Background: Interlocking nails are becoming a common alternative to plates used to stabilize the femur following corrective surgery for medial patellar luxation. Intraoperative manipulation of the femoral condyle can lead to loss of initial nail stability, increasing the risk of malalignment. The use of cancellous bone compaction, as opposed to traditional reaming, has the potential to improve the mechanical properties of the nail-bone construct. Objectives: To evaluate the effect of compaction on the microstructure and mechanical properties of the bone/nail interface in a simulated femoral condylar bone model. Methods: Foam models of different densities (7.5, 10, 12.5, 15, and 20 PCF, n=5/group) were prepared using either standard line-to-line reaming (7 mm) or sequential compaction using custom mandrels of increasing diameters from 4 mm to 7 mm. Five samples from each group were tested in mediolateral bending. Impaction stiffness was assessed for each mandrel size and I-Loc nail in compacted foams (n=4/group). Three specimens per group were evaluated by micro-computed tomography (micro-CT) to define the effects of compaction on foam microstructure. Results: Compaction increased both construct bending stiffness, as well as load at 5 mm displacement across all tested foam densities (p<0.0001). Impaction test showed increasing stiffness and load at 32 mm from 4 mm mandrel to 7 mm mandrel, with the I-Loc nail performing similarly to the 6 mm mandrel. Micro-CT scan results demonstrated that higher density foams (10 PCF and above) exhibited more pronounced differences between drilled and compacted samples. Compaction effects on microstructure were quantified, showing increased local density and altered pore morphology in compacted regions. Conclusion: Compared to conventional reaming, cancellous bone compaction significantly increases the immediate stability of the bone/nail interface in a distal femoral osteotomy model.
Read
