Patellar alignment evaluated by MRI

We analyzed the congruence of the articular cartilage surfaces and the corr esponding subchondral bone in the patellar joint. 20 volunteers underwent M RI investigations of the right patellar joint in 20 degrees and 45 degrees flexion in the axial plane. The sulcus, congruence, and lateral patellofemo ral angles, measured on MRI slices centered through the midtransverse patel la, were recorded. In 20 degrees and 45 degrees knee flexion, the bony sulc us and lateral patellofemoral angles were significantly different from the respective cartilagineous angle. We conclude that 1) measurement of the bon y sulcus and lateral patellofemoral angles does not allow conclusions about the articular cartilage surface and its thickness, 2) the bony congruence angle corresponds well to the articular cartilage surface as an indicator o f patellar centralization.