Test results

Background
A comparison of different calcaneus plates with locked screws in an experimental calcaneus fracture model under biocompatible loading was intended.

Methods
Four plate models were tested:  three models with uniaxially locked screws (Synthes, Newdeal, Darco), and one model with polyaxially locked screws (90±15°) (Intercus).  Synthetic calcanei (Sawbones) were osteomized to create a fracture model and the plates were fixed onto them.  Seven specimens for each plate model were subjected to cyclic loading (preload 20 N, 1,000 cycles with 800 N, 0.75 mm/s), and load to failure (0.75 mm/s). Motion, forces, plastic plate deformation, and remaining depression of the posterior joint facet were analyzed.

Results
During cyclic loading, the plate with polyaxially locked screws showed statistically significant lower displacement in the primary loading direction than the plates with uniaxially locked screws [mean values (mm) of maximum displacement, during cyclic loading:  Intercus, 3.13±0.68; Synthes, 3.46±1.25; Darco, 4.48±3.17; Newdeal, 5.02±3.79; Oneway ANOVA, p<0.001).  No statistically significant differences were found in relation to loads to failure and correspondent displacement except remaining joint depression.

Conclusion
The tested plate with polyaxially locked screws (Rimbus/Intercus) provides higher stability during cyclic loading in an experimental setting than the plates with uniaxially locked screws (Newdeal, Darco, Synthes).