Imaging in the Failed Total Knee Arthroplasty




Introduction


In the patient with a failed total knee replacement (TKA), imaging modalities represent an integral part of diagnostic evaluation. As joint replacement arthroplasty becomes more common with the aging population and implant longevity improves, the number of patients requiring imaging evaluation for their TKA will continue to increase. This chapter discusses diagnostic imaging of the failed TKA, including the roles of radiographs, radionuclide scans, computed tomography (CT), and magnetic resonance imaging (MRI).




Radiographic Assessment


Standard radiographs used in the initial evaluation include weight-bearing anteroposterior (AP), lateral, tangential axial (Merchant), and long leg alignment views of the knee ( Fig. 4.1 ). The radiographs are evaluated for component alignment, size, and any overhang, stress fracture, component loosening, periprosthetic lucencies, osteolysis, wear of the polyethylene insert with loss of joint space or asymmetric joint space, and heterotopic ossification. The femoral component should be in 4 to 7 degrees of anatomic valgus, and the anterior flange should be in contact with the anterior cortex without notching. Any overhang should be noted. Femoral component overhang of greater than 3 mm doubles the risk of clinically important knee pain 2 years after TKA. The tibial component should be perpendicular to the long axis of the tibia on the AP radiograph and perpendicular or posteriorly sloped, appropriate for the implant design, on the lateral radiograph. The likelihood of tibial tray loosening is increased when it is placed in greater than 5 degrees of varus. The tibial tray should cover at least 85% of the tibial surface without overhang. Medial overhang of the tibial component can be a source of pain due to impingement on the pes anserinus or medial collateral ligament.




FIGURE 4.1


Normal total knee arthroplasty (TKA).

Standard anteroposterior ( A ), lateral ( B ), Merchant ( C ), and long standing ( D ) views of a TKA.

(From Scott, WN. Insall and Scott Surgery of the Knee. 5th ed. New York: Churchill Livingstone; 2012:1218.)


Preoperative and postoperative films are compared for size of the femoral component relative to the original anatomy, posterior condylar offset, patella height, and position of the joint line in relation to the patella. It is important to distinguish true patella baja, caused by a short patellar tendon, from iatrogenic patella baja, which results from a raised joint line, because the treatments of these conditions differ.


The value of oblique radiographs in accurately delineating the peripheral margins of osteolytic lesions is uncertain. Previous studies have suggested that plain radiographs, despite multiangle and multiprojection approaches, often underestimate the size of the osteolytic lesion. However, a study by Miura and colleagues demonstrated that radiographic analysis using the oblique posterior condylar view is reproducible and is significantly more accurate than standard radiographs for the detection of radiolucencies or osteolysis of the posterior aspects of the femoral condyles.


Patellofemoral Evaluation


On the Merchant view, the patella should be centered in the trochlear groove. Radiographic evidence of maltracking, including lateral tilt and subluxation, on an axial weight-bearing radiograph has been shown to more closely correlate with clinical symptoms than a standard unloaded Merchant view does. Risk factors for overstuffing of the patellofemoral compartment are noted, including anterior translation of the femoral component, oversizing of the femur, and creation of an aggregate patellar thickness thicker than on the contralateral side.


Loosening


Serial radiographs are an essential component in the evaluation of the painful TKA ( Fig. 4.2 ). Radiographic signs of loosening include progressive increase in radiolucent lines, changes in component position, subsidence, fracture of the cement mantle, and reaction about the tip of stemmed components. The cement–bone or component–bone interface is closely evaluated; loosening is suspected with all radiolucencies greater than 2 mm. Ritter and co-workers found that proper preparation of the cancellous bone and pressurization of the cement can reduce the initial occurrence of a radiolucent line. A loose tibial component frequently shifts into varus alignment, whereas a loose femoral component typically shifts into flexion. Visualization of osteolysis located in the posterior condyles may be obscured by the femoral component.




FIGURE 4.2


Component loosening: periprosthetic lucent zones.

A and B, Lateral radiographs demonstrate obvious loosening and subsidence of both the femoral and the tibial components. C and D, Anteroposterior radiographs demonstrate progressive radiolucencies under the tibial component.


