INDICATIONS AND CONTRAINDICATIONS

Indications for removing an acetabular component at the time of revision total hip arthroplasty have been influenced by component design, advances in bearing materials, and ease or difficulty of removing the component.

Regardless of these changing influences, there are some absolute indications for acetabular component removal. Loose acetabular components should be revised at the time of surgery. A patient with asymptomatic or mildly symptomatic loosening not associated with progressive osteolysis may be simply observed with scheduled clinical and radiographic follow-up. However, should a patient with acetabular loosening come to surgery for any reason, an acetabular revision should be carried out. A worn all-polyethylene acetabular component that is contributing to pain, instability, or osteolysis is also an indication for acetabular revision because it has no modular capability to allow for easy bearing surface exchange. Chronic infection of the hip is also an absolute indication for implant removal, because of the ability of numerous bacteria to form biofilms, which make treatment of the infection ineffective without component removal. Acetabular component removal may also be indicated in acute postoperative infections of the hip if done early, because component removal and rereaming are easily accomplished before bio-ingrowth takes place. Major malposition of an acetabular component is another indication for removal if the malposition leads to instability, impingement, or wear (vertical cup) or if one needs to restore the hip center for proper biomechanics. Lastly, a damaged cup that can no longer support weight-bearing forces is an absolute indication for removal and revision.

Relative indications for acetabular removal and reconstruction include components with a historically high failure rate. This includes some early nonmodular designs and some components with poor polyethylene interlock mechanisms. Acetabular component removal and revision might also be considered in a young patient with an early failure, to take advantage of new bearing surfaces that typically are not compatible with early cup designs. A damaged acetabular component that is still structurally sound is also an indication for removal and revision, especially if the polyethylene interlock mechanism has been rendered ineffective. This has been listed as a relative indication because cementation of a new polyethylene liner into the existing shell may be considered.

Indications for retaining an acetabular component are that the component is well fixed, structurally sound, appropriately positioned, and without significant wear. An acetabular component with minor malposition may be left in place if the malposition may be addressed by a polyethylene liner exchange using a hooded or lipped liner, or a lateralized liner in the case of a hip center that is too medial. Minor malposition may also be tolerated during an isolated femoral revision if lateral offset and version corrections may be accomplished on the femoral side to accommodate the acetabular malposition. As a general rule, if the acetabular malposition had any bearing on the failure of the initial surgery and was not just an incidental finding intraoperatively, then removal and revision of the acetabular component should be carried out.

Isolated acetabular insert exchange may be carried out in select situations involving modular acetabular components. The same indications for retaining a well-fixed acetabular component must be met, and compatible inserts should be available. This requires a preoperative knowledge of the type of implant being revised, whether the modular inserts in question are available, and specifics about the locking mechanism involved. Clinical results have been encouraging, even when procedures are associated with osteolytic lesions (Fig. 39-1).^2,4 If a locking mechanism has been damaged or a corresponding acetabular insert is unavailable, a compatible insert may be cemented into an existing well-fixed acetabular shell.^5–7 These constructs have shown initial promising results, but their durability over time has not been proven. Isolated acetabular insert exchange may halt progressive osteolytic changes, allow for subtle changes in position and stability, and provide the ability to take advantage of newer bearing materials. Although seemingly simple to carry out, insert exchange has been associated with significant complications, particularly postoperative instability.⁸

FIGURE 39-1 Acetabular osteolysis secondary to polyethylene wear. Preoperative radiograph compared with radiograph 3 years after isolated polyethylene liner exchange with débridement and grafting of the osteolytic lesions.

PREOPERATIVE PLANNING

A typical workup in planning a revision hip procedure will focus on determining the source of the failure. Obviously, infection requires component removal, and ascertaining its presence to the best of one’s ability should be performed before surgery. No test for infection is conclusive, but negative sedimentation rate, C-reactive protein, and isotope scans are typically predictive of absence of infection. Loosening is another indication for acetabular revision and may be determined by careful scrutiny of serial radiographs. Component migration, complete radiolucent lines in all three zones, radiolucent lines 2 mm or greater in any zone, radiolucent lines that initially appear after 2 years, and progression of radiolucent lines after 2 years all correlate with acetabular component loosening.⁹

Wear may be assessed radiographically by looking for asymmetric positioning of the femoral head within the acetabulum or for the development of osteolytic lesions in the periprosthetic regions of the bone. Patients with wear may also develop late instability secondary to the unconstrained nature of the articulation of the femoral head in the worn polyethylene. Acetabular component positioning may be difficult to determine based on plain radiographs. Component inclination is easier to assess than version, which may require fluoroscopic assessment or CT to determine.

Exposure may be selected based on surgeon’s comfort and expertise; however, all acetabular revisions require circumferential exposure of the entire periphery of the acetabular component. In addition to the planned component removal, plans for the proposed reconstruction must also be taken into account, especially with regard to potential structural bone grafting. Lateral exposure to the hip has been associated with a lower rate of instability after acetabular revision⁴; however, the posterior approach is more extensile and may be converted into an extended trochanteric osteotomy if necessary. If the femoral component is to be revised, its removal should be completed early in the surgery to allow better access to the acetabulum. Cement in the femoral canal may be left in place if indicated after the femoral removal reinsertion technique described by Nabors and colleagues¹⁰ or removed after acetabular revision to minimize blood loss. If the femoral component is left in place, the modular head should be removed if possible, and sufficient exposure obtained to mobilize the femur clear of the acetabulum.

With the posterior approach, the anterior capsular attachment on the femur should be released or excised, leaving enough capsular tissue for repair posteriorly. This may be tedious and difficult to accomplish anteriorly if the femoral component is left intact but is critical to gaining adequate exposure. The extensive nature of this release with a retained femoral component may contribute to the high rate of instability after isolated acetabular revision.⁸

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The Cementless Tapered Stem Femoroacetabular Osteoplasty Reconstruction of Acetabular Bone Deficiencies Using the Antiprotrusio Cage The Cemented Stem Management of Postoperative Hematomas The Cemented Stem

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