Older Horses Means Older Joints

Older horses means older joints

Degenerative joint disease (DJD) or Osteoarthritis has always been an issue affecting a large proportion of the horse population both young and old, but particularly mature horses that have a lot of miles on the clock. We are now able to keep our older horses in better condition due to improved dental care, technological improvements in diet and advances in veterinary medicine, particularly Cushing’s treatment. We are riding our senior horses to an older age and therefore diagnosing more osteoarthritis.

DJD can affect any joint within a horse’s body but there are certain joints that are affected more frequently. Hock joints, coffin joints and pastern joints are the most common.

DJD is a very complex and painful disease caused by progressive damage and destruction of the cartilage within the joint from ‘wear and tear’. The joint sack (synovial membrane) may also become inflamed and in more progressive cases new bone (osteophytes) may be laid down. This process will go on to cause poor performance and lameness. The joint may become swollen, hot and painful with decreased movement and stiffness.

There are a multitude of different causes. Intrinsic factors include poor conformation, genetic susceptibility and Osteochondrosis Dessicans (OCD). Extrinsic causes such as previous traumatic injury, repetitive concussive forces, joint sepsis from a penetrating wound and poor hoof trimming/foot balance are also commonly seen.

Diagnosis is achieved by a full, veterinary lameness examination. The initial examination and palpation may be revealing in some severely-affected animals but in other more subtle, poor-performance cases, nerve blocks and joint blocks may be employed. Radiographs can then be taken to confirm the diagnosis.

Case Study
A recent case of mine was ‘Lucy’, an 18 year old mare, with a history of stiffness at the start of exercise which loosened off with work. This then progressed into a subtle right forelimb lameness. Investigation The mare was examined and some abnormal, bony prominences were felt in the pastern region indicating ‘ring bone’. This may not be associated with the joint and therefore might be unrelated to the lameness. Lucy was slightly lame in a straight line but she was obviously lame on the lunge. A nerve block was placed at the level of the fetlock, numbing the area below. She went sound, thus indicating the lameness was caused by pain below the fetlock.

Later investigations revealed some improvement to a palmer digital nerve block at the level of the mid pastern. Radiographs were taken and showed definite arthritic changes to the pastern joint and less severe ones in the coffin joint. With information from the earlier nerve blocks together with the radiographs, the most likely cause of lameness would be osteoarthritis of the pastern joint. One has to remember that radiographic changes do not always equate to clinical lameness.

Diagnosis
To definitively diagnose the source of lameness, It was decided to carry out a pastern joint block once the horse was lame again (after the present nerve block had worn off). This does carry some risk, as there is potential to take infection into the joint with the needle. The procedure has to be carried out under strict aseptic conditions. Lucy went sound quickly after the injection confirming the diagnosis of pastern osteoarthritis.

Treatment
As stated earlier osteoarthritis is a complex disease and thus has a multitude of different forms of treatment. The treatment is very much case-dependant and will be tailored to suit an individual. DJD cannot be cured and the aim is to reduce the pain associated with the joint and slow down the progression enabling the horse to continue with its athletic function as much as possible.

It was decided to inject corticosteroids into the joint to act as a local, potent anti-inflammatory, reducing inflammatory mediators and slowing down the degenerative process and reducing the pain.

Lucy has also started on a glucosamine and chondroitin sulphate oral supplement; the mode of action is to increase the production of lubricant within the joint and also to protect the cartilage. This will act on all of Lucy’s joints since we know from the x-rays that the right fore pastern is not alone in developing DJD. There are many oral, joint health supplements (neutraceuticals) on the market but they vary a lot in concentration, bio-availability and price. Using a good quality product such as Synequin is always advisable.

Lucy is also starting a course of oral non-steroidal antiinflammatories (NSAID’s), phenybutazone (bute), again to reduce inflammatory mediators within the joint and reduce pain associated with movement.

Other forms of treatment include:

Disease modifying agents – Intra-articular or intra-muscular polysulphated glucosaminoglycans (Adequan), intramuscular pentosan polysulphate (Cartrophen) or intra-articular sodium hyaluronate (Hyonate). Results vary greatly between individuals and the injections are reasonably expensive. I will use Hyonate in high motion joints such as the fetlock because it can assist with joint lubrication.

Regenerative therapies such as IRAP (interleukin – 1 receptor antagonist protein), PRP (platelet rich plasma) and stem cell therapy. These are expensive procedures and although the research results appear to be beneficial it is debatable whether they are economically viable.

Tiludronic acid (Tildrun) reduces the bone cells responsible for reabsorption called ‘osteoclasts’. This drug is used specifically on ‘bone spavin’ (DJD of the lower hock joints) to reduce the speed of progression.

Follow up
We now have to keep our fingers crossed and hope that Lucy responds favourably to the treatments that we have given her. She will continue regular light work, trying to stay off the road as much as possible to reduce the concussive forces on her legs. We will reduce the bute to the lowest dosage possible that makes Lucy sound. There are long term side effects with NSAID’s but in my experience these are unusual and being comfortable is preferable to being in pain. We may need to repeat the intra-articular corticosteroid injection within six months.

Prevention
A lot is still unknown about this disease process and therefore prevention is tricky. The most practical approach is not to buy a horse with poor conformation or the early signs of DJD. This means that getting a veterinary pre-purchase examination is a good start. Flexion tests will be carried out and though some consider them controversial, I feel that they can detect early stages DJD, which would otherwise be missed by purely riding and observing horses’ gaits. Oral neutraceuticals can help slow down the disease process. Riding your horse sensibly is the key; the harder you work them on unsuitable surfaces, the more wear and tear the joints will undergo. Regular, appropriate farriery is also a must to keep the hoof, and thus the leg, balanced correctly.

By Dr Mark Sanderson BVM&S MRCVS

Further Advice