By: 1 June 2011

The purpose of our study was to evaluate the clinical value of hybrid SPECT/CT for the assessment of patients with painful total knee arthroplasty (TKA).

Twenty-three painful knees in patients following primary TKA were assessed using Tc-99m-HDP-SPECT/CT. Rotational, sagittal and coronal position of the TKA was assessed on 3D-CT reconstructions. The level of the SPECT-tracer uptake (0-10) and its anatomical distribution was mapped using a validated localisation scheme. Univariate analysis (Wilcoxon-Mann-Whitney, Spearmean`s-rho test, p < 0.05) was performed to identify any correlations between component position, tracer uptake and diagnosis.

SPECT/CT imaging changed the suspected diagnosis and the proposed treatment in 19/23 (83%) knees. Progression of patellofemoral OA (n = 11), loosening of the tibial (n = 3) and loosening of the femoral component (n = 2) were identified as the leading causes of pain after TKA.

Patients with externally rotated tibial trays showed higher tracer uptake in the medial patellar facet (p = 0.049) and in the femur (p = 0.051). Patients with knee pain due to patellofemoral OA showed significantly higher tracer uptake in the patella than others (p < 0.001).

SPECT/CT was very helpful in establishing the diagnosis and guiding subsequent management in patients with painful knees after TKA, particularly in patients with patellofemoral problems and malpositioned or loose TKA.

Total knee arthroplasty (TKA) is the treatment of choice for patients with disabling primary osteoarthritis (OA) of the knee joint. Although TKA is a very successful surgical procedure in patients with OA and it generally leads to satisfactory long-term results, failure does occur in a considerable number of patients resulting in persistent or recurrent knee pain1-4. The most common causes are considered to be infection, loosening, instability, prosthetic malposition, arthrofibrosis and patellofemoral disorders1-4. Clinically it can be difficult to differentiate between causes which necessitate surgical treatment from those which could be treated non-surgically1-3. Hence, identifying the underlying cause of the pain is of paramount importance for guidance of optimal patient management. To date no optimal `single-stage` sensitive and specific diagnostic imaging modality, which integrates mechanical and metabolic data has been reported for this group of patients1-3,5,6.

Radiographs are considered to be the primary standard imaging technique in patients with knee pain after TKA1-3. However, these are only helpful in detecting gross prosthetic malposition, radiolucencies and fractures. Plain radiographs are less sensitive in detecting more common but subtle abnormalities such as early loosening or minor implant malposition1-3. Radiographs are also subject to measurement inaccuracy due to variability in reproducible patient positioning5-7.

Computer tomography (CT) has its value in identifying TKA malposition and may reveal the extent and size of periprosthetic lucencies not apparent on plain radiographs8,9. Although bone scans or single emission computerised tomography (SPECT) give important information on the osseous metabolism and joint homeostasis10,11 their clinical value is limited due to the poor accuracy in localising the increased tracer uptake12. Hybrid SPECT/CT which combines the strengths of SPECT and CT may be useful in patients with knee pain after TKA, particularly when other radiographic imaging provides insufficient, ambigous or non-specific information5,6.

The primary purpose of this study was to evaluate the clinical value of SPECT/CT in patients with knee pain after primary TKA. The hypothesis was that the use of SPECT/CT has a substantial clinical impact in terms of establishment of diagnosis and guidance of further management in these patients.

A total of 23 consecutive patients who have previously undergone primary TKA and complained about postoperative knee pain were prospectively collected and investigated. The patients were all recruited during a six month period at a university affiliated hospital specialised in knee surgery. Patients who had undergone a revision surgery previously were excluded. There were no other exclusion criteria.

All patients (mean age 69