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 and allowing early removal of postoperative cast support.
The implant positioning in the middle phalanx is in the proximal epiphyseal region. The distal end of the plate should not impinge on the proximal attachment of the distal interphalangeal joint capsule as well as the extensor process. The distal plate screws should engage a substantial portion of the palmar/plantar eminence fragment to provide maximum strength of the fixation.
3. Reduction and placement of transarticular screw
The luxation is reduced and the pastern joint realigned. An axially positioned transarticular 4.5mm cortex screw is placed in lag fashion angling from the dorsal distal aspect of the proximal phalanx into the proximal palmar/plantar aspect of the middle phalanx. This screw should cross the articulation near the junction of the palmar/plantar ¼ and dorsal ¾, ensuring that the screw purchase in the middle phalanx is within the eminence and avoids the region of the navicular apparatus. This screw will maintain reduction for the remainder of the fixation and provides transarticular compression.
4. Plate selection and preparation
A combination of two 4 hole or a 4 and 5 hole narrow LCPs 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 middle phalanx. The distal end of the plate is then bend slightly to ensure that the middle phalangeal plate screw is directed into the major substance of the eminence fragment.
5. Plate fixation
Application of the first plate
The first plate is applied abaxial to the transarticular lag screw and is fixed to the proximal aspect of the middle phalanx using a 5.0 head locking screw through the stacked combi-hole.
Application of the second plate
Now the second plate is applied in similar fashion to the opposite abaxial site.
Fixation to the proximal phalanx
The plates are fixed to the proximal phalanx using 5.5 mm cortex screws placed in a load position in the most proximal combi-hole of the plates but are not fully tightened.
Transarticular lag screws
Now, 5.5 mm cortex screws are placed in lag fashion through the combi-hole adjacent to the joint engaging the proximal palmar aspect of the middle phalanx. Care must be taken to adjust the angle of the screw in the sagittal plane to avoid the previously placed transarticular lag screw and the locking plate screws.
Once the transarticular screws are tightened, the most proximal screws are fully tightened to provide additional transarticular compression.
Insertion of remaining screws
The remaining holes are filled with 5.0 mm locking head screws.
The final construct configuration is confirmed 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.