Pergamon Safety Science Vol. 27, No. 2/3. pp. 129- 139. 1997

0 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain

0925.7535/97 $17.00 + 0.00

PII: SO9257535(97bOO75-X

OVEREXERTION-INJURY TYPES AMONG FEMALE SWEDISH NURSES AND NURSING AUXILIARIES: AN AGE-RELATED PROBLEM?

Lucie Laflamme *

Division of Social Medicine, Depatfment of Public Health Sciences, Karolinska Institute, S- 7 72 83 Sundbyberg, Sweden National Institute of Public Health, Injury Prevention Programme, P.O. Box 27848, S-l 1593 Stockholm, Sweden

Abstract-The study examines the age-related risk of types of overexertion injuries among female nurses and nursing auxiliaries in Sweden, Overexertion-injury rate ratios (ORRS) were measured, all injuries aggregated and for two injury types, employing five age categories and four years of observation (1980 to 1995). The results indicate that there is an association between overexertion-injury type and year of observation, and reveal significant interaction between year and age, in the case of each injury type, for nursing auxiliaries but not for nurses. The findings suggest that, for nursing auxiliaries, ORRs do not follow the same trend in all age groups. It is concluded that as the occurrence of overexertion-injury events is influenced by many factors, the prevention of such injuries needs to be envisaged in a variety of ways. 0 1997 Elsevier Science Ltd. All rights reserved.

Keywords: Age-related overexertion risk; Nurses; Nursing auxiliaries; Injury types: Cluster analysis

1. Introduction

Overexertion injuries, i.e. musculoskeletal complaints resulting from single or multiple exertions, have become one of the leading items on the occupational-safety agenda of many industrialized countries (Keyserling et al., 1991; Kemmlert et al., 1993; Kumar, 1994). To emphasize what has been pointed out in an earlier review (Kumar, 19941, overexertion is a physical activity in which level of effort exceeds normal physiological and mechanical (physical) tolerance limits. But what may be considered a normal physical or physiological standard (age and gender taken together or separately) remains unclear. Likewise, it is unclear what level of requirement in terms of strength may be considered risk-neutral with regard to

* Tel.: + 32-468-6290500; Fax: + 32-468-986367.

129

130 L. Laflamme

occupational overexertion injuries, although some studies show that as the strength required for the performance of a task increases, so too does injury incidence (see Kumar, 1994).

The work-related factors contributing to the occurrence of overexertion injuries have been classified by Keyserling et al. (1991) into six categories: Forceful exertions, awkward postures, localized contact stresses, vibration, temperature extremes, and repetitive motions or prolonged activities. Thus, the classification encompasses not only injuries with an acute origin, but also those arising from long-term exposure to mechanical load and which cannot be related to any single causal event. It serves to highlight the wide diversity of tasks and occupations in which there is a risk of excessive exertion, and the fact that overexertion injuries are incurred by workers from both the industrial and service sectors.

Further, since individual factors such as age influence the occurrence of overexertion injuries (Kumar, 1994), the current aging of work forces in many countries undoubtedly makes the problem more acute. The extent to which age and aging are determining factors in injury occurrence has not yet been fully clarified (Laflamme and Menckel, 1995), and the issue now requires thorough consideration. For instance, if work organizations, occupational tasks, work-station designs and work aids are conceived so as to minimize the risk of injuries due to overexertions, it would be both regrettable and costly to fail to take into account the potential effects of age.

This article addresses age-related injuries due to overexertion among two groups of Swedish health-care workers: female nurses and female nursing auxiliaries (groups corre- sponding to those covered by the British job titles ‘registered’ nurse and ‘state-enrolled’/‘aux- iliary’ nurse, respectively). Male workers were excluded from the study because they constitute only a small proportion of this work force, and due to possible gender differences in job performance and risk exposure at comparable ages. The occupations were chosen for two reasons: first, injuries due to overexertions became a major and increasing safety problem for these workers during the 80s (see further); second, over the same period, the working populations in both occupations were clearly aging.

