The nature of dressage places unique stresses on the horse’s body. At the higher levels, the movements are precise and slowed down so there is less forward momentum than with, for example, a jumping horse. However, there is a tremendous amount of upward, sideways (lateral) or turning momentum. In addition, with the dressage horse working properly, the majority of the horse’s mass is propelled from the hindquarters and the horse works from a constant and somewhat crouching stance. Therefore, the stifle joint is a very important and relatively often-injured joint in the dressage horse. The stifle joint corresponds to the human knee joint and is comprised of the distal end of the femur, the menisci, the cruciate ligaments, the proximal tibia, the vestigial fibula and the patella (kneecap). Like the human knee, the joint has a relatively large range of motion, a property imparted from its unique structure. The structure of the stifle provides for tremendous power but subjects the components of the joint to forces that can lead to injury. With dressage horses, veterinarians often become involved earlier in the process of diagnosing injury to the musculoskeletal system than in other disciplines. Because of the precision, power, symmetry and rideability required of the dressage horse, dressage trainers know that very mild or subtle pain can cause difficulty for the horse in performance and seek veterinary advice before the horse may show clinical lameness. Stifle pain can manifest itself in subtle ways that a sensitive rider, trainer and veterinarian may be able to identify before more significant injury leads to overt lameness.
Common clinical signs that the stifles may be hurting include abduction of the upper hind limb as it is carried forward, which may be observed as a somewhat circular movement of the limb, rather than a straight movement forward. The horse may shorten the stride of the limb and be unwilling to reach under with it, which may alter the willingness or quality of the half pass away from the affected side. The horse may not maintain weight for as long on the limb in the passage and particularly the piaffe. There may be an irregular gait or rhythm in the extended trot. These issues are not diagnostic of stifle pain, but are consistent with it and may lead one to focus on this joint. More significant and long-standing stifle issues may lead to clinical signs that are more specific for the stifle. These would include palpable increases in the amount of fluid within the stifle joints, thickening of the soft-tissue structures around the joint, pain on flexion and manipulation of the joint and signs of obvious lameness in the affected limb.
The diagnosis of lameness in the stifle is confirmed by injecting anesthetic into the stifle and observing for an improvement in the horse’s gait or the elimination of lameness. It may be possible to identify the stifle as the source of the problem without this step but it is important to positively identify the source of pain. If the stifle is, in fact, the joint involved, it is even more important to identify which of the many important structures associated with the joint is injured, as the treatment plan is very much dependent on what is injured and the extent or severity of the injury. As with many injuries in the horse, it is the veterinarian’s job to decide if a horse can safely continue to train with a certain injury or if he requires rest. Therefore, the exact nature of the injury is important to determine so the most appropriate treatment can be instituted.
Radiography, diagnostic ultrasonography and diagnostic arthroscopy are the main tools in the veterinarian’s toolbox with which to accurately diagnose and treat stifle injury. Magnetic resonance imaging (MRI) produces excellent images of the interior of the horse’s stifle, but there are practical issues, such as the need for the horse to be under general anesthesia and risks of injury from positioning the horse within the machine, that make this modality less useful.
Once an anatomic diagnosis is made, the treatments are varied. It may be appropriate to simply rest the horse briefly and prescribe a short course of anti-inflammatory medication. It may be indicated to inject the horse’s stifle joints with an anti-inflammatory medication such as hyaluronic acid, a corticosteroid or possibly a biologic such as IRAP (interleukin receptor antagonist protein) or PRP (platelet-rich plasma). The intra-articular use of stem cells may be beneficial. For more severe injuries, arthroscopic surgery for treatment and positive identification of a lesion may be indicated and is usually combined with rest, medication and a careful rehabilitation program.
The prognosis for stifle injuries in the dressage horse depends on the structure injured, the severity of the injury and the level at which the horse is required to work.
As with the human athlete, the earlier the problem is identified and properly treated, including making changes in the training program, the more successful we can be at keeping the horse in top form.
Greg Staller, DVM, received his doctor of veterinary medicine degree from the University of California at Davis in 1987. With primary interests in surgery, lameness diagnosis and treatment, ultrasonography, ophthalmology and internal medicine, he is a Diplomate of the American College of Veterinary Surgeons and an FEI Official Veterinarian in the disciplines of dressage, three-day eventing and combined driving. Married to FEI dressage rider Catherine Haddad, he is the founder and owner of Running ‘S’ Equine in Califon, New Jersey, and provides sports-medicine services in Wellington, Florida, and Aiken, South Carolina, during the winter season.