Alleviating four-legged problems
Ergonomic interventions can reduce injury potential for equine veterinarians
By Meghan Rogers, Kinley Taylor and David Kaber
Equine veterinarians or “horse doctors” are exposed to physically strenuous work tasks on a daily basis, which can cause bodily injury. Although serious acute trauma can occur from the occasional horse kick or other events, the most common injuries are work related musculoskeletal disorders (WMSDs) due to cumulative micro-trauma. Recent studies in Applied Ergonomics have quantified this problem, revealing that 100 percent of surveyed equine veterinarians reported suffering from musculoskeletal discomfort within a 12-month period.
The prevalence rate is higher than those for veterinarian healthcare counterparts, as well as nurses, doctors and dentists for human patients. The high prevalence rate also leads to high costs for individual practices in terms of lost work days due to injury and the need to train additional labor on work activities, etc.
While previous studies have surveyed veterinarians to identify what they believe are leading factors in injuries, research based on quantitative ergonomic analysis needs to identify the actual tasks that contribute to cumulative trauma injuries. This study sought to identify potential risk factors for work-related musculoskeletal disorders in large animal operations, to quantify the extent of veterinarian exposure and recommend control measures.
These objectives were met by following a procedure that involved analyzing typical veterinary tasks for treating large animals; screening veterinary jobs for ergonomics-related risk factors associated with WMSDs in other domains using both qualitative and quantitative methods; identifying ergonomics guideline violations in current task designs; and recommending ergonomic interventions to improve veterinary task safety. The risk assessment focused on the potential for distal upper extremity and low-back disorders. The study was expected to reveal those tasks contributing most to the overall risk of veterinarian injury.
Methods and results
In the first phase of the study, we shadowed equine veterinarians at a university veterinary hospital. Veterinary tasks were observed by two researchers over seven different days, resulting in observations of 18 different tasks and 26.5 hours of video. Ten of the 18 tasks were identified for further screening due to previous reports that they were considered hazardous to workers. These tasks included restraint, lameness exams, injections, rectal palpations, dental work, surgery, positioning, lifting, performing ultrasounds and obstetric procedures. A hierarchical task analysis (HTA) was conducted for all of the observed tasks using the videotapes as well as verbal protocols of the participants recorded by the researchers. HTA diagrams were used as a basis for identifying areas of particular risk factor exposure or areas in need of ergonomic interventions.
A subjective screening tool developed by The Ergonomics Center of North Carolina determined which of the 10 observed tasks posed certain levels of risk to veterinarians. The tool incorporates aspects of other validated ergonomic assessment techniques (e.g., hand activity level, National Institute for Occupational Safety and Health (NIOSH) lifting equation, rapid upper-limb assessment, Borg scale), to identify ergonomic risks. The target tasks were assigned “low,” “moderate” or “high” subjective ratings for the potential risk factors of extreme posture, high force and repetitive motion.
Two ergonomists rated each body part based on observations in the field and videotapes. These ratings were weighted and summed for a total job score. Results were averaged between raters. The mean score was used to categorize jobs into one of three ergonomic risk groups, also designated as “high,” “moderate” and “low.” Lameness exams, rectal palpations, positioning and obstetric procedures all had high risk scores.
In addition, participants identified areas of body discomfort via a survey. Results revealed that veterinarians experienced the greatest discomfort in the areas of the lower back and upper extremities. These results were consistent with the output from the subjective screening tool, which most frequently gave the highest risk ratings to the hands/wrists, arms, back and shoulders. Subsequently, job risk was quantified further by calculating the product of the severity of exposure to risk factors (i.e., the job screening scores) and the frequency of task performance (times per day and year). The top six tasks (lameness exams, ultrasounds, lifting, restraint, injections and rectal palpations) were separated for further analysis based on the job risk and their contributions to work-related musculoskeletal disorders as reported in the literature.
In a second and final phase of the study, we conducted a quantitative ergonomic analysis of veterinarian work tasks identified as high risk in the first phase. Data collection also was performed at a university veterinary hospital using an animal patient typically used by the teaching unit. The participants included two experienced veterinarians (one female and one male). They were outfitted with an electro-goniometer on their wrist and four force sensing resistors (FSRs) located at the palm of the hand.
The twin axis electro-goniometer was used to measure flexion-extension and radial-ulnar deviation at the wrist with an accuracy of plus or minus two degrees. The FSRs were placed in the center of the participant’s hand, taped to the palm using medical tape and covered with a latex glove. The sensors had an active surface area of a half inch in diameter and hand forces were measured in pounds using the ergoPAK system. Each participant performed the six high-risk tasks twice, with the exception of the injection task (due to the nature of the task and the safety of the animal). Video recordings were made for data verification and further postural analysis.
This quantitative body of data was used as a basis for identifying violations of validated ergonomic criteria, including strain index levels and the NIOSH spinal compressive force limit (770 pounds). The raw posture data, as shown in Figure 1, revealed that lameness exams (among the top six high risk tasks) exposed the veterinarians to the most extreme wrist postures in terms of flexion, extension and ulnar deviation. The strain index was used to assess whether the observed wrist postures contributed to a high risk of developing distal upper-extremity disorders. Results revealed that lameness exams, lifting and performing ultrasound procedures put the veterinarians at high risk for such disorders.
The raw force data, detailed in Figure 2, revealed that performing ultrasounds and lifting medical equipment required the greatest amounts of force at the hands. Comparison of average low-back compressive forces, determined using the University of Michigan’s 3-D static strength prediction program (3DSSPP) with NIOSH spinal compression limits indicated that none of the observed tasks exceeded the defined criterion. Finally, another objective measure of job risk due to veterinarian work mix was calculated as the product of task frequency and the ratio of job demand divided by worker capacity (as determined with the 3DSSPP software). It was revealed that the six tasks under study contributed to veterinarian risk of injury with ultrasounds being the highest, followed by restraint, lifting, palpations, lameness exams and injections as the lowest.
