Authors of section

Authors

Jörg Auer, Larry Bramlage, Patricia Hogan, Alan Ruggles, Jeffrey Watkins

Executive Editor

Jörg Auer

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Plate fixation/transarticular lag screws

1. Principles

Complete cartilage removal

Complete cartilage removal is important to provide for maximum contact between the opposing subchondral bone plates. With compression, generated by the fixation technique, frictional forces are generated between the subchondral bone plates, which maximizes strength and stability of the fixation, providing maximum patient comfort and allowing early removal of postoperative cast support.

Complete cartilage removal...

Plate placement

The implant is positioned over the proximal and middle phalanx in the sagittal plane. The distal end of the plate is placed in the proximal region of the middle phalanx.
The distal end of the plate should not impinge on the proximal attachment of the distal interphalangeal joint capsule as well as the extensor process (A).
The palmar/plantar position of the transarticular screws and distal plate screw should lie within the palmar/plantar eminences (B) to avoid the palmar/plantar aspect of the distal interphalangeal joint capsule and navicular apparatus.

Plate placement

AO teaching videos

Arthrodesis of the PIP joint using a 3-hole 4.5 DCP and lag screws

2. Preparation and approach

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

plate fixation transarticular lag screws

3. Reduction

In most cases the palmar eminence fragments are small and anatomical reduction and fixation of the fracture fragment to the parent middle phalanx is not required when performing arthrodesis of the pastern joint.

In most cases the palmar...

In cases, where the eminence fracture fragment is of sufficient size lag screw fixation of the large eminence fragment to the parent middle phalanx should be employed to increase the stability of the repair.

In cases, where...
In cases, where...

4. Fixation with proximal interphalangeal locking plate

Plate selection

A proximal interphalangeal locking plate (PIP) is advocated as it is specifically designed for pastern arthrodesis. Other plate constructs have been used successfully, including narrow, 4.5 mm, 3 and 4-hole DCPs and LC/DCPs, as described in the next section.

plate fixation transarticular lag screws

Plate preparation

Extending the digit realigns the articulation into normal anatomic configuration.
The plate is contoured to approximate the sagittal dorsal surface of the distal proximal phalanx and proximal middle phalanx with the stacked combi-hole of the plate positioned over the proximal end of the middle phalanx.
The distal end of the plate is bent slightly to ensure that the distal plate screw is inserted directly below the subchondral plate and into the proximal palmar/plantar aspect of the middle phalanx.

plate fixation transarticular lag screws

Plate application

The plate is held in position and compressed to the distal proximal phalanx by placing the push-pull device in the middle combi-hole.
Check the positioning of the implant and the proposed screw position with appropriate imaging technology.

The plate is held ...

The hole for the first screw is drilled just distal to the subchondral plate and the length of the drill hole is determined. Now the 5.0 mm locking head screw is inserted applying appropriate locking technique.

The hole for...

A 4.5 mm cortex screw is placed in load position in monocortical fashion. The screw should not be fully tightened, so the plate is not yet fully compressed to the bone and dynamic compression is not engaged.
The push-pull device is now removed.

2nd screw with gap

Insertion of transarticular lag screws

Two 5.5 mm cortex screws are now placed transarticularly in lag fashion extending from the dorsal distal proximal phalanx into the proximal palmar/plantar middle phalanx. They cross the joint at the junction of the palmar/plantar ¼ and the dorsal ¾.
The two glide holes are prepared first, but it is important that first one screw hole is finished and the screw inserted before the thread hole for the second screw is prepared.
The transarticular screw that is on the side where the palmar/plantar eminence fracture is located, may need to be directed slightly away from the fracture to avoid entering the fracture line. In addition, positioning in the sagittal plane may require modification to avoid the lag screw if one has been used to affix a large eminence fragment to the parent middle phalanx.
The screws are placed medial and lateral to the plate and parallel to the sagittal plane.
Real time imaging is useful to direct screw positioning and intraoperative imaging of some nature is necessary to confirm proper implant position.

Two 5.5 mm cortex screws...

It is very important that the glide holes for the transarticular lag screws in the dorsal distal aspect of the proximal phalanx are appropriately countersunk to ensure the screw heads engage the dorsal cortex in an appropriate fashion and thereby avoid bending, weakening and potentially breaking the screw head.

It is very important...

It is also important, that screws of appropriate length are used; they should not penetrate beyond the palmar/plantar cortex of the middle phalanx. For the transarticular lag screws, a screw measuring 4-6 mm less than the measured length is appropriate and prevents placing a screw which protrudes beyond the palmar/plantar cortex of the middle phalanx.

plate fixation transarticular lag screws

Applying compression

Once the transarticular lag screws are fully tightened, the proximal plate screw is fully tightened, which compresses the plate to the bone and provides additional axial compression between the subchondral plates of the proximal phalanx and the middle phalanx.

