**7. Materials and methods**

This was a retrospective study that assessed the clinical surgical records of dogs treated for patellar luxation from January 2005 to January 2016 at the Veterinary Hospital, Federal University of Minas Gerais (FUMG) in Brazil. Data describing age, body weight and the degree of patellar luxation at admission were collected for each animal. The animals were then categorized based on body weight (≤5, 5–15 and ≥15 kg), age (<12, 12–24 and >24 months) and degree of luxation according to Putnam's [10] classification as adapted by Singleton [19]. In addition, data relative to the intraoperative period were recorded; these included the presence of stifle joint damage, classified as patellar or extrapatellar lesions and the frequency of postoperative re-luxation. The associations between patellar or extra-patellar lesions and the animal's age, body weight and degree of luxation were investigated. Patellar lesions included the presence of cartilage erosion, the extent of the erosion (one-fourth, one-half or the full patellar articular surface), the morphology of the patella (concave or flat), the exposure of subchondral bone and the presence of enthesophytes. Extra-patellar lesions included the presence of erosion and subchondral bone exposure in the medial or lateral femoral condyles, the presence of osteophytes, synovitis, capsular thickening or shallowing of the trochlea, an absent or convex trochlear groove, cruciate ligament rupture and injury of the long digital extensor tendon and the menisci.

The frequency of lesions in the stifle joint was subjected to descriptive analysis, and the rate of patellar re-luxation was assessed using the chi-square test. The significance level was set at *P* < 0.05.

This retrospective study also included the clinical records of eight cats (13 joints) treated for patellar luxation. Data describing age, body weight and the degree of patellar luxation at admission were collected for each animal.
