Medial joint line obliquity and medial meniscus tear were associated with medial meniscal extrusion: A case-control...

Medial meniscal extrusion is a key factor in accelerating knee osteoarthritis. Medial joint line obliquity causes increased contact pressure on the medial meniscus, which potentially induces medial meniscal extrusion. Our hypothesis was that medial joint line obliquity contributes to an increase in medial meniscal extrusion in both supine and upright position during early-stage knee osteoarthritis (KOA).

We analysed 124 knees with early-stage KOA. Medial joint line obliquity (knee joint line obliquity ≤ - 3°) and posterior tibial slope ( ≥ 6°) were assessed using standing full-length lower extremity radiography and magnetic resonance imaging, respectively. Medial meniscal extrusion was measured using ultrasonography in the supine and upright positions. Cases with excessive posterior tibial slope were excluded to minimise the influence of the posterior tibial slope, and the remaining 89 knees were divided into medial joint line obliquity (n = 45; age = 58.3 ± 10.5 years) and control groups (n = 44; age = 59.8 ± 11.9 years). Each measurement was compared between the two groups using t-test or chi-square test. Multiple regression analysis was performed to determine the independent factor for medial meniscal extrusion.

The medial joint line obliquity group showed significantly higher medial meniscal extrusion than the control group (supine, 3.0 ± 1.0 vs. 2.4 ± 0.9 mm, p = 0.004; upright, 3.7 ± 1.0 vs. 3.2 ± 1.1 mm, p = 0.023). Meniscal tear was present in 75.6% and 75% of the medial joint line obliquity and control groups, respectively, with no significant difference in tear type distribution (p = 0.999). Medial joint line obliquity and medial meniscus tear were independent factors for increased medial meniscal extrusion in both the supine (p = 0.002 and p = 0.003, respectively) and upright positions (p = 0.017 and p = 0.001, respectively).

Medial joint line obliquity and medial meniscus tear may be risk factors for medial meniscal extrusion in both the supine and upright positions in early-stage KOA.

Level IV.