Objective: To compare rates of contralateral cranial cruciate ligament rupture (CCLR) in Labradors based on age and weight at initial rupture, sex, and tibial plateau angle (TPA) and to determine whether Labradors that rupture their initial cranial cruciate ligament (CCL) at an earlier age (<4 years) are more likely to rupture their contralateral side within a certain period of time.
Study design: Case series.
Animals: Labradors (n=94) that had tibial plateau leveling osteotomy (TPLO).
Methods: Two groups: no contralateral rupture (NR) and contralateral rupture (CR) were compared for significant (P<.05) differences in percentage of subsequent cruciate tears using a Wilcoxon's rank-sum tests for continuous variables and Fisher's exact test for sex. Adjusted odds ratios for likelihood of subsequent cruciate tears (yes/no) were estimated using logistic regression. Associations of these characteristics with time to subsequent rupture were assessed using Kaplan-Meier survival analysis estimation. Predictors of presentation with bilateral ruptures (BR) versus single rupture were also evaluated using Wilcoxon's rank-sum tests and a generalized Fisher's exact test.
Results: Subsequent CCLR occurred in 45 dogs (48%), and BR on admission were identified in 10 dogs (10.6%). Comparing NR and CR dogs, there were no significant differences between age or weight at initial rupture, sex or TPA; however there were associations toward longer time to CR for dogs older than the median age and female dogs (intact and spayed). There were no significant differences in age, sex, weight, or TPA of dogs with bilateral CCL ruptures compared with initial unilateral ruptures; however, there was a trend toward dogs presenting at an older age and with lower TPA's in the BR group. Among the 84 NR/CR dogs, the median time to rupture of the contralateral CCL was 5.5 months (95% CI 5.2-5.7).
Conclusions: Age and weight at initial rupture, sex, and TPA does not affect likelihood or rate of contralateral CCL rupture or presentation with bilateral CCL ruptures.
Clinical relevance: Approximately 50% of Labradors will rupture the contralateral CCL within 5.5 months of the initial rupture but age, weight, sex, and TPA cannot be used as predictive features.