Objective: The purpose of this study was to assess the incremental value of technetium-99m-methyl diphosphonate (Tc-MDP) single-photon emission computed tomography/computed tomography (SPECT/CT) over Tc-MDP two-phase bone scan (TPBS) in the assessment of the patients with pain following knee arthroplasty.
Patients and methods: Tc-MDP TPBS and Tc-MDP SPECT/CT were performed in 49 patients with knee pain after knee arthroplasty. The scans were reviewed by two readers (nuclear medicine physician and musculoskeletal radiologist). Tc-MDP SPECT/CT studies were interpreted in conjunction with TPBS in this retrospective study to identify the pain generator in painful knee prosthesis. The final diagnosis was established based on a combination of histopathological/cytological findings, other imaging findings (e.g. MRI, radiolabelled white scan), clinical decisions, and management outcomes (including subsequent intraoperative findings).
Results: In diagnosing infection or aseptic loosening, a definitive outcome regarding the presence/absence of aseptic loosening or periprosthetic infection was obtained in 41 patients. (a) Sensitivity of Tc-MDP SPECT/CT [100%; 95% confidence interval (CI): 66.4-100%] was higher than Tc-MDP TPBS (88.9%; 95% CI: 51.8-99.7%). (b) Specificity of Tc-MDP SPECT/CT (75%; 95% CI: 53.3-90.2%) was considerably higher than Tc-MDP TPBS (30%; 95% CI: 11.9-54.3%). Alternative diagnoses were identified in 21/49 (43%) patients on Tc-MDP SPECT/CT, which could not be ascertained on Tc-MDP TPBS alone.
Conclusion: Tc-MDP SPECT/CT has better sensitivity and specificity compared with Tc-MDP TPBS in diagnosis of aseptic loosening and periprosthestic infection in patients with painful knee arthroplasty. Tc-MDP SPECT/CT identified alternative causes of pain in 43% of patients, which was not identified by Tc-MDP TPBS.