Imaging description

The master knot of Henry is best seen on coronally oriented cross-sectional imaging such as CT or MRI of the foot. After extending past the sustentaculum tali, the flexor hallucis longus (FHL) crosses from lateral to medial over the dorsal surface of the flexor digitorum longus (FDL). This cross-over is termed the master knot of Henry (Figure 70.1). At this cross-over, these two tendons are enclosed together and attached to the vault of the arch of the foot. Just distal to the master knot of Henry, there is a ligamentous attachment between the two tendons. This ligament can be proximal to distally oriented from the FHL to the FDL; it can be distal to proximally oriented from the FHL to the FDL; or it can be bifid with both distal to proximal and proximal to distal oriented ligaments as they extend from the FHL to the FDL.

Importance

Depending on the orientation of the ligament by the master knot of Henry, rupture of the FHL or FDL proximal to the master knot of Henry may not cause loss of toe flexion. When the ligament is oriented distal to proximal from the FHL to the FDL, rupture of the FHL proximal to the master knot of Henry will not cause loss of toe flexion. Conversely, when the ligament is proximal to distal from the FHL to the FDL, rupture of the FDL proximal to the knot will not cause loss of toe flexion. With a bifid ligament, then rupture of either the FHL or FDL proximal to the knot will not cause loss of toe flexion.