Figure 1.

Patellar tendon buckling was observed when the knee was extended. In this post-TKA patient (F, aged 75 years), both proximal and distal buckling is seen, with a particularly large amplitude buckle in the proximal tendon. When the knee is flexed, the tibia can be seen to be rotated, and buckling is extinct. Distances between the nearest buckle and the distal anatomical landmark (the tibial tuberosity, D_D) and proximal anatomical landmark (the distal edge of the patella, D_P) were measured. Buckling magnitude was separately calculated based on tendon lengths measured from images in which a wire was used to measure tendon length; Buckling magnitude was calculated as the difference in the distance between insertion points at maximum extension and maximum flexion. Note: due to the limited size of the transducer, proximal and distal data were collected separately in this study. In the image above, two ultrasound images are shown together for illustrative purposes.