Irregularity of medial femoral condyle on MR imaging serves as a possible indicator of objective severity of medial-type osteoarthritic knee-a pilot study.

Irregularly described contour of the femur and the tibia on magnetic resonance (MR) imaging is commonly seen in osteoarthritic (OA) knees. The aim of this study is to examine the relationship between irregularity of contour of medial femoral condyle (tentatively named I-index) and severity of OA. Twenty-six medial-type OA knees with a mean age of 63.8 were studied. All patients had undergone MR imaging to measure the I-index using image analysis software, and its relationship to Lysholm score was examined. The I-index negatively correlated with Lysholm score (r = -0.55, p < 0.01). The I-index for each Kellgren and Lawrence grade was significantly different. We have concluded that the I-index is a potent indicator to objectively describe the severity of OA especially for the advanced stage OA.