Fluoroscopically positioned radiographs can assist in ensuring an optimal view of the interface, particularly in uncemented prostheses ( Fig. 4.3 ). Although arthrography is rarely necessary, loosening is suggested by any flow of iodinated contrast material into the area of lucency. However, the absence of contrast flow does not exclude the diagnosis. For unicompartmental knee arthroplasty, lucency at the tip of the femoral peg is most associated with loosening of the femoral component.




FIGURE 4.3


Tibial component loosening.

A, Standard anteroposterior (AP) radiograph. B, Fluoroscopically positioned AP radiograph demonstrates a radiolucent line under the tibial component that was not visualized on A . There was intense uptake underlying the medial tibial tray on the bone scan.


Ligamentous Instability


Stress radiographs can be helpful in diagnosing subtle varus and valgus instability ( Fig. 4.4 ). Posterior cruciate ligament (PCL) instability can be detected by obtaining weight-bearing lateral radiographs in both flexion and extension. PCL instability is present when the femorotibial contact position is substantially more anterior in deep flexion than in full extension.




FIGURE 4.4


Medial collateral ligament (MCL) laxity.

Anteroposterior valgus stress radiograph of the knee with widening of the medial joint compartment indicating MCL laxity.


Wear


Polyethylene wear can result in joint asymmetry on an AP radiograph and is frequently associated with osteolysis. It is suggested by interval decrease in the space between the femoral condyles and the tibial baseplate on serial AP and lateral radiographs. One study that used ultrasound for the assessment of polyethylene wear reported the ability to determine wear with an accuracy of 0.5 mm.




Computed Tomography


Historically, CT was considered to be of limited utility because of the beam-hardening artifact that is produced when the metal severely attenuates the x-ray beam. Recent advances in the form of multidetector CT using high photon techniques helps overcome this problem. In addition, images can be reformatted, producing sagittal and coronal views.


Using modern techniques, CT scans are valuable in determining the size and extent of osteolytic lesions, proximity of the lytic areas to the prosthesis, and involvement of the cortical bone ( Fig. 4.5 ). Reish and co-workers showed that plain radiographs are inadequate for evaluating periprosthetic osteolysis in TKA. Only 8 (17%) of 48 lesions detected by multidetector CT were visible on the standard radiographs. In addition, CT slices using a specific protocol allow an exact analysis of the axial alignment in patients with suspected malrotation of the femoral or tibial component or both ( Fig. 4.6 ). A line drawn along the posterior aspects of the femoral condyle should be parallel to the epicondylar axis. Even 4 degrees of internal rotation of the femoral component can lead to patellar maltracking. Greater degrees of internal rotation can lead to patellar subluxation, patellar dislocation, and patellar prosthetic failure. In addition, it has been shown that increased internal rotation of the femoral component is associated with increased lateral flexion laxity and less favorable clinical outcomes. Tibial component rotation is assessed in relation to the medial third of the tibial tubercle. In a study of patients with stiffness complicating TKA, Bédard and colleagues found that 33 of 34 patients had internal rotation of the tibial component, with a mean rotation of 13.7 degrees (range, 1 degree external rotation to 35 degrees internal rotation). Twenty-four of the patients also had modest internal rotation of the femoral component, with a mean of 3.1 degrees. The authors recommended routine CT scanning of patients with stiffness complicating TKA to identify internally rotated components.




FIGURE 4.5


A, Although the femoral osteolysis is apparent on this anteroposterior radiograph, the extent of the tibial osteolysis was not appreciated initially. B, The size and extent of the tibial osteolysis is much better visualized on this axial computed tomographic image through the tibial component.



FIGURE 4.6


Axial computed tomographic images of different femoral components in 1 degree ( A ), 7 degrees ( B ), and 10 degrees ( C ) of internal rotation in relation to the transepicondylar axis. Notice the resultant lateral patellar subluxation in B and lateral patellar tilt in C .




Magnetic Resonance Imaging


As with CT, the role of MRI has traditionally been limited due to metal artifact but has increased with the availability of new MRI software and imaging techniques ( Fig. 4.7 ). Examples of strategies to minimize artifacts include orienting the frequency-encoding gradient along the long axis of the prosthesis, using fast spin-echo sequences, using three-dimensional acquisitions and thin sections, using high matrix size, increasing receiver bandwidth, reducing interecho spacing, and using short tau inversion recovery (STIR) fat-suppression sequences.




