Influence of tibial plateau leveling osteotomy on strains placed on the patellar ligament: an ex vivo study in cranial cruciate deficient stifles

Background Cranial cruciate ligament (CrCL) disease is a frequent cause of pelvic limb lameness in dogs. Tibial plateau leveling osteotomy (TPLO) is a common surgical intervention but can result in postoperative patella desmitis. The underlying causes are not fully understood, but can involve increased strain on the patella ligament. The aim was to assess the impact of different tibial plateau angles (TPAs) post-TPLO on patellar ligament strain in CrCL-deficient stifles during weight-bearing stance. Methods Patellar ligament strain was measured using a 3D method of digital image correlation to calculate Green–Lagrange strain (unitless measure), specifically E ₃₃ , to yield the axial strain. Twelve pelvic limbs harvested from seven previously owner-consented euthanized dogs (> 20 kg) without pelvic limb or girdle pathology were dissected out and fitted to a custom-built jig. The limbs were positioned to mimic a loadbearing standing animal and 120 Newtons of force were applied. Strain, change in strain, and percent change in strain were measured or calculated on pre-TPLO (intact and transected CrCL) and various post-TPLO TPAs. Data were compared using a linear mixed model and applying Dunnett method of multiple comparisons (control: pre-TPLO intact CrCL) where significance was interpreted at p  < 0.05. The hypothesis was that patellar ligament strain would not differ across various TPAs compared to CrCL-intact stifles, simulating weight bearing at a standard standing angle. Results Post-TPLO TPAs of 0° (P = 0.019) and 5° (P = 0.031) increased in patellar strain compared to pre-TPLO intact CrCL constructs. However, the change in patellar ligament strain was only different at 0° (P = 0.047) TPA. Whereas the percent change in strain were different at -5° (P = 0.041), 0° (P = 0.013) and 5° (P = 0.026) TPAs compared to pre-TPLO intact CrCL construct. The median magnitude of percent change in strain were 35.1%, 37.0% and 79.0% for − 5°, 0° and 5°, respectively. Conclusion TPLO rotation angle influences patellar ligament strain. TPLO with a 10° TPA is less likely to cause patellar ligament strain, but further research is needed for short or long-term outcomes in a live animal canine model is warranted.