A bone patellar-tendon bone graft is the gold standard for replacement of a torn cruciate ligament in the knee, where a part of the patellar tendon is used as the graft material.
The central one third of this tendon can be 'harvested', together with a bone block at each end - the upper block from the patella (kneecap) itself and the lower block from the tibia bone (shin). This harvested tendon is thus 'bone-patellar tendon-bone' in structure.
Arthroscopic Anatomic Single-Bundle Anterior Cruciate Ligament Reconstruction Using Bone–Patellar Tendon–Bone Autograft: Pearls for an Accurate Reconstruction. Chahla J, Moatshe G, Cinque ME, Godin J, Mannava S and LaPrade RF. Arthrosc Tech. 2017 Aug; 6(4): e1159–e1167.