We found associations between joint‐specific hand symptoms and self‐reported and performance‐based measures of functional status, including those associated with lower‐extremity function. These associations were independent of demographic factors, BMI, hip and knee symptoms, radiographic hip and knee OA, and depressive symptoms, and were seen in both African Americans and Caucasians, and in both women and men.
Hand joint symptoms and disability represent the true impact of hand joint disease on an individual. It is not surprising that individuals reporting symptoms in the hands might also report difficulty performing tasks using the upper extremities. While this was the case in our study, we also observed associations between hand joint symptoms and HAQ questions aimed at activities primarily involving lower extremity or mixed lower and upper extremity function (data not shown). Because participants who report symptoms in the hands might be predisposed to report other joint symptoms or decreased function in general, we controlled for depressive symptoms and also tested performance‐based measures of lower extremity function, perhaps less likely to be influenced by reporting bias. These results corroborated the self‐reported functional measure, showing that those with joint‐specific hand symptoms were more likely to have worse functional status by performance measures. The associations between all affected hand joint sites and decreased ability to perform these functional lower extremity tasks suggest that joint‐specific hand symptoms are related to an overall or “systemic” decrease in physical function that goes beyond reporting of symptoms in the hand joints. It is likely that performance of tasks seemingly requiring the use of just the upper or lower extremities is more complex and requires good function of the entire musculoskeletal system, as has been suggested for hand function and ability to climb stairs or rise from a chair.4
Primary OA is a generalised musculoskeletal condition whose hallmark is hand OA; joint pathology at other sites may in some cases be more subtle, even preradiographic, but nevertheless contribute to functional difficulties. Moreover, systemic mediators of inflammation may affect upper and lower extremities simultaneously. Finally, functional self‐efficacy (a person's confidence in their ability to complete a task) is an important factor affecting functional performance as shown for people with knee OA.16
Chronic hand symptoms may influence functional self‐efficacy, perhaps by contributing to depression, which has been shown to play a role in determining self‐efficacy for general physical tasks.17
As above, our observations were independent of depressive symptoms.
Although hand OA is generally more common in women than men, it is clinically important to realise that men were not spared from impaired functional status associated with joint‐specific hand symptoms. Moreover, although little data exist on racial/ethnic differences in hand OA, neither were African Americans spared from impaired functional status in association with these hand symptoms. In addition, the associations between hand symptoms and function were just as strong in those with isolated hand symptoms as in those with hand symptoms and concomitant hip or knee symptoms. In one instance, the impact of number of hand joints with symptoms upon HAQ score was actually stronger in those without hip symptoms. The meaning of this counterintuitive interaction is unclear, and we suspect this interaction is unlikely to be clinically relevant.
The serial HAQ scores models we examined showed that the majority of the confounding of associations between joint‐specific hand symptoms and total HAQ scores was related, as expected, to concomitant hip and knee symptoms and hip and knee radiographic OA. Although depressive symptoms were strongly associated with worse function, once hip and knee factors were accounted for, depressive symptoms did not significantly further explain the associations between hand joint variables and function.
One potential limitation of our study is the lack of radiographic characterisation of hand OA to allow correlation with joint‐specific hand symptoms. This limits some comparisons with previous studies using radiographic definitions of disease. A modest association between radiographic hand OA and hand pain was demonstrated in the Rotterdam study, although this same study found that only radiographic MCP and CMC OA were associated with hand disability.18
Other studies have shown weaker correlations between radiographic hand OA and hand symptoms.4,19
In rheumatoid arthritis (RA), pain has a greater impact than radiographic damage on HAQ scores.20
We cannot be certain that MCP and other symptomatic hand joints were due to OA, rather than RA, calcium pyrophosphate deposition disease or haemochromatosis. We feel that this is unlikely because of the low prevalence of these conditions and our exclusion of participants with inflammatory conditions on hip or knee radiographs. Our variable comprising symptoms in at least 2 of 3 hand joint sites (DIP, PIP or CMC), as done in the BLSA study,15
captures a joint distribution typical for hand OA. Importantly, our hand symptom data were joint‐specific, and not generic hand pain, lessening the likelihood of misclassification of the aetiology of the hand symptoms. Lastly, an overemphasis on hand radiographs may miss what is clinically important. For example, data from the Framingham study have shown that of hand joints with clinical symptoms, 40% of men and 58% of women had accompanying radiographic OA. In contrast, of joints with radiographic hand OA, only 8% of men and 17% of women had clinical symptoms.21
Since hip x
rays were only obtained on women 50 years of age or older, our results cannot be generalised to younger women. Finally, this analysis does not include information on symptoms or radiographic evidence of spine OA, commonly seen in association with hand OA,22
which could potentially contribute to the reporting of difficulty with, or performance of, lower‐extremity tasks.23
This study has significant strengths including its biracial composition of men and women, its population‐based design, the inclusion of knee and hip radiography in a single study and its joint‐specific hand symptoms definitions. Although the results strictly apply only to the 6 townships from which the sample was drawn, the characteristics of the sample, regarding age and BMI, are reflective of the increasing age and obesity status of the United States in general, making it likely that these associations may be applicable to a wider population.
In summary, individuals with symptomatic hand joints are likely to have functional limitations that go beyond tasks involving the upper extremities alone. Our results suggest that arthritis studies using either self‐reported or performance‐based functional measures need to consider the impact of symptomatic joints in sites other than the joint site of interest, even if the measures being utilised appear to be specific for the joint site under study.