Unlocked and locked elastic stable intramedullary nailing in an ovine tibia fracture model: A biomechanical study

• Elastic stable intramedullary nails in ovine tibiae were cyclically loaded.
• Interlocking systems enhance strongly the stability of ESIN.
• Stiffness of the bone-implant-compound decreases with number of cycles.
• Some systems are strong enough to force a penetration of the opposite bone end.

In the present study, four different systems of elastic stable intramedullary nails (unlocked, Ender stainless steel nails locked with 3-mm screws, titanium nails locked with end caps, titanium nails locked with plugs and 3-mm screws) were implanted in cadaveric ovine tibiae. Fractures were simulated by a transverse diaphyseal osteotomy. The specimens were subjected to simultaneous axial and torsional fatigue loading of 5000 and 1000 cycles, respectively. The unlocked systems failed at an axial load of 200 N peak amplitude. End caps systems withstood axial loads up to 800 N for 1000 cycles, and ender nails and plugs lasted up to 1000 N for 1000 cycles. All systems showed a decrease of axial stiffness with higher loads and endured cycles. Ender nails and nails locked with plugs failed by penetration of the distal epiphysis rather than by loosening of the interlocking system. Overall, the titanium nails locked with plugs and 3-mm screws exhibited superior test results.