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Crippling arthritis in Arabian horses

Quick facts

In the Midwest, crippling arthritis affects older Arabian horses. About 46 percent of Arabians in Minnesota have a gap in the back of their knee joint, which makes them more prone to arthritis after a knee injury. These horses should be treated more aggressively for knee injuries.

What is carpometacarpal syndrome?

Carpometacarpal syndrome is a crippling form of arthritis identified in horses by University of Minnesota researchers. It mainly affects Arabians, at least in the upper Midwest.

The syndrome involves instability in the horse’s knee. This leads to a bony reaction, which resembles the callus from a healing fracture. You can see this defect on the inside of the leg.

The bone tries to bridge the lowest joint in the knee to increase its stability. By the time the lower joint fuses, the upper joints are also arthritic.

bony growth
Horses with carpometacarpal syndrome develop a bony growth on the inside of their knee.

Signs of carpometacarpal syndrome

Horses will show a gradual onset of increasingly severe lameness. This seems to occur with the development of the bony bump on the inside of the knee. Affected horses will not willingly flex their knee. For example, they may be sore after farrier work. Most horses are too lame to ride.

Which horses are affected?

We found 31 horses with the unusual form of carpometacarpal joint arthritis. Of these horses, 74 percent of the affected horses were Arabian.

The syndrome affects older Arabians. On average, diagnosis for this syndrome occurs at 14.4 years of age. Both mares and geldings were affected equally.


In seven of the 31 horses we looked at, the syndrome affected both forelegs. Two horses were still in work but the others were too lame for riding. None of the horses had previous leg surgery but eight had known trauma to the knee.

At the time of the study,

  • Ten horses had been euthanized for severe lameness

  • Five horses lived over five years after being retired from riding

  • Four of the affected horses were necropsied (autopsied), and the anatomy of the lower knee joint was examined.

During the necropsies, two different types of connection between the medial splint bone and the cannon bone were found. In most horses, these bones contact each other at two sites. In some, the back connection is missing, which leaves a gap between the bones. In Minnesota, 46 percent of Arabians and 13 percent of non Arabians are missing have this gap. Horses examined in California and Florida didn’t have this type of anatomy.

Horses that have this gap in the back of the knee joint can’t withstand trauma to the knee as well as other horses. Injury to the knee can lead to instability and arthritis in these horses.


You can’t prevent injuries in horses but you can recognize the increased risk for arthritis in Arabians. Thus, knee injuries should be cared for more aggressively in Arabians than routine.

Surgery to fuse the lower joint has been performed on a few horses to prevent continued joint degeneration and allow these horses to remain in work. The procedure needs to be done before the arthritis has advanced to other knee joints.

Erin Malone, DVM

Reviewed in 2018

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