Morphological micro-computed tomography assessment of cleaned freeze-dried compacted cancellous bone allografts

Bone grafting is widely used in reconstructive surgery, with allogeneic grafts serving as an important alternative to autologous bone. The influence of compaction on the microarchitecture of cleaned cancellous bone allografts remains insufficiently understood. This study investigated the effects of different compaction levels on cleaned cancellous bone chips using micro-computed tomography (micro-CT), with particular focus on structural parameters relevant to graft architecture. Cancellous bone from 15 femoral heads was processed into bone chips, chemically cleaned, and compacted to three density levels (low: 0.15 g/cm³, medium: 0.26 g/cm³, high: 0.41 g/cm³). A structural allograft served as a reference. Microarchitectural parameters, including bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), connectivity density (Conn.D), structure model index (SMI), and degree of anisotropy (DA), were analyzed. Increasing compaction led to a significant increase in BV/TV (7.0% to 13.6%), Tb.N, and Conn.D, along with a marked reduction in Tb.Sp (1.97 mm to 0.85 mm; p < 0.001). At high compaction, BV/TV, Tb.N, and Tb.Sp approached the values of the structural allograft reference. However, Tb.Th decreased slightly, and SMI remained consistently high (approximately 2.4), indicating a predominantly rod-like architecture. Compared with the reference, morselized grafts showed lower anisotropy and connectivity. In conclusion, compaction significantly altered graft microarchitecture, increasing density and connectivity while reducing pore size. At high compaction, selected parameters approached those of the structural allograft reference, although differences in Tb.Th, Conn.D, SMI, and DA remained. Even at high compaction, comparatively large pore sizes were maintained, but the biological implications of this finding cannot be determined from micro-CT data alone. These findings highlight the need to balance structural densification with preservation of microarchitectural features potentially relevant for graft incorporation.