Understanding tibial plateau leveling osteotomies in dogs
You've heard a lot about TPLO and have possibly even referred patients for it, but you may still question exactly how it is performed and how it stabilizes the stifle. This surgeon walks you through the procedure so you'll be better equipped to educate your clients about its basis, some of its intricacies, and its potential complications.
Figure 7 To place the most proximal jig pin, the surgeon uses a slow-speed, high-torque power drill to insert the pin from
medial to lateral so that the jig is parallel to the sagittal plane of the stifle. An assistant (in the background) guides
the surgeon during pin placement so that the proximal jig pin is perpendicular to the sagittal plane of the stifle in both
craniocaudal and proximodistal directions.
The limb is precisely positioned, the jig is assembled, and a slow-speed, high-torque power drill is used to insert the proximal
jig pin (Figure 7). After the pin is seated, it is cut flush with the surface of the jig to allow passage of the saw blade in later stages of
Figure 8. The surgeon's view of the TPLO jig while standing at the foot of the dorsally recumbent patient. Note the jig is
parallel to the stifle's sagittal plane.
Next, the surgeon establishes a small soft tissue corridor for the distal jig pin. The surgeon inserts the distal pin in a
similar manner as that used for the proximal jig pin, using care to keep it parallel to the proximal pin. Set screws are used
to tighten the jig onto each of the jig pins (Figure 8). A small area of periosteum is elevated to prepare the bone for precise placement of the osteotomy.
An assistant places a small Hohmann retractor under the patellar ligament to retract it away from the saw blade. An appropriately
sized TPLO biradial saw blade (Slocum Enterprises) is positioned in the desired location on the medial tibial cortex. The
surgeon stabilizes the saw blade between the thumb and first finger until a reasonable kerf is established. Proper centering
of the osteotomy kerf about the approximate proximal point of the tibial functional axis is confirmed. Surgical assistants
help the surgeon keep the osteotomy blade centered about the proximal jig pin in all planes while cooling the saw blade with
lactated Ringer's solution. The axis of the saw blade (like the most proximal jig pin) should be perpendicular to the stifle's
sagittal plane in both the craniocaudal and proximodistal directions. Additionally, the saw blade should penetrate the caudal
tibial cortex perpendicular to the tibial functional axis. Before the osteotomy is completed, the saw blade is removed, and
a small, sharp osteotome is used to create reference marks to indicate the displacement needed along the osteotomy to accomplish
satisfactory tibial plateau leveling (Figure 9). The osteotomy is then completed, and the gauze sponges are removed.
Figure 9. An osteotome and mallet are used to make reference marks on each side of the osteotomy to correspond with the desired
amount of tibial plateau rotation.
Figure 10. A Jacobs chuck is applied to the temporary Steinmann pin so that the pin can be used as a handle, and the tibial
plateau is slowly rotated around the proximal jig pin until the reference marks line up.
The surgeon inserts an appropriately sized Steinmann pin temporarily into the plateau segment from cranial to caudal and slowly
rotates the segment around the proximal jig pin until the reference marks line up (Figure 10). No effort is made to keep the medial surface of the tibial segments flush as this will typically create tibial malalignment.17 An appropriately sized Kirschner wire is passed across the osteotomy from the proximal-most end of the tibial tubercle into
the tibial plateau to provide temporary stabilization during subsequent bone plate application. This Kirschner wire must penetrate
the tibial tubercle proximal to the insertion of the patellar ligament to minimize the risk of tibial tubercle fracture.11 The surgeon performs the tibial compression test to ensure that cranial tibial thrust has been eliminated. The temporary
Steinmann pin used for plateau rotation is removed.