Table 1 presents the age distributions of female workers in these occupations at three different points in time during the 80s: 1980, 1985 and 1990 (the last three census years in Sweden). The numbers of nurses and nursing auxiliaries increased during the 8Os, net entry into the occupations being reflected by increases of 34.5% and 11 .O% between 1980 and 1990, respectively. Further, among nurses, the proportions of workers in all the age categories above 34 rose, while those in the categories 16-24 and 25-34 fell considerably. Among nursing

Table 1 Age distribution (%) of female Swedish nurses and nursing auxiliaries in 1980, 1985 and 1990”

Age 1980 1985 1990

N A T N A T N A T

16-24 8.4 29.1 23.5 4.7 23.1 17.8 4.5 18.5 19.1 25-34 37.2 26.6 29.4 32.6 28.6 29.8 26.4 27.6 27.2 35-44 28.5 19.8 22.2 34.1 22.7 26.0 34.0 24.0 27.1 45-54 16.7 15.2 15.6 20.1 16.4 17.4 24.1 19.0 20.6 55-65 9.2 9.3 9.3 8.4 9.2 9.0 11.0 10.9 1 I.0

N 46384 I 24 629 171013 51475 I 26 849 I78 324 62 404 138353 200757

“N = nurses; A = nursing auxiliaries; T = total

Overexertion injuries in ,femaie Swedish nwws and mtrsing nuxiliaries 131

auxiliaries, the proportion of workers in all the age categories above 24 rose, while that in the category 16-24 fell.

A review of the scientific literature reveals that earlier studies of injuries due to overexer- tions among health-care workers have dealt mainly with nursing auxiliaries, probably because they, from among all direct providers of patient care, tend to incur the greatest proportion of such injuries. Some studies have also shown that the risk for auxiliaries of sustaining overexertion injuries increased steadily over the 1980s (Jensen, 1990; Personic, 1990; Laflamme et al., 1997). For nursing auxiliaries, as also for nurses, the literature indicates that young workers are most at risk of overexertion injuries to the back sustained while lifting patients, female workers being especially vulnerable (Rae McAbee, 1988; Jensen, 1990; Personic, 1990; Engkvist et al., 1992; Laflamme et al., 1997).

Such findings, however, were obtained during periods of recruitment to the occupations, rather than at times of personnel cutbacks, work rationalization and pressure for efficiency of the kind that Sweden, among other countries, has experienced since the early 90s. Because of such recent changes, and also due to the effect that they may have had on task allocation, in particular in relation to the distribution of occupational assignments and thereby injury risks between age strata, the extent to which earlier results still apply has become unclear. Previous studies have already revealed that depressed conditions on the labour market and consequent changes in the age composition of the work force may entail that workers from some age groups are exposed to greater injury risks (Laflamme and Menckel, 1996; Laflamme et al., 1996).

An all-age-aggregated picture of the types of events leading to occupational injuries among female Swedish nurses and nursing auxiliaries in 1980, 1985, 1990 and 1995 is presented in Table 2. Overexertion injuries remained the leading problem throughout the period, but such injuries were incurred less frequently than expected in 1995 (based on a Chi-squared test for association between injury type and year of observation). Note that the considerable reduction observed in the total number of injuries between 1990 and 1995 is not peculiar to the occupations under study, but is part of a phenomenon that has been detected in most employment sectors and occupations in Sweden. Among other possible explanations for the reported downward injury trend in the nursing sector are fewer workers employed (see bottom row in Table 21, aging of the work force (see Table 3), and changes to Swedish labour legislation (and the country’s injury-compensation system) in the early 90s. These changes entailed considerably reduced injury-declaration on the part of employers, who no longer receive compensatory payments for the first four days of absence from work of injured employees.

Table 2 Types of injurious events among Swedish female nurses and nursing auxiliaries”

Main event 1980 198.5 I990 I995 Total

Overexertions 1475 (1603.2) 1994 (1917.5) 2140 (2008.2) 479 (559.2) 6088 Slips, trips, falls 576 (488.7) 546 (584.6) 549 (612.2) I85 (170.5) 1856 Contacts w. objects 525 (503.5) 574 (602.2) 582 (630.7) 231 (175.6) 1912 Other 76 (56.6) 58 (67.7) 51 (70.9) 30 (19.7) 215 Total injuries 2652 3172 3322 925 10071

Exposed workers I71 013 I78 324 200755 170204h

“Observed values (expected values); xz = 101.75; df = 9; P = lo-’ hEstimated frequency (see Table 3).

