by Sheri Spencer

Created on: October 29, 2007   Last Updated: June 25, 2009

The stifle joint of the horse is designed similarly to the human knee, in that it is the joint between the femur (thigh bone) and the tibia, with a "knee cap," the patella, that resides in the front of the joint. The stifle joint can be identified at the front of the hind leg, just around and below the conjunction of skin to the abdomen on a healthy-weight horse. The bony lump that can be felt at the top of the joint is the patella, and the dip immediately below is the stifle joint. The stifle joint is the largest joint in the horse's body.

Conformation and Anatomy

The stifle should be level in height to the elbow of the horse, and for a stronger hind leg, the joint should be placed forward so that the thigh is more rectangular in shape, as opposed to a V shape when placed further back. Also, when placed further back it indicates that the horse has a shorter femur and will not have as much power. Full muscling over the joint, indicating better strength, contributes to the rectangular shape from both the side and rear views. When looking from the rear, the stifle should be the widest part of the hind quarters.

At the bottom of the femur are two rounded bone structures called condyles, one medial (towards the centre of the horse) and one lateral (towards the outside of the horse). Stabilizing the joint at the top of the tibia is the tibial spine, a narrow ridge, which fits neatly between the condyles. Between the junction of the tibia and femur are C shaped cartilages called menisci (singular = meniscus) which keep the joint in position and absorb shock.

The patella rides in the trochlear groove, a crease between the condyles on the femur, which helps to reduce friction and catalyzes extension power from the femur to the tibia.

The term "stifle joint," however, actually refers to two separate joints that make up the collective stifle. The first is the femoro-tibial joint which, as the name suggests, connects the femur and tibia. The second is the femoro-patellar joint which connects the femur and patella. The femoro-patellar provides the largest articulation of the stifle. Both joints of the stifle have their own joint capsules whose linings produce synovial fluid which serves to lubricate the joint surfaces.

The stifle and hock joint share reciprocal action. Essentially, this means that the stifle and hock extend and flex in unison. The superficial digital flexor muscle and gastrocnemius muscle, which run down the back of the leg, are responsible for the reciprocal

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