Dr. Judith L. Mulholland

An animal with sinker has suffered near or total destruction of the inter-laminar bond at the toe and the pedal bone is loose within the hoof. The further you raise the sole from the ground, the further the bony column can sink (founder). The hoof is mobile because it is no longer attached, and sinker could also be described as walking through the bottom of the sole of your shoe or, if you could imagine pulling a sock on and going straight through the toe. The horse’s leg has not changed only the attachment to the hoof has changed. Therefore, the bony column is usually still aligned normally and is not always rotated despite this description usually being used. In fact the mobile hoof capsule is counter rotating as the bone is forced through the sole by the weight of the horse. This is important to understand because the word rotation is used so often in association with laminitis and all descriptions are of the bones rotating. If we concentrate on the only freely mobile part of the foot during laminitis “the hoof” this condition is much easier to understand.

Sinker is life threatening! Depending upon the type of treatment and individual case, it may take hours, days or weeks to occur. In the worst cases, the horse sloughs the hoof wall from one or more hooves leaving the sensitive structures completely exposed, or the pedal bone prolapses through the sole (as above). Horses can survive this extreme form of laminitis if given constant nursing. During this time the feet are at risk from injury and infection. If a hoof is cast, the pedal bone penetrates the sole, or the coronary bands have ruptured, the Veterinarian may suggest euthanasia as the kindest option. This may be a decision determined by the degree of suffering, expense of treatment, as well as emotions. Despite the best of efforts not all horses with acute laminitis can be saved, it would be cruel to try. A soft, inflamed coronary band with a dip felt behind its edge and low distal phalanx position on x-ray, indicate severe loss of laminitic attachment. The further back the ridge behind the coronary band can be felt towards the heels, the greater the loss of laminitic bond. These cases should be carefully monitored for the first 60 - 90 days after which the risks reduce as new attachment forms and grows down from the coronary band.

Nothing nailed to the hoof or pressing on the sole or frog will prevent "sinker" laminitis if the damage is already done. A sinker hoof is not obvious; the horse may not adopt a classic laminitic stance or may be misdiagnosed as having azoturia (tied up) or even hypocalcaemia. In all severe cases of laminitis, Veterinary treatment for anti-inflammatory and pain relief is needed until the horse shows prolonged steady improvement. If not correctly managed, pain and inflammation can lead to further bouts of laminitis.

Horses which have sloughed the whole hoof have been nursed through the crisis on very thick, soft bedding. They cannot stand to defecate or urinate. This problem must be addressed so that the environment for the horse is hygienic. They need to be turned every 4 hours so that they do not develop pressure sores, ischaemia and muscle necrosis. They benefit from physiotherapy and massage. The feet must be dressed and bandaged to prevent further damage and infection. Over a period of 3 - 5 months a new hoof will begin to grow down. The heels will reach the ground surface first (approx 3 months) and the hoof which grows may be perfectly normal as it does not have to overcome the effects of a laminitic wedge. Hooves that prolapse through the sole will also recover but may have long term damage to the pedal bone due to necrosis of the bone. It is a dedicated owner, constant nursing, and attention to detail that restores quality of life. There are many horses who are living proof that the most severe form of laminitis “sinker” can be survived. However, the chance of restoring the horse to 100% soundness is low.

When sustained long-term pain relief is required there are many pharmaceutical and organic anti-inflammatory/pain relieving preparations available (DMSO, MSM, devils claw (herb), arnica etc.) which have minimal side effects. This is important as gastrointestinal tract ulceration and haemorrhage can result as a side effect of the use of NSAID’s to relieve pain. Therefore,  you must manage the pain so that the animal is eating which will help protect the digestive tract from these side effects while keeping the dose as low as possible. You are damned if you do and damned if you don’t.  How can you keep the use of pain relievers down?  Keep the feet cool by using ice baths. Get them onto a soft surface, apply the correct farriery principles and try some other products, MSM, Arnica, Devils Claw,  etc. Ask your veterinarian about integrating natural therapies and/or using commercial preparations with the least side effects when sustained long-term treatment is required.

Farriery is very important at this stage and the heel should form the primary weight bearing area of the hoof. The posterior surface area can be increased to relieve pressure at the toe by fitting bar shoes. The surface the horse is kept on, feeding and management are critical. If the hooves are shod and the heels raised, wedged, or the sole is filled with silicone etc., and the horse is no better then it may have been better to do less. If the horse is not worse then wait and see. However, if the horse is immediately worse after shoeing the effort was in vain. In these cases the farriery should be reassessed and the horse returned to a more comfortable state. When you place pads and wedged pads over the sole you can no longer see what is happening and they often contribute to sole pressure. I have seen many laminitic equines worse after shoeing, and then made to suffer through this for several days before the shoes are removed or changed. Therefore, I prefer to be conservative and manage the horse with trimming or basic shoeing, on a sandy or soft surface so the horse can make itself comfortable. In severe cases, bar shoes and/or hospital plates may be required. My favourite shoe for ponies and smaller breeds is an open toe bar shoe (reverse shoe), it provides posterior support and the open toe relieves all pressure under the damaged laminae which can be resected if necessary. The ponies thrive in them, they are cost effective for the client and easy to fit on very small feet.