132 L. Laflamme

Table 3 Age distribution of Swedish female health-care workers in 1990 and 1994, and estimate of the number and proportion of female nurses and nursing auxiliaries by age category in 1994

Age Health-care workers Nurses and nursing auxiliaries in 1994

1990 1994 %A Nurses Auxiliaries Total

N N N 8 N % N %

16-24 51445 18518 - 36.0 1814 3.31 16346 14.17 18160 10.67 25-34 97 860 65914 - 32.6 I I 090 20.23 25 715 22.34 36 865 21.66 35-44 106 104 92426 - 12.9 18474 33.69 28901 25.05 47 375 27.83 45-54 78973 84 145 + 6.5 15996 29.17 28016 24.25 44012 25.86 55-65 42915 41225 + 8.3 7456 13.60 16336 14.16 23 192 13.98

N 379 356 302 258 - 20.3 54830 100.0 115374 100.0 170 204 100.0

In this study, the question of age-related overexertion injuries is investigated longitudinally, and attention is paid to various patterns in overexertion-injury circumstances. Data analysis was performed in order to typify the circumstances of occurrence of overexertion injuries in the study population and to examine whether these patterns were age and time (year) specific.

2. Materials and methods

A retrospective longitudinal analysis was conducted over a 15-year period (I 980- 1995) using four years of observation (I 980, 1985, 1990 and 1995) and five age categories (ten-year strata from ages 16-24 to 55-65). Numerator (injury) data were taken from the Work Injury Information System maintained by Sweden’s National Board of Occupational Safety and Health (the ISA), and denominator (exposed-worker) data from the registers of Statistics Sweden (the country’s national statistical agency).

The three first years of reference were selected to match the last three Swedish census years ( 1980, 1985, 1990). For the final year (19951, however, the most recent year for which injury data were available at time of analysis, no census data at specific occupation level (nurse or nursing auxiliary) were available. Accordingly, denominators (number of workers exposed by age category) for each occupation were imputed on the basis of data obtained from Statistics Sweden on the total number of female workers employed as health-care workers at the end of 1990 and end of 1994. The assumption was made that the change in the proportion of the total number of female health-care workers in each age category between 1990 and 1994 could be used to estimate the numbers and proportions of women employed in the occupations of nurse and nursing auxiliary at the end of 1994 (see Table 3).

In the absence of actual data, this method of denominator estimation was regarded as preferable to using the proportions for each occupation in 1990 (the most recent figures available). Substantial personnel cutbacks took place in the Swedish health-care sector in the early 90s; and, since the ‘last-in-first-out’ rule was applied fairly systematically there was a differential rate of lay-off between age categories. Because of further redundancies during 1995, however, this estimation method may have given rise to an overestimation of the number of workers in all age categories and both occupations, and therefore to a systematic underestimation of injury risks. This source of error might be particularly important for

O~vrexerrion injuries in female Swedish nurses and nursing auxiliaries 133

Table 4 Characteristics of two overexertion-injury types one variable at a time, all years aggregated (1980, 1985, 1990, 1995)

Variable Category

Type of injury Sprain, strain 93.6 Skeletal, internal 1.9 Other 4.5

Part of body injured Back Neck Shoulder or arm Other (e.g. hand, wrist, lower limb)

86.9 13.1

Causal agent Other person (e.g. patient) 85.2 Material, product, furniture, etc. 14.8

Cluster I (n = 4489) %

Cluster 2 Total (n = 1599) (n = 6088) % 0%

87.9 92.1 4.6 2.6 7.5 5.3

_ 64. I _ 9.7

45.5 12.0 54.5 14.3

74.4 82.4 25.6 17.6

younger workers, since under the ‘last-in-first-out’ system they are most immediately affected by personnel cutbacks.

