Abstract
Keywords
Introduction
Work related musculoskeletal disorders (WRMDs) are a health problem of the loco-motor apparatus, and a common problem in working populations in western countries [1]. They also constitute significant ergonomic problems encountered in the workplaces [2]. There is some evidence to suggest that WRMDs are associated with exposures to risk factors in the work place [1–4], with complaints usually consisting of a range of symptoms and disorders localized in the neck, shoulder, elbow, wrist, hand, back as well as the lower limb [1, 5]. Work related musculoskeletal disorders are the leading causes of occupational disability [2, 6].
According to the National Institute for Occupational Safety and Health (NIOSH), a high incidence of WRMDs has been reported among workers of bottling industry, compared to other manufacturing and services industries [7]. This has been attributed to the involvement of sustained awkward static postures, which is characteristics of the categories of workers; as well as the repetitive manual handling activities/motion associated with the majority of the different stages of the beverage bottling industry job tasks [8–10]. This trend of work situations poses health risk both for individual workers and the bottling company production line.
Studies have implicated WRMDs as a major cause of work-related disabilities and lost-time illness injuries in both developed, and industrially developing countries and this has been attributed to the poor working conditions [4, 11– 14]. The problem is extremely serious in the developing countries owing to the absence of an effective work injury prevention programme [12, 15]. The bottling industry has become one of the most important food industries since the invention of carbonated water and the discovery of the fermentation process. It is a large employer of labour in Nigeria, ranging from executive to casual job positions, as well as numerous individual dealers and retailers whose business revolves around products from the bottling industry.
The starting point of a bottling process begins at the de-palletizing workstation where the factory workers manually unload new cases of bottles from a pallet onto a conveyor [8]. The process of unloading new cases of bottles from a pallet onto a conveyor involves excessive overhead reaching at the beginning of a new pallet and forward bending toward the end of the unloading process [16]. Other bottling tasks, such as bottle screening, beverage bottling and crowning as well as palletizing operation have been categorized as high risk for developing WRMDs in at least one part of the body [8]. It has been suggested that an association exist between WRMDs and certain multiple physical work task variations especially repetitive machine paced tasks [17], various postural stresses [5, 8], forceful exertion – sustained static muscle action [18], contact machine stress [17] as well as work organizational and demographic confounders [8, 18].
The main focus of an ergonomics intervention is to make tasks and environments compatible with the abilities and limitations of people [19]. In most cases, this usually begins with baseline risk identification and epidemiological investigations [8]. Association between WRMDs and the working-posture assumed by beverage bottling factory workers has remained grossly understudied. Although studies have been done on work-related musculoskeletal disorder among beverage workers, none has reported the condition among African or developing country setting. Also a specific objective assessment has not been attempted to delineate association between different workstations postures of beverage workers and the occurrence of musculoskeletal disorders. This is the gap sought to be filled by the present study. Specifically, the study sought to investigate the association between working postures of beverage bottling factory workers in a developing country setting and reported musculoskeletal discomfort.
Methods
Participants
A total of 301 beverage industry workers (from eight work-stations of palletizing, depalletizing, bottle screening, compounding, carbonating, water treatment and crowning) participated in the study. They were recruited from three bottling companies located in Eastern Nigeria. Only workers who have worked for at least one year in the work-stations were allowed to participate in the study. Workers were recruited into the study if they could comprehend written English and/or Igbo language and consented to participate in the study. Supervisors or others who are not involved in direct manual handling in these work-stations were excluded from the study.
Research protocol
Prior to the commencement of this study, approval was sought for and obtained from the Research and Ethic Committee of Lagos University Teaching Hospital, Idi-Araba, Lagos, Nigeria. Cross-sectional design was employed in this study. The participants’ posture was assessed while at their duty post using Rapid Entire Body Assessment (REBA) [20] after which they were requested to complete a modified Standard Nordic Musculoskeletal questionnaire (NMQ) [21]. The detail descriptions of the NMQ and REBA have been given in previous publication [22]. As a recap, the REBA scores, risk levels and the corresponding action levels needed are as follows: REBA score of 1 means no risk and no action required; Scores 2– 3 is a low risk and may require change. With scores between 4 and 7, medium risk is described and further investigation is needed with change needed soon. Scores 8– 10 signifies high risk, and needing immediate investigation and change. A REBA score of 11 and above is described as very high risk and entails that immediate change is required[20].
There are three stages involved in this study. The first stage involved meetings with the employees of the selected beverage bottling companies, during which the aims and objectives of the study and procedures were discussed with the hope of getting approval. The voluntary consent form applicable to this study was also discussed to assure the participants of absolute confidentiality. The questionnaires, each bearing a serial number, were handed out to workers; the Igbo version was administered only to participants who could not comprehend written English Language. The second stage involves video-taping of workers as they were on their duty post carrying out their tasks; participants video clip was crossed tagged against the serial number on his/her questionnaire to enable easy references. The third stage involved the REBA frame-by-frame analysis of working posture by utilizing the memory card, laptop computer, goniometer, and a water-based felt tip marker. For each working posture, the video recording was paused and a felt-tip marker was used to draw lines on the computer screen. Then, body postures and joint angles were measured with a goniometer. Specifically, the most severe instances of flexion/extension/twist of neck and ulnar/radial deviations of the hands and wrists were sought as well as the pronation/supination of the forearm and elbows, shoulder abduction adduction, trunk twisting, forward bending, and feet location and support. Observations for the more severe posture and joint angles were made while the workers were carrying out their tasks.
