Navicular degeneration

• This is part of navicular syndrome which relates to changes in the navicular apparatus (podotrochlear apparatus): the navicular bone, DDFT, the coffin joint, the navicular bursa, the collateral sesamoidean ligament (CSL) and the collateral sesamoidean impar ligament (CSIL)
• The navicular bone is also known as the distal sesamoidean bone. Navicular degeneration arises from a variety of pathologies….

  • Focal loss of the medullary architecture with medullary sclerosis
  • Fibrocartilaginous change of the flexor surface of the bone
  • This may eventually lead to traumatic fibrillation of the deep digital flexor tendon which may lead to adhesion formation between the tendon and bone.
  • This can lead to bursitis
  • Enthesophyte formation on the proximal and distal borders of the bone
• label the image

  A) suspensory

  B) impar

  C) DDFT

  
• The cause is unknown but it is likely biomechanical but there may also be a vascular component. Risk factors are…

  • Genetics
  • There is a higher risk in warmbloods, Tbs and quarter horses but it is not as common in Arabians and Friesians. It has not been seen in donkeys or ponies possibly due to the different  conformation, biomechanics and forces
  • Age - it typically occurs in older horses (older than 10 years old)
  • Conformation is very important
  • A long toe and low heel is commonly associated with this condition as well as a broken back HPA.
• Navicular degeneration has an insidious onset of bilateral forelimb lameness, this is initially intermittent so owners see this as a change in performance. These horses are sound in straight line (perhaps with a reduced stride length), lame on lunge and rarely positive to hoof testers (if present it is commonly when pressure has been applied across the heel bulbs or the frog).
• Diagnosis involves perineural anaesthesia where lameness in the contralateral limb becomes apparent, it is not uncommon to be unable to identify lameness until the perineural anaesthesia has been performed.

  A) complete

  B) abaxial

  C) specific

  D) DDFT

  E) contralateral

  
• Diagnostic imaging can also be used

  • MRI
  • Radiography
  • Typically three orthogonal views are taken
  • Lateral medial
  • Palmar proximal - palmar distal oblique
  • Dorsal proximal - palmar distal oblique
• the dorsal proximal - palmar distal oblique view will show the presence of synovial invaginations (miscalled vascular channels). These can be present in all horses so the interpretation is quite subjective. The size, shape and position is important. Larger invaginations and the presence of excessive numbers (especially when abaxially positioned towards the slopping borders) are likely to be indicative of degeneration
• There are no cures for navicular degeneration….

  A) analgesoa

  B) corrective

  C) DDFT

  D) rolled

  E) corticosteroids

  F) palmar digital neurectomy