Component Removal 

 

 

INDICATIONS/CONTRAINDICATIONS

The most common reason for removal of well-fixed components in total hip arthroplasty (THA) is infection. Other important indications for component removal include malpositioned implants causing pain or instability, wear and osteolysis, and adverse local tissue reactions related to metal on metal hip systems where a monoblock cup or modular stem requires removal.

There are no contraindications to component removal. Removal of well-fixed implants, either cemented or uncemented, should be weighed against component retention. For the treatment of infection, the benefit is obvious; however, in other cases, the surgeon should carefully consider the effect of component removal and the likelihood of obtaining another well-fixed implant in the remaining bone. The potential challenges of removing a well-fixed component include bone loss, fracture, increased surgical time, and increased cost. Specifically, the surgeon should pay special attention to the remaining bone stock. On the acetabular side, the surgeon should note how medially the acetabular component was placed and the potential for medial wall perforation or pelvic discontinuity when attempting removal. On the femoral side, the challenge exists when removing well-fixed uncemented implants in the presence of very thin cortices. The surgeon should aim to retain well-fixed, well-positioned implants that allow for restoration or offset and leg lengths and stability with the use of modular components.

Well-fixed Femoral Components

Removal of a well-fixed femoral component may be required:

1. In the presence of infection

2. With instability secondary to femoral component malposition

3. If unable to obtain a stable implant or appropriate soft tissue tension using modular head extensions because of the new position of a revised acetabular component

4. In the presence of significant proximal femoral osteolysis and a well-fixed femoral component that has the potential for subsequent failure

5. If nonmodular femoral components are in place and the existing femoral head is small and does not allow placement of a bipolar device (i.e., construction of a tripolar)

6. When the damage of the trunnion or taper is so severe that placing a new femoral head would be unacceptable

7. In the presence of corrosion and adverse tissue reactions to modular neck implants

8. For exposure of the acetabulum in the case of a monoblock femoral component

A malpositioned (excessively anteverted or retroverted) femoral component that is causing instability almost always requires removal because it is difficult to compensate for this problem by other means. To determine whether a malrotated stem is the cause of instability, the surgeon must determine intraoperatively both the version of the stem and its combined version with the acetabulum. The surgeon should also consider the modularity of the system already in place when deciding to revise a well-fixed femoral component. In

addition, in cases where both the acetabular and femoral components are malpositioned, it might be easier to revise the well-fixed acetabular component before attempting removal of the well-fixed femoral component.

A well-fixed nonmodular component occasionally presents problems for the hip surgeon. For one, nonmodular heads cannot be changed and may limit the ability to adjust the length and offset

 

 

necessary to create a stable construct. This difficulty can be somewhat overcome with the use of

specialized liners (lipped, oblique, offset, eccentric) or if the head allows for the placement of a bipolar component (to create a tripolar design). Secondly, in the absence of the ability to exchange parts, significant damage to the taper is an indication to remove a well-fixed component as it may adversely affect the new femoral head.

Modular technology provides greater flexibility when dealing with a well-fixed femoral stem if it is in acceptable position; however, there are still circumstances in which the surgeon may still choose to revise the component. One such circumstance is when a larger diameter femoral head (greater than or equal to 36 mm) is favored due to a lower risk of dislocation and may not be compatible with the present taper. In these cases, the surgeon may consider using a tripolar construct to provide a large-diameter articulation (Fig. 22-1).

Well-fixed femoral components may require revision in the presence of adverse local soft tissue reactions. These can occur secondary to corrosion of a cobalt-chromium femoral head on a titanium stem or from the taper body junction of a titanium femoral component with a cobalt-chromium modular neck as seen in Figure 22-2.

 

 

 

FIGURE 22-1 Tripolar articulation.

 

 

 

FIGURE 22-2 Corrosion of trunnionosis associated with modular neck design.

Well-fixed Acetabular Components

Much like on the femoral side, the decision to retain or replace a well-fixed acetabular component requires careful consideration of the trade-offs in construct stability.

Several series have demonstrated that cemented all-polyethylene acetabular components in good position can be retained without substantially increasing the subsequent revision rate; however, a majority of surgeons opt to replace these components during revision surgery (4). The reasons for this decision are likely twofold. For one, retaining the cup limits the ability to upsize the femoral head diameter. Secondly, these cemented components can generally be removed efficiently and with minimal disruption to the surrounding osseous structures.

