Arthrodesis can be achieved with a dorsal plate or several transarticular cortex screws applied in either palmaro-/plantaroproximal to apicodistal or dorsodistal to proximopalmar/plantar direction.
Exploration of the joint
The distal interphalangeal joint is distended and the arthroscope inserted using routine technique through a stab incision located 2-3 cm proximal to the coronary band and 2-3 cm lateral to the sagittal plane. The instrument portal is made identically to the initial incision, mirrored on the sagittal phalangeal plane.
The joint is explored with the help of the hook probe.
Any visible articular cartilage is removed with a 2-0 sized curette. Careful use of an oscillating saw with a 1 cm wide blade or a small bur (see left) may be very efficient in partial cartilage removal of the distal interphalangeal joint. An additional approach can be prepared into the palmar/plantar articular recess to remove additional cartilage.
In the presence of severe periarticular new bone formation joint motion may be greatly impaired, rendering cartilage removal significantly more difficult. In those cases cartilage removal may be abandoned to prevent additional damage to sensitive structures near the joint.
3. Insertion of transarticular screws
After removing as much articular cartilage as possible, the mechanical bur is redirected and the extensor process of the distal phalanx is shaved down. A trough of the appropriate width of the plate is prepared along the extensor process of the distal phalanx and extended distally to assure insertion of the distal locking head screw without penetrating the distal interphalangeal joint and to facilitate proper bone-plate contact. The laminae in this region are shaved away as well.
Determining screw position
The bur is removed and a hypodermic needle is inserted through the stab incision to mark the direction and entry point for the first transarticular cortex screw followed by taking a lateromedial radiograph.
Alternatively, a 2 mm drill bit can be used and advanced for approximately 4 mm in a plane slightly diverging from the mid-sagittal plane. From the lateral view the drill bit should be directed perpendicularly to the sole of the foot.
A DP and lateromedial radiograph is taken to verify location and direction of the drill bit.
Drilling the glide holes
The needle or the drill bit is exchanged for a 5.5 mm drill bit. Considering potential changes in orientation of the drill bit in relation to the position of the needle or the 2 mm drill bit respectively the glide hole across the middle phalanx is prepared.
Note: insertion of a periosteal elevator into the joint space through the arthroscope portal to separate the articular surfaces of the middle and distal phalanges facilitates recognition of entering the joint space without penetrating the distal phalanx.
The arthroscope is removed and the same procedure is repeated through the arthroscope portal.
Note: it is important to drill the two glide holes first before one screw is inserted because one can not afford to loose any threads in the distal phalanx because of accidental penetration of the 5.5 mm drill bit into the distal phalanx.
Preparing the thread hole
The 4.0 mm drill guide is inserted into one of the glide holes and the thread hole is prepared into the distal phalanx. Careful drilling is important to recognize the transition of the drill bit from the distal phalanx into the sole of the hoof capsule.
The countersink is used to prepare a depression for the screw head. Special attention is given that the depression is oriented axially relative to the glide hole concentrating on the palmaroproximal rim of the glide hole to facilitate proper seating of the screw head in the glide hole.
Determining screw length
The screw length is determined with the depth gauge.
Note: this is a blind hole and therefore the exact screw length is difficult to determine.
Tapping the hole
The 5.5 mm tap is used to prepare the threads in the thread hole.
Note: special attention is given to appreciate the end of the drill hole to prevent stripping of the threads in this blind hole.
Insertion of the first screw
A 5.5 mm cortex screw 4-6 mm shorter than the measured hole is inserted and solidly tightened.
Note: it is very important to first finish implantation of one screw before the thread hole for the second screw is prepared.
Insertion of the second screw
The thread hole for the second 5.5. mm cortex screw is now prepared, the length determined, the threads prepared, the screw inserted and tightened. Solid tightening of both screws is verified again.
Intraoperative radiography is used to assure proper screw length.
4. Plate application
A 2-3 cm incision is prepared on the dorsal midline above the coronary band. The extensor tendon is split in the sagittal plane.
Preparing the plate bed
A 1 cm wide osteotome is used to prepare the plate bed underneath the coronary band down to the previously prepared trough.
A proximal interphalangeal locking plate (PIP = LCP) is advocated because of the significant advantages of this plate compared to the others. Other plate constructs can be used such as the narrow, 4.5 mm, 3-hole DCPs and LC-DCPs. Here, the use of the PIP is described.
Note: the PIP is slightly longer than the 4.5 mm, 3-hole DCP and LC-DCP and may protrude over the proximal interphalangeal joint. This should be corrected by advancing the plate further distally and rechecking positioning on lateromedial radiographs.
The PIP plate is positioned over the dorsal aspect of the distal plate.
The location of the plate is verified radiographically. Lead beads are taped on the dorsal hoof wall perpendicularly over the distal stacked combi-hole of the plate to help identify the entry point of the 8 mm drill hole to provide access for the screw hole preparation. If needed, the plate location is changed to facilitate ideal plate and screw placement in all planes.
Note: in this cadaveric specimen the plate placement is too proximal because its proximal aspect is protruding over the middle phalanx.
An 8 mm hole is prepared from the marked site to the bone plate.
The LCP drill guide is introduced into the stacked combi-hole and tightened.
Note: the drawing contains a US-version of the LCP drill guide,...
...whereas the photograph depicts the European version introduced across the dorsal hoof wall into the PIP.
The 4.3 mm thread hole is carefully prepared into the distal phalanx. Frequent radiographic evaluation of drill penetration is advocated.
Careful drilling is important to recognize the transition of the drill bit from the distal phalanx into the sole of the hoof wall.
The drill guide is removed, the depth measured and a screw 4 mm shorter than measured is inserted and provisionally tightened.
A 5.5 mm cortex screw is inserted in load position through the proximal most plate hole. Both plate screws are now solidly tightened.
Note: only a 4.5 mm cortex screw was inserted in the the cadaveric specimen on the left.
A 5.0 mm locking head screw is now inserted and tightened through the middle plate hole.
The final construct is confirmed radiographically in both routine planes.
5. Closure of the hoof wall
A small portion of a gentamycin-impregnated collagen sponge is inserted into the hole across the dorsal the hoof wall to fill the space between the surface of the distal phalanx and the hoof wall.
The rest of the hole is filled with antibiotic-impregnated polymethylmethacrylate (PMMA) or artificial hoof resin. The edges are sealed with cyanoacrylate glue.
If desired a Kevlar® strip can be glued over the top or additional artificial hoof resin is applied (see picture left) followed by non-adhesive tape covered.
Alternate closure techniques of the hoof wall are described for distal sagittal phalangeal fractures.
Regional limb perfusion with broad spectrum antibiotics is strongly encouraged at the end of the surgery.
A half-limb cast is applied for recovery from general anesthesia and is exchanged shortly thereafter for an additional 3-4 weeks. Stall rest is for 60 days, followed by hand-walking for 60 days. Then paddock exercises are recommended for a minimum of 90 - 120 days. Ideally, horses should not be returned to active training prior to 10 months.
Radiographic evaluation is performed every 60 days until the fracture has healed (generally 4-6 months).