The Direct Anterior Approach to Hip Reconstruction

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SECTION III Intermediate Direct Anterior Approach Topics

is obtained with the pelvic tilt matched to the patient’s preoperative standing radiograph using the relationship between the coccyx and the pubic symphysis as well as the appearance of the obturator foramen. To accom plish this, the patient position or the fluoroscopic beam can be tilted in either the cephalad or caudad direction. This becomes essential in order to place the acetabulum in the true “functional position.” It has been demon strated that, if the acetabular component is positioned appropriately from a supine pelvis radiograph, up to 31% will become malpositioned upon standing. 2 This is a change that can occur because of the dynamic inter action between the lumbar spine, pelvis, and hip with postural changes. The image should also demonstrate neutral pelvic rotation by assessing the symmetry of the obturator foramina and ischial spines as well as the alignment of the coccyx with the pubic symphysis. Again, either the patient or the fluoroscopic machine can be tilted to obtain an optimal image. Lastly, a radiopaque rigid bar is placed across the pel vis to recreate the bi-ischial line, and its intersection to the lesser trochanters is identified ( Figure 14.1 ). This mea surement is not used to determine LLD between the two sides but rather is used as a reference point to assess for any changes that occur on the ipsilateral side once the trials or final implants are placed. A comparison is made between this preprocedural image and the same image with trial or final implants in place to assess for the change in leg length that occurred during compo nent implantation. The change in ipsilateral leg length can then be objectively calculated.

Confirmation of Femoral Neck Osteotomy The level of femoral neck resection can be confirmed intra operatively and modified based on preoperative templating. There is a propensity to underresect the femoral neck, which makes acetabular exposure and preparation more difficult. Reaming Fluoroscopy can be used during acetabular preparation but is not something of routine use for some of the authors. It can specifically be used to determine sizing as well as depth and medialization and is helpful during a surgeon’s learn ing curve. It can also be used in more difficult cases, such as severe dysplasia or revision THA. It is important to note that fluoroscopy during this step does not substitute for good acetabular exposure. Overreliance on fluoroscopy in cases of poor exposure could lead to errant reaming and unintended acetabular bone loss. Acetabular Component Position Acetabular component position including inclination and version is determined using fluoroscopy. This can be done on a pelvis or hip image depending on the size of the intensifier ( Figure 14.2 ). A key step before impaction is to confirm the proper preoperative pelvic rotation. There is a tendency with traction or manipulation that malro tation of the pelvis occurs toward an iliac oblique view. This will result in improper assessment of acetabular ver sion. In addition, one can confirm that the component is fully “seated” as well as screw placement if needed.

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FIGURE 14.1 A preoperative image of a patient undergoing right THA with a radiopaque bar placed across the bi-ischial line.

FIGURE 14.2 Acetabular cup insertion under fluoroscopic guidance allowing for “fine-tuned” adjustments to version and inclination.