For each occupation, all injuries classified in the ISA system as having ‘overexertion of a part of the body’ as a ‘main event’ in the injury sequence were selected. Injuries incurred on the way to and from the workplace were excluded. This gave a total of 6088 injury events, of which 55 18 were experienced by nursing auxiliaries and 570 by nurses. The ISA’s concept of ‘overexertion injury’ exclusively refers to injuries, such as sprains or strains, that are sustained in conjunction with heavy lifting, awkward working postures, sudden violent movements, and so on (NIOSH, 1983), and which can be related to a specific event or point in time. ‘Overexertion injury’ is one of the ten main categories of the ISA variable ‘Main event’, which refers to the force or energy that causes an accident. The classification is stated by the ISA to be based on IL0 recommendations for the structuring of accident-data sets (ISA, 1995). The categorization of an injury as an overexertion injury - rather than a disease - is made, in Sweden, by the Labour Inspectorate, which receives all injury declarations from employers and then forwards them to the ISA.

In order to classify injuries due to overexertions by type, three variables available in the ISA were utilized: part of the body injured, nature of injury, and main external agent. The data were processed by applying a cluster-analysis method to coded values of these variables (see first and second columns, Table 4). Cluster techniques are generally employed in order to classify objects of study (injuries in this case) according to similarities between them. There are several such methods, and the choice between them depends, among other things, on the number of observations available (Aldenderfer and Blashfield, 1991). As the number of observations was large for the current study ‘Quick Cluster’ (SPSS, 1990), a method based on nearest centroid sorting (Anderberg, 1973), was selected. Employing this procedure, any one case is assigned to that cluster for which the distance between the case and the centre of the cluster (centroid) is longest. SPSS’s ‘Quick Cluster’ employs squared Euclidean distance as its measure, which weights all cluster variables equally. If variables are measured in units that are not comparable, the procedure gives greater weight to variables with larger variance.

Overexertion injury rate ratios (ORRS) and 95% confidence intervals (95% CIs) were calculated using the Poisson-regression method. The year 1980 and the age category 2 55 were used to provide reference values. The regression models (one each for all injuries

134 L. Laflamme

aggregated and by cluster) were first fitted with number of accidents as the dependent variable, and year and age category as independent variables. The model was then extended to include the interaction term ‘year and age category’, and tests for interaction effects were conducted. The likelihood ratio statistics (LRSs) of the extended model were used to determine whether an interaction term should be included in any of the regression models, a p-value equal to or less than 0.05 being the criterion for inclusion (Kleinbaum et al., 1988). The number of exposed workers was used as the rate multiplier. The regression models were fitted using the statistical package EGRET (~1.02).

3. Results

3. I. ORRs all injuries aggregated

Table 5 presents overexertion injury rate ratios (ORRS) with 95% confidence intervals by year and age category for both occupations aggregated and by occupation, all injuries aggregated. The ORRs for both occupations aggregated and those for auxiliary nurses are derived from the Poisson regression model that includes the interaction term ‘age and year’. Including the interaction term significantly improved the fit of the model (LRS p = O.OOl>, meaning that the year and age variables had a combined effect as well as main independent effects on injury rates in these two cases. No interaction effect, however, was found for nurses (LRS p = 0.28).

Table 5 shows that ORRs were significantly higher in 1985 and 1990 than in 1980 for both

Table 5 Overexertion injury rate ratios (ORRS) with 95% confidence intervals by year, age category and occupation, all accidents aggregated

Variable Both occupations” Nursing auxiliariesb NursesC

Year 1980 1985

1990

1995

“ke 16-24

25-34

35-44

45-54

55+

I .oo 1.00 I .oo 1.82 1.81 I .91

(1.42-2.34) (I .40-2.34) (1.50-2.58) 1.41 1.31 2.51

(1.10-1.81) (1.01-1.70) (1.94-3.25) 0.47 0.46 0.89

(0.34-0.64) (0.33-0.64) (0.65-1.23)

2.73 2.10 2.00 (2.20-3.34) (1.68-2.62) (1.36-2.91)

0.96 1.03 0.93 (0.76-1.21) (0.81-1.31) (0.68-1.27)

1.16 1.26 1.04 (0.91-1.46) (0.98- I.601 (0.77-1.41)

I .48 1.51 1.16 (1.17-1.88) (1.18-1.93) (0.85-1.58)