Removal of the well-fixed acetabular component should be considered when:

1. There is presence of infection.

2. There is metal on metal failure in a hip resurfacing or THA and the monoblock cup requires removal.

    

    

    

3. There is a malpositioned acetabular component leading to the following:

   1. Instability

   2. Iliopsoas impingement (Fig. 22-3)

   3. Excessive polyethylene wear

   4. Ceramic liner fractures or squeaking

4. Revision is required secondary to osteolysis, bearing wear or femoral component loosening, and the acetabular component may not accommodate (cementing or locking) a polyethylene insert and use of a larger femoral head (uncommon today).

5. Severe osteolysis is present, and leaving the cup may risk subsequent failure and revision. This is especially important in first-generation uncemented cups with poor track records.

The first consideration in these cases is component position. Components that are malpositioned (version or inclination) should be removed as they are associated with a higher rate of instability and wear and ultimately component loosening (5,6,7). While component inclination can be accurately determined utilizing standard AP radiographs of the hip, measurement of acetabular version from preoperative radiographs can be more challenging and less consistent. Preoperative CT remains the gold standard for confirmation of suspected implant malposition; however, recent studies utilizing computer-based 2D/3D reconstruction techniques performed on radiographs alone may provide a good alternative (8,9,10,11). The next most important factor to consider is the availability of replacement liners for the implanted cup. Finding a matched liner can be problematic with older style implants. A mismatched liner can be cemented into a well-fixed cup if necessary although this may not be possible with small-diameter, shallow, or thick-walled acetabular cups (12,13). Also important to consider is whether the implanted cup has any known design problems. Early cups with noncongruent polyethylene designs or known locking mechanism shortcomings have been associated with significant backside wear, osteolysis, and early failure (14). In these cases, it may be advisable to proceed with cementing in a new liner or cup revision. Cups with a documented history of poor intermediate- or long-term survival (such as some first-generation HA cups) should also be considered for revision.

If significant osteolysis is present, this further complicates the decision to retain or remove a well-fixed uncemented cup. Although such cups can be easily removed with modern techniques, the remaining bone may have large segmental defects that can make subsequent reconstruction very difficult. Research from the Rush and the Mayo groups demonstrates good results with retention of well-fixed cups in the presence

of significant periacetabular osteolysis. In situations where removal of the cup is critical to construct stability,

good results may be obtained with cup retention and bone grafting with the use of the “trapdoor” technique (15,16). In this technique, a rectangular window is made in the bone approximately 2 cm superior to the retained component in order to create access to debride and bone graft lesions both anterior and posterior to the cup. Following completion of grafting, the rectangular cortical segment can be replaced and then rotated 90 degrees to help contain the graft material.

 

FIGURE 22-3 Iliopsoas impingement with under-anteverted cup.

 

 

 

PREOPERATIVE PLANNING

Preoperative planning is vital to the success of a revision operation around the hip. Specifically, identification of implanted components by obtaining operative reports and implant stickers is critical. It is often the case that manufacturers have specific tools to aid the surgeon in removal of implants safely and with minimal loss of periacetabular bone stock. Along these lines, certain implants, by virtue of their geometry or surface coating, may require specialized techniques for removal, for example, extensively coated stems and cemented implants that are precoated with PMMA; both may be removed most easily with extended greater trochanteric osteotomies.

Finally, as discussed previously, identification of components with known problems is important when deciding to remove or retain the implant.

 

 

 

SURGERY

Positioning, Draping, Approach

Patient positioning will depend on the approach utilized. The author's preference is for a posterior approach that allows access to the posterior column and is compatible with either a Wagner or laterally-based extended trochanteric osteotomy.

Removal of the Femoral Head

Removal of a modular femoral head facilitates acetabular exposure, particularly in cases in which the femoral component will be retained. Translation of the femur anteriorly when performing a posterior approach requires release of the anterior capsule and creation of a soft tissue pocket where the trunnion can rest. Care should be taken at the time of placing retractors into osteolytic or damaged periacetabular bone because damage can occur when attempting to retract the femoral component away in order to visualize the acetabular component.

Removal of Cemented Acetabular Components

Cemented all-polyethylene acetabular components typically are removed without difficulty using a combination of a high-speed burr and osteotomes. The Exeter group has described a cement-withincement technique similar to that used for revision of femoral components when the cement mantle is pristine. Removal of a loose cemented acetabular component usually is fairly easy. It is uncommon in North America to have to remove a well-fixed

cemented acetabular component. Cement that is penetrating past the medial wall of the acetabulum, should be removed with great caution and only if clinically necessary. This cement may be adherent to intrapelvic structures and can cause grievous injury if removed. A preoperative CT angiogram may be helpful to identify the relevant anatomy. In some cases, a retroperitoneal approach to remove retained cement may be necessary.

