The effect of screw thread length on initial stability of Schatzker type 1 tibial plateau fracture fixation: a biomechanical study

BACKGROUND: This study compares the cyclic loading properties and failure loads of two screw combinations on a synthetic Schatzker type 1 tibia fracture model. Our hypothesis was that after adequate compression with first a partially threaded screw, addition of a fully threaded screw would provide more stability than an addition of a second partially threaded screw. METHODS: The Schatzker type 1 tibial plateau fracture model was created. Fixation was obtained in group A (n = 10) with two partially threaded screws and in group B (n = 10) with one fully threaded screw and one partially threaded screw. Load-displacement evaluation was made at each 1000-cycle interval up to 10,000 cycles. Failure load was identified as the load creating a 2-mm displacement. Two-factor (groups and periods) repeated measurement analysis of variance and independent sample t tests were used. RESULTS: According to the two-factor repeated analysis, there was no significant difference for periods (p = 0.29) and time-period interaction (p = 0.59) (Wilk’s Lambda F value, 1.507 and 0.871, respectively). In the test of between-subject effects, there was no significant difference between groups in terms of cyclic loadings (p = 0.06, F = 4.065). However, in the t test for each 1000-cycle interval, the value of mean displacement in group B was significantly lower than that in group A in the initial, 1000-, 2000-, and 3000-cycle intervals (p = 0.023, 0.031, 0.025, 0.043, respectively). The mean displacement and standard deviations increased with the number of cycles. The mean range of displacement initially was 0.66 mm for group A and 0.36 mm for group B. The mean range of displacement after 10,000 cycles was 0.79 mm for group A and 0.44 mm for group B. The mean failure load value was 682 ± 234 N for group A and 835 ± 245 N for group B. In independent sample t tests, there were no significant differences between the two groups in terms of failure load (p > 0.05). CONCLUSIONS: Obtaining fixation with one partially and one fully threaded screw can minimize displacement at the fracture site at early cyclic loadings.