POD lesions occur in the fetlock joints of both front and hind legs, and are particularly associated with racehorses in training. The lesions vary from very mild bruising of subchondral bone (Grade 1) to complete loss and collapse of the articular cartilage (Grade 3) which is the smooth surface that lines joints. It occurs due to the repetitive and high-speed nature of the training regimes associated with training of racehorses. The constant forces passed through the back of the fetlock joint, which absorbs a large amount of force during high speed work, results in the wear and tear of the articular cartilage of this joint. It is a very common condition in racehorses- in some studies it has been found in up to 80% of the population. Due to the nature of the disease it is more common in older horses that have spent a lot of time in training, although it can be found in 2yos as well.
Diagnosis
Lameness will improve following intra articular blocking of the fetlock joint. From here a diagnosis is usually made by taking x-rays of the fetlocks. POD lesions can be difficult to detect due to the often subtle changes seen on radiographs. Lesions are graded on a scale from 1-3. Grade 1 and 2 lesions can be the most difficult to detect and will often be graded based on the secondary changes that are highly associated with PODs which include; changes to the proximal sesamoid bones, a flattening in appearance of the palmar condyles, and changes to the front of the lower cannon bone. Grade 3 lesions can be seen as an increase in radiodensity or a lucency of the distal condyle of the cannon bone along with the secondary changes already mentioned above. Some of these changes can be seen in the attached picture. Sometimes radiography will not be sensitive enough to detect POD lesions in this case if they are still suspected MRI is the most sensitive technique to diagnose them and is also the best way to accurately grade the lesions.
Clinical Signs
- Lameness originating in the fetlock joint developing over a period of time
- Poor action (shortness of stride in front, plaiting gait behind) developing over a period of time
- Often lameness or poor action may be worse when coming back into work after a spell
- Pain on flexion of fetlock joint
- May have heat or swelling of fetlock joint
- A horse that is unwilling to trot and is keener to jump straight into a canter/gallop
- Lameness may improve during exercise- horses may ‘warm out’ of lameness
- Many horses will have a referred back pain
Red circle shows a mottling in appearance of the condyle and the arrows show the pathology this represented. Blue circle shows flattening of the palmar condyle and the blue circle with arrows shows the changes to the sesamoid bones that are highly associated with POD lesions. Image courtesy of Equine Veterinary Journal.
Management
It is difficult to predict what the outcome for a horse diagnosed with POD lesions will be. The higher the grade of lesion the worse the prognosis will be and Grade 3 POD lesions can certainly have a negative effect on the performance of a horse due to the pain they cause.
Often the changes seen at the time of diagnosis are irreversible and so spelling may not be the answer. It is thought that Grade 3 lesions are irreversible and therefore spelling will be of little benefit. Furthermore, as mentioned previously, the lameness and poor action due to PODs is often at its worst when the horse returns from a spell and can make it difficult to get enough work into the horse to return them to full fitness after a break.
Lower grade lesions however have been shown to improve with appropriate time out of training. In one study a minimum of 4 months was needed to see improvement in the lesions. Any shorter than this is not sufficient for the bone to repair fully and may cause more damage if training resumes during the resorpitive phase of bone healing.
Medicating the fetlocks with intraarticular corticosteroids will often lead to an improvement in the condition and allow for training to continue. The duration of effect and the quality of effect will be highly variable depending on each individual horse. The use of certain other medications and supplements such as Pentosan, Hyaluronic Acid (Matrix) and Epitalis Forte may be beneficial in some cases. Changes in training practices may help in individual cases. Swimming and the use of treadmills are usually beneficial in that they reduce the load through the fetlocks.
Furthermore, training uphill may or may not be beneficial depending on whether the lesions are in the front or hind fetlocks. Uphill gallops tend to shift the weight of the horse to his hind limbs therefore may be helpful if PODs lesions are present in front fetlocks but will be contraindicated if they are in present in hind fetlocks.