Severity of patellar luxation and frequency of concomitant cranial cruciate ligament rupture in dogs: 162 cases (2004-2007).

Objective: To evaluate severity of medial patellar luxation (MPL) and frequency of concomitant cranial cruciate ligament rupture (CCLR) in dogs.

Design: Retrospective case series.

Animals: 162 dogs (266 stifle joints).

Procedures: Medical records of 162 small-breed dogs with MPL were reviewed. Signalment, body weight, luxation grade, bilateral or unilateral MPL, CCLR, and difference in luxation grades between stifle joints were evaluated. Association between severity of MPL and CCLR was investigated.

Results: 58 dogs had unilateral MPL, and 104 dogs had bilateral MPL. Dogs ranged from 8.4 months to 16.7 years of age (mean, 5.7 years), and mean body weight was 5.45 kg (12 lb). Forty-one percent of all dogs had concomitant CCLR. Mean age for dogs with MPL alone was 3.0 years, which differed significantly from mean age of dogs with MPL and concomitant CCLR (7.8 years). Dogs with grade IV MPL were significantly more likely to have concomitant CCLR than were dogs with any other grade of MPL. In dogs with bilateral MPL and unilateral CCLR, there was a significantly higher grade of luxation in the stifle joint with CCLR.

Conclusions And Clinical Relevance: Small-breed dogs with MPL and concomitant CCLR were older than were dogs with only MPL. Dogs with grade IV MPL were more likely to have CCLR than were dogs with other grades of MPL. Most dogs with concomitant CCLR had a higher MPL grade in the affected stifle joint than in the intact joint. These findings should be beneficial in client education and clinical diagnosis.