Implant Removal in Revision Hip Arthroplasty

Introduction

The key aims of revision total hip arthroplasty are (1) to extract failing, malaligned, or infected components, ensuring minimal damage to host bone and soft tissue; (2) to implant new components to provide long-term stable fixation; and (3) to manage bone loss by augmenting deficient bone stock. The importance of access to recent, high-quality, presurgical imaging to facilitate accurate preoperative assessment and to roadmap the execution of the perioperative plan cannot be overstated.

Although the classic principles of preserving maximal intact host bone during implant removal remain a fundamental tenet of revision hip surgery and provide an optimum platform on which to build a successful reconstruction, the successes achieved using enhanced fixation porous cups and contemporary periarticular augments have further expanded the boundaries for managing local bone deficits. The ease of implant removal depends on the implant design and the method of fixation employed at the primary procedure, how well the primary procedure was performed, the host response to the implant, and the cause of implant failure. Thus, the removal of cemented components presents challenges that differ from the removal of components fixed without cement. Loose implants may be “tapped” out, whereas solidly fixed components can be technically difficult to remove. This chapter will discuss the principles and techniques applied to different etiologic settings for the removal of failing acetabular and/or femoral components. Emphasis will be placed on preoperative planning and the surgical approach in the revision setting; discussion will focus on the management of difficult scenarios, such as the distally fixed broken stem.

Indications/Contraindications

Once the decision has been made to proceed with revision surgery, general principles dictate that failed or failing implants should be removed and replaced. Certain indications for implant removal are clearer than others. Broken components (i.e., catastrophic implant failure) obviously need removal, but the indications for changing implants in cases of instability can be more subtle. Removal of otherwise well-fixed and well-functioning implants may also be indicated when performing revision surgery for other reasons if such components have been shown to be unacceptably underperforming, have been flagged or recalled because of inherent in situ failure risk, or pose a potential risk to patient safety.

Despite recent improvements in bearing surface material properties, aseptic loosening usually secondary to osteolysis remains one of the main causes of failed hip arthroplasty. Removal of loose implants is usually clearly indicated, but the paired primary component may be left in situ if solid fixation, component compatibility, and adequate soft tissue balancing can be ensured in combination with the new revision implant. Changing a loose acetabular component may require the replacement of a modular femoral head to achieve these goals. A monoblock stem that is not compatible with the new socket or that provides inadequate soft tissue tension may have to be removed despite being well fixed. A similar need to remove an otherwise well-fixed and well-performing femoral stem may present in instances in which safe access to the acetabulum cannot be achieved through other means. Removal might also be necessary during an intended isolated single-component revision when the component to be left in situ is inadvertently damaged (e.g., trunnion damage, scratching of the head on a monoblock stem) or shows unanticipated signs of preexisting damage or wear.

If detected early enough, osteolytic defects around solidly fixed implants with satisfactory position and an intact locking mechanism may be managed without component removal. Bearing surface exchange, with or without bone grafting of the osteolytic defect, may allow satisfactory definitive treatment. Cementing a new liner into a well-fixed acetabular shell is another good option in suitable patients if the available liner is not compatible with the in situ socket. This technique can also be considered when a liner of increased constraint, obliquity, or posterior wall height is required for the treatment of instability. This technique uses removal of the liner alone, without removing a well-fixed acetabular component—typically an easy task that does not require any specialized techniques.

Cement-in-cement revision of the femur is appropriate when the cause of revision is not on the femoral side and the cement-bone interface remains pristine. Bonding of the new cement to the old mantle is good and allows implantation of a smaller cemented stem. Specific cemented revision stems are available for this purpose, and the technique has good reported medium-term results. Recent evidence may also support consideration of the less technically demanding in-cement revision, in instances again in which the integrity of the in situ cement mantle remains unquestioned. This technique is identical to the cement-in-cement technique except that the removed stem is replaced by another identically sized stem without the need to cement it. Either technique may be suitable when treating the failed acetabular component for which the stem requires removal only to grant access to the acetabulum. Any correction of femoral version is impossible with the in-cement technique, although a higher-offset stem of the same size may be used. Substantial correction of femoral version may not be possible with the cement-in-cement technique, although minor correction is possible as long as the cement mantle is not fractured in the process and a smaller stem is used.

Traumatic postoperative periprosthetic fractures more commonly affect the femur. The femoral component may be retained in the treatment of Vancouver classification types A and C fractures, which do not violate the bony interface with the stem or the cement mantle. Type B1 fractures are identified by the presence of a well-fixed stem, which can be retained. Type B2 fractures (with a loose component) and B3 fractures (with inadequate bone) require the stem and any cement mantle (if present) to be removed before reconstruction is begun.

Two or more episodes of recurrent dislocation indicate the need to proceed to revision in medically fit patients. Well-fixed components may be retained in the following instances:

• Subtle malalignment of the socket can be treated by retention of the acetabular shell and exchange of the liner to an oblique liner, higher-offset liner, or a liner with an elevated rim.

• Exchange to a liner with an increased internal diameter accommodating a larger femoral head is sufficient to prevent dislocation of well-aligned components. Increased femoral head diameter-to-neck diameter ratio increases range of motion to impingement (of the neck on the acetabular component) and increases the “jump distance” to dislocation once impingement occurs.

• Exchange of the femoral head to provide a longer neck length addresses inadequate soft tissue tension.

• Exchange to a constrained liner (compatible with a well-fixed and well-aligned acetabular shell) or cementing of a constrained liner into a noncompatible well-fixed shell of adequate diameter is suitable.

