Sole support v frog support

Following laminitis, the feet should be supported through the full solar surface, not just through the frog.  

1.  When frog support only is used on a laminitic foot, the pedal bone is left unsupported with the potential for (further) rotation, sinking and penetration (the example shows a foot with dorsal and palmar rotation):

The laminae are not properly connected after laminitis.  The force of the horse's weight acts downwards on the pedal bone (P3) (blue arrow).  A frog support is supposed to support the back of the foot, but the back of the foot is not affected by laminitis and should already be well supported by the horse's own frog.  Fitting a frog support potentially lifts the front of the foot off the ground, giving the tip of P3 a hole to fall down into.
On conforming bedding the front of the foot will be supported so the risks of fitting a frog support should be minimized, but the frog support is unlikely to provide any better support than the bedding alone (and may lead to thrush, excess pressure and atrophy of the frog).
The dorsal and palmar rotation should be corrected immediately.  The purple dotted line shows the breakover bevel back to the outer edge of the true white line.  The heel/bottom of the foot trim to return the palmar angle to 3 to 5 degrees is not shown, but see below *.
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2.  When full solar surface support is used on a laminitic foot, the pedal bone is supported and the potential for (further) rotation, sinking and penetration is minimized:

​The laminae are not properly connected after laminitis.  The force of the horse's weight acts downwards on the pedal bone (P3) (blue arrow).  The foot in front of the true white line is not stable and should not bear weight - the dotted purple line shows the breakover bevel needed to bring breakover back to the outer edge of the true white line, to more stable foot.  With full solar surface support fitted, the pedal bone is fully supported, and the ground reaction force acting through the solar support (green arrows) can oppose the horse's weight (dark blue arrow) and any further displacement of the pedal bone (turquoise arrow) - the pedal bone has increased stability.  See image below for how the realigned foot would look with full solar surface support. 
​Conforming bedding may support the foot adequately and whilst a laminitic horse is on wall to wall deep conforming bedding, extra support may not be needed, but if a horse is not fully comfortable, padding the full solar surface should be tried and the horse assessed to find optimum comfort.
As above, the dorsal and palmar rotation should be corrected immediately.
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3.  When the heels are high (i.e. there is palmar rotation), extra support may be needed beneath the frog so that the frog shares weight bearing with the rest of the solar surface, while waiting for realigning trimming to lower the heels and return the palmar angle to normal.  However, there should be frog support PLUS full solar surface support (both supports will usually be made from the same material, e.g. EVA foam), and never frog support alone for the reasons given above.

​Raul Bras, in his chapter on Solear Support Techniques (in Equine Laminitis edited by Belknap, Wiley, 2017) says that over the last 25 years it has become routine for acute laminitis cases to have the sole and bars as well as the frog supported with pliable material.  He states that it is likely that applying supportive material to the whole solar surface of the foot will provide support to the pedal bone (P3), but that using frog support has not been proven to greatly improve support of the pedal bone, and therefore it may be more effective to provide support to the entire sole and the entire solar surface of the pedal bone.  Supportive materials used should be similar in hardness/firmness to the horse's frog, and include EVA foam, closed-cell foam and impression material.  Discussing frog supports, he warns of pressure around the coronary band from fixings used, suggests that they frequently move out of place, and cautions that no research supports their use.  He concludes "it is likely that the greater surface area of the sole addressed by the sole support (especially the dorsal aspect of the sole), the more support will be provided to the DP" (distal phalanx/P3).

It is very important that sole support does not adversely affect the already compromised foot, and thought should be given to the material and design used and to ensure that pressure is released during hoof flight.  Dr Taylor (see below) suggests using a shallow air space beneath the margin of the pedal bone when the sole is very thin or perforated.  However, if used both the position of the air space and the horse's comfort must be checked regularly, as we have seen the use of an air hole allow the pedal bone to penetrate the sole in a foot that hadn't been correctly realigned.
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The realigned foot with the front of the pedal bone left unsupported by using frog support only.

The realigned foot with pedal bone fully supported by full solar surface support.

Jonathon Merritt, Helen Davies and Andrew Parks say, in their chapter on the Digital Biomechanics Relevant to Laminitis (in Equine Laminitis edited by Belknap, Wiley, 2017) that the pedal bone may be supported from below by forces transmitted from the solar surface of the hoof, and that "increasing support from the sole may assist in reducing the force on the lamellar junction."

​In 2014 Dr Debra Taylor published a paper describing the laminitis rehabilitation protocol that returned 14 out of 14 horses, many with significant rotation and sinking, to their pre-laminitis level of comfort.  The hoof care method used the full solar surface to support the pedal bone (P3), protecting the sole during weight bearing by using foam rubber pads and/or dental impression material inside hoof boots (or casts).  

See Section 2.3:
Taylor D, Sperandeo A, Schumacher J, Passler T, Wooldridge A, Bell R, Cooner A, Guidry L, Matz-Creel H, Ramey I, Ramey P
Clinical Outcome of 14 Obese, Laminitic Horses Managed with the Same Rehabilitation Protocol
Journal of Equine Veterinary Science Volume 34, Issue 4, Pages 556–564, April 2014 (online 05 Feb 2014)
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See also:
Solar penetration
Robert Bowker Hoof Anatomy Videos

* The realigning trim restores the palmar angle to 3 to 5 degrees (by lowering the heels gradually) and returns the wall at the toe to being parallel to the dorsal surface of P3 (by following the correct new wall growth beneath the coronary band).
See Recognizing and Treating Rotated Hoof Capsules - Pete Ramey
​Realigning Trim

A laminitic foot with dorsal and palmar rotation. Note the correct new growth at the toe beneath the coronary band, and the lack of sole depth beneath the tip of P3.

During realigning trimming the heels are (gradually) lowered to restore the palmar angle to 3-5 degrees, wall flare removed and the sole protected to increase sole depth beneath P3.

The realigned foot - toe parallel to P3, palmar angle 3-5 degrees, good sole depth and concavity.