Vertical position of the patella in the stifle joint of clinically normal large-breed dogs

Abstract

Objective - To define the vertical position of the patella in clinically normal large-breed dogs. Sample Population - Cadavers of 13 clinically normal large-breed dog. Procedure - Both hind limbs were harvested with intact stifle joints and mounted on a positioning device that allowed full range of motion of the stifle joint. Lateral radiographic views were obtained with the stifle joints positioned at each of 5 angles (148°, 130°, 113°, 96°, and 75°). Vertical position of the patella through a range of motion was depicted on a graph of mean stifle angle versus corresponding mean proximal patellar position (PPP) and distal patellar position (DPP) relative to the femoral trochlea for each dog. Ratio of length of the patellar ligament to length of the patella (L:P) was determined for each dog. Overall mean, SD, and 95% confidence intervals for L:P were calculated for all dogs. Results - Evaluation of vertical position of the patella through a range of motion revealed a nearly linear relationship between joint angle and PPP and joint angle and DPP. Evaluation of L:P results did not reveal significant differences between limbs (left or right) or among joint angles. Overall mean ± SD L:P for all dogs was 1.68 ± 0.18 (95% confidence interval, 1.33 to 2.03). Conclusions and Clinical Relevance - The L:P proved to be a repeatable measurement of vertical patellar position, which is independent of stifle angles from 75° to 148°. This measurement could be used as a quantitative method for diagnosing patella alta and patella baja in large-breed dogs.