Patients with a spontaneous or surgically fused hip usually experience impaired functionality affecting the adjacent joints. Patients also may experience problems in daily activities due to impaired range of motion, leg length discrepancy, or limping. ¹ A conversion to total hip arthroplasty (THA) may be a solution to these problems but is often challenging due to many potential problems (Table 28.1). ^2-11

Patients who underwent hip arthrodesis most often had this performed at a very young age for many potential indications, such as avascular necrosis, destructive rheumatoid arthritis, or septic arthritis. Hip arthrodesis bears the benefit that it precluded a joint replacement in young patients in an era in which THA was not as well established as today. However, hip arthrodesis is at long term also borne with multiple problems, including spine-related problems, knee arthritis, and leg length discrepancy. ¹ In addition, many of our contemporary patients are seeking an active lifestyle and therefore often request a conversion to THA.

Conversion from a fused hip toward a fully mobile THA could be a solution but has been associated with many potential complications. ^2-11 The most problematic issue is the atrophy of the hip deltoid including the abductors. These muscles are the most important stabilizers of the hip joint and support a swift gait pattern. However, most often, these muscles have not been used normally for many years in arthrodesis cases. Problems such as a persistent Trendelenburg gait pattern or instability of the joint can occur. ^1-11 Therefore, violation of the periarticular muscles should be prevented at all times in order to minimize the risk for these complications. This is one of the major advantages of the DAA. In addition,
access to the anterior column and the fused hip can be swiftly achieved in a muscle-sparing way through the Smith-Peterson interval, leaving it easier to remove anteriorly located plates and other fusion material.

As part of our regular preoperative templating, we take an anteroposterior pelvic radiograph with a marker. Most patients have the femur fused in 30° of flexion, external rotation, and slight abduction. Therefore, we preferably perform templating on both hips if possible (Figure 28.1).

In order to improve intraoperative visibility toward the acetabulum, the anterior column, and the iliac wing, we prefer to use an extensile iliofemoral approach (see Chapter 22). This allows the surgeon to thoroughly assess the bony pelvic anatomy, which improves adequate reaming. Most patients have some osteopenia on the affected side; therefore, careful reaming is of the utmost importance.

In case an anterior plate is still in place, the extensile iliofemoral approach allows for easy access to the plate and the plate will be removed during the procedure. In case a posterior fixation is present, we prefer to leave the plate in place and cut the screws in situ during the conversion procedure. In case this would be deemed impossible based on a preoperative computed tomographic scan, we prefer to work in two stages. In the first stage, we remove the posterior plate followed by 10 days of clindamycin 600 mg every 8 hours to minimize the risk of infection. For this reason, we generally leave a 6-week time interval before moving forward to the second stage.