Revision hip arthroplasty begins with extrication of the retained components before surgical reconstruction. Although the removal of loose implants may be relatively straightforward, the removal of well-fixed implants can be time consuming and extremely damaging to host bone. The diversity of implants used necessitates an equally diverse approach to component removal. Preoperative planning as well as the understanding of the basic principles and techniques used for prosthesis removal are imperative before undertaking revision hip arthroplasty. This chapter highlights the operative techniques and tools used to extract acetabular components, femoral components, and cement in an expeditious and bone-preserving manner.
Acetabular revision indications include component malposition, mechanical loosening, significant polyethylene damage, hip instability after isolated femoral revision, and infection.
Femoral revision indications include aseptic loosening, severe osteolysis, malposition, severe thigh pain, infection, excessive damage to the Morse taper, inadequate exposure during acetabular revision, instability after revision of the acetabular component with inadequate neck length or offset options, and monoblock stem mismatch of the femoral head or damage to a monoblock stem femoral head.
Well-fixed implants in proper orientation should not be removed if at all possible.
Careful preoperative planning, technical expertise, patience, and a stepwise logical progression will result in safe and successful removal of components and cement while preventing complications.
Adequate exposure of the implant to be removed is paramount.
Careful removal of tissue, bone, or cement from the lateral shoulder region of the femoral stem is crucial before extrication to prevent fracture of the greater trochanter.
Extended proximal femoral osteotomy is useful when a well-bonded distal cement-bone interface, varus or valgus remodeling of the proximal femur, cement extending down the canal past the apex of the anterior bow of the femur are present and in removal of well-fixed, noncemented implants.
With today’s aging population and the trend for younger patients to undergo hip arthroplasty because of the proposed increased longevity of implants, the need for revision arthroplasty will continue to grow. Component and cement removal in revision hip arthroplasty can be a grueling task, especially if the prosthesis is well fixed. The surgeon must be familiar and comfortable with the basic techniques and principles of implant removal. Expeditious removal of cement and acetabular and femoral components with bone-preserving techniques is of paramount importance to reduce bone loss and complications and preserve hip function. This chapter addresses an array of techniques used to remove femoral and acetabular prostheses and retained cement.
ACETABULAR COMPONENT REMOVAL
Indications and Contraindications
The indications for acetabular revision include malposition, mechanical loosening, significant polyethylene damage, hip instability after isolated femoral revision, and infection. Well-fixed implants in proper orientation should not be removed if at all possible. Acetabular shells that are stable and in good position with severe retroacetabular osteolysis may be removed. However, the defect left may portend a complicated acetabular reconstruction. Consideration should be given to grafting the acetabular defect through a “trapdoor” in the ilium or holes in the shell with retention of the component.
A simple exchange of the polyethylene liner should be considered in osteointegrated cups in a suitable position. Preoperative planning is important to determine the type and size of acetabular shell present. This will determine the available polyethylene liners and head sizes that can be used during the reconstruction. Moreover, the locking mechanism may require replacement after polyethylene extraction.
Changing the acetabular liner may be relatively straightforward. Some manufacturers have tools specifically designed for removal and insertion. If no tools are available, a liner extractor can be used ( Fig. 32-1 ). Drilling a 3.2-mm screw hole eccentrically in the polyethylene liner and using a 6.5 mm × 40 mm cancellous screw also is effective in removing the worn implant liner. As the screw is advanced, the polyethylene liner and shell are separated when the screw engages the metal shell. If a new polyethylene liner is not available or a poor or damaged locking mechanism is of concern, a new polyethylene shell can be cemented into a well-fixed cup. Several studies suggest that this technique is as strong as or stronger than most commercial locking mechanisms.
A comparison of the biomechanical strength of a cemented acetabular liner into a metal shell versus a standard modular component revealed the cemented construct failed at or greater than the torque required for failure by the standard modular component. This was confirmed by Meldrum and Hollis, who determined that the cement-liner interface failed at significantly higher push-out and lever-out strengths than did modular controls. Several variables have been proposed to improve the strength of this construct, including scored liners, grooved liners, type of grooves, and scored acetabular shells. In a study by Bonner et al, all undersized cemented liners, regardless of these variables, were found to be stronger than their modular controls. The optimal cement mantle thickness was determined to be 2 mm. Short-term results of up to 2 years have been promising; however, the long-term durability of this technique is not known. Over the past few years, several companies have manufactured liners designed to be cemented in revision hip arthroplasty.
