A Multimodal Assessment of Cementless Tibial Baseplate Fixation using Radiography, Radiostereometric Analysis, and Magnetic Resonance Imaging.

Fixation in cementless total knee arthroplasty (TKA) is provided by osseous integration. Radiography, radiostereometric analysis (RSA), and magnetic resonance imaging (MRI) were used simultaneously to investigate fixation. Relationships between RSA-measured implant micromotions and MRI-evaluated osseous integration at the component-bone interface were assessed in 10 patients up to six months post-operation. Supine MRI (using multispectral imaging sequences) and RSA exams were performed to evaluate osseous integration and measure longitudinal migration, respectively. Inducible displacement was measured from standing RSA exams. Radiolucent lines were detected on conventional radiographs. Six of ten patients had fibrous membranes detected on MRI. No fluid or osteolytic interfaces were found, and no components were scored loose. Six of ten patients had radiolucent lines detected. Average maximum point motion (MTPM) for longitudinal migration at 6 months was 0.816 mm (range 0.344-1.462 mm). Average maximum point motion (MTPM) for inducible displacement at 6 months was 1.083 mm (range 0.553-1.780 mm). Fictive points located in fibrous-classified baseplate quadrants had greater longitudinal migration than fictive points located in baseplate quadrants with normal interfaces at two weeks (p = 0.031), six weeks (p = 0.046), and three months (p = 0.047), and greater inducible displacements at three months (p = 0.011) and six months (p = 0.045). Greater early micromotion may be associated with the presence of fibrous membranes at the component-bone interface. This article is protected by copyright. All rights reserved.