Franklin SP, Park RD, Egger EL. Departments of Clinical Sciences, James L. Voss Veterinary Teaching Hospital, Colorado State University, Fort Collins, Colorado 80523, USA. JAAHA 2009 May-Jun 45 3 112-7 Although osteoarthritis (OA) is a common and debilitating condition in the canine patient, few data are available on OA of the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints. Review of medical records of 49 dogs with a radiographic diagnosis of MCP or MTP OA presented over a 7-year period demonstrated that OA was an "incidental finding" for the majority of animals (n=35), while 14 dogs were identified as clinically lame as a result of MCP or MTP OA. Dogs that were clinically lame as a result of MCP or MTP OA were significantly more likely to have visible swelling over the affected digits. Five times as many dogs were diagnosed with MCP OA than with MTP OA, and the majority of dogs had radiographic changes on multiple digits. Review and scoring of radiographs (n=44 dogs) for six radiographic signs of OA followed by logistic regression analysis demonstrated that the two lateral digits of the front limb were significantly more likely to have osteophytosis and enthesophytosis than the two medial digits. Osteoarthritis of MCP and MTP joints has unique radiographic features that are not seen in the stifle, hip, shoulder, or elbow; these features can complicate accurate diagnosis, particularly differentiation from primary bone neoplasia. These data underscore the clinical relevance of this condition and provide useful information detailing which and how many digits are most commonly affected, potentially assisting discrimination between OA and neoplasia.