New Functional Interpretation of the Musculus Popliteus and the Musculus Extensor Digitorum Longus for the Stifle Joint According to Their Origin Coordinates in Dogs

The stifle joint is among the most commonly injured joints in dogs. Detailed functional information is required to identify the causes of damage and determine the most appropriate treatment strategy. The lateral condyle of the femur and its attaching structures play an important role in joint stability, which is essential for proper joint movement. The long digital extensor and popliteus muscles originate from the lateral condyle, and their functions have not been described properlyresulting in contrasting functional interpretations. In this study, we suggest new functional hypothesses for these muscles based on their origin coordinates from the lateral condyle in dogs. The popliteus muscle may act as either an extensor or a flexor depending on the stifle angle during the stance phase, in addition to facilitating rotational movement. The long digital extensor muscle functions as an extensor of the joint and may prevent the lateral condyle from slipping caudally during stifle extension. It may also help prevent cranial tibial thrust on the lateral side of the tibial plateau during extension. From a parcticioner point of view we suggest that, during the stifle surgery, the muscles are preserved as much as possible.