1 Principles topenlarge
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.
Intraoperative radiographic control is essential for proper placement of the interfragmentary 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 also serve as temporary fixation.
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.
2 Approach topenlarge
Displaced fractures should be repaired through an open approach, not exclusively through stab incisions. In sagittal biarticular fractures the routine lateral approach, extending further distally is used. In spiral fractures the normal lateral approach is used with additional stab incisions relative to the fracture configuration.
If necessary for visualization and reduction, a dorsal incision into the fracture plane may be required. This incision can be extended 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.
3 Fixation topenlarge
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.
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 inserted is determined by the length and configuration of the fracture.
Care should be taken to avoid placing multiple screws in the central “waist” of the proximal phalanx. This causes a stress riser in the bone and may lead to the development of transverse fractures.
Preparing the glide hole
A 4.5 mm cortex screw is typically used for this procedure. The 4.5 mm glide hole is drilled to the level of the fracture line using preoperative planning and/or radiographic control.
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.
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.
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 distal screw
Next the most distal screw is placed using identical lag technique at or just proximal to the epicondylar fossa of the distal proximal phalanx. Once this screw is tightened, the 2 mm drill bits can be removed.
The remaining screws are now inserted. The number of the screws used depends on the size of the bone and the configuration of the fracture. The screws are typically placed 20-25 mm apart.
If the fracture plane spirals medially or laterally, the screw orientation is rotated as well to keep them perpendicular to the fracture plane.
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.