Problems originating from the stifle joint are a common cause of rear limb lameness and reduced performance. This is particularly
true in the western performance horse and horses in other disciplines that require a lot of work off of the hind end, including
reiners, cutters, dressage horses, and jumpers.
Lameness originating from the stifle joint can be characterized as a reduced cranial phase of the stride, and can range from
mild to severe. Often the lameness is worse when the affected leg is on the outside of the circle. Additionally, the shortness
of stride may be more evident at a walk than at a jog.
Accurate palpation of the stifle joint is crucial in all cases of rear limb lameness. Once you become familiar with the amount
of synovial fluid in the normal stifle joint, it is relatively easy to detect an excess amount of fluid. The stifle joint
is composed of 3 synovial cavities. The medial femorotibial joint is the most commonly affected, and particular attention
should be paid to this joint space during palpation. This joint can be palpated just caudal to the medial patellar ligament.
An excess of joint fluid in this pouch can be the first sign of a stifle problem. The femoropatellar joint pouch can also
be easily palpated medial and lateral to the middle patellar ligament. The lateral femorotibial joint space is not as easily
palpated, but is the joint space least likely to have a problem.
Many horses with stifle problems will be positive to all 3 rear limb flexions, but the upper limb or stifle flexion is the
most sensitive. Many horses with stifle problems will be very resistant to this flexion, and may attempt to abduct the limb
or even hop up in an attempt to relieve pressure on the medial femorotibial joint.
When the clinical signs, palpation, and response to flexion suggest a stifle problem, I generally proceed with diagnostic
imaging prior to performing diagnostic anesthesia. Radiography is an important step in the diagnostic workup of equine stifle
problems, but usually requires sedation to get good cassette placement. I find diagnostic ultrasound of the equine stifle
to be more sensitive than radiographs, and this usually does not require sedation so that I can still pursue diagnostic anesthesia
if necessary. My typical diagnostic workup in the horse that I suspect has a stifle problem is to ultrasound the joint first.
When the results of the ultrasound are not conclusive, I usually then proceed with diagnostic anesthesia of the stifle joint.
I begin by blocking the medial femorotibial joint. There is an anatomic communication between the medial femorotibial joint
and the femoropatellar joint, but blocking these pouches should be done independently as there tends to be a variable response
to diagnostic anesthesia. The lateral femorotibial joint is an anatomically distinct joint and should be blocked separately.
I prefer to wait a minimum of 10-15 minutes after each block to determine if there is improvement. If some improvement is
noted, I will perform serial examinations at 10 minute intervals. Some of the soft tissue structures of the stifle may take
longer than typical to be anesthetized, so do not be too hasty in assessing the response to stifle joint anesthesia.
As stated before, diagnostic imaging of the stifle includes radiology and ultrasonography. The standard radiographic projections
include a caudocranial, lateral, flexed lateral, and oblique (caudal lateral-cranial medial oblique). In certain cases where
a patellar fracture is suspected, a skyline view of the patella and trochlear ridges can be performed. As a lot of horses
resent having the radiographic cassette placed between their back legs, adequate sedation is necessary for the safety of the
people involved and equipment. The areas of particular concern in the stifle include the medial femoral condyle, the lateral
and medial trochlear ridges, proximomedial tibia, and the articular surface of the patella.