Proper anatomic reduction is imperative for proper limb conformation. Reduction can be difficult and is aided by the careful use of Hohmann retractors and bone reduction forceps. Often, a separate transphyseal bridge is used to achieve temporary reduction prior to placement of the bone plate. The transphyseal bridge is usually placed caudal to the intended location of the plate.
Because of the fracture configuration and direction of displacement, the medial aspect of the fracture becomes the tension surface and implants placed on this surface are stressed primarily in tension. Fixation of the medial aspect of the tibial epiphysis is the essential aspect of this repair.
In some circumstances Hohmann retractors can be used within the physis to aid reduction. The fracture hematoma and debris is removed from the fracture bed. Reduction is performed by tenting the fracture ends out of the incision and then applying traction on the distal limb and downward pressure on the proximal aspect of the tibial metaphysis.
A transphyseal bridge using 4.5 mm cortex screws and 1.25 mm figure-of-8 wire is often used to achieve and maintain reduction of the fracture fragments. The transphyseal bridge is placed caudal to the intended position of the bone plate.
4. Plate selection and preparation
For most foals a 6 –hole narrow plate is appropriate for fracture fixation. DCP, LC-DCP and LCP have been used for this repair.
With the fracture reduced and stabilized by the transphyseal bridge, a narrow bone plate (locking compression plate in this instance) will be applied to span the medial aspect of the physis just cranial to the collateral ligament. A soft aluminum template is used to determine the appropriate contour for application of the 6 hole LCP to the medial aspect of the proximal tibia, cranial to the transphyseal bridge (and collateral ligament in the clinical case).
Plate preparation and position
The 6 hole LCP is contoured to match the aluminum template.
The plate is applied such that the stacked combi-hole is positioned directly over the medial aspect of the proximal tibial epiphysis after contouring is complete. It’s important to be sure the screw will be positioned fully in the epiphysis. Contouring of the plate could change the intended direction of the locking head screws and should be considered prior to placement of the screws.
5. Plate application
Securing the plate to the bone
The LCP is held in position and compressed to the bone using the push-pull device positioned in the DCU portion of the 3rd combi-hole. Alternatively, a 4.5 mm cortex screw can be placed in lag fashion through the plate and into the metaphyseal fragment. In either instance, the plate is compressed to the bone and held in place while the epiphyseal screw is placed.
Placing the epiphyseal screw
The 4.3 mm threaded drill sleeve is placed in the stacked combi-hole overlying the epiphysis. Fluoroscopic or radiographic monitoring is essential to ensure appropriate drill bit placement and to avoid entering the femorotibial joint. The 4.3mm drill bit is used to prepare the hole to a depth of approximately 55 mm.
The hole is measured to ensure it will accept a 50 mm, 5.0 mm locking head screw, which is subsequently placed in the hole using the power driver with the 4 nM torque limiting device. Final tightening is achieved by hand.
Insertion of the remaining screws
Using the universal drill guide, a 3.2 mm hole is prepared in the neutral position of the DCU portion of plate hole #4 and #5, the depths are measured, threads are prepared with the 4.5 mm tap protected by the 4.5 mm drill sleeve, and appropriate length 4.5 mm cortex screws are inserted and tightened.
Using lag technique, 4.5 mm cortex screws are placed in plate holes #2 and #3 to engage the metaphyseal fragment just distal to the physis. A 5.0 mm locking head screw is placed in plate hole #6. The hole is prepared using the 4.3 mm drill through the 4.3 mm sleeve threaded into the locking portion of the combi-hole. The depth of the hole is measured and the self-tapping 5.0 mm locking screw of appropriate length is inserted using the 4 nM torque limiting device. All screws are again hand-checked for tightness.
Fixation with two plates
In some cases it is necessary to apply two plates to assure adequate holding power of the implants in the epiphysis providing the stability of the fracture fixation needed for an uncomplicated postoperative period. In this case the two plates chosen should be of different lengths to reduce the danger of stress concentration.
6. Overview of rehabilitation
Stall rest for 4-6 weeks is recommended and further activity determined after follow up radiographic evaluation.
Plate removal is recommended if the growth plate appears viable. A period of pasture activity for at least 2 weeks is recommended prior to plate removal.