Patellar tendon bearing P.O.P. cast is indicated in the following fracture -
Sarmiento's total contact below knee cast/PTB cast

Sarmiento PTB (patellar tendon bearing) plaster, is a carefully moulded patellar tendon bearing below knee plaster which is used in fractures of shaft of tibia in the later stages of conservative treatment when the fracture is more stable (& sticky) and requires the stimulus of direct weight bearing.



It is firmly moulded over-anterior tibial surface, lateral peroneal mass and posterior gastrocnemius mass in order to achieve a triangular shape which will prevent rotation and angulation of fragments. And a hydraulic environment provided by soft tissue is responsible for returning of the fracture to its preload state on the release of pressure (i.g., weight bearing).
Patellar moulding is done in 45° extension (flexion). Most of the pressure is taken over gastrocnemius mass rather than over the bony prominences. 80% of weight is still taken through the leg. That's why it is not recommended for unstable early fractures.
Patella
Tibia
Medial malleolus
Femur