In acute fractures there is usually some degree of hemarthrosis and lavage is used to enhance visibility. This is performed by placing an egress cannula through the medial instrument portal.
The dorsal compartment of the middle carpal joint should then be evaluated completely and any additional lesions noted.
Any loose cartilage and bone debris is debrided.
4. Placement of hypodermic needles
Insertion of needles
An 18 gauge spinal needle is inserted percutaneously under arthroscopic visualization so that it passes in the center of the fracture portion half way between the fracture line and the junction of the second and third carpal bones. The needle is passed across the joint and embedded in the soft tissue of the lateral joint capsule.
This needle is the critical directional guide for implant placement.
Once the spinal needle has been placed, an additional18 gauge needle is inserted into the carpometacarpal joint directly below the initial needle placed.
5. Screw fixation
Based on the radiographs a stab incision is made over the medial aspect of the third carpal bone half way between the spinal needle and the needle in the carpometacarpal joint using the spinal needle as a guide for the dorso-palmar positioning.
Drilling the glide hole
A 3.5 mm glide hole is drilled across the fragment using the spinal needle as a guide to place the glide hole approximately perpendicular to the sagittal fracture line.
The drill depth and direction can be verified using an intraoperative radiographic view.
Drilling the thread hole
The 2.5 mm drill guide is inserted into the glide hole and a 2.5 mm hole is drilled through the third carpal bone just stopping short of the junction of the 3rd and 4th carpal bone (to a depth of about 40 mm).
The glide hole is lightly countersunk at the dorsal surface and debris flushed.
Determining screw length
Correct screw length is determined using the depth gauge (screw length should be at least 4 mm shorter than the depth of hole). Generally a 36 mm long screw is used.
Tapping the hole
The hole is tapped with a 3.5 mm tap protected by the 3.5 mm drill guide. This should be done by hand.
The 3.5 mm screw of appropriate length is inserted and tightened under arthroscopic visualization.
Pearl: Use two fingers and thumb when doing final tightening, thereby avoiding excessive torque and potential breaking of the screw head.
After the screw is tightened any debris or elevated cartilage at fracture line is removed.
Confirmation of fixation
Intraoperative radiographs are taken to confirm screw length and correct positioning.
All incisions are sutured (only skin sutures are necessary). A sterile bandage is placed over the carpal region. Perioperative antibiotics are indicated for 24 h and the horse should be placed on antiinflammatory medication for 5 – 7 days. The horse should be confined to a stall (box) but hand walking is commenced at 2 weeks.
The horse can usually go back into race training at 3 months but only after clinical and radiographic examination and clearance by veterinary surgeon.