Fig. 6
From: Three-dimensional motion of the patella in French bulldogs with and without medial patellar luxation
Zero-pose and axes for the patella. Patellar motions were measured relative to this pose. Every dog has its own reference pose. However, all models were build following the same kinematic chain. Joint coordinate systems were aligned to the axes of the global coordinate system (+x points caudally, +y points medially and + z upwards). Note that the patella was rotated 30° around the Y-axis relative to the patellofemoral joint. Green, blue, and red dots indicate that those axes point into the picture