1 Principles topenlarge
Anatomic reduction of the articular surface is of paramount importance for successful surgical management and future comfort. Failure to properly reduce the fractures and create friction between the fracture components will load the cortex screws in bending, leading to implant breakage. Failure to reconstruct the articular surface will lead to osteoarthritis and lameness.
Reconstruction of the bony column of the proximal phalanx preserves limb length, promotes load sharing between the bone fragments and implants, and improves comfort. Generally, only fractures with at least one intact strut of bone extending from joint to joint are amendable to internal fixation with screws. Reconstruction then starts with the fragments comprising the proximal articular surface.
Direct examination of the proximal portion of the fracture via an open approach reduces the need for radiographic control. However, placement of the distal implants often requires the use of radiographic markers for intraoperative radiographic control.
AO teaching video
Lag screw fixation of a multifragment proximal phalanx fracture
2 Positioning and approach topenlarge
The horse is positioned in lateral recumbency with the intact strut of bone of the proximal phalanx positioned towards the surgery table. Therefore, if the intact strut is located medial, the affected limb is positioned uppermost. The incision is always made along the comminuted side of the fracture.
Comminuted fractures, which have an intact strut of bone extending from the fetlock to the pastern joint should be repaired with an open approach. Some screws may be placed through stab incisions.
3 Reduction and fixation topenlarge
Sequence of reduction
In general, the dorsal plane fracture of the medial aspect of the proximal phalanx, if present, is reduced and repaired first (2 to 3), followed by the repair of the dorsal plane fracture on the lateral aspect of the bone (1 to 4), to create a two-part fracture. Finally any sagittal fractures are repaired (1 to 2).
Reduction and screw fixation
Once adequate exposure is achieved, and the fractures planes are debrided, the fragments comprising the proximal articular surface are reduced.
Reduction is maintained with pointed reduction forceps until compressed with cortex screws in lag fashion, as shown with insertion of the first screw...
...and the fifth screw, repairing the sagittal fracture.
Each fracture line is repaired in sequence of the numbers shown in the drawing.
Diameter of the cortex screw is determined by the size of the fracture fragments. Whenever possible, 4.5 and 5.5 mm screws should be used.