Mechanical Assessment of Local Bone Quality to Predict Failure of Locked Plating in a Proximal Humerus Fracture Model

Abstract

The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability.

Secondary Perforation Risk in Plate Osteosynthesis of Unstable Proximal Humerus Fractures: A Biomechanical Investigation of the Effect of Screw Length

“…Loading only the humeral head is a limitation to the study as there are currently no available in vivo studies, describing screw perforating from such a perspective, but only from in vitro testing . On the basis of in vivo loading data, biomechanical testing setups that load from 25° lateral angulation have been developed, inducing primary varus bending . However, the related failure mode was screw cut‐out type failure rather than screw perforation .…”

“…On the basis of in vivo loading data, biomechanical testing setups that load from 25° lateral angulation have been developed, inducing primary varus bending . However, the related failure mode was screw cut‐out type failure rather than screw perforation . Testing for screw cut‐out type failure is clinically relevant, as it is reported in high rates .…”

Intraoperative Mechanical Measurement of Bone Quality With the DensiProbe

“…R€ oderer et al (29) could demonstrate in a recently published cadaver study that DensiProbe measurement of 19 proximal humerus specimens reliably can predict BMD measured by QCT. Significant differences of cancellous bone quality within various regions of the humeral head were observed and may have an influence on future implant design.…”

Augmentationstechnik am proximalen Humerus

“…In weiteren Studien konnten die Reproduzierbarkeit der Methode gezeigt werden [17,18]. Weiter konnten 2 Schrauben identifiziert werden (.…”