Abnormal activation of knee and ankle flexors-extensors is related to altered gait in ankylosing spondylitis?

Introduction. Ankylosing Spondylitis (AS) is a rheumatic disease that predominantly affects axial joints, producing a rigid spine from the occiput to the sacrum. AS patients could experience a progressive spinal kyphosis, from a biomechanical point of view this may induce a forward and downward displacement of the centre of mass (COM) in the sagittal plane [1]. Even though there is a clinical evidence of an altered posture, only one previous study involving AS EMG during gait, have been reported [2]. This study was aimed at examining abnormal EMG patterns of AS subjects, evaluating the role played in AS gait pattern alterations. Materials and methods. We recruited 14 AS subjects (age: 49±1 years, BMI: 25±3 Kg). Six cameras BTS motion capture system (60-120 Hz) and surface EMG (PocketEMG, 16 channels) synchronized with 2 Bertec force plates (FP4060-10) were used. 3D-motion analysis of independent barefoot walking was conducted. Surface electromyographic (EMG) data of rectus femoris (RF), tibialis anterior (TA) and gastrocnemius medialis (GM) muscles were collected; hips, knees and ankles flexion-extension moments and ground reaction forces were evaluated. Results. RF signals were prolonged at initial contact and non activation was registered during terminal stance and initial swing phases, TA activity was delayed during swing, GM muscle always showed a delayed activation during the stance phase. An increased ankle dorsiflexion and knee flexion, a decreased hip extension moments were registered at heel strike, together with an excessive posterior and a lower vertical force. Conclusion. Our data confirm delays in GM activation as in [3]; the presence of co-contractions in GM and TA could be related to the kinetic alterations and the lack of heel rocker, due to difficulties in accomplishing the shock absorption.