The association between gout and radiographic hand, knee and foot osteoarthritis: a cross-sectional study

A link has been established between gout and OA, which could explain the distribution of joints affected by gout, particularly the tendency for the first metatarsophalangeal joint (1^st MTPJ) to be affected [1]. Previous studies have shown that joints affected by acute attacks of gout are more likely to display clinical or radiographic features of OA [2, 3]. This is particularly true for the 1^st MTPJ, mid-foot, knees and the distal interphalangeal finger joints [2]. Furthermore, monosodium urate (MSU) crystal deposits at the tibio-talar joints have been shown to occur at sites of degenerative cartilage lesions [4]. A recent primary-care based case–control study however, did not find evidence between gout and clinically-assessed nodal OA, although people with gout were more likely to have hallux valgus and chronic pain in the knee and big toe, compared to age- and gender-matched controls without gout [5].

The aim of this study was to investigate the association between gout and radiographic OA by comparing the presence and severity of radiographic hand, knee and foot OA in adults with and without gout.

Following exclusions for non-consent for medical record review (n = 109), inflammatory arthritis (n = 67) and no radiographs (n = 29), 1797 participants were eligible for sampling (Fig. 1). Fifty-three participants with gout were identified (CASHA n = 11, CASK n = 17, CASF n = 25). Each was matched for age (±2 years) and gender to four individuals without gout from the same study cohort, with the exception of one gout individual from CASF for whom only three matched controls could be identified. Baseline demographic and clinical characteristics of the two groups are shown in Table 1. Mean BMI, diuretic use, ischaemic heart disease and hyperlipidaemia were higher in those with gout compared to those without gout. Knee and foot pain were more frequent and CC less frequent in those with gout than in those without.

The rationale for investigating the association between gout and nodal OA was as an exemplar of generalised OA. However, no significant association was found between gout and radiographic hand OA. These findings are consistent with the only previous study examining the association between gout and hand OA, where nodal OA was found to be no more common in those with gout than those without gout [5]. There were several differences between that study and our current study. Although both studies used participants recruited from primary care, the previous study included younger adults (aged ≥30 years), based the diagnosis of gout on specialist clinical opinion, and used self-report instruments to assess clinical OA [5]. In contrast, in our study, OA was radiographically assessed; nevertheless, the definition of radiographic hand OA affecting at least two rays on each hand was comparable.

Although not statistically significant, there were findings in this study suggesting that participants with gout were more likely to have widespread or severe OA involvement of small joints in the hand and foot compared to those without gout but less likely to have TF or PF OA.

At the foot, individuals with gout were more likely to have foot OA, severe foot OA, and specific involvement of the 1st MTP, N1stCJ, TNJ and multiple joints compared to those without gout. 1st MTPJ involvement is not surprising as it is a common site for both OA and gout, and an association with OA has been suggested as a possible explanation for the striking predilection of gout for this joint [1, 15]. Previous research has also shown that the mid-foot region can be commonly affected by gout when clinical OA is evident [2], which is consistent with our observation that people with gout had a higher likelihood of mid-foot OA. The frequency of OA at individual foot joints may reflect the association of gout with generalised OA or that the pain associated with gout could alter biomechanics of the foot potentially predisposing to subsequent OA [2, 4].

This study, to our knowledge, is the first to examine the relationship between gout and radiographic OA across multiple joint sites. The study was undertaken in a primary care setting so the results are generalizable to most people with gout who are managed entirely in primary care. The major limitation of the study was inadequate statistical power, making it liable to a type II error. The study involved secondary analysis of data from three existing cohorts and therefore the number of available gout cases was limited. The sample population may also have differed from the general population as the frequency of radiographic OA was found to be considerably higher in these participants, who had all reported joint pain at the hand, knee or foot in the last year, than in other adult general populations. Therefore, an association between gout and OA may have been masked. A further caveat is the reliance on primary care records to diagnose gout, and whilst morbidity coding in the participating practices undergoes regular quality review [16, 17] and previous work has suggested that diagnosis of gout by GPs is reasonably accurate [18], there is still a risk of misclassification bias. Synovial fluid MSU crystal identification is the gold standard for the diagnosis of gout [19], however, this is rarely performed in primary care. It is, however, reassuring that only a small minority of participants had radiographic CC.

In summary, no statistically significant association was observed between gout and hand, knee and foot OA, however there were findings to suggest that people with gout were more likely to have OA affecting the small joints of the hands and feet but less likely to have large joint OA at the knee. Further research is needed to understand the relationship between gout and OA, using robust case definitions based on crystal identification and imaging. Such studies will provide important insights into the aetiology, co-occurrence and clinical presentation of both conditions.

Ethical approval was obtained for all three cohorts (North Staffordshire LREC (1430); Coventry REC (10/H1210/5). All participants provided written informed consent and were also asked for consent to review their medical records.

Not applicable as no identifying personal information is being published in this manuscript.

Requests for further detail on the dataset and queries relating to data sharing arrangements may be submitted to Edward Roddy, e.roddy@keele.ac.uk. Participants were not asked for informed consent for data sharing although the presented data are anonymised and risk of identification is low.