Excessive Derotational K-Wire Angulation Decreases Compression by Headless Compression Screw

Abstract

Background Scaphoid fracture is the most common carpal bone fracture. Open reduction internal fixation of scaphoid fractures typically undergo stabilization by a single headless compression screw (HCS). During screw insertion, a derotational Kirschner wire (K-wire) is often placed for rotational control of the near and far fragment. Questions/Purposes The aim of this study was to determine if there is an angle of derotational K-wire placement in relation to the axis of a HCS that compromises the amount of compression generated at a fracture site by the HCS. We hypothesize that increased off-axis angle will lead to decreased compression across the fracture site. Methods A Cellular Block 20 rigid polyurethane foam (Sawbones, Vashon, WA) scaphoid model was created to eliminate variability in bone mineral density in cadaveric bone. MiniAcutrak HCS screws (Acumed, Hillsboro, OR) were used for testing. Three conditions were tested: (1) HCS with derotational wire inserted parallel to the HCS (zero degrees off-axis); (2) HCS with derotational wire inserted 10 degrees off-axis; and (3) HCS with derotational wire inserted 20 degrees off-axis. Results A statistically significant difference in the mean compression of the control group (56.9 N) was found between the mean compression with the derotational K-wire placed 20 degrees off-axis (15.2 N) ( p = 0.001). Conclusions Compression at the fracture site could be impeded by placing an excessively angulated off-axis derotation wire prior to insertion of the HCS. Clinical Relevance Our study adds a new detail to the optimal technique of HCS placement in scaphoid fractures to improve compression and fracture union.

Keywords: angulation; compression; derotational K-wire; headless compression screw; scaphoid fracture.

Fig. 1

Custom polyurethane (PU) scaphoid jig with load cell 2 mm from second PU sheet to measure compression from headless compression screw (HCS). Elastic bands provide standardized preload while also preventing rotation of the top block. θ represents off-axis angle between derotational Kirschner wire (K-wire) and HCS. Derotational K-wire 1 mm superior to HCS central plug. * Off-axis derotational K-wire.

Fig. 2

Effect of derotational Kirschner wire (K-wire) angle on compression by headless compression screw (HCS) across polyurethane block fracture site. Control = 0 degree derotation K-wire off-axis relative to HCS. X = mean compression by degree off-axis. *indicates statistically significant difference for 20 degrees off-axis group relative to the control group (0 degree) by Dunnett's post-hoc testing.