The effects of locked and unlocked neutralization plates on load bearing of fractures fixed with a lag screw.

Objectives: Because locked plates as a neutralization device for lag screw fracture fixation have different biomechanics than that of unlocked plates, we investigated how this would affect lag screw load at the fracture site. The purpose of this study was to assess the load at a fracture site compressed with a lag screw when both locked and unlocked plates are used as neutralization devices.

Materials And Methods: Nine cadaver femurs had a mid-shaft oblique fracture created and were fixed with a lag screw, incorporating load transducers at the fracture site and lag screw. Three neutralization plate constructs (a standard plate, a locked plate, and an offset locked plate) were sequentially applied and loaded. Loads at the fracture site and the lag screw were measured after sequential application of axial loads.

Results: Plate application to the lag screw fixations did not significantly change (P > 0.26) the load at the fracture site or on the lag screw that were approximately 200 N. The unlocked, locked, and offset locked plates behaved similarly. The addition of a load to the specimens did not change the lag screw loads but increased the average fracture loads by approximately 20% of the applied load.

Conclusions: Unlocked and locked neutralization plates do not affect the initial compressive load across a fracture fixed by a lag screw, and both behave similarly in transferring the load when the fracture was loaded. For a well-fixed stable fracture fixed with a lag screw, there is no advantage in using a more expensive locked plate over a standard plate for neutralization purposes if adequate screw purchase can be achieved.