Flexor hallucis longus tenosynovitis at the knot of Henry.

The master knot of Henry can be found plantar to the cuneiform, where the flexor digitorum longus (FDL) and flexor hallucis longus (FHL) cross.

 A sagittal fat suppressed fast spin-echo T2-weighted image through the midfoot reveals peritendinous edema and fluid around the flexor hallucis longus at the level of the navicular and medial cuneiform. In this region, the flexor hallucis longus tendon (FHL) crosses deep to the adjacent flexor digitorum longus tendon (FDL). This intersection point is called the master knot of Henry.

A coronal inversion recovery-weighted image at the level of the cuneiforms confirms peritendinous edema and fluid involving the flexor hallucis longus (FHL) and flexor digitorum longus (FDL).

The axial fat suppressed fast spin-echo proton density-weighted image through the midfoot showing fluid intensity signal around the flexor hallucis longus tendon (FHL).