Navicular degeneration

Question 1

What are the structures highlighted in this radiograph?
what is the arrow pointing to?

Answer 1

Arrow and blue line - brocken back hood pastern axis (increased extension of the distal interphalangeal joint)
Yellow - DDFT (runs allong the flexor surface of the navicular)
Green - Suspensory (collateral) ligament
Blue - distal sesamoidian ligament (Impar ligament - supports the navicular bone

Question 2

what is navicular degeneration?

Answer 2

• Focal loss of the medullary architecture with medullary sclerosis
• Fibrocartilagenous change of the flexor surface of the bone
• Traumatic fibrillation of the deep digital flexor tendon which may lead to adhesion formation between the tendon and bone
• Enthesophyte formation on the proximal and distal borders of the bone

Question 3

what are the clincial signs of navicular disease?

Answer 3

• Insidious onset bilateral forelimb lameness
  
  • Initially intermittent
  • Change in performance
• Sound in straight line
  
  • Lame on lunge (when lame leg is on the inside)
• Rarely positive to hoof testers (but if present will be when pressure is appled between frog and hoof wall or across heel bulbs)

Question 4

How is navicular degeneration diagnosed?

Answer 4

• Positive response to Palmer Distal Nerve Block (PDNB)
  
  • Typically complete resolution
  • Lameness switches to other leg
  • Not definitive to navicular degeneration
• Anaesthesia of navicular bursa more specific
  
  • Not frequently performed in primary practice
  • ↑ complexity
  • Requires radiographic guidance + contrast

Question 5

what radiographic views can be used for diagnosis of navicualr degeneration?

Answer 5

three orthogonal views:
* Lateral media
* Dorsoproximal- palmarodistal oblique (85 degee upright navicular) (shows the presence of synovial invaginations in the distal border and cysts)
* palmero proximal-palmero distal oblique (45degree) (flexor/skyline navicular)

Question 6

what are the advantages of MRI for diagnosis of navicualr degeneration?

Answer 6

Advantages
- Diagnosis of multiple pathologies
- Early diagnosis of bone pathology

Disadvantages: Cost

Question 7

What are the concervative management options for navicular degenration?

Answer 7

• Analgesics
• Corrective farriery
  
  • Wedges - reduces externtion of distal interphalangeal joint
  • Rolled toe - ease breakover allowing foot to lift off ground more quickly and reduce leverage of the dorsal toe
  • Bar shoes - stablise for and prevent further collapse of the heel
• Corticosteroids (triamcinolone, methylprednisolone) into the distal phalangeal joint (or burssa but harder)
• Bisphoshonates (tiludronate, clodronate)
• (Vasodilators e.g. isoxuprine)

Question 8

what is the surgical treatment for navicular degeneration?

Answer 8

Palmar digital neurectomy
* Provides pain relief but:
* Nerve sensation will eventually restore
* Complications include neuroma and catastrophic DDFT breakdown, pedal osteitis/foot penetrations

Other surgical procedures unproven

Question 9

what is the aetiology and risk factors for navicualr degeneration?

Answer 9

Aetiopathogenesis
* Unknown but most likely biomechanical
* Possibly some vascular component

Risk factors
* Genetic component
* ↑ WBs, TBs, Quarterhorses
* ↓Arabians, Friesians
* Not seen in donkeys or ponies
* Typically older horses >10yo
* Conformation very important