Cemented Component Removal
The removal of a cemented, all-polyethylene acetabular component requires adequate circumferential exposure of the bone-cement interface. This may require removal of host bone to widen the aperture of the acetabulum that may have narrowed from remodeling or heterotopic ossification. A high-speed burr, rongeur, or small osteotomes may be used to accomplish this. Once the acetabulum is adequately exposed, extraction is relatively uncomplicated.
Drilling a ¼-inch hole in the central aspect of the polyethylene cup and inserting a threaded acetabular extractor into the hole may assist in extraction of grossly loose components. This may occur easily with little force. If the component is not easily removed by using this technique, both the cup-cement and the cement-bone interface can be independently loosened to facilitate implant removal.
The peripheral margin of the cup-cement interface is disrupted with the use of a straight osteotome or a high-speed burr. A curved osteotome is then inserted in a circumferential manner in an attempt to free the cemented polyethylene cup. The Moreland acetabular gouge (DePuy, Warsaw, Ind.) may be used to loosen the cup-cement interface, assisting in the extraction process ( Fig. 32-2 ). The Explant system (Zimmer, Warsaw, Ind.) also may be used to disrupt this polyethylene-cement interface; however, it was designed to remove noncemented acetabular components (discussed below).
Once the component is loose, a large polyethylene grasper can be used to remove the implant. Gentle side-to-side and twisting maneuvers are recommended while attempting to free the component. Levering and prying are discouraged because this approach may result in fracture and acetabular bone destruction. If these techniques are unsuccessful an acetabular reamer may be used to ream the component away to the cement interface. An alternate method includes sectioning of the polyethylene with a high-speed burr to ease its removal.
After cup removal, the remaining cement may be removed under direct vision with the use of osteotomes, curettes, or a high-speed burr. Sectioning the remaining cement facilitates cement removal and decreases the amount of host bone injury. Cement anchoring holes usually are present within the pubis, ischium, and ilium. Removal of these may be needed to allow implantation of the new acetabular shell. The risk of bone loss and fracture are especially present when multiple cement anchoring holes have been used; thus care should be exercised during removal.
Intrapelvic cement is frequently left in situ unless the patient has unremitting symptoms. The intrapelvic cement fragments typically are larger than their respective acetabular defect. If required, the intrapelvic cement may be removed through a separate ilioinguinal incision. More recently, Smith and Eyres describe the safe removal of massive intrapelvic cement with ultrasonic instruments.
Cementless Component Removal
As previously described for cemented acetabular removal, the removal of a cementless acetabular component begins with adequate exposure of the implant-bone interface. If the component is modular, removal of the polyethylene liner provides better visualization of the surrounding metal component margins. Nonmodular acetabular components must be addressed with the polyethylene in place. If screws are present, preoperative planning should have determined the appropriate screwdriver necessary. If a screw was stripped from the previous insertion or during attempted removal, or the appropriate screwdrivers are not available, a high-speed metal cutting burr may be used to remove the screw head. A screw removal set can then be used to remove the shanks of the screws after the acetabular shell has been removed. Broken screws that do not interfere with new component implantation may be left in situ.
Once the polyethylene liner and screws have been removed and the outer confines of the metal shell are clearly visualized, extraction can be undertaken. Before the introduction of the Explant system, removal of a well-fixed acetabular component was carried out with high-speed burrs, straight and curved osteotomes, and acetabular gouges. Components close to Kohler’s line were frequently sectioned and sequentially removed to prevent disruption of the bony architecture. Alternatively, Daum and Calhoun have described the use of an angled punch against the superior aspect of the acetabular component through a keyhole made in the bone. This technique uses tensile forces to dislodge the bone-implant interface. No complications were reported with this technique. However, this technique does require removal of superior acetabular host bone.
More recently the Explant system has facilitated the removal of acetabular shells in an expedient fashion with minimal bone loss ( Fig. 32-3 ). Femoral head sizes (22 mm, 26 mm, 28 mm, 32 mm) are available fixed at a specific distance from a 2-mm thick blade. If no screws are present, the polyethylene is left in place and the femoral head of the explant is inserted into the polyethylene liner and a short, stout blade penetrates the dense peripheral bone, thus creating a channel. Once the starter blade has disrupted the superficial bone-implant interface a thin, full-radius long blade is used to complete the removal process. If screws are present they may be removed before use of the Explant and a trial liner placed to allow centering of the femoral head within the acetabular cup. Once the acetabular component is circumferentially loosened, the cup can be removed with a large acetabular grasper.