Ergonomics interventions were formulated with the intent of mitigating some of the risks identified for equine veterinarians. The recommendations were organized in terms of interventions at the horse, interventions in the “path” between the horse and the veterinarian (i.e., how the veterinarian interacts with the animal) and interventions at the source of the procedure (i.e., the veterinarian). The interventions were classified further based on the type of control to be applied, including engineering controls, or modifications to the design of the system; administrative controls, or modifications to the work process; and personal protective equipment (PPE) to be worn by the veterinarian.
Based on the results of the quantitative data analysis, lameness exams, lifting and ultrasounds were identified as having the highest priority for interventions. (Note: PPE controls were identified only for the ultrasound task.) All recommendations were reviewed for practicality by an experienced equine veterinarian who identified any caveats to the interventions.
Lameness exams. Interventions to mitigate the risks of performing lameness exams should reduce the forces and awkward postures required of veterinarians. To help cut the amount of time spent in a sustained awkward posture, an engineering control in the form of a hoof jack could be used to lift the horse’s leg. This intervention may have limited usefulness if the lameness exam requires flexing the fetlock joint versus just holding the horse’s leg passively up in the air.
Also, flexion tests, as part of lameness exams, could be conducted on an elevated platform to reduce bending. The platform should have a sloped ramp in order to allow the horse to trot off immediately after the flexion test. Additionally, administrative controls such as restricting the number of lameness exams performed sequentially, training in postures that increase bending at the knees instead of flexion at the back, or requiring that flexion tests be performed in a seated position should be implemented.
A stool could be practical for a front leg flexion test, but it probably would not be tall enough to work for a hock flexion test. It also is important to ensure that the horse is well-behaved to avoid the potential for acute injury that can happen if the horse kicks the veterinary staff members.
Lifting. Recommendations for lifting interventions involve engineering controls in the form of buckets with larger diameter handles or two handles. This would help with coupling issues and distribution of the load. Administrative controls such as filling buckets with water at the destination instead of carrying a full bucket or using a two-person lift when performing heavy lifting and carrying tasks should be adopted. If a second person is not available, a cart should be used in lieu of carrying heavy objects by hand. Finally, it is important when lifting to bend down at the knees and avoid excessive forward and lateral flexion at the back.
Ultrasound. Engineering controls for ultrasound procedures should be put in place to raise the animal when performing ultrasounds underneath the body or to the lower extremities. This will mitigate bending by veterinarians. The horse could be placed in lifted stocks or on a raised platform during these tasks. If raising the animal is not possible, administrative controls should be applied, such as requiring veterinarians to sit on a stool (lower the body) or assume a kneeling posture with the aid of knee pads. This is preferable to postures that require significant flexion of the back. However, kneeling during ultrasounds limits the veterinarian’s ability to move away from the animal quickly to avoid being kicked.
Conversely, if the area to be probed is high on the animal, the veterinarian should stand on a miniature stepladder to prevent working with his or her arm elevated above shoulder level. Another option when working high on the animal is to sit on a raised stool next to the horse, but only if the horse is restrained in stocks.
Based on review of previous research and results in the area of musculoskeletal disorders among veterinarians, it can be seen that such injuries are extremely prevalent, and they have a major impact on private practice operations as well as the careers of individual veterinarians. A number of studies have been performed to assess the prevalence rates of WMSDs among large animal veterinarians; however, few studies have provided insight into which tasks may be causing cumulative traumas as well as the magnitude of risk factor exposure (e.g., postures and forces).
So this study focused on ergonomic evaluations of equine veterinarian tasks to identify risk factors and what levels exceeded ergonomic guidelines for injury prevention. Recommendations of interventions for the identified hazardous tasks were outlined to mitigate the risks seen in those tasks and increase the safety of the worker. Future research is needed to assess the effectiveness of specific interventions (e.g., ultrasound scanning and system technologies) for reductions in cumulative trauma disorders for veterinarians.
Meghan Rogers is a usability researcher at Delta Air Lines in Atlanta. During the time of this study, Rogers was a graduate student and NIOSH fellow at North Carolina State University in the Department of Industrial and Systems Engineering. As a graduate research assistant, she worked on a variety of human factors/ergonomics projects through the Ergonomics Lab and The Ergonomics Center of North Carolina before graduating with her master’s degree in industrial engineering. She previously received her bachelor’s degree in mechanical engineering from Georgia Tech and subsequently worked as a human factors engineer at Gulfstream Aerospace.
Kinley Taylor has a master’s degree and a bachelor’s degree in industrial and systems engineering from North Carolina State University. Her research is focused on ergonomics, human factors and safety with an interest in healthcare applications. For graduate school, she received a fellowship from NIOSH.
David Kaber is a professor of industrial and systems engineering at North Carolina State University and associate faculty in biomedical engineering and psychology. He is a recent fellow of the Human Factors & Ergonomics Society. His background is in occupational safety and ergonomics. His Ph.D. is from Texas Tech University, and he previously worked as an assistant professor at Mississippi State University. He has published more than 50 journal articles and 100 conference proceedings papers. He recently edited the book Advances in Cognitive Ergonomics with Guy Boy. His research interests include ergonomics-related risk factors in manual tasks and injury potential, virtual reality and haptic interface design for motor skill rehabilitation, and models and measures of human behavior with advanced automated systems.