Fracture stabilisation

Question 1

Following AO principles

Answer 1

▪5.5mm screws
▪Less use of external fixators
▪Most fixation without plates

Question 2

Challenges

Answer 2

▪Size
▪Soft tissue injury

Question 3

Management of fractures

Answer 3

▪Immediate pre-operative stabilization
▪Methodical surgical planning
–Use of diagnostic imaging
– Arthroscopy
– Standing?
▪Appropriate stabilisation techniques
– key to ensure the fracture doesn’t destabilise post-op. e.g. Robert Jones or casts

Question 4

Diagnostic imaging

Answer 4

• CT & MRI are great to view whole fracture and decide optimal site to place screws

Question 5

Normal restoration of what is vital to the success of the procedure?

Answer 5

• the articular surface

Question 6

Why is intra-operative arthroscopy useful?

Answer 6

• determines whether the fixation has led to a normal articular surface

Question 7

Standing surgery

Answer 7

• routinely performed for fractures of the 3rd metacarpal bone and proximal phalanx
• these fractures are often relatively simple and so repair can be performed with some screws inserted under sedation and a distal limb nerve block

Question 8

AO principles of fracture repair

Answer 8

1. Fracture reduction and fixation to restore anatomical relationships
   – ensures functional repair
2. Fracture fixation providing absolute or relative stability as the “personality” of the fracture, the patient, and the injury requires
   – trying to ensure that everything is stabilised as far as possible within the context of the fracture itself, but also the expectation of the horse and owner
3. Preservation of the blood supply to soft tissues and bone by gentle reduction techniques and careful handling
   – screws inserted through stab incisions
   – plates can be inserted with stab incisions then further incisions directly over the screw holes
4. Early and safe mobilization and rehabilitation of the injured part and the patient as a whole
   – need to ensure that the fracture is strong enough to allow the animal to be mobilised without risking the integrity of the repair

Question 9

Types of screws

Answer 9

▪Lag screws
▪Position screws
▪Plate screws

Question 10

Lag screws

Answer 10

▪ Achieve compression which is essential for direct healing
▪ Attempting to bridge the 2 parts of bone into direct contact and ultimately into compression so that the synthesis of new bone can occur directly at the point of the fracture
▪ Don’t want to have any gaps that would then have to fill up with callus

Question 11

Which screw is most commonly used in equine practice?

Answer 11

• lag screw

Question 12

Lag screw technique

Answer 12

1. Drill the neocortex. The drill is exactly the same diameter as the screw itself. This allows the screw to slide directly in and out of the hole and doesn’t engage with the bone in any way. This is known as a glide hole.
2. A drill sleeve is placed into the glide hole to ensure that the 2nd drill bit follows in the exact same direction as the first one. This drill bit is smaller and is drilled into the far cortex, ensuring that it doesn’t extend through the soft tissue or skin.
3. Countersink the screw where you use a cutting bit to cut out the bone surface to match the shape of the screw head
4. Measure which uses a thin metal rod which is passed through both screw holes. It has a little hook which allows you to reach and feel the edge of the far cortex and then use the body of the instrument to push down into the countersink, allowing you to read off the length of the screw that’s required.
5. The penultimate step is to tap the far screw hole. The tap is exactly the same diameter as the screw, but cuts the diet thread into the bone, which has been drilled with the narrow diameter bit
6. Final step is to actually insert the screw itself. Now as the screw it tightened it will slide through the near fragment, which is drilled to the same overall diameter of the screw, but its going to grip into the threads which are cut into the far side. Consequently the fracture fragment will be pulled into position and compressed.

Question 13

Lag screw technique simplified

Answer 13

• Drill, drill, countersink, measure, tap and screw.

Question 14

Position screws

Answer 14

▪ Each screw size has two drill diameters associated with it:
– Thread hole diameter
–Glide hole diameter (exactly the same width as the screw)

▪ Smaller drill bit used to create the thread holes.
– These are essentially the same width of the main body of the screw, minus the threads, which is the core diameter seen in the pic on slide.

▪ Positional screws aim to keep everything exactly in the same place - just use the smaller drill bit to drill all of the bone and then tap a thread through the full length of the screw
– We can use this as other screws are already holding the fractures in compression and just using additional screws to increase the stability of the fracture.

▪ Can also do this if there’s a risk of the far side of the fracture collapsing inwards into the medulla of the bone.

Question 15

Plate screws

Answer 15

▪Various plates used in fracture repair
– DCP
– LC-DCP
– LCP

LC-DCP & LCP hugely improve the stability of the fracture by fixing in both the bone and the plate to form a completely rigid structure

Question 16

DCP

Answer 16

= dynamic compression plate

Question 17

LC-DCP

Answer 17

= limited contact dynamic compression plate

Question 18

LCP

Answer 18

= locking compression plate
- although expensive do significantly improve our ability to stabilise many complicated fractures

• Instead of having a situation where the plate and the screw can mode independently the LCP uses a screw which has an additional thread in its head to engage with the plate
  – This adds a huge amount of rigidity to the plate structure and also means that we don’t have to contour the plate so perfectly to the contour of the bone.

Question 19

Common equine fracture repairs

Answer 19

• Most common fractures repaired by internal fixation would be 3rd metacarpal bone and proximal phalanx

Question 20

Internal fixation for other orthopaedic conditions

Answer 20

• screws can be used to apply compression across subchondral bone cysts (a particular manifestation of osteochondrosis)
  – By placing a lag screw across the cyst the compression is thought to stimulate healing
• Another very common application in certain practices is to correct angular limb deformity in foals where screws are used to slow down growth on 1 side of the growth plate and allow the other edges to catch up so that the leg gradually straightens.