Neck Solutions

From: NIOSH Publication No. 97-141 Musculoskeletal Disorders and Workplace Factors

Definition of Posture for Neck and Neck/Shoulder Pain

We included those articles that mentioned neck posture or head postures, adverse or extreme head or neck postures, or static postures of the head and/or neck.

Studies Reporting on Posture as a Work Factor for Neck and Shoulder Pain

We included 31 studies of the association between extreme or static posture and neck and neck/shoulder pain, including TNS. Studies usually focused on the different prevalences of neck symptoms and/or physical findings in workers in occupations or tasks requiring some combination of forceful, repetitive movements, and extreme or static postures of the upper extremity, and compared them to workers in occupations without those requirements.

Twenty-seven studies that considered extreme or static posture found a statistically significant positive association between posture and neck or neck/shoulder pain; three had non-significant findings, 13 studies had estimations of risk. Eleven studies did not report their results in terms of ORs or PRRs; of these, all but one found a significant relationship.

Studies Meeting the Four Evaluation Criteria
Of the 31 studies evaluating neck postures and neck pain, the four investigations mentioned above [Ohlsson et al. 1995; Jonsson et al. 1988; Kilbom and Persson 1987; Kilbom et al. 1986] fulfilled the four evaluation criteria. Three of these studies [Jonsson et al. 1988; Kilbom et al. 1986; Kilbom and Persson 1987], dealt with the same cohort; female electronics workers followed for 3 successive years. These studies found significant association between posture variables and neck pain; however, none used methods that reported ORs.

Studies Not Meeting the Four Criteria for Posture and Neck and Shoulder pain
Bernard et al. [1993] carried out a cross-sectional study of 894 newspaper employees using a questionnaire survey for case definition based on frequency, duration, and intensity of symptoms in the neck. Exposure was based upon both questionnaire and job analysis. Time spent on the telephone was associated with an increased prevalence of neck pain, with a slightly elevated OR of 1.4. Analysis was controlled for age, gender, height, psychosocial factors, and medical conditions.

Kukkonen et al. [1983] compared 104 data entry operators with 57 female workers in varying office tasks. Neck pain was based on pre-determined symptom and physical exam. Exposure was based on observation of posture, movements and working techniques, assessment of equipment, interview with workers and supervisors. An intervention consisting of adjustment of office furniture and equipment was carried out. The study group was given a short course of basic training on pertinent aspects of ergonomics. Four lessons on relaxation was given by means of exercises. There was no controlling of confounders. There was a significant decrease in tension neck syndrome among the cases involved in the intervention compared to those workers who had no change.

Linton and Kamwendo [1989] surveyed 22,180 employees undergoing screening examinations at their occupational health care service in Sweden. Neck cases defined from questionnaire responses as those persons reporting “yes” to having seen a health care professional for neck pain in the last year. Cases were compared to “non-cases” defined by outcome (neck pain). Exposure was based on questionnaire responses regarding heavy lifting, monotonous or assembly line work, sitting, uncomfortable work postures (bending and twisting), and vibration. The psychosocial work environment was also studied; the analysis was stratified for age and gender.

As part of a longitudinal study, Viikari-Juntura et al. [1994] studied 154 subjects from Helsinki, Finland that originally entered the study in 1955, and had repeated cross-sectional exams from 1961 to 1963. During that time, 1084 subjects underwent cross-sectional examination. In 1985, a questionnaire was sent to all subjects; 801 (74%) responded. Of the respondents, 180 lived in the Helsinki area. It was from this group that 162 responded. Eight were excluded due to illnesses. Outcome was based on questionnaire data for this study — because of small number of abnormal physical findings, the physical exam was eliminated from analysis. Exposure was also based on survey, asking the amount of work with hands overhead, work in forward bent position, and work in twisted or bent position. This analysis was controlled for physical and creative hobbies, with no interactions seen.

In a cross-sectional study of machine operators, carpenters were compared to office workers by Tola et al. [1988], who used a postal questionnaire to obtain both health outcome and exposure information. Analysis used “occupation” to examine relationships. Pain Drawing Diagrams were used to distinguish body areas. For the logistic regression model a 12 month prevalence of neck and shoulder symptoms on 8 days or more was used. The logistic regression models were adjusted for years working in an occupation and age.

