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This approach has been applied by the specialist orthopaedic and spinal surgeons at Willows Referral Service in the management of a number of conditions including limb deformities, humeral condylar fissures, fractures, patellar luxation, limb sparing surgery for bone cancer, and various spinal diseases including cervical spondylopathy (Wobbler syndrome), atlantoaxial subluxation, lumbosacral stenosis, spinal fractures and discospondylitis.
Limb deformities can result from a number of underlying problems, however the most common are due to abnormal bone growth or due to a fracture which has healed in an abnormal orientation. In both cases virtual surgical planning and 3D printing can be extremely helpful in achieving the best possible realignment of the affected limb.
A high quality CT scan is obtained of the affected bones. The scan is converted to 3D virtual bones on a computer – Figure 1 shows a deformed femur (yellow) next to a mirror image of the normal opposite femur (purple). A virtual operation can be performed whereby the deformed femur is cut, and the two ends lined up to exactly match the mirror image of the opposite femur Figure 2. In this way normal alignment of the bone can be restored Figure 3. Figure 4 shows a similar case with both femoral and tibial deformities – in this case the normal, opposite limb is shown in blue, and the deformed limb in yellow. The femur was realigned using virtual surgery first and then the tibia was realigned to properly aligned the lower limb Figure 5. Patient-specific surgical guides were then designed. Firstly an osteotomy guide was created, with a flat surface to guide the necessary bone cuts which are made in theatre with an oscillating saw Figure 6. This guide had a lower surface shaped to fit precisely onto the femur in a unique position, ensuring correct positioning of the bone cuts. The pins used to attach the guide to the bone are then attached to a second guide, automatically re-aligning the bone to the pre-planned position Figure 7. Similar guides were created for the tibia Figure 8. All four guides, and the bones themselves, were 3D printed and sterilised ready for use in theatre. Both bones were realigned using the guide system during the same operation, with metal plates and screws used to stabilise the bone cuts. A post-operative CT scan showed very good final limb alignment Figure 9.
The same osteotomy and reduction guide system can be used in the treatment of developmental limb deformities. Figure 10 shows a right forelimb deformity affecting a small terrier. A CT scan was performed and a 3D virtual representation of the affected limb created Figure 11. Virtual surgery was performed – the bones were cut, and the lower limb realigned to the correct orientation with respect to the elbow joint Figure 12. Osteotomy and reduction guides were created Figure 13, 3D printed, and used in theatre. Final limb alignment was very good Figure 14.
Humeral condylar fissures
HCF is a crack in the bone at the level of the elbow joint Figure 15, which can cause lameness or can lead to a fracture. This condition is treated by placement of a large screw across the fissure, from one side of the humeral condyle to the other. It is essential that this screw is placed very accurately since the condyle is relatively small, and the screw must be large enough to strengthen the condyle sufficiently – a poorly positioned screw could enter the elbow joint causing injury and persistent lameness. The ideal position of the screw can be identified using a computer aided surgical planning Figure 16. A drill guide can then be designed to fit onto the bone surface on the outer aspect of the bone, and guide the direction of the drill bit and screw as pre-planned. This technique allows consistent and accurate screw placement with only a limited surgical approach Figure 17.
One of the many challenges associated with fracture surgery is restoring the normal alignment of the bone before applying some form of fixation device (e.g. a metal plate and screws). This becomes significantly more difficult if the bone is fragmented into multiple small pieces and can’t be put back together like a jigsaw puzzle Figure 18. In many cases a better approach is to realign the top and bottom parts of the bone, allowing the fractured section to heal on its own. Achieving ideal realignment of these bone sections can be quite difficult. In such cases CT data can be used to create virtual 3D models of the fractured bone. The orientation of the top and bottom sections of the fractured bone can be adjusted to match a mirror image of the opposite intact bone, and surgical guides designed to recreate this optimal alignment in theatre Figure 19. In some cases this can be achieved without any requirement to surgically expose the fracture at all, better preserving the ability of the fracture to heal Figure 20. Post-operative CT showed very good realignment of the fracture Figure 21 which went on to heal uneventfully Figure 22.
There are several possible causes of patellar luxation, each with its own often quite different treatment approach. One cause is excessive bending or twisting of the femur, problems typically treated by cutting and straightening the femur. This surgery can be technically challenging especially in small dogs, since often small, but very accurate, corrections are required. The use of virtual surgical planning, and patient-specific osteotomy and reduction guides allows carefully planned corrections to be achieved in theatre Figure 23. In this case the femoral varus angle (a measure of the amount of curvature of the femur) has been reduced from 17 degrees to 3 degrees, realigning the patella with its groove on the distal femur.
Traditionally, the only possible treatment for dogs with tumours affecting the bones of the limbs was amputation. Although this remains the best available option in many cases, it is sometimes possible to remove the tumour whilst preserving a comfortable, functional limb. This surgery is however complex, and requires very strong implants to be placed across the gap in the bone left when the tumour is removed. 3D prints of the affected bones allow the surgery to be practiced, ensuring that correct limb alignment and length are achieved Figure 24. In the case shown (a Great Dane with a bone tumour affecting the lower radius bone) the patient was so large that a customised plate needed to be designed and made Figure 25. This plate was contoured to the correct shape using the 3D-printed model before surgery, making the operation itself much easier Figure 26. Figure 27 shows post-op X-Rays, and the patient walking two days following surgery.
Several conditions affecting the spinal cause problems because they result in instability and excessive movement which can cause pain and injury the spinal cord. These conditions are treated by placing implants to stabilise the affected region of the spine. Examples of such conditions include cervical spondylopathy (Wobbler syndrome), atlantoaxial subluxation, lumbosacral stenosis, spinal fractures and discospondylitis.
Spinal stabilisation is technically challenging for several reasons, not least the difficulty of placing screws or pins into the vertebrae (the bones) of the spine without damaging the spinal cord and the nearby blood vessels – injury to either with a drill bit or screw would have potentially disastrous consequences. Traditionally these problems often necessitated the placement and smaller, less strong implants. Using CT data, the ideal position of vertebral screws can be planned on a computer Figure 28. The large central hole contains the spinal cord, and the two smaller lower holes each contain a large artery. Drill guides can then be designed which fit onto the surface on the outer aspect of the vertebrae and guide the directions of the drill bits and screws as planned Figure 29. This technique allows consistent and accurate screw placement with only a limited surgical approach – Figure 30 shows post-op CT pictures from a dog with Wobbler syndrome treated by spinal stabilisation. The long screws are very strong, but can only be placed using patient-specific drill guides. Figure 31 shows images from two spinal fractures stabilised using the same guide system.