Data analysis
The data collected were analyzed using SPSS (version 15.0), and presented using descriptive statistics of frequency and percentages. Inferential statistics of chi-square was used to determine association between variables. The level of significance was set at p < 0.05.
Results
Physical characteristics
A total of 301 fully filled copies of the questionnaire were returned from 367 copies that were distributed, giving 82.16% response rate. Also, 301 copies of REBA form were available for the final analysis. Table 1 showed the physical characteristic of the respondents; 222 (73.8%) and 79 (26.2%) of the respondents were males and females respectively. The highest educational attainment of the majority of the respondents was either primary education 142 (47.2%) or secondary education 102 (34.2%). The majority 89 (29.6%) of the respondents had spent between 5–6 years on the job (Table 1). Depalletizing unit had the highest 113 (37.5%) number of respondents (Table 1).
Pattern distribution of WRMDs in the different workstations is represented in Table 2. At least half of the workers in the all the workstations reported WRMDs of the neck, shoulder, upper back and lower back. WRMDs of the elbow were most prevalent at the water filling and compounding workstations with over half of the workers in these workstations reporting elbow symptoms. The compounding and water treatment workstations recorded workers with the highest prevalence of knee. More than 50% of workers these workstations reported WRMDs of the knee. See details in Table 2.
REBA analysis of participants’ postures and presentations at different workstations
At palletizing workstations, video analysis revealed that the neck was recurrently bent forward in excess of 20° and many times twisted. At the depalletizing workstation, the back was bending forward greater than twenty degrees and being twisting to the side while placing cases on the conveyor. This was also done in extreme repetitions per minute (more than 4x). Here also, subjects often stood on one leg to reach the top or very bottom layers of the pallets and lorries rendering the leg posture unstable. Shoulders of the workers at both the palletizing and depalletizing units were being raised and abducted greater than 45 degrees while reaching overhead to remove or put back cases onto the upper layers of conveying lorries or pallets. In both workstations, handgrips were less stable and wrist flexion usually greater than 15 degrees. Generally, poor quality of forward-bent postures and over-reaching of the shoulder while twisting the neck were common among the depalletizers and palletizers.
Sustained posture was the most common observed in the carbonation, compounding and water treatment workstations. The most notable in the bottle filling and crowning work stations were ranged from repetitive motion to rapidly changing postures due to machine paced operations in these workstations. The details posture rating according to REBA is presented in Table 3.
The value of REBA ground scores for the majority of the respondents in all the workstations ranged from 7 to 18 indicating medium postural risk level for 7.0% (21), high postural risk level for 55.8% (168), and very high postural risk level for 37.2% (112) of the workers; None of the respondents in all the workstations were in the low postural risk level (Table 3). Chi-Square statistics showed that there was an association between the reported WRMDs in the workstations and postural risk level of the respondents (Table 4). In all the body regions, higher prevalence of WRMDs was reported among the respondents with high or very high risks posture scores compared to those with medium. Chi-Squared test showed that there was a significant difference between respondents with medium risk – those with REBA score of 4≤7 and those with high or very high risk levels - REBA scores > 7 for wrist (p = 0.03), upper-back (p = 0.016) and neck (p = 0.02) respectively (Table 4).
Discussion
To our knowledge this is the first study in Africa or developing country setting that sought, with specific objective assessment, to delineate association between different workstations postures of beverage workers and the occurrence of musculoskeletal disorders. Specifically, the research study sought to determine the patterns of work-related musculoskeletal discomforts (WRMDs) and also to evaluate the association between postural risks and occurrence of WRMDs among beverage bottling workers. A high prevalence of WRMDs was reported in this study for almost all body parts, with the shoulder symptoms being the most commonly affected in all the workstations. This was followed by the neck, upper back and low-back in all the workstations. The finding shows that WRMDs was a common occurrence among this category of workers. Studies have shown that WRMD is extremely common among beverage bottling workers [23, 24], with the bottling industry ranked sixth among 470 industries in terms of prevalence of WRMDs [7]. However, these studies were done in the developed countries and never sought any specific factors associated with WRMDs in this population. In our study, the observed higher prevalence of WRMDs in the shoulder may be due to the fact that the tasks are performed above shoulder, repetitive in nature and required sustained static used of the shoulder muscles. It has been reported that increased activities of postural muscles are associated with altered pattern of motor activity and may eventually lead to musculoskeletal disorders [25, 26]. Ezeukwu and colleagues [17], in their study suggested that there is an association between WRMDs and certain multiple physical work task variations especially repetitive machine paced tasks.
