Lag screw insertion is routinely done under arthroscopic control.
Prognosis is dependent on accurate articular reduction, and the amount of bone loss in the fracture site. In the majority of these cases surgery is performed to salvage the joint and save the horse’s life. Failure to treat these cases surgically results in joint collapse and eventual laminitis in opposite weight bearing limb.
Reduction of the fracture is achieved by flexion of the carpal region. Sometimes prior removal of bone fragments and debris is necessary to achieve reduction. Frontal fractures of the both facets of the third carpal bone are repaired with two cortex screws of 4.5 mm diameter. Very occasionally three screws are deemed necessary.
In acute fractures there is frequently marked hemarthrosis and lavage will be necessary to permit 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. These fractures usually have significant displacement with a large fracture gap seen during arthroscopy.
Any loose cartilage and bone debris is debrided.
This picture shows the defect after debridement and reduction by flexion.
4. Placement of hypodermic needles
Insertion of needles
The proximal medial and lateral margins of the fracture are defined by arthroscopically guided percutaneous insertion of 18 gauge hypodermic needles.
It is important that these needles are placed perpendicular to the dorsal surface of the carpus in order to accurately delineate the fracture width.
Two 18 gauge spinal needles are then placed over the central portion of the radial and intermediate facets of the third carpal bone. These two needles are close and parallel to the proximal articular surface and directed approximately perpendicular to the fracture line. These needles are critical guides for implant placement. Once the spinal needles have been placed, the lateral and medial hypodermic needles are removed.
A further 18 gauge needle is inserted into the carpometacarpal joint.
A flexed LM and ...
…skyline radiographic views are taken to provide the proximal-distal location of the lag screw.
5. Screw fixation
Based on the radiographs two stab incisions are placed over the dorsal aspect of the radial and the intermediate facets respectively. Their positioning is based on radiographs of spinal needle placement.
Preparing the glide holes
Two 4.5 mm glide holes are drilled through fragment until they enter the fracture line (the distance is predetermined by measurement by the radiographs).
The drill depths can be verified using an intraoperative radiograph.
Drilling the thread hole
The 3.2 mm drill guide is inserted into one glide hole and the 3.2 mm thread hole is drilled through the remaining third carpal bone. The hole is drilled through the entire parent third carpal bone so that maximal screw length can be used.
The first hole is countersunk at the dorsal surface and debris is flushed.
Determining screw length
Correct screw lengths are determined using a depth gauge. The screws used are generally 36 mm long.
Tapping the hole
The first hole is tapped with a 4.5 mm tap protected by the corresponding drill guide. This should be done by hand.
The first 4.5 mm cortex screw of appropriate length is inserted and tightened under arthroscopic visualization.
Insertion of the second screw
Preparation of the thread hole, countersinking, determining the depth of the hole and tapping of the thread hole are subsequently performed, followed by inserting and tightening of the second screw. After the screws are tightened remove any debris or elevated cartilage at the fracture line.
Pearl: Use two fingers and thumb when doing final tightening, thereby avoiding excessive torque and potential breaking of screw head. Intraoperative radiographs are taken to confirm screw length and correct positioning.
The reduction of the fracture is observed arthroscopically and the joint flushed to remove any debris.
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 on the carpus. A sleeve cast is applied to the carpus to protect the repair during anaesthetic recovery and the early postoperative period. Perioperative antibiotics for 24 h are indicated 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 level of activity that the horse can return to will be dictated by soundness 4-6 months after surgery and the degree of post traumatic osteoarthritis that develops.