Introduction
An increase in the participation in paid work of people in the age of 45–65 is considered necessary to afford the costs that are generated by the ageing of the population (Gobelet et al.
2007; Ilmarinen
2001; European Commission
2004). However, current knowledge about the health status and the functional capacity (the ability to perform work-related activities) of this worker category (Kenny et al.
2008; Berg van den et al.
2009; Broersen et al.
1996) raises the question whether this pursuit is realistic. Older workers with chronic diseases or disorders are specifically at risk of developing work disabilities and loosing their job (Kenny et al.
2008; Schuring et al.
2007). Regarding rheumatic diseases ample evidence indicates that rheumatoid arthritis (RA) has a negative impact on the work participation of patients (Zirkzee et al.
2008; Chorus et al.
2000). For osteoarthritis (OA), however, there is limited information with regard to work participation (Gobelet et al.
2007; Merx et al.
2007) and functional capacity for work-related activities (Bieleman et al.
2007). This disorder is of particular interest because of its increasing prevalence, related to the ageing of populations and the rising prevalence of overweight and obesity (Issa and Sharma
2006). Since people with OA often experience limitations in physical functioning, an effect on work participation may be anticipated. There is a lack of knowledge about the work status and functional capacity of people with early OA compared to healthy people. As a consequence, the need for (preventive) interventions to maintain functional capacity and to stimulate work participation remains unclear.
Several work-related and individual factors are related to work ability (Berg van den et al.
2009). One of the individual factors is the functional capacity, which can be assessed with a Functional Capacity Evaluation (FCE). An FCE is an evaluation of the capacity to perform activities that is used to make recommendations for participation in work, while considering the person’s body functions and structures, environmental factors, personal factors and health status (Soer et al.
2009). FCE’s are used in many countries worldwide in rehabilitation, occupational health care and insurance settings. Performance-based data provide clinicians with additional information about functioning that would be missed when relied on self-reports only (Reneman et al.
2002).
The aims of this paper were to assess the self-reported health status and the observed functional capacity of people with early OA in hips and/or knees and to compare these to a reference sample of healthy workers, matched for age and controlled for sex. It was assumed that the functional capacity of healthy workers was sufficient to meet the physical demands in their jobs. This comparison, therefore, enabled assessment of the functional capacity of subjects with OA in relation to physical job demands.
Research questions were:
1.
Is the self-reported health status of subjects with early OA different from healthy workers?
2.
Is the observed functional capacity of subjects with early OA different from healthy workers?
3.
Is the functional capacity of subjects with early OA sufficient to meet physical job demands?
Results
Subjects
Subject characteristics and self-reported health status are presented in Table
1. Compared to healthy workers, subjects with early OA were older and less than half of them had a paid job. Women with early OA had a statistically significantly higher BMI than the female healthy workers.
Table 1
Subject characteristics
n
| 15 | 183 | | 78 | 92 | |
Paid job (%) | 47 | 100 | | 47 | 100 | |
Age in years: |
Mean (SD) | 58 (5.3) | 52 (4.1) | −6 (−8.2– − 3.8)* | 56 (4.8) | 52 (4.0) | −4 (−5.3– − 2.7)* |
Range | 48–65 | 46–61 | | 48–66 | 46–59 | |
Body mass index# | 25.8 (5.3) | 25.6 (3.9) | −0.2 (−1.9–2.3) | 26.2 (4.3) | 24.1 (3.1) | −2.1 (−3.2– − 0.9)* |
SF-36# |
Physical function | 80.5 (8.2) | 96.6 (5.7) | 16.1 (12.9–19.3)* | 69.8 (22.8) | 94.7 (8.1) | 24.9 (19.8–30.0)* |
Physical role | 80.4 (32.8) | 93.1 (19.2) | 12.7 (1.3–24.1)* | 56.6 (43.5) | 93.4 (19.6) | 36.8 (26.4–47.2)* |
Bodily pain | 71.9 (12.8) | 90.3 (12.7) | 18.4 (11.5–25.3)* | 64.3 (19.1) | 92.1 (9.9) | 27.8 (23.2–32.4)* |
General health | 48.2 (18.3) | 75.0 (13.7) | 26.8 (19.2–34.4)* | 52.6 (18.7) | 76.7 (15.0) | 24.1 (18.4–29.8)* |
Social function | 92.0 (11.6) | 91.3 (13.2) | −0.70 (−7.8–6.4) | 74.5 (20.4) | 90.6 (11.8) | 16.1 (11.0–21.2)* |
Emotional role | 95.2 (17.8) | 96.7 (15.3) | 1.5 (−6.9–9.9) | 82.0 (32.9) | 91.8 (23.5) | 9.8 (1.0–18.6)* |
Mental health | 80.6 (11.3) | 72.4 (10.2) | −8.2 (−13.8– − 2.6)* | 73.7 (13.7) | 71.0 (9.0) | −2.7 (−6.3–0.9) |
Vitality | 66.4 (13.2) | 69.1 (11.5) | 2.7 (−3.6–9.0) | 59.8(16.6) | 66.0 (13.0) | 6.2 (1.6–10.8)* |
Health status comparison
The subjects with OA reported statistically significantly lower scores than the healthy workers on the physical component of SF-36, for both sexes. On the mental component, the CHECK women also scored statistically significantly lower than the healthy subjects, with exception of the mental health scale. The scores on the mental component of SF-36 for the male healthy workers and the men with OA were similar, but on the mental health subscale, the men with OA scored significantly higher than the healthy working men. Because of the higher mean age and the small number of the male subjects with OA, afterwards a corrected analysis was performed, in which they were compared to an age-matched subsample of 30 healthy workers (mean age 58). This analysis generated similar results on all scales (not presented here). The healthy working men and women had very similar scores, whereas in the OA subjects, the men scored higher than the women.