Participants from the Depalletizing, Palletizing, Crowning and Screening workstations reported more WRMDs when compared with their counterpart from Carbonating, Bottle-Filling, Compounding and Water Treatment workstations. The reported WRMDs follow similar trend in some categories of workstations, and probably described these workers’ workstations peculiarity, vis-à-vis the demand of the tasks of these workstations. Workers from the Carbonating, Bottle-Filling, Compounding and Water Treatment workstations are more exposed to less manual tasks. At the compounding stations, WRMDs were mostly reported in the neck, shoulder, low-back and upper back; for the carbonating stations WRMDs were mostly reported in the lower back and knee; the low-back and knee were the mostly reported sites of WRMDs at the water treatment workstations.
Regarding workers from Depalletizing, Palletizing, Crowning and Screening workstations WRMDs were mostly reported in the shoulder followed by the neck, upper back and low-back. This observation has been attributed to the high manual task involved in the workstations. For instance, de-palletizing workstation is the starting point of a bottling process and it requires the workers to manually unload new cases of bottles from a pallet onto a conveyor [8]. The process of unloading new cases of bottles from a pallet onto a conveyor involves excessive overhead reaching at the beginning of a new pallet and forward bending toward the end of the unloading process [16, 27]. Bottling tasks, such as bottle screening operation, beverage bottling and crowning as well as palletizing have been categorized as high risk for developing WRMDs in at least one part of the body [8]. According to the observation from the videotaping, workers from the Carbonating, Bottle-Filling, Compounding and Water Treatment workstations were more involved in less manually involving activities while arrangement of bottles into the bottle washer (depalletizing) and palletizing tasks in beverage bottling has been identified as the most ergonomically unsound[8].
The reported high prevalence WRMDs in this study may also be attributed to other jobs’ psychosocial co-founding variables. A recent study found an association between prevalence of WRMDs and job psychosocial risks among the bottling workers [20]. According to the study, workers whose scores were rated as high organizational risk reported higher prevalence of prevalence of WRMDs in at least one body part compared to those with low or medium organizational risk ratings. The finding of the present study that about 60% and 37% of the workers work with high and very high risk postures respectively implies that the working posture is very conductive for the occurrence of WRMDs requiring an immediate corrective action - action level 4 or 5 [20] The final REBA score of 9 and above indicating high to very high risk calls for further investigation and immediate engineering and/or work method changes to reduce or eliminate musculoskeletal disorder risk. The finding of this study revealed that the shoulder is the most affected body part in bottling tasks; although symptoms may not be associated with working postures; reflecting that factors outside working posture may be acting in a complex manner to provoke symptoms.
The observed REBA scores and risk levels among the workers were significantly associated with overall prevalence of WRMDs as well as WRMD at neck, wrist and upper back. This suggests that by adopting awkward, sustained and/or repetitive postures at work, bottling workers most often suffer WRMD in at least one body part particularly the neck, wrist and upper back. This lends credence that altered patterns of postural muscle activity are associated with WRMD, a finding that has important implications for the assessment and treatment of WRMDs among this occupational group with emphasis on education of good working posture. It can therefore be inferred that habitual use of abnormal postures may result in increased mechanical muscle load and possibly precipitate WRMDs.
Given that job psychosocial co-founding variables have been implicated for WRMDs among beverage workers [22], future studies looking at effectiveness of interventions to reduce MSDs should also target interventions on job psychosocial factors. The high postural risk factors for WRMDs seen among the workers have implications for the ergonomic health of the beverage workers and invariably the companies’ production line. Certainly, efforts to reduce WRMDs should include ergonomic postural education, as well as worksite restructuring to eliminate or reduce awkward postures with ergonomic modifications to keep vulnerable joints within the optimal range of motion and positions during work tasks. Additionally, management may consider rotating workers from one task to another as a way to reduce repeated and sustained awkward postures that can lead to WRMDs. Lastly, further workstation specific investigation for other possible co-founding variables may be necessary. All workplace parties should be encouraged to meaningfully participate in problem identification, risk assessment, implementation, and evaluation stages of any control measures taken.
Limitations
The major limitation of our study is the design. The cross sectional design implored in our present study does not infer causality but only provided insight into the association between posture and WRMDs in beverage bottling workers. Also, the relatively fewer individuals with medium risk exposure compared to the number with high and very high risk category may have reduced the power of the sample to be able to draw credible comparison between posture risk ratings. However the sample size was adequately powered to compensate for the possible type 1 error.
Conclusion
In conclusion, this study has been able to show that WRMDs is of common occurrence among beverage bottling workers. The body parts commonly affected were shoulder, neck and low-back and upper back in that order. The observed higher prevalence of WRMDs in this category of workers has been attributed to the fact that tasks are performed above shoulder, and are repetitive in nature and required sustained static used of the shoulder muscles.
Conflict of interest
None to declare.