The use of the Explant system in the setting of eccentric polyethylene wear or in a polyethylene liner with an inappropriate head size can cause excessive bone loss and should be avoided. Replacing the worn liner or the inappropriate head size liner with a trial liner of appropriate head size before the use of the Explant can prevent this undue event. Spiked components may require the removal of the metal spikes with a high-speed metal burr from inside the well-fixed shell before use of the Explant tool to allow complete disruption of the bone-implant interface. However, most spikes are not porous coated and remove little bone excess with cup removal. Targeting templates have been designed for the AML/Trilock and ACS (DePuy) acetabular components with spike fixation. Mitchell et al used the Explant system in 31 well-fixed, cementless, acetabular components. The time taken for cup removal did not exceed 5 minutes in any case. Bone loss was minimal and no complications were reported.
FEMORAL COMPONENT EXTRACTION
Improved femoral cementing techniques and the demand to remove implants for reasons other than aseptic loosening have added to the difficulty of femoral revision. Preoperative radiographs are instrumental in determining whether the femoral component is well fixed. In cementless femoral components the Engh classification is extremely useful in determining the stability of the implant. Cemented implants have a system to grade implant stability, as described by Gruen et al and Harris et al. Extraction of a well-fixed cemented or cementless femoral component can be extremely challenging. This endeavor can become time consuming and may be quite damaging to the remaining host bone. Removal of loose components typically is less arduous and destructive to the host bone as long as appropriate instruments and techniques are used.
Indications and Contraindications
Indications for the removal of cemented and cementless femoral components include aseptic loosening, severe femoral osteolysis, malposition, severe thigh pain, infection, excessive damage to the Morse taper, inadequate exposure during acetabular revision, instability after revision of the acetabular component with inadequate neck length or offset options, and monoblock stem mismatch of the femoral head or damage to a monoblock stem femoral head. Removal of well-fixed, well-functioning implants usually is contraindicated. On occasion, manual extraction of a loose femoral component is all that is required. However, in the majority of cases the techniques described are necessary to extract a femoral component during revision total hip arthroplasty.
Isolated Femoral Head/Neck Exchange
In cases in which acetabular revision is indicated and a modular femoral component is well fixed and in an appropriate position, an isolated head/neck exchange should be considered. Indications for exchange include the need for adequate exposure, damage to the current femoral head/neck, need to change neck length or offset to equalize leg length or balance the soft tissues around the hip, or the need to change femoral head size to maximize stability or polyethylene thickness. A retrograde blow with a mallet on a disimpaction tool placed at the base of the femoral head usually can accomplish this. Identification of the femoral component type and manufacturer is necessary preoperatively so that the appropriate replacement head/neck is available.
Cemented Femoral Component Removal
In a majority of cases the removal of cemented femoral components includes the disruption of the implant-cement interface, removal of the component, and subsequent extraction of retained cement. As described for acetabular component removal, the entire proximal margin of the femoral component must first be adequately visualized before attempted removal. This is routinely performed with the use of a high-speed pencil-tip burr or an osteotome. Careful removal of tissue, bone, or cement from the lateral shoulder region of the stem is crucial before extrication to prevent fracture of the greater trochanter. A loose component that has subsided may have bone overgrowth in the vicinity of the collar. This bone must be removed before implant withdrawal.
Polished stems or grossly loose stems may be removed with a retrograde blow with a tamp, a nonmodular femoral component extractor, or a universal extraction device. A carbide-tipped burr may be used to notch the femoral neck to allow the universal extraction device or nonmodular extraction device to attach to the prosthesis securely.
Well-fixed, textured, porous coated, and precoat components commonly require that the implant-cement interface be disrupted before disimpaction. Flexible osteotomes may be used; however, they run the risk of femoral fracture or perforation. A high-speed, thin, pencil-tip burr is extremely effective for this task and reduces the risk of fracture during disruption of the implant-cement interface. A thin layer of cement is removed at the cement-prosthesis interface circumferentially. If a collar impedes this process medially, a carbide-tipped metal cutting bur can be used to remove the collar and allow access to the medial implant surface.
Highly textured, well-fixed, cemented femoral stems often are not easily removed. The previously described techniques only afford access to the metaphyseal region of the stem. If the prosthesis-cement enhancement extends beyond the metaphysis an extended proximal femoral osteotomy may be required. Likewise, an extended proximal femoral osteotomy is useful in the presence of a well-bonded distal cement-bone interface, varus or valgus remodeling of the proximal femur, and if cement extends down the canal past the apex of the anterior bow of the femur ( Fig. 32-4 ).