To develop a radiographic atlas for the classification of osteoarthritis (OA) in commonly affected joints of the foot based on observations of osteophytes and joint space narrowing, and to assess its intra- and inter-examiner reliability.

Weightbearing dorso-plantar and lateral foot radiographs from people aged over 65 years were examined, and an atlas was developed incorporating characteristic OA features of five foot joints: the first metatarsophalangeal joint, the first cuneo-metatarsal joint (1^st CMJ), the second cuneo-metatarsal (2^nd CMJ), the navicular-first cuneiform joint and the talonavicular joint. To assess the reliability of the atlas, two examiners independently rated 50 radiographs on two separate occasions.

Observations using the atlas demonstrated moderate to excellent reliability within examiners (percentage agreement from 86 to 99% and weighted κ from 0.45 to 0.95), and, with the exception of joint space narrowing of the 2^nd CMJ from the lateral projection, fair to excellent reliability between examiners (percentage agreement from 86 to 97% and weighted κ from 0.32 to 0.87). Intra-class correlation coefficients for the overall foot OA score (representing the sum of observations for all joints from both feet) ranged between 0.83 and 0.89 for intra-examiner comparisons, and between 0.72 and 0.74 for inter-examiner comparisons.

Radiographic features of OA in commonly affected foot joints can be documented with high levels of agreement within examiners and moderate levels of agreement between examiners. Provided single examiners or consensus gradings are used, the atlas appears to be a useful tool to assist in the standardization of foot OA assessment for epidemiological and clinical studies.