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Bent Limbs in Foals


Horses are athletic animals used for their performance in a variety of disciplines and tendon and ligament injuries are therefore common. Different types of tendon and ligament injuries are seen depending on the horse’s age and the discipline, for example superficial digital flexor tendon injuries in racehorses and event horses when galloping and jumping at speed puts significant strain on these structures. Tendon and ligament injuries can occur as a single, traumatic event. More commonly however, there is a progressive degenerative process (like ‘repetitive strain injury’) that causes weakening of the internal fibres’ biomechanical structure. Beyond a certain point, the fibres fail and this ultimately culminates in tendon/ligament breakdown as the final event. The severity of a tendon or ligament injury depends on both the primary structure affected and the associated structures. The number of fibres that can fail as a result of injury will also vary, from mild (around 10% of the total fibres) to complete rupture (100% disruption of fibres). Severity will dictate the prognosis for return to exercise and the time period required for healing and rehabilitation. Older horses may also require longer to heal than younger ones.


by Susan Donaldson BVMS MRCVS


Foals can either be born with bent limbs or these may develop over the first few months of life, often being caused by other developmental problems. In this article, we will look at the significance of these bent limbs, what kinds of deformities occur and how these can be treated.


Why are bent limbs a problem? Any deviation from a straight leg can alter the foal's foot placement and therefore lead to uneven pressure being placed on the joints. Once the foal has stopped growing, any bend in the limb will be permanent and the uneven strain on joints can influence future soundness for athletic performance.


Bent limbs can be divided into angular deformities and flexural deformities.


Flexural deformities are identified by assessing the foal's limbs from the side. The most common of these is 'contracted tendons' where the


tendons which run down the back of the limb are too tight meaning the limb cannot be


Veterinarians use ultrasound (figure 1 from the mare, then


straightened. Forelimbs are most commonly affected. If the foal is able to move and feed


mild cases often simply require careful


monitoring and no specific treatment. In severe cases, treatment includes intravenous injections of


oxytetracycline; which is an antibiotic but has the useful side effect of relaxing tendons and ligaments; and


bandaging and splinting of the limbs to attempt to straighten the leg, allowing the foal to move around and the tendons stretch. In older foals, tendons


may become contracted after a period of rapid


Update on tendon and ligament injuries


shows an ultrasound image of a superficial digital flexor tendon lesion) to assess the initial type and extent of tendon and ligament injuries. Measurements usually include the length of the tendon/ligament affected and the percentage of the overall tendon/ligament affected (cross sectional area). In some, there are no core lesions visible within the tendon/ligament; however the overall size is increased and there is loss of border definition. Serial ultrasound examinations are also important to monitor the healing process; however it is important to understand that the appearance of tendon/ligament fibres on ultrasound does not give a direct measure or guarantee of internal, biomechanical strength.


to stretch and by use of anti-


The prognosis associated with tendon/ ligament injuries generally depends on which tendon is affected, the severity or extent to which it is affected and what impact this has on the horse in terms of future performance. This information can also be used to determine the most appropriate therapeutic strategy and the approximate time required for the injury to heal. Tendon/ligament injuries heal via the formation of scar tissue. This forms over a period of around three months and then it subsequently remodels (increasing in strength), with maximum strength gained


inflammatory drugs. If the tendons do not relax, the foal's foot will begin to take on a 'boxy' or 'club foot' appearance. In such cases, surgical intervention may be indicated. Where surgery is performed, normally the accessory ligament of the deep digital flexor tendon (ALDDFT) or 'inferior check ligament'


The other kind of flexural deformity which is seen in young foals is laxity of the tendons. Hindlimbs and specifically hind fetlocks are most


commonly affected, with foals often being


described as being 'down' on their fetlocks. In general, affected foals require little or no


treatment, unless the deformity is so severe that the heels and


fetlocks make contact with the ground and therefore require


protection by bandaging. Glue-on shoes can also be used.


Carpal Valgus. Photo by Luanne Hunt.


growth and initially these foals can be treated by restricting their exercise, trimming of the heels to help the tendons


Angular limb deformities (ALD) can be defined as a deviation of the leg


from a straight line when the limb is looked at from the front or back. The


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By Luanne Hunt BVM&S, MRCVS


at around 7-9 months, giving a total of 10-12 months for healing. This scar tissue functions in place of the original tendon or ligament fibres, but unfortunately it will never have the same biomechanical strength as the original or normal tissue and because of this, re-injury is a concern in these horses. Treatment plans for tendon and ligament injuries therefore have two main goals; to resume work or exercise as quickly as possible and minimise the risk of re- injury (once exercise is resumed).


Foal with severe flexural deformity of forelimbs. Photo by Luanne Hunt.


joint, most commonly the knee (carpus), but the fetlock, hock or even a


combination of joints can be affected. We can also describe the direction the leg is deviated in: deviation to the outside (laterally) is described as valgus, whilst deviation to the inside (medially) is described as varus.


which attaches the deep We can divide ALD into problems which digital flexor tendon to the back of the knee is cut.


the foal is born with and those which occur during growth, usually in the first six months of life. Those noticed at birth or soon after are perinatal deformities and those developing during growth are acquired deformities. It is very common for foals to be born with a mild carpal valgus where both forelegs are slightly deviated to the outside from the knee and a slight toed-out conformation; as these foals grow and their chests widen these problems often self-correct. In premature foals, the small bones in the knee and hock may not have calcified properly and therefore are softer meaning that they can be 'crushed' when the foal is moving, leading to bent legs and in time, if untreated, arthritis in the affected joints. These bones are best assessed by x-rays. If the foal is only mildly affected, bandaging or splinting and box rest can be used while the bones become more calcified.


Acquired ALD is likely to have a number of contributing factors, including injury, overfeeding or nutritional imbalances, and inflammation of the growth plate in the cannon (physitis).


So how can ALD be treated? deviation can be centred over one specific X-rays of a bent leg will allow the


Rehabilitation Rehabilitating horses with tendon and/ or ligament injuries generally involves a period of box rest with a controlled hand-walking program; followed by a slow and gradual increase in work level. This is because the newly formed scar tissue is quite weak (as is the normal intact tendon or ligament in an unfit horse) and conditioning is required to improve strength without predisposing the structure to re-injury. The idea of a controlled and gradually increasing exercise program is to allow remodelling and adaptation to an increase in workload. Swimming and the use of underwater treadmill systems can also be utilised in rehabilitation programs.


Other treatment modalities Regenerative medicines have become more widely used and available over the last ten years. There are many cases of tendon/ligament injuries where regenerative therapies can be used to potentially accelerate the healing process and/or improve scar tissue strength and function. It is important however to realise that none of these treatments are a substitute for a proper rehabilitation program. The main benefit is to improve the quality of healing and therefore decrease the likelihood of re-injury. The injury site or ‘lesion’ within the tendon or ligament is injected with a product to minimise inflammation and improve healing. The product used is determined by the age, appearance and type of lesion. Examples of regenerative therapies available for use in the horse include:


PRP – Platelet Rich Plasma Platelets are small cell fragments that circulate in the blood. Their main function is to help form a blood clot when there is bleeding. However, they also contain high levels of growth factors that encourage healing. Using a horse’s own blood, veterinarians can separate


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