Introduction

Patella alta is defined as proximal displacement of the patella within the femoral trochlear groove. Patella alta has been associated with medial patellar luxation (MPL) in large-breed dogs.

Objectives

The objectives of our study were to evaluate the ratio of patellar ligament length (L) and patellar length (P) in three small-dog breeds with and without MPL and to compare the L:P ratio between clinically normal stifle joints and the stifle joints with MPL.

Methods

Mediolateral radiographs of the stifle joints of 194 Pomeranians (35 controls), 74 Chihuahuas (24 controls), and 41 Poodles (16 controls) were used to calculate the L:P ratio. The dogs were divided into 4 groups: normal, MPL grade 1, MPL grade 2, and MPL grade 3. The mean ± SD was calculated for each group in each breed. Two-way ANOVA was used to compare differences in the L:P ratio among the three breeds, and among the four groups. A p value of < 0.05 was considered significant.

Results

The overall mean ± SD of L:P in Pomeranian, Chihuahua, and Poodle were 1.81 ± 0.18, 1.85 ± 0.18, and 1.79 ± 0.17, respectively. The L:P ratio was not significantly different among the three breeds, among the four MPL groups, and among the four MPL groups within each breed.

Conclusions

No correlation was found between the vertical patellar position and MPL in these breeds. Unlike previous reports in large breed dogs with MPL, increased length of the patellar ligament does not play a role in the pathophysiology of MPL in these small-dog breeds.