Locking plates in osteoporosis: a biomechanical cadaveric study of diaphyseal humerus fractures.

OBJECTIVE: To determine whether locking plates offer an advantage in fixation of fractures in osteoporotic humeral bone.
DESIGN: Biomechanical testing of 18 matched pairs of osteoporotic human cadaver humeri plated posteriorly with either all locked or all nonlocked screws. An established protocol was used to test the constructs with torque applied to a peak of ±10 Nm for 1000 cycles at 0.3 Hz or until failure. Eighteen pairs were tested for failure, 11 pairs were tested for cycles survived, and 10 pairs were tested for stiffness.
SETTING: University biomechanical laboratory. MAIN OUTCOME MEASUREMENTS: Percentage surviving testing, mean cycles survived, and stiffness.
RESULTS: We observed catastrophic failure of the constructs in 47% of the samples. Humeri plated with nonlocking plates failed at a higher rate than those with locking plates (67% nonlocking vs 28% locking, n = 18 pairs, P = 0.008). Locking constructs also outperformed nonlocking constructs in mean cycles survived (707 cycles locking, 345 cycles nonlocking, n = 11 pairs, P < 0.05) and stiffness at 10 cycles (0.853 Nm/degree locking vs 0.416 Nm/degree nonlocking, n = 10 pairs, P < 0.001).
CONCLUSIONS: Locking plates were shown to provide improved mechanical performance over nonlocking plates in torsional cyclic loading in a osteoporotic cadaveric fracture model. Our results confirm general conclusions of previous work that used a synthetic bone model of osteoporosis, but we found a high rate of catastrophic failure, questioning the validity of the previously published synthetic model of osteoporosis (overdrilling of synthetic bone) for this application.