EVALUATION OF ERGONOMIC RISK FACTORS AMONG VETERINARY ULTRASONOGRAPHERS

Introduction

Txhe reported prevalence of work-related musculoskeletal symptoms among human-patient sonographers ranges from 65% to 91%.1-11 Performing sonography involves frequent wrist motion, awkward trunk and upper extremity posture while manipulating a hand-held transducer, and exerting upper extremity forces to sustain contact with the patient. Sonographic procedures typically range from 10 –to 60 min perpatient session.4 Various contact angles may create awkward wrist, arm, and shoulder postures. Sonography may also require that the operator moves into awkward neck and trunk positions to access the patient and/or view the monitor to ensure the necessary anatomic location, image, or therapeutic focus. The musculoskeletal symptom risk factors associated with human-patient sonography are associated with musculoskeletal disorders (MSD).4-7, 9 In response to high musculoskeletal symptom prevalences in human-patient sonography, the Occupational Safety and Health Administration (OSHA) and Society of Diagnostic Medical Sonography (SDMS) created the Industrial Standards for the Prevention of Work-Related Musculoskeletal Disorders in Sonography to reduce musculoskeletal symptoms and MSDs among sonographers.12

The demands of performing veterinary sonography are similar to those associated with performing sonography in human patients. These similarities suggest that sonographers examining animals are exposed to analogous physical risk factors as their counterparts, who examine people. However, industry standards for MSD risk prevention currently do not exist for professionals performing sonography on animals. Given that the exposures between veterinary and human-patient sonography appear similar, the OSHA/SDMS guidance document, recommendations, and procedures should be applicable to veterinary sonography. Our cross-sectional study aimed to evaluate the prevalence of musculoskeletal symptoms among veterinary sonographers and identify associated risk factors within the industry. Our ultimate goal was to adapt the OSHA/SDMS guidelines as suitable to veterinary sonography and evaluate effectiveness in risk factor mitigation.

Materials and Methods

We developed a comprehensive 59-question survey to evaluate the characteristics of a sonographer population, exposures, perceptions, musculoskeletal complaints, and outcomes related to sonography activities, exposures, and experiences. The survey included 15 questions associated with personal characteristics and general workplace conditions, 25 questions related to potential ergonomic risk factors, and 19 addressing musculoskeletal symptoms. The survey was developed following standardized survey methods used by ergonomists and epidemiologists to evaluate risk factors for musculoskeletal symptoms. The team of one veterinary radiologist, two ergonomists, and one biostatistician/epidemiologist developed survey questions specific to potential exposures associated with musculoskeletal symptoms based upon their extensive knowledge of the ergonomic and epidemiologic literature and then evaluated the instrument by a test administration to six veterinary radiologists. Using the feedback from this initial testing, the final survey was developed. The survey was approved by the Human Research Board at Colorado State University and was distributed via email using electronic databases made available by a number of veterinary professional associations with members likely to be engaged in sonography, including the American College of Veterinary Radiologists (ACVR), the American College of Veterinary Internal Medicine (small animal internal medicine and cardiology), and the American College of Veterinary Surgeons (equine.) A total of 1486 veterinary professionals were sent our survey. Responses were anonymous and de-identified (IP addresses from response computer were deleted) using a university licensed, web-based survey tool, EFM Continuum™ (Vovici, Rockland, MA). Data were coded and managed using Microsoft Excel (Microsoft Corporation, Redmond, WA) and transferred to SAS 9.0 (Cary, NC) for statistical analysis. Descriptive statistics were generated and frequencies and associations were investigated using a logistic regression. The relationship between musculoskeletal symptoms and physical exposure factors were evaluated first using univariate analysis to identify variables with P-values ≤ 0.25 for inclusion in the model. These variables were included in a multivariate logistic regression model to develop a final explanatory model for musculoskeletal symptoms. The model was reduced using a manual backward stepwise technique that included eliminating the largest P-values individually at each step until all remaining variables were significant at the 5% level (P ≤ 0.05). Interactions were also analyzed for association however none were significant at the 5% level. Therefore, none were included in the final multivariate model. The odds ratio (OR) and 95% confidence interval (CI) were calculated for each variable that contributed significantly to the explanatory model.

