Locking plate fixation with and without inferomedial screws for proximal humeral fractures: a biomechanical study.

PURPOSE. To compare the efficacy of locking plate fixation with and without inferomedial screws in maintaining the reduction of a proximal humeral fracture. METHODS. 22 synthetic humerus models were used. A standardised 3-part proximal humeral fracture with a 4-mm wedge segment was created and fixed with a locking plate and screws with (n=11) and without (n=11) inferomedial screws. The intrafragmentary motion of the construct at 250, 500, 750, and 1000 cycles of 532 N loading, and the load to failure of the 2 groups were compared. RESULTS. Locking plate fixation with inferomedial screws reduced the mean intrafragmentary motion in all cycles (p<0.01) and increased the load to failure (1452 N vs. 1159 N, p<0.001), compared to fixation without inferomedial screws. CONCLUSION. Additional inferomedial screws provide medial column support for fracture healing. This may reduce intrafragmentary motion and thus implant complications resulting from varus malalignment such as screw perforation or loss of reduction.