performed every 3 months for 24 months. Radiographic evaluation included grading of the host and graft union and assessment of implants and grafts. Technetium-99m-hydroxymethylene diphosphonate radionuclide uptake was measured. Sheep were euthanatized 24 months after surgery, and bone formation was evaluated via histomorphometric analysis of fluorochrome labeling.
Complete union was detected on radiographs by 21 months in all sheep but developed earlier in sheep that received an autograft versus in those that received an allograft. Radionuclide uptake peaked at 3 months and returned to presurgical values at 12 months. Histomorphometric analysis revealed fluorochrome labeling corresponding to each time point, with most bone formation at 9 through 15 months. Scintigraphy findings did not correlate well with fluorochrome labeling of newly formed bone.
Although bone production around cortical bone grafts was detected by use of scintigraphy, this method did not provide accurate assessment of graft incorporation in sheep. Furthermore, bone produced by activated periosteum could not be distinguished scintgraphically from bone that replaced the graft. Intercalary autografts healed more rapidly and had greater incorporation into the host bone, compared with findings for allografts.
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ABSTRACT: We assessed healing of a 3.5 cm autograft transport segment, denuded of periosteum, and docked to the healthy distal femur with an intramedullary nail. We hypothesized that healing relates to proximity to the healthy distal femur and to mechanical loading patterns. Total bone area, area of new bone apposition, and quality of new bone formed in the 2 weeks after surgery, and area and degree of perfusion 16 weeks after surgery were measured as a function of proximity and loading patterns (as defined by the major and minor centroidal axes, CA). At 16 weeks, no significant differences in early bone apposition or perfusion were observed as a function of distance from the healthy distal femur. Qualitatively, bone was well perfused, both vascularly and pericellularly, and highly remodeled. When cross-sections were pooled from distal to proximal through the docking zone and normalized for total bone area, significant differences in the amount of early proliferative woven bone were related to loading patterns. In contrast, no differences in normalized perfusion area were attributable to loading patterns. Furthermore, early bone apposition and perfusion decreased with increasing radial distance from the bone surface toward the intramedullary nail. Finally, no differences were observed in areas of resorption within the docking zone compared to baseline levels measured in the control (in bone removed to create the defect zone at the time of surgery). Interestingly, infilling of resorption spaces within docking zone specimens related significantly to predominant loading patterns, where areas within the major CA exhibited significantly more infilling.Journal of Orthopaedic Research 12/2010; 28(12):1657-64. DOI:10.1002/jor.21190 · 2.99 Impact Factor