Micromotion at the fracture site after tibial nailing with four unreamed small-diameter nails--a biomechanical study...

Intramedullary nailing is the treatment of choice in tibia fractures allowing for closed fracture reduction and internal fixation. Small-diameter nails that preserve the endosteal blood supply act as load-sharing devices after proximal and distal locking. Despite fracture healing is influenced by movements at the fracture gap, no data are available reporting on the micromovements at the fracture site if small-diameter nails were used.

Using a Sawbone distal tibia fracture model, we assessed offset, elastic, plastic, permanent, and overall deformation at the fracture site for four small-diameter tibia nails (Expert, Synthes, Saluburg, Austria; Connex, ITS Spectromed, Lassnitzhöhe, Austria; Versanail, DePuy, Vienna, Austria; T2, Stryker, Vienna, Austria) after mechanical testing with a servohydraulic material testing machine. Cyclic loading was performed with a sinusoidal load of 700 N (+/-600) for 40,000 cycles representing 6 weeks of full weight bearing.

Offset deformation was significantly higher for the Connex nail when compared with other nails (p < 0.001). Regarding elastic deformation, no significant difference was recorded between the implants. Plastic deformation was significantly lower if the Connex nail was used (0.134 [+/-0.053] mm; p < 0.001). Elastic deformation did not exceed 0.7 mm and plastic deformation did not exceed 0.4 mm. Regarding permanent and overall deformation, no significant difference between the implants was recorded.

Considerable deformation at the fracture gap can be assumed even after partial weight bearing with 100 N. Despite comparable material properties, differences in axial micromotion were recorded among the nail types used in this series. The number of distal locking screws (three or four) did not substantially influence the axial movements at the fracture gap.