CASE STUDY – a subchondral bone cyst in the stifle

Manchengo, a three year old thoroughbred, was admitted to NEH after showing signs of lameness at trot. Upon examination at NEH he was found to be intermittently 3/10 right hind lame at trot. A swelling was noticed around the inside of his stifle, thought to be consistent with joint distention of the stifle.

The stifle was blocked with a local anaesthetic and the horse was trotted up once again. The degree of lameness was markedly improved allowing us to deduce that it was the right stifle causing the lameness seen.

Manchengo was taken to our radiography suite and the following stifle X-ray was acquired.

Can you name the bones in the x-ray?

Can you see the cause of lameness? And if so, what can be done to help?



The x-ray is a caudo-cranial (from tail towards head) projection of an equine stifle. The x-ray shows four different bones; the femur (1), the patella (2), the tibia (3) and the fibula (4).

There is a large, round lucency (dark area) towards the bottom left of the femur – in the medial condyle (shown by the arrow). This a ‘subchondral  bone cyst’, a relatively common cause of lameness in horses. They can develop in a number of locations, but the most common site is the stifle as shown here.

There are a number of different treatments which have been used for subchondral bone cysts. The most simple is injection of the joint with steroids, and a period of rest. This approach isn’t very successful with large cysts in the stifle, and surgery is often advised. Surgical treatments include:

  • Arthroscopic (key-hold surgery) guided medication of the cyst with steroids
  • Arthroscopic debridement and evacuation of the cyst
  • Placement of a screw across the cyst

The technique chosen depends on a number of factors, such as the age of the horse, size and nature of the cyst and previous treatments undertaken. In this case it was elected to place screw across the cyst.

The x-ray above is of the same horse 3 months later after successful surgical screw placement. The cyst was healing well and the horse’s lameness had resolve. At this stage, the horse was able to start slowly increasing its workload.

Matthew Heaton BVetMed MRCVS

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