Long-term results after total condylar knee arthroplasty. Significance of radiolucent lines.

In a prospective study of 123 total condylar knee arthroplasties, radiolucent lines were noted at the bone-cement interface about the tibial component in 65% of the knees. In 36%, the line was thin (less than 2 mm) and under either the medial or lateral tibial plateau. In 22%, thin lines were seen under both the medial and lateral plateaus. There was no statistically significant correlation between the occurrence of thin radiolucent lines in any location and the eventual postoperative clinical result. In 7%, thick lines (greater than 2 mm) were noted about the central peg of the prosthesis as well as under both plateaus and were associated with poor results. A 1-mm radiolucent interface was attached to various tibial components, which were then cemented into cadaver knees. For the polyethylene total condylar component, flexion or rotation of the prosthesis more than 5 degrees, angulation of the roentgen beam more than 6 degrees, or offsetting the beam more than 2.5 cm prevented visualization of the radiolucent line. With metal-backed components, more than 4 degrees of flexion obscured the lines. Therefore, extremely careful positioning of postoperative radiographs is essential for evaluating radiolucent lines after total knee arthroplasty.