Once the transarticular lag screws are fully tightened, the proximal plate screw is fully tightened,...

Insertion of the remaining screw

Finally, the middle hole of the plate is filled using an 5.0 mm locking head screw.

The final construct configuration is checked with appropriate imaging to ensure appropriate length and positioning of all implants.

middle phalanx dorsal subluxations

5. Fixation with a DCP or LC-DCP

Plate selection

A 3- or 4 hole Dynamic Compression Plate (DCP) can be used successfully for this procedure. Another alternative represents the 3- and 4 hole Limited Contact Dynamic Compression Plates (LC-DCPs).

plate fixation transarticular lag screws

Plate preparation

The plate is contoured to approximate the dorsal surface of the distal proximal phalanx and proximal middle phalanx.
The distal end of the plate is then bend slightly to ensure that the middle phalangeal plate screw is directed just distal to the subchondral plate into the proximal and axial aspect of the middle phalanx.

The plate is contoured to approximate the dorsal surface ...

Plate application

The plate is held in position by hand, with the help of a bone holding clamp, or as shown here with the large pointed reduction forceps.
The use of appropriate imaging technology to check the positioning of the implant and the proposed screw position is strongly encouraged.

The plate is held ...

The thread hole for the first 5.5mm cortex screw is drilled just distal to the subchondral plate across the entire bone, and the length of the drill hole is determined, and tapped followed by insertion of the selected screw.

The thread hole for the first 5.5mm cortex screw is drilled just distal ...

A 5.5 mm cortex screw is placed in load position through the middle plate hole. The screw should not be fully tightened, so the plate is not yet fully compressed to the bone and dynamic compression is not engaged.

2nd screw with gap

Insertion of transarticular lag screws

Two 5.5 mm cortex screws are now placed transarticularly in lag fashion extending from the dorsal distal proximal phalanx into the proximal palmar/plantar middle phalanx. They cross the joint at the junction of the palmar/plantar ¼ and the dorsal ¾.
The two glide holes are prepared first, but it is important that first one screw hole is finished and the screw inserted before the thread hole for the second screw is prepared.
The transarticular screw that is on the side where the palmar/plantar eminence fracture is located, may need to be directed slightly away from the fracture to avoid entering the fracture line. In addition, positioning in the sagittal plane may require modification to avoid the lag screw if one has been used to affix a large eminence fragment to the parent middle phalanx.
The screws are placed medial and lateral to the plate and parallel to the sagittal plane.

Two 5.5 mm cortex screws...

Real time imaging is useful to direct screw positioning and intraoperative imaging of some nature is necessary to confirm proper implant position.

plate fixation transarticular lag screws

It is very important that the glide holes for the transarticluar lag screws in the dorsal distal aspect of the proximal phalanx are appropriately countersunk to ensure the screw heads engage the dorsal cortex in an appropriate fashion and thereby avoid bending, weakening and potentially breaking the screw head.

plate fixation transarticular lag screws

It is also important, that screws of appropriate length are used; they should not penetrate beyond the palmar/plantar cortex of the middle phalanx. For the transarticular lag screws, a screw measuring 4-6 mm less than the measured length is appropriate and prevents placing a screw which protrudes beyond the palmar/plantar cortex of the middle phalanx.

plate fixation transarticular lag screws

Applying compression

Once the transarticular lag screws are fully tightened, the middle plate screw is fully tightened, which compresses the plate to the bone and provides additional axial compression between the subchondral plates of the proximal phalanx and the middle phalanx.

Once the transarticular lag screws are fully tightened, ...

Insertion of the remaining screw

Finally, the proximal hole of the plate is filled with a unicortical 4.5mm cortex screw.

plate fixation transarticular lag screws

Confirmation of fixation

The final construct configuration is checked with appropriate imaging to ensure appropriate length and positioning of all implants.

plate fixation transarticular lag screws
plate fixation transarticular lag screws

6. Aftercare

The horse is placed in a half-limb cast for 2 weeks post surgery. That cast is removed with the horse standing and sedated and replaced by a bandage.
The horse is confined in the stall for 3 months. In the second 6 weeks a progressive program of hand-walking exercise is introduced.
Clinical and radiographic follow-up is performed at 3 months post surgery. If complications such as excessive lameness or implant-associated complications are not evident, the horse is allowed increasing amounts of paddock exercise.
Lameness should dissipate by 6-8 months postoperatively to a level consistent with reintroduction to intended use.

plate fixation transarticular lag screws