Loosening

Some revisions will be necessary because the implants have loosened. When they were first put in, the large metal and plastic implants of joint replacement were placed with the intention of staying fixed for a long time. They were either cemented into position or bone was expected to grow into the surface of the implant. In either case, the implant was firmly fixed to bone.

However, the friction of the joint surfaces rubbing against each other wears away the surfaces of the implant, creating tiny particles. These particles accumulate around the joint. In a process called aseptic, or noninfected, loosening, the bonds of the implant to the bone are destroyed by the body's attempts to digest the wear particles. When the prosthesis becomes loose, the patient may experience pain, deformity, or instability. In addition, the process of digestion, or lysis, of wear particles also digests normal bone. This can weaken or even fracture the bone, and jeopardize the success of the revision surgery. In this event, surgery will also address the bone stock deficiencies. Aseptic loosening is the most common mode of failure of hip and knee implants.

Infection

Infection is another physiologic cause of implant failure. The large foreign metal and plastic implants can serve as a surface for bacteria to latch onto. In addition, the tissue that has been previously operated on has an altered blood supply, which may not be adequate to fight infection. Even if the implants remain well-fixed, the pain, swelling, and drainage often make revision necessary. Lastly, the chronic fight against an infection can weaken the patient and endanger their life. Realistic risk of infection with current surgical techniques and antibiotic regimens is about 0.5%. 4 Jiranek WA, Hanssen AD, Greenwald AS: Antibiotic-Loaded Bone Cement For Infection Prophylaxis in Total Joint Replacement. J Bone Joint Surg Am 2006, 88:2487-2500

Dislocation

Dislocation is yet another mode of failure of joint replacement surgery.5 Shinar AA, Harris WH: Bulk structural autogenous grafts and allografts for reconstruction of the acetabulum in total hip arthroplasty. A sixteen-year average follow-up. J Bone Joint Surg Am 1997; 79:159-168 (Dislocation is a sudden popping out or migration of the implant from its normal position.) It is more commonly a problem of hips rather than knees. The rate of dislocation after hip replacement ranges from zero to 10%, but averages about one in 50 patients. Some of these patients will experience multiple dislocations and require revision. The dislocation may be caused by loosening, inadequate soft tissues, bony or scar tissue impingement, incompatible component position, neurologic factors (such as neuropathy or Parkinsonism), or patient noncompliance.

Patient-Related Factors

Younger and more active patients have a higher rate of revision. 6 Huo MH, Parvizi J, Gilbert NF. What's New in Hip Arthroplasty. J Bone Joint Surg Am 2006, 88:2100-2111 7 Archibeck MJ, White RE. What's New in Adult Reconstructive Knee Surgery. J Bone Joint Surg Am 2005, 87:1656-1665 Obese patients have a higher incidence of wear and loosening. Patients whose primary surgery was performed for inflammatory arthritis, patients with avascular necrosis, and patients with a previous hip fracture are at higher risk for loosening. These anatomic and physiologic conditions lead to the necessity of joint revision surgery.

Physical Examination

The history and physical examination will identify patients who have a change in their pain level. Also, information can be obtained regarding activity levels and use of assistive devices, such as crutches or a cane. Pain of the hip may present as either groin or buttock pain. In addition, pain of the hip can sometimes be perceived of as knee pain, and vice versa. Swelling of the knee can be assessed easily, but swelling of the hip area may be more subtle. Mechanical failure or infection may also present with redness and warmth of the affected joint. A limp or deformity may be identified.

X-Rays

X-rays taken of the area around the joint replacement yield important clues regarding stability of the implant. Failure due to the most common cause, aseptic loosening, can be identified by several findings. For example, the implant may have moved, compared to previous X-rays, or there may be a lucent line between the component and the cement or bone, signifying that the bond between the bone and implant has degraded. Areas of bone loss, or lysis, can be identified. Mechanical failure with broken implants or severe wear is also assessed by comparison to previous X-rays. For these reasons, serial follow-up radiographs are recommended to catch joint failure at an early stage.

Laboratory Tests

Common laboratory tests for possible failed joints include a complete blood count, an erythrocyte sedimentation rate (ESR), and a C-reactive protein test (CRP). These studies are most helpful in the detection of infected joint replacements. The blood count may identify an anemia from chronic disease, and rarely may detect an elevated white blood cell count. The ESR and CRP may be abnormal in the presence of an inflammatory process, such as infection.

Additional Tests

Joint fluid may be removed with a needleand analyzed, a technique called aspiration, to give clues as to a possible infection. The knee joint can usually be reached with a needle in the physician's office, but the hip more commonly requires a setting that has fluoroscopic X-ray capabilities. In addition, scintigraphic studies that use short-acting radioactive isotopes may be used. Short-acting radioactive isotopes which are injected into the bloodstream may be used. One scintigraphic study, the Technetium99 bone scan, can detect abnormal bone activity such as infection, fracture, or irritation from prosthetic motion. Another study, the Indium111 scan, may be used to detect infection. All of these methods can be used when the natural history of joint replacement changes and revision becomes a possibility.

