Can locking screws allow smaller, low-profile plates to achieve comparable stability to larger, standard plates?

The open reduction and internal fixation of radial shaft fractures and osteotomies with standard 3.5-mm plates can be complicated by tendon irritation, hardware prominence, and fracture through the screw holes. With the advent of locking plate technology, implant companies and some surgeons have recommended expanding the indications for these devices; for example, using smaller, low-profile locking plates to suffice where a standard, larger plate would traditionally be used. We analyzed whether there is merit to this strategy. We hypothesized that, in an established cadaveric fracture fixation model, a smaller, low-profile plate with multiple locking screws could maintain adequate fixation stiffness with the potential to minimize hardware-related complications.

Seven matched pairs of fresh-frozen cadaver radii were used. A 5-mm osteotomy gap was created at the midpoint of each specimen and the simulated fracture in one radius from each pair was fixed with a 3.5-mm plate and six nonlocking, standard screws. The contralateral radius was fixed using an equivalent-length 2.7-mm plate with eight locking screws. The radii were subjected to controlled bending and torsional loads and the bending and torsional stiffnesses were documented. Cyclic dorsal-to-volar bending was then applied and resistance to fatigue bending assessed.

The 2.7-mm locking plate was approximately one third as stiff as the 3.5-mm nonlocking plate (P < 0.02). Under physiological loading conditions, the 3.5-mm plate was superior to the 2.7-mm plate with respect to bending stiffness in all four directions, torsional stiffness in both directions, osteotomy gapping, and osteotomy angulation (P < 0.02 for all tests). The performance gap did not narrow with cyclic testing.

The theoretical structural benefit from the locking screws did not make up for the smaller size of the 2.7-mm plate. This held true in all bending planes, torsion, and cyclic loading, and outweighed any biologic differences between the specimens, including the presence or absence of osteoporosis. This is the first study to rigorously compare these two constructs and we conclude that the mechanical properties of the standard 3.5-mm plate are superior to the locking 2.7-mm plate in all regimes tested.