Radial displacement of the medial meniscus and Fairbank's signs.

Radial displacement of the medial meniscus in knees that have not undergone meniscectomy was measured using magnetic resonance imaging. In age matched subjects, the amount of displacement was compared with the presence or absence of radiographic signs described by Fairbank. A medial displacement index, defined as the ratio of meniscal overhang to meniscal width, was used to quantify meniscal displacement. The medial displacement indices for knees with and without radiographic signs were 0.45 +/- 0.22 and 0.08 +/- 0.10, respectively (mean +/- standard deviation). Differences were highly significant. The greatest meniscal displacements were seen in knees with radiographic Fairbank's signs; no knee with such signs had an undisplaced meniscus. It is concluded that radiographic signs of osteoarthritis known to follow meniscectomy can develop in knees that exhibit significant radial displacement of the medial meniscus. Radial displacement may be related to loss of meniscal function because the radiographic signs are similar to those that follow meniscectomy.