Benefits and Limits

Revision joint surgery, as previously stated, can be a major procedure that requires complex techniques. It can also have a higher complication rate than primary surgery. In addition, some patients are not medically able to tolerate a long and difficult surgical procedure.

Because of this, nonoperative treatment options are sometimes considered as a first step in the treatment of a failed implant. Obviously, problems that would damage remaining bone quality or make later treatment difficult would eliminate the nonsurgical options. Also, patients treated nonsurgically must realize that they may have significant limits on their function and activity.

Pain that is caused by a failed joint replacement may initially be treated with an increase in pain medications. These treatments may be limited by side effects, such as gastrointestinal upset and ulcers, drowsiness, and constipation. Increased reliance on assistive devices, such as a cane, crutches, or a walker, may be used to postpone revision. Likewise, a brace may decrease episodes of instability or dislocation. These techniques may be cumbersome and a burden to the patient, however. Modification and restriction of activity itself can be used to decrease symptoms. The less active a patient is, the less likely they are to be symptomatic. Finally, some infected joint replacements are treated with suppressive antibiotics to control the infection symptoms. This approach has a variable success rate and would not be expected to eradicate the infection.

Surgical Intervention and Considerations: Hip Surgery

Surgical intervention with joint replacement surgery9 Schmalzreid TP, Callaghan JJ: Wear in total hip and knee replacements. J Bone Joint Surg Am 1999; 81:115-136 can be a complex and challenging procedure. Several potentially difficult portions of the surgery must be considered. Common to all joint revisions is an assessment of existing bone quality, removal of the failed components, reconstruction of remaining bone and soft-tissue structures, and successfully fixing the new components to the bone.

Consideration of each of these challenges is essential to produce successful revision joint surgery.

In hip revision surgery, both the femoral (stem and ball) components as well as the acetabular (socket) portion must be addressed.

• The hip bones may have deficiencies due to lysis and loosening, fracture, or shielding of the bone from normal stress. These deficiencies are graded according to several classification methods.
• Once this assessment is performed, a method to remove the existing components is selected. If some parts of the implant are still functioning, efforts may be made to retain them. Specialized removal techniques7 Archibeck MJ, White RE. What's New in Adult Reconstructive Knee Surgery. J Bone Joint Surg Am 2005, 87:1656-1665 have been developed, including surgically splitting the femur bone to remove the cement and implants, as well as power and hand instruments, which accurately cut around the prosthesis.
• When the failed components are removed, the remaining bone may require a complex reconstruction, involving larger or longer implants, bone grafting using ground-up bone or large segments of bone, and possibly cement and metal cages.
• Finally, the selected revision hip implant must be firmly fixed to the bone, either through bone growing into small pores in the outer layer of the implant or by cementing the construct into place.

Surgical Intervention and Considerations: Knee Surgery

Knee revision surgery entails consideration of the femur (thigh bone), tibia (shin bone), and patella (kneecap) components.

• Bone stock deficiencies are classified according to several grading systems, and lysis, fracture, or stress shielding can lead to bone loss.
• The failed components are removed by a combination of surgical methods and specialized instruments. Reconstruction may require implants with extensions to reach better-quality bone and that effectively replace lost ligament stability.
• Ground-up or bulk bone graft may be used.
• An implant is fixed in place through cemented or bone in-growth techniques.

Before Surgery

Preoperatively, blood donation may be required, due to the extensive dissection necessary to perform this surgery. Additionally, antibiotics will be given either before or early in the case to aid in prevention of infection. The patient will be brought to the operating room suite and anesthetized9 Schmalzreid TP, Callaghan JJ: Wear in total hip and knee replacements. J Bone Joint Surg Am 1999; 81:115-136 for pain control and muscle relaxation.

Considerations

The surgical incision may utilize the site of the previous incision or it may be placed in another location. It is likely that a more-extended incision will be used in order to facilitate implant and scar removal as well as simplify the insertion of the new component. Great care is taken during dissection, as the normal position and appearance of nerves and blood vessels can be altered by the previous surgery and wear of the old components. The failed implants and any old cement pieces are removed using specialized techniques.10 Hanssen AD, Rand JA: Evaluation and treatment of infection at the site of a total hip or knee arthroplasty. Instr Course Lect 1999; 48:111-122 In addition, abnormal bone and scar tissue is removed to achieve a new bed for fixation of the prosthesis.

Techniques

Reconstruction of the hip or knee bones must then be performed. Some procedures will have bone almost equal to a primary procedure. Others will have more-severe bone loss. In these cases, revision will require the use of bone graft and/or metallic plates, cages, and screws. Once bone has been reconstructed, the process of implantation can begin.

Several techniques are available to implant the revision joints.

After Surgery

Once the components are in place, the closure of tissue layers is performed. Drains are placed to collect any fluids or blood. The joint may be protected after surgery in a brace or splint. The medical condition of the patient is closely monitored and blood count is assessed. Antibiotics and some method of blood clot prevention will be continued in the postoperative period and thus complete the steps of the surgical procedure.