Results

We recorded 246 responses from sonographers for an overall 15% response rate. There was a 27% response rate from ACVR diplomats and residents, including a 31% response rate from diplomats. The majority of the responding sonographers were female, 56.3%, and the mean age was 42.5 years, (Tables 1 and 2). The sample population consisted of 55.1% radiologists, 31% veterinary internal medicine specialists or cardiologists, 8.6% surgeons, 3.3% technicians, and 2% general practice veterinarians. Reported heights and weights were used to calculate the body mass index (BMI), which revealed a mean value of 24.6 kg/m². Over 70% of respondents perform ultrasound examinations primarily on small animals, such as dogs and cats, while 29.5% performed examinations on both large and small animals. Most sonographers (75%) considered their working conditions to be good. Over half, 53.7%, had at least 10 years of experience in the veterinary sonography field. The overall self-reported prevalence of work-related musculoskeletal symptoms was 62% among the survey respondents (Table 3). Pain was reported during and after exams by 66.8% and 64.6% of sonographers, respectively. Sixty-two percent of respondents classified their pain as moderate to severe. The most frequently reported specific musculoskeletal symptoms were shoulder and upper arm pain (11.6%), followed by hand and wrist pain (7.7%). However, 72.9% of the sonographers experienced discomfort in multiple body areas such as hand, arm, elbow, shoulder, neck, and/or back.

Musculoskeletal symptom risk factors including force, repetition, and awkward postures were evaluated. Shoulder abduction greater than 45° was reported by 21.8% of respondents and 72% reported a least 15° shoulder abduction while performing sonography. Awkward back postures, including extension and flexion, were reported by 31.3% and back rotation was reported by 37.1% of respondents. Awkward neck postures in extension or flexion were reported by 17.4%. Respondents were given a table of movements that may contribute to job-related injury and were asked to rate each task on a scale of 0–10 on how much of a problem they perceived it to be when performing the ultrasound. Forty-seven percent of respondents rated sustained shoulder abduction over 60° as a moderate to major problem (ratings ≥ 4.) Sustained neck rotation (42.9%) or repetitive neck rotation (32.8%) was also considered moderate to major problems.

Evaluation of perceived force requirements indicated that 35.9% used moderate to heavy force while scanning. Ninety percent reported either using sustained pressure on the transducer, scanning with a twisted wrist, gripping the transducer with high pressure, or a combination of all three. Assessment of perceived levels of difficulty or problem revealed that sustained transducer pressure (50.6%), sustained twisting of the wrist (34.5%), and transducer grip (27.1%) were ranked moderate to major problems with ratings ≥ 4 (on a scale of 0–10) by reporting sonographers. Also, 29.8% of sonographers reported that one or more transducers do not feel appropriate for their hand size (Table 4).

The most common ultrasound examinations included abdomen, thorax, or both, by 68.8% of veterinary sonography professionals. The abdomen was reported to be the most difficult area to examine by 40.8% of respondents. Thirty-nine percent of sonographers used nonadjustable tables and 67.8% used adjustable chairs; however, only 18.8% of veterinary sonographers consistently used normal height chairs. Instead, the majority used stools or multiple seating arrangements (63.8%). Ten percent of sonographers reported they used a cable-supporting device when scanning. Over half of the sonographers, 58.4%, indicated they performed ultrasound procedures greater than 3 h per day, and 75.9% reported individual examinations that lasted >20 min per patient session. Over 40% of professionals reported they work at least 5 days a week. Fifty-three percent of sonographers reported they perform the same examination, such as abdominal scans, repeatedly throughout the workday.

Nearly all, 90.5%, of the sonographers reported that they have worked some portion of their career in pain. Sixty-two percent of respondents reported that their musculoskeletal symptom pain level associated with sonographic activities was moderate to severe and 9.4% had lost work time due to musculoskeletal symptoms (Table 3). Nearly half, 47%, reported suffering a muscle strain type injury (Table 5).