Functional capacity comparison
The FCE test results for the male subjects are presented for separate age categories and for the total group (Table
2).
Table 2
FCE performances of male subjects with early OA (CHECK, n = 15) and male healthy workers (n = 183)
Lifting low (kg) | 45–54 | 31.8 (7.4) | 44.9 (12.3) | 13.2 (1.0–25.4)* |
55–65 | 34.1 (6.1) | 43.0 (14.5) | 9.0 (3.5–14.4)* |
All | 33.5 (6.3) | 44.3 (13.0) | 10.9 (7.0–14.8)* |
Lifting Overhead (kg) | 45–54 | 19.8 (2.9) | 20.1 (4.8) | 0.4 (−4.4–5.2) |
55–65 | 17.3 (3.9) | 18.9 (4.6) | 1.6 (−1.4–4.5) |
All | 17.9 (3.7) | 19.7 (4.8) | 1.8 (−0.7–4.3) |
Carry 2 hand (kg) | 45–54 | 46.3 (13.4) | 46.4 (11.0) | 0.1 (−11.0–11.3) |
55–65 | 35.7 (11.5) | 43.1 (12.7) | 7.4 (−0.9–15.7) |
All | 38.5 (12.5) | 45.4 (11.7) | 7.0 (0.7–13.1)* |
Overhead work (s) | 45–54 | 236 (103) | 269 (127) | 33 (−93–160) |
55–65 | 207 (61) | 270 (102) | 63 (−0.4–127.1) |
All | 214 (72) | 270 (119) | 55 (−7–117) |
Dynamic bend (s) | 45–54 | 51 (7) | 47 (6) | −4 (–11–3) |
55–65 | 62 (16) | 66 (128) | 4 (−74–82) |
All | 60 (15) | 48 (7) | −12 (3–21)* |
Rep. side reach (s) | 45–54 | 76 (17) | 80 (12) | 4 (−11–19) |
55–65 | 95 (20) | 80 (11) | −15 (−30–0.0) |
All | 91 (21) | 80 (13) | −11 (−23–2) |
The capacity for ‘lifting low’ was significantly lower in the CHECK men from both age-groups compared to the healthy workers. The other tests showed no significant differences between the subjects with OA and the reference data in the age categories. For the comparisons between the total groups, the differences in the tests lifting low, carrying-2-handed and dynamic bending were significant; the healthy workers lifted and carried more weight and were faster on dynamic bending.
In Table
3, the FCE test results for the female subjects are presented.
Table 3
FCE test performances of female subjects with early OA (CHECK, n = 78) and female healthy workers (n = 92)
Lifting Low (kg) | 45–54 | 19.0 (6.9) | 25.7 (8.7) | 6.7 (3.3–10.1)* |
55–65 | 15.5 (6.8) | 23.6 (7.3) | 8.1 (4.5–11.6)* |
All | 17.0 (7.0) | 24.8 (8.5) | 7.8 (5.3–10.2)* |
Lifting overhead (kg) | 45–54 | 9.2 (3.8) | 11.5 (3.4) | 2.3 (0.8–3.8)* |
55–65 | 7.0 (3.1) | 10.5 (3.3) | 3.5 (1.9–5.1)* |
All | 8.0 (3.6) | 11.2 (3.3) | 3.2 (2.1–4.2)* |
Carry 2 hand (kg) | 45–54 | 22.1 (5.6) | 28.3 (7.5) | 6.2 (3.3–9.0)* |
55–65 | 17.1 (6.4) | 26.6 (8.0) | 9.5 (6.0–13.1)* |
All | 19.3 (6.5) | 27.7 (7.7) | 8.3 (6.1–10.5)* |
Overhead work (s) | 45–54 | 163 (67.8) | 239 (111) | 77 (42–112)* |
55–65 | 157 (79.4) | 234 (75) | 76 (36–117)* |
All | 160 (74) | 233 (103) | 73 (45–101)* |
Dynamic bend (s) | 45–54 | 55 (16.0) | 45 (5.6) | −10 (−16– − 4)* |
55–65 | 64 (15.2) | 46 (7.1) | −18 (−24– − 13)* |
All | 60 (16) | 45 (6) | −15 (−19– − 11)* |
Rep. side reach (s) | 45–54 | 84 (25.8) | 74 (9.1) | −10 (−19–0.0)* |
55–65 | 90 (15.5) | 78 (10.2) | −13 (−19– − 6)* |
All | 87 (21) | 75 (9) | −12 (−17– − 7)* |
The female subjects with OA performed significantly lower than the female healthy working subjects on all tests. In both groups, the younger subjects performed higher than the older; the differences were larger in the OA subjects.
