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

Choice of treatment

Cast application is not recommended as management option of incomplete fractures of the proximal phalanx, except for first aid and transport. With persistent or severe lameness, internal fixation is the much better option for long term soundness than external coaptation.

Internal fixation using cortex screws applied in lag fashion reduces the shear forces across the fracture line by interfragmentary compression and neutralizes the inherent torsional forces caused by the anatomical configuration of the sagittal groove of the proximal phalanx.

Take care to thread the entire transcortex, while not endangering the soft tissues beyond the bone, and pay close attention to adequate countersinking. Technique errors may lead to complications and possibly implant failure.

Torsional forces

Intraoperative imaging

Intraoperative radiographic control is essential for proper placement of the interfragmentary screw(s) across the proximal phalanx. Either a real-time imaging system or anatomic references, such as a 2 mm drill bit, can be used.

Intraoperative imaging

2. Preparation and approach

Preparation

This procedure is performed with the patient in lateral recumbency.

Approach

Multiple stab incisions can be used as surgical approach to the bone. If detailed identification of the anatomic landmarks is desirable or necessary, a longer incision along the lateral aspect of the proximal phalanx is preferred.

Lateral approach

3. Fixation

Reduction

Incomplete fractures require no reduction.

Screw configuration

Since the fracture originates at the proximal articular surface, the fixation always starts immediately below the fetlock joint.
Either one or two screws can be inserted in lag fashion immediately distal to the joint surface.

Screw configuration

Dorsal screw placement

Screw position

The 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.

Positioning 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 immediately past the fracture plane using preoperative planning and/or intraoperative radiographic control.

Drilling 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.

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

Screw insertion

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.

Screw insertion

Parallel horizontal screw configuration

Parallel horizontal screw configuration is utilized for some incomplete fractures of the proximal phalanx that extend at least one third of the way down the length of the proximal phalanx and for unstable fractures.

Parallel horizontal screw configuration

Placement of the initial screw in the triangular configuration is slightly more dorsal than in the frontal configuration.

A second screw is placed palmar/plantar to the initial screw, parallel to the first screw, again just distal to the joint.

Completed fixation with parallel horizontal screw configuration

4. Aftertreatment

Recovery

In short incomplete fractures of the proximal phalanx, recovery in a soft bandage is typically sufficient.
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.

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 surgery are taken.

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

screw fixation

Complications and results