gms | German Medical Science

Objectives: Proximal humerus fractures are very frequently observed injuries. Although their plating is an established procedure, it is still associated with a high rate of secondary screw perforation. Less rigid dynamic constructs may reduce stresses at the bone-implant interface and prevent cut-through in poor bone quality without compromising the overall construct stability. The aim of this study was to develop and test biomechanically a prototype plate for fixation of proximal humerus fractures which integrates a new gliding screw concept enabling dynamic compression in the fracture gap.

Methods: The design of the prototype implant was adopted from PHILOS plate by replacing its proximal locking holes with four short barrels inclined at 30° for fixation with 3.5mm gliding shaft screws. Following, three-part proximal humerus fractures were simulated in twenty-four paired human cadaveric specimens. Eight pairs were randomly assigned for pairwise fixation with either a prototype gliding plate or a PHILOS plate. In addition, four pairs were fixed with the gliding plate whose proximal screw tips were augmented with bone cement. All humeri were cyclically tested in 30° adduction under progressively increasing cyclic loading until detection of screw perforation. Initial construct stiffness was evaluated from machine data. Varus tilting, screw telescoping and screw cut-through were captured by optical motion tracking.

Results and conclusion: Initial stiffness (N/mm) was 581.3±239.7 for gliding plate, 631.5±160.0 for PHILOS and 440.2±97.6 for gliding augmented plate, without significant differences between the three fixation methods, P=0.11. Varus tilting (°) after 7500 cycles was comparable between gliding plate (2.6±1.9), PHILOS (1.2±0.6) and gliding augmented plate (1.7±0.9), P=0.10. Similarly, screw cut-through (mm) after 7500 cycles was similar between gliding plate (3.02±2.85), PHILOS (1.30±0.44) and gliding augmented plate (2.83±1.18), P=0.13. Telescoping of the most proximal screw (mm) after 7500 cycles was 0.37±0.31 for gliding plate and 0.89±0.76 for gliding augmented plate, with no significant difference between them, P=0.24. Cycles until 5° varus tilting were 12702±3687 for gliding plate, 13948±1295 for PHILOS and 13189±2647 for gliding augmented plate, without significant differences between the plating techniques, P=0.66. Although from biomechanical perspective plate fixation with the new gliding concept did not show considerable advantages in comparison to PHILOS plating, based on the initiation of screw telescoping it may represent a valid alternative to the latter, especially in terms of cut-out prevention.