The horn-lamellar (HL) zone is another of the five soft-tissue parameters that Dr. Redden measures on his radiographs. The measurement explores the relationship of the face of PIII to the outer horn wall. If you look closely at a true lateral radiograph taken with soft-tissue detail, you will find that an opaque line separates the horn and the laminae. Measuring the HL zone helps determine if pathology in this area involves the horn or the laminae.
Use the following steps to measure the HL zone consistently:
Beginning just below the extensor process, draw a line perpendicular to the edge of the hoof wall. Measure the length of this line in millimeters. Notice the barium paste used for a wall marker. This helps us determine exactly where the outer hoof wall begins.
Draw a second line from the apex (tip) of the coffin bone perpendicular to the edge of the outer hoof wall. Measure the length of this line in millimeters.
These two measurements determine the HL zone. When referring to the HL zone, the top number is given first followed by the bottom number. In this particular case, the HL zone measures 22/30.