The Stifle Joint

by Emily Douglas-Osborn BVSc CertAVP MRCVS

The stifle joint is similar to the human knee, it is located at the top of the hind limb in the horse. The femur runs from the hip down to the stifle, then the tibia runs from the stifle down to the hock. The stifle has a bone on the front called the patella – this is similar to the human knee cap (figure 1).

The stifle is one of the more complex joints within the horse. It actually consists of two joints; the femoropatellar joint, and the femorotibial joint, which can be split into medial and lateral compartments. There are a total of fourteen ligaments, and two cartilaginous discs called menisci, which ensure that the femur and tibia move easily relative to each other, and absorb concussion (figure 2). The bony structures also act as origins and insertions for some of the more powerful hindlimb muscles, making this high-motion joint very important.

Lameness involving the stifle is not uncommon in equine practice, and early diagnosis is key to a good outcome. These issues may either be developmental, or injuries that are acquired through trauma. Lameness, varying from mild poor performance, to acute severe lameness, may be noted, along with swelling of the joint space. Radiography and ultrasonography are usually the imaging modalities of choice for the stifle joint, allowing the best evaluation of both the bony and soft tissue structures respectively.

Conditions of the stifle:

Fractures:

The stifle is not an uncommon kick site in the horse, and as such may become fractured (figure 4). These injuries vary in their configuration and severity. Horses may present with moderate to severe lameness, and are often entirely unable to move. Some types may carry a good prognosis with rest or surgery, while others can be catastrophic.

Wounds:

The size of the stifle joint also means that it is a common site for wounds. Wounds which have entered the joint space itself result in infection, which causes severe lameness, usually with a large amount of joint swelling. These horses require arthroscopy surgery to flush the infection out of the joint, but the prognosis is generally good.

Osteochondrosis dissecans (OCD) and osseous cyst-like lesions (OCLLs):

The stifle joint is also a common site for OCD/OCLLs, a multifactorial condition of juvenile horses in which ossification defects develop within the joint cartilage (figure 3). These defects can go on to cause inflammation within the joint, although the horse often does not become lame until work is started, and the lameness is usually mild initially. Arthroscopy surgery can be done to address these defects, and carries a prognosis of 65-85% returning to work. If left untreated, these lesions do go on to cause osteoarthritis, and the prognosis after this is poorer, so early diagnosis and intervention is key to a good result.

Osteoarthritis:

Osteoarthritis is usually secondary to other issues in the stifle, such as OCD/OCLLs or meniscal injuries. As the stifle joint is so mobile, osteoarthritis can be more challenging to manage in this joint. Various joint medication options exist, such as steroid anti-inflammatories, hyaluronate, polyacrylamide gel, or stem cells.

Meniscal injuries:

Injuries to the cartilage pads between the femur and tibia are usually secondary to trauma, and can be visualised using ultrasonography (figure 5). In addition to this, there can also be associated bone damage, collateral ligament

About the Author:

Emily Douglas-Osborn BVSc CertAVP MRCVS damage and joint effusion. Surgery is often needed to debride the lesion and encourage healing. Joint injections can also be considered to help reduce inflammation. The prognosis for return to work following these injuries is usually guarded, with osteoarthritis being a common sequela. Half to two thirds of horses return to work, depending on the severity of the injury.

Collateral ligament injuries:

Also often secondary to trauma, collateral ligament injuries have to be carefully managed, as comlpete rupture of either collateral ligament can destabilise the entire limb. Box rest and controlled exercise are indicated while the ligament heals and regains strength.

Cruciate ligament injury:

Whilst not common, cruciate ligament injuries do occur in horses, and around 50% do well with surgical debridement. Rupture of a cruciate ligament, however, will destabilise the joint and does not usually carry a favourable prognosis. If you have any concerns regarding soundness or poor performance in your horse, or about the stifle joint specifically please contact your vet.

Emily completed her internship at Avonvale before gaining experience in all aspects of artificial insemination at Twemlows, as well as working in ambulatory practice. Emily holds a certificate in Advanced Veterinary Practice and has a keen interest in lameness and poor performance.

Avonvale Equine Practice, Ratley Lodge, Ratley, Banbury OX15 6DT www.avonvaleequine.co.uk Tel: 01295 670501