Medial meniscus injury changed plantar pressure distributions and decreased posture stability especially in those with varus alignment: a cross-sectional study based on a wearable smart plantar pressure system.

Background: Medial meniscus (MM) injuries are common and often contribute to knee osteoarthritis (KOA). While studies focus on joint degeneration, the role of extrinsic factors such as postural control remains underexplored. This study investigated how MM injuries affected postural control, particularly plantar pressure distribution, with an emphasis on lower limb alignment.

Methods: 83 participants were recruited: 29 healthy subjects, 29 MM patients with neutral alignment (-3°< hip-knee-ankle angle (HKA) ≤ 3°), and 25 MM patients with varus alignment (HKA > 3°). Plantar pressure was measured using a shoe-integrated detection system. Normalized peak force, center-of-pressure (COP), and time-to-boundary (TTB) were measured during walking and single-leg stance (SLS).

Results: During walking, compared to the healthy group, the varus alignment group showed lower peak force for the posterior heel (P = 0.012), lateral midfoot (P = 0.024) and hallux (P = 0.009). When the two sides were compared, the varus group exhibited a lower peak force in the anterior heel (P = 0.004) and hallux (P = 0.017) of the affected sides, the neutral (P = 0.043) and varus (P = 0.045) groups all showed higher medio-lateral COP of the unaffected sides, indicating the COP shifting laterally. In SLS test, the two MM groups demonstrated increased peak force of the third (P = 0.037) and fifth (P = 0.040) metatarsals compared to the healthy group, the peak force of the posterior heel were lower in the varus alignment group compared to the healthy group (P = 0.007) and the neutral alignment group (P = 0.008). And the TTB absolute value of medial-lateral direction of the two MM groups were lower than healthy controls (P = 0.029). The area under the receiver operating characteristic curve (AUC = 0.698, P = 0.016) suggested that peak force of posterior heel had good performance to discriminate varus alignment group from neutral alignment group.

Conclusion: MM injuries, especially with varus alignment, lead to significant changes in plantar pressure distribution and postural stability. These insights are clinically significant for designing early, biomechanically-informed rehabilitative strategies to optimize recovery and prevent further joint degeneration following MM injuries.