Welch et al. [1995] examined 39 electricians at a screening convention using surveys to collect information on symptoms and exposures. The questionnaire included questions concerning the frequency of tasks performed, including the percent of time spent hanging duct work. The analysis did not control for confounders except for length of employment.

Strength of Association for Posture

Ohlsson et al.’s [1995] study, discussed previously, compared female industrial workers performing repetitive tasks to referents without such exposure and found significant associations (p<0.05) between (1) neck and neck/shoulder diagnoses with time spent in neck flexion, with critical angles greater than 15°; and (2) neck/shoulder diagnoses and time spent with upper arm abduction greater than 60°.

Kilbom et al. [1986], in the initial paper concerning the electronic workers, reported two findings: (1) that the more dynamic the working technique, the fewer neck symptoms experienced by electronic workers; and (2) that the greater the average time per work cycle spent in neck flexion, the greater the association with symptoms in the neck and neck/shoulder angle. A statistically significant association (p<0.05) was also obtained from the job analysis variables describing neck forward flexion and upper arm elevation and neck and neck/shoulder disorders. Jonsson et al. [1988], in the follow-up study, performed an analysis that grouped the different parts of the neck and upper extremity into a health outcome labeled “cervicobrachial disorder” (unlike the cross-sectional study by Kilbom et al. [1986] that used “neck” and shoulder”). They found that the relationships between MSDs and neck forward flexion, upper arm elevation, and cervicobrachial disorders weakened (compared with the results that Kilbom et al. [1986] had found), but that the results still remained statistically significant in some of the multifactorial analyses (no numerical results were reported). The most important finding, according to the authors, was that reallocation to more varied work tasks was a strong predictor of improvement over the second year. This change would have decreased static loading and increased the dynamic pattern of movements of the workers.

Of those studies not fulfilling the four criteria, results regarding extreme or static posture were similar to those of the studies which did fulfill them. Sakakibara et al. [1995] found a significant difference in the prevalence of neck MSDs when they examined orchard workers who picked and bagged pears and two months later picked and bagged apples. Exposure was assessed by job analysis and posture measurements of two representative workers. Arm and neck elevation was significantly greater for bagging pears (more than 90° for 75% of the time) than for bagging apples (less than 40% of the time). The same authors found similar results in 1987 when only the symptoms of orchard workers were studied. They found significant a positive association between posture and neck pain, reporting histograms (not ORs) in their article.

Although they did not mention the participation rates in their methods, Aaras [1994], Veiersted and Westgaard [1994], and Bjelle et al. [1981] found significant relationships between postures and neck MSDs (they fulfilled the other three criteria). Veiersted and Westgaard [1994] found an association between “perceived strenuous postures” and neck pain (OR 7.2), but found that these perceived postures were not reflected in any of the conventional EMG parameters (static, median or peak loads) measured in the participants. One explanation for these results may be information bias, if the data concerning perceived strenuous posture are from questionnaires. Another explanation may be that EMG testing results reflect parameters for a single day, whereas symptoms were asked about concerning the entire previous year.

Several studies that carried out no independent assessment of ergonomic factors, but relied on self-reported exposure found significant relationships between posture variables and neck disorders. Ekberg et al. [1994] found an OR of 4.8 for the variable “work with lifted arms,” and an OR of 3.6 for “uncomfortable sitting position” and neck pain. Hales et al. [1994] found that “use of bifocals” (OR 3.8) in VDT users was significantly associated with neck MSDs; this variable was interpreted to be a surrogate for neck posture, as bifocals require either neck flexion or extension for eye accommodation when viewing a VDT screen. Bernard et al. [1994] reported that as workers’ time spent on the telephone increased, so did the ORs for neck symptoms, and interpreted this variable as a surrogate for static posture requiring neck deviation to cradle the telephone receiver. Holmström et al. [1992] found that the odds of workers with neck pain reporting working with hands above their shoulders for greater than 4 hrs/day compared with those reporting less than 1 hr/day was 2.0, a statistically significant finding. Bergqvist et al. [1995a] reported an OR of 4.4 for workers using highly placed keyboards in their logistic modeling of neck pain. Kuorinka and Koskinen [1979] found an increased OR (4.1) of neck pain for scissor makers (chosen for their stereotypic, repetitive work using extreme postures) compared to shop assistants, although no quantitative measurements or observations of neck posture were reported. One study by Hunting et al. [1981] showed a fairly strong association (OR 4.9) with constrained postures and neck MSDs in those workers having neck flexion of more than 56° and an OR of 9.9 from the comparison of groups. Several articles with significant posture and neck pain associations dealt with comparisons of workers in occupations chosen for higher observed combinations of exposure factors and compared them to workers with fewer observed exposure stressors: Viikari-Juntura et al. [1994], OR 3.9 to 4.2; Milerad and Ekenvall [1990], OR 2.6; and Wells et al. [1983], OR 2.57.

