Introduction
Total knee arthroplasty (TKA) is a reliable and reproducible procedure for treatment of the arthritic knee. Despite generally successful outcomes, some patients experience clinical failure with symptoms of pain and impaired function. Although the impact of this failure can be disabling, it is important to determine the cause of the problem before further surgical or nonsurgical intervention is considered, because the etiology may be one of a spectrum of conditions. It is helpful to differentiate between intraarticular and extraarticular causes of pain and disability.
A systematic approach to each case helps to establish the appropriate diagnosis. Evaluation begins with a thorough history, which should include a complete description of the symptoms including time of onset, duration, and severity; limitation of activities; need for assistive devices; complaints with other joints; and comorbidities. It is also helpful to review past medical records, including the operative report from the index procedure and subsequent surgical procedures. A comprehensive physical examination should include not only the involved extremity but the hips and spine, because knee pain may be referred from a remote site. Radiographs, serologic tests, and knee aspiration can provide additional evidence to support a specific diagnosis. More advanced tests, such as bone scanning, computed tomographic (CT) scanning, or magnetic resonance imaging (MRI), can be obtained if the presumptive diagnosis becomes elusive or further support is needed in determining the treatment plan. An important principle in the management of these cases is to confirm the diagnosis before surgical intervention is performed.
Differential Diagnosis
The etiology of pain after TKA can be broadly classified into extraarticular and intraarticular causes ( Boxes 5.1 and 5.2 ). Many of these conditions are related comorbidities that may have been present at the time of the index procedure. Common conditions that may refer pain to the knee include degenerative arthritis of the hip and neurologic problems such as lumbar spinal stenosis, lumbar radiculopathy, and neurogenic claudication. These conditions are usually confirmed by the physical examination and imaging studies. Many times, physicians simply fail to consider these possible conditions as the source of the patient’s pain.
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