Dolph Houben

127 Transplant chimerism in bone VCA 6 RNA analyses From the same pulverized bone samples, RNA was extracted as described above and RT-qPCR was performed to assess gender-specific RNAs. We observed that male RNA is still expressed indicating that at least some allogeneic cells remain viable in both groups, with no significant difference between the groups (Fig. 9). Figure 9: RT-qPCR analyses of RNA extracted from pulverized bone transplant samples. both groups show relative expression of SRY. No significant difference was found between the groups. RPL-4 was used as a housekeeper. Mean relative expression of SRY in the AV+ group:1.0x10 -2 (SD 2.0x10 -2 ), AV- group: 1.0x10 -4 (SD 2.0x10 -4 ), Male control: 2.0x10 - 2 (SD 8.0x10 -3 ), H2O control samples were not detected with qPCR. Discussion Reconstruction of large segmental bone defects remains a difficult clinical problem. Current treatment options include cryo-preserved bone allografts and vascularized bone autografts. Allograft segments are readily available and selected to match defect size and shape. With internal fixation, they provide desirable immediate stability. They remain largely necrotic over time and are therefore susceptible to infection, non-union and late stress fracture [18, 19] . Vascularized bone autografts for large defects are largely limited to the fibula and iliac crest free flaps. They remain viable due to the microsurgical repair of their blood supply. Healing is more assured and rapid than nonviable banked allograft bone. Resistance to infection and the ability to hypertrophy are other desirable qualities. [20, 21] . Donor site morbidity can be significant. The shape of the transferred fibula or iliac crest seldom closely matches the defect morphology. This reduces initial stability, with the risk of early stress-fracture and loss of fixation [22, 23] .