For those studies that did not find a significant relationship, 2 out of the 3 did not carry out observation or measurement (ergonomic assessment) of the neck or upper extremity postures. Ferguson [1976] stated that seven body dimensions were measured in the telephonists studied, but that neither discomfort nor aching were linked with any of these body postures. The article does not mention the body postures that were measured. Ferguson’s conclusion, that “physical complaints in telephonists are probably due to static load on joints and muscles occasioned by the fixed forward bent position determined by visual, auditory and manipulative tasks.” Ferguson’s data are contrary to the conclusions presented. These conclusions may then only be speculative.

Temporality for Extreme or Static Postures

The prospective study by Veiersted and Westgaard [1994] followed the development of trapezius myalgia among 30 female chocolate manufacturing workers. Seventeen workers developed the pain within 6 to 51 weeks of starting work. Perceived strenuous postures on the assembly line were found to contribute to the disorders. Although retention of subjects was low (55%), the authors found that the “drop-outs” did not differ in exposure estimates and symptom reporting from those retained in the study. The prospective study of Viikari-Juntura et al. [1994] used self-reported symptoms and exposure defined by occupational status to find a temporal relationship between the development of severe and persistent severe neck pain and jobs involving dynamic work, static posture, and whole body vibration, as compared to office work.

Consistency in Association for Extreme or Static Postures and Neck Shoulder Pain

Of the 31 studies we reviewed reporting results on the association between specific or static posture and neck and neck and shoulder pain, 27 found statistically significant associations. There were many different studies reporting ORs of greater than 3.0 with CIs above 1, indicating that the effects were not explained by chance. Consistent associations were also found in those studies dealing with specific postures and neck pain across many industries, from fish workers [Ohlsson et al. 1995] to fruit pickers [Sakakibara et al. 1995], to assembly line workers [Jonsson et al. 1988], to garment workers [Vihma et al. 1982; Andersen and Gaardboe 1993a,b].

Coherence of Evidence for Extreme Or Static Postures

See section above under Coherence of Evidence for Force.

Exposure response Relationship for Specific or Static Postures

The study by Ohara et al. [1976], mentioned earlier, not only portrayed the multifactorial nature of neck and shoulder pain, but documented that an increase in specific and static postures by cash register operators using new registers placed on unsuitable counter heights increased symptoms in neck pain.

Several studies have suggested an exposure response effect between increased level or duration of exposure and an increase in number of cases of neck pain. Burt et al. [1990], in their investigation at a major urban newspaper, found that an increase in the self-reported percentage of time spent typing at VDT keyboards was associated with a moderate increase in neck symptoms. (Job analysis found a significant relationship between independent observation of time spent typing and self-reported time) Keyboard time was considered by the authors to be a surrogate for time spent with the neck held in static postures with arms unsupported. Rossignol et al. [1987] found that the prevalence of neck symptoms among 1,545 clerical workers increased with the number of hours per day using VDTs. Knave et al. [1985] found that, among VDT operators, total daily working hours and time spent at the VDT screen were significant risk factors for neck pain. Andersen and Gaardboe [1993a,b] found an exposure response relationship between persistent neck pain and years of being a sewing machine operator, controlling for age.

Conclusions Regarding Extreme or Static Postures

Overall, the strength of the association (OR ranging from about 1.6 [Vihma et al. 1982] to 7 [Veiersted and Westgaard 1994], dropping the outliers) between specific postures and neck MSDs was similar between studies using the most restrictive criteria and carrying out a prospective design and those that used symptom-based health outcome or self-reported exposures to static or specific postures and cross-sectional methods. We conclude that there is strong evidence for support of an association between static or specific postures and neck and neck/shoulder MSDs based on strength of association criteria. A positive relationship has been observed between exposure to this risk factor and neck or neck and shoulder pain in studies where chance, bias, and confounding can be ruled out with reasonable confidence.