Removing a solidly fixed, cemented or cementless acetabular component with minimal bone loss while avoiding further structural damage to the pelvis can be technically challenging as well as time consuming. The success of total hip arthroplasty (THA) depends in large part on the quality, volume, and location of host bone after implant removal. If revision surgery is not done meticulously, significant damage can occur to the host acetabulum or pelvis, further complicating reconstruction. Key factors in achieving successful acetabular implant removal are preoperative planning, selection of the correct surgical approach to provide adequate exposure, availability of correct instruments, and competence with a variety of surgical techniques.
Indications and Contraindications
A solidly fixed acetabular component may be removed during revision surgery because of chronic infection, hip instability (e.g., improper component orientation, need for a constrained prosthesis), or severe osteolysis that cannot be dealt with satisfactorily while retaining the original component. In cases of excessive polyethylene wear but a well-positioned shell, the acetabular component can remain in situ, and the polyethylene liner can be exchanged, provided the acetabular component is modular with an intact locking mechanism and the cup is solidly fixed to the pelvis. Cementation of a new liner into a well-fixed shell also is an option when the locking mechanism is damaged or the matching liner is unavailable. Revision of the acetabular component is indicated when loosening and change of the component position is identified radiographically or when stability of the component is lost with intraoperative manipulation. In all cases, the surgeon should understand why the hip is being revised and how extraction of the implant will be done.
The first step in preoperative planning is to determine the manufacturer of the component from the surgical implant labels or operative notes. Radiographs can be used when surgical notes are unavailable. Judet radiographic views or computed tomography (CT) scans can supplement standard preoperative radiographs. Anteroposterior pelvic and lateral hip radiographs can determine cup placement and the extent of bone loss and identify an associated fracture or pelvic dissociation.
During the preoperative workup, the surgeon should compare and analyze serial radiographs and identify the specific tools needed for implant removal. For example, if acetabular screws were used in the previous arthroplasty, the correct screwdriver must be selected for removal, and the surgeon must understand how the locking mechanism works for the polyethylene liner in a cementless cup.
In cases of severe component migration, such as intrapelvic component migration, angiography or CT-angiography of the pelvis is important for determining the proximity of the iliac vessels to the migrated component. A vascular or general surgeon may be needed for extraction of an intrapelvic component or in case complications arise.
In any revision THA, the surgical exposure must be extensile to enable component removal. A posterior approach is ideal for revision hip surgery because it allows optimal access to the acetabulum and is extensile for other reconstruction options, such as a trochanteric osteotomy. The modified trochanteric slide osteotomy as described by Gross and colleagues is a well-established technique used to facilitate exposure for complex hip revision surgery. It preserves the posterior structures (i.e., posterior capsule and short external rotators), potentially reducing postoperative instability while providing excellent surgical exposure.
Cemented Acetabular Component
If a cemented acetabular component has to be removed, it is loosened and then extracted from the cement mantle. This can be achieved by using curved osteotomes between the interface of the component and cement mantle ( Fig. 45.1 ). Osteotomes are used around the circumference to loosen the component, which is then lifted out. A grasper can be used to remove the liner with a gentle side-to-side and twisting motion. Levering or prying is not recommended for fear of causing fracture or acetabular bone damage.
Osteotomes are used between the host bone and cement mantle to carefully remove the cement, leaving as much host bone intact as possible. Often, osteotomes are used to split the cement mantle into pieces, which are then removed piecemeal. The use of a high-speed pencil-tip bur can assist in developing the interface between the polyethylene and cement and the cement and host bone. Sectioning the underlying cement mantle facilitates its removal and decreases the chance of host bone loss or injury.
When an all-polyethylene cup is cemented directly into the host acetabulum, another technique uses acetabular reamers to ream away as much of the polyethylene as possible. After the polyethylene liner becomes thin and flexible, an osteotome can be used to lift the cup out.
Cementless Acetabular Components
The first step in removing a cementless acetabular component is extraction of the polyethylene liner. Identifying the specific locking mechanism and steps needed to disengage the liner are important because each manufacturer has specialized instruments and techniques for removal. If the locking mechanism is damaged or tools are unavailable, other methods of removing the liner exist. If the rim of the liner protrudes beyond the metal cup, it may be possible to pry the liner out of place with an osteotome. An alternative technique is to drill a hole centrally into the liner and advance a 6.5-mm acetabular screw into the hole. As the screw advances, the liner is expelled from the shell.
There are several options for removing a solidly fixed acetabular shell. Careful use of the appropriate surgical tools and techniques can minimize the amount of host bone loss during the process. For example, the correct screwdriver must be available for acetabular screws during cup removal. If the screw heads are stripped, a high-speed bur is used to decapitate the screw heads. After the acetabular component is removed, the remaining screw shafts are removed with pliers or trephines. Traditional curved osteotomes can be used ( Fig. 45.2 ), but excessive bone loss can occur using this technique.