Pancarpal arthrodesis

In the distal radius it is best to keep the implants in the metaphysis only, which is better able to withstand the stress concentration rather than extending the plates into the diaphysis of the radius, which increases the risk of postoperative fracture at the end of the plate.

This procedure is performed with the patient placed in lateral recumbency and through the approach for total arthrodesis.

Traumatic injuries do not require an osteotomy, but deforming arthritic injuries may require a corrective osteotomy for realignment of the limb. For simple degenerative arthritis without limb deformity an osteotomy is not necessary.
If an osteotomy is needed, it is performed through the affected arthritic joint. For a partial carpal arthrodesis this is always the affected joint. For a pan-carpal arthrodesis the osteotomy is performed through the most deformed articulation.

The angulation of the osteotomy is estimated from the preoperative radiographs.
The postoperative goal after the osteotomy is to have the limb in slight flexion with slight remaining varus deviation to assure that the tension surface of the reconstruction is in the location where the plates will be placed.

Therefore the plane of the osteotomy should diverge slightly from dorsal to palmar and should remove a wedge of bone smaller than the calculated amount as determined from the radiographs. If the osteotomy is done in the antebrachial carpal joint the surgeon must be aware that the accessory carpal bone is present in the posterior aspect of that joint and stop the osteotomy short of that bone.

Once the osteotomy is created the wedge of bone to be discarded is removed using the bone saw and rongeurs. The limb is then corrected into the new alignment and a radiograph taken if needed.

Since pan-carpal arthrodesis is normally performed in unstable injuries, dynamic condylar plates should be used over the area of maximum instability in buttress function and to reestablish weight bearing capability.
A second broad dynamic compression or locking plate of approximately 9-10 holes is normally used to improve rotational stability and the strength of the fixation.

The plates are contoured to the surface of the bone with the dynamic condylar plate placed medially or laterally over the area of maximum injury.

The implants are attached to the distal radius first and extended distally.
Bending templates and the dynamic condylar screw aiming device should be used in the contouring of the plate to reestablish normal anatomic alignment.
The dynamic condylar plate is applied first with the barrel of the plate at the level of the distal radial physeal scar. This location normally allows insertion of the barrel of the plate, the DCS-plate and two additional screws in the distal radius.

The limb is then reduced into anatomic alignment and the distal screws are inserted into McIII to reestablish the normal anatomy.
In most locations 5.5 mm cortex screws are used unless the injury dictates the use of another size screw.

Screws are inserted through the plate into the injured carpal bones using lag- or plate screw technique dependent upon the types of fractures or injuries encountered.

The second plate is placed dorsomedially. Locking plates are advantageous in this location because of their increased strength.
Two screws in this plate are inserted proximal to the DCS-barrel into the distal radius. These screws are important because they reinforce the area of stress concentration created by the barrel of the DCS plate in the distal radius.
This implant is applied as a neutralization plate and compression is rarely used. Screws can be used in lag fashion through the plate if dictated by the injury.
The second plate is shorter than the dynamic condylar plate and extends into the proximal McIII.

In this case the joints were fused using a dynamic condylar plate laterally and a 9-hole DCP cranially.

Antibiotic containing implants (PMMA beads or collagen sponges) are placed alongside both plates and the exposure closed using the annular ligament of the carpus, the common digital extensor tendon distally and fascia between the common digital extensor and extensor carpi radialis muscles and tendons proximally, the subcutaneous tissue and the skin sequentially.
Suction drainage is almost always used with pan-carpal arthrodesis because of the large number of implants and the traumatic injury which requires the arthrodesis.

After closure a sterile dressing is placed on the wound and a cast is applied from the elbow to the distal aspect of the metacarpus just above the metacarpophalangeal joint. Allowing the metacarpophalangeal joint to maintain flexion and extension greatly increases the ability of the horse to move comfortably postoperatively.
The cast is maintained in place for 30 days with a cast change at 2 weeks postoperatively. The cast change can be performed standing or under general anesthesia depending on patient compliance.
After cast removal full limb bandages are maintained until swelling is eliminated.
Stall rest with no free-choice exercise is maintained for 60 days.
Follow up radiographs at 60 days will determine the next step in the reconvalescent period. Normally 30 days of gradually increasing exercise is recommended prior to resumption of free-choice exercise. Pan-carpal rthrodesis is for non-athletic purposes only.