Mechanical comparison of application of locking intramedullary nail to locking compression plate in the ovine metatarsus

BACKGROUND: The metatarsal bone is commonly utilized in preclinical fracture models in sheep. A majority of studies achieve fracture stabilization with bone plating, but more recently intramedullary interlocking nails (IMN) have been utilized. The mechanical properties of this unique surgical technique utilizing an IMN has not yet been fully elucidated or compared to the traditional locking compression plating (LCP) technique. We hypothesize that a mid-diaphysis metatarsal critical-sized osteotomy stabilized with an IMN will provide equivalent mechanical stability to LCP with less variance of mechanical properties across specimens. METHODS: Sixteen ovine hind limbs were transected at the mid tibia with soft tissue intact and utilized for implantation. A 3-cm osteotomy was created in the mid-diaphysis of all metatarsi. For the IMN group, a 147 mm × 8 mm IMN was implanted from distal to proximal through the sagittal septum of the distal metatarsus and the bolts locked in place using an IMN guide system. For the LCP group, a 3.5-mm 9-hole LCP was secured to the lateral aspect of the metatarsus with three locking screws in the proximal and distal holes leaving the central three holes empty. All metatarsal constructs were fitted with three strain gages on proximal and distal metaphyses and the lateral aspect of the IMN or LCP at the osteotomy site. Non-destructive mechanical testing was performed in compression, torsion, and four-point bending. RESULTS: The IMN constructs showed overall greater construct stiffness with less variance in strain between constructs than the LCP constructs in 4-point bending, compression, and torsion. CONCLUSIONS: IMN constructs may provide superior mechanical properties for a critical-sized osteotomy model of the ovine metatarsus when compared to lateral LCP constructs. Further in vivo investigation comparing characteristics of fracture healing between IMN and LCP is warranted.