Plain radiographs: (a) Anteroposterior and (b) lateral radiographs of a TKA demonstrating unspecific osteolysis and subchondral sclerosis (arrows). These findings made us suspect an infection
In cases where a suppurating fistula is present, fistulography could demonstrate continuity between the fistulous tract and the deep tissues and prostheses (Fig. 8.2a). It is very useful in the assessment of a periprosthetic abscess with fistulous tract (Fig. 8.2b–d).
Fistulography: (a) The introduction of low-osmolar nonionic radiographic contrast media in a suppurating fistula demonstrated continuity between the fistulous tract and the deep soft tissues (arrow). (b) Axial radiograph with contrast media showing a suppurating fistula in the lateral compartment of a TKA (arrow). (c) Lateral radiograph of a TKA with contrast media (arrow) showing the same findings. (d) US longitudinal view showing a periprosthetic abscess (cross) with a fistulous tract (arrow)
8.4 Ultrasonography (US)
In revision TKR planning, a presurgical US can be useful to visualize the relationship between the prosthesis and the popliteal vascular bundle (Fig. 8.3a). US can also evaluate the bone-prosthesis interface in the marginal areas related to subluxations and/or sustentation defects (Fig. 8.3b).
Ultrasonography (US): (a) US Doppler can help us visualize the normal relationship between a TKA and the popliteal vascular bundle. (b) The US longitudinal view let us evaluate the bone-prosthesis interface (arrow). (c) Note effusion and synovial hypertrophy (arrow). (d) A little periprosthetic abscess was also found. (e) Longitudinal US Doppler view showing a neurological complication (the peroneal nerve is thickened and with hypoechogenicity; (f) US Doppler view in axial, showing the same neurological complication
US can be used to assess joint effusions. US is a diagnostic technique that permits the differentiation between effusion and synovial thickening (Fig. 8.3c). The normal synovium is a thin membrane. When it becomes inflamed, diffuse or nodular thickening of the membrane is seen, which may show increased vascular flow on Doppler US. US is very useful for the diagnosis of soft tissue swelling, to follow its progression or regression and to make the diagnosis of a periprosthetic abscess (Fig. 8.3d).
US Doppler can also be used to evaluate vascular and neurological complications (Fig. 8.3e, f).
8.5 Bone Scintigraphy
Bone scintigraphy is not affected by orthopedic hardware and is the current imaging modality of choice for suspected joint replacement infection (Fig. 8.4). Bone scintigraphy is sensitive for identifying the failed TKA but cannot be used to determine the cause of failure.
Positive bone scintigraphy in three phases (b1–b3) and leukocyte scans (b4–b5) made us suspect an infection of the tibial component
In 1990 Rand et al.  reported that indium 111 (111 In) leukocyte scanning had an accuracy of 84%, a sensitivity of 83%, and a specificity of 85%. In 1997 Nijhof et al.  found that the sensitivity of indium-111-labeled immunoglobulin G (In-111-IgG) scintigraphy for infection was 1.0; for TKA the specificity was 0.5. In-111-IgG was shown to be a highly sensitive and fairly specific tool for detecting late infections of TKAs.
In 2001 Van Acker et al.  compared fluorine-18 fluorodeoxyglucose PET (FDG-PET), technetium-99m hexamethylpropylene amine oxime (HMPAO)-labeled white blood cell (WBC) scintigraphy, and bone scintigraphy in the assessment of painful TKAs. It was concluded that WBC scintigraphy in combination with bone scintigraphy had a high specificity in the detection of infected TKAs. FDG-PET seemed to offer no additional benefit.
In 2000 Teller et al.  compared preoperative sequential imaging with joint aspiration and clinical assessment during revision TKA. Sequential technetium-99-hydroxymethyl diphosphonate and indium-111 leukocyte imaging were 64% sensitive and 78% specific. Positive scintigraphy increased the likelihood of finding infection intraoperatively from 14% to 30%, although negative scintigraphy decreased this likelihood to 7%. Based on this study, the routine use of sequential technetium-99-hydroxymethyl diphosphonate and indium-111 leukocyte imaging was not recommended for differentiating occult infection from mechanical failure in painful, loose TKA.
In 2000 Scher et al.  analyzed the predictive value of indium-111 leukocyte scans in the diagnosis of infected TKA. The results of this study suggested limited indications for the use of the indium-111 scan in the evaluation of painful TKA. A negative indium scan may be helpful in ruling out infection in cases in which the diagnosis is not otherwise evident. Indium scans were found to have a 77% sensitivity, 86% specificity, 54% and 95% positive and negative predictive values, and 84% accuracy for the prediction of infection.
In 2001 Joseph et al.  investigated the reliability of combined indium-111 leukocyte/technetium-99m sulfur colloid scans, with and without the addition of blood pooling and blood flow studies, in the diagnosis of infected TKA. Routine use of these radionuclide scans was not supported by this study. Results for imaging alone included 100% specificity, 46% sensitivity, 100% positive predictive value, 84% negative predictive value, and 88% accuracy. Inclusion of blood pooling and flow phase data improved results to 66% sensitivity, 89% negative predictive value, and 90% accuracy, with reductions in specificity (98%) and positive predictive value (91%).
In 2002 Larikka et al.  evaluated the usefulness of 99mTc-labeled ciprofloxacin imaging in detecting the presence of infection in patients with symptomatic TKAs. 99mTc-ciprofloxacin imaging showed diagnostic sensitivity of 86% and a specificity of 78% for correctly diagnosing the presence of infection.
In 2004 von Rothenburg et al.  evaluated the diagnostic accuracy of 99mTc-labeled antigranulocyte antibody Fab’ fragments in infected TKA. They found a sensitivity of 93%, a specificity of 65%, and a positive predictive accuracy of 63%. There was a negative predictive accuracy of 94%. The high negative predictive accuracy in the whole group suggested that the scan can be used to exclude infection.
In 2008 Rubello et al.  evaluated the clinical efficacy of a dual-time acquisition protocol consisting of early 4 hours and delayed 20–24-h imaging with antigranulocyte scintigraphy (LeukoScan) in the diagnosis of infection in painful TKA. The results of this study suggested that delayed LeukoScan imaging was important in identifying false-positive results detected on early imaging. Thus, a dual-time, 4-h early and 20–24-h delayed LeukoScan imaging approach should be recommended to increase the diagnostic accuracy of the scintigraphy, with the exception of patients with a negative early LeukoScan examination, in whom the acquisition of delayed imaging appears unnecessary. Concomitant antibiotic therapy did not influence the diagnostic value of LeukoScan.