Subchondral bone pain is a common condition, particularly of the racehorse, but also recognised in endurance horses and occasionally eventers. Various terms have been given to describe the disease, including maladaptive remodelling, sclerosis of the lateral condyles, and most recently, palmar/plantar osteochondral disease (POD). The diagnosis is relatively difficult, as advanced imaging is required, either scintigraphy or magnetic resonance imaging. However, the clinical signs are quite distinctive, with mild lameness, or often simply 'poor action', and minimal palpable abnormalities. The action is often improved, or lameness switches to the other limb, following anaesthesia of the lateral (especially in the hindlimb) or the lateral and medial (more commonly in the forelimb) palmar/plantar metacarpal/metatarsal nerves, at the level of the distal end of the splint bones. Radiology is usually disappointing, with no detectable abnormalities. Specialised views such as flexed plantardorsal (dorsopalmar) oblique and proximal dorsolateral - distal palmarmedial and proximal dorsomedial - distal palmarlateral oblique views may highlight some increased radiodensity and sometimes some focal radiolucencies within the palmar/plantar condyles of the metacarpus/metatarsus. However, these findings are seldom definitive.
The first and most important criteria when managing any lameness particularly in the racehorse is rest. It is well recognised that rest is of limited benefit in the management of plantar osteochondral disease. Generally rest periods of 6 weeks or less appear to exacerbate the condition. Presumably the sudden change in exercise intensity results in further derangement of the complex remodelling process of metacarpal/tarsal condyles. It is often reported that rest is not helpful in the management of POD. However, rest can be very effective, but must be prolonged. Generally a period of 6 months out of training will be necessary and anything less than this is unhelpful. Though a prolonged period of rest, this is often not as impractical as it at first sounds. Effectively, following diagnosis, the horse is removed from training until the next season. Our experience has been that prolonged rest is usually effective in the management of this condition, for a period of time. However, it is not curative. Thus following 6 months of rest a horse might be anticipated to perform well for the following season, but progressive loss of action and poor performance will recur in later seasons.
One of the principal difficulties with managing POD is that it is an incurable disease causing poor performance, and thus efficacy is very hard to define. If presented in a positive light, many treatments can be perceived as effective by trainers and indeed veterinary surgeons, and there is no gold standard effective treatment to compare. Intra-articular medication of POD was widely discounted at one stage. However, in our series of cases the majority of horses did respond to intra-articular anaesthesia as well as perineural. Thus there is a rationale behind intra- articular medication. The most widely used drugs for intra- articular medication are cortisones. If the horse is to remain in training, rather than undergo prolonged rest, then medication of the fetlock with cortisone with 5 mg of triamcinolone is usually used in the first instance. Autologous conditioned serum (Irap) is also widely used in the management of POD. However, the rationale for this particular agent hinges around the simplicity of using Irap in a horses in training, where there is no concern about drug withdrawal times.
Other agents which have been used include platelet rich plasma, including lyophilised platelet rich fraction. This is rich in growth factors, particularly transforming growth factor beta1 though a clear mechanism of alteration of bone remodelling is not apparent. Intra-articular ketorolac has been advocated. This is a nonsteroidal anti-inflammatory drug, used for post operative analgesia in human surgery, but is of short duration of action. Thus it is hard to see a specific mechanism of action which will be beneficial in the long term management of POD.
Intra-articular stanozolol has been shown to have significant benefits in clinical use. This is an anabolic steroid that is water soluble. However, the drug withdrawal implications of using anabolic steroids in horses in training should be considered carefully. In particular, anabolic steroids are banned on all training establishments and therefore the horse should be removed to a convalescent yard prior to treatment.
Agents which act directly on the bone modelling process are potentially of use in this condition. We use tiludronate (Equidronate) extensively in the management of POD. The rationale is that this is a drug which acts on bone and POD is a disease of bone, therefore we'll use it. However, electron microscopy of POD does show significant osteoclastic activity, which potentially would be modulated by treatment with tiludronate. Generally, we administer one-third of the systemic dose by intravenous regional perfusion to the affected metatarsus/carpus, with the remainder of the drug being administered by intravenous infusion. We believe that the agent is effective in the management of this condition. However, the earlier comments about presenting treatment in a positive way apply. Accurate assessment of efficacy would at least require a case series and likely a comparison with another treatment, and this is not available yet.