Functional capacity versus physical job demands
To assess whether the functional capacity of subjects with early OA was sufficient to meet the physical job demands, the results were compared to the fifth percentile of the results of the healthy workers. In Table
4, these p
5 scores are presented, followed by the proportion of subjects with OA that performed below this cut-off value.
Table 4
Proportions of subjects with early OA (CHECK) performing below (<) fifth percentile (p5) of reference data of healthy workers
Lifting low | 45–54 | 16 kg | 0 | 35 |
55–65 | 0 | 55 |
Lifting high | 45–54 | 7 kg | 0 | 33 |
55–65 | | 0 | 50 |
Carrying | 45–54 | 16 kg | 0 | 20 |
55–65 | 0 | 45 |
Overhead Work | 45–54 | 101 s | 0 | 20 |
55–65 | 9 | 25 |
Dynamic Bend | 45–54 | 55 s | 33 | 38 |
55–65 | 45 | 65 |
Rep. Side Reach | 45–54 | 93 s | 0 | 22 |
55–65 | 0 | 40 |
The men with early OA all scored above p5, except on the dynamic bending test. One of the older men scored below p5 on the overhead working posture test. On all tests, 20–40% of the younger women and 25–65% of the older women scored below p5.
Discussion
This study revealed that both the 15 male and the 78 female subjects from a subsample from the CHECK cohort at baseline reported a worse physical health status (SF-36) compared to the healthy ageing workers, whereas the women also reported a worse mental health status on 3 out of 4 scales. On the FCE, the female CHECK subjects performed significantly lower than their healthy working counterparts on all 6 tests. The male subjects with OA performed lower on 3 out of 6 tests. A substantial proportion of female subjects demonstrated functional capacities that would be considered insufficient to meet the lowest category of physical job demands.
The worse physical health status as reported on the SF-36 can be attributed to the knee or hip complaints of the subjects, but other physical factors may also have influenced their health status. Serious comorbidity was an exclusion criterion for the CHECK cohort, but back pain and other musculoskeletal discomfort were frequently reported. Contrarily, an over representation of physically strong and healthy volunteers in the reference population may have introduced bias that explains part of the observed differences. Still, the early phase of OA is clearly accompanied by self-reported limitations in physical function and physical roles for both sexes and also by mental health limitations for women.
The worse self-reported health status of the subjects with early OA compared to the healthy working subjects was also reflected in a lower functional capacity as measured on the FCE. The pain and stiffness in the hips or knees, possibly in combination with other health complaints, seem to have affected their performance in work-related physical activities. We reported earlier that in this sample the subjects with low self-reported functional status showed lower performances on the FCE (Bieleman et al.
2009).
About half of the subjects with early OA in this study did not have a paid job. Either or not having a paid job has been reported to explain part of the performance on an FCE (Bieleman et al.
2007). For example, on ‘lifting low’ the average difference between women from this study with paid work and those without paid work was 4.7 kg (19.4 kg vs. 14.7 kg). However, after correcting for this factor, there still remains a substantial difference between the capacities of the working subjects with early OA and the reference group of healthy workers. Therefore, it was concluded that in the early phase of OA of the hips and knees a decreased functional capacity is seen, both in working people and even more in people without paid work. The impact of the OA, as measured by self-reports and an FCE and compared to healthy workers, seems to be stronger in women than in men, both physically and mentally. Mental health factors may be related to having a job, either because a job requires for example vitality, or because of the social relations that a job may offer. Since many women in the study never had a job, this may explain the differences with the men.
The basis assumption for clinical interpretation of the results was that the functional capacity of healthy workers, used as reference data in this study, is equal to or exceeding their workload. For this reason, these data may be considered the “norm” to which the functional capacity of the subjects with OA could be compared (Soer et al.
2009). To be precise, the p
5 scores of the reference data for working subjects with the physically least demanding jobs (DOT-1; sedentary work) were used as reference. A substantial proportion of the female CHECK subjects performed lower than this p
5 score. For the persons with paid work amongst them, the low performance indicated that they could be considered to be at risk of not meeting their physical work load. For those without paid work, a low functional capacity might impair their physical activities of daily living (ADL) and leisure. The influence of OA on role participation has been identified as an important research issue (Gignac et al.
2008; Hunt et al.
2008). The subjects without paid work formed the majority of the group who performed lower than p
5, which is consistent with the earlier discussion on the relation between having paid work and FCE performance.
It may be argued that only patients with OA who are physically functioning relatively well are able to perform paid work and to live an active lifestyle in ADL and leisure. However, work and an active lifestyle can also be postulated to have beneficial effects on physical functioning and health. Physical activity in Japanese women with hip OA was related to both work status and to the degree of OA, but only the women without paid work were physically inactive, whereas the workers were not (Hirata et al.
2006). The hypothesis of a physically conditioning effect of work and an interaction with life-style seems to be supported by other observations in our study. The female healthy workers had a significantly lower BMI than the women with early OA (24.1 vs. 26.2). The smaller impact of early OA on health and functional status in men compared to women could also illustrate the conditioning effect of work. The men without paid work only recently retired and may still have had the conditioning benefit of their past working life, whereas many of the women reported never to have had paid work. Furthermore, the women also performed lower on FCE tests that do not relate to knee or hip function, such as working overhead. Yet, considering the cross-sectional nature of our study and the small number of male subjects, full explanations for these observations cannot be given. The relations between work, health status and functional capacity should be studied longitudinally.
Another limitation of the study is that no more than 6 tests in our protocol matched those from the reference study. However, these tests cover the aspects of strength, static endurance and speed/mobility. Together, this should provide a valid impression of the ability to perform work-related activities, relevant for people with early OA. The validity of shorter FCE protocols, which obviously have practical advantages, has been demonstrated in a recent study (Gross et al.
2007). Several alternative explanations besides the OA may theoretically explain parts of the differences in results between the groups, as for example testing order and fatigue, age, and willingness to give maximal effort. Considering age, the CHECK subjects were up to 65 years old whereas the oldest working subjects were 61. Soer et al. (
2009) constructed a regression model for predicting the result on ‘lifting low’ in which the coefficient for age was −0.2 kg/year. Applying this value to the difference in mean age between our groups (6 years for men, 4 years for women) would generate an expected difference of 1.2 and 0.8 kg, respectively. Clearly, the differences we found were much larger than could be expected only on the basis of the age difference. Hence, it appears that the functional limitations of the subjects with early OA should actually be attributed to the observed lower capacity that accompanied their complaints.
Functional capacity is one of the several components that determine work ability and social participation (Berg van den et al.
2009; Hunt et al.
2008). Experts in the field of disability claims and return to work have different opinions on the utility of FCE (Wind et al.
2006), but FCE information had complementary value according to most insurance physicians (Wind et al.
2009). Our study indicates a potential preventive use of FCE. The results demonstrated that less than half of the subjects with early OA had paid work and that both their self-reported health status and their functional capacity were significantly lower compared to healthy working subjects. A substantial proportion of women did not meet the physical job demands. Therefore, considering the aim to increase the work participation (preventive) interventions would be needed. For the workers amongst our subjects, adapting the working situation and maintaining functional capacity is recommendable. For others who consider finding a job (again), increasing their functional capacity and selecting jobs without heavy physical demands is advisable to facilitate actual work participation.
Acknowledgments
“CHECK is funded by the Dutch Arthritis Association on the lead of a steering committee comprising 16 members with expertise in different fields of OA chaired by Prof. J.W.J. Bijlsma and coordinated by J. Wesseling, MSc. Involved are: Academic Hospital Maastricht; Erasmus Medical Center Rotterdam; Jan van Breemen Institute/VU Medical Center Amsterdam; Kennemer Gasthuis Haarlem; Martini Hospital Groningen/Allied Health Care Center for Rheumatology and Rehabilitation Groningen; Medical Spectrum Twente Enschede/Twenteborg Hospital Almelo; St. Maartenskliniek Nijmegen; Leiden University Medical Center; University Medical Center Utrecht and Wilhelmina Hospital Assen.” Grants for this study were received from NutsOhra Fonds and Mobiliteitsfonds HBO. The authors are grateful to the subjects who actively participated in the study and to the students that led the FCE tests. Also they thank Anita Mooij and Annet ter Avest, research nurses of the Medisch Spectrum Twente and the Ziekenhuisgroep Twente, Wim Hilberdink, physical therapist in Groningen, and Janet Wesseling, CHECK-coordinator, for their contributions to the study.