The Direct Anterior Approach to Hip Reconstruction

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CHAPTER 14 Role of Fluoroscopic Imaging and Image Guidance

Final Leg Length Assessment Once trials or final components are inserted, another AP pelvis image is obtained in neutral rotation and pelvic tilt matching the preoperative standing pelvis radiograph. The radiopaque rigid bar is again placed across the bi-ischial line. Comparison of this image with preprocedural fluo roscopy can give objective data on the change in leg length on the ipsilateral side ( Figure 14.3A and B ). Reconstruction of Global Offset In addition to providing information on limb length, fluoroscopy provides valuable information on offset. Reconstruction of global offset, a sum of both acetabular and femoral offsets, has been shown to lead to improved stability, range of motion, and abductor strength while decreasing wear. 3,4 In conjunction with accurate limb length restoration, proper offset restoration has been shown to lead to improved patient outcomes with an additive effect. 5 The introduction of fluoroscopy to the DAA provides real-time information regarding offset. To accomplish this, a measurement is made between the teardrop and a longitudinal line down the center of the femoral shaft (femoral shaft axis) while keeping in mind a consistent abduction or adduction position of the limb. The global offset is maintained within ±4 mm. Ideally, this is compared with a contralateral normal hip if possible but may not be feasible if the patient has bilateral hip arthrosis at presentation during the index THA.

Femoral Component Position Dedicated AP and lateral images of the hip with trial components are obtained. Assessment can be made to ensure appropriate sizing and alignment before opening of the final implants. Final Implant Position Images including a lateral hip are taken with the final implants in place to confirm femoral implant size and posi tion, to ensure the prosthetic hip is fully reduced without any interposed tissue, and to rule out any obvious fractures ( Figure 14.4 ). It is important to note that these images are not meant as a substitute for direct visual confirmation of hip reduction, inspection for interposed soft tissue, and evaluation of the neck and calcar for fracture. The major advantage with this technique is that it reduces any “sur prises” one may encounter with films taken in the recovery room or during the first office visit. Fluoroscopic “Illusions” Distortion is a phenomenon that can alter the image in image-intensified fluoroscopy. Image-intensified fluoro scopic machines, which are commonly used in ortho paedic operating rooms, are susceptible to external electromagnetic fields (EMFs) that cause image aber rations. This effect is well documented in the radiology and applied physics literature but has not been discussed much at all in the orthopaedic literature.

A FIGURE 14.3 A, With the trial implants in, the radiopaque bar is placed across the bi-ischial line. A comparison is made with the preoper ative image to quantify the change in leg length as well as offset. B, As done with the trial components, the radiopaque bar can be used again after the insertion of the final implants. Copyright © Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. 2024 B