New navicular case study

    This is a 9 year quarter horse gelding that has had lameness issues since he was 3-4 years old.  He has never been used outside of light training.  I feel this type of navicular bone disease must have a genetic component as lesions where noted at an early age.  This horse responded early on to low level mechanics that included a four point style shoe with digital breakover at the tip of p3.  It progressed to needing significant mechanical enhancement but did respond to the enhanced mechanics applied  via a rockered 4 point rail shoe.  The horse was 4/5 bilateral lame on front before shoeing and 1/5 immediately post shoeing.  A significant improvement was noted after the below shoeing method.  The horse was euthanized due severity of disease and dissection was performed to further evaluate the navicular bone and compare to the radiographs.  You will see below the lucent lesions noted in the high beam dorsopalmar radiographs and the 65 dg dorsopalmar radiographs.  These lesions are present on the flexor surface of the navicular bone in which interacts with the flexor tendon.  Note the tissue protruding from the lesions.   This is tendonious tissue that has grown into the tendon and anchors the tendon to the navicular bone.  I can imagine that at lower palmar angle the attachment tugging at the navicular bone lesions is terribly painful.  This also explains why an increase in palmar angle and reduced digital breakover that reduced leverage and tension on the DDFT is so very helpful in this situation.

     Many medical therapies are used in treatment of  navicular disease however without appropriate mechancial treatment many medical therapies only offer temporary relief.  Bursa injections, coffin joint injections, isoxoprine and tildren are common treatments.  But you can see that without mechanical therapy that offers appropriate physical relief it can be difficult to manage.  Cases like this can be difficult to manage at a performance level long term with mechanics and medical therapies and all but impossible without mechanical therapy.



 

Note the lucent regions on the radiographs and the corresponding lesion below.  The tendon has grown into the navicular bone secondary to years worth of the tendon rubbing against the roughened flexor surface of the navicular bone.  This causes abrasions on the tendon that leads to the adhesions connecting it to the navicular bone.

Viewing from front of hoof with navicular bone flipped up to expose the flexor (back) surface of the navicular bone in which the tendon glides over then attaches to coffin bone.

Note the two adhesions on flexor surface.  These where cut away from tendon 

This drawing shows the DDFT in green and adhesions in red

 The above drawing shows the ddft (green) coursing over the navicular to attach to the palmar surface of the coffin bone.  The adhesions (red) are drawn in between the flexor surface and the tendon.

     Below are pre- and post-shoeing radiographs.  Note the drastic changes in palmar angle, tendon surface angle and distance of navicular bone to the condyle of proximal second phalanx (short pastern).  In the rocker shoe the system is  now a self adjusting mechanism with greatly decreased load on lesions and a greatly reduced leverage on the ddft.  Again, this horse's lameness improved at least 80 percent with application of this shoe.