Augmented 4-screw vs. nonaugmented 6-screw PHILOS plating in low-bone quality proximal humerus fractures: a...

Proximal humerus fractures are frequent in patients with low bone quality. PHILOS plates are widely used with either minimally invasive plate osteosynthesis (MIPO) or open reduction and internal fixation (ORIF) techniques. However, it remains unclear whether plating with 4 cement-augmented proximal screws provides biomechanical stability comparable to using 4 nonaugmented proximal screws plus 2 additional calcar screws in unstable low bone quality proximal humerus fractures.

Fourteen paired human cadaveric humeri with low bone quality and simulated unstable 3-part proximal humerus fractures (AO 11-B1) were assigned to 2 groups - 4S+ and 6S - and stabilized using PHILOS plates with 4 proximal head screws in both groups. In the 6S group, 2 additional calcar (inferomedial support) screws were used, whereas in the 4S+ group, the 4 screw tips were augmented with bone cement. Cyclic axial loading tests were conducted until failure. Interfragmentary movements were monitored via motion tracking.

Initial axial construct stiffness and cycles to failure showed no significant differences between groups (P = .171, P = .397). Although interfragmentary movements were slightly higher in the 4S+ group, this difference was not significant (P ≥ .071). Under cyclic loading, the 6S group exhibited a significant progressive increase over cycles for varus deformation (P = .029), humeral head displacement (P = .038), and screw bending in row A (P = .003), whereas no significant increase over cycles was observed in the 4S+ group and between the groups.

From a biomechanical perspective, PHILOS plating with 4 cement-augmented screws demonstrated comparable stability versus plating with 4 nonaugmented head screws plus 2 additional calcar screws, suggesting that the former fixation technique represents a valid alternative to the latter, particularly in case of low bone quality.