A biomechanical comparison of Schuhli nuts or cement augmented screws for plating of humeral fractures

Schuhli locking nuts can be used in poor quality cortical bone to enhance f ixation stability as an alternative to cement augmented screws. This study compared the fixation strength and stability of plate constructs using Schu hli locking nuts with standard screws and cement augmented screws for fixat ion of simulated humeral shaft fractures in a test model with osteoporosis, The constructs were tested in axial compression, 4-point bending, and tors ion to determine fixation stability. The humeri were cycled in torsion (4.5 Nm) for 1000 cycles to simulate upper extremity use during the early posto perative period and retested for stability. The Schuhli locking nuts and ce ment augmented screws had significantly greater fixation stability than the standard screws before (range, 6-14 times greater) and after cycling in to rsional loading (range, 3-3.6 times greater). Although cement augmented scr ews and Schuhli augmentation showed increased fixation stability compared w ith the standard screws in axial and 4-point bending before cycling (range, 1.3-1.4 times greater), this was not significant. Compared with Schuhli fi xation, cement augmented screws showed no significant difference in fixatio n stability in all loading modes before and after cycling. Schuhli locking nuts offer the stability of cement augmentation while avoiding its potentia l adverse effects on fracture healing with extravasation and thermal necros is.