Following hip arthroplasty, the prosthetic femoral neck can be targeted. Intra-articular placement can be confirmed by fluid aspiration, loss of pressure resistance to injection or iodinated contrast instillation. For most injections, a 22-gauge 3.5- or 5-in spinal needle is adequate. Slight flexion of the hip can help to relax the anterior joint capsule and facilitate intra-articular access. Several fluoroscopic targets are feasible, including the lateral aspect of the subcapital femoral neck ( Fig. Using this technique, the needle trajectory is often so far lateral to the groin that it is unnecessary to palpate and mark the location of the femoral artery. This anterolateral approach moves the needle entry site lateral to the groin and femoral neurovascular bundle. With the patient positioned supine and the hip externally rotated, the C-arm is angled laterally from the straight AP axis until the beam profiles the femoral neck and greater trochanter (approximately 25 degrees). C-arm units allow the radiation source and detector to be angled along any desired trajectory, thereby optimizing the success and safety of the procedure. Several fluoroscopic techniques can be employed to gain intra-articular access. If there are no restrictions in patient positioning, the “frog-leg” lateral projection is obtained by flexing, abducting, and externally rotating the hip and directing the beam either vertically or slightly cranially (∼20 degrees) ( Figs. Because the anterior and posterior head–neck junctions are not superimposed in this position, a ridge of femoral head osteophytes can give the false-positive appearance of a sclerotic fracture line ( Fig. In external rotation, the greater and lesser trochanters partially or completely overlap the femoral neck and intertrochanteric region ( Fig. The most common positioning error is external rotation. In this position, the contours of both greater and lesser trochanters should be visible, increasing sensitivity in the detection of subtle destructive lesions and nondisplaced fractures. Internal rotation helps to compensate for femoral anteversion and brings the femoral neck and head–neck junction into appropriate planes relative to the beam of the x-ray. In the absence of known trauma or suspected proximal femoral fracture, the ipsilateral hip is internally rotated approximately 15 degrees to obtain the AP view ( Fig.

Picture of normal hip xray