Evaluation of available data revealed several risk factors to be predictive for musculoskeletal symptoms, including being female gender (OR, 4.55; 95% CI, 2.04–10.19), increasing age (5-year increments, OR, 1.06; 95% CI, 1.01, 1.10), having suffered previous work-related trauma (OR, 6.86; 95% CI, 1.71, 27.40), not consistently using a normal height chair (OR, 2.63; 95% CI, 1.19, 5.80), and shoulder abduction 15–45° (OR, 2.34; 95% CI, 1.11, 4.92) (Table 6).

Discussion

The high prevalence of musculoskeletal symptoms among our population of veterinary sonographers is consistent with that reported among human-patient sonographers.2-11 The patient-sonographer position similarities between veterinary and human-patient sonography are greatest for small animal examination and affect the upper extremities, shoulders, neck, and back. Small animal patients are typically positioned on examination tables, much like human patients, and similar physical demands on the musculoskeletal systems are required by sonographers to perform the scanning and treatment tasks. Although the survey responders were predominantly imaging dogs and cats, equine sonography also likely poses ergonomic risks for multiple reasons. Sonographer position relative to the patient is less comparable to sonographers examining human patients, but physical strain on the musculoskeletal system is readily apparent and there are more situations requiring awkward positioning. Additional risks exist, such as being kicked or bitten by the patient.

Nearly all responding veterinary sonographers have worked some portion of their career in pain and some have reported lost work time. Similarly, the SDMS reported that over 80% of human-patient sonographers performed scanning while suffering pain.12 Importantly, human-patient sonography risk factors are significantly correlated with increasing severity of musculoskeletal symptoms.6 Our findings also suggest that exposure to risk factors over time may be related to musculoskeletal symptoms in veterinary sonography and that their ubiquitous nature may be due to a lack of guidelines and training in ergonomic standards and controls.

The most frequently reported conditions were carpal tunnel syndrome (CTS) and tendonitis. A similar CTS prevalence rate of 4.5% was reported among human-patient sonographers.3 Also, high-pressure transducer hand grip in human-patient sonography was significantly correlated to symptoms associated with CTS.5 The similar prevalence of CTS among small animal and human-patient sonographers suggests that similar risk factors may be present in both professions.

In our study, many respondents who reported pain related to scanning experienced the pain within 5 years of starting to perform ultrasound exams, similar to prior research on human-patient sonographers.12 We also found that 5-year increases in age were associated with increasing musculoskeletal symptoms (OR, 1.06; 95% CI, 1.01, 1.10). This was not surprising, given that there is also an association between age, cumulative exposure, and susceptibility to musculoskeletal symptoms in human-patient sonographers; age was associated with both hand and back musculoskeletal symptoms.7 Previous work-related trauma was also associated with experiencing musculoskeletal symptoms (OR, 6.86; 95% CI, 1.71, 27.40) and was reported by 20% of the respondents. These findings are consistent with human-patient studies that have shown the association between previous trauma and reported musculoskeletal symptoms.7

Seventy-five percent of sonographers in our study considered their working conditions to be good. This suggests that veterinary professionals are not aware of ergonomics and the role that work methods and environment play in relation to their risks for musculoskeletal symptoms and MSDs. The veterinary sonographer profession may be largely unaware of the SDMS/OSHA human-patient guidelines and therefore could mistakenly perceive good working conditions despite their exposures to musculoskeletal symptoms, MSD risk factors and adverse outcomes. Alternatively, the survey question, “what best describes your working conditions?” may have been answered in a general sense by many respondents, most of whose work life is not spent entirely in ultrasound. This type of question is typically asked in surveys to determine biopsychosocial factors in work-related musculoskeletal symptoms and disorders.13

The increased female risk for musculoskeletal symptoms in our population is consistent with other data.1 The mean BMI for veterinary sonographers suggests they are on the upper limit of the normal healthy range. Although 5 unit increases in BMI from this study were not associated with musculoskeletal symptoms, increased BMI has been identified as a MSD risk factor in other studies.1

