Double Approach Strategy for Acetabulum Reconstruction of Bipolar Prosthesis Intrapelvic Migration

Intrapelvic migration of a hemiarthroplasty is rare and requires careful planning due to proximity of neurovascular and visceral structures. Traditional approaches may be inadequate or unsafe for retrieval. Our double approach strategy—ilioinguinal for safe removal and anterolateral for reconstruction-offered a less invasive and controlled alternative to transabdominal exposure [6]. When intra-pelvic prosthetic protrusion occurs, and the migrated components are near vital structures, a comprehensive approach involving both the internal and external aspects of the pelvis is required. A two-staged operation performed in a single surgical session has been recommended to obtain a direct and extensive view of the neurovascular and visceral structures, allowing for their mobilization, retraction and protection. This approach minimizes risks and complications during the removal of intra-pelvic components and enables an accurate and stable reconstruction of the hip [7].

Thorough preoperative evaluation and meticulous planning are essential. Image studies should encompass AP pelvic x-rays, AP and lateral hip images to assess for pelvic discontinuity. To evaluate the bone defect, a contrast-enhanced CT provides invaluable detail. Additionally, angio-CT plays a critical role in visualizing vascular structures and their relationships to nearby nerves, urogenital, and digestive systems. This includes detailed assessment of veins and the lower urinary system during late-phase imaging. In our case study, it is vital to evaluate the bone defect and association between intra-pelvic vital structures before the surgery. It is also preferable to more invasive and expensive methods such as the arteriogram, venogram, and the angio-MRI [8].

The migrated bipolar cup can remain inaccessible through a conventional approach to the hip joint, making its removal both challenging and risky [7]. A retroperitoneal approach through the lateral window of the ilioinguinal or Stoppa approach can facilitate relatively safe and simple removal of prosthetic components with severe medial migration [9,10]. If the displaced implant is positioned more medially and adheres to critical intra-pelvic structures, with the iliopsoas muscle damaged and foreign components in contact with the peritoneum, a transabdominal approach is often the optimal choice [8].

The ilioinguinal approach described by Letournel in 1961 is the approach of choice for the exposure, reduction, and fixation of fractures involving the anterior column of the acetabulum and the inner surface of the innominate bone. Through this approach, it is possible to access the internal iliac fossa, or even sacroiliac joint if needed [11]. In our case, a double approach from anterolateral and ilioinguinal was employed to retrieve the migrated components. The ilioinguinal approach provided adequate view and direct control of intra-pelvic migrated prosthesis while being less invasive than the transabdominal approach. Within the three-window view of ilioinguinal approach, the first (lateral) window offered sufficient access for socket removal, eliminating the need to utilize the second and third windows. After removal of the migrated bipolar prosthetic cup with head through ilioinguinal approach, the anterolateral approach was facilitated reconstruction and socket implantation. The replacement was performed staged but in a single session without objective data indicative of infection[8]. Adequate preoperative planning is critical for surgeons who perform hip revisions. A useful classification allows the surgeons to decide the treatments and compare results. Numerous classification schemes have been proposed to describe the extent of periacetabular bone loss in revision THA, with Paprosky classification being one of the commonly used systems [12] (Figure 3).

In most situation, the acetabular component dislocated into the pelvis is assumed to indicate a pelvic discontinuity. The complex, uncontained acetabular defects usually require more complicated reconstruction techniques for treatment, such as ‘‘cage-and-augment’ ,‘‘cup-and-augment’’, ‘‘cup-and- cage’’, or custom triflange to provide mechanical stability [13,14]. However, in our case, the preoperative image revealed the pelvic anterior and posterior columns remain intact. After careful removal of the bipolar cup with head, it was determined in the anterolateral approach that contact with the host bone over 50% was possible, which was able to provide mechanical stability. This aligns the principles used in the treatment of Paprosky type IIC defect.

The acetabular reconstruction was done using bulk femoral head allograft bone impaction grafting to stabilize the impaired medial wall, reduce the volume of acetabular bone loss and potentially restore bone stock. After reverse reaming, larger bone contact was achieved through choosing a jumbo TM cup, with placement in the high hip center [15]. TM cup is then utilized as this method was suggested for many complex primaries and revisions in THA [16,17]. The porous metal cups allow rapid and enhanced biologic fixation of the acetabular cups into the bone. Moreover, highly porous Trabecular Metal™ cups (Zimmer) are quite possible to utilize in reasonable primary stability and reinforced by effective screw fixation, even with <50% bone contact.[18] Bony union and stability of revised TM cup are also observed in our case of one year follow-up.