Cement in bone holes may be removed easily utilizing a Steinmann pin placed into the center of the lughole, and the rotational force will result in subsequent extraction.

Removal of Well-fixed Cementless Acetabular Components

The first step of removing cementless acetabular components is removing the polyethylene liner (Fig. 22-4). Contemporary implants may feature specialized adaptations of the locking mechanism that allow removal with standard OR instruments; however, many times, this approach yields disappointing results. When dealing with more traditional designs, the locking mechanism usually can be disengaged by placing a 6.5-mm screw or tap through a predrilled hole in the periphery of liner. When the screw or tap comes into contact with the metal acetabular component, it will push out the PE liner as seen in Figure 22-4.

The next step is removal of any screws present in the cup. If the implant system is known, then the appropriate screwdriver should be available in the operating room. If the screws are stripped or

 

 

otherwise damaged, it may be necessary to use a pencil-tipped burr at the cup-screw interface to burr the screw head and surrounding metal to free the cup. Retained screws can then be retrieved with a standard broken screw set.

 

 

 

 

FIGURE 22-4 Polyethylene liner removal technique utilizing screw through polyethylene.

 

Removal of the cup itself may be accomplished by placing a series of thin curved osteotomes around the edge of the cup and gently undermining the back of the shell circumferentially. While effective, this technique can result in a more than ideal bone loss, especially when dealing with osteopenic patient or patients with large segmental defects (17). Alternatively, several companies make size-specific tools for removal of cups that help minimize bone loss. An example can be seen in Figure 22-5. These tools feature blades contoured to the cup radius that can precisely disrupt the bone-implant interface. Studies by Preiss et al. (18) indicate lower bone volume loss with the use of these instruments. This technique is very reliable in the authors' hands and provides a valuable addition to the revision hip armamentarium.

The authors prefer the following steps for removal of a well-fixed acetabular component:

 

1. Removal of polyethylene with screw push-out technique.

2. Removal of screws.

3. Pencil-tipped burr around periphery of cup to expose the implant-bone interface.

4. Replacement of polyethylene with same or trial if previous polyethylene insert is an elevated liner.

5. Use of shorter Explant blade around the periphery of the cup, four quadrant pass (make sure you have sharp blades).

6. Use of longer Explant blade in the depth of the cup, four quadrant pass.

7. Center the femoral head of the Explain device in the polyethylene then turn the blade to unite the four previous deep passes. If the quality of the bone is good, it may require several passes before the blade can get around the implant. If the surgeon attempts to turn the blade without having the femoral head centered within the polyethylene or if (alternatively) the blade is used without a head, the blade will bend and will change the diameter of the blade risking excess bone removal.

8. Once the cup is loose, the cup usually comes out by hand.

 

 

 

 

FIGURE 22-5 “Explant” device.

 

Removal of Cemented Femoral Components

The difficulty of removing cemented stems can vary considerably depending on the type of implant and operative approach. Careful preoperative planning with a focus on avoiding potential complications maximizes the chance of a successful procedure.

Preoperative identification of the stem-type, fixation of the cement-implant and implant-cement interface is critical as it will determine instrumentation choice and whether or not a femoral osteotomy is likely to be required.

Polished implants generally can be removed without difficulty using a footed impactor. If the cement mantle is pristine, cementing a smaller diameter femoral component into the cement mantle may be an option in selected cases. If the cement mantle is not appropriate for a cement-within-cement technique, then the retained cement can then be removed either from the top of the femur or through an extended osteotomy in some cases.

Roughened or precoated cemented implants are significantly more difficult to remove and often require a trochanteric osteotomy prior to component removal if they are well fixed (19,20). An extended trochanteric osteotomy

 

 

is recommended for well-fixed rough-surface cemented implants in order to minimize femoral perforations and fractures and to aid in placement of distally fixed femoral revision components (the author's preferred type of

revision implant).

If the decision is made to not perform an extended greater trochanteric osteotomy (ETO), then the surgeon must avoid fracture of the greater trochanter (20). This risk can be reduced by ensuring complete removal of overhanging bone, soft tissue, and cement from the lateral aspect of the femur. A high-speed burr is often the most expeditious method of completing this task.