We identified a significant association between shoulder abduction and musculoskeletal symptoms; shoulder abduction <20 was a contributing factor to the development of injury in sonographers.11 We hypothesize that exposure to shoulder abduction in combination with force and repetition during veterinary sonography increases the odds of experiencing musculoskeletal symptoms. Also, awkward back postures in extension, flexion back rotation were reportedly common. The prevalence of back and neck musculoskeletal symptoms in human-patient sonographers ranges from 18.5% to 67%.6, 7 We found that 81.2% of veterinary sonographers did not use a normal height chair consistently and there was an association between this and musculoskeletal symptoms. A similar association has been was identified between uncomfortable chairs that created awkward trunk postures and back-related musculoskeletal symptoms.7

Evidence of association requires ergonomic evaluation, which includes the degree of abduction, frequency, duration, and force. The epidemiologic evidence for risk is strongest where there are combined exposures to multiple physical factors.1 The National Institutes for Occupational Safety and Health (NIOSH) reports that there is sufficient evidence for a positive association between exposure to combined risk factors, for example, between force, repetition, and awkward posture, and tendonitis and/or CTS, and between awkward back postures and lower-back pain.1

While the overall response rate was only 15%, the responders included 31% of board-certified radiologists. Since these are among the largest population of full-time sonographers, that response rate can be considered representative sampling of veterinary sonographers at large. In addition, while overall participation was low, the response rate of a survey cannot be used to predict the magnitude of nonresponse bias. When the correlation between the measure of interest and propensity to participate is low, nonresponse bias is also low.14

Selection bias could have influenced these results in several regards. Those with musculoskeletal symptoms may have been more likely to respond, but on the other hand, individuals who have suffered significant musculoskeletal symptoms may have already stopped performing sonography and may not have responded to the survey. While participation propensity may have been correlated with the presence of musculoskeletal symptoms and, as a result, musculoskeletal symptoms prevalence may have been overestimated, this is unlikely to have occurred because the observed prevalence in our study was similar to that observed in human-patient sonographers.2-11 The observed associations between the risk factors of interest and musculoskeletal symptoms may also have been affected by nonresponse bias if these associations were different among those who participated in the survey and those who did not. However, age and gender are not well-known risk factors among the general public and are therefore unlikely to have affected participation propensity. While appropriate chair use, previous work-related trauma, and shoulder abduction may have increased the likelihood of participation among persons with musculoskeletal symptoms, our results were similar to those found in human-patient sonographers.6, 7 Further, risk factors such as awkward back posture, which may have increased participation among musculoskeletal symptom respondents, were not significantly associated with musculoskeletal symptoms in our study. This suggests that the awareness of risk factors was unlikely to have had a great effect on participation propensity among persons with musculoskeletal symptoms.

Recall bias can also occur in surveys, with respondents having difficulty accurately remembering details about past activities, environmental conditions, or other variables. This could result in a differential bias toward certain risk factors being missed. Response bias can also affect survey results since some people may not accurately report their weight, height, actual work time, or amount of force needed to perform their work. For example, BMI has been found to be associated with musculoskeletal symptoms by some investigators, but not in our study. If BMI was reported inaccurately, that could underestimate the risk for musculoskeletal symptoms.

In summary, the prevalence of musculoskeletal symptoms among veterinary sonographers is similar to that of human-patient sonographers.2-11 Many of the same musculoskeletal symptom risk factors may exist among both groups of professionals. Veterinarians performing small animal sonographic examinations and treatments could potentially benefit from adopting the OSHA/SDMS guidance for human-patient sonographers, which recommend height-adjustable chairs with lumbar support and swivel casters to promote neutral trunk postures and to prevent shoulder abduction > 30°.12 We found that 81.2% of veterinary sonographers did not consistently use a normal height chair and there was an association between this, and also between shoulder abduction, and musculoskeletal symptoms. The SDMS/OSHA guidelines also recommend monitors that are height adjustable, mounted separately, are moveable from the control panel, and have tilt functionality to enable standing or seated postures for users to achieve neutral neck postures while viewing during scan procedures. The guidelines recommend that monitors be movable with single-hand forces or effort thereby allowing users to work easily while maintaining healthy neck postures.12