Exploring the potential of combining kinematics and EMG to enhance identification of individuals with subacromial shoulder pain

Around 7% to 27% of the population is affected by musculoskeletal diseases involving the shoulder girdle; around 44% to 65% of affected individuals have subacromial shoulder pain (SSP) [1]. Kinematic alterations and electromyographic activity (EMG) in the shoulder joint complex have been described; however, there is no consensus in the literature regarding alterations in individuals with SSP [2,3]. Does concatenating kinematics and EMG improve the ability to differentiate individuals with SSP from pain-free controls? One hundred sixteen participants (41 men and 75 women) were recruited for this study. 56 had SSP (age: 26.9±7.02 years, height: 166.8±7.96 m and BMI: 24.4±3.53 kg/m2), and 60 were pain-free (age: 22.3±3.03 years, height: 166.5±837 m and BMI: 23.6±2.96 kg/m2). Three-dimensional kinematics of the frontal, sagittal and transverse plane angles of the scapula, trunk, and arm and filtered, rectified and smoothed signals of surface electromyography of the acromial, clavicular and spinal deltoid; ascending, transverse and descending trapezius, serratus anterior and biceps brachii muscles were performed. The task involved shoulder flexion/extension and abduction/adduction movements starting from anatomical position until reach the maximum range of motion, in each plane respectly and then returning to initial position. The Movement Deviation Profile (MDP) [4] method was used to analyse kinematics and EMG separately and then combined. The z-score of the MDP mean was calculated to compare the standardised results between groups with and without SSP. A multivariate analysis with Bonferroni post-hoc test compared the groups considering p < 0.05. There was an interaction between the two groups during flexion/extension (λ=0.844, F=6.885, P<0.0001) and abduction/adduction (λ=0.917, F=3.396, P<0.02). There was a difference in kinematics and kinematics with EMG in flexion/extension and only in kinematics in abduction/adduction (Table 1).Download : Download high-res image (98KB)Download : Download full-size image To the best of our knowledge, no studies compare the difference in the kinematics, EMG and kinematics combined with EMG to compare SSP and pain-free volunteers. Our result corroborates the literature by showing that the kinematics of patients with SSP differs from that of pain-free controls and that the differences are more evident during flexion-extension [5]. Despite the limited scientific evidence and the lack of consensus on an altered motor pattern in the shoulder muscles, it is not uncommon for studies to show similarities or slight differences in the EMG activity of patients with SSP. However, the MDP allowed us to evaluate concatenated kinematics and EMG and showed that we only found differences during flexion/extension. This finding may be because the kinematics during flexion showed a greater difference in z-score than abduction since the EMG alone showed no difference between the groups. Thus, concatenating kinematics and EMG does not improve the ability to differentiate individuals with SSP from pain-free.