FIGURE 4.7


Magnetic resonance imaging of painful total knee arthroplasty (TKA).

Coronal ( A ) and sagittal ( B ) magnetic resonance images of a painful TKA. Use of protocols that minimize metal artifact permits visualization of the interfaces around the components and of the surrounding soft tissues. Notice the normal iliotibial band (long arrow) and chronic medial collateral ligament injury (short arrows) in A and the normal extensor mechanism in B .


These improvements have allowed for the evaluation of both intracapsular and extracapsular components of the TKA. Sofka and associates showed that MRI scans with metal subtraction software had diagnostic value in 20 (43.5%) of 46 cases of problematic TKA with negative plain radiographs, ultimately leading to further surgical or other therapeutic interventional procedures in these cases. The diagnoses included osteolysis, synovitis, bursitis, ligamentous or tendinous injury, fat-pad scarring, pigmented villonodular synovitis, and intramuscular hematoma. In addition, MRI is commonly used as a second- or third-line modality when radiographs are negative and the cause for a painful knee is uncertain.




Nuclear Medicine Scans


Bone Scan


A positive technetium-labeled bone scan is extremely sensitive for detecting bone remodeling changes around prosthetic joints and can indicate loosening, infection, or stress fracture. Diffuse uptake may be present in complex regional pain syndrome (CRPS). Several studies have reported that bone scans were neither sensitive nor specific for differentiating infection from aseptic loosening. Three-phase bone scans do little to improve the accuracy of diagnosing infection. Levitsky and co-workers reported a sensitivity of 30%, a specificity of 86%, and an accuracy of 68%, whereas Love and colleagues reported a sensitivity of 76%, a specificity of 51%, and an accuracy of 62% for diagnosing infection ( Table 4.1 ). Increased uptake on the three-phase technetium bone scan can persist indefinitely after TKA, which limits the usefulness of this test. In one study, increased periprosthetic uptake persisted for more than 1 year after surgery in 89% of tibial components and 63% of femoral components.



Table 4.1

Sensitivity, Specificity, and Accuracy of Nuclear Medicine Scans in the Diagnosis of Prosthetic Joint Infection






































































































































































































Type of Arthroplasty Sensitivity (%) Specificity (%) Accuracy (%)
Bone Scan
Weiss et al, 1979 Hips 100 77
Love et al, 2008 Hips/Knees 50
Three-Phase Bone Scan
Levitsky et al, 1991 Hips/Knees 30 86 68
Palestro et al, 1991 Knees 67 70
Love et al, 2008 Hips/Knees 76 51 62
Magnuson et al, 1988 Hips/Knees 100 18 53
McKillop et al, 1984 Hips/Knees 80
Mountford et al, 1986 Hips 80
Aliabadi et al, 1989 Hips 37 100
Bone/Gallium Scan
Merkel et al, 1986 Hips/Knees 66 81 77
Gomez-Luzuriaga et al, 1988 Hips 70 90 80
Kraemer et al, 1993
Love et al, 2008 Hips/Knees 79 59 66
Labeled Leukocyte Imaging
Pring et al, 1986 Hips/Knees 100 89
Magnuson et al, 1988 Hips/Knees 88 73
McKillop et al, 1984 Hips/Knees 50 100
Wukich et al, 1987 Hips/Knees 100 45
Palestro et al, 1991 Knees 67 78
Johnson et al, 1988 Hips 100 50
Leukocyte/Bone Imaging
Wukich et al, 1987 Hips/Knees 85 85
Palestro et al, 1991 Knees 89 75
Johnson et al, 1988 Hips 88 95
Love et al, 2008 Hips/Knees 70
Leukocyte/Marrow Imaging
Mulamba et al, 1983 Hips 92 100
Palestro et al, 1991 Knees 100 97
Love et al, 2008 Hips/Knees 96 87 91
Joseph et al, 2001 Hips/Knees 100 46
Love et al, 2004 Hips/Knees 100 91 95
FDG-PET
Zhuang et al, 2001 Hips/Knees 90 89 89

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May 29, 2019 | Posted by in ORTHOPEDIC | Comments Off on Imaging in the Failed Total Knee Arthroplasty
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