1 Principles topenlarge
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.
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.
2 Preparation and approach top
This procedure is performed with the patient in lateral recumbency.
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.
3 Fixation top
Incomplete fractures require no reduction.
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.
Dorsal screw placement
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.
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.
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.
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.
The 4.5 mm countersink is used to prepare uniform seating of the screw head and to ensure concentric loading of the screw head.
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.
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.
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.
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.
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.
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.