1.00 1.00 I .oo

“Based on regression model with interaction term ‘year and age’; LRS df = 12, p = 0.001. ‘Based on regression model with interaction term ‘year and age’; LRS df = 12, p = 0.001. ‘Based on regression model without interaction term ‘year and age’: LRS df = 12, p = 0.28

Overexertion injuries in female Swedish nurses and nursing auxiliaries 135

Table 6 Relationshio between accident tvue. and vear of iniurv”

Pattern 1980 1985 1990 1995 Total

I. Back or neck injuries 1131 1446 1592 320 4489 1087.6 1470.3 1577.9 353.2

2. Shoulder/arm or other injuries 344 548 548 159 1599 387.4 523.7 562.1 125.8

Total 1475 1994 2140 419 6088

Exposed workers 171013 178324 200 755 170204b

“Observed value and Expected t,alue; xz = 20.48; df = 3; p = IO-’ bEstimated frequency (see Table 3).

nursing auxiliaries and nurses, but were lower in 1995. Further, ORRs were consistently higher for younger workers (16-24) than for those aged 55 and over in the cases of both nursing auxiliaries and nurses. Auxiliaries aged 45-54, but not nurses, had a significantly higher ORR than their counterparts aged 55 and over.

3.2. Types of overexertion injuries

Two main patterns were obtained from the cluster analysis. Their characteristics are shown in Table 4, where the percentage of injuries in each category of each variable is presented one pattern at a time. As might have been expected, both patterns are dominated by sprain or strain as type of injury. In both cases also, patients are the most frequent causal agent involved in an injury. But the clusters differ from each other with regard to part of the body injured. Cluster I (n = 4489) encompasses injuries incurred to the back or neck, while Cluster 2 (n = 1599) comprises injuries to the shoulder or arm, or to other parts of the body.

Table 6 shows that there is a strong and significant relationship between injury type and year of observation (x2 = 20.48; df = 3; p < 10W3) and reveals a trend towards a smaller proportion of injuries from Cluster I (involving the back or neck) over time, and with 1995 having the highest proportion of injuries from Cluster 2 (involving other parts of the body). There are differences between observed and expected values for each pattern in every year of reference, but the differences are most pronounced in 1980 and 1995.

No significant relationship was found between injury type and occupation, injuries in both clusters being as frequent as expected by chance for both occupations ( p = 0.50).

3.3. ORRs by type, year and occupation

Table 7 presents overexertion injury rate ratios (ORRS) with 95% confidence intervals by year and age category for both occupations aggregated and by occupation, one cluster at a time. Note, Based on the LRS p-values (see legend of Table 7) the ORRs for both occupations aggregated and nursing auxiliaries are derived from the Poisson regression model that includes the interaction term ‘age and year’, whereas the ORRs for nurses are based on a pure main-effects model.

Table 7 shows that Cluster-l ORRs were higher in both 1985 and 1990 than in 1980 for both nursing auxiliaries and nurses, but that this was not the case in 1995. Also, Cluster-l

136 L. Lujlumme

Table 7 Overexertion injury rate ratios (ORRs) with 95% confidence intervals by occupation, cluster, year and age category

Variable Both occupations Nursing auxiliaries Nurses

Cluster I” Cluster 2” Cluster I” Cluster 2b Cluster I’ Cluster 2d

Year 1980 1985

1990

1995

A‘V 16-24

25-34

35-44

45-54

55+

I .oo 1 .oo 1.82 1.82

(I .32-2.52) (1.23-2.70) 1.57 1.18

(1.14-2.15) (0.79- 1.76) 0.49 0.44

(0.33-0.73) (0.24-0.73)

3.64 1.40 (2.76-4.80) (0.97-2.01)

1.35 0.38 (1.01-1.80) (0.25-0.58)

1.45 0.7 I ( 1 .OS- 1.96) (0.48- 1.07)

1.74 1.11 (I .28-2.35) (0.75- 1.64)

I .oo 1 .oo

1 .oo 1.00 1.79 1.84

(I .28-2.50) t 1.23-2.76) I .46 1.08

( 1.05-2.03) (0.7 I- 1.66) 0.48 0.43

(0.3 I-0.73) (0.25-0.73)

