Examination of Proximodistal Patellar Position in Dogs with the Stifle at Full Extension.

Objective:  The aim of this study was to determine the factors related to functional patella alta, with which the proximodistal patellar position exceeds the reference range of healthy small dogs proximally when the stifle is at full extension.

Study Design:  Mediolateral-view radiographs of dogs weighing less than 15 kg were obtained and classified into the medial patellar luxation (MPL) and control groups. The reference range of the proximodistal patellar position was determined from the control group. In both groups, a patellar position exceeding this reference range proximally was considered functional patella alta. Multiple logistic regression analysis was performed to examine the factors related to functional patella alta. A receiver operating characteristic (ROC) curve was made for each factor.

Results:  Overall, radiographs of 127 stifles of 75 dogs were obtained. Eleven stifles in the MPL group and one stifle in the control group were determined to be functional patella alta. The factors associated with functional patella alta included a greater full extension angle of the stifle joint, longer patellar ligament, and shorter femoral trochlear length. The full extension angle of the stifle joint had the biggest area under the ROC curve.

Conclusion:  Mediolateral radiographs of the stifle joint in full extension are clinically important in dogs with MPL because some dogs might have a proximally positioned patella that is recognizable only when the stifles are extended.