The risk of complications also increases when insufficient exposure is obtained prior to implant extraction. As mentioned previously, for well-fixed implants, an extended trochanteric osteotomy can be immeasurably helpful in gaining access to the stem. The length of the osteotomy should be planned to allow for 5 to 6 cm of press fit of an uncemented distally fixed stem distal to the osteotomy. Once the osteotomy is opened, cement can be removed in pieces with hand instruments. Generally, the stem can be removed safely with an impactor once the majority of exposed cement is removed. This will usually result in a portion of cement being retained distal to the osteotomy site.

The removal of cement distally can be approached in two ways: (a) a drill and tap technique or (b) with the use of ultrasonic tools. The drill and tap technique involves drilling a hole through the center of the cement column to a depth of about 1 cm, inserting a tap, and backslapping out a cylinder of cement. It is critical that the drill hole be centered in the cement mantle. This will be repeated until the entirety of the column is removed. Ultrasonic tools work by melting the cement mantle and allowing for it to be extracted in small pieces. The benefit of this technique is a decreased risk of fracture or perforation of the femoral shaft (21). Ultrasonic energy differentially affects materials based on density and thus provides immediate tactile and audible feedback when the operator utilizes the instrument on cortical bone instead of on cement. This further reduces the chances of fracture intraoperatively. There are complications inherent to the use of the ultrasonic technique as well—most notably, thermal necrosis of bone may be present in up to 10% of patients in some series (21,22). The incidence of complications can be decreased with use of proper technique. Techniques for removal are operator dependent, but an effective method is piercing the mantle to a depth of about 5 mm with ultrasonic energy and then allowing the disrupted cement to resolidify so that it can be removed with a slap hammer.

Removal of Proximally Coated, Cementless Femoral Components

Proximally coated stems are the most unpredictable in terms of removal difficulty. For this reason, it is critical to determine the exact make and model of the implanted stem. The large majority of these stems rely on in- or ongrowth surfaces proximally to provide ultimate fixation; however, depending on the model, there may be a variable amount of distal ongrowth present. Proximal fixation stems with bioreactive coatings (such as corundumized surface blasting) on the distal portion or even uncoated titanium stems may attain enough distal fixation to make removal of the implant from the top of the femur impossible. In these cases, it is advisable to use a good-length extended trochanteric osteotomy to facilitate safe removal (23).

 

 

Removal without an ETO (proximal fixation-only implant)

 

 

Clear the lateral shoulder.

 

 

Disrupt the cement mantle anteriorly, posteriorly, and laterally with a pencil-tipped burr. If present, remove the implant collar medially using a metal-cutting burr.

 

 

Use thin osteotomes to disrupt the proximal interface circumferentially. Backslap the implant using appropriate tools.

 

Removal with a posterior-based Paprosky-type ETO (distal fixation present) (see Fig. 22-6)

 

 

By all means, preserve soft tissue attachments on the fragment. The posterior border of the vastus lateralis

needs to be identified and retracted anteriorly. The location of the distal horizontal arm of the osteotomy should be identified, and the vastus laterlis should be elevated only in this location.

 

Perform the osteotomy from proximal to distal down the posterior border of the femoral bone. Proximally, the saw can be carried over the shoulder of the implant and distally over the lateral aspect of the femoral component. In cases of cemented stems, the osteotomy can be made with the saw and carried across the cement and anterior cortex. This is not possible when larger diameter stems are in situ, as trying to get around these implants with the saw may risk making the osteotomy fragment to small.

 

Make the distal cut with a high-speed burr as templated preoperatively (allowing for 5 to 6 cm of press fit, usually 12 cm from the tip of the trochanter) and extending laterally to encompass ⅓ the diameter of the proximal femoral shaft.

 

Use a Gigli saw around the medial portion of the stem to disrupt the medial interface.

 

Use a pencil-tipped burr to interrupt the ingrown surface around the nonosteotomized portion of bone and distal to the osteotomy.

 

Remove the implant with slap hammer that adapts to implant-specific instrumentation or a vice-grip extractor that is fastened to the proximal implant.

 

 

 

 

 

 

FIGURE 22-6 Wagner (solid line) and Paprosky style (dotted line) extended trochanteric osteotomies are drawn up in (1). Sequence of steps for Wagner osteotomy are shown in (2) to (6). Cable cerclage of osteotomy site (7). (By permission of Mayo Foundation for Medical Education and Research. All rights reserved.)

