Length Matters: Short Base-Plate Angle Guides May Lead to Guide-Wire Mal-Positioning When Inserting a DHS. A Radiographic Modeling Study.

ABSTRACT

The dynamic hip screw (DHS) consists of a barrel-plate fixed to the relatively-straight proximal femoral shaft, and a screw which slides within the barrel at a fixed angle, usually 135°. The guide-wire is inserted using a guide at the set angle. Guide design varies between manufacturers, with some new guides being particularly short. We analysed the impact of guide design on the resulting trajectory of the guidewire, and its potential to cause a surgical error. Twenty AP hip radiographs were analysed. Trauma Cad (Brainlab, Munich, Germany) software was used to template a 4-hole 135° DHS onto the intact femur with the screw positioned in the center of the head. A template of a Stryker (Michigan, USA) 135° DHS guide (37 mm long) was then overlaid at the hip screw entry point, and the set trajectory marked. The divergence between the two trajectories was measured (α angle). The distance the guide would have to be moved inferiorly to attain the correct position in the head was then noted. The median divergence (α angle) caused by the guide relative to the ideal position was 6° (range 2-12). This led to the guidewire placement being a median of 9.1 mm (range 3-23) superior in the head (ß).To achieve the correct position of the wire in the head, the guide needed to be moved inferiorly a median of 8 mm (range 2-10). © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38574-577, 2020.