2.80 1.07 (2.1 l-3.73) (0.74- 1.55)

1.43 0.43 ( 1.06- 1.93) (0.27-0.66)

1.57 0.79 (1.16-2.13) (0.52- 1.20)

1.81 1.07 (I .32-2.47) (0.79- 1.6 I)

1 .OO 1.00

1.00 1.92

(I .40-2.64) 2.71

(2.02-3.65) 0.88

(0.64- 1.28)

2.65 (I .70-4.10)

1.72 (0.81-1.71)

1.28 (0.89- 1.84)

1.06 (0.71-1.56)

1.00

1 .OO 2.07

(1.21-3.54) 1.96

(1.16-3.32) 0.91

(0.50- 1.67)

0.76 (0.32- 1.82)

0.47 (0.26-0.85)

0.59 (0.34- 1.03)

1.35 (0.80-2.27)

I .oo

“Based on regression model with interaction term ‘year and age’; LRS df = 12, p = 0.001. bBased on regression model with interaction term ‘year and age’: LRS df = 12, p = 0.006. ‘Based on regression model without interaction term ‘year and age’; LRS df = 12, p = 0.94. ‘Based on regression model without interaction term. No LRS possible due to lack of convergence.

ORRs in all age categories were significantly higher than that of the oldest group of workers (2 55) in the case of nursing auxiliaries, but a significant result was only found for the youngest workers (16-24) in the case of nurses. For Cluster 2, ORRs higher than in 1980 were found only in 1985 for nursing auxiliaries, and in 1985 and 1990 for nurses. For both occupations aggregated and by occupation, none of the other age categories had ORRs significantly higher than that of older workers.

4. Discussion

The results of the current study suggest that younger workers may be a specific risk group with regard to overexertion injuries. They also indicate, at least in the case of nursing auxiliaries, that workers aged 45-54 might constitute a risk group that has hitherto been neglected (see Jensen, 1990; Personic, 1990).

The study presents a two-category typology of injuries due to overexertions, and considers each category’s distribution over time and by age for each occupation. It reveals that there is an association between injury type and year of observation, and also significant interaction between year and age, for each injury type, among nursing auxiliaries but not among nurses.

Overexertion injuries in female Swedish nurses and nursing auxiliaries 137

4.1. The two-category typology

The injury typology presented is mainly based on differences with regard to the ISA variable ‘Part of the Body Injured’. For this reason, the findings lack the richness of those obtained from an earlier descriptive investigation of injuries due to overexertions sustained by male and female Swedish nursing auxiliaries during the 1980s (80-81, 85-86 and 90-91; see Laflamme et al., 1997). The former analysis was conducted at a time when Sweden’s Work Injury Information System contained a variable called ‘Activity Performed by the Injured Worker at Time of Accident’. Data for this variable were sufficiently informative for statistical analysis to shed light on critical tasks associated with particular injury clusters, e.g. the lifting of patients or the handling of equipment. The variable was revised in 1992, but at the cost of some informational value and inter-temporal reliability. For instance, whereas we know that the lifting of a patient was associated with an overexertion injury in more than 80% of cases in 1980, 1985 and 1990, lifting of patients is not referred to at all in the data for 1995. Instead, more than 85% of the coded activities for 1995 fall into the category ‘Caring and Related Tasks’. On the basis of ISA data from previous years and evidence generated by earlier studies, there are good reasons to believe that the lifting of patients remained an activity at risk for the occupations concerned in 1995. At least in the case of the overexertion injuries encompassed by Cluster 1 (those to the back or neck), the evidence offered by previous studies is now overwhelming (Rae McAbee, 1988; Jensen, 1990; Personic, 1990; Engkvist et al., 1992; Laflamme et al., 1997).

4.2. Time and age-related ORRs

From another perspective, the inclusion of an additional, more recent year of observation (1995) enabled the current study to reveal that the most common overexertion injuries - those to the back or neck (Cluster 1) - were incurred less frequently than expected in 1995, whereas those classified as ‘shoulder/arm or other’ (Cluster 2) had become more frequent.

