Comparison of stability of plate fixateurs with parallel and oblique screw directions

• Published in: Zeitschrift fur Orthopadie und Unfallchirurgie Vol. 153; no. 2; p. 160
• Main Authors: Ackermann, O, Mauk, P J, Beuke, T, Roslawski, L, Lahner, M, Eckert, K, von Schulze Pellengahr, C
• Format: Journal Article
• Language: German
• Published: Germany 01-04-2015
• Subjects: Bone Plates; Bone Screws; Equipment Design; Equipment Failure; Fracture Fixation, Internal - instrumentation; Fracture Fixation, Internal - methods; Humans; Osteoporotic Fractures - surgery; Tensile Strength
• ISSN: 1864-6743
• DOI: 10.1055/s-0034-1396187

One of the main failure mechanisms of modern plate fixateurs is the tearing of the whole plate-screw construct out of the osteoporotic bone. The aim of this study was to show whether an oblique screw placement can improve the fixation of the plate to the bone.
A steel probe was fixed to a synthetic bone (Fa. Sawbones) with standard titanium fixed-angle screws in parallel and 55° oblique positioning. We tested the static tear force and the dynamic stability (force distance 1.4 or 1.6 mm, 610 and 900 N, frequency of force shift of 560 or 380/min). Endpoint was a visible tear of the artificial bone. In addition we performed a morphological analysis of the torn fragments.
The maximal tear force was 2.04 kN (1.95-2.13) for oblique and 2.66 kN (2.55-2.77) for parallel placement (p < 0.05). With a parallel positioning a higher number of force shifts were performed before a visual tear appeared. With parallel positioning the screw canal was torn with an intact surrounding corticalis; in oblique positioning the threads remained intact, the corticalis was torn out with a wedge.
An oblique screw positioning does not result in a higher tear force in modern plate fixateurs.