The flexor hallicus longus (FHL) is the primary flexor muscle of the big toe. It originates at the back of the leg, transitions into a long tendon as it enters the foot and attaches on the bottom of the big toe.

The peroneus brevis (PB) muscle starts in the leg and continues along the outside of the ankle. It then takes a sharp turn and ends on the outside of the foot. The peroneus brevis works with the peroneus longus (PL) to turn the ankle and foot outward. 

The FHL to PB tendon transfer is a surgery to improve the function of the foot. The FHL is passed behind the ankle to the outside of the foot to either assist or replace the damaged PB tendon.

The goal of this surgery is to restore the power of the ankle and foot to turn outward, which is required for cutting and turning movement.