The Direct Anterior Approach to Hip Reconstruction

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CHAPTER 14 Role of Fluoroscopic Imaging and Image Guidance

recognize if distortion is occurring and compensates for any alteration of the image when measuring leg length ( Figure 14.8 ). A digitally placed bi-ischial line could potentially lead to misleading information on leg length, resulting in errors. Novel Fluoroscopic Technologies It is well known that ideal acetabular and femoral compo nent positioning improves THA outcomes and longevity. However, there is still significant room for improvement in our accuracy of component positioning, and as demand increases, we will need to make sure that we have simple, efficient, reproducible, and cost-effective methods to reli ably improve our positioning of THA components. Various component positioning aids exist for both the posterior and anterior approach, with fluoroscopy being one of the most common aids used in the DAA. Fluoroscopy can be used in isolation for guidance in THA, or additive technologies can be used for assistance with intraoperative navigation. In the past decade, several companies have entered into this space of fluoroscopic navigation for DAA THA. OrthoGrid (OrthoGrid Systems, Midvale, UT, USA) is a unit that mounts onto the image intensifier of the fluoro scopic C-arm and provides the surgeon with a grid overlay within the fluoroscopic field of view or, in the newer itera tion of this technology, a computer interprets the amount of distortion from a dot matrix overlay and digitally corrects the distorted image and then overlays a virtual grid on the fluoroscopic image ( Figure 14.9 ). The grid is used to interpret the amount of offset and length variation between both hips and to assist with acetabular component abduction. The

main feature of this technology is the fact that the device is placed within the imaging field and either accounts for the distortion seen or digitally corrects for it. Radlink (Radlink, Inc., El Segundo CA, USA) is a digital technology that can stitch C-arm images together to provide a wider field of view for side-to-side compari son of hips. Digital overlay tools are then provided to the surgeon to evaluate cup position, limb length, and offset using these stitched fluoroscopic images ( Figure 14.10 ). Velys (DePuy Synthes Joint Reconstruction, Warsaw, IN, USA), formerly known as JointPoint, is a fluoroscopic navigation tool that allows the surgeon to preoperatively digitally template and then overlay these digital templates on the intraoperative fluoroscopic images to guide com ponent positioning and limb length and offset restoration. This technology also allows the surgeon to digitally over lay the operative hip on top of the fluoroscopic images of the nonoperative hip as an alternative method of side-to side comparison ( Figure 14.11 ). Outcomes Two previous case series studies have reported the accu racy of component positioning performed through the various approaches with the patient positioned in the

FIGURE 14.8 This image portrays the straight radiopaque bar with a subtle “wave” to it demonstrating the presence of distortion. The use of the radiopaque bar over a digitally placed line helps account for such image alterations. FIGURE 14.9 An intraoperative fluoroscopic image during DAA THA demonstrating symmetric limb lengths when accounting for fluoro scopic distortion (ie, the distorted grid line passes through the lesser trochanter at the same height [large single-sided arrows] on both sides). This image also illustrates the amount of distortion seen at the periphery of the image by the amount of deviation of the radiopaque gridlines from the straight line drawn on top of the saved fluoro scopic image (small single-sided arrows). In this case, 9 and 7 mm of error were measured on the patient’s right and left sides, respectively, resulting in a combined 1.5 cm of fluoroscopic distortion. Copyright © Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. 2024