Background: Developmental dislocation of the patella (DDP) is rare in humans but common in dogs. The canine syndrome, termed patellar luxation (PL), is an inherited condition related to genetic selection of dogs with conformational defects. Breeds with short, bowed legs, including chihuahuas, toy poodles, and bull terriers are predisposed to medial patellar luxation (MPL). Dogs with occult MPL have abnormal patellar tracking but don’t experience visible lameness or exercise intolerance. Management of occult MPL is influenced by the risks and costs of surgical intervention versus the potential risks and costs of avoiding surgery.

Objective: To determine the risk of long-term lameness and the rate of subsequent surgery in dogs with occult grade II MPL.

Method: We performed a retrospective dog owner survey and reviewed the clinical records of adult dogs diagnosed with occult grade II MPL. We included asymptomatic dogs managed non-surgically, with a minimum of 4-years’ follow-up. We used clinical records and owner questionnaires to identify dogs who developed clinically-relevant lameness on a previously asymptomatic limb.

Results: Thirty-eight dogs were included, with an average follow-up of 4.25-years. Seventeen dogs returned for unscheduled MPL surgery at an average of 15 months after initial presentation. A further two dogs developed chronic lameness which was not managed surgically.

Conclusion: Fifty percent of adult dogs with occult grade II MPL developed chronic lameness or required surgery.