Antinuclear antibodies in primary osteoarthritis of the knee: a case-control study

Objective: Although osteoarthritis (OA) is widely accepted as a degenerative disease, autoimmune processes are believed to be involved in the pathogenesis. There are limited studies in this area and most of them focused on antibodies against chondrocyte membrane. In an attempt to address the paucity of evidence in this regard, we explored the clinical significance of antinuclear antibody (ANA) in primary osteoarthritis of the knee (OAK). Method: We studied 106 patients with primary osteoarthritis of at least 1 knee and 63 healthy controls from two tertiary centres in Malaysia from September 2005 to May 2012. All subjects were tested for ANA by immunofluorescence testing, and a titer of 1:40 and above was considered positive. Besides, the radiographs of bilateral knees were evaluated for grading, tibiofemoral compartment involvement and total knee replacement (TKR) implants. We compared the clinical characteristics between the ANA positive and ANA negative OAK cases. Results: The incidence of ANA positivity among the cases (39.4 %) was higher than the controls (27 %) but this difference was statistically insignificant (p=0.754). ANA positive cases showed significantly higher incidence of bilateral and Grade IV OAK with higher frequency of TKR. In the multiple regression analysis, bilateral OAK (p< 0.0001; odds ratio 9.00), Grade IV OAK (p<0.001, odds ratio 3.44) and TKR (p=0.009; odds ratio 2.97) remained associated with ANA positivity. Conclusions: ANA test is a potential prognostic tool in primary OAK and its positivity is associated with the clinical outcomes of bilateral, Grade IV OAK and TKR.