The Difference in Medial Meniscal Extrusion between Non-Weight-Bearing and Weight-Bearing Positions in People with and without Medial Compartment Knee Osteoarthritis

Background: Medial meniscal extrusion (MME) has been correlated with medial meniscal injury and progression of medial knee osteoarthritis (OA). Objective: To examine the difference in MME between non-weight-bearing (supine) and weight-bearing (standing) positions in patients with and without medial knee OA. Determine the correlation between body mass index (BMI), Kellgren-Lawrence (KL) grade, Knee Osteoarthritis Outcome Score (KOOS), and MME. Design: Prospective. Setting: Tertiary institution PM&R Department. Participants: Forty five participants (29 female, 16 male), 24 with healthy knees and 21 with OA. Methods or Interventions: A single physician sonographer measured supine and standing MME with ultrasound (US) on each participant. The physician was blinded to all measurements. BMI was recorded on all participants. KL grades and KOOS questionnaires were obtained for the OA group. Main Outcome Measures: MME in supine and standing positions, change in MME from supine to standing, BMI, KL grade, and KOOS subscale scores. Results: MME increased.52 mm from supine to standing (P <.001). MME was greater in the OA group in both the supine (P =.002) and standing (P <.001) positions. Increasing BMI was moderately correlated with increasing MME (supine P =.001, standing <.001). Increasing age was correlated with increasing MME (supine P =.012, standing P =.002). Increasing KL grade (from 1 to 4) was correlated with increasing MME (supine P =.015, standing =.006). There was a small-to-moderate correlation between KOOS activities of daily living (ADL) subscale score and change in MME from supine to standing (P =.035). The change in MME from supine to standing positions had a small-to-moderate correlation (P =.035) with KOOS ADL subscale score alone but did not correlate with any of the other KOOS subscale scores or KOOS total scores. Receiver operating characteristic curve analysis suggested a standing MME value of 4.2 mm provides a positive likelihood ratio of 6.02 for knee OA. Conclusions: MME is greater in those with OA and with weight-bearing. MME correlates with BMI, age, KL grade, and the KOOS ADL subscale score. Finally, standing MME of 4.2 mm yielded a higher positive likelihood ratio to differentiate between healthy knees and those with medial compartment OA than the previously reported value of 3.0 mm.