A: Joint replacement surgery has been shown to decrease pain and increase function in the vast majority of patients. Once a patient progresses through the postoperative period, symptoms of pain, as well as the stability and motion of the joint, should remain stable for an extended period of time.
The natural history of failed implant surgery is an increase in pain, a change in the position of the implant, or a decrease in the function of the implant with limp or dislocation. Patients who demonstrate these symptoms and signs may require revision joint surgery. Therefore, a standard assessment8 is performed, including a history and physical examination, X-rays, laboratory tests, and possibly aspiration or scintigraphic studies.
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 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.
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.
Joint fluid may be removed with a needle and 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.