Increased focal bone tracer uptake at the popliteus muscle origin in primary TKA compared with revision TKA

The purpose of the study was to investigate if the TKA design (cruciate retaining (CR), posterior stabilized (PS), revision prostheses) had an influence on the bone tracer uptake (BTU) pattern at the origin of the popliteus muscle. A total of 92 knees (male:female = 46:46) which had undergone prior TKA were included in this retrospective study, comprising the following 3 groups: (i) CR primary TKA (n = 45); (ii) PS primary TKA (n = 24); (iii) revision TKA (n = 23). All patients received a SPECT/CT after TKA surgery. SPECT/CT images were reviewed for the presence of BTU in the lateral femoral condyle (origin of the popliteus muscle) by two observers using Syngo.via software (Siemens Healthcare, Erlangen, Germany). The observers recorded the BTU pattern qualitatively in the lateral femoral condyle as either (i) absent; (ii) present and diffuse; and (iii) present and focal in the region of the popliteus muscle origin. In patients with a CR and PS design, focal increased BTU at the origin of the popliteus muscle was found in 80.0% and 83.3% respectively. Diffuse BTU was the predominant finding in patients with revision TKA (60.9%). The patterns of BTU did not show significant differences between the CR and the PS design. However, patterns of BTU differed significantly between primary TKA designs and revision TKA (p < 0.001). Differences in patterns of BTU at the popliteus muscle origin between primary TKA and revision prosthesis may be the result of decreased insertional tensile forces of the popliteus muscle after revision surgery due to increased stability provided by the revision design.