Screw fixation

An alternate technique represents computer-assisted surgery, which is presently rarely available.

This technique involves initial CT- or 3-D fluoroscopic (A,B) imaging data of the involved bone identified with a digital reference base (DRB), transfer of the data to the navigation computer (C), planning of screw location, -orientation and –length with the help of a mouse on the navigation computer screen, and real time navigational assistance during screw insertion (see below).
The camera (D) provides real-time navigation assistance.

A screen shot during preparation of the thread hole in an abaxial fracture of the distal phalanx.
Three different orthogonal views are shown. The red bar represents the planned direction for a 4.5 mm screw, whereas the green bar represents the 3.2 mm drill bit entering the glide hole already prepared up to the fracture pane. The drill bit has penetrated the glide hole for 19.4 mm (see picture bottom right).
Note: the two bars are represented in correct scale relative to their diameter.
The axial trajectory view represents the perfect alignment of the drill (yellow circle), the planned screw diameter (red circle), and the drill bit (green circle.)
Note: the sizes of the circles are not proportional to their diameter in this projection.

Interfragmentary compression is achieved through insertion of at least one screw placed in lag technique. Ideally, a second screw should be inserted to provide additional compression and rotational stability.

In abaxial articular fractures there is usually not enough space for two 4.5 mm screws. However, it may be possible to insert one 4.5 mm and one 3.5 mm screw or a Kirschner wire.
Insertion of two 3.5 mm screws is another option though less stable.

The screws can be inserted in a dorsopalmar/plantar direction or in a palmaro/plantarodorsal direction (left). However, if an attempt is made to use two interfragmentary screws, they should be inserted in dorsopalmar/plantar direction

Note: Displaced fractures are usually reduced when non-weight bearing.

With the appropriate preparation and draping of the surgical site, this procedure is performed with the patient placed in lateral recumbency.

The entry and exit point of the future screw is marked on the hoof wall with a small barium bleb.

The CT-scan is performed and the screw axis determined and compared with the barium blebs. If the blebs are not in the correct location, they are changed in relation to the determined screw axis. The old blebs are removed.
The foot is re-scanned and the above procedure repeated until the blebs are in line with the screw axis.

The entry and exit point for a second screw are marked using the technique just described.

The foot is prepared for aseptic surgery.

The distance from the surface of the hoof to the fracture plane is determined.

The aiming device with the 4.5 mm drill sleeve is applied over the two blebs and the 4.5 mm glide hole is drilled to the predetermined depth.

The hoof is re-scanned and entry of the glide hole across the fracture plane (red arrow) is checked. If necessary, the glide hole is extended until it reaches the fracture plane.

The distal interphalangeal joint is distended and the arthroscope inserted using routine technique through a stab incision located 2 cm proximal to the coronary band and 2 cm lateral to the sagittal plane.
The joint is explored and the fracture identified and, if needed, anatomically reduced through manipulations with the 3.2 mm drill guide inserted into the glide hole after loosening the aiming device. Once the fracture is reduced the aiming device is tightened again.

The thread hole is drilled across the fragment.

If the drill bit for the thread hole is too short to reach the end of the bone, the aiming device is removed, the hole across the hoof wall expanded with a 10 mm drill bit. Reapplication of the aiming device is optional because the glide hole is in place and concentric completion of drilling the thread hole can be accomplished by inserting the 3.2 mm drill guide into the glide hole.

The threads are cut with the 4.5 mm tap guided through its corresponding sleeve.

Note: This step is out of routine screw insertion sequence.

An 8-10 mm hole is drilled across the hoof wall along the glide hole to the surface of the distal phalanx.

A countersink depression is prepared in the surface of the distal phalanx.

The prepared hole is thoroughly flushed with a bulb syringe to remove debris from tapping and enlarging the hole in the hoof wall.

The screw of predetermined length is inserted and tightened.

Compression of the fracture is observed arthroscopically.

A second 3.5 mm or 4.5 mm screw is inserted using the technique just described.

A small portion of a gentamycin-impregnated collagen sponge is inserted in each hole to fill the space between the surface of the distal phalanx and the hoof wall.

The rest of the hole is filled with antibiotic-impregnated polymethylmethacrylate (PMMA). The edges are sealed with cyanoacrylate glue. If desired a Kevlar® strip can be glued over the top followed by non-adhesive tape covered.

An alternate techniques involves the insertion of artificial hoof resin.

The surface of the artificial hoof resin plugs are shaped to conform to the hoof surface.

The holes are covered by an additional artificial hoof pad that extends over the immediate hoof surface.

The patch is pressed onto the hoof wall with tightly applied wrapping tape around the entire hoof circumference and left hardening.

After 5-10 minutes the wrapping tape is removed and the surface of the patch adjusted as needed.

The surgical site can be covered by non-elastic tape.

Horses are usually in stall rest and hand-grazing only for at least 60 days. Then hand walk or machine walk for an additional 60 days before allowing turnout in a very small paddock. Most horses get about a minimum of 6 months before returning to training.

It takes about 6 to 9 months for the hoof wall defects to grow out.

Intra-articular medications depend on surgeons preference and the degree of articular damage seen at the time of surgery.

Imaging

Follow up radiographs are usually taken in 60 days postoperatively. If necessary, additional radiographs are taken at a later stage. Return to work depends on the healing progress.

Prognosis

The prognosis for return to work is good to guarded, dependent upon the articular damage acquired at the time of injury.