Elbow Dysplasia – What is normal?

Elbow Dysplasia is a very common cause of lameness in growing dogs and it can lead to serious arthritis. Where is the dog’s elbow and how does it compare to our own? There are some important differences and in the article orthopaedic expert Rob Rayward sets the scene.

Where is the elbow joint in dogs and cats?

skeleton showing elbowThe elbow joint is the joint in the front leg between the upper limb bone (humerus) and the lower limb bones (radius and ulna). It is a composite joint since it involves more than 2 bones.



It consists of three separate joints:

  • The humeroulnar joint (between the humerus and ulna)
  • The humeroradial joint (between the humerus and radius)
  • The radioulnar joint (between the radius and ulna)
canine elbow line drawing

Line drawing to show the bones of the canine elbow joint

All three joints are collectively termed the elbow joint and they share a common joint cavity. The elbow is a hinge joint and allows movement in one plane, much like a door hinge does.  The radioulnar joint allows a pivoting movement of the ulna around the radius which accounts for the rotation that is possible at the elbow joint. This rotation is especially important in cats where it is apparent when they climb and catch and hold prey.

The main movements of the elbow joint are flexion (bending) and extension (straightening) and hence the joint capsule is relatively loose at the front (cranial) and back (caudal) to allow this movement. The sides of the elbow joint are supported by well developed medial (inside) and lateral (outside) ligaments which are termed ‘collateral ligaments’. They limit movement of the joint and prevent it from opening up medially or laterally. The ‘beak’ on top of the ulna, termed the anconeal process, fits into a depression on the back of the humerus when the elbow joint straightens. This further limits the movement of the elbow joint.The ends of the bones within the joint capsule are lined by articular cartilage. This smooth white surface provides a low friction interface between the bone ends. A small volume of joint (synovial) fluid is present in the normal elbow joint and this is important for lubricating the joint and providing a route for nutrition to be delivered to the cartilage cells.

In Elbow Dysplasia things don’t quite fit properly!

The ends of the radius and ulna bones form the floor of the joint and the end of the humerus forms the roof of the joint. The floor of the joint will be completely level and the roof of the joint will perfectly match the shape of the floor in a normal elbow joint. In elbow dysplasia, which we will be discuss in more detail in the next article, we will see that the floor may not be correctly aligned or there may be a mismatch between the floor and the roof. This will have consequences for how well the joint glides and may predispose to joint damage and osteoarthritis.

Similarities and differences with our elbows

There are many similarities when we compare our elbows with those of our pet dogs or cats. We too have composite elbow joints which are primarily hinged but allow a degree of rotation.

joggers!The most obvious difference between us is that we don’t tend to walk on our arms. This has consequences when we consider the forces that pass through our own elbow joints and those of our pets. The forces in our pets’ front legs are relatively greater than in ours. Furthermore the forces in our pets’ front legs are greater than those in their back legs. The front legs also tend to act as the ‘brakes’ whilst the back legs are more involved in propulsion.

This information is helpful when we consider which activities may aggravate a painful or arthritic elbow joint. Any activities which tend to require marked braking including jumping down from heights or sudden deceleration which may occur after chasing a thrown object have that potential. Running will also dramatically increase the loads in the elbow joints over those found during walking activity. Running activities are often avoided in animals recovering from elbow surgery.