OBJECTIVE: To evaluate the effect of the tibial plateau levelling osteotomy (TPLO) procedure on the patellar tendon angle (PTA) in dogs with naturally occurring cranial cruciate ligament rupture. STUDY DESIGN: Prospective observational clinical study. ANIMALS: Dogs with naturally occurring CrCL rupture that had a TPLO performed (n = 40). METHODS: Preoperative tibial plateau angle (TPA) and PTA were measured on radiographic images of affected stifle joints at 90° and standing angle (135°) respectively. The TPA and PTA were measured after TPLO was performed. Regression analysis was performed to evaluate the effect of preoperative TPA and PTA and postoperative TPA on postoperative PTA. Linear regression analysis was performed to evaluate the correlation between postoperative TPA and PTA. RESULTS: The mean (± SD) preoperative TPA and PTA were 26.5 ± 3.8° and 105.7 ± 3.8° respectively. The postoperative TPA and PTA values were 7.6 ± 3.3° and 91.4 ± 5.5°, respectively. Regression analysis showed that higher preoperative PTA and postoperative TPA are associated with a larger difference between the postoperative PTA and 90°. There was a positive correlation between postoperative TPA and PTA. CONCLUSION: The TPLO procedure alters the PTA to 90° in dogs with cranial cruciate ligament rupture similar to tibial tuberosity advancement (TTA). CLINICAL SIGNIFICANCE: The TPLO may provide dynamic stability to the cranial cruciate deficient stifle by altering the TPA relative to the patellar tendon and creating a PTA of 90°. The biomechanical principle and mechanism of action of TPLO may be similar to TTA.