Wednesday, Feb 3, 2010 - the Carpus (Knee)

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Vet Tip of the Day:
Key words - horse knee conformation, carpus anatomy

Today we'll take a quick look at anatomy then focus on conformation. The equine knee, or carpus, is anatomically related to your wrist. It is located in the center of this radiograph, and as you can see, it contains two rows of bones. Therefore there are three joints in the carpus, from top to bottom they are the radiocarpal joint, the intercarpal joint, and the carpometacarpal joint. Review: Remember when discussing the cannon bone and splint bones they were related to the metacarpal bones of your hand (between your wrist and knuckles).  In the lower half of this radiograph you can see the cannon bone (metacarpal III) centrally, with the medial and lateral splint bones (metacarpals II and IV) on either side. While a common site of fracture in race horses, lameness directly related to the knee is less common in lower impact performance horses. However, when evaluating a horse for purchase or suitability for athletic performance, it is important to be able to assess a horse's knee conformation accurately.

There are several common  faults that occur at the knee. Looking at the diagram on the left, you will notice the leg on the left is "back at the knee" or "calf-kneed", the middle leg is correct, and the leg on the right is "over at the knee" or "buck-kneed". Obviously, the horse with the straight conformation (in the middle) is most desirable.

Another common conformational fault in knees is the "Bench knee" or "Offset knee".  Looking at the horse from the front, if you draw a straight line down the center of the forelimb, continuing through the middle of the knee and down to the ground, in a bench-kneed horse that line will not continue through the center of the cannon bone, pastern and hoof below the knee. This horse's leg below the knee is offset to the outside, so that the vertical line passes along the inside edge of the cannon bone, instead of the middle. This results in an imbalanced leg with more weight bearing through the inside splint bone which predisposes the horse to develop "splints" or excessive bone production along the inside or medial splint bone.

Tommorrow is Thursday, so look forward to this week's High Desert Veterinary Tale: Good News/Bad News.