Authors of section

Authors

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

Executive Editor

Jörg Auer

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Screw fixation

1. Principles

Anatomic reduction

Anatomic reduction of the articular surface is of paramount importance for successful surgical management and future athletic soundness. Failure to properly reduce the fracture and create friction between the two fracture components will load the cortex screws in bending, leading eventually to implant breakage. Failure to reconstruct the proximal articular surface will lead to osteoarthritis and lameness.

A dorsal incision into the fracture plane and possibly an arthrotomy of the dorsal joint capsule of the fetlock joint may help to achieve perfect anatomic reduction. The result should always be confirmed radiographically once temporary fixation is in place.

Loading the cortex screws in bending

Intraoperative imaging

Intraoperative radiographic control is essential for proper placement of the screws across the proximal phalanx. Either a real-time imaging system or anatomic references, such as 2 mm drill bits, can be used.
The radiographic markers are placed after reduction has been achieved and maintained with reduction forceps. The drill bits serve as markers as well as temporary fixation devices.

Intraoperative radiographic control

Pitfall: Arthroscopic evaluation

Arthroscopic evaluation prior to reduction and fixation of the fracture may complicate the procedure because of extravasation of fluid into the soft tissue and loss of the normal anatomical landmarks.

AO teaching video

Lag screw fixation of a displaced monoarticular fracture of the proximal phalanx

2. Approach

Preparation

This procedure is performed with the patient in lateral recumbency.

Displaced fractures should be repaired through an open approach, not stab incisions. The normal lateral approach works well for all two-part fractures.
The bone should always be approached from the side through which the fracture exits.

Lateral approach

3. Reduction

Reduction is achieved by palpation of the proximal aspect of the bone and visualization of the fracture through the open approach.

Reduction

Option: dorsal incision

If necessary for visualization and reduction, a dorsal incision into the fracture plane may be performed. This incision can be extended proximally to include an arthrotomy of the dorsal joint capsule of the fetlock joint to ensure perfect anatomic reduction. This approach also allows removal of debris from the fracture plane.

Option: dorsal incision

Confirmation of reduction

Reduction is confirmed radiographically showing the temporary fixation devises (2 mm drill bits, reduction forceps) and hypodermic needles strategically placed.

Confirmation of reduction

4. Fixation

Screw configuration

Since the fracture originates at the proximal articular surface, the most proximal screw(s) is/are always implanted immediately below the fetlock joint.
The screws can either be aligned in a dorsal plane or in a triangular configuration.

Screw configuration

Dorsal screw placement

In the dorsal plane screw placement, a single screw is placed distal to the mid-sagittal groove of the proximal articular surface and centered in the dorsal two thirds of the palpable width of the bone. The number of screws is determined by the length and configuration of the fracture. The most distal screw should be inserted no closer than 15 mm from the distal most extent of the fracture.

Position of the first screw

Preparing the glide hole

A 4.5 mm cortex screw is typically used for this procedure. The 4.5 mm glide hole is drilled parallel to the fetlock joint using preoperative planning and/or radiographic control.

Preparing the glide hole

Alternative

An alternate option involves insertion of a periosteal elevator into the fracture plane through the dorsal incision. The glide hole is subsequently prepared across the fracture plane, which is now easily appreciated.

Alternative: insertion of perosteal elevator

The 3.2 mm insert drill sleeve is inserted into the glide hole and used to anatomically reduce the fracture. Once achieved, reduction is maintained with the help of reduction forceps.

Reduction with drill sleeve

Identifying the glide hole

In the presence of soft-tissue swelling it may be difficult to find the glide hole with the 3.2 mm drill bit. In such a case the 4.5 mm drill bit is removed but the drill guide left in place. A 2.5 mm Steinmann pin is introduced into the glide hole. The drill guide is removed, turned around and the 3.2 mm drill guide placed over the Steinmann pin and using rotating movements worked into the glide hole.

Identifying the glide hole

Preparing the thread hole

The 3.2 mm thread hole is prepared using the 3.2 mm insert drill sleeve. The thread hole is drilled through the entire transcortex of the proximal phalanx.

Preparing the thread hole

Pitfall: blind hole

Not exiting the drill hole through the transcortex leads to a blind hole and may result in serious complications and potential lack of interfragmentary compression of the fracture.

Pitfall: blind hole

Countersinking

The 4.5 mm countersink is used to prepare uniform seating of the screw head and to ensure concentric loading of the screw head.

Countersinking

This is especially important at an oblique bone surface relative to the screw axis. In this case special attention has to be given to the proximal half circle of the hole. However, care must be taken to prevent penetration of the screw head through the near cortex.

Pitfall: Countersinking in oblique bone surface

Measuring screw length

The depth gauge is used to measure the proper length of the screw. The depth gauge should always be inclined proximally to measure the maximum length of the cortex screw appropriate for the bone.

Measuring screw length

Pitfall

Inclining the depth gauge distally measures a screw length that does not engage all of the far cortex and encourages stripping of the screw during tightening, resulting in inadequate compression of the fracture plane.

Pitfall: inclining the depth gauge distally

Insertion of the first screw

The 4.5 mm tap, protected by the 4.5mm tap (drill) sleeve, is used to prepare the thread hole for screw insertion. A screw of the proper length is chosen and solidly tightened.

Insertion of the first screw

Additional screws

The number of the screws used depends on the length and configuration of the fracture. When screws are placed in the dorsal plane, they are typically placed 20-25 mm apart.
The most distal screw should be no closer than 15 mm from the distal most extent of the fracture.
If the fracture plane spirals medially or laterally, the screw orientation is rotated as well to keep them perpendicular to the fracture plane.

Additional screws

Triangular screw configuration

Triangular screw configuration represents another option of screw placement.

The initial screw in the triangular configuration is placed slightly more dorsal than in the dorsal configuration.
A second screw is placed palmar/plantar to the initial screw, parallel to the first screw, again just distal to the joint.
A third screw is placed in the dorsal plane 25 mm distal to the proximal screws in the center of the proximal phalanx.
If the fracture plane spirals medially or laterally, the orientation of the screws are rotated as well to keep them perpendicular to the fracture plane.
A fourth screw can be used if the fracture length dictates it.

Triangular screw configuration

5. Aftertreatment

Recovery

For all complete fractures, external coaptation is recommended for recovery from general anesthesia. The surgeon may prefer to use a temporary immobilization device that is removed immediately after recovery from anesthesia. Half-limb casts, if elected, should be removed shortly after recovery from anesthesia.

Postoperative management and exercises

Postoperative management includes box stall confinement for 8 weeks with hand-walking exercise beginning 2-4 weeks postoperatively. The operative site is bandaged for 4 weeks after surgery and analgesics used for 10 days postoperatively.

screw fixation

Radiographic follow up

Fracture healing is followed radiographically at 8 weeks post surgery. If the fracture is healing satisfactorily small paddock exercise for 4 weeks followed by field exercise is prescribed. Additional radiographs 12-16 weeks post injury are taken.

Return to training is typically 3-4 months post surgery.

Complications and results