Painful Knee Arthroplasty

Abstract

A triple-tracer nuclear medicine study that incorporates 99m Tcsulfur colloid, 111 In-labeled leukocytes, and 99m Tc-methylene diphosphonate can be useful for the diagnosis of aseptic loosening in a patient after total-knee arthroplasty, as demonstrated in this case study. The triple-tracer technique takes less time and is more accurate than a bone scan alone. Thi s article discusses the importance of the use of a tripletracer study in the postoperative knee to diagnose an aseptic knee. The components of the triple tracer will be discussed, as well as how the results of this study can aid the orthopedic surgeon in designing a treatment plan that will be successful for the patient. CASE REPORTA 59-y-old woman with a history of rheumatoid arthritis and osteoarthritis presented with 6 mo of progressive right knee pain, which did not improve with conservative management. She had undergone cemented total-right-knee arthroplasty 2 y previously for osteoarthritis. She was previously pain-free and had not undergone recent trauma. She was afebrile and had a mildly elevated white blood cell count of 10.7 billion/L. A triple-tracer study was requested to evaluate for septic prosthesis loosening.The patient was first injected with 373.7 MBq (10.1 mCi) of 99m Tc-sulfur colloid, and spot views of the knees were obtained. The patient was then injected with 20.72 MBq (0.56 mCi) of 111 In-labeled leukocytes, and similar-projection 24-h delayed images of the knees were obtained. Lastly, the patient was injected with 862.1 MBq (23.3 mCi) of 99m Tc-methylene diphosphonate, and acquisition of dynamic flow and static blood-pool images followed immediately afterward. After 3-4 h of tracer localization, spot views of the knees were obtained.Comparison of the 99m Tc-sulfur colloid and 111 In-labeled leukocyte images (Fig. 1) did not demonstrate discordant uptake of the latter to suggest infection. On the 3-phase 99m Tc-methylene diphosphonate bone scan, there was periprosthetic hyperemia near the tibial component on the early images (Fig. 2). On the delayed images, there was increased uptake at the interface between the tibial plateau native bone and the prosthesis, worse medially (Fig. 3).The triple-tracer findings were consistent with aseptic failure of the prosthesis. Surgical exploration did not reveal any signs of infection; however, the tibial component had subsided into the medial tibial plateau and was easily