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

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.

PHB, crystalline and amorphous magnesium alloys: promising candidates for bioresorbable osteosynthesis implants?

In this study various biodegradable materials were tested for their suitability for use in osteosynthesis implants, in particular as elastically stable intramedullary nails for fracture treatment in paediatric orthopaedics. The materials investigated comprise polyhydroxybutyrate (PHB), which belongs to the polyester family and is produced by microorganisms, with additions of ZrO2 and a bone graft substitute; two crystalline magnesium alloys with significantly different degradation rates ZX50 (MgZnCa, fast) and WZ21 (MgYZnCa, slow); and MgZnCa bulk metallic glasses (BMG). Push-out tests were conducted after various implantation times in rat femur meta-diaphysis to evaluate the shear forces between the implant material and the bone. The most promising materials are WZ21 and BMG, which exhibit high shear forces and push-out energies. The degradation rate of ZX50 is too fast and thus the alloy does not maintain its mechanical stability long enough during the fracture-healing period. PHB exhibits insufficient mechanical properties: it degrades very slowly and the respective low shear forces and push-out energy levels are unsatisfactory.