Summary
Introduction: Medial patellar luxation is thought to be associated with a high proximal position
of the patella in the trochlear groove.
Objective: To determine whether the ratio of patellar ligament length and patellar length (L:P)
is influenced by the stifle angle (75°, 96°, 113°, 130°, and 148°) in small dog breeds
and to compare the L:P ratio in dogs of three small dog breeds with and without medial
patellar luxation.
Methods: A mediolateral radiograph of the stifle joint was used to measure the L:P ratio in
the stifle joints of dogs of three small breeds with and without medial patellar luxation.
The L:P ratio was evaluated at five stifle angles (75°, 96°, 113°, 130°, and 148°)
in 14 cadavers (26 stifle joints) of small dog breeds in order to identify the best
stifle angle to measure the L:P ratio. Then the mean ± SD L:P ratio was calculated
for normal stifles and stifles with medial patellar luxation grades 1, 2, and 3 in
194 Pomeranians, 74 Chihuahuas, and 41 Toy or Standard Poodles.
Results: The L:P ratio was the same for all five stifle angles in the cadavers (p = 0.195).
It was also not significantly different in the three breeds (p = 0.135), in normal
and medial patellar luxation-affected stifles overall (p = 0.354), and in normal and
medial patellar luxation-affected joints within each breed (p = 0.19).
Clinical significance: We conclude that a proximo-distal patellar position is not associated with medial
patellar luxation in Pomeranians, Chihuahuas, and Toy or Standard Poodles. Thus a
longer patellar ligament length does not play a role in the pathophysiology of medial
patellar luxation in these small dog breeds.
Keywords
Medial patellar luxation - proximo-distal patellar position - small dog breeds - patella
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