 

Removal of Extensively Coated, Cementless Femoral Components

Removal of an extensively coated femoral component presents a formidable problem to the revision hip surgeon. Patience and attention to detail are necessary to minimize risk of significant damage to the surrounding bone stock. For well-fixed implants, a generous extended trochanteric osteotomy is required for safe removal. Once the osteotomy is made, disrupt the interface anteriorly and posteriorly using a high-speed pencil-tipped burr. A Gigli saw can then be used to free the medial border of the stem. The stem then needs to be cut with a metal-cutting burr just proximal to the distal extent of the osteotomy. The proximal portion of the stem is removed as described above for a proximally porous-coated stem. Use trephines, ideally 0.5 mm larger than the stem diameter, to remove the distal portion of the component. This will usually require several trephines to accomplish as they will dull quickly when used on ingrowth surfaces. Irrigate liberally when using trephines to prevent thermal

 

 

necrosis to the surrounding bone. Use of fluoroscopy is very helpful when removing long curved stems in order to avoid perforation of the distal bone.

Removal of Well-fixed Tapered Fluted Stems

One of the only reasons to attempt removal of well-fixed tapered fluted implants is in the presence of infection. On most occasions, the proximal modular portion can be removed without difficulty, but there are instances where modular implants become cold-welded together. These titanium stems achieve excellent ongrowth to the distal femur. They are difficult to remove and their design makes it hard not to damage bone at the time of removal. Several important points are as follows: (a) The majority of these implants have a kink or bow below the modular junction that does not allow the use of a straight trephine, (b) the larger diameter below the junction tapers down to a smaller diameter and requires the use of a larger trephine that may risk perforating the femur as it is brought distally, and (c) these implants are commonly used in situations where there is already compromised bone; therefore, removing these implants risks significant further bone loss as the ongrowth is circumferential and into the flutes.

For the author, there is no easy way to remove these implants. The steps are the following:

 

1. Extended trochanteric osteotomy as described previously to below the level of the bend of the implant.

2. Removal of the proximal body.

3. Attachment of the proximal body extractor and attempt at removal.

4. Cutting the titanium stem below the implant bend.

5. Use of a 3.2-mm-long drill bit to drill within the flutes of the distal implant in a circumferential manner.

6. Use of a thin flexible osteotome around the stem or alternatively a trephine used under fluoroscopy to avoid femoral bone perforation.

7. Using a metal-cutting burr to make a slot into the superior aspect of the distal remaining portion.

8. Using a square tip impactor onto the slot to disimpact the distal portion.

9. If all attempts fail, performing a vertical episiotomy of the distal bone in order to obtain circumferential exposure of bone and removal. The vertical bony osteotomy can then be cabled or wired together.

    

   COMPLICATIONS

   The most common complications of component extraction are related to the damage or inappropriate removal of native bone stock. These complications can significantly compromise subsequent reconstruction.

   As discussed earlier in this chapter, the key to avoiding bone loss during removal of the acetabular component is ensuring that the entire bone-cup interface is disrupted prior to final implant removal. This is particularly relevant in patients with limited bone stock or osteopenia, in whom it is possible to fracture or avulse a large segment of bone. In extreme cases, it is even possible to produce a complete pelvic discontinuity during cup removal. Unfortunately, even with the most careful technique, some amount of periacetabular bone loss is likely unavoidable with ingrown acetabular cups, but for standard acetabular component removal, placement of an acetabular component 4 mm larger than that removed is common.

   Contained cavitary defects may be filled with cancellous bone graft, whereas larger areas of segmental bone loss will likely require structural grafting or highly porous metal augments for reconstruction. In the rare case that a pelvic discontinuity is created, a treatment strategy is individualized.

   Fracture and bone loss are also sequelae of femoral component removal and most commonly include

    

   fracture of the greater trochanter or cortical perforation. Much as is the case for the acetabular side, the key to avoiding these complications is clearing a path for the implant prior to removal and disruption of the available bone-implant interface. Fracture of the trochanter, if not addressed or if it results in nonunion with proximal migration, will result in a Trendelenburg gait and decreased patient satisfaction. These fractures should be treated with a trochanteric claw device or wiring of the trochanter if needed, but the results of this approach is not always optimal (24). Cortical perforation happens most commonly during removal of distal cement. The incidence may be reduced by using correct technique and ultrasonic instruments as discussed previously. Intraoperative fluoroscopy or radiographs will be invaluable in cases of suspected perforation and should be carefully inspected for extension of a fracture line. If a cortical perforation is identified, the area must be exposed to delineate the extent of damage. A femoral component long enough to bypass the defect by two cortical diameters should be implanted to prevent the creation of a stress riser at the level of the osteotomy. A strut allograft may also be placed over the defect and held in place with cables.

    

    

    

    

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