For the whole study period, and as mentioned above, the results also reveal that, in the case of nursing auxiliaries, the interaction term ‘year and age’ makes a significant additional contribution to the explicative value of all three models (one for all injuries aggregated, and two by injury type). This can be regarded as providing evidence that, at least during this particular study period, time and age jointly and not just independently affected the accident- risk distribution. In other words, non-specific (all injuries aggregated) and specific (by type) ORRs do not follow the same trend for all age groups. In the case of nurses, the absence of significant interaction in the case of Cluster I (the only interaction effect that it was possible to test for) indicates that time and age contributed independently but not jointly to injury-risk distribution.

Further, in the case of Cluster 1, for both nursing auxiliaries and nurses, ORRs were significantly higher in all age categories than among older workers (the reference age-group), and also higher in 1985 and 1990 - but not in 1995 - than in 1980 (the reference year). The two occupations showed a different profile in the case of Cluster 2 where significant differences by year were found only for 1985 in the case of nursing auxiliaries and for 1985 and 1990 among nurses. No significant Cluster-2 differences by age were observed for auxiliaries, and only one (that for the youngest group of workers) in the case of nurses.

138 L. Liq7umme

4.3. Implications for precention

Since the occurrence of overexertion-injury events is influenced by many factors, the prevention of such injuries should probably be envisaged in a variety of ways. As already suggested in the literature, prevention might be achieved by new forms of work organization and ergonomic job design or re-design (Kumar, 1994), by the re-design of facilities, work aids, tools and working methods (Keyserling et al., 1991), or by avoiding risk factors such as lack of freedom of movement and inadequate staffing (Rae McAbee, 1988). Training and re-training might also be essential (Rae McAbee, 1988). In all cases, as this study clearly reveals, the targeting of preventive measures should take into account the possibility of quite rapid changes in the pattern of overexertion injuries both by type and in terms of the age groups most at risk.

4.4. Contributions and shortcomings of the study

The most significant contributions of the study lie in its categorization of injuries due to overexertions among nurses and nursing auxiliaries into two types (based on bodily location of injury), and in the characterization of these types with regard to differences in age and time.

The study, however, was unable to shed light on the work loads or demands associated with the tasks during which overexertion injuries were incurred, among either nurses or nursing auxiliaries. It lacks precision in this respect because there was an absence of information in the data set employed on the tasks performed by workers of different ages during the various years of observation. A further limitation of the study lies in the impossibility of thoroughly examining age-related ratios for Cluster-2 overexertion injuries among nurses. This was due to the relatively small number of injuries of this kind that they sustained in each year.

Further, the possibility that denominators for 1995 may have been overestimated ought to be re-emphasized. The problem is most critical for the age categories 16-24 and 25-34, and might imply a systematic underestimation of ORRs, both all injuries aggregated and by injury type. In particular, it might be the case that the ORR of nursing auxiliaries aged 16-24 was higher than the figure presented, which might entail a significant difference compared with the reference group.

Finally, the possibility of a general underestimation of the total number of injuries sustained by workers of both occupations and in all age groups for 1995 ought to be re-emphasized. Indeed, the substantial reduction in the number of reported injuries, which is more likely to be attributable to lower declaration incentives prompted by changes in Swedish labour legislation than to the effect of any preventive measures, indicates that the magnitude of injury risk for this year may be underestimated. Consequently, the absence of significance found in all instances of comparison between 1995 and 1980 does not have the degree of reliability of other findings.

5. Conclusions

In accordance with previous investigations, this study suggests that a number of specific age groups should receive particular attention when it comes to the prevention of overexertion injuries. However, the study reveals that such age groups may vary according to occupation, to which type of overexertion injury is targeted, and possibly over time. The study also supports

Owrexerrion injuries in female Swedish nurses and nursing auxiliaries 139

the view that overexertion injuries cannot be regarded as a problem exclusively related to age (see also Rae McAbee, 1988), a lack of exclusivity which has preventive implications. The year-age statistical interaction observed in the case of nursing auxiliaries suggests that demographic (aging of the work force) and time-related (economic and organizational) factors both independently and jointly determine the risks of overexertion injuries, both qualitatively and quantitatively.

Additional studies are needed to investigate causes and background of changes in injury rates.

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