Elbow Dysplasia

Introduction

Elbow Dysplasia is an often debilitating condition affecting predominantly large and medium breeds of dog. In particular the condition is common in Labradors, Retrievers and Rottweilers. Clinical signs of forelimb lameness and stiffness after rest are often seen in pups at six months of age but may be seen between six and nine months. As the condition generally affects both elbows, the lameness may not be noticed due to the symmetric gait abnormality produced by clinically symmetric pathology. The disease is at least partially under genetic control and thus screening programs such as the Elbow Scoring Scheme have been devised in order to reduce the incidence of this condition in future generations.

Anatomy

The elbow joint is a Ginglymus or hinge joint. It is made up of three bones: Humerus, Radius and Ulna. The elbow joint is therefore three joints with the Humeroradial, Humeroulnar and Radioulnar joints. The Humeroradial and Humeroulnar joints are involved with elbow flexion and extension, whilst the radioulnar joint permits pronation and supination by allowing these bones to rotate around one another.

Humeral Condyles Highlighted in pink
The Radial Head is highlighted in pink.
The Medial Coronoid is seen in pink below and Humeral Condyles.

The elbow is designed to absorb forces that are perpendicular to the ground and the load is shared evenly between the medial and lateral compartments. The medial compartment is the interface between the medial (inner) humeral condyle and the medial coronoid process, whilst the lateral compartment is the interface between the lateral humeral condyle and the radial head. If the elbow develops normally these two compartments should share the load between them:

The load share between compartments in the normal elbow

This even loading means that the cartilage in each compartment is being exposed to normal physiological stresses and there is no over loading of one compartment’s cartilage surface. Cartilage like other tissues can be damaged by being overloaded. As cartilage functions to provide a low friction (Teflon on Teflon) and insensitive contact surface between opposing components of a joint, injury will negate these functions by exposing sensitive and higher friction bone.

Pathology

The inciting pathology used to be seen exclusively as a failure of the normal process of transformation of cartilage to bone (endochondral ossification) within the elbow itself. Failure of this normal process was felt to be the cause of fragment formation within the elbow, either in the form of cartilage flaps (Osteochondrosis Dissecans of the Medial Humeral Condyle) or fracture and/or fragmentation of the medial coronoid process. Over a number of years it has become clear that these fragments are the effect rather than the cause of elbow problems. Of course in some cases these fragments may themselves cause pain, but in many patients the fragments are merely an indication that the joint load is asymmetric.
In order for the elbow to develop normally, the paired bones of the forearm or Antebrachium (the Radius and Ulna) must grow perfectly synchronously throughout the growth phase of the dog. In patients that have spurts of growth (often between 4 and 6.5 months) one of these bones may lag behind the other. We can see in the image below the difference between the development of the normal and the dysplastic elbow.

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Here the growth rate of the radius and ulna are synchronous resulting in a normal elbow.
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In this image the radius lags behind the ulna during the critical growth phase, resulting in elbow incongruence.

In the second image above the rate of growth of the radius and ulna diverge or are not parallel. As a result of this the elbow becomes incongruent due to either a relatively short radius or ulna depending on which bone had the slowest growth. The effect of this is to change the shape of the elbow:

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Short Ulna Syndrome resulting from slowed Ulnar Growth
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Here the radius has lagged behind the ulna resulting in short radius syndrome.

With this change in geometry comes a change in the forces experienced in the two compartments of the elbow, in particular the load through the medial compartment increases exposing the cartilage here to greater than physiologic stress with every step. The result is fragmentation of the coronoid and damage to the articular cartilage of the medial humeral condyle and the articular surface of the medial coronoid.

The image shows cartilage loss on the medial humeral condyle and ulnar surface (pink exposed bone to the left) and preservation on the lateral condyle and Radial Head.

It is this damage that results in long term joint pain and progressive Degenerative Joint Disease. Removal of fragments alone will not influence this articular surface pathology. Ideally we would shift the load from the damaged medial compartment over to the intact lateral compartment. In older dogs this will reduce the pain that arises from contact between these two sensitive and high friction surfaces, whilst in younger dogs, this would perhaps result in preservation of articular cartilage and thus low friction movement.

Introducing PAUL

It is exactly this aim of reducing painful contact and preserving cartilage that lies behind the surgical technique devised by Ingo Pfeil from Dresden. By performing an osteotomy of the ulna and applying a stepped plate designed by Kyon, the Ulnar load can be reduced.

Technique

The ulna is cut 3.5 to 4.0 cm distal to the elbow joint. A plate with a 2 or 3mm step is applied to the lateral surface of the ulna. This plate is a modified ALPS (Advanced Locking Plate-Kyon AG) plate which means that it is a locking plate with the benefits that the non uniform contact and Titanium composition has in terms of healing:

The uneven undersurface means reduced periosteal compression and more rapid healing. The thicker proximal portion pushes the proximal ulna medially.

The rationale is based on the fact that upon waking and activation of the Triceps muscle, the ulna straightens and this reduces the medial contact:

The plate pushes the proximal ulna medially.
When the patient pulls on the triceps post surgery, the proximal ulna is pulled into alignment and the medial compartment is unloaded.

If we look at these images from the front we can see the effect of this correction on the elbow joint itself:


This “Geometry Modifying” procedure alters the pressure profile across the elbow and should bring both short and long term benefits to the articular surface and therefore the patient suffering from Elbow Dysplasia.

Our results and the results of other surgeons using this technique has been very positive and this procedure can be used for those patients that have had a poor outcome following the traditional technique of arthroscopic fragment retrieval. In my view, the best results however are likely to be derived from applying this technique early in the disease process and before other techniques have been used.

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