The Value of (99m)Tc-HMPAO-WBC Scan in the Diagnosis of Infection after Total Knee Arthroplasty

ABSTRACT

PURPOSE: The early diagnosis and detection of prosthetic infection after TKA is very important and difficult for deter- mination of the plan in management and reduction of complications. In these reasons, this study was performed to evaluate the usefulness and limitation of (99m)Tc-HMPAO(Technetium (99m)-hexamethyl- propylene amine oxime)-labeled WBC scan in the patients with clinically suspicious prosthetic infection. MATERIALS AND METHODS: The study subjects were 25 patients(3 men and 19 women, mean age 66.5 years) performed (99m)Tc-HMPAO WBC scan in the patients with clinically suspicious prosthesis infection after TKA from January, 2005 to May, 2007. And in 6 patients who had undergone bilateral arthroplasty, we regarded one patient as two cases. Thus, total 31 prostheses were included in this study. Final diagnosis of infection was based on bacteriological result by intrao- perative cultures, surgical findings, and histological evidence intraoperatively obtained in the suspicious site and clinical follow-up. RESULTS: In the final diagnosis, we confirmed that total 16 prosthetic joints were infected. Of these infected prostheses, increased (99m)Tc-HMPAO WBC scan uptake waspositive in 15, negative in 1. Finally, 15 cases were confirmed as nonin- fected prosthesis, 6 showed positive by (99m)Tc-HMPAO WBC scan uptake, 9 showed negative. Over all sensitivity, speci- ficity, and positive predictive value for diagnosisof infected TKA were 93.75, 60%, and 71.43%. CONCLUSION: (99m)Tc-HMPAO WBC scan was a highly sensitive method for the diagnosis of prosthetic infection after TKA. But low specificity and high false positive of (99m)Tc-HMPAO WBC scan demand more clinical follow-up for confirmed diagnosis. To increase specificity, additionally scan will be needed.