Influence of tibial plateau angle in cranial cruciate ligament-deficient stifle on patellar ligament strain: an ex vivo study

OBJECTIVE The aim was to investigate the patellar ligament strain with varying degrees oftibial plateau angles (TPAs) after tibial plateau leveling osteotomy (TPLO) in a cranial cruciate ligament (CrCL)-deficient stifle during the stance phase. METHODS 12 pelvic cadaver limbs were secured to a custom-built jig to mimic a loadbearing stance after which an axial load of 120 N was applied. Patellar ligament strain, change in strain, and percent change in strain were calculated on pre-TPLO (intact and transected CrCL) and post-TPLO tibial TPAs of -5 degrees, 0 degrees, 5 degrees, 10 degrees, and 15 degrees. Strain was measured using a 3-D digital image correlation to calculate Green-Lagrange strain (E33). Data were compared using a linear mixed model and applying the Dunnett method of multiple comparisons (control was pre-TPLO intact CrCL). RESULTS The post-TPLO TPAs of 0 degrees and 5 degrees increased in patellar strain compared to pre-TPLO intact CrCL constructs, whereas no significant changes were seen at a TPA of -5 degrees, 10 degrees, and 15 degrees. Significant changes in patellar ligament strain were noted at a TPA of 0 degrees and 5 degrees. The percent change in strain differed at -5 degrees, 0 degrees, and 5 degrees TPAs. The median magnitude of percent change in strain was 35.1%, 37.0%, 79.0%, -7.1%, and -21.1% for -5 degrees, 0 degrees, 5 degrees, 10 degrees, and 15 degrees, respectively. CONCLUSIONS Significant increases in patellar ligament strain (CrCL-deficient stifle) during the stance phase were observed at TPAs of 0 degrees and 5 degrees. CLINICAL RELEVANCE A TPA post-TPLO > 5 degrees and < 15 degrees is less likely to cause an increase in patellar ligament strain; however, further research is needed to investigate the clinical relevance of these findings.