Biomechanical comparison of single versus double plate osteosynthesis in acromion type III fractures

One of complications of the reverse shoulder arthroplasty is acromion fractures, and its therapy is controversial. The aim of the study was to investigate the double-plate osteosynthesis for these fractures.

An acromion type III fracture according to classification of Levy was simulated in 16 human shoulder cadavers, and the specimens were randomly divided into two groups. Single-plate osteosynthesis was performed in the first group (locking compression plate) and double-plate osteosynthesis (locking compression plate and one-third tubular locking plate) in the second group. Biomechanical testing included cycling load and load at failure on a material testing machine. During the test, the translation was measured using an optical tracking system.

The load at failure for the single-plate osteosynthesis was 167 N and for the double-osteosynthesis 233.7 N (P = 0.328). The average translation was 11.1 mm for the single-plate osteosynthesis and 16.4 mm for the double-plate osteosynthesis (P = 0.753). The resulting stiffness resulted in 74.7 N/mm for the single-plate osteosynthesis and 327.9 N/mm for the double-plate osteosynthesis (P = 0.141).

Results of the biomechanical study showed that double-plate osteosynthesis had biomechanical properties similar to those of single-plate osteosynthesis for an acromion type III fracture at time point zero. The missing advantages of double-plate osteosynthesis can be explained by the choice of plate configuration.