Often foals are born with angular deformities of their limbs. By this, we mean that if you stand in front of the animal, the forelimb does not appear to be straight. The same can be true of the hindlimbs, which are obviously best viewed from behind. The picture below shows a 9 week old Thoroughbred foal with an angular deviation of his right forelimb. The problem is clearly located at the distal growth plate of the radius, and this deformity is termed a carpal valgus. If the angular deviation was towards the midline, it would be termed a varus deformity.
In many cases these angular deformities will correct themselves as the foal grows. With valgus deformities, a medial extension glue-shoe can often assist in natural correction, but this requires the foal to be stable rested so that the shoe remains attached. With this foal, the referring vets had concluded that the angular deformity was worsening and so a surgical intervention was indicated. Placement of a transphyseal screw, which bridges the growth plate on the medial aspect of the limb will retard the rate of growth and allow the outside of the radius to catch-up and cause the limb to straighten. This procedure is done under general anaesthesia as strict asepsis is required when inserting an implant into the bone. The positioning of the screw is critical as you will see from the intra-operative radiographs that we use to assess correct direction of the drill and subsequent insertion of the correct length screw.
Radiograph with drill in situ to assess the correct depth of the guide hole for the screw.
Intraoperative radiograph to check transphyseal screw position prior to final tightening.
Once the screw is placed, the foal has sterile dressings applied which keep the wound covered for three weeks. After dressings are removed, the foal can be managed as normal. The foal is then closely monitored for angular correction which relies on rate of growth of the animal; no growth, no correction. Once the limb is judged to be straight, the screw is removed under general anaesthetic.
As you can see, the right forelimb has corrected well and the screw now needs to be removed.
This is a preoperative radiograph showing the screw 85 days after placement. As you can see there has been no unwanted reaction in the growth plate so on-going development of the foal will be normal. The cosmetic result will be excellent and the animal should achieve his full athletic potential on the racecourse.
Intraoperative picture showing screw removal.