ANATOMY

    The articular surfaces of the coffin joint (also called the corono-pedal joint, the distal interphalangeal joint and the DIP joint) are entirely within the horny hoof but the joint capsule does extend above the level of the coronet of the cranial and caudal surfaces of the second pedal bone (P₂).  The joint capsule on the abaxial side is not strongly supported by the collateral ligaments, thus infection here can drain to the exterior via a fistula above the abaxial coronet and behind P₂ or, less frequently, in front of P₂.

    The cruciate (or distal interdigital) ligament is complex and has an important function in restricting the divergence of the claw.  The ligament inserts on the abaxial border of the navicular bone and widens to merge with the digital cushion, forming a semi-rigid wall behind the coffin joint.  The coffin joint is thus protected on three sides by the hoof and caudally by the collateral and cruciate ligaments, leaving only the most cranial portion of the joint capsule vulnerable.  This arrangement permits the spread of foot rot infection from the interdigital region into the cranial part of the coffin joint.

    The navicular bursa is situated between the navicular bone and the deep flexor tendon.  The bursa does not communicate with the distal interphalangeal joint, being seperated from it by the navicular bone and the distal sesamoid ligament, nor does it communicate with the sheath of the flexor tendon.  Because the bursa is surrounded by strong fibers, considerable pressure is exerted on it during weight bearing and locomotion.  Infection can spread from the bursa further up the digit.  The insertion of the deep flexor on the coffin bone (P₃) makes direct access from the sole to the bursa impossible except by deep penetration; however, infection can enter the bursa under either edge of the tendon.  Infection of the articulation between the navicular bone and the coffin bone can extend into the coffin joint, especially if there is osteomyelitis of the navicular bone.  The deep flexor tendon is caudally fused to the digital cushion.  This fusion and that of the cruciate ligament form a relatively solid structure of the heel.  The sheath of the deep flexor tendon begins above the digital cushion.  The shape of the coffin bone (P₃) of the hind digit's medial claw differs from that of the lateral claw.  The

    The axial groove is a small depression located in the middle of the axial border of the animal's sole; this is the thinnest area of the sole.  The only natural depression of the sole, it readily accumulates dirt, debris, and anaerobic bacteria, which can undermine the sole.