PRP is commonly used to treat recent injuries of the deep and superficial digital flexor tendons, the suspensory ligament and other ligaments. There are also some reports of successfully using PRP directly into joints, usually following arthroscopic (keyhole) surgery. PRP can also be used in a gel form to enhance wound healing, but this formulation is not yet widely used.
The main advantage to using PRP is that it is an autologous product, meaning that a horse can provide its own, almost unlimited supply. Only PRP made from your horse’s own blood is used, which greatly decreases the chance of an adverse transfusion reaction. Another great advantage is that PRP can legally be used in competition horses where drug testing would detect commonly used controlled substances such as corticosteroids.
PRP is easy to manufacture (see below) and only requires collecting venous blood from a vein (usually your horse’s jugular vein) instead of more invasive techniques, such as bone marrow collection that is required for harvesting (mesenchymal) stem cells. The entire PRP production takes approximately 15-20 minutes, so it is a quick process that some vets can even perform at your yard. PRP is also considerably less expensive than other biological treatments such as IRAP or stem cell therapy.
Because PRP is a fairly new treatment technique, we do not know the optimal dosage and frequency of administration (how much, how often) in horses. There are a number of commercial preparation systems available that concentrate platelets with different methods, such as filtration or centrifugation (spinning down). However, the protocols are not exactly standardised and there can be a large variation in the concentration of platelets in different PRP products.
In some cases, injection of PRP can cause scar tissue to form in the area instead of promoting cellular healing of the injury. This can be a desired outcome in some structures, such as certain ligament insertions into bone, but can be an unwanted side effect in others. PRP products will always contain a variable concentration of white blood cells; the resulting inflammatory reaction in target tissues can potentially slow the intended healing process.
PRP is made from your horse’s own blood. A 50-60 ml sample of venous blood is collected (usually from your horse’s jugular vein) into a syringe that contains an anticoagulant to stop the blood from clotting. This blood is then injected into a specially designed filter, which collects the platelets (blood cells that stop bleeding) but allows the remaining blood to pass through. The platelets are then collected from the filter in a syringe containing sterile isotonic saline solution. This preparation can then be injected into the lesions, usually under ultrasound-guidance. Approximately 6-8 ml of PRP preparation is obtained from 50 ml of collected venous blood. This method can be performed at the yard where the horse lives, so the whole collection and injection process can be done in one visit to the horse.
Another way to produce PRP involves centrifuging the venous blood sample in a laboratory and collecting only certain portions. However, this process is more labour intensive, requires laboratory equipment, and necessitates two visits to see the horse.
All steps in PRP production and injection must be done under sterile conditions to avoid the risk of infection.
PRP contains higher levels of platelets compared to blood alone. Platelets contain a high amount of growth factors (important for regulating a variety of cellular processes) that promote the formation of new blood vessels, and can increase the number of some cells, including cells that create bone and tendon tissue. PRP may also have an analgesic effect and can form a scaffold on which tissue repair can take place.
The most common way that PRP is administered is by direct sterile injection into the damaged tissue under ultrasound-guidance. PRP appears to be most effective when injected into a discrete area of damage, e.g. a ‘core lesion’. It appears that it can also be used safely in injuries where there may be some leakage out of the damaged area and into the surrounding tissues, but PRP may potentially be less effective in these cases.
The optimal treatment regimen for PRP is unknown, but the most common protocol currently consists of a single injection of PRP into a tendon or ligament lesion 7-10 days after the injury. Ideally, enough PRP should be injected to fill the entire soft tissue defect, which can be monitored under ultrasound-guidance. Occasionally PRP preparations are injected mixed with stem cells, but there is little information available as to whether this protocol has advantages over the injection of either component by itself.
More recently PRP has also been injected in joints with soft tissue and/or cartilage damage. Usually intra-articular PRP medication is performed following a joint surgery such as arthroscopy.
Following injection with PRP your horse will usually be off work for at least a week before gentle work can be reintroduced. However, the exact exercise regime after treatment will be dictated by the type and extent of injury that is being treated.
A bandage will be applied for several days after PRP treatment. Your horse should be monitored carefully for any sign of infection, such as severe lameness, heat or swelling. If these signs occur following PRP treatment you should call your vet immediately.
Very occasionally, a horse can show signs of severe pain immediately after a PRP injection. If this reaction occurs, it is usually in the first 15 minutes. The injection area should be iced and the horse should be immediately re-examined by your vet.
There are not many evidence-based scientific studies available for horses that have been treated with PRP. However, the considerable amount of anecdotal information available does suggest that PRP increases the rate and quality of healing of soft tissue injuries.