Effect of distal interlocking of a cephalomedullary femoral nail on peri-implant fractures: A sawbone biomechanical analysis

Background: A large proportion of hip fractures involve inter-trochanteric fractures which are managed by cephalomedullary nails. There is ongoing debate about the advantages and disadvantages of locked versus unlocked long cephalomedullary femoral nails in the treatment of intertrochanteric fractures. The objectives of our study are to evaluate the biomechanical effects of a distal interlocking bolt on the type of peri-implant fractures in a healed intertrochanteric fracture with long cephalomedullary nail fixation.

Methods: 20 femoral sawbone specimens were prepared with the TFN-ADVANCED Proximal Femoral Nailing System (TFNA) and divided into 2 groups: locked and unlocked. The specimens were subjected to axial loading force until failure. Compressive forces, strain and fracture patterns were compared between the 2 groups.

Results: There was no significant difference in the mean load to failure of the unlocked specimens compared to locked specimens. However, there was significant difference in the mean compressive stress at the time of failure with the unlocked specimen (1.79±0.17 MPa) compared to the locked group (1.92±0.05 MPa) (p < 0.05). Video review analysis showed unlocked specimens consistently having basi-cervical type peri-implant fractures while locked specimens showed complex, compound fractures of the head-neck region with 2 or more fracture propagation points.

Conclusion: Distal-locked long cephalomedullary nails in a healed intertrochanteric fracture model are able to tolerate higher compressive stress at the point of failure but demonstrate more complex peri-implant fracture patterns in the femoral head-neck region as compared to unlocked specimens.