If these conditions are not met, one or—less commonly—both components may have to be removed.

Given the propensity for intrinsic biofilm formation, consensus recommendations for the treatment of nonacute periprosthetic infection (i.e., > 3 weeks’ duration) include removal of all foreign implant material, usually followed by a 2-stage reconstruction. Although single, or 1-stage, revisions are reported to have a lesser effective pathogen eradication rate, they remain an important option and, in specific circumstances, may be clinically optimal care.

Refractory local infection and/or otherwise unsalvageable massive local bone loss can elicit catastrophic concerns when contemplating revision hip surgery. In such instances, the surgeon's armamentarium may need to expand to consideration of excisional arthroplasty (e.g., Castle or Girdlestone procedures ) or the use of bone-replacing tumor prostheses (i.e., proximal femoral replacements ). Acceptable functional outcomes can usually be achieved with either option after failed primary arthroplasty, although patient satisfaction with these methods is variable.

Other causes of revision specific to the use of alternative bearing surfaces include squeaking that is deemed unacceptable to the patient or, rarely, fracture of a ceramic-on-ceramic bearing couple, which generally requires implant removal. Management of raised serum metal ions in association with a metal-on-metal bearing couple is controversial, especially in the setting of an asymptomatic patient with an otherwise well-functioning hip replacement. In the symptomatic patient, with or without the presence of so-called pseudotumor , removal of components becomes necessary to allow revision to an alternative bearing surface. The same treatment may be recommended in the asymptomatic patient with radiographic evidence of suboptimal acetabular component positioning leading to edge loading (i.e., an inappropriately abducted or anteverted acetabular component). Failure of hip resurfacing secondary to femoral neck fracture clearly requires the removal of at least the femoral component, if not both components, to convert to a non–metal-on-metal bearing combination.

Preoperative Planning

Preoperative planning for implant removal in hip revision surgery cannot be separated from preoperative planning for hip reconstruction and remains a critical step. Planning for implant removal should respect the previous approaches employed and resultant surgical scars while focusing on selection of the appropriate approach to the hip, including the requirement for an extensile exposure or osteotomy, and choice of the appropriate instruments required to remove failed components. Planning must therefore consider decisions made at the primary procedure regarding the choice of implant design and the method of fixation employed, how the primary procedure was approached and how well it was performed, the host response to the primary implant, and the cause of implant failure.

Thus, relevant documentation and background information from the primary procedure, including implant labels showing the manufacturer, brand, size, and catalogue number of the components, need to be available. The function of the liner locking mechanism of an uncemented component should be understood and specialized tools for removal of the liner made available. The correct screwdriver for screw removal and other specialized tools for implant removal, including broken screws, should also be at hand. On the femoral side, if a cemented stem was precoated with methacrylate, removal may be significantly more challenging and femoral osteotomy may be required. The distal extent of any porous coating and the point at which any changes in stem geometry occur (i.e., where the metaphyseal taper meets the cylindrical distal stem) should also be recorded and accurately templated.

Up-to-date and previous (serial) plain radiographs of the hip (if available) should include an anteroposterior (AP) view of the pelvis, a centered AP view of the hip and femur, and a lateral radiograph of the involved hip of sufficient length. Accurate and easily verifiable standardized templating markers should be clearly visible to permit precise measurement and sizing. Views of the distal femur up to and including the knee joint should also be considered mandatory. Judet views (45-degree paired obliques) allow assessment of the integrity of the anterior and posterior columns and may improve the assessment of the extent of any osteolytic lesions. Vascular contrast studies may be indicated if there is concern that the iliac vessels may be damaged during removal of the acetabular component, which are often closer to the operative field than initially appreciated. If the vessels lie between the implant and the bone, a retroperitoneal approach to the socket may be favored. An adequate picture of the distal extent and distribution of any femoral cement mantle guides the direction of osteotomes, chisels, and other cement-removal instruments at the time of revision surgery. A good-quality lateral view is particularly useful in this regard. Magnetic resonance imaging (MRI) can demonstrate cement that does not contain radiopaque barium, and a computed tomography (CT) scan can provide a more accurate picture of 3-dimensional bone loss. The contemporary criteria for the radiographic determination of loosening of cemented and uncemented components have been published elsewhere and are beyond the scope of this chapter.

Preparation for an extensile exposure, osteotomy, or cortical window should be done preoperatively and all suitable instruments made available. The templated length of an extended trochanteric osteotomy (ETO) measured on the AP radiograph should ensure that any broken stem fragments, femoral stem porous coating, or retained cement can be readily accessed from reliable and reproducible landmarks that can be verified intraoperatively. Preoperative planning for implant removal cannot be separated from planning for femoral reconstruction. The templated femoral stem length should bypass the distal extent of any osteotomy by a suitable distance, usually said to be a minimum of 2 diaphyseal diameters, ideally preserving isthmic fit. Optimal surgical care will also include preoperative planning for a range of contingency options should intraoperative circumstances dictate a deviation from the initial plan.

It is usually very helpful to have available the specific matched (proprietary) extractor for the particular in situ stem or for part of a stem (in the case of modular stems or a modular centralizer attached distally to an uncemented stem). If unfamiliar with a particular stem design, it is prudent for the surgeon to directly contact the manufacturer/supplier to obtain any specific extraction instructions and to make sure that any required instruments are made available at the time of surgery.

Description of Techniques

With a clear understanding of the indications and after a preoperative plan has been formulated, the surgical approach, acetabular implant removal, and femoral implant removal can be considered.