CHAPTER OUTLINE
Preoperative Planning 304
Instrumentation 304
Segmental Cement Extraction Systems 307
Ultrasonic Cement Removal Devices 307
Surgical Techniques 309
Cement fixation in total hip replacement is widely performed and if carried out well leads to excellent and durable results. Cementing techniques that improve the interlock between the cement and bone result in increased radiographic survivorship in both acetabular and femoral fixation. However, failure does occur and is usually a result of aseptic loosening because of particulate polyethylene debris and its associated inflammatory response and bone loss. With better cementation methods, removal of cement can be difficult in such situations, especially in the presence of infection when all the cement must be removed. Cement removal techniques are required that allow for safe extraction with no iatrogenic bone loss so that later reconstruction is not compromised. This can be a challenging task, and the surgeon should be acquainted with all the surgical techniques required to do this safely without further jeopardizing bone integrity. Preoperative planning is paramount, with provision made for any adverse intraoperative events. An intimate knowledge of the components to be removed will further aide the extraction process and final reconstruction. Preoperative planning, the instrumentation required, and the surgical techniques for safe removal of components and cement are discussed in this chapter.
PREOPERATIVE PLANNING
The key to success in revision hip replacement surgery includes a thorough understanding of the indications to remove components, careful preoperative planning, and the choice of the appropriate surgical approach. The removal of implants and cement involves several phases, including achievement of adequate exposure; identification of components and their safe removal; and visualization of the cement-implant interface and piecemeal removal of the cement.
Optimal exposure is mandatory to allow safe access to components and the use of specialized cement extraction techniques. Appropriate instrumentation is required and may include hand-held instruments, high-speed drills and burs, segmental extraction systems, and ultrasonic devices ( Table 41-1 ). The use of fluoroscopy is helpful and can aid in prevention of inadvertent injury. Lithotripsy and lasers have also been employed to weaken the bone-cement interface, allowing straightforward cement removal, but we are not aware of the use of either technique in common orthopedic practice.
| Component-specific removal devices |
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| Hand-held cement extraction devices |
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| Ultrasonic cement removal devices |
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INSTRUMENTATION
Component-Specific Removal Devices
Components must be safely extracted before the cement can be removed, unless they are roughened or precoated. In those circumstances it is often impossible to remove the implant first, particularly when well fixed as in the treatment of infection. The femur must be opened through an extended femoral osteotomy, and the implant can then be mechanically debonded and removed. If the implant is grossly loose, it can be removed with its intact cement mantle. However, the cement is usually left in situ and must be removed separately.
Femoral Component
The femoral component is usually dealt with first to a help in acetabular exposure. If the system has a modular head, this can be removed with a punch or a holder with wedges that when pushed in disengage the head. If an isolated acetabular revision is anticipated, then the Morse taper should be protected.
The femoral component can now be removed using extraction devices available from the manufacturer or universal extractors. These devices include J-shaped hooks that engage holes specially designed in the shoulder of the prosthesis; closed loop devices that engage the collar of the component; and clamps that tighten on screw engagement and then attach to a slotted slap hammer ( Fig. 41-1 ). Many commercially available cement and implant removal systems have a universal extractor that engages the Morse taper to allow the implant to be tapped out. It is important to bear in mind that if the stem has a collar and has subsided with surrounding bone, then this must be cleared or fracture of the calcar may ensue. If there is an overriding greater trochanter, this must be debulked or an avulsion may occur on extraction, especially if the prosthesis has a broad shoulder. Finally, if there is cement over the shoulder of the implant, then the cement must be removed before the implant can be safely extracted.
Acetabular Component
On the acetabular side, various systems with claws can be used to engage the cup from the inside and then to distract the cup ( Fig. 41-2 ). If the interface is well bonded, then the polyethylene liner can be reamed using acetabular reamers until the cement mantle is reached. Attention is then turned to removing the remaining cement. The Explant system (Zimmer, Warsaw, IN) is used to remove uncemented shells. This system can be applied to cemented cups and can be used to extract the polyethylene cup. It consists of short and long curved blades that follow the contour of the acetabular cup. The device is centered within the polyethylene liner or a polyethylene liner trial, and the blades are rotated around a handle that allows rapid and complete loosening of the shell with minimal damage to the underlying bone. A mallet is used to engage the short blade into the interface; the short blade is then rotated 360 degrees, after which a long blade is used. However, wear can lead to eccentric centering of the device and with variability in the cement mantle may lead to inadvertent bone loss where the cement mantle is thin. Different femoral heads sizes are available for centering, including 22, 26, 28, and 32 mm. Blades of different diameters, from 42 to 72 mm, are also available ( Fig. 41-3 ).
Hand-Held Tools
Polymethylmethacrylate bone cement has mechanical properties that allow it to withstand forces several times body weight. It is much weaker than cortical bone and is weaker in tension than in compression. The various revision instruments rely on disrupting this interface once the implant has been removed without compromising the integrity of the underlying bone.
Femur
In the femur the instruments are used in the plane along the longitudinal axis of the bone, using T or V splitters or offset circular chisels without entering the cortical bone ( Fig. 41-4 ). These splitters have to be used with extreme caution if the cement mantle is thick. In such situations we prefer to thin the cement mantle to a manageable thickness first with a high-speed bur and then to use the splitters. The T splitter is ideally suited to disrupting a well-bonded cement-bone interface. The vertical limb of the T acts as a cutting chisel to break the cement, and the horizontal limb of the T acts as a shovel to scoop the underlying broken cement. As already stated, this is not effective if the cement mantle is thick. The V splitter is useful for creating stress longitudinal fractures in the cement to allow piecemeal removal of the cement. The debris is removed with gouges so that third body particles are not dispersed, and irrigation is used to prevent excess heat buildup when high-speed burs are used. All instruments have extended shafts so that more distal diaphyseal cement can be removed, and this is aided by the use of long-handled fluorescent lights and grasping forceps. Once the cement has been removed, the distal cement restrictor or plug can be drilled and extracted with special taps ( Fig. 41-5 ). For this to be accomplished, the medullary canal is sized and an appropriately sized drill guide that fills the medullary canal is used. A drill is then inserted centrally through the guide into the medullary canal to allow central drilling of the cement. It must be noted that this is not a foolproof method, and the surgeon must exercise extreme caution to make sure that the drilling of the plug remains central to avoid a cortical perforation. For a thick cement column before the plug, it is best to repeat this steps multiple times rather than risk an uncontrolled perforation. Once the plug has been drilled, an appropriately sized tap is threaded into the hole, and with reverse tapping the cement or plastic fragment captured by the tap is removed in a retrograde fashion. Any remnants of cement or restrictor can be removed with reverse cutting hooks, which come in different sizes ( Fig. 41-6 ). An olive-tipped guidewire can be used as a feeler to make sure the cortex has not been breached.
