Vertical patellar position in large-breed dogs with clinically normal stifles and large-breed dogs with medial patellar luxation

Objective-To further define vertical patellar position, as measured by the ratio of patellar ligament length to patellar length (L:P), in large-breed dogs with clinically normal stifles and compare that to the L:P of large-breed dogs with medial patellar luxation (MPL). Study Design-Retrospective study. Sample Population-Large-breed dogs (n = 50) with clinically normal stifle joints and 30 large-breed dogs with MPL. Methods-Large-breed dogs with clinically normal stifle joints or MPL were identified and divided into groups (NORM and MPL, respectively). L:P values were determined for each dog by 4 observers from single lateral stifle radiographs. L:P was compared between NORM and MPL groups and 95% confidence intervals (CIs) were calculated. Results-All 4 observers found a significantly higher L:P (more proximally positioned patella) for the MPL group compared with the NORM group. Overall mean (+/- SEM) L:P were: NORM, 1.71 +/- 0.020 and MPL, 1.87 +/- 0.025. The 95% CI was determined to be 1.45-1.97 for the NORM group and 1.57-2.17 for the MPL group. Conclusions-Large-breed dogs with MPL had a significantly more proximal vertical patellar position compared with large-breed dogs with clinically normal stifles. Large-breed dogs with L:P values > 1.97 are considered to have patella alta. Clinical Relevance-Proximal displacement of the patella within the femoral trochlear groove may play a role in MPL in large-breed dogs. (c) Copyright 2006 by The American College of Veterinary Surgeons.