Dynamic muscle proprioception impairment in adolescent idiopathic scoliosis revealed by tendon vibration

While recent studies have drawn attention to the potential role of proprioceptive dysfunction in the development of AIS, its precise characterization remains incomplete. Most research has focused on static proprioception, revealing generally mild or inconsistent deficits. By contrast, dynamic muscle proprioception, particularly the ability to encode limb movement kinematics, remains largely unexplored. This study is the first to assess both static and dynamic muscle proprioception within the same body segment in severe AIS. Fifty-one AIS participants and 31 age-matched controls underwent proprioceptive assessment. Static proprioception was assessed using a knee joint position matching task, while dynamic muscle proprioception was evaluated through vibration-induced movement illusions applied to both legs. Leg movements were recorded with a 3D motion-capture system. Static position-matching performance did not differ between AIS participants and controls. By contrast, vibration-induced illusory movements revealed significant group differences: 27% of AIS participants failed to perceive movement illusions in at least one condition versus 5% of controls, and AIS participants reported reduced illusion amplitudes and velocities (p < 0.01) with moderate effect size (partial η²≈0.08). This impairment was most pronounced in single-curve AIS participants, who showed significantly lower illusion amplitudes and velocities than both controls (p < 0.001, Cohen's d = 0.43) and double-curve AIS (p < 0.05, Cohen's d = 0.28), whereas double-curve AIS did not differ from controls. These findings demonstrate a predominant impairment in Ia-mediated movement perception in severe AIS. The greater impairment observed in single-curve AIS indicates that muscle proprioceptive dysfunction may vary across clinical subtypes, supporting the existence of distinct sensory phenotypes in AIS.