Incomplete Ossification of Humeral Condyle

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Also known as: IOHC

Introduction

The humeral condyle develops from three separate ossification centres: a medial ossification centre, a lateral centre and a smaller centre that goes on to form the medial epicondyle. The medial and lateral centres should fuse at between 8 and 12 weeks of age in dogs.

Incomplete Ossification of the Humeral Condyle (IOHC) is characterised by the presence of a fissure between the medial and lateral condyles of the humerus, which corresponds to the location of the cartilagenous plate that separates the two ossification centres prior to their fusion.

IOHC is therefore a developmental failure of fusion of these centres of ossification.

There is often extension of the fissure to the supratrochlear foramen proximal to the growth plate, probably due to stress fracture.

The condition is most commonly seen in the English Springer Spaniel, Cocker Spaniel and other Spaniel breeds, but also the Labrador and Rottweiler.

Dogs with IOHC may show no signs, may present with lameness, or may present suffering from a humeral condylar fracture secondary to their condition.

Clinical Signs

Dog with lameness: elbow lameness can occur with IOHC. It can be intermittent and mild or constant and severe, and does not respond well to NSAIDs.

Range of motion is not usually affected, and there is rarely elbow effusion.

Dog with fracture: a history of acute deterioration and severe lameness with no particular history of trauma, is often present. There may have been lameness prior to the acute presentation. There will be acute pain and swelling in the affected elbow.

Diagnosis

Diagnosis of IOHC requires visualisation of a condylar fissure.

High-quality, craniocaudal radiographs may enable visualisation of the fissure, but the xray beam has to be exactly parallel to the fissure for it to be evident. Therefore several craniocaudal projections may be required.

The fissure may be partially extending to the supratrochlear foramen, or it may be complete.

CT is the preferred imaging technique for visualising the fissure.

Elbow arthroscopy may also be useful.

For dogs with fractures, radiography usually shows fracture of the lateral condyle. CT may reveal a fissure in the contralateral humerus, which supports the diagnosis of a fracture secondary to IOHC.

CT may reveal that the intracondylar margins of the fracture are sclerotic, and this will also be apparent intraoperatively. The bone in the centre of the condyle will not be as soft as normal epiphyseal or metaphyseal bone.

The contralateral elbow should also be assessed as the condition is often bilateral.

Treatment

Dog with lameness: dogs with IOHC but without a fracture are treated by placement of a transcondylar screw, usually a lag screw. A second point of fixation is not required.

Dogs usually respond very favourably and the lameness can resolve completely.

Dog with fracture: the principles of repair follow those of any humeral condylar fracture, but there is a greater risk of implant failure. Bone union does not commonly occur in cases of IOHC and drilling small bone tunnels across the condyle may help with this. The lack of bone union means that there is increased risk of fatigue failure of the screw, therefore the largest possible screw, most commonly a 4.5mm cortical bone screw, should be used.

Dogs without clinical signs: IOHC may be found in a dog without clinical signs, such as if the contralateral limb of a dog with a fracture is CT scanned. It is difficult to calculate the risk of fracture in the patient and the prevalence of the condition is unknown. The risks of anaesthesia and surgery should be weighed up against the benefits of placing a transcondylar screw. The decision should be made individually for each case.


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References

Pasquini,C. (1999) Tschauner's Guide to Small Animal Clinics Sudz Publishing

Moores, A. (2006) Humeral Condylar Fractures and IOHC in dogs In Practice 28, 391-397




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