Compaction Effect on Different Densities of Cancellous Bone and Immediate Stability of an Angle Stable Interlocking Nail in a Distal Femoral Osteotomy Model

Introduction: Interlocking nails are commonly used in distal femoral varus correction associated with medial patellar luxation. Intraoperative femoral condyle manipulation may weaken the nail/bone interface, jeopardize initial nail stability prior to locking and increase the risk of malalignment. Bone compaction, as opposed to traditional reaming, potentially improves the nail/bone interface mechanical properties. Our aim was to evaluate the effect of compaction on the mechanical properties of the bone/nail interface in a femoral condylar bone model.

Materials and Methods: Foam models of different densities (7.5, 10, 15, and 20 PCF, n = 5/group) were prepared using either standard line-to-line reaming (7 mm) or sequential compaction with custom 4 to 7-diameter mandrels. Five samples per group were tested in mediolateral bending. Impaction stiffness was assessed for each mandrel size and a 7 mm I-Loc nail in compacted foams. Three specimens were evaluated by micro-CT to define the effects of compaction on foam microstructure.

Results: Compaction increased initial construct stiffness and load across all tested foam densities (p < 0.0001). Impaction showed increasing nail/foam interface bending stiffness from 4 to 7 mm mandrel with the 7 mm I-Loc nail performing similarly to the 6 mm mandrel. Micro-CT scans demonstrated that higher-density foams (15 and 20 PCF) exhibited more pronounced differences between drilled and compacted samples. Compaction effects on microstructure showed increased local density and altered pore morphology in compacted regions.

Discussion/Conclusion: In a distal femoral osteotomy model, cancellous bone compaction significantly increases the immediate stability of the bone/nail interface regardless of bone density, which may prove beneficial in juvenile bone.

Acknowledgment

L.M.D. is an inventor of an I-Loc Angle Stable Interlocking Nail, US Patent #8,435,238 B2, he receives royalties from Michigan State University and teaching honorarium: BioMedtrix/Movora I-Loc program. This study was funded by the Michigan State University Endowed Research Fund.

Publication History

Article published online:
15 July 2025