One of the most important aspects of the management of laminitis is knowing which cases warrant treatment. In addition to clinical and radiographic signs, various procedures may be used to assess the severity of cases of laminitis.
Dr Ric Redden, a leading authority on laminitis, has described a technique of digital venography - ie radiographic examination of the foot using contrast materials injected into the veins. So far he has performed the procedure in over 100 laminitic feet. He suggests that the procedure is practical and readily available in equine practice. In contrast, other techniques of assessing the vasculature in laminitis cases, such as nuclear scintigraphy, angiography and ultrasound- or laser- Doppler flowmetry require complex and expensive equipment.
Briefly, the technique is as follows:
* the horse is sedated and the foot anaesthetised by blocking the medial and lateral palmar nerves at the level of the apex of the sesamoid bones.
* the horse`s shoe is removed and the foot is thoroughly cleaned
* the skin of the pastern is clipped and prepared aseptically
* 2 or 3 layers of an adhesive bandage are applied around the fetlock
* a butterfly catheter is inserted in to the digital vein at mid-pastern level. (It is easier to do this before applying the tourniquet.)
* a tourniquet is placed tightly around the fetlock. (If the tourniquet is not tight enough , filling defects may occur leading to misinterpretation of the venogram.)
* 20-25ml of contrast material ( eg Renografin 76; diatrizoate sodium) is steadily infused, whilst applying digital pressure over the vein to prevent ballooning. Two 23ml syringes are used. The first is injected with the foot loaded. The knee is pulled slightly forward while injecting the second syringe. This unloading ensures lamellar filling.
* when all the contrast material has been injected the catheter is occluded with a haemostat and taped to the fetlock.
* Radiographs are taken immediately. For the most informative results, all views must be taken within 30 to 40 seconds of injection. Two different exposures are taken of each of 3 views: lateromedial. dorsopalmar and 65° dorsopalmar
The extent of the perfusion deficit correlates well both with the clinical and radiological severity and with the outcome. In particular, horses showing marked lack of contrast (ie poor perfusion) in the following 3 key areas have a grave prognosis despite aggressive treatment:
* lamellar vessels
* circumflex area (ie around the distal border of the pedal bone)
* terminal arch
One surprising finding is that after undergoing venography, some horses, with apparently severe damage to the foot, are clinically improved. Horses that have been examined using venography often show a more rapid rate of horn growth on the examined foot than on the other.
Dr Redden speculates that the beneficial effect of venography might be due to
* improved perfusion resulting from injection of fluids under pressure into the veins.
* dissolution or removal of microthrombi allowing reperfusion
* the contrast material may reduce oedema of the laminar tissues and of the cells lining the blood vessels.
He considers it unlikely that the increased horn growth rate is purely coincidental for two reasons. Firstly the effect has been noticed in several very severe cases of laminitis. Secondly, improvement is seen only in the foot that undergoes venography. In horses with bilateral laminitis in which venography is performed on just one foot, improvement only occurs in that foot .
"The unexpected clinical improvements following digital venography was a bonus for these horses and their owners " said Dr Redden. "It is an observation that warrants further study".
For more details see:
Possible therapeutic value of digital venography in two laminitic horses. R F Redden. Equine Veterinary Education (2001) 13 (3) 125 -127
A technique for performing digital venography in the standing horse. R F Redden. Equine Veterinary Education (2001) 13 (3) 128 - 134