Complete cartilage removal is important to provide for maximum contact between the opposing subchondral bone plates. With compression, generated by the fixation technique, frictional forces are generated between the subchondral bone plates, which maximizes strength and stability of the fixation, providing maximum patient comfort.
The implant positioning in the middle phalanx is just distal to the proximal articular surface. The distal end of the plates should not impinge on the proximal attachment of the distal interphalangeal joint capsule and should be positioned abaxially to avoid the extensor process.The distal plate screws should engage a substantial portion of the palmar/plantar eminence fragments to provide maximum strength of the fixation.
It is important, that the screws through the distal aspect of the plates engage the eminence fragments to provide for reestablishment of the palmar/plantar support and to reduce the fractures on the palmar/plantar aspect of the middle phalanx.
Two plates are necessary to neutralize the bending forces acting across the pastern joint and provide transarticular compression to encourage arthrodesis.
3. Reduction and fixation of the larger eminence fragment
In most cases, the proximal articular surface of the middle phalanx is reconstructed with the joint dorsally luxated to allow direct visualization of the major fracture fragments. Alignment is generally achieved through a combination of flexion and extension of the digit and placement of large pointed reduction forceps to engage the major eminence fragments from dorsal to palmar/plantar.
Fixation of the larger eminence fragment
Once the larger eminence fragment is reduced a 4.5 mm cortex screw is placed in lag fashion from dorsal to palmar/plantar to compress the reduced fracture fragments.
4. Plate selection and preparation
A combination of PIP plates and/or 4-5 hole narrow LCP are used in most cases. Other plate constructs have been used successfully, including narrow, 4.5 mm DCPs and LC-DCPs. The technique for fixation with DCP or LC/DCP is described for uniaxial eminence fractures as an example. For more details click here.
The plates are contoured to approximate the dorsal surface of the distal proximal phalanx and proximal middle phalanx with the stacked combi-hole into the plate positioned over the proximal end of the middle phalanx. The distal end of the plate is bent slightly to ensure that the middle phalangeal plate screw is directed into the major substance of the eminence fragment.
5. Reduction and plate fixation
Application of the first plate
The second eminence fracture is reduced with a pointed reduction forceps. Once reduced, either a 5.5 mm or a 5.0 mm locking head screw is positioned through the distal hole of the first plate. This screw is located abaxial to the first screw and engages the major eminence fracture fragment that has not been stabilized by the axial lag screw.
Application of the second plate
The second plate is applied on the opposite abaxial side and, the distal plate screw should engage the corresponding or ipsilateral eminence fragment.
Fixation to the proximal phalanx
The middle and proximal phalanges are realigned and the plates fixed to the proximal phalanx using 5.5 mm cortex screws placed in a load position in the second hole proximal to the joint.
Insertion of remaining screws
The remaining holes are filled with locking screws with both juxta-articular locking screws placed bicortically and the proximal most locking screw in a four-hole plate monocortically.
The final construct configuration is checked with appropriate imaging to ensure appropriate length and positioning of all implants.
It is important that screws of appropriate length are used and that they do not protrude significantly beyond the palmar/plantar cortex of the proximal and middle phalanges.
The horse is put in a half-limb cast for recovery. This cast is changed 2-3 weeks post surgery. The horse is maintained in the second cast or a bandage cast for an additional 3-6 weeks, depending on the perceived strength and stability of the fixation and horse’s progress postoperatively. The horse is confined in the stall for 3 months. After 6 weeks, providing the horse’s clinical and radiographic progress is satisfactory, hand-walking exercises are introduced. After 3 months, including the 6 weeks of hand-walking exercise, gradual access to free paddock activity is allowed providing the clinical and radiographic progress is satisfactory.