The Relationship of Meniscal Extrusion to Subchondral Bone Density in Medial Knee Osteoarthritis.

Background: The hoop function of the meniscus plays a crucial role in stress distribution across the knee joint. While medial meniscal extrusion is known to contribute to the progression of medial knee osteoarthritis (OA) by altering load distribution within the knee joint, its exact effect on living humans remains unclear. Purpose: To investigate the influence of meniscal extrusion on subchondral bone density distribution in patients with medial knee OA. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This retrospective study included 59 patients with medial knee OA (OA group) and 19 control participants (non-OA group). Radiographic parameters, including the hip-knee-ankle angle (HKA) and meniscal extrusion ratio (MER), were assessed. The subchondral bone density was evaluated using computed tomography-osteoabsorptiometry to analyze the high-density area (HDA) in the medial and lateral compartments on the articular surface of the proximal tibia. Correlations between these parameters were assessed using single and multiple regression analyses, with subgroup analysis conducted in OA patients with and without meniscal tears. Results: In the OA group, the HKA, medial MER (MMER), and the ratio of the medial compartment HDA to the total HDA (medial ratio) were -7.4°, 64.8%, and 81.8%, respectively. In the non-OA group, these values were -2.1°, 12.5%, and 62.0%. Simple regression analysis showed that, in the OA group, the medial ratio was correlated with HKA ( Conclusion: MMER had a greater influence on the mediolateral distribution of subchondral bone density in patients with medial knee OA than lower limb alignment, suggesting that the hoop function of the meniscus plays a more important role in altering stress distribution than leg alignment.