The results from the explorative correlation analyses in the present study indicate statistically significant associations between work ability and the different quantitative tests on physical capacity as well as HADS (depression and anxiety) questionnaire results. Further analyses using multiple regression models suggest that the results from tests on physical capacity and sensorineural/vascular staging are not statistically significant predictors of work ability, but that psychological mood, whether assessed as depression or as anxiety, is a statistically significant predictor of work ability. According to the overall resulting model, approximately 42% of the variation in WAI is explained by age and psychological mood.
Age has previously been shown to affect work ability, especially in physically demanding jobs
, though for men performing mental work, there was no systematic decline in the index up to the age of 57 years. The authors of that study explained this by a decline in physical capacity due to “no participation in regular physical training”. This could be a plausible explanation but as age increases, so may the effects from work and other exposures increase that can affect health and functioning and, consequently work ability. The associations between WAI and the test results from measuring hand grip strength, finger strength and manual dexterity seem to be apparent because these values change with age. This may indicate that the effect from vibration exposure is not severe enough, that the affected individuals do not subjectively consider themselves affected or that conditions mainly affecting the hands are not sufficiently recognized in the WAI.
[10, 11] have reported similar relations to those found in the present study with dexterity and hand grip-strength correlated to dysfunction (in terms of the DASH score and ADL). Cederlund et al. report statistically significant correlations between (dominant hand) hand grip strength and manual dexterity (measured using the Purdue Pegboard®) and difficulties in ADL performance, and conclude that difficulties in managing daily activities are commonly seen among vibration-exposed workers. In comparison to ADL during leisure time, work ability may be spurred by a stronger drive or may depend on other aspects of motivation
. It is therefore important to consider not only the individual’s physical capacity but also their psychological symptoms, which seem to have a significant impact on WAI. A worker with an injury or disease in the hands or fingers resulting in physical dysfunction must not only be given proper treatment to avoid any further dysfunction, but must also receive appropriate caretaking for any psychological symptoms, in order to minimize their suffering and restore as much as possible of their potential work ability. This can raise questions as to whether the self-reports of work ability using the WAI adequately reflect a potential decline in physical capacity; it is possible that the questionnaire may put too much focus on the psychological mood. However, this consideration is in contrast to a previous study
 on the association between functional capacity and work ability where the authors claim with some certainty that “the used work ability index measured primarily physical features of work ability”. Their methods of measuring “mental capacity”, however, involved using tests of visuomotor speed (measured using the digit symbol test) and perceptual and conceptual ability, and not questionnaires.
The average WAI score of 30, in this sample of workers with HAVS, falls in the category of moderate (27–36) work ability, which can be considered, in comparison, as quite low. There are few studies reporting on mean WAI score among blue collar workers; however, de Zwart et al.
 investigated the reliability of WAI among construction workers (aged 40 years and above) with a result of WAI around 40, which belongs to the category of good work ability. A study on Finnish dairy farmers
 reported a mean WAI score of 36 among female workers and 39 among male workers. The difference between the current WAI score and the previously reported may be explained by the participation of former patients with existing symptoms in the current study. There is also a possibility of further decrease in mean WAI score due to psychological mood disorders as a result of the hand symptoms and disability.
The present study is an attempt to explore the possibility of creating a model that can predict work ability to a sufficient extent. The associations between WAI and test results from measuring hand grip strength, finger strength and manual dexterity seem to be apparent because these values change with age. Accordingly, the test results may be difficult to use as a direct instrument for assessing work ability but may still have a role as a complementary measurement in the clinical examination and assessment. However, the results reflects measurements from a limited group of hand arm vibration-exposed patients and therefore need to be interpreted with caution and confirmed in larger studies. The physical capacity in terms of measurements of hand and finger strength and manual dexterity may also be too limited or specific which can raise the question of whether another measure or other measures of physical capacity would be more relevant in explaining the level of work ability in these patients.
This study, however based on a small sample and exploratory, may hopefully offer some insight into how to advice the clinician when assessing patients with HAVS. The clinician may use the WAI and the psychological test as a complement to the more established tests of physical capacity in the hand in order to achieve a more general picture of the workers’ health. This can be especially important if there is not a clear relationship between staging of symptoms/signs of vibration injury and work ability, as indicated by the multiple regression model. Furthermore, the results from psychological testing may show that the psychological mood of patients with hand symptoms exposed to vibrating tools must be taken into deeper consideration.
The challenge is to provide adequate guidelines with a sound basis when more objective assessments are needed, for instance when issuing physicians’ (sick-leave) certificates and when assessing patients for rehabilitation or financial compensation. In order to make these assessment systems fair and appropriate, there is a need for objective methods which can be used instead of subjective assessments. It is not sufficient to focus on the staging of symptoms and signs in these affected workers. The SWS, though criticized for its shortcomings, is used (in some countries) for decisions on financial compensation and also to determine fitness for work
. This may be misleading and can result in incorrect conclusions. There is a need for improvement of the communication and understanding between different operators (e.g. occupational/primary health care services, employers, employees and the social insurance agency) on this issue
[29, 30]. Hopefully some new perspective on this complex condition of vibration injury can contribute to an improvement in assessment systems.