Muscle activation asymmetry in patients after hip replacement evaluated using surface electromyography

Cescon, Corrado and Trucco, Marco and Barbero, Marco (2019) Muscle activation asymmetry in patients after hip replacement evaluated using surface electromyography. In: 9° Giornata della Ricerca della Svizzera Italiana, March 15th, 2019, Lugano, Switzerland.

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BACKGROUND: Surface electromyography (EMG) has been often used, in the last years, as a tool to assess and evaluate different diseases and disorders. Despite its effectiveness in analyzing of muscle fatigue was largely shown, there is still lack of information regarding the evolution of EMG fatigue signals in persons with hip replacement during sub-acute period. PURPOSE: the aim of this study was to evaluate EMG muscle fatigue and asymmetry between healthy and operated limb, and how these parameters changed during two-week rehabilitation. METHODS: Forty-three patients (28 females) with hip replacement were enrolled in the study. Surface EMG signals were recorded from vastus medialis (VM) and lateralis (VL) muscles using adhesive concentric ring electrodes (OT-Bioelettronica, Torino, Italy) during isometric squat. A force platform was used to provide a visual feedback in order to have equal distribution of the body weight on the two legs. Patients were asked to maintain a squat position with their back against a wall and knees flexed at 120° for 60 seconds. The measurements were repeated in three sessions (T0 two-three days after the operation, T1 after one week, and T2 after two weeks of rehabilitation). Muscle force was measured separately during leg extension using a hand-held dynamometer (MicroFet, Hoggan ind. Salt Lake City, USA). Borg scale, numeric rating scale (NRS) for pain, Timed Up and Go (TUG) Test, were collected during each session. In addition, a Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) was used to assesses pain stiffness and physical function before the rehabilitation cycle and two months after the discharge from the clinic, as well as a EQ-5D questionnaire to measure the health-related quality of life. EMG signals were analyzed in order to extract amplitude (ARV) and mean power frequency (MNF). Linear regression analysis was applied in order to extract initial values and slopes of the two variables. Statistical analysis was performed using non parametric paired tests between the two limbs (Wilcoxon signed-rank test). RESULTS: MNF showed a statistically significant decrease in both legs indicating muscle fatigue during the task. A statistically significant asymmetry of ARV was observed between the two legs at T0, with the operated leg showing lower EMG amplitude as expected. The asymmetry was progressively reducing at T1 and disappeared at T2. Force asymmetry between the two legs at T0 was also observed, with the operated leg showing lower force. The force asymmetry did not change significantly during the two weeks of rehabilitation. No correlation was observed between EMG amplitude asymmetry and force asymmetry, while a significant correlation was observed between amplitude asymmetry and WOMAC total score. MNF slope did not change significantly during the three sessions, indicating no variations of muscle fatigue in the vastii muscles. CONCLUSION: An asymmetry of muscle activation was observed after the hip replacement, with lower EMG amplitude in the operated limb, and this asymmetry was progressively reduced during the rehabilitation period, disappearing after two weeks. IMPLICATIONS: EMG signal amplitude asymmetry showed to be a promising tool to assess muscle activity during a rehabilitation period.

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