Medial radial displacement (MRD) of the medial meniscus is a feature proving a dysfunction in the medial meniscus in osteoarthritis (OA) of the knee. MRD was measured in radiographic pre-OA knee and early osteoarthritis of the knee (early-OA) longitudinally using ultrasound (US) to investigate the characteristics involved in the onset and progression of OA.
Fifty-five patients with pain on the medial side of the knee participated in the present study. It was possible to follow-up 46 patients for 5 years, and, thus, they were divided into 32 pre-OA patients (female: 59%, mean age: 69.0 years) and 14 early-OA patients (female: 78%, mean age: 74.4 years) based on radiography at the baseline time-point. MRD was measured in standing and supine positions at baseline and after 1 and 5 years using US. MRD corrected with the skeletal size, i.e., the medial displacement index (MDI), was analyzed. The pre- and early-OA groups were divided into subgroups at 5 years: stable and OA progression groups, following the Kellgren/Lawrence classification, and ⊿MDI (gap of the MDI between the standing and supine positions) were retrospectively compared between the subgroups at baseline, 1 and 5 years.
In the overall pre-OA group, MDI increased by 7% and 10% at 5 years in the supine and standing position, showing a significant increase (P = 0.044, 0.0147). ⊿MDI was significantly greater in the subgroup with OA progression in the pre- and early-OA groups (P = 0.02 and 0.03, respectively), and was continuously 6-7% in the pre-OA progression group, showing that the displacement rate was 2-fold or higher than in the stable group.
An increase in ⊿MDI on US may be an important risk factor for the disease stage progression of OA and useful as a feature predicting the onset of radiographic knee OA.