The purpose of this study was to evaluate the morpho-functional change of the patellar ligament in dogs affected by cranial cruciate ligament rupture. The hypothesis is that it may show increased thickening and stiffness with increasing days from trauma to diagnosis. Understanding this aspect have implications on the choice of timing to treat patients suffering from cranial cruciate ligament rupture, and also in the contextualization of patellar ligament desmitis pictures after surgical treatment with tibial plateau levelling osteotomy or tibial tuberosity advanced. Thirty-three dogs were affected affected by unilateral cranial cruciate rupture were examined and divided into three groups based on the time elapsed from the onset of lameness to diagnosis: Group 1 (from 1 to 15 days), Group 2 (from 16 to 60 days), Group 3 (over 60 days). Conventional B-mode ultrasonographic and elastosonographic examinations of patellar ligament were performed without sedation for each dog. At the ultrasonographic examination, all dogs showed alterations in the echostructure of the patellar ligament. In addition, the patellar ligament tended to become harder and less soft with increasing days after rupture, although there were not significant differences between groups. Our results showed that as time increases between the onset of cranial cruciate ligament rupture and diagnosis and treatment, the patellar ligament progressively thickens and loses its elasticity.