SURFACE EMG EVALUATION OF MEDICAL SONOGRAPHY SCANNING TASK

SURFACE EMG EVALUATION OF MEDICAL SONOGRAPHY SCANNING TASK – A PILOT STUDY Arijit Sengupta, Ph. D. and Gul Ahmed, M. S Occupational Safety and Health Engineering Department of Mechanical and Industrial Engineering New Jersey Institute of Technology, Newark, NJ 07079, USA

High musculoskeletal disorder (MSD) rates for sonographers � Point prevalence for neck and shoulder pain for the general population is 13 to 22%, and for sonographers it is between 63 to 91%. � 80% of sonographers seek treatment for MSI. � 20% leave the profession due to persistent pain. Village, J. , & Trask, C. (2007). Ergonomic analysis of postural and muscular loads to diagnostic sonographers. International Journal of Industrial Ergonomics, 37(9 -10), 781 -789

Task characteristics of medical sonographers Generally involves having a patient lie or sit next to the ultrasound system and, with a probe connected to the system held in one hand, pressing it against various parts of the patient at different angles while operating the control panel with the other hand. Scan time – 10 - 30 minutes / patient. 8 to 10 patients per day

Combined results based on three Canadian and one US survey of sonographers. n= 1621 Anatomical sites for most frequently reported discomfort by sonographers * www. sdms. org/pdf/sonoergonomics. pdf (Carmel Murphy, and Andre Russo; 2000)

Discomfort Survey (Continued) Tasks that aggravate musculoskeletal symptoms (mean scores on a 5 point scale)

Work related factors that are injurious to sonographers Extended reaching. Sustained contraction of shoulders, upper back and upper extremities is required to support the arm in position and to optimize the image. � Application of a push force, to manipulate the image, which varies for different scan types. � Repetitive movements of the shoulder, forearm, wrist, hand fingers are required to fine -tune image, while manipulating with transducer. � �

Previous studies of shoulder and neck muscle loads and arm posture Murphey and Milkowski (2006), Journal of Diagnostic Medical Sonography, 22(5), 298 -305. 22 sonographers (6 male, 16 female), study objective – quantifying muscle load with simulated arm positions of sonographers. � Reducing the shoulder abduction angle from 75 o to 30 o resulted in a 46% decrease in firing of shoulder muscles. � However, no push force was applied on the probe by hand during EMG data collection.

Previous studies … shoulder/neck muscles loading (Cont. ) VILLAGE & TRASK, (2007), International Journal of Industrial Ergonomics, 37(9 -10), 781 -789 Video-based analysis for 24 full scans (528 min) by 11 sonographers, and EMG of 11 scans by 3 sonographers. The study objective was to compare various type of scans, e. g. carotid scan, abdominal, obstetrical or leg scans. � Shoulder muscles were found to work 90% of the time statically at 3 to 10% of MVC - medium risk rating for shoulder-neck MSDs. � The shoulder was unsupported (static tension) for 73% of scanning time. � 68% of scanning time with >30 o shoulder abduction.

Previous studies … shoulder/neck muscles loading (Cont. ) Suzuki et al. , (2012, 2013), Journal of Medical Ultrasonics. Study objective was to determine the best location of the sonography console. � Forearm and shoulder muscle activity while subjects (6 m, 2 f) manipulating sonography console, placed at various horizontal and vertical positions. � 4 inch to the right of body mid-line horizontally, and at elbow height vertically, found to be the optimum position of the console that reduces sonographers muscle loading and achieved optimum posture.

The pilot study objective � To systematically evaluate the effect of reach distance, humeral rotation and downward push force on the probe, in terms of surface EMG of shoulder muscles. � Hypotheses: EMG will be significantly affected by each of these three variables: reach, humeral rotation and push force.

Experimental Method � 10 participants � right handed male college students, (mean age = 26. 5 years, height =177 cm, and weight = 78. 0 kg) � 3 independent variables: � Push force – 3 levels (relaxed holding, + 22 N, +44 N, each for 5 seconds, randomized) –monitored by a load cell [Village & Trask 2007] � Reach – 3 levels (normal, maximum, extreme) [Sengupta and Das 2004] � Shoulder rotation – 3 levels (-45 o, 0 o, 45 o randomized) [Brookham et al. 2010] � 4 dependent variables: � EMG from trapezius, suprascapular fossa, triceps, and pectoralis major muscles - % MVC

Surface electrode locations Middle trapezius Supraspinatus Triceps Pectoralis major

Experimental Setup • Subject was seated in an Normal reach Maximum reach adjustable office chair. • Table height was adjusted to subject’s elbow height • Push force level was Load Cell transducer displayed on a monitor Extreme reach • The chair was turned to obtain the desired humeral rotation angles. • MVC EMG’s were collected for normalization

Data Analysis � EMG data (1000 Hz) using data log software RMS averaged over 2 seconds normalized % MVC’s were used in statistical analysis. Raw EMG Push Force � A repeated measure ANOVA using Minitab statistical software

ANOVA Results Push force, reach level, and interaction of reach level and push force were significant (p<0. 05) for the four muscle activities. � Effect of shoulder rotation was non significant (except triceps). � Since the interaction of reach and force was significant, mean effects of individual combinations of reach and force were compared using Tukey’s joint confidence interval (p<0. 05) �

Results: Mean EMG (%MVC) of chest and arm muscles EMG increasing significantly with push force from low to high � Normal reach in general produced lower muscle activity � Means that do not share a letter (A, B, C, D) are significantly different (p<0. 05).

Results: Mean EMG (%MVC) of shoulder muscles EMG is highest for extended reach and low push force combination and is significantly higher than others. � EMG generally lowest at medium push force for all reach levels. � No significant change for maximum and normal reach levels. � Means that do not share a letter (A, B, C) are significantly different (p<0. 05).

Discussion Simplified shoulder biomechanics -when the arm is abducted an upward force applied at hand, it may result in reduction of shoulder torque (T 1 < T 2), and consequently muscle activation.

Discussion of the results � Increasing push force on the transducer increased the EMG triceps and perctoralis major , the prime movers of elbow and shoulder extension. � For higher push force, extending reach levels also increased these muscle activities. � The EMG activities of the trapezius and supraspinatus were highest at low push force with extreme reach.

Discussion of the results (cont. ) � Guidelines suggest that for sub-maximal hand exertion tasks, the shoulder muscle activation should be limited to 10%-14% of MVC for long lasting intermittent or dynamic work. The EMG activity of the trapezius and supraspinatus muscles for 6 of the 10 experimental subjects were well above this limit, for extreme reach and low hand force. This posture and force combination may be risk factor for shoulder MSD. � Mean increase in trapezius from normal to extreme reach was 76%, which was comparable to 78% found by Murphey and Milkowski (2006), for shoulder abduction angle 30 o with a support and angle increasing to 75 o unsupported.

Conclusions, recommendation and limitations � � � Results in terms of the variation of muscle activity with reach, shoulder rotation and push force are applicable in planning and layout design of sonographers’ workstation with a view to reducing the risk of shoulder/neck MSD. Maintain upright posture, position as close as possible to the patient. Minimize extended reach with unsupported arm (light force), provide pillow or arm support. Only shoulder muscle activity were examined in this study of injury risk. Trained medical sonographers of both sexes as subjects would provide more validity of the results.

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