تجزیه و تحلیل ارگونومیک بارهای وضعیتی و عضلانی برای سونوگرافیست های تشخیصی

Musculoskeletal disorders are prevalent in diagnostic sonographers. This study quantifies the postural and muscular loads during ultrasound scanning. Video-based stop-motion postural analysis at 4 samples/minute for 24 full scans (527.5 minutes) by 11 sonographers showed sonographers spend 68% of scanning time with >30o shoulder abduction, 63% with >30o shoulder outward rotation, and 37% with the neck bent forward, laterally or twisted >20o. The shoulder was observed to be unsupported, or static, for 73% of scanning time and this was significantly higher for carotid scans compared with abdominal, obstetrical or leg scans (p<0.05). Electromyography (EMG) was collected for seven scans performed by three sonographers on three shoulder muscles: Supraspinatus, infraspinatus, and trapezius; as well as for flexor carpi ulnaris. Static (0.10) amplitude probability distribution functions (APDFs) for all three shoulder muscles exceeded 3% MVC corresponding to a “medium” risk rating for shoulder–neck disorders. Mean forearm flexor EMG was 3.96 kg (SD 2.94), with occasional peak forces as high as 27.6 kg. Relevance to industry Diagnostic sonographers experience long durations in static shoulder abduction and outward rotation, with high peak and sustained grip forces. These risk factors are consistent with the high prevalence of neck and upper limb musculoskeletal disorders and symptoms reported by many sonographers.

1.1. Musculoskeletal pain and injuries among sonographers Numerous studies have been conducted in the past decade documenting musculoskeletal injuries and symptoms among sonographers in the US (Smith et al., 1997; Pike et al., 1997), and Canada (Muir et al., 2004; Wihlidal and Kumar, 1997; Russo et al., 2002). Although the point prevalence for neck and upper limb pain for the general population is 13–22%, for sonographers it is between 63% and 91% (Brown and Baker, 2004). Wihlidal and Kumar (1997) reported three clusters of pain syndromes: Neck and interscapular pain; shoulder and upper arm, elbow and hand/wrist pain; and frontal headaches and visual discomforts. There is a considerable level of disability associated with these injuries: 80% of sonographers seek treatment for MSIs (Muir et al., 2004); 46% use physiotherapy or medication to control the pain (Smith et al., 1997); 16.7% missed work due to symptoms while a further 9.4% reduce their hours, 14.6% reduce their regular duties, 21.2% use sick leave, and 11.75% use vacation days (Wihlidal and Kumar, 1997). Although an estimated 20% of sonographers leave the profession due to persistent pain (Brown and Baker, 2004), only 12.9% of Canadian (Wihlidal and Kumar, 1997) and 4% of US (Vanderpool et al., 1993) sonographers reported the injuries to Workers’ Compensation. 1.2. Risk factors for neck/shoulder and upper limb injuries Musculoskeletal symptoms or discomfort have been found to be correlated with a number of workplace factors: Long scan duration (Muir et al., 2004; Vanderpool et al., 1993), high scan frequency (Muir et al., 2004); a higher number of obstetrical scans (Muir et al., 2004); and the use of manually propelled devices (Smith et al., 1997). Studies of sonography work suggest shoulder risk factors include habitual arm abduction and isometric static loading, forceful gripping and applying pressure through the transducer, and habitual rotation of the upper spine (Brown and Baker, 2004). Constrained work involving repetitive movements with the hands and static muscle loading of the neck and shoulder have been shown to be risk factors for the neck/shoulder (Winkel and Westgaard, 1992a and Winkel and Westgaard, 1992b), and neck and intrascapular pain has been shown to be significantly related to sustained shoulder abduction, twisting of the neck and trunk, repetitive twisting of the neck and trunk and clerical activities in sonographers (Wihlidal and Kumar, 1997). Risk factors for hand/wrist and elbow disorders include forceful or sustained gripping, high repetitions and awkward bending/twisting postures (Silverstein, 1985). Although these hand/wrist risk factors have been studied extensively in short-cycle tasks of assembly lines and meat processing work, to our knowledge they have not been studied in sonographers. 1.3. Mechanism of injury at the shoulder Three mechanisms have been suggested for shoulder injury. The first is mechanical compression of the supraspinatus tendon between the humeral head and the acromion process (Garg et al., 2006). The second is a reduction in the blood supply to the supraspinatus and infraspinatus muscles and tendons due to an increase in intra-muscular pressure when the arm is elevated (Garg et al., 2006); fatigue and reduced blood flow occur at moderate levels of abduction (30°), even without a load in the hands. The third mechanism occurs when prolonged static contractions (as little as 3–5% MVC) of the trapezius muscle result in an overload of type I muscle fibers (Jonsson, 1988), which may lead to selective motor unit fatigue and damage (Hagberg et al., 1995). 1.4. Objectives This study will investigate the postural and muscular loads involved in performing ultrasound sonography scans, specifically the extent of abduction and outward rotation of the shoulder, neck bending/twisting and unsupported shoulder postures, and electromyography (EMG) of three neck/shoulder muscles (trapezezius, supraspinatus and infraspinatus) as well as the gripping force of the flexi carpi ulnaris holding the transducer. These will be compared with guidelines and studies of other workers from the scientific literature.

Quantification of the posture and muscle loads of sonographers performing actual scans shows long durations of static and awkward shoulder abduction and outward rotation, measured both with stop-motion video tape postural assessment and with electromyography of the shoulder muscles. High and sustained grip forces were found, which have not previously been quantified for the hand/wrist. These risk factors are consistent with the high prevalence of neck and upper limb musculoskeletal disorders and symptoms reported by many sonographers in studies conducted in the US and Canada. The wide variability in posture and muscle load among sonographers measured in our study warrants further investigation to develop effective controls measures to reduce risk of injury.