By Stuart Pearson BVM&SCertAVP(ESO)MRCVS – CHESHIRE EQUINE CLINIC
Common causes of traumatic injuries to the stifle of the horse include kicks from a field companion or collision with an obstacle, especially when attempting to clear fixed fences during cross country events. These are painful injuries, and initial assessment may not reveal the true extent of damage. More often than not, the resulting damage is minor, but occasionally things can be more troublesome. In this article I will highlight a few important elements that enable me to accurately assess this large, complex joint area.
A sound knowledge of anatomy is key to any orthopaedic assessment, and is an area that veterinarians constantly review. The equine stifle is equivalent to the human knee and consists of three bones, the femur (thigh), the tibia (shin) and the patella (kneecap). There are numerous soft tissue structures including menisci (cushioning pads), patellar, collateral and cruciate ligaments.
Unlike the human knee, which is one joint, the equine stifle has three separate joint compartments and extra-capsular cruciate ligaments. This leads to a relatively stable structure, which limits the number of injuries caused by twisting or excess rotation (although they can still occur). However it is still prone to injury from direct impact. This is due in part to the thin covering of tissue overlying these boney and ligamentous structures. Therefore kicks to the stifle area, and indeed collision with cross-country fences or the like, can lead to significant stifle damage.
Initial assessment of the injury can be a challenge as trauma to the stifle often leads to a horse that is alarmingly lame – regardless of the actual severity of any damage. So it is necessary to determine whether the injury is a relatively benign subcutaneous haematoma (blood accumulation under the skin) or periosteal bone bruising (bruising of the bone surface) – or, in fact, a more serious fracture. Each of these injuries will require different treatment and management considerations. Therefore, after careful physical examination it is often necessary to perform radiography (x-rays) and/or ultrasonography to rule in/out significant stifle damage.
Determining the type of impact that caused the injury – for example, if the horse has attempted to clear a solid fence with the stifle in a flexed position where the patella is not well protected – will dictate which radiographic views are necessary to fully assess the stifle. Radiography under these circumstances should include a skyline view of the patella to see any fractures that would not be visible from more typical x-ray positions. Obtaining a skyline x-ray takes consideration and planning – such as having the appropriate number of people to hold the horse and flex its leg correctly for imaging – but this can still be done with all modern mobile digital systems out at the yard, preventing the need to travel an injured animal.
The soft tissue structures of the stifle (including ligaments and menisci) can be assessed alongside bone and joint surfaces via ultrasonography. Ultrasonography is almost always a valuable addition to radiography and with an experienced operator can reveal conditions that would otherwise be undiagnosed. For instance a tearing of a ligament, displaced bone fragment or haemarthrosis (bleeding into the joint).
• Other imaging modalities
Nuclear scintigraphy (bone scan) is a screening tool to locate areas of increased metabolic activity in tissue or bone, which could indicate location of injury. This is usually performed when trying to isolate a site of lameness or pain in the horse when cause is unknown, therefore only occasionally would scintigraphy need to be used when trauma to this area has already been determined. However, when a problem is not readily apparent on radiographs or ultrasonography, such as a stress fracture, scintigraphy can be useful to obtain detail of the physiological state of the bones and aid diagnosis.
3-D imaging has revolutionised our ability to diagnose injury in the lower limb of the horse. Unfortunately, there are practical constraints that limit the use of magnetic resonance imaging (MRI) and computed tomography (CT) on the equine stifle, due mainly to its large size and accessibility of the camera. Both of these technologies would create a 3-D image of the stifle, but as yet are not widely available.
Diagnostic arthroscopy – or keyhole surgery – is the “gold standard” for assessing the internal joints. In addition to aiding diagnosis, it also allows for surgical treatment of torn or damaged tissue – including bone fragment removal or fracture repair. Despite it being a useful option, it is important to consider that surgery in the horse is not to be undertaken without careful consideration and planning: anaesthetising large animals is complicated and carries much greater risk compared to humans or other smaller animals.
If seen promptly and then managed appropriately, the prognosis for many traumatic injuries to the stifle is good. Treatment is often conservative with medication designed at reducing inflammation and rest before an appropriate rehabilitation program is instigated. Cheshire Equine Clinic have trained orthopaedic clinicians with many years of experience in dealing with musculoskeletal problems and are able to provide accurate diagnosis and provide the necessary treatment to maximise a successful outcome after injury.
For further advice Stuart can be contacted at firstname.lastname@example.org or 01829 770999