Jason Werle MD FRCSC1, Kelly Johnston MD FRCSC1, Nicholas Desy MD FRCSC1 and Stuart Goodman MD PhD FRCSC2 1Division of Orthopaedic Surgery, Department of Surgery, University of Calgary, Calgary, AB, Canada 2Department of Orthopaedic Surgery, Stanford University, Stanford, CA, USA As many as one in five primary TKA patients are not satisfied with the outcome of their TKA surgery.1 This can be concerning for the patient and surgeon alike. TKA patients experiencing pain require significant healthcare resources to evaluate and manage. Ensuring that evidence‐based investigations are employed will translate into appropriate use of these limited resources. Investigating the painful TKA requires a systematic approach that ensures both intra‐ and extra‐articular etiologies are assessed.2 Potential intra‐articular etiologies include: infection, instability in flexion, mid‐flexion, or extension, component malalignment, crepitation and patellar clunk syndrome, patellofemoral symptoms, such as maltracking, or avascular necrosis, aseptic loosening, hypersensitivity to metal or cement, complex regional pain syndrome, or pseudoaneurysm.3,4 Extra‐articular causes of pain after TKA should be considered when infection and other intra‐articular pathologies have been ruled out. Potential causes include referred or secondary pain from spine, hip, foot, or ankle disease that has not yet been diagnosed, as well as vascular pathology, tendinitis, bursitis, iliotibial band syndrome, or medical comorbidities, such as metabolic bone disease or psychological illness.5 Understanding an algorithm with evidence‐based investigations for common causes of painful TKA ensures that correctable problems are addressed. Intervening with revision TKA when the etiology is unclear generally leads to poor results.6>–8 The quality of literature addressing appropriate investigations for a painful TKA is highly variable with level II–IV evidence. The majority of the outcome papers are case series or cohort studies. There are no randomized trials. A thorough pain history can assist with the diagnosis. This should include an assessment of the character, location, onset, radiation, intensity, and duration of the pain as well as provoking and palliating factors. A history of prior infection is a critical finding.9 Start‐up or initiation pain is consistent with aseptic loosening, whereas pain that is constant and does not abate should raise suspicion for periprosthetic joint infection (PJI).7 Details of the TKA surgery and postoperative course including odds ratio (OR) records and perioperative notes can provide information on surgical complications such as prolonged postoperative wound drainage, delayed wound healing, return trips to the operating room, and treatment with antibiotics following surgery.7 The patient’s medical history, medications, allergies including metal sensitivities, and expectations for the surgical outcome of the TKA should also be assessed. Physical examination should include a general exam with vital signs, height, weight, body mass index (BMI), general appearance, and gait. Detailed inspection of the skin can reveal the previous surgical scars, skin lesions, erythema, swelling/effusion, vascular changes, and draining sinus tracts. Gait should be specifically assessed for antalgia, varus/valgus thrust, and a Trendelenburg’s sign.7 A focused examination of the knee should include measurement of active and passive range of motion, assessment for extensor lag, evaluation of stability to varus and valgus stressing in full extension, mid‐flexion (30–60°), and 90° of flexion, and palpation for areas of focal tenderness or swelling. Patellar tracking should be examined throughout the range of motion. A neurovascular examination should be performed assessing peripheral pulses, motor function, and sensation in the lower extremity. Examination of joints above (hip, lumbar spine) and below (foot and ankle) the affected knee should be performed to rule out extra‐articular sources of pain such as lumbar radiculopathy, vascular claudication, or referred pain from hip arthritis.7 Obtaining serial radiographs can assist with the evaluation of implant stability over time.4,7 Lucent lines at the bone–implant or bone–cement interface that are complete or greater than 2 mm may indicate loosening.10 Implant position changes are pathognomonic for implant loosening. Three‐foot standing, anteroposterior, and lateral and patellofemoral radiographs of the affected TKA are useful for assessing the mechanical and anatomic axes of the lower extremity, as well as component positioning. CT assists with the evaluation of component rotation and areas of osteolysis, which are often underestimated on plain radiographs.11 Malrotation of the femoral component, typically internal rotation, can lead to pain following TKA through early failure due to instability.12 Malalignment of the TKA can lead to failure due to implant wear and aseptic loosening.13 CT can assist with diagnosis of both of these conditions. Complete blood count (CBC)/white blood cell count (WBC) Complete blood count or serum white cell count and differential testing is not useful in the evaluation of pain following TKA.14 The sensitivity of the WBC count was 55% and specificity was 66% in the diagnosis of TKA infection in a recent study by Toossi.15 However, a CBC may be helpful in the diagnosis of cases of acute hematogenous infection in the setting of a previously well‐functioning arthroplasty. Erythrocyte sedimentation rate (ESR) ESR remains elevated for up to three months post TKA. It is a sensitive but nonspecific test for the evaluation of PJI. Levitsky et al. reported that the ESR was statistically significantly higher in TKA patients with definitive infection. Also, they reported that an elevated ESR (>30 mm/h) had a sensitivity of 60% and a specificity of 65% for PJI.16 Spangehl et al. identified a sensitivity of 0.82 and a specificity of 0.85 for the ESR in 202 revision arthroplasty patients.17 C‐reactive protein (CRP) CRP can remain elevated for up to three weeks post TKA. Spangehl et al. identified a sensitivity of 0.96 and a specificity of 0.92 for CRP testing in patients with PJI.17 Hardcastle identified that a preoperative abnormality of either CRP or ESR significantly increased the risk of re‐operation for all reasons (OR = 3.2; p = 0.0028), infection (OR 4.0; p = 0.034), and revision for aseptic loosening (OR = 3.69; p = 0.044).18 Alternatively, a normal ESR and CRP are reliable for predicting the absence of infection.17 If the ESR and/or CRP are elevated in a patient with a painful TKA, aspiration of the knee is necessary to rule out PJI.19,20 Synovial fluid should be sent for cell count and differential, aerobic, and anaerobic culture and sensitivity, TB and fungal culture (depending on patient comorbidities, immunosuppression, and tuberculous infection prevalence). A synovial fluid WBC count between 1100 and 3000 cells/mm3 is strongly suggestive of a deep PJI.19,21 These values are substantially lower than the 50 000 cells/mm3 threshold for diagnosis of septic arthritis in a native knee. If the percentage of neutrophils is between 60 and 80%, infection is likely. As well, when the WBC count is below 1100 cells/mm3 and the neutrophil percentage is less than 64%, the negative predictive value of knee aspiration is 98.2%; when both values are above these thresholds, the positive predictive value is 98.6%.8 It is important to note that these values are only accurate more than six weeks following TKA surgery due to postoperative inflammation that can impact cell count and differential aspiration results prior to that time period. Preoperative aspiration had a sensitivity of 67% and a specificity of 96% and, therefore, has been identified as the most useful single test in the workup of the painful TKA.16
51
The Painful Total Knee Arthroplasty
Clinical scenario
Top three questions
Question 1: For patients with painful TKA, what are the best evidence‐based clinical investigations to assess for intra‐ and extra‐articular etiologies in the initial work‐up?
Rationale
Clinical comment
Available literature and quality of the evidence
Findings
History/old records
Physical examination
Plain radiographs/three‐foot standing images
Computed tomography (CT) scans
Laboratory tests (CBC, ESR, C‐reactive protein)
Knee aspiration
